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JP2008258928

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2008258928
An object of the present invention is to provide a microphone capable of detecting vibration
related to sound with high sensitivity. A microphone (1A) of the present invention is attached to a
diaphragm (2) that vibrates under sound pressure and a bobbin (21) integrated on the back side
of the diaphragm (2), and moves along the direction in which the diaphragm (2) vibrates. The
light from the light source from which the coherent light is emitted is made incident on the
diffraction grating piece 30A and causes the two diffracted lights diffracted by the diffraction
grating piece 30A to interfere with each other and the vibration plate 2 moves. And a diffraction
grating interferometer 3A for detecting the displacement of the diaphragm 2 from the phase
change of the interference light which is changed according to the movement of the diffraction
grating piece 30A. [Selected figure] Figure 1
???????
[0001]
The present invention relates to a microphone that receives an acoustic wave by a diaphragm
and outputs an audio signal. Specifically, it is equipped with a diffraction grating that moves with
the vibration of the diaphragm, and it is possible to detect the amount of displacement of the
diaphragm due to sound waves using optical interference of light emitted from the coherent light
source and diffracted by the diffraction grating. It is
[0002]
FIG. 13 is a block diagram showing an example of a conventional microphone, and FIG. 13 is a
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side sectional view showing an outline of the configuration of a dynamic microphone.
[0003]
The conventional microphone 101 includes a diaphragm 102 for receiving a sound wave, a voice
coil 103 attached to the diaphragm 102, a yoke plate 104 disposed opposite to the voice coil
103, and a magnet 105.
[0004]
In the microphone 101, a center pole 106 disposed opposite to the inside of the voice coil 103 is
attached to the magnet 105, and a magnetic circuit is configured by the magnet 105, the yoke
plate 104, and the voice coil 103.
[0005]
In addition, the microphone 101 includes an acoustic resistance element 108 such as a baffle
plate, and a sound wave introduction port 109 through which air passes along with the vibration
of the diaphragm 102.
[0006]
In the above-described conventional dynamic microphone, the mass of the voice coil integrated
with the diaphragm occupies most of the mass of the vibration system, thereby deteriorating the
high frequency characteristic.
In addition, although it is minute, braking by electromagnetic induction may slow the movement
of the free diaphragm and degrade the characteristics.
[0007]
In addition, in the condenser microphone as well, vibration is limited by the deflection of the
diaphragm due to electrostatic force due to the application of the phantom voltage.
In addition, metal deposition on the diaphragm is necessary to form an electrode, which also
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causes increase in the mass of the vibration system.
[0008]
For this reason, while high sound quality is becoming mainstream by sampling of SACD (Super
AudioCD) and 24bit-96kHz, the limit of recording of high frequency sound of 20kHz or more is
particularly limited for the above-mentioned conventional analog microphones. Yes, it is a
bottleneck in the case of recording content that makes full use of the high frequency
reproduction that is the feature of the above-mentioned recording method.
[0009]
Also, with regard to the dynamic range, the dynamic range up to 144 dB, which is possible with
24-bit recording, has not been fully utilized.
[0010]
Furthermore, in a recording site using a microphone, in the conventional microphone, it is
necessary to supply phantom power from the mixing console to the noise increase due to the
long distance routing with the cable through which the analog signal flows, and to the condenser
microphone. , Has become an obstacle to the digitization of the recording and production system.
[0011]
On the other hand, a microphone has been proposed in which a diaphragm is configured by a
diffraction grating and a signal corresponding to an acoustic wave is output from diffracted light
that is irradiated to and diffracted by the diaphragm (for example, see Patent Document 1).
[0012]
JP 2005-318462 A
[0013]
In the conventional analog microphone, there is a problem that the voice coil occupies most of
the mass of the vibration system and the high frequency characteristic is deteriorated.
[0014]
Also, in a microphone using a conventional diffraction grating, the diffraction grating is formed
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on the surface of the diaphragm that receives the sound pressure, so a special diaphragm is
required, cost increases, and the characteristics of the diaphragm deteriorate. There was a
problem that.
[0015]
The present invention has been made to solve such a problem, and an object of the present
invention is to provide a microphone that can detect vibration related to sound with high
sensitivity.
[0016]
In order to solve the problems described above, the microphone of the present invention is
attached to a diaphragm that receives and vibrates a sound wave and a support member
provided on the back side of the diaphragm, and the diffraction moves along the vibration
direction of the diaphragm. The light from the grating and the light source from which the
coherent light is emitted is made incident on the diffraction grating, and causes the two
diffracted lights diffracted by the diffraction grating to interfere with each other, according to the
amount of movement of the diffraction grating moving by the vibration of the diaphragm. And a
grating interferometer for detecting the displacement of the diaphragm from the phase change of
the interference light to be changed.
[0017]
In the microphone of the present invention, the light emitted from the light source is diffracted
by the diffraction grating through a predetermined optical path, and the two diffracted lights
diffracted by the diffraction grating are interfered, and the phase is changed according to the
amount of movement of the diffraction grating. A changing interference signal is obtained.
[0018]
Then, when the diaphragm receives a sound wave and vibrates, an audio signal according to the
displacement amount of the diaphragm can be obtained from the phase change of the
interference signal.
[0019]
According to the microphone of the present invention, by providing the diffraction grating in
place of the voice coil used in the dynamic microphone, it is possible to reduce the mass of the
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vibration system by having a configuration equivalent to that of the conventional dynamic
microphone.
In addition, the detection of the displacement amount of the diaphragm is performed in a
noncontact manner using light (laser light), whereby the influence of an electric field or a
magnetic field can be eliminated.
This can improve the sensitivity and frequency response.
Further, since the present invention can be realized with the same configuration as the
conventional one, it is possible to provide a microphone with improved sensitivity and frequency
response at low cost.
[0020]
Hereinafter, embodiments of the microphone of the present invention will be described with
reference to the drawings.
[0021]
<The example of composition of the microphone of a 1st embodiment> Drawing 1 is a block
diagram showing an example of the microphone of a 1st embodiment, and the outline of the
composition of the microphone of a 1st embodiment is shown in Drawing 1. It is illustrated in a
side sectional view.
[0022]
The microphone 1A of the first embodiment includes a diaphragm 2 that receives sound
pressure, and an optical block 4 that constitutes a diffraction grating interferometer 3A that
measures the amount of movement of the diaphragm 2.
Further, the microphone 1 </ b> A includes an acoustic resistance element 5 a such as a baffle
plate and a sound wave introduction port 5 b through which air passes along with the vibration
of the diaphragm 2.
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[0023]
The diaphragm 2 has an outer peripheral portion supported by the plate 20, and a cylindrical
bobbin 21 as an example of a support member is integrated with the back side of the inner
peripheral portion, for example. 21 reciprocates in parallel along the traveling direction of the
sound wave.
[0024]
The diffraction grating interferometer 3 </ b> A includes the diffraction grating piece 30 </ b> A
inside the bobbin 21.
In the diffraction grating piece 30A, the small piece on which the reflection type diffraction
grating is formed is bonded and fixed to the bobbin 21 in such a direction that the diffraction
grating is perpendicular to the vibration direction of the diaphragm 2.
The diffraction grating may be directly formed integrally with the bobbin 21.
[0025]
Here, the length of the diffraction grating piece 30A along the vibration direction of the
diaphragm 2 is equal to or slightly longer than the maximum movement distance of the
diaphragm 2, and it is sufficient if the length is about several mm. The increase in mass of the
vibration system due to the attachment of the
[0026]
In a conventional dynamic microphone as shown in FIG. 13, an air core coil fused with a resin is
used, but the coil is made of metal and therefore occupies most of the mass of the vibration
system.
[0027]
On the other hand, in the microphone 1A of the present embodiment, the bobbin 21 is a
component for fixing the diffraction grating piece 30A, and it is only necessary to ensure the
rigidity necessary to support the diffraction grating piece 30A. The mass of the vibration system
can be reduced by making it into the minimum shape by making a notch or a hole.
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[0028]
<Configuration Example of Diffraction Grating Interferometer in First Embodiment> FIG. 2 is a
configuration diagram showing an example of the diffraction grating interferometer in the first
embodiment, and next, the microphone of the first embodiment The configuration of the
diffraction grating interferometer 3A constituting 1A will be described.
[0029]
The diffraction grating interferometer 3A is an example of a grating interferometer, and a
semiconductor laser (LD) 31 which is an example of a coherent light source, a lens 32 for
narrowing light emitted from the semiconductor laser 31 at a predetermined radiation angle, and
the semiconductor laser 31. And a polarization beam splitter (PBS) 33 that splits the light emitted
from the light into two lights with different polarization components and superposes the two
lights with different polarization components.
[0030]
The polarization beam splitter 33 is an example of a first polarization unit, and is emitted from
the semiconductor laser 31 and the light narrowed by the lens 32 is incident thereon, and the
incident light from the semiconductor laser 31 is split into a P component and an S component.
Polarized light is reflected and P-polarized light is transmitted.
Here, if the light from the semiconductor laser 31 is linearly polarized light, if the polarization
direction is inclined 45 ░ and incident on the polarization beam splitter 33, the intensities of the
split lights become equal.
[0031]
Further, the diffracted light of S polarization returned to the polarization beam splitter 33 is
reflected, the diffracted light of P polarization is transmitted, and the two diffracted lights are
superimposed.
[0032]
The diffraction grating interferometer 3A reflects the S-polarized light emitted from the
semiconductor laser 31 and reflected by the polarization beam splitter 33 to be incident on the
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diffraction grating piece 30A, and passes through a predetermined optical path to the diffraction
grating piece 30A. A mirror 34 a is provided to reflect the back-diffracted light and make it enter
the polarization beam splitter 33.
[0033]
Also, the diffraction grating interferometer 3A reflects the S-polarized light reflected by the
polarization beam splitter 33 and the mirror 34a and incident on the diffraction grating piece
30A and returning it to the diffraction grating piece 30A, and diffraction A lens 36a narrows the
light diffracted by the grating piece 30A and the light reflected by the mirror 35a, and the
quarter-wave plate 37a converts the polarization state of the light reflected by the mirror 35a.
[0034]
The mirror 35a is reflected by the polarization beam splitter 33 and the mirror 34a and is
incident on the point P of the diffraction grating piece 30A, and the S-polarized light diffracted by
the diffraction grating piece 30A is vertically reflected and reflected by the mirror 35a The light
is returned to the point P of the diffraction grating piece 30A.
[0035]
The optical axis of the 1?4 wavelength plate 37a is arranged to be inclined 45 ░ with respect to
the polarization direction of the light, and the S polarized light reflected by the mirror 35a and
returned to the diffraction grating piece 30A is converted to P polarized light.
[0036]
Thus, the S-polarized light emitted from the semiconductor laser 31 and reflected by the
polarization beam splitter 33 reciprocates in a predetermined optical path and is diffracted twice
by the diffraction grating piece 30A, and the quarter-wave plate 37a is By passing twice, it is
converted into P-polarized light, returns to the polarization beam splitter 33, and transmits
through the polarization beam splitter 33.
[0037]
Similarly, the diffraction grating interferometer 3A reflects the P-polarized light emitted from the
semiconductor laser 31 and transmitted through the polarization beam splitter 33 to be incident
on the diffraction grating piece 30A, and passes the predetermined light path to the diffraction
grating piece A mirror 34 b is provided to reflect the diffracted light back to 30 A to be incident
on the polarization beam splitter 33.
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[0038]
In addition, the diffraction grating interferometer 3A transmits the polarization beam splitter 33,
is reflected by the mirror 34b, reflects the P-polarized light that is incident on the diffraction
grating piece 30A and is diffracted and returns it to the diffraction grating piece 30A. And a lens
36b for narrowing the light diffracted by the diffraction grating piece 30A and the light reflected
by the mirror 35b, and a quarter-wave plate 37b for converting the polarization state of the light
reflected by the mirror 35b.
[0039]
The mirror 35b transmits the polarization beam splitter 33, is reflected by the mirror 34b, is
incident on the point P of the diffraction grating piece 30A, P-polarized light diffracted by the
diffraction grating piece 30A is vertically reflected, and is reflected by the mirror 35b The
reflected light is returned to the point P of the diffraction grating piece 30A.
[0040]
The optical axis of the 1?4 wavelength plate 37b is disposed at an angle of 45 ░ with respect to
the polarization direction of the light, and P-polarized light reflected by the mirror 35b and
returned to the diffraction grating piece 30A is converted into S-polarization.
[0041]
As a result, the P-polarized light emitted from the semiconductor laser 31 and transmitted
through the polarization beam splitter 33 is reciprocated in a predetermined optical path and
diffracted twice by the diffraction grating piece 30A. By passing the light beam one time, it is
converted into S-polarization, returns to the polarization beam splitter 33, and is reflected by the
polarization beam splitter 33.
[0042]
Therefore, the S-polarized light and the P-polarized light emitted from the semiconductor laser
31 and split by the polarization beam splitter 33 respectively pass through predetermined optical
paths and are diffracted by the diffraction grating piece 30A, and are returned to the polarization
beam splitter 33 for superposition. Be done.
[0043]
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The diffraction grating interferometer 3A includes a lens 38 for narrowing the light
superimposed by the polarization beam splitter 33, and a beam splitter (BS) 39 for splitting the
light narrowed by the lens 38, superimposed by the polarization beam splitter 33.
The beam splitter 39 is an example of a light splitting means, and is constituted by a half mirror
or the like having a predetermined transmittance (reflectance), and the light beam superimposed
by the polarization beam splitter 33 is split into two.
