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JP2006050099

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DESCRIPTION JP2006050099
PROBLEM TO BE SOLVED: To provide an optical microphone capable of realizing a small pencil
microphone type shape having a high degree of freedom in mechanical design and making it
possible to prevent the deterioration of sound wave detection accuracy due to circuit parts and
the like in such a shape. . SOLUTION: An inclined flat mirror 16 is provided on a part of a wall
surface of a cylindrical mirror 4 for transmitting a sound wave, and the laser light generating
unit 2 and the photoelectric conversion unit 6 can be arranged on the opening of the cylindrical
mirror 4 side. Make it Furthermore, a shielding plate 17 is provided at the opening on the side
opposite to the sound source of the cylindrical mirror 4 to make the acoustic impedance at the
opening on the side opposite to the sound source constant. [Selected figure] Figure 4
Optical microphone
[0001]
The present invention relates to an optical microphone that converts a sound wave into an
electrical signal using a light beam, and more particularly to a miniaturized so-called pencil
microphone type optical microphone.
[0002]
As a microphone which is a device for converting sound waves into an electric signal, a dynamic
or condenser microphone using a diaphragm is generally used.
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On the other hand, microphones have been proposed that detect sound waves using light beams
such as laser light without using a diaphragm (see, for example, Patent Documents 1 and 2). JPA-59-157620 JP-A-2002-78093
[0003]
Many microphones using the conventional light beam have a problem that the device is large and
can not obtain sufficient frequency characteristics as an acoustic microphone, or extreme
detection directivity is generated. Was difficult. Prior to the present invention, the inventor
invented a small, high-sensitivity optical microphone that efficiently enhanced the detection
sensitivity of the sound wave without expanding the detection area of the sound wave and
improved the frequency characteristics and directivity. In the above invention, the light path
forming surface of the light beam in the shape of a star polygon in the acoustic signal detection
field, and the light beam output means and the light beam detection means are arranged on
substantially the same plane. It has been difficult to realize a compact so-called pencil
microphone type optical microphone with low design freedom.
[0004]
A pencil microphone is a rod-like microphone device, which has a sound wave detection unit at
one end and contains circuit parts and a power source inside the rod-like main body, and is
widely used as an instrument recording or vocal microphone The detection directivity of the
sound wave detection unit of the pencil microphone has high sensitivity in the longitudinal
direction of the axis of the rod-like microphone, and the sound wave detection unit is used in the
sound source direction.
[0005]
When one opening of the optical path forming means of the optical microphone is positioned at
one end of the pencil microphone to realize a pencil microphone type optical microphone, the
other opening of the light path forming means is the main body of the pencil microphone It will
open to the inside.
Since the circuit components are placed inside the body of the pencil microphone, the acoustic
impedance of the back space of the optical path forming means differs depending on the place.
For this reason, if the reflection of the sound wave in the back space is not uniform, the sound
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field in the acoustic signal detection field is disturbed by the non-uniform reflected sound from
the back space, and the accuracy of the sound wave detection is degraded.
[0006]
Therefore, according to the present invention, an optical microphone having a high mechanical
design freedom and capable of realizing a small pencil microphone shape, and preventing such
deterioration in sound wave detection accuracy due to circuit parts and the like when such a
shape is used. Intended to provide.
[0007]
The present invention has the following configuration as means for solving the above-mentioned
problems.
[0008]
(1) A light beam output means for outputting a light beam, A light beam output from the light
beam output means is reflected and intersected a plurality of times to form an optical path in a
star polygon, and a region including this optical path Optical path forming means for modulating
a light beam in the shape of the star polygon with a sound wave passing through a certain
acoustic signal detection field, and detecting the modulation amount of the light beam emitted
from the optical path forming means A light beam detection means for outputting a
corresponding electric signal, the light path forming means has a cylindrical structure whose
inner wall surface is a mirror surface, and the light path of the shape of the inner wall and the
star polygon is formed And the inner wall surface has a light beam output from the light beam
output means, and an optical path in the shape of a star polygon in the acoustic signal detection
field. Make it incident as it is formed A reflection surface, the light beam incident on the optical
path forming means and the light beam emitted from the optical path forming means are
reflected at substantially the same point on the small reflection surface and enter and exit from
the acoustic signal detection field The light path forming surface in the shape of a star-shaped
polygon, and the light beam output means and the light beam detection means are disposed on
different planes.
[0009]
In this configuration, the optical path forming means of the optical microphone forms an optical
path of a star-shaped polygon in the acoustic signal detection field for the light beam output from
the light beam output means. Since the small reflection surface that reflects light is provided, it is
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possible to bend the light path of the light beam, and it becomes possible to arrange the light
beam output means and the light beam detection means on a plane different from the light path
forming means. A light beam output means and a light beam detection means can be arranged on
the side of the opening opposite to the sound source direction of the light path forming means of
the mold structure.
Therefore, the degree of freedom in design can be increased, and it becomes easy to miniaturize
the optical microphone and to design a pencil-type optical microphone.
[0010]
Furthermore, in this configuration, the light beam output from the light beam output means is
reflected by the small reflection surface, enters the optical path forming means, and is repeatedly
reflected by the inner wall surface of the optical path forming means, thereby achieving a star on
one plane. An optical path having a polygonal shape is formed, and the light is reflected again by
the small reflection surface and emitted from the optical path forming means and guided to the
light beam detecting means. At this time, the incident angle of the light beam entering the optical
path forming means is By setting the angle at which the incidence and the emission due to the
reflection of the small reflection surface occur at substantially the same point, the small
reflection surface may be provided at one place in the optical path forming means, and the small
reflection surface can be miniaturized. The disturbance of the sound field in the acoustic signal
detection field due to the surface can be made extremely small, which enables the design of a
small and high-performance optical microphone.
[0011]
(2) A shielding means is provided to make the opening on the opposite side of the light source
direction of the light path forming means in a sealed state or a semi-sealed state.
[0012]
In this configuration, since the optical microphone seals one opening of the optical path forming
means by the shielding means in a sealed or semi-sealed state, various components disposed on
the opening side opposite to the sound source direction of the optical path forming means It is
possible to reduce the influence of the reflection of the sound wave by this, and to make the
acoustic impedance almost constant regardless of the position.
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Therefore, the detection accuracy of the sound wave can be enhanced.
In addition, it is possible to change directivity by optimizing the volume of the back space
opposite to the sound source direction of the acoustic signal detection field in the closed state or
controlling the introduction of sound waves from the outside in the semi-closed state. is there.
[0013]
In the optical microphone of the present invention, a small reflection surface is provided on a
part of the inner wall surface of the optical path forming means for the optical path of the light
beam, and the optical path is bent by this reflecting means to form the optical path forming
means (cylindrical mirror) It is possible to freely set the positional relationship between the
output means and the light beam detection means, and it is possible to increase the freedom of
design of the shape of the optical microphone, and to easily manufacture a small pencil
microphone type optical microphone etc. Become.
[0014]
In addition, by providing a shielding means that has light transparency and is completely sealed
or semi-sealed at the opening on the opposite side of the sound source direction of the acoustic
signal detection field to restrict the flow of air, The acoustic impedance in the space on the back
side can be made constant, and a compact pencil microphone type optical microphone with high
detection accuracy of the sound wave can be manufactured, and the directivity of sound wave
detection can be controlled.
[0015]
[Basic Configuration] FIG. 1 is a configuration diagram showing a basic configuration of the
optical microphone of the inventor's prior application made prior to the present invention, (A) is
a top view seen from the sound source side, (B) Is a side view, and (C) is a top view in the case of
using a polygon mirror instead of a cylindrical mirror.
The optical microphone 1 includes a laser beam generation unit 2 and a light source system lens
unit 3 which are light beam output means, a cylindrical mirror 4 which is an optical path forming
means, and a detection system lens unit 5 and a photoelectric conversion unit 6 which are light
beam detection means. Have.
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[0016]
The laser beam generation unit 2 includes a semiconductor laser element and a laser drive circuit
(not shown), and emits a laser beam 7.
The light source system lens unit 3 condenses the laser light 7 emitted from the laser light
generation unit 2 and converts it into a laser beam 8 which is substantially parallel light with a
predetermined spot diameter.
The cylindrical mirror 4 has a cylindrical shape and the entire inner wall surface is a mirror
surface 4m, and a notch 4k or a hole 4a is formed in part of the inner wall surface, and the
incident laser beam 8 is reflected a plurality of times. The modulation is performed a plurality of
times.
Here, in the following description, it is assumed that the notch 4 k is formed in the cylindrical
mirror 4. The cylindrical mirror 4 is arranged so that the laser beam 8 incident on the acoustic
signal detection field 9 inside thereof is reflected by the mirror surface 4 m multiple times to
form a star-shaped polygonal light path. That is, the laser beam 8 output from the laser beam
generation unit 2 and the normal line at the intersection of the laser beam 8 with the circle
inscribed in the mirror surface 4m (shown by dotted lines in FIGS. 1A and 1C) The incident angle
∠A is arranged to be a predetermined angle. As a result, at each reflection point of the laser
beam 8 on the mirror surface 4m, light is incident at an incident angle ∠A with respect to the
normal at the reflection point on the mirror surface 4m.
[0017]
FIG. 1 shows the case where the incident angle ∠A to the cylindrical mirror 4 is 6 degrees.