[0044]
Further, the diffraction grating interferometer 3A is a second polarization means which is
inclined 45 ░ with respect to the polarization direction of the light reflected and incident by the
beam splitter 39 and splits the incident light into two light having different polarization
components. As a polarization beam splitter (PBS) 40, a photoelectric converter (PD) 41a as a
light receiving unit to which light reflected by the polarization beam splitter 40 is incident, and a
light receiving unit to which light transmitted through the polarization beam splitter 40 is
incident The photoelectric converter (PD) 41 b of
[0045]
Further, the diffraction grating interferometer 3A is provided with a 1?4 wavelength plate 42
whose optical axis is inclined 45 ░ with respect to the polarization direction of the light
transmitted through the beam splitter 39 and which converts the polarization state of the
incident light.
Furthermore, the diffraction grating interferometer 3A is inclined 45 ░ with respect to the
polarization beam splitter 40, transmits the beam splitter 39, and the light whose polarization
state is converted by the 1?4 wavelength plate 42 is converted into two light beams having
different polarization components. A polarization beam splitter (PBS) 43 as a second polarization
unit to split, a photoelectric converter (PD) 44 a as a light reception unit as a light reception unit
to which light reflected by the polarization beam splitter 43 is incident, and a polarization beam
splitter 43 A photoelectric converter (PD) 44 b as light receiving means for receiving light is
provided.
[0046]
<Operation Example of Diffraction Grating Interferometer in First Embodiment> Next, an example
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of the operation of the diffraction grating interferometer 3A in the first embodiment will be
described.
[0047]
The light emitted from the semiconductor laser 31 is narrowed into an appropriate beam by the
lens 32 and split into two beams by the polarization beam splitter 33.
The light reflected by the polarization beam splitter 33 is S-polarized, and the transmitted light is
P-polarized.
If the light from the semiconductor laser 31 is linearly polarized light, the light beams to be split
become equal in intensity by being incident on the polarization beam splitter 33 whose
polarization direction is inclined 45 ░.
[0048]
The light (S polarized light) reflected by the polarization beam splitter 33 is reflected by the
mirror 34 a and is incident on the point P of the diffraction grating piece 30A.
Similarly, the light (P-polarized light) transmitted through the polarization beam splitter 33 is
also reflected by the mirror 34 b and is incident on the point P of the diffraction grating piece
30A.
[0049]
The light incident on the diffraction grating piece 30A is diffracted in the direction shown by the
following equation (1).
sin ? 1 + sin ? 2 = n и ? / ? (1) where ? 1: incident angle, ? 2: diffraction angle, ?: grating
pitch, ?: wavelength of light, n: diffraction order
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The diffraction orders in the two optical paths are the same.
[0050]
As described above, the S-polarized light emitted from the semiconductor laser 31 and reflected
by the polarization beam splitter 33 is reflected by the mirror 34a and is incident on the point P
of the diffraction grating piece 30A and is diffracted.
The S-polarized light (first-order diffracted light) diffracted by the diffraction grating piece 30A
passes through the lens 36a and the 1?4 wavelength plate 37a, is vertically reflected by the
mirror 35a, and returns along the same optical path. And is incident on a point P of the
diffraction grating piece 30A through the lens 36a and is diffracted.
[0051]
Here, since the optical axis of the quarter-wave plate 37a is inclined 45 ░ with respect to the
polarization direction of light, the light which has passed through the quarter-wave plate 37a
twice and returned to the point P of the diffraction grating piece 30A Is P-polarized.
[0052]
The P-polarized light (second-order diffracted light) diffracted by the diffraction grating piece
30A is again reflected by the mirror 34a and returns to the polarization beam splitter 33. Since it
is P-polarization, it is transmitted through the polarization beam splitter 33.
[0053]
On the other hand, the P-polarized light emitted from the semiconductor laser 31 and
transmitted through the polarization beam splitter 33 is similarly reflected by the mirror 34 b
and incident on the point P of the diffraction grating piece 30 A and diffracted.
P-polarized light (first-order diffracted light) diffracted by the diffraction grating piece 30A
passes through the lens 36b and the 1?4 wavelength plate 37b, is vertically reflected by the
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mirror 35b, and returns along the same optical path. And is incident on a point P of the
diffraction grating piece 30A through the lens 36b and is diffracted.
[0054]
Since the optical axis of the quarter-wave plate 37b is also inclined 45 ░ with respect to the
polarization direction of light, the light passing through the quarter-wave plate 37b twice and
returning to the point P of the diffraction grating piece 30A is S-polarized light It has become.
[0055]
Then, the S-polarized light (second-order diffracted light) diffracted by the diffraction grating
piece 30A is again reflected by the mirror 34b and returns to the polarization beam splitter 33.
Since it is S-polarization, it is reflected by the polarization beam splitter 33.
[0056]
Thereby, the light emitted from the semiconductor laser 31 and split into S-polarization and Ppolarization by the polarization beam splitter 33 is diffracted by the diffraction grating piece 30A
through predetermined optical paths and is returned to the polarization beam splitter 33. Are
superimposed.
[0057]
The light superimposed by the polarization beam splitter 33 passes through the lens 38 and is
split into two by the beam splitter 39.
[0058]
The light of S-polarization and P-polarization reflected by the beam splitter 39 is incident on the
polarization beam splitter 40 inclined 45 ░ with respect to the polarization direction.
The light reflected by the polarization beam splitter 40 is incident on the photoelectric converter
41 a, and the light transmitted through the polarization beam splitter 40 is incident on the
photoelectric converter 41 b.
[0059]
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In the photoelectric converter 41a and the photoelectric converter 41b, the interference signal
shown in the following equation (2) is obtained.
A cos (4 и K и x + ?) (2) where K = 2? / ?, x: moving amount of the diffraction grating piece
(diaphragm), ?: initial phase
[0060]
As a result, in the photoelectric converter 41a and the photoelectric converter 41b, signals
different in phase by 180 ░ can be obtained.
[0061]
On the other hand, the S polarized light and P polarized light transmitted through the beam
splitter 39 become circularly polarized light in the opposite direction by passing through the 1?4
wavelength plate 42 whose optical axis is inclined 45 ░ to the polarization direction.
The circularly polarized light beams rotating in opposite directions are superimposed to form
linearly polarized light, which is incident on the polarization beam splitter 43, and the light beam
reflected by the polarization beam splitter 43 is incident on the photoelectric converter 44a. The
light transmitted through the light source is incident on the photoelectric converter 44b.
[0062]
The polarization direction of the linearly polarized light incident on the polarization beam splitter
43 rotates once when the diffraction grating piece 30A moves by ? / 2 in the X direction by the
vibration of the diaphragm 2 shown in FIG.
Therefore, in the photoelectric converter 44a and the photoelectric converter 44b, an
interference signal similar to that of the equation (2) can be obtained.
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[0063]
Since the photoelectric converter 44 a and the photoelectric converter 44 b are 180 ░ out of
phase and the polarization beam splitter 43 is inclined 45 ░ with respect to the polarization
beam splitter 40, the signals obtained by the photoelectric converters 44 a and 44 b are , 90 ░
out of phase with the signal obtained by the photoelectric converters 41a and 41b.
[0064]
Here, in the detection optical system based on the diffraction grating interferometer 3A
described above, since the optical system is symmetrical with respect to the perpendicular H
passing through the point P of the diffraction grating piece 30A, the Y direction orthogonal to
the vibration direction of the bobbin 21 Even if the diffraction grating piece 30A moves, the
position measurement error does not occur.
In addition, by equalizing the optical path lengths of the two optical paths incident on the point P,
the influence of the wavelength fluctuation of the light source is eliminated.
[0065]
As described above, in the microphone 1A of the present embodiment, since the voice coil used
for the dynamic microphone is not necessary, the mass of the vibration system can be reduced,
and the sensitivity and the frequency response are improved.
In addition, since a magnetic circuit including a magnet having a large volume is not required,
the degree of freedom in acoustic design is increased.
[0066]
Furthermore, since it is not influenced by an electric field or a magnetic field in noncontact
detection by a laser and is not influenced by an electric field or a magnetic field, the movable
range of the diaphragm can be made large, and a wide dynamic range can be obtained.
[0067]
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<The example of composition of the signal processing part of the microphone of this
embodiment> Drawing 3 is a functional block diagram showing an example of the signal
processing part of the microphone of this embodiment.
In the signal processing unit 10A, the electric signal output from the photoelectric converter 41a
and the photoelectric converter 41b shown in FIG. 2 is input to the differential amplifier 50a
which is a differential amplification unit, and in the differential amplifier 50a, the photoelectric
converter 41a , 41b are differentially amplified, and a signal in which the DC component of the
interference signal is canceled is output.
[0068]
Further, the electric signals output from the photoelectric converter 44a and the photoelectric
converter 44b shown in FIG. 2 are input to the differential amplifier 50b which is a differential
amplification means, and in the differential amplifier 50b, the electric signals from the
photoelectric converters 44a and 44b The electrical signal is differentially amplified, and a signal
in which the DC component of the interference signal is canceled is output.
[0069]
Therefore, the DC components of the two outputs different in phase by 180 ░ are canceled in
each of the photoelectric converter 41a and the photoelectric converter 41b, and the
photoelectric converter 44a and the photoelectric converter 44b, and the differential amplifier
50a and the differential amplifier An A-phase signal and a B-phase signal are obtained from 50b,
and the A / B-phase signal is input to a digital signal processing unit (incremental signal
generator) 51.
[0070]
FIG. 4 is a functional block diagram showing an example of the digital signal processing unit in
the present embodiment.
In the digital signal processing unit 51, two output signals having different 90 ░ phases from
the differential amplifier 50a and the differential amplifier 50b shown in FIG. 3 are respectively
input to the A / D converters 52a and 52b and converted into digital signals. Ru.
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[0071]
The correction circuit 53 removes the DC offset from the digital signals converted by the A / D
converters 52a and 52b, and adjusts the gain and the phase to correspond to a sin wave signal
and a cos wave signal, respectively.
[0072]
Then, the angle ? is uniquely determined by the following equation (3), and the position (angle)
on the Lissajous figure of the output waveform as shown in FIG. 5 is determined.
? = tan <?1> (y / x) (3) Here, the range of ? is ? (? / 2) <? <(? / 2).
[0073]
The calculation of ? may be performed using an approximate expression, but using the look-up
table 54 enables high speed calculation.
[0074]
The determined angle ? is integrated by an accumulator 55 to obtain an integrated
displacement amount.
Further, this displacement data is input to an audio D / A converter 56a to obtain an analog
audio signal.
Alternatively, displacement amount data is input to the digital audio interface 56b to obtain a
digital audio signal.
[0075]
As described above, in the microphone 1A of the present embodiment, direct output can be
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obtained in digital, and it is easy to cope with optical transmission by digital signal and the like.
In addition, digital output can be sampled at high speed, and noise reduction by oversampling
and noise shaving can be expected.
[0076]
<Configuration Example of Microphone of Second Embodiment> FIG. 6 is a configuration
diagram showing an example of a microphone of the second embodiment, and in FIG. 6, an
outline of the configuration of the microphone using a transmission type diffraction grating. Is
shown in a side sectional view.
[0077]
The microphone 1B of the second embodiment includes the diaphragm 2 that receives sound
pressure, and the diffraction grating interferometer 3B that measures the amount of movement
of the diaphragm 2.
[0078]
The diaphragm 2 has an outer peripheral portion supported by the plate 20, and a cylindrical
bobbin 21 is, for example, integrated on the back side of the inner peripheral portion, and when
the diaphragm 2 receives a sound pressure, the bobbin 21 moves in the sound wave traveling
direction Reciprocate in parallel along the
[0079]
The diffraction grating interferometer 3 </ b> B includes the diffraction grating piece 30 </ b> B
on the bobbin 21.
In the diffraction grating piece 30B, the small piece on which the transmission type diffraction
grating is formed is adhered and fixed to the bobbin 21 in such a direction that the diffraction
grating is perpendicular to the vibration direction of the diaphragm 2.
The diffraction grating may be directly formed integrally with the bobbin 21.
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[0080]
<Configuration Example of Diffraction Grating Interferometer in Second Embodiment> FIG. 7 is a
configuration diagram showing an example of a diffraction grating interferometer in the second
embodiment, and next, the microphone of the second embodiment The configuration of the
diffraction grating interferometer 3B constituting 1 B will be described.
[0081]
The diffraction grating interferometer 3B includes a semiconductor laser 31 which is an example
of a coherent light source, and a lens 32 which narrows light emitted from the semiconductor
laser 31 at a predetermined radiation angle.
Further, the diffraction grating interferometer 3B splits the light emitted from the semiconductor
laser 31 into two light beams of S-polarization and P-polarization and makes them incident on
the diffraction grating piece 30B, while being diffracted by the diffraction grating piece 30B and
returning S A polarization beam splitter 33 is provided which superposes two light beams of
polarized light and P polarized light.
[0082]
Further, the diffraction grating interferometer 3B reflects the light of S-polarized light
transmitted through the diffraction grating piece 30B and returns it to the diffraction grating
piece 30B, and transmits the diffraction grating piece 30B and transmits the diffracted Ppolarization light. A reflection prism 45 that reflects light and returns it to the diffraction grating
piece 30B, and quarter wavelength plates 46a and 46b that convert the polarization state of the
light reflected by the reflection prism 45 are provided.
[0083]
The reflecting prism 45 is reflected by the polarization beam splitter 33 and is incident on the
diffraction grating piece 30B, and the light of S-polarized light transmitted through the
diffraction grating piece 30B and diffracted is reflected by one surface, and the diffraction
grating piece in the same optical path It is returned to 30B.
[0084]
The optical axis of the 1?4 wavelength plate 46a is arranged to be inclined 45 ░ with respect to
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the polarization direction of the light, and the S-polarized light emitted from the semiconductor
laser 31 and reflected by the polarization beam splitter 33 is The light is reciprocated along the
optical path and diffracted twice by the diffraction grating piece 30B, and is converted into Ppolarized light by passing through the 1?4 wavelength plate 46a twice and returned to the
polarization beam splitter 33 and transmitted through the polarization beam splitter 33 .