Further, in the optical microphone 1, as shown in FIG. 1B, the optical paths of the laser beam 8
are formed substantially on the same plane. In the following description, a plane on which the
optical path of the laser beam 8 is formed is referred to as an XY plane, and an axis
perpendicular to the XY plane is referred to as a Z axis.
[0018]
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Further, as shown in FIG. 1C, instead of the cylindrical mirror 4, the polygonal prism mirror 14
having a polygonal opening surface and a mirror surface on the inner wall surface and in which a
notch 14k or a hole 14a is formed in part is shown. It is also possible to use. The detection
system lens unit 5 repeatedly reflects light from the cylindrical mirror 4 and condenses the
emitted laser beam 8 to converge it on a detection element (not shown) constituting the
photoelectric conversion unit 6. The photoelectric conversion unit 6 detects the modulation
amount of the laser beam 8 converged on the detection element (not shown) by the detection
system lens unit 5, and outputs an electrical signal according to the modulation amount.
[0019]
Next, the operation of the optical microphone 1 will be described. As is well known, sound waves
are vibration components of the density of air, and in the space where sound waves are
propagating, a distribution of large and small in the optical refractive index of air is generated
according to the degree of density. Moving. Therefore, when the laser beam is allowed to pass
through the space where the sound wave is propagating, the laser beam is modulated according
to the inclination of the refractive index at the passing point, and the modulation amount
changes with the movement of the distribution of the refractive index. The laser beam undergoes
modulation correlated to the acoustic wave.
[0020]
The optical microphone 1 emits the laser beam 7 from the laser beam generator 2, converts the
laser beam 7 into a laser beam (parallel beam) 8 by the light source system lens unit 3, and the
acoustic signal detection field 9 by the cylindrical mirror 4. A plurality of reflections are made so
as to form a star-shaped polygonal light path inside. As a result, in the acoustic signal detection
field 9, the laser beam 8 is modulated by the sound wave 12 by approximately the number of
times of reflection as in the case of the linear light path. Then, the modulated laser beam 8 is
guided to the photoelectric conversion unit 6 through the detection system lens unit 5, and the
modulation amount of the laser beam 8 corresponding to the inclination of the refractive index of
air is detected. Output a signal.
[0021]
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Further, in the acoustic signal detection field 9 in the cylindrical mirror 4, since the laser beam 8
does not pass through the central region, the region having no acoustic signal detection
sensitivity (hereinafter referred to as a central region 10). And a region with a high density of
optical paths with high concentration of (crossed) optical paths is formed in a ring shape so that
a plurality of optical paths are concentrated (crossed) immediately surrounding the central
region 10 without this acoustic signal detection sensitivity. (Hereinafter referred to as a ringshaped region 11). As described above, the acoustic signal detection sensitivity in the acoustic
signal detection field 9 has an uneven sensitivity distribution, and the modulation of the laser
beam 8 by the sound wave 12 output from the sound source 13 is performed around the ringshaped region 11.
[0022]
Therefore, the detection area of the sound wave 12 can be limited space, and the number of
actions of the sound wave 12 on the laser beam 8 can be made efficient without expanding the
acoustic signal detection field 9 which is the area for detecting the sound wave 12 Can be
increased, and the detection sensitivity of the sound wave 12 in a limited space can be effectively
enhanced.
[0023]
Next, the incident angle of the laser beam of the cylindrical mirror will be described.
FIG. 2 is a top view showing an optical path in the shape of a star-shaped polygon formed in a
cylindrical mirror, where (A) is an incident angle ∠A of 12 degrees, (B) is an incident angle ∠A
of 24 degrees In the case of (C), the incident angle ∠A is 48 degrees.
[0024]
As described above, the incident angle ∠A to the cylindrical mirror 4 is defined as the angle
between the laser beam 8 and the normal line at the intersection of the laser beam 8 and the
circle inscribed in the mirror surface 4 m of the cylindrical mirror 4. As shown in FIG. 2,
according to the incident angle of the laser beam 8, the light path pattern of the star-shaped
polygon shape of the laser beam 8 formed in the acoustic signal detection field 9 changes, and
the region with high optical path density The diameter of a certain ring-like region 11 changes.
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In addition, it is possible to change the detection directivity of the sound wave (acoustic signal)
12 by changing the diameter of the ring-shaped area 11.
[0025]
For example, as shown in FIG. 2A, when the incident angle is set so that the optical path is
concentrated near the center of the acoustic signal detection field 9, a ring-shaped region 11
with high acoustic signal detection sensitivity near the center Is formed to lower the detection
sensitivity of the peripheral region. Therefore, in the optical microphone 1, the suppression effect
is not remarkable even when sound waves of different phases are applied to the vicinity of the
center and the periphery of the acoustic signal detection field 9, and the figure of eight acoustic
signal detection sensitivity is It becomes an optical microphone close to bi-directional.
[0026]
Further, as shown in FIGS. 2B and 2C, when the incident angle is set so that the optical path is
concentrated in the peripheral portion of the acoustic signal detection field 9, a ring having high
acoustic signal detection sensitivity in the peripheral portion The region 11 is formed. In this
case, when the sound source 13 is on the axis perpendicular to the light path of the laser beam 8
in the shape of a star polygon at the center of the acoustic signal detection field 9, the sound
wave 12 is in the ring region 11 with high detection sensitivity. Since the phase is the same in
any part, no suppression effect occurs. On the other hand, when the sound source 13 is located
at a position away from the vertical axis, the sound signal detection sensitivity is suppressed by
the suppression effect because the ring region 11 with high detection sensitivity is modulated by
the sound wave 12 different in phase depending on the position. The result is an optical
microphone with narrow directivity in both directions of the aforementioned axis. As described
above, in the optical microphone 1, the detection directivity of the sound wave can be changed
by changing the incident angle of the laser beam 8 to the cylindrical mirror 4.
[0027]
First Embodiment FIG. 3 is a schematic configuration view of a cylindrical mirror of an optical
microphone according to a first embodiment of the present invention, in which (A) is a front
view, (B) and (D) are side views, C) and (E) are top views. 3B and 3C show the case where the
incident angle 入射 A of the laser beam 8 to the cylindrical mirror 4 is set to 6 degrees as an
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example, and FIGS. 3D and 3E show the cylinder The case where the incident angle ∠A of the
laser beam 8 to the mirror 4 is set to 48 degrees is shown. Since the optical microphone 1a
shown in FIG. 3 has substantially the same configuration as the optical microphone 1 shown in
FIG. 1, only different parts will be described in detail. Further, in the following description of the
first embodiment, the plane in which the light path of the star-shaped polygon of the laser beam
8 is formed is referred to as an XY plane, and the axis perpendicular to the XY plane is referred
to as a Z axis. Further, in FIG. 3, the incident angle is an angle between the laser beam 8 and the
normal to the mirror 4m at the reflection point of the laser beam 8 on the mirror 4m.
[0028]
As shown in FIG. 3, the optical microphone 1a guides a part of the inner wall surface 4m of the
mirror surface of the cylindrical mirror 4 to the inner wall surface of the cylindrical mirror 4 by
the laser beam 8 from the laser light generator 2 So as to form an optical path in the shape of a
star-shaped polygon, it is replaced by a flat mirror (small reflection surface) 16 inclined at a
predetermined angle ∠ C with respect to the axis of the cylindrical mirror 4 (Z axis in FIG. 3) The
positional relationship between the laser beam generator 2 and the photoelectric converter 6 and
the cylindrical mirror 4 can be changed according to the angle. Further, according to this
configuration, it is possible to guide the laser beam 8 to the acoustic signal detection field 9 and
form an optical path in the shape of a star-shaped polygon without providing the light
transmitting portion on the wall surface of the cylindrical mirror 4.
[0029]
Although ∠ C can take an arbitrary value according to the mechanism design, in FIG. 3, ∠ C is
45 degrees, and an example of making an optical path in the shape of a star polygon on the XY
plane enter and exit from the Z axis direction It shows.
[0030]
The incident angle ∠A of the laser beam 8 is set by the laser beam 8 to form an optical path in
the shape of a star polygon on the XY plane, and is set to an angle at which the incident point
and the outgoing point of the laser beam 8 coincide.
For example, in the case of the optical microphone 1a according to the first embodiment, by
setting the incident angle ∠A of the laser beam 8 to an angle such as 6, 12, 24 or 48 degrees
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when ∠ C is 45 degrees. Since the laser beam 8 is reflected at approximately one point 16 p of
the plane mirror 16 and enters and exits, the plane mirror 16 may be small enough to have some
allowance for the diameter of the laser beam 8.
[0031]
The width of the plane mirror in the Y-axis direction is about the same as the distance between
the reflection points so that the size of the plane mirror 16 does not affect the reflection points
on both sides of the light path 16p in the shape of a star polygon. Set
[0032]
Therefore, in the optical microphone 1a, although the shape of the cylindrical mirror 4 is not a
simple cylindrical shape, the flat mirror 16 is small and hardly affects the sound wave passing
through the acoustic signal detection field 9. In addition, since the sound wave does not leak
from the wall surface of the cylindrical mirror 4, the degree of freedom in mechanism design can
be enhanced without causing a decrease in the detection sensitivity of the sound wave or a
decrease in the detection accuracy. It is possible to design a compact optical microphone of the
so-called pencil microphone type.
[0033]
Second Embodiment FIG