[0085]
Similarly, the reflection prism 45 transmits the polarization beam splitter 33 and is incident on
the diffraction grating piece 30B, and the light of P polarization transmitted and diffracted by the
diffraction grating piece 30B is reflected by the other surface, and in the same light path It is
returned to the diffraction grating piece 30B.
[0086]
The optical axis of the 1?4 wavelength plate 46b is arranged to be inclined 45 ░ with respect to
the polarization direction of the light, and the P-polarized light emitted from the semiconductor
laser 31 and transmitted through the polarization beam splitter 33 has a predetermined optical
path. And are diffracted twice by the diffraction grating piece 30B, and are converted into Spolarized light by passing through the 1?4 wavelength plate 46b twice and returned to the
polarization beam splitter 33 and reflected by the polarization beam splitter 33 .
[0087]
Therefore, the S-polarized light and the P-polarized light emitted from the semiconductor laser
31 and split by the polarization beam splitter 33 respectively pass through predetermined optical
paths and are diffracted by the diffraction grating piece 30B, and are returned to the polarization
beam splitter 33 and overlapped. Be done.
[0088]
The following configuration of the diffraction grating interferometer 3B is the same as that of the
first embodiment, and a lens 38 for narrowing the light superimposed by the polarization beam
splitter 33 and a lens 38 superimposed on the polarization beam splitter 33 A beam splitter 39 is
provided to split the light.
The beam splitter 39 is configured of a half mirror or the like having a predetermined
transmittance (reflectance), and the light beam superimposed by the polarization beam splitter
05-05-2019
20
33 is split into two.
[0089]
Furthermore, the diffraction grating interferometer 3B is tilted 45 ░ with respect to the
polarization direction of the light reflected and incident by the beam splitter 39, and splits the
incident light into two light beams having different polarization components, and The
photoelectric converter 41a receives the light reflected by the polarizing beam splitter 40, and
the photoelectric converter 41b receives the light transmitted through the polarizing beam
splitter 40.
[0090]
Further, the diffraction grating interferometer 3B is provided with a 1?4 wavelength plate 42
whose optical axis is inclined 45 ░ with respect to the polarization direction of the light
transmitted through the beam splitter 39, and which converts the polarization state of the
incident light.
Furthermore, the diffraction grating interferometer 3B is inclined 45 ░ with respect to the
polarization beam splitter 40, transmits the beam splitter 39, and the light whose polarization
state is converted by the 1?4 wavelength plate 42 is converted into two light components having
different polarization components. A polarization beam splitter 43 to be split, a photoelectric
converter 44a to which light reflected by the polarization beam splitter 43 is incident, and a
photoelectric converter 44b to which light transmitted through the polarization beam splitter 43
is incident.
[0091]
<Operation Example of Diffraction Grating Interferometer in Second Embodiment> Next, an
example of the operation of the diffraction grating interferometer 3B in the second embodiment
will be described.
[0092]
The light emitted from the semiconductor laser 31 is narrowed into an appropriate beam by the
lens 32 and split into two beams by the polarization beam splitter 33.
05-05-2019
21
The light reflected by the polarization beam splitter 33 is S-polarized, and the transmitted light is
P-polarized.
[0093]
The S-polarized light reflected by the polarization beam splitter 33 and the P-polarized light
transmitted through the polarization beam splitter 33 are respectively incident on the diffraction
grating piece 30B.
[0094]
The light incident on the diffraction grating piece 30B is diffracted in the direction indicated by
the above-mentioned equation (1), whereby the S-polarized light (first-order diffracted light)
transmitted through the diffraction grating piece 30B and diffracted is 1 The light is reflected by
one surface of the reflecting prism 45 through the quarter wave plate 46a, returns to the same
optical path, passes through the quarter wave plate 46a, is incident on the diffraction grating
piece 30B, and is diffracted.
[0095]
Here, since the optical axis of the 1?4 wavelength plate 46a is inclined 45 ░ with respect to the
polarization direction of light, the light passing through the 1?4 wavelength plate 46a twice and
returned to the diffraction grating piece 30B is P-polarized light It has become.
[0096]
Then, the P-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization beam splitter 33, and
since it is P-polarization, it is transmitted through the polarization beam splitter 33.
[0097]
On the other hand, P-polarized light emitted from the semiconductor laser 31 and transmitted
through the polarization beam splitter 33 is similarly incident on the diffraction grating piece
30B and diffracted.
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P-polarized light (first-order diffracted light) transmitted through the diffraction grating piece
30B and diffracted (first-order diffracted light) passes through the 1?4 wavelength plate 46b, is
reflected by the other surface of the reflecting prism 45, and returns along the same optical path.
The light is incident on the diffraction grating piece 30B through the wave plate 46b and is
diffracted.
[0098]
The optical axis of the 1?4 wavelength plate 46b is also inclined 45 ░ with respect to the
polarization direction of the light, so the light passing through the 1?4 wavelength plate 46b
twice and returned to the diffraction grating piece 30B becomes S polarization. There is.
[0099]
Then, the S-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization beam splitter 33, and
since it is S-polarization, it is reflected by the polarization beam splitter 33.
[0100]
Thereby, the light emitted from the semiconductor laser 31 and split into S polarized light and P
polarized light by the polarization beam splitter 33 respectively passes through predetermined
optical paths and is diffracted by the diffraction grating piece 30 B and returned to the
polarization beam splitter 33 Are superimposed.
[0101]
The light superimposed by the polarization beam splitter 33 passes through the lens 38 and is
split into two by the beam splitter 39.
[0102]
The light of S-polarization and P-polarization reflected by the beam splitter 39 is incident on the
polarization beam splitter 40 inclined 45 ░ with respect to the polarization direction.
The light reflected by the polarization beam splitter 40 is incident on the photoelectric converter
41 a, and the light transmitted through the polarization beam splitter 40 is incident on the
photoelectric converter 41 b.
05-05-2019
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[0103]
In the photoelectric converter 41a and the photoelectric converter 41b, the interference signal
shown in the above-mentioned equation (2) is obtained, and in the photoelectric converter 41a
and the photoelectric converter 41b, signals different in phase by 180 ░ are obtained.
[0104]
On the other hand, the S polarized light and P polarized light transmitted through the beam
splitter 39 become circularly polarized light in the opposite direction by passing through the 1?4
wavelength plate 42 whose optical axis is inclined 45 ░ to the polarization direction.
The circularly polarized light beams rotating in opposite directions are superimposed to form
linearly polarized light, which is incident on the polarization beam splitter 43, and the light beam
reflected by the polarization beam splitter 43 is incident on the photoelectric converter 44a. The
light transmitted through the light source is incident on the photoelectric converter 44b.
[0105]
The polarization direction of the linearly polarized light incident on the polarization beam splitter
43 rotates once when the diffraction grating piece 30B moves by X / 2 in the X direction by the
vibration of the diaphragm 2 shown in FIG.
Therefore, in the photoelectric converter 44a and the photoelectric converter 44b, an
interference signal similar to that of the equation (2) can be obtained.
[0106]
Since the photoelectric converter 44 a and the photoelectric converter 44 b are 180 ░ out of
phase and the polarization beam splitter 43 is inclined 45 ░ with respect to the polarization
beam splitter 40, the signals obtained by the photoelectric converters 44 a and 44 b are , 90 ░
out of phase with the signal obtained by the photoelectric converters 41a and 41b.
05-05-2019
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[0107]
The configurations and operations of the photoelectric converters 41a and 41b and the signal
processing unit that processes the signals output from the photoelectric converters 44a and 44b
are the same as the techniques described with reference to FIGS. 3 and 4.
[0108]
As described above, even if a transmission type diffraction grating is used, an audio signal can be
obtained on the same principle as a microphone using a reflection type diffraction grating, and
the mass difference due to the difference in the configuration of the diffraction grating or the
optical path that can be incorporated. The microphone can be designed in consideration of the
configuration of
[0109]
In the microphone 1B of the second embodiment, the reflecting prism 45 may be disposed inside
the bobbin 21 and the optical block 4 constituting the diffraction grating interferometer 3B may
be disposed outside the bobbin 21.
[0110]
<Configuration Example of Microphone of Third Embodiment> FIG. 8 is a configuration diagram
showing an example of a microphone of the third embodiment, and in FIG. 8, a transmission type
diffraction grating is used and a light emitting / receiving unit An outline of the configuration of
a microphone in which a beam splitter and the like are unitized is illustrated in a side sectional
view.
[0111]
The microphone 1C of the third embodiment includes a diaphragm 2 that receives a sound
pressure, and a light emitting / receiving composite unit 6 that configures a diffraction grating
interferometer 3C that measures the amount of movement of the diaphragm 2.
[0112]
The diaphragm 2 has an outer peripheral portion supported by the plate 20, and a cylindrical
bobbin 21 is, for example, integrated on the back side of the inner peripheral portion, and when
the diaphragm 2 receives a sound pressure, the bobbin 21 moves in the sound wave traveling
direction Reciprocate in parallel along the
05-05-2019
25
[0113]
The diffraction grating interferometer 3 C includes the diffraction grating piece 30 B on the
bobbin 21.
In the diffraction grating piece 30B, the small piece on which the transmission type diffraction
grating is formed is bonded and fixed to the bobbin 21 in such a direction that the diffraction
grating is perpendicular to the vibration direction of the diaphragm 2.
The diffraction grating may be directly formed integrally with the bobbin 21.
[0114]
<Configuration Example of Light Emitting and Receiving Combined Unit in Third Embodiment>
FIG. 9 is a configuration diagram showing an example of a light emitting and receiving combined
unit in the third embodiment. Next, the microphone according to the third embodiment is
described. The configuration of the light emitting / receiving complex unit 6 constituting the
diffraction grating interferometer 3C in 1C will be described.
[0115]
The light emitting / receiving composite unit 6 includes a housing member 60 as a substrate for
housing a light emitting element and a light receiving element, a lens portion 61, and a
polarization portion 62 (62a, 62b, 62c and 62d) for transmitting only a predetermined
polarization component. A phase plate 63 for converting the polarization state of the light, and a
light branching portion 64 for dividing light to be irradiated to the diffraction grating piece 30B
and for dividing second-order diffracted light obtained by being diffracted by the diffraction
grating piece 30B Equipped with
[0116]
The housing member 60 includes a semiconductor laser 71, which is an example of a coherent
light source for emitting light, and photodetectors 72 (72a, 72b, 72c, and 72d), which are
photoelectric converters for photoelectrically converting interference light to generate an
interference signal. A semiconductor substrate 73 for installing a semiconductor laser 71 and
applying an electrical signal, and a semiconductor substrate 74 for installing each photo detector
and extracting an electrical signal.
05-05-2019
26
[0117]
The light branching portion 64 splits the light emitted from the semiconductor laser 71 into two
light beams having different polarization components and emits the light, and also separates the
second-order diffracted light diffracted by the diffraction grating piece 30B shown in FIG. It has a
section 78 and light branching films 79a, 79b, 79c, 79d for splitting the light superposed in the
polarization separating section 78.
[0118]
An interference signal corresponding to the amount of light obtained by photoelectric conversion
by each photodetector 72 is detected by a signal processing unit (not shown) via the
semiconductor substrate 74.
The signal processing unit (not shown) obtains a phase difference based on the obtained
interference signal, and outputs a position signal indicating the relative movement position of the
diffraction grating piece 30B.
[0119]
The lens unit 61 is an optical element such as a lens having a predetermined numerical aperture,
and the light emitted from the semiconductor laser 71 is incident and focused, and the light split
and emitted by the polarizing unit 62 is incident thereon. It is squeezed.
In the lens unit 61, the degree of integration can be increased by disposing in the same package
a lens that controls the beam diameter of both the light emitted to the outside and the light
received, and the manufacturing process can be simplified, and the entire apparatus can Can
increase the reliability of
[0120]
The polarization units 62 a, 62 b, 62 c and 62 d transmit only predetermined polarization
components of the lights Ld 1, Ld 2, Ld 3 and Ld 4 incident from the phase plate 63 and emit the
05-05-2019
27
light to the lens unit 61.
Each polarization part 62 should just be arrange | positioned at 45 degree space | interval (for
example, 5 degrees, 50 degrees, 95 degrees, 140 degrees), and can be arrange | positioned,
without receiving restrictions in the attitude | position at the time of attachment of the
polarization part 62.
By providing such a polarization part 62 between the phase plate 63 and the lens part 61, there
is also an advantage that the entire unit can be made compact.
[0121]
The phase plate 63 is stacked so as to be sandwiched between the polarization unit 62 and the
light branching unit 64.
The phase plate 63 is, for example, a 1?4 wavelength plate, and performs conversion between
circularly polarized light and linearly polarized light.
The phase plate 63 receives light from the semiconductor laser 71 through the lens unit 61.
The phase plate 63 converts, for example, light from the semiconductor laser 71, which is
linearly polarized light, into circularly polarized light and irradiates it to the polarization
separation unit 78.
The phase plate 63 receives the lights Ld1, Ld2, Ld3, and Ld4 emitted from the light branching
films 79a, 79b, 79c, and 79d, converts the lights into circularly polarized light, and emits the
circularly polarized light.
That is, a configuration is adopted in which conversion of light from the semiconductor laser 71
and conversion of light from the light branching film 79 are shared by one phase plate 63.
05-05-2019
28
[0122]
The polarization separation unit 78 includes, for example, a polarization beam splitter, and the
light emitted from the semiconductor laser 71 is incident through the phase plate 63.
In the polarization separation unit 78, the light of S polarization is reflected and the light of P
polarization is transmitted, and the incident light is split into two.
Further, the second-order diffracted light from the diffraction grating piece 30 B is incident on
the polarization separation unit 78, and the two second-order diffracted lights are superimposed
and emitted to the light branching film 79.
[0123]
The reflectances of the light branching films 79a, 79b, 79c, and 79d are set to 1/4, 1/3, 1/2, and
1, respectively.
That is, the light branching film 79d is a total reflection surface.
For this reason, it becomes possible to divide the incident light into lights Ld1, Ld2, Ld3 and Ld4
with substantially the same light quantity.
[0124]
In the light emitting / receiving composite unit 6, the housing member 60, the lens unit 61, the
polarization unit 62, the phase plate 63, and the light branching unit 64 described above are
disposed in the same package and configured as an independent unit. Ru.
Each of these members is configured to be laminated and integrated.
05-05-2019
29
[0125]
That is, by combining the members into an integrated structure, the light emitting / receiving
composite unit 6 facilitates precise position adjustment, and it is not necessary to take a large
space for arranging parts, and the microphone can be made smaller and lighter. Can be
In addition, by storing the respective members in the same housing member, it is possible to
reduce the influence of the environmental change and the temporal change, and it is possible to
minimize the deviation at the time of adjustment and the like. The overall reliability can be
enhanced.
[0126]
<Operation Example of Light Emitting / Combination Combined Unit in Third Embodiment> Next,
an example of the operation of the light emitting / receiving combined unit in the third
embodiment will be described.
[0127]
The light emitted from the semiconductor laser 71 is irradiated to the lens unit 61.
The light emitted from the semiconductor laser 71 is narrowed by the lens unit 61 and is
incident on the phase plate 63 formed of a 1?4 wavelength plate.
[0128]
The light incident on the phase plate 63 passes through the phase plate 63 and is converted into
circularly polarized light.
That is, linearly polarized light emitted through the phase plate 63 can be converted into
circularly polarized light regardless of the polarization direction of the light emitted from the
semiconductor laser 71.
05-05-2019
30
As a result, the polarization component of the light emitted from the semiconductor laser 71 can
be freely selected without being inclined by 45 ░ with respect to the polarization separation unit
78.
[0129]
The light having passed through the phase plate 63 is split into s-polarized light and p-polarized
light by the polarization separation unit 78, and enters the diffraction grating piece 30B.
[0130]
The light incident on the diffraction grating piece 30B is diffracted in the direction indicated by
the above-mentioned equation (1), whereby the S-polarized light (first-order diffracted light)
transmitted through the diffraction grating piece 30B and diffracted is 1 The light is reflected by
one surface of the reflecting prism 45 through the quarter wave plate 46a, returns to the same
optical path, passes through the quarter wave plate 46a, is incident on the diffraction grating
piece 30B, and is diffracted.
[0131]
Here, since the optical axis of the 1?4 wavelength plate 46a is inclined 45 ░ with respect to the
polarization direction of light, the light passing through the 1?4 wavelength plate 46a twice and
returned to the diffraction grating piece 30B is P-polarized light It has become.
[0132]
Then, the P-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization separation unit 78,
and since it is P-polarization, it is transmitted through the polarization separation unit 78.
[0133]
On the other hand, P-polarized light emitted from the semiconductor laser 71 and transmitted
through the polarization separation unit 78 is similarly incident on the diffraction grating piece
30B and diffracted.
P-polarized light (first-order diffracted light) transmitted through the diffraction grating piece
05-05-2019
31
30B and diffracted (first-order diffracted light) passes through the 1?4 wavelength plate 46b, is
reflected by the other surface of the reflecting prism 45, and returns along the same optical path.
The light is incident on the diffraction grating piece 30B through the wave plate 46b and is
diffracted.
[0134]
The optical axis of the 1?4 wavelength plate 46b is also inclined 45 ░ with respect to the
polarization direction of the light, so the light passing through the 1?4 wavelength plate 46b
twice and returned to the diffraction grating piece 30B becomes S polarization. There is.
[0135]
Then, the S-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization separation unit 78,
and since it is S-polarization, it is reflected by the polarization separation unit 78.
[0136]
Thus, the light emitted from the semiconductor laser 71 and split into S-polarized light and Ppolarized light by the polarization separation unit 78 passes through predetermined optical
paths, is diffracted by the diffraction grating piece 30B, and returns to the polarization
separation unit 78 next time. Origami is superimposed.
[0137]
The light (second-order diffracted light) superimposed by the polarization separation unit 78 is
split into light Ld1, Ld2, Ld3, and Ld4 by the light branching films 79a, 79b, 79c, and 79d.
The split lights Ld1, Ld2, Ld3 and Ld4 are respectively incident on the phase plate 63.
At this time, each light is circularly polarized in the opposite direction.
[0138]
05-05-2019
32
When this light is received by the photodetector through a polarizing plate that transmits only a
specific polarization component, the amplitudes of the two superposed second-order diffracted
lights of this light are A1 and A2, and the direction orthogonal to the grating of the diffraction
grating piece 30B (grating The amount of movement in the vector direction) is x, the initial phase
is ?, and K = 2? / ?. When first-order diffracted light is used in the first and second
diffractions, specific polarization components are used. When taken out, an interference signal I
such as the following equation (4) is obtained.
I = A1 <2> + A2 <2> + 2 и A1 и A2 cos (4 и K и x + ?) (4)
[0139]
The interference signal I changes by one period as the diffraction grating piece 30B moves by ?
/ 4 in the grating vector direction.
[0140]
The light components Ld1, Ld2, Ld3 and Ld4 that have passed through the phase plate 63 are
each transmitted by the polarization unit 62 so that only predetermined polarization components
are transmitted.
Each polarization part 62 is set to have an interval of 45 ░, but in this example, only the
polarization direction of 0 ░ is transmitted in the polarization part 62a, and the polarization
direction of 45 ░ in the polarization part 62b. The polarization unit 62c transmits only the
90.degree. Polarization direction, and the polarization unit 62d transmits only the 135.degree.
Polarization direction.
At this time, the intensities of the lights Ld1, Ld2, Ld3 and Ld4 transmitted through the
respective polarization parts 62 are represented by the following formulas (5) to (8), respectively.
[0141]
B + A cos (4.K.x + .delta.) (5) B + A cos (4.K.x + 90.degree. +. Delta.) (6) B + A cos (4.K.x +
180.degree. +. Delta.) (7) B + A cos (4 ..) K и x + 270 ░ + ? (8) where B = 1?4 (A1 <2> + A2 <2>),
A = 1/2 и A1 и A2.
05-05-2019
33
[0142]
The equation (5) represents the intensity of the light Ld1 transmitted through the polarization
unit 62a, the equation (6) represents the intensity of the light Ld2 transmitted through the
polarization unit 62b, and the equation (7) transmitted the polarization unit 62c The intensity of
the light Ld3 is represented, and the equation (8) represents the intensity of the light Ld4
transmitted through the polarization unit 62d.
[0143]
Each light represented by these equations passes through the lens 61 and is imaged on the
photodetectors 72a, 72b, 72c and 72d.
Then, each of the photo detectors 72 photoelectrically converts the light represented by the
above equation to generate an interference signal.
[0144]
Here, the DC component of the interference signal can be removed by subtracting Equation (5)
and Equation (7).
Further, the DC component of the interference signal can be removed by subtracting the
equations (6) and (8).
Further, since the subtracted signals are 90 ░ out of phase with each other, a signal for
detecting the moving direction of the diffraction grating piece 30B can be obtained.
[0145]
As described above, in the microphone 1C according to the third embodiment, the semiconductor
laser, the four photoelectric converters, the various beam splitters, and the quarter wavelength
plate that constitute the diffraction grating interferometer are replaced with the light emitting
and receiving unit 6 Thus, it is possible to configure with small size, light weight and low cost.
05-05-2019
34
[0146]
<The example of composition of the microphone of a 4th embodiment> Drawing 10 is a block
diagram showing an example of the microphone of a 4th embodiment, and in Drawing 10, the
composition of the microphone using two reflection type diffraction gratings Is shown in a side
sectional view.
[0147]
The microphone 1D according to the fourth embodiment includes the diaphragm 2 that receives
sound pressure and the light emitting / receiving composite unit 6 described in FIG. 9 and
includes the diffraction grating interferometer 3D that measures the amount of movement of the
diaphragm 2. .
[0148]
The diaphragm 2 has an outer peripheral portion supported by the plate 20, and a cylindrical
bobbin 21 is, for example, integrated on the back side of the inner peripheral portion, and when
the diaphragm 2 receives a sound pressure, the bobbin 21 moves in the sound wave traveling
direction Reciprocate in parallel along the
[0149]
The diffraction grating interferometer 3 </ b> D includes diffraction grating pieces 30 </ b> A at
two positions inside the bobbin 21.
The diffraction grating piece 30A1 and the diffraction grating piece 30A2 are adhesively fixed to
the bobbin 21 in such a direction that the small pieces on which the reflection type diffraction
grating is formed are perpendicular to the vibration direction of the diaphragm 2.
In the diffraction grating piece 30A1 and the diffraction grating piece 30A2, the bobbin 21 has a
predetermined rigidity so that the directions of the diffraction grating become parallel with a
predetermined high accuracy and the accuracy can be maintained.
The diffraction grating may be directly formed integrally with the bobbin 21.
05-05-2019
35
[0150]
As described with reference to FIG. 9, in the light emitting / receiving composite unit 6, the light
emitted from the semiconductor laser 71 is divided into two and light of S polarization and P
polarization is emitted.
[0151]
In the diffraction grating interferometer 3D, the S-polarized light emitted from the light emitting
/ receiving complex unit 6 is incident on one diffraction grating piece 30A1 and is diffracted, and
the P-polarized light is incident on the other diffraction grating piece 30A2 and diffracted Each
part is arranged so that the optical path to be formed is formed.
In this example, the S-polarized light emitted from the light emitting / receiving complex unit 6 is
directly incident on the diffraction grating piece 30A1, and the P-polarized light is reflected by
the mirror 47 to form an optical path incident on the diffraction grating piece 30A2. .
[0152]
Also, the diffraction grating interferometer 3D converts the polarization state of the light
reflected by the mirror 48a by reflecting the light of S-polarized light diffracted by the diffraction
grating piece 30A1 back to the diffraction grating piece 30A1, and 1/1 A four-wave plate 49a is
provided.
[0153]
Further, the diffraction grating interferometer 3D converts the polarization state of the light
reflected by the mirror 48b by reflecting the P-polarized light diffracted by the diffraction grating
piece 30A2 back to the diffraction grating piece 30A2, and 1/1 A four-wave plate 49 b is
provided.
[0154]
In the mirror 48a, the S-polarized light diffracted by the diffraction grating piece 30A1 is
vertically reflected and returned to the diffraction grating piece 30A1 along the same optical
05-05-2019
36
path.
The optical axis of the quarter-wave plate 49a is disposed at an angle of 45 ░ with respect to the
polarization direction of light, and S-polarized light is reflected by the mirror 48a and passes
through the quarter-wave plate 49a twice. Is converted to P polarization.
[0155]
Similarly, in the mirror 48b, the P-polarized light diffracted by the diffraction grating piece 30A2
is vertically reflected and returned to the diffraction grating piece 30A2 in the same optical path.
The optical axis of the quarter-wave plate 49b is disposed at an angle of 45 ░ to the polarization
direction of the light, and the light of P-polarization is reflected by the mirror 48b and passes
through the quarter-wave plate 49b twice. Is converted to S-polarization.
[0156]
Thus, the light emitted from the semiconductor laser 71 of the light emitting / receiving complex
unit 6 described in FIG. 9 is split into the light of S polarized light and P polarized light by the
polarization separating section 78 and emitted from the light emitting / receiving complex unit 6
The s-polarized light thus obtained is incident on the diffraction grating piece 30A1 and
diffracted, and the p-polarized light is reflected by the mirror 47 and made incident on the
diffraction grating piece 30A2 and diffracted.
[0157]
The S-polarized light diffracted by the diffraction grating piece 30A1 passes through the 1?4
wavelength plate 49a, is vertically reflected by the mirror 48a, returns along the same optical
path, and passes through the 1?4 wavelength plate 49a to the diffraction grating piece 30A1. It is
incident and diffracted.
[0158]
Here, since the optical axis of the quarter-wave plate 49a is inclined 45 ░ with respect to the
polarization direction of light, the light passing through the quarter-wave plate 49a twice and
returned to the diffraction grating piece 30A1 is P-polarized light It has become.
05-05-2019
37
[0159]
Then, the P-polarized light diffracted by the diffraction grating piece 30A1 returns to the
polarization separation unit 78 described in FIG. 9, and since it is P-polarization, it is transmitted
through the polarization separation unit 78.
[0160]
On the other hand, P-polarized light diffracted by the diffraction grating piece 30A2 passes
through the 1?4 wavelength plate 49b, is vertically reflected by the mirror 48b, returns along the
same optical path, and passes through the 1?4 wavelength plate 49b to form a diffraction grating
piece It is diffracted by being incident on 30A2.
[0161]
Here, since the optical axis of the 1?4 wavelength plate 49b is also inclined 45 ░ with respect to
the polarization direction of light, the light passing through the 1?4 wavelength plate 49b twice
and returning to the diffraction grating piece 30A2 is S-polarized light It has become.
[0162]
Then, the S-polarized light diffracted by the diffraction grating piece 30A2 is reflected by the
mirror 47 and returns to the polarization separation unit 78 described in FIG. 9, and since it is S
polarization, it is reflected by the polarization separation unit 78.
[0163]
As a result, the light emitted from the semiconductor laser 71 and split into S-polarized light and
P-polarized light by the polarization separation unit 78 respectively passes through
predetermined optical paths and is diffracted by the diffraction grating piece 30A1 and the
diffraction grating piece 30A2. The light returned to is superimposed.
[0164]
The light superimposed by the polarization splitter 78 is divided into four by the light branching
films 79a, 79b, 79c, and 79d described in FIG. 9, and the split lights are respectively divided by
the phase plate 63 and the polarizer 62. Only a specific polarization component is transmitted,
incident on predetermined photodetectors 72a, 72b, 72c and 72d, and photoelectrically
converted to obtain an interference signal.
05-05-2019
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[0165]
As described above, in the microphone 1D according to the fourth embodiment, the two
diffraction grating pieces 30A1 and 30A2 move in the same direction, so that one is first-order
diffracted light L (1) and the other is first-order diffracted light L The amount of displacement of
the diaphragm 2 is determined using (-1).
[0166]
<Configuration Example of Microphone According to Fifth Embodiment> FIG. 11 is a
configuration diagram showing an example of a microphone according to the fifth embodiment.
In FIG. 11, a configuration of a microphone using two reflective diffraction gratings Is shown in a
side sectional view.
[0167]
A microphone 1E according to the fifth embodiment includes a diaphragm 2 that receives sound
pressure, and the light emitting / receiving composite unit 6 described in FIG. 9 and includes a
diffraction grating interferometer 3E that measures the amount of movement of the diaphragm 2.
.
[0168]
The diffraction grating interferometer 3 </ b> E includes diffraction grating pieces 30 </ b> A at
two positions inside the bobbin 21 integrated with the back side of the diaphragm 2, for example.
The diffraction grating piece 30A1 and the diffraction grating piece 30A2 are adhesively fixed or
integrally formed on the bobbin 21 in such a direction that the small pieces on which the
reflection type diffraction grating is formed are perpendicular to the vibration direction of the
diaphragm 2 respectively. It is molded.
[0169]
In the diffraction grating interferometer 3E, the S-polarized light emitted from the light emitting /
receiving composite unit 6 is reflected by the mirror 47a and enters the diffraction grating piece
30A1, and the P-polarized light is reflected by the mirror 47b and is reflected by the diffraction
grating piece 30A2. An optical path incident on the light source is formed.
05-05-2019
39
[0170]
Thus, by bending the light path using the mirror 47a and the mirror 47b, the space occupied by
the light path can be reduced to a minimum, and miniaturization can be achieved.
[0171]
The other configuration and operation of the microphone 1E of the fifth embodiment are the
same as the microphone 1D of the fourth embodiment described with reference to FIG.
[0172]
<Configuration Example of Microphone of Sixth Embodiment> FIG. 12 is a configuration diagram
showing an example of a microphone of the sixth embodiment. In FIG. 12, the incident angle of
the diffraction grating and the outgoing angle of the first-order diffracted light are The outline of
the configuration of the microphones arranged to be in the same Littrow arrangement with ? is
shown in a side sectional view.
[0173]
The microphone 1F of the sixth embodiment includes the diaphragm 2 that receives sound
pressure, and the light emitting / receiving complex unit 6 described in FIG. 9 and includes the
diffraction grating interferometer 3F that measures the amount of movement of the diaphragm 2.
.
[0174]
The diffraction grating interferometer 3F includes diffraction grating pieces 30A at two positions
inside the bobbin 21 integrated with the back side of the diaphragm 2, for example.
The diffraction grating piece 30A1 and the diffraction grating piece 30A2 are adhesively fixed or
integrally formed on the bobbin 21 in such a direction that the small pieces on which the
reflection type diffraction grating is formed are perpendicular to the vibration direction of the
diaphragm 2 respectively. It is molded.
[0175]
05-05-2019
40
In the diffraction grating interferometer 3F, the first-order diffracted light L (1s) in which the
incident angle ?s of the incident light L (s) of S polarized light emitted from the light receiving
and emitting unit 6 with respect to the diffraction grating piece 30A1 is diffracted by the
diffraction grating piece 30A1. The light path is formed to be equal to the emission angle of.
In addition, the first-order diffracted light L (in which the incident angle ?p of the P-polarized
incident light L (p) emitted from the light receiving / emitting composite unit 6 and reflected by
the mirror 47 with respect to the diffraction grating piece 30A2 is diffracted by the diffraction
grating piece 30A2 An optical path is formed to be equal to the emission angle of 1p).
[0176]
The diffraction grating interferometer 3F is a quarter wavelength plate 49a that converts the
polarization state of S polarized light that is diffracted back by the diffraction grating piece 30A1,
and P polarized light that is diffracted back by the diffraction grating piece 30A2. A quarter-wave
plate 49b is provided to convert the polarization state.
[0177]
The optical axis of the quarter-wave plate 49a is arranged to be inclined 45 ░ with respect to the
polarization direction of light, and S-polarized light is diffracted by the diffraction grating piece
30A1 and passes through the quarter-wave plate 49a twice. Is converted to P-polarization.
[0178]
Similarly, the optical axis of the quarter-wave plate 49b is also inclined 45 ░ with respect to the
polarization direction of the light, and the P-polarized light is diffracted by the diffraction grating
piece 30A2 to form the quarter-wave plate 49b. By passing twice, it is converted into Spolarization.
[0179]
The other configuration and operation of the microphone 1F of the sixth embodiment are the
same as the microphone 1D of the fourth embodiment described with reference to FIG.
[0180]
Here, the optical path length A-B of one diffracted light, that is, the distance from the light
receiving and emitting complex unit 6 to the diffraction grating piece 30A1, and the optical path
05-05-2019
41
length C D-E of the other diffracted light, that is, the light emitting and receiving complex unit
The first-order diffracted lights are made to interfere with each other from the two optical paths
by equalizing the distances from the point No. 6 to the diffraction grating piece 30A2 through
the mirror 47.
[0181]
As a result, the number of diffractions becomes one each, the number of mirrors used is reduced,
and downsizing and cost reduction can be achieved.
[0182]
The invention applies to microphones which can obtain audio signals directly as digital signals.
[0183]
It is a block diagram which shows an example of the microphone of 1st Embodiment.
It is a block diagram which shows an example of the diffraction grating interferometer in 1st
Embodiment.
It is a functional block diagram which shows an example of the signal processing part of the
microphone of this Embodiment.
It is a functional block diagram showing an example of a digital signal processing unit in the
present embodiment.
It is a graph which shows an example of an output waveform.
It is a block diagram which shows an example of the microphone of 2nd Embodiment.
It is a block diagram which shows an example of the diffraction grating interferometer in 2nd
Embodiment.
05-05-2019
42
It is a block diagram which shows an example of the microphone of 3rd Embodiment.
It is a block diagram which shows an example of the light emission / reception combined unit in
3rd Embodiment.
It is a block diagram which shows an example of the microphone of 4th Embodiment.
It is a block diagram which shows an example of the microphone of 5th Embodiment.
It is a block diagram which shows an example of the microphone of 6th Embodiment.
It is a block diagram which shows an example of the conventional microphone.
Explanation of sign
[0184]
1A, 1B, 1C, 1D, 1E, 1F ... microphone, 10A ... signal processing unit, 2 ... diaphragm, 20 ... frame,
21 ... bobbin, 3A, 3B, 3C, 3D , 3E, 3F: diffraction grating interferometer, 30A, 30B: diffraction
grating piece, 31: semiconductor laser, 32: lens, 33: polarization beam splitter (PBS), 34a, 34b и и
Mirrors, 35a, 35b и и и Mirrors, 36a, 36b и и и Lenses, 37a, 37b и и и 1?4 wavelength plate, 38 и и и и и и и
и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и 37a, 37b и и и и и и и и и 39 Beam
splitter 41a, 41b: photoelectric converter 42: 1?4 wavelength plate 43: polarization beam splitter
44a, 44b: photoelectric converter 45: reflecting prism 46a, 46b ... / 4 wavelength plate, 47 ...
mirror, 48a, 48b ... mirror, 49a, 49b ... 1/4 wavelength plate, 50a, 50b ... differential amplifier, 51
... digital signal processing unit, 6 иии Photoluminescence complex unit
05-05-2019
43
mass of the vibration
system.
[0027]
On the other hand, in the microphone 1A of the present embodiment, the bobbin 21 is a
component for fixing the diffraction grating piece 30A, and it is only necessary to ensure the
rigidity necessary to support the diffraction grating piece 30A. The mass of the vibration system
can be reduced by making it into the minimum shape by making a notch or a hole.
05-05-2019
6
[0028]
<Configuration Example of Diffraction Grating Interferometer in First Embodiment> FIG. 2 is a
configuration diagram showing an example of the diffraction grating interferometer in the first
embodiment, and next, the microphone of the first embodiment The configuration of the
diffraction grating interferometer 3A constituting 1A will be described.
[0029]
The diffraction grating interferometer 3A is an example of a grating interferometer, and a
semiconductor laser (LD) 31 which is an example of a coherent light source, a lens 32 for
narrowing light emitted from the semiconductor laser 31 at a predetermined radiation angle, and
the semiconductor laser 31. And a polarization beam splitter (PBS) 33 that splits the light emitted
from the light into two lights with different polarization components and superposes the two
lights with different polarization components.
[0030]
The polarization beam splitter 33 is an example of a first polarization unit, and is emitted from
the semiconductor laser 31 and the light narrowed by the lens 32 is incident thereon, and the
incident light from the semiconductor laser 31 is split into a P component and an S component.
Polarized light is reflected and P-polarized light is transmitted.
Here, if the light from the semiconductor laser 31 is linearly polarized light, if the polarization
direction is inclined 45 ░ and incident on the polarization beam splitter 33, the intensities of the
split lights become equal.
[0031]
Further, the diffracted light of S polarization returned to the polarization beam splitter 33 is
reflected, the diffracted light of P polarization is transmitted, and the two diffracted lights are
superimposed.
[0032]
The diffraction grating interferometer 3A reflects the S-polarized light emitted from the
semiconductor laser 31 and reflected by the polarization beam splitter 33 to be incident on the
05-05-2019
7
diffraction grating piece 30A, and passes through a predetermined optical path to the diffraction
grating piece 30A. A mirror 34 a is provided to reflect the back-diffracted light and make it enter
the polarization beam splitter 33.
[0033]
Also, the diffraction grating interferometer 3A reflects the S-polarized light reflected by the
polarization beam splitter 33 and the mirror 34a and incident on the diffraction grating piece
30A and returning it to the diffraction grating piece 30A, and diffraction A lens 36a narrows the
light diffracted by the grating piece 30A and the light reflected by the mirror 35a, and the
quarter-wave plate 37a converts the polarization state of the light reflected by the mirror 35a.
[0034]
The mirror 35a is reflected by the polarization beam splitter 33 and the mirror 34a and is
incident on the point P of the diffraction grating piece 30A, and the S-polarized light diffracted by
the diffraction grating piece 30A is vertically reflected and reflected by the mirror 35a The light
is returned to the point P of the diffraction grating piece 30A.
[0035]
The optical axis of the 1?4 wavelength plate 37a is arranged to be inclined 45 ░ with respect to
the polarization direction of the light, and the S polarized light reflected by the mirror 35a and
returned to the diffraction grating piece 30A is converted to P polarized light.
[0036]
Thus, the S-polarized light emitted from the semiconductor laser 31 and reflected by the
polarization beam splitter 33 reciprocates in a predetermined optical path and is diffracted twice
by the diffraction grating piece 30A, and the quarter-wave plate 37a is By passing twice, it is
converted into P-polarized light, returns to the polarization beam splitter 33, and transmits
through the polarization beam splitter 33.
[0037]
Similarly, the diffraction grating interferometer 3A reflects the P-polarized light emitted from the
semiconductor laser 31 and transmitted through the polarization beam splitter 33 to be incident
on the diffraction grating piece 30A, and passes the predetermined light path to the diffraction
grating piece A mirror 34 b is provided to reflect the diffracted light back to 30 A to be incident
on the polarization beam splitter 33.
05-05-2019
8
[0038]
In addition, the diffraction grating interferometer 3A transmits the polarization beam splitter 33,
is reflected by the mirror 34b, reflects the P-polarized light that is incident on the diffraction
grating piece 30A and is diffracted and returns it to the diffraction grating piece 30A. And a lens
36b for narrowing the light diffracted by the diffraction grating piece 30A and the light reflected
by the mirror 35b, and a quarter-wave plate 37b for converting the polarization state of the light
reflected by the mirror 35b.
[0039]
The mirror 35b transmits the polarization beam splitter 33, is reflected by the mirror 34b, is
incident on the point P of the diffraction grating piece 30A, P-polarized light diffracted by the
diffraction grating piece 30A is vertically reflected, and is reflected by the mirror 35b The
reflected light is returned to the point P of the diffraction grating piece 30A.
[0040]
The optical axis of the 1?4 wavelength plate 37b is disposed at an angle of 45 ░ with respect to
the polarization direction of the light, and P-polarized light reflected by the mirror 35b and
returned to the diffraction grating piece 30A is converted into S-polarization.
[0041]
As a result, the P-polarized light emitted from the semiconductor laser 31 and transmitted
through the polarization beam splitter 33 is reciprocated in a predetermined optical path and
diffracted twice by the diffraction grating piece 30A. By passing the light beam one time, it is
converted into S-polarization, returns to the polarization beam splitter 33, and is reflected by the
polarization beam splitter 33.
[0042]
Therefore, the S-polarized light and the P-polarized light emitted from the semiconductor laser
31 and split by the polarization beam splitter 33 respectively pass through predetermined optical
paths and are diffracted by the diffraction grating piece 30A, and are returned to the polarization
beam splitter 33 for superposition. Be done.
[0043]
05-05-2019
9
The diffraction grating interferometer 3A includes a lens 38 for narrowing the light
superimposed by the polarization beam splitter 33, and a beam splitter (BS) 39 for splitting the
light narrowed by the lens 38, superimposed by the polarization beam splitter 33.
The beam splitter 39 is an example of a light splitting means, and is constituted by a half mirror
or the like having a predetermined transmittance (reflectance), and the light beam superimposed
by the polarization beam splitter 33 is split into two.
[0044]
Further, the diffraction grating interferometer 3A is a second polarization means which is
inclined 45 ░ with respect to the polarization direction of the light reflected and incident by the
beam splitter 39 and splits the incident light into two light having different polarization
components. As a polarization beam splitter (PBS) 40, a photoelectric converter (PD) 41a as a
light receiving unit to which light reflected by the polarization beam splitter 40 is incident, and a
light receiving unit to which light transmitted through the polarization beam splitter 40 is
incident The photoelectric converter (PD) 41 b of
[0045]
Further, the diffraction grating interferometer 3A is provided with a 1?4 wavelength plate 42
whose optical axis is inclined 45 ░ with respect to the polarization direction of the light
transmitted through the beam splitter 39 and which converts the polarization state of the
incident light.
Furthermore, the diffraction grating interferometer 3A is inclined 45 ░ with respect to the
polarization beam splitter 40, transmits the beam splitter 39, and the light whose polarization
state is converted by the 1?4 wavelength plate 42 is converted into two light beams having
different polarization components. A polarization beam splitter (PBS) 43 as a second polarization
unit to split, a photoelectric converter (PD) 44 a as a light reception unit as a light reception unit
to which light reflected by the polarization beam splitter 43 is incident, and a polarization beam
splitter 43 A photoelectric converter (PD) 44 b as light receiving means for receiving light is
provided.
[0046]
<Operation Example of Diffraction Grating Interferometer in First Embodiment> Next, an example
05-05-2019
10
of the operation of the diffraction grating interferometer 3A in the first embodiment will be
described.
[0047]
The light emitted from the semiconductor laser 31 is narrowed into an appropriate beam by the
lens 32 and split into two beams by the polarization beam splitter 33.
The light reflected by the polarization beam splitter 33 is S-polarized, and the transmitted light is
P-polarized.
If the light from the semiconductor laser 31 is linearly polarized light, the light beams to be split
become equal in intensity by being incident on the polarization beam splitter 33 whose
polarization direction is inclined 45 ░.
[0048]
The light (S polarized light) reflected by the polarization beam splitter 33 is reflected by the
mirror 34 a and is incident on the point P of the diffraction grating piece 30A.
Similarly, the light (P-polarized light) transmitted through the polarization beam splitter 33 is
also reflected by the mirror 34 b and is incident on the point P of the diffraction grating piece
30A.
[0049]
The light incident on the diffraction grating piece 30A is diffracted in the direction shown by the
following equation (1).
sin ? 1 + sin ? 2 = n и ? / ? (1) where ? 1: incident angle, ? 2: diffraction angle, ?: grating
pitch, ?: wavelength of light, n: diffraction order
05-05-2019
11
The diffraction orders in the two optical paths are the same.
[0050]
As described above, the S-polarized light emitted from the semiconductor laser 31 and reflected
by the polarization beam splitter 33 is reflected by the mirror 34a and is incident on the point P
of the diffraction grating piece 30A and is diffracted.
The S-polarized light (first-order diffracted light) diffracted by the diffraction grating piece 30A
passes through the lens 36a and the 1?4 wavelength plate 37a, is vertically reflected by the
mirror 35a, and returns along the same optical path. And is incident on a point P of the
diffraction grating piece 30A through the lens 36a and is diffracted.
[0051]
Here, since the optical axis of the quarter-wave plate 37a is inclined 45 ░ with respect to the
polarization direction of light, the light which has passed through the quarter-wave plate 37a
twice and returned to the point P of the diffraction grating piece 30A Is P-polarized.
[0052]
The P-polarized light (second-order diffracted light) diffracted by the diffraction grating piece
30A is again reflected by the mirror 34a and returns to the polarization beam splitter 33. Since it
is P-polarization, it is transmitted through the polarization beam splitter 33.
[0053]
On the other hand, the P-polarized light emitted from the semiconductor laser 31 and
transmitted through the polarization beam splitter 33 is similarly reflected by the mirror 34 b
and incident on the point P of the diffraction grating piece 30 A and diffracted.
P-polarized light (first-order diffracted light) diffracted by the diffraction grating piece 30A
passes through the lens 36b and the 1?4 wavelength plate 37b, is vertically reflected by the
05-05-2019
12
mirror 35b, and returns along the same optical path. And is incident on a point P of the
diffraction grating piece 30A through the lens 36b and is diffracted.
[0054]
Since the optical axis of the quarter-wave plate 37b is also inclined 45 ░ with respect to the
polarization direction of light, the light passing through the quarter-wave plate 37b twice and
returning to the point P of the diffraction grating piece 30A is S-polarized light It has become.
[0055]
Then, the S-polarized light (second-order diffracted light) diffracted by the diffraction grating
piece 30A is again reflected by the mirror 34b and returns to the polarization beam splitter 33.
Since it is S-polarization, it is reflected by the polarization beam splitter 33.
[0056]
Thereby, the light emitted from the semiconductor laser 31 and split into S-polarization and Ppolarization by the polarization beam splitter 33 is diffracted by the diffraction grating piece 30A
through predetermined optical paths and is returned to the polarization beam splitter 33. Are
superimposed.
[0057]
The light superimposed by the polarization beam splitter 33 passes through the lens 38 and is
split into two by the beam splitter 39.
[0058]
The light of S-polarization and P-polarization reflected by the beam splitter 39 is incident on the
polarization beam splitter 40 inclined 45 ░ with respect to the polarization direction.
The light reflected by the polarization beam splitter 40 is incident on the photoelectric converter
41 a, and the light transmitted through the polarization beam splitter 40 is incident on the
photoelectric converter 41 b.
[0059]
05-05-2019
13
In the photoelectric converter 41a and the photoelectric converter 41b, the interference signal
shown in the following equation (2) is obtained.
A cos (4 и K и x + ?) (2) where K = 2? / ?, x: moving amount of the diffraction grating piece
(diaphragm), ?: initial phase
[0060]
As a result, in the photoelectric converter 41a and the photoelectric converter 41b, signals
different in phase by 180 ░ can be obtained.
[0061]
On the other hand, the S polarized light and P polarized light transmitted through the beam
splitter 39 become circularly polarized light in the opposite direction by passing through the 1?4
wavelength plate 42 whose optical axis is inclined 45 ░ to the polarization direction.
The circularly polarized light beams rotating in opposite directions are superimposed to form
linearly polarized light, which is incident on the polarization beam splitter 43, and the light beam
reflected by the polarization beam splitter 43 is incident on the photoelectric converter 44a. The
light transmitted through the light source is incident on the photoelectric converter 44b.
[0062]
The polarization direction of the linearly polarized light incident on the polarization beam splitter
43 rotates once when the diffraction grating piece 30A moves by ? / 2 in the X direction by the
vibration of the diaphragm 2 shown in FIG.
Therefore, in the photoelectric converter 44a and the photoelectric converter 44b, an
interference signal similar to that of the equation (2) can be obtained.
05-05-2019
14
[0063]
Since the photoelectric converter 44 a and the photoelectric converter 44 b are 180 ░ out of
phase and the polarization beam splitter 43 is inclined 45 ░ with respect to the polarization
beam splitter 40, the signals obtained by the photoelectric converters 44 a and 44 b are , 90 ░
out of phase with the signal obtained by the photoelectric converters 41a and 41b.
[0064]
Here, in the detection optical system based on the diffraction grating interferometer 3A
described above, since the optical system is symmetrical with respect to the perpendicular H
passing through the point P of the diffraction grating piece 30A, the Y direction orthogonal to
the vibration direction of the bobbin 21 Even if the diffraction grating piece 30A moves, the
position measurement error does not occur.
In addition, by equalizing the optical path lengths of the two optical paths incident on the point P,
the influence of the wavelength fluctuation of the light source is eliminated.
[0065]
As described above, in the microphone 1A of the present embodiment, since the voice coil used
for the dynamic microphone is not necessary, the mass of the vibration system can be reduced,
and the sensitivity and the frequency response are improved.
In addition, since a magnetic circuit including a magnet having a large volume is not required,
the degree of freedom in acoustic design is increased.
[0066]
Furthermore, since it is not influenced by an electric field or a magnetic field in noncontact
detection by a laser and is not influenced by an electric field or a magnetic field, the movable
range of the diaphragm can be made large, and a wide dynamic range can be obtained.
[0067]
05-05-2019
15
<The example of composition of the signal processing part of the microphone of this
embodiment> Drawing 3 is a functional block diagram showing an example of the signal
processing part of the microphone of this embodiment.
In the signal processing unit 10A, the electric signal output from the photoelectric converter 41a
and the photoelectric converter 41b shown in FIG. 2 is input to the differential amplifier 50a
which is a differential amplification unit, and in the differential amplifier 50a, the photoelectric
converter 41a , 41b are differentially amplified, and a signal in which the DC component of the
interference signal is canceled is output.
[0068]
Further, the electric signals output from the photoelectric converter 44a and the photoelectric
converter 44b shown in FIG. 2 are input to the differential amplifier 50b which is a differential
amplification means, and in the differential amplifier 50b, the electric signals from the
photoelectric converters 44a and 44b The electrical signal is differentially amplified, and a signal
in which the DC component of the interference signal is canceled is output.
[0069]
Therefore, the DC components of the two outputs different in phase by 180 ░ are canceled in
each of the photoelectric converter 41a and the photoelectric converter 41b, and the
photoelectric converter 44a and the photoelectric converter 44b, and the differential amplifier
50a and the differential amplifier An A-phase signal and a B-phase signal are obtained from 50b,
and the A / B-phase signal is input to a digital signal processing unit (incremental signal
generator) 51.
[0070]
FIG. 4 is a functional block diagram showing an example of the digital signal processing unit in
the present embodiment.
In the digital signal processing unit 51, two output signals having different 90 ░ phases from
the differential amplifier 50a and the differential amplifier 50b shown in FIG. 3 are respectively
input to the A / D converters 52a and 52b and converted into digital signals. Ru.
05-05-2019
16
[0071]
The correction circuit 53 removes the DC offset from the digital signals converted by the A / D
converters 52a and 52b, and adjusts the gain and the phase to correspond to a sin wave signal
and a cos wave signal, respectively.
[0072]
Then, the angle ? is uniquely determined by the following equation (3), and the position (angle)
on the Lissajous figure of the output waveform as shown in FIG. 5 is determined.
? = tan <?1> (y / x) (3) Here, the range of ? is ? (? / 2) <? <(? / 2).
[0073]
The calculation of ? may be performed using an approximate expression, but using the look-up
table 54 enables high speed calculation.
[0074]
The determined angle ? is integrated by an accumulator 55 to obtain an integrated
displacement amount.
Further, this displacement data is input to an audio D / A converter 56a to obtain an analog
audio signal.
Alternatively, displacement amount data is input to the digital audio interface 56b to obtain a
digital audio signal.
[0075]
As described above, in the microphone 1A of the present embodiment, direct output can be
05-05-2019
17
obtained in digital, and it is easy to cope with optical transmission by digital signal and the like.
In addition, digital output can be sampled at high speed, and noise reduction by oversampling
and noise shaving can be expected.
[0076]
<Configuration Example of Microphone of Second Embodiment> FIG. 6 is a configuration
diagram showing an example of a microphone of the second embodiment, and in FIG. 6, an
outline of the configuration of the microphone using a transmission type diffraction grating. Is
shown in a side sectional view.
[0077]
The microphone 1B of the second embodiment includes the diaphragm 2 that receives sound
pressure, and the diffraction grating interferometer 3B that measures the amount of movement
of the diaphragm 2.
[0078]
The diaphragm 2 has an outer peripheral portion supported by the plate 20, and a cylindrical
bobbin 21 is, for example, integrated on the back side of the inner peripheral portion, and when
the diaphragm 2 receives a sound pressure, the bobbin 21 moves in the sound wave traveling
direction Reciprocate in parallel along the
[0079]
The diffraction grating interferometer 3 </ b> B includes the diffraction grating piece 30 </ b> B
on the bobbin 21.
In the diffraction grating piece 30B, the small piece on which the transmission type diffraction
grating is formed is adhered and fixed to the bobbin 21 in such a direction that the diffraction
grating is perpendicular to the vibration direction of the diaphragm 2.
The diffraction grating may be directly formed integrally with the bobbin 21.
05-05-2019
18
[0080]
<Configuration Example of Diffraction Grating Interferometer in Second Embodiment> FIG. 7 is a
configuration diagram showing an example of a diffraction grating interferometer in the second
embodiment, and next, the microphone of the second embodiment The configuration of the
diffraction grating interferometer 3B constituting 1 B will be described.
[0081]
The diffraction grating interferometer 3B includes a semiconductor laser 31 which is an example
of a coherent light source, and a lens 32 which narrows light emitted from the semiconductor
laser 31 at a predetermined radiation angle.
Further, the diffraction grating interferometer 3B splits the light emitted from the semiconductor
laser 31 into two light beams of S-polarization and P-polarization and makes them incident on
the diffraction grating piece 30B, while being diffracted by the diffraction grating piece 30B and
returning S A polarization beam splitter 33 is provided which superposes two light beams of
polarized light and P polarized light.
[0082]
Further, the diffraction grating interferometer 3B reflects the light of S-polarized light
transmitted through the diffraction grating piece 30B and returns it to the diffraction grating
piece 30B, and transmits the diffraction grating piece 30B and transmits the diffracted Ppolarization light. A reflection prism 45 that reflects light and returns it to the diffraction grating
piece 30B, and quarter wavelength plates 46a and 46b that convert the polarization state of the
light reflected by the reflection prism 45 are provided.
[0083]
The reflecting prism 45 is reflected by the polarization beam splitter 33 and is incident on the
diffraction grating piece 30B, and the light of S-polarized light transmitted through the
diffraction grating piece 30B and diffracted is reflected by one surface, and the diffraction
grating piece in the same optical path It is returned to 30B.
[0084]
The optical axis of the 1?4 wavelength plate 46a is arranged to be inclined 45 ░ with respect to
05-05-2019
19
the polarization direction of the light, and the S-polarized light emitted from the semiconductor
laser 31 and reflected by the polarization beam splitter 33 is The light is reciprocated along the
optical path and diffracted twice by the diffraction grating piece 30B, and is converted into Ppolarized light by passing through the 1?4 wavelength plate 46a twice and returned to the
polarization beam splitter 33 and transmitted through the polarization beam splitter 33 .
[0085]
Similarly, the reflection prism 45 transmits the polarization beam splitter 33 and is incident on
the diffraction grating piece 30B, and the light of P polarization transmitted and diffracted by the
diffraction grating piece 30B is reflected by the other surface, and in the same light path It is
returned to the diffraction grating piece 30B.
[0086]
The optical axis of the 1?4 wavelength plate 46b is arranged to be inclined 45 ░ with respect to
the polarization direction of the light, and the P-polarized light emitted from the semiconductor
laser 31 and transmitted through the polarization beam splitter 33 has a predetermined optical
path. And are diffracted twice by the diffraction grating piece 30B, and are converted into Spolarized light by passing through the 1?4 wavelength plate 46b twice and returned to the
polarization beam splitter 33 and reflected by the polarization beam splitter 33 .
[0087]
Therefore, the S-polarized light and the P-polarized light emitted from the semiconductor laser
31 and split by the polarization beam splitter 33 respectively pass through predetermined optical
paths and are diffracted by the diffraction grating piece 30B, and are returned to the polarization
beam splitter 33 and overlapped. Be done.
[0088]
The following configuration of the diffraction grating interferometer 3B is the same as that of the
first embodiment, and a lens 38 for narrowing the light superimposed by the polarization beam
splitter 33 and a lens 38 superimposed on the polarization beam splitter 33 A beam splitter 39 is
provided to split the light.
The beam splitter 39 is configured of a half mirror or the like having a predetermined
transmittance (reflectance), and the light beam superimposed by the polarization beam splitter
05-05-2019
20
33 is split into two.
[0089]
Furthermore, the diffraction grating interferometer 3B is tilted 45 ░ with respect to the
polarization direction of the light reflected and incident by the beam splitter 39, and splits the
incident light into two light beams having different polarization components, and The
photoelectric converter 41a receives the light reflected by the polarizing beam splitter 40, and
the photoelectric converter 41b receives the light transmitted through the polarizing beam
splitter 40.
[0090]
Further, the diffraction grating interferometer 3B is provided with a 1?4 wavelength plate 42
whose optical axis is inclined 45 ░ with respect to the polarization direction of the light
transmitted through the beam splitter 39, and which converts the polarization state of the
incident light.
Furthermore, the diffraction grating interferometer 3B is inclined 45 ░ with respect to the
polarization beam splitter 40, transmits the beam splitter 39, and the light whose polarization
state is converted by the 1?4 wavelength plate 42 is converted into two light components having
different polarization components. A polarization beam splitter 43 to be split, a photoelectric
converter 44a to which light reflected by the polarization beam splitter 43 is incident, and a
photoelectric converter 44b to which light transmitted through the polarization beam splitter 43
is incident.
[0091]
<Operation Example of Diffraction Grating Interferometer in Second Embodiment> Next, an
example of the operation of the diffraction grating interferometer 3B in the second embodiment
will be described.
[0092]
The light emitted from the semiconductor laser 31 is narrowed into an appropriate beam by the
lens 32 and split into two beams by the polarization beam splitter 33.
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The light reflected by the polarization beam splitter 33 is S-polarized, and the transmitted light is
P-polarized.
[0093]
The S-polarized light reflected by the polarization beam splitter 33 and the P-polarized light
transmitted through the polarization beam splitter 33 are respectively incident on the diffraction
grating piece 30B.
[0094]
The light incident on the diffraction grating piece 30B is diffracted in the direction indicated by
the above-mentioned equation (1), whereby the S-polarized light (first-order diffracted light)
transmitted through the diffraction grating piece 30B and diffracted is 1 The light is reflected by
one surface of the reflecting prism 45 through the quarter wave plate 46a, returns to the same
optical path, passes through the quarter wave plate 46a, is incident on the diffraction grating
piece 30B, and is diffracted.
[0095]
Here, since the optical axis of the 1?4 wavelength plate 46a is inclined 45 ░ with respect to the
polarization direction of light, the light passing through the 1?4 wavelength plate 46a twice and
returned to the diffraction grating piece 30B is P-polarized light It has become.
[0096]
Then, the P-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization beam splitter 33, and
since it is P-polarization, it is transmitted through the polarization beam splitter 33.
[0097]
On the other hand, P-polarized light emitted from the semiconductor laser 31 and transmitted
through the polarization beam splitter 33 is similarly incident on the diffraction grating piece
30B and diffracted.
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P-polarized light (first-order diffracted light) transmitted through the diffraction grating piece
30B and diffracted (first-order diffracted light) passes through the 1?4 wavelength plate 46b, is
reflected by the other surface of the reflecting prism 45, and returns along the same optical path.
The light is incident on the diffraction grating piece 30B through the wave plate 46b and is
diffracted.
[0098]
The optical axis of the 1?4 wavelength plate 46b is also inclined 45 ░ with respect to the
polarization direction of the light, so the light passing through the 1?4 wavelength plate 46b
twice and returned to the diffraction grating piece 30B becomes S polarization. There is.
[0099]
Then, the S-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization beam splitter 33, and
since it is S-polarization, it is reflected by the polarization beam splitter 33.
[0100]
Thereby, the light emitted from the semiconductor laser 31 and split into S polarized light and P
polarized light by the polarization beam splitter 33 respectively passes through predetermined
optical paths and is diffracted by the diffraction grating piece 30 B and returned to the
polarization beam splitter 33 Are superimposed.
[0101]
The light superimposed by the polarization beam splitter 33 passes through the lens 38 and is
split into two by the beam splitter 39.
[0102]
The light of S-polarization and P-polarization reflected by the beam splitter 39 is incident on the
polarization beam splitter 40 inclined 45 ░ with respect to the polarization direction.
The light reflected by the polarization beam splitter 40 is incident on the photoelectric converter
41 a, and the light transmitted through the polarization beam splitter 40 is incident on the
photoelectric converter 41 b.
05-05-2019
23
[0103]
In the photoelectric converter 41a and the photoelectric converter 41b, the interference signal
shown in the above-mentioned equation (2) is obtained, and in the photoelectric converter 41a
and the photoelectric converter 41b, signals different in phase by 180 ░ are obtained.
[0104]
On the other hand, the S polarized light and P polarized light transmitted through the beam
splitter 39 become circularly polarized light in the opposite direction by passing through the 1?4
wavelength plate 42 whose optical axis is inclined 45 ░ to the polarization direction.
The circularly polarized light beams rotating in opposite directions are superimposed to form
linearly polarized light, which is incident on the polarization beam splitter 43, and the light beam
reflected by the polarization beam splitter 43 is incident on the photoelectric converter 44a. The
light transmitted through the light source is incident on the photoelectric converter 44b.
[0105]
The polarization direction of the linearly polarized light incident on the polarization beam splitter
43 rotates once when the diffraction grating piece 30B moves by X / 2 in the X direction by the
vibration of the diaphragm 2 shown in FIG.
Therefore, in the photoelectric converter 44a and the photoelectric converter 44b, an
interference signal similar to that of the equation (2) can be obtained.
[0106]
Since the photoelectric converter 44 a and the photoelectric converter 44 b are 180 ░ out of
phase and the polarization beam splitter 43 is inclined 45 ░ with respect to the polarization
beam splitter 40, the signals obtained by the photoelectric converters 44 a and 44 b are , 90 ░
out of phase with the signal obtained by the photoelectric converters 41a and 41b.
05-05-2019
24
[0107]
The configurations and operations of the photoelectric converters 41a and 41b and the signal
processing unit that processes the signals output from the photoelectric converters 44a and 44b
are the same as the techniques described with reference to FIGS. 3 and 4.
[0108]
As described above, even if a transmission type diffraction grating is used, an audio signal can be
obtained on the same principle as a microphone using a reflection type diffraction grating, and
the mass difference due to the difference in the configuration of the diffraction grating or the
optical path that can be incorporated. The microphone can be designed in consideration of the
configuration of
[0109]
In the microphone 1B of the second embodiment, the reflecting prism 45 may be disposed inside
the bobbin 21 and the optical block 4 constituting the diffraction grating interferometer 3B may
be disposed outside the bobbin 21.
[0110]
<Configuration Example of Microphone of Third Embodiment> FIG. 8 is a configuration diagram
showing an example of a microphone of the third embodiment, and in FIG. 8, a transmission type
diffraction grating is used and a light emitting / receiving unit An outline of the configuration of
a microphone in which a beam splitter and the like are unitized is illustrated in a side sectional
view.
[0111]
The microphone 1C of the third embodiment includes a diaphragm 2 that receives a sound
pressure, and a light emitting / receiving composite unit 6 that configures a diffraction grating
interferometer 3C that measures the amount of movement of the diaphragm 2.
[0112]
The diaphragm 2 has an outer peripheral portion supported by the plate 20, and a cylindrical
bobbin 21 is, for example, integrated on the back side of the inner peripheral portion, and when
the diaphragm 2 receives a sound pressure, the bobbin 21 moves in the sound wave traveling
direction Reciprocate in parallel along the
05-05-2019
25
[0113]
The diffraction grating interferometer 3 C includes the diffraction grating piece 30 B on the
bobbin 21.
In the diffraction grating piece 30B, the small piece on which the transmission type diffraction
grating is formed is bonded and fixed to the bobbin 21 in such a direction that the diffraction
grating is perpendicular to the vibration direction of the diaphragm 2.
The diffraction grating may be directly formed integrally with the bobbin 21.
[0114]
<Configuration Example of Light Emitting and Receiving Combined Unit in Third Embodiment>
FIG. 9 is a configuration diagram showing an example of a light emitting and receiving combined
unit in the third embodiment. Next, the microphone according to the third embodiment is
described. The configuration of the light emitting / receiving complex unit 6 constituting the
diffraction grating interferometer 3C in 1C will be described.
[0115]
The light emitting / receiving composite unit 6 includes a housing member 60 as a substrate for
housing a light emitting element and a light receiving element, a lens portion 61, and a
polarization portion 62 (62a, 62b, 62c and 62d) for transmitting only a predetermined
polarization component. A phase plate 63 for converting the polarization state of the light, and a
light branching portion 64 for dividing light to be irradiated to the diffraction grating piece 30B
and for dividing second-order diffracted light obtained by being diffracted by the diffraction
grating piece 30B Equipped with
[0116]
The housing member 60 includes a semiconductor laser 71, which is an example of a coherent
light source for emitting light, and photodetectors 72 (72a, 72b, 72c, and 72d), which are
photoelectric converters for photoelectrically converting interference light to generate an
interference signal. A semiconductor substrate 73 for installing a semiconductor laser 71 and
applying an electrical signal, and a semiconductor substrate 74 for installing each photo detector
and extracting an electrical signal.
05-05-2019
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[0117]
The light branching portion 64 splits the light emitted from the semiconductor laser 71 into two
light beams having different polarization components and emits the light, and also separates the
second-order diffracted light diffracted by the diffraction grating piece 30B shown in FIG. It has a
section 78 and light branching films 79a, 79b, 79c, 79d for splitting the light superposed in the
polarization separating section 78.
[0118]
An interference signal corresponding to the amount of light obtained by photoelectric conversion
by each photodetector 72 is detected by a signal processing unit (not shown) via the
semiconductor substrate 74.
The signal processing unit (not shown) obtains a phase difference based on the obtained
interference signal, and outputs a position signal indicating the relative movement position of the
diffraction grating piece 30B.
[0119]
The lens unit 61 is an optical element such as a lens having a predetermined numerical aperture,
and the light emitted from the semiconductor laser 71 is incident and focused, and the light split
and emitted by the polarizing unit 62 is incident thereon. It is squeezed.
In the lens unit 61, the degree of integration can be increased by disposing in the same package
a lens that controls the beam diameter of both the light emitted to the outside and the light
received, and the manufacturing process can be simplified, and the entire apparatus can Can
increase the reliability of
[0120]
The polarization units 62 a, 62 b, 62 c and 62 d transmit only predetermined polarization
components of the lights Ld 1, Ld 2, Ld 3 and Ld 4 incident from the phase plate 63 and emit the
05-05-2019
27
light to the lens unit 61.
Each polarization part 62 should just be arrange | positioned at 45 degree space | interval (for
example, 5 degrees, 50 degrees, 95 degrees, 140 degrees), and can be arrange | positioned,
without receiving restrictions in the attitude | position at the time of attachment of the
polarization part 62.
By providing such a polarization part 62 between the phase plate 63 and the lens part 61, there
is also an advantage that the entire unit can be made compact.
[0121]
The phase plate 63 is stacked so as to be sandwiched between the polarization unit 62 and the
light branching unit 64.
The phase plate 63 is, for example, a 1?4 wavelength plate, and performs conversion between
circularly polarized light and linearly polarized light.
The phase plate 63 receives light from the semiconductor laser 71 through the lens unit 61.
The phase plate 63 converts, for example, light from the semiconductor laser 71, which is
linearly polarized light, into circularly polarized light and irradiates it to the polarization
separation unit 78.
The phase plate 63 receives the lights Ld1, Ld2, Ld3, and Ld4 emitted from the light branching
films 79a, 79b, 79c, and 79d, converts the lights into circularly polarized light, and emits the
circularly polarized light.
That is, a configuration is adopted in which conversion of light from the semiconductor laser 71
and conversion of light from the light branching film 79 are shared by one phase plate 63.
05-05-2019
28
[0122]
The polarization separation unit 78 includes, for example, a polarization beam splitter, and the
light emitted from the semiconductor laser 71 is incident through the phase plate 63.
In the polarization separation unit 78, the light of S polarization is reflected and the light of P
polarization is transmitted, and the incident light is split into two.
Further, the second-order diffracted light from the diffraction grating piece 30 B is incident on
the polarization separation unit 78, and the two second-order diffracted lights are superimposed
and emitted to the light branching film 79.
[0123]
The reflectances of the light branching films 79a, 79b, 79c, and 79d are set to 1/4, 1/3, 1/2, and
1, respectively.
That is, the light branching film 79d is a total reflection surface.
For this reason, it becomes possible to divide the incident light into lights Ld1, Ld2, Ld3 and Ld4
with substantially the same light quantity.
[0124]
In the light emitting / receiving composite unit 6, the housing member 60, the lens unit 61, the
polarization unit 62, the phase plate 63, and the light branching unit 64 described above are
disposed in the same package and configured as an independent unit. Ru.
Each of these members is configured to be laminated and integrated.
05-05-2019
29
[0125]
That is, by combining the members into an integrated structure, the light emitting / receiving
composite unit 6 facilitates precise position adjustment, and it is not necessary to take a large
space for arranging parts, and the microphone can be made smaller and lighter. Can be
In addition, by storing the respective members in the same housing member, it is possible to
reduce the influence of the environmental change and the temporal change, and it is possible to
minimize the deviation at the time of adjustment and the like. The overall reliability can be
enhanced.
[0126]
<Operation Example of Light Emitting / Combination Combined Unit in Third Embodiment> Next,
an example of the operation of the light emitting / receiving combined unit in the third
embodiment will be described.
[0127]
The light emitted from the semiconductor laser 71 is irradiated to the lens unit 61.
The light emitted from the semiconductor laser 71 is narrowed by the lens unit 61 and is
incident on the phase plate 63 formed of a 1?4 wavelength plate.
[0128]
The light incident on the phase plate 63 passes through the phase plate 63 and is converted into
circularly polarized light.
That is, linearly polarized light emitted through the phase plate 63 can be converted into
circularly polarized light regardless of the polarization direction of the light emitted from the
semiconductor laser 71.
05-05-2019
30
As a result, the polarization component of the light emitted from the semiconductor laser 71 can
be freely selected without being inclined by 45 ░ with respect to the polarization separation unit
78.
[0129]
The light having passed through the phase plate 63 is split into s-polarized light and p-polarized
light by the polarization separation unit 78, and enters the diffraction grating piece 30B.
[0130]
The light incident on the diffraction grating piece 30B is diffracted in the direction indicated by
the above-mentioned equation (1), whereby the S-polarized light (first-order diffracted light)
transmitted through the diffraction grating piece 30B and diffracted is 1 The light is reflected by
one surface of the reflecting prism 45 through the quarter wave plate 46a, returns to the same
optical path, passes through the quarter wave plate 46a, is incident on the diffraction grating
piece 30B, and is diffracted.
[0131]
Here, since the optical axis of the 1?4 wavelength plate 46a is inclined 45 ░ with respect to the
polarization direction of light, the light passing through the 1?4 wavelength plate 46a twice and
returned to the diffraction grating piece 30B is P-polarized light It has become.
[0132]
Then, the P-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization separation unit 78,
and since it is P-polarization, it is transmitted through the polarization separation unit 78.
[0133]
On the other hand, P-polarized light emitted from the semiconductor laser 71 and transmitted
through the polarization separation unit 78 is similarly incident on the diffraction grating piece
30B and diffracted.
P-polarized light (first-order diffracted light) transmitted through the diffraction grating piece
05-05-2019
31
30B and diffracted (first-order diffracted light) passes through the 1?4 wavelength plate 46b, is
reflected by the other surface of the reflecting prism 45, and returns along the same optical path.
The light is incident on the diffraction grating piece 30B through the wave plate 46b and is
diffracted.
[0134]
The optical axis of the 1?4 wavelength plate 46b is also inclined 45 ░ with respect to the
polarization direction of the light, so the light passing through the 1?4 wavelength plate 46b
twice and returned to the diffraction grating piece 30B becomes S polarization. There is.
[0135]
Then, the S-polarized light (second-order diffracted light) that has been transmitted through the
diffraction grating piece 30B and diffracted is returned to the polarization separation unit 78,
and since it is S-polarization, it is reflected by the polarization separation unit 78.
[0136]
Thus, the light emitted from the semiconductor laser 71 and split into S-polarized light and Ppolarized light by the polarization separation unit 78 passes through predetermined optical
paths, is diffracted by the diffraction grating piece 30B, and returns to the polarization
separation unit 78 next time. Origami is superimposed.
[0137]
The light (second-order diffracted light) superimposed by the polarization separation unit 78 is
split into light Ld1, Ld2, Ld3, and Ld4 by the light branching films 79a, 79b, 79c, and 79d.
The split lights Ld1, Ld2, Ld3 and Ld4 are respectively incident on the phase plate 63.
At this time, each light is circularly polarized in the opposite direction.
[0138]
05-05-2019
32
When this light is received by the photodetector through a polarizing plate that transmits only a
specific polarization component, the amplitudes of the two superposed second-order diffracted
lights of this light are A1 and A2, and the direction orthogonal to the grating of the diffraction
grating piece 30B (grating The amount of movement in the vector direction) is x, the initial phase
is ?, and K = 2? / ?. When first-order diffracted light is used in the first and second
diffractions, specific polarization components are used. When taken out, an interference signal I
such as the following equation (4) is obtained.
I = A1 <2> + A2 <2> + 2 и A1 и A2 cos (4 и K и x + ?) (4)
[0139]
The interference signal I changes by one period as the diffraction grating piece 30B moves by ?
/ 4 in the grating vector direction.
[0140]
The light components Ld1, Ld2, Ld3 and Ld4 that have passed through the phase plate 63 are
each transmitted by the polarization unit 62 so that only predetermined polarization components
are transmitted.
Each polarization part 62 is set to have an interval of 45 ░, but in this example, only the
polarization direction of 0 ░ is transmitted in the polarization part 62a, and the polarization
direction of 45 ░ in the polarization part 62b. The polarization unit 62c transmits only the
90.degree. Polarization direction, and the polarization unit 62d transmits only the 135.degree.
Polarization direction.
At this time, the intensities of the lights Ld1, Ld2, Ld3 and Ld4 transmitted through the
respective polarization parts 62 are represented by the following formulas (5) to (8), respectively.
[0141]
B + A cos (4.K.x + .delta.) (5) B + A cos (4.K.x + 90.degree. +. Delta.) (6) B + A cos (4.K.x +
180.degree. +. Delta.) (7) B + A cos (4 ..) K и x + 270 ░ + ? (8) where B = 1?4 (A1 <2> + A2 <2>),
A = 1/2 и A1 и A2.
05-05-2019
33
[0142]
The equation (5) represents the intensity of the light Ld1 transmitted through the polarization
unit 62a, the equation (6) represents the intensity of the light Ld2 transmitted through the
polarization unit 62b, and the equation (7) transmitted the polarization unit 62c The intensity of
the light Ld3 is represented, and the equation (8) represents the intensity of the light Ld4
transmitted through the polarization unit 62d.
[0143]
Each light represented by these equations passes through the lens 61 and is imaged on the
photodetectors 72a, 72b, 72c and 72d.
Then, each of the photo detectors 72 photoelectrically converts the light represented by the
above equation to generate an interference signal.
[0144]
Here, the DC component of the interference signal can be removed by subtracting Equation (5)
and Equation (7).
Further, the DC component of the interference signal can be removed by subtracting the
equations (6) and (8).
Further, since the subtracted signals are 90 ░ out of phase with each other, a signal for
detecting the moving direction of the diffraction grating piece 30B can be obtained.
[0145]
As described above, in the microphone 1C according to the third embodiment, the semiconductor
laser, the four photoelectric converters, the various beam splitters, and the quarter wavelength
plate that constitute the diffraction grating interferometer are replaced with the light emitting
and receiving unit 6 Thus, it is possible to configure with small size, light weight and low cost.
05-05-2019
34
[0146]
<The example of composition of the microphone of a 4th embodiment> Drawing 10 is a block
diagram showing an example of the microphone of a 4th embodiment, and in Drawing 10, the
composition of the microphone using two reflection type diffraction gratings Is shown in a side
sectional view.
[0147]
The microphone 1D according to the fourth embodiment includes the diaphragm 2 that receives
sound pressure and the light emitting / receiving composite unit 6 described in FIG. 9 and
includes the diffraction grating interferometer 3D that measures the amount of movement of the
diaphragm 2. .
[0148]
The diaphragm 2 has an outer peripheral portion supported by the plate 20, and a cylindrical
bobbin 21 is, for example, integrated on the back side of the inner peripheral portion, and when
the diaphragm 2 receives a sound pressure, the bobbin 21 moves in the sound wave traveling
direction Reciprocate in parallel along the
[0149]
The diffraction grating interferometer 3 </ b> D includes diffraction grating pieces 30 </ b> A at
two positions inside the bobbin 21.
The diffraction grating piece 30A1 and the diffraction grating piece 30A2 are adhesively fixed to
the bobbin 21 in such a direction that the small pieces on which the reflection type diffraction
grating is formed are perpendicular to the vibration direction of the diaphragm 2.
In the diffraction grating piece 30A1 and the diffraction grating piece 30A2, the bobbin 21 has a
predetermined rigidity so that the directions of the diffraction grating become parallel with a
predetermined high accuracy and the accuracy can be maintained.
The diffraction grating may be directly formed integrally with the bobbin 21.
05-05-2019
35
[0150]
As described with reference to FIG. 9, in the light emitting / receiving composite unit 6, the light
emitted from the semiconductor laser 71 is divided into two and light of S polarization and P
polarization is emitted.
[0151]
In the diffraction grating interferometer 3D, the S-polarized light emitted from the light emitting
/ receiving complex unit 6 is incident on one diffraction grating piece 30A1 and is diffracted, and
the P-polarized light is incident on the other diffraction grating piece 30A2 and diffracted Each
part is arranged so that the optical path to be formed is formed.
In this example, the S-polarized light emitted from the light emitting / receiving complex unit 6 is
directly incident on the diffraction grating piece 30A1, and the P-polarized light is reflected by
the mirror 47 to form an optical path incident on the diffraction grating piece 30A2. .
[0152]
Also, the diffraction grating interferometer 3D converts the polarization state of the light
reflected by the mirror 48a by reflecting the light of S-polarized light diffracted by the diffraction
grating piece 30A1 back to the diffraction grating piece 30A1, and 1/1 A four-wave plate 49a is
provided.
[0153]
Further, the diffraction grating interferometer 3D converts the polarization state of the light
reflected by the mirror 48b by reflecting the P-polarized light diffracted by the diffraction grating
piece 30A2 back to the diffraction grating piece 30A2, and 1/1 A four-wave plate 49 b is
provided.
[0154]
In the mirror 48a, the S-polarized light diffracted by the diffraction grating piece 30A1 is
vertically reflected and returned to the diffraction grating piece 30A1 along the same optical
05-05-2019
36
path.
The optical axis of the quarter-wave plate 49a is disposed at an angle of 45 ░ with respect to the
polarization direction of light, and S-polarized light is reflected by the mirror 48a and passes
through the quarter-wave plate 49a twice. Is converted to P polarization.
[0155]
Similarly, in the mirror 48b, the P-polarized light diffracted by the diffraction grating piece 30A2
is vertically reflected and returned to the diffraction grating piece 30A2 in the same optical path.
The optical axis of the quarter-wave plate 49b is disposed at an angle of 45 ░ to the polarization
direction of the light, and the light of P-polarization is reflected by the mirror 48b and passes
through the quarter-wave plate 49b twice. Is converted to S-polarization.
[0156]
Thus, the light emitted from the semiconductor laser 71 of the light emitting / receiving complex
unit 6 described in FIG. 9 is split into the light of S polarized light and P polarized light by the
polarization separating section 78 and emitted from the light emitting / receiving complex unit 6
The s-polarized light thus obtained is incident on the diffraction grating piece 30A1 and
diffracted, and the p-polarized light is reflected by the mirror 47 and made incident on the
diffraction grating piece 30A2 and diffracted.
[0157]
The S-polarized light diffracted by the diffraction grating piece 30A1 passes through the 1?4
wavelength plate 49a, is vertically reflected by the mirror 48a, returns along the same optical
path, and passes through the 1?4 wavelength plate 49a to the diffraction grating piece 30A1. It is
incident and diffracted.
[0158]
Here, since the optical axis of the quarter-wave plate 49a is inclined 45 ░ with respect to the
polarization direction of light, the light passing through the quarter-wave plate 49a twice and
returned to the diffraction grating piece 30A1 is P-polarized light It has become.
05-05-2019
37
[0159]
Then, the P-polarized light diffracted by the diffraction grating piece 30A1 returns to the
polarization separation unit 78 described in FIG. 9, and since it is P-polarization, it is transmitted
through the polarization separation unit 78.
[0160]
On the other hand, P-polarized light diffracted by the diffraction grating piece 30A2 passes
through the 1?4 wavelength plate 49b, is vertically reflected by the mirror 48b, returns along the
same optical path, and passes through the 1?4 wavelength plate 49b to form a diffraction grating
piece It is diffracted by being incident on 30A2.
[0161]
Here, since the optical axis of the 1?4 wavelength plate 49b is also inclined 45 ░ with respect to
the polarization direction of light, the light passing through the 1?4 wavelength p
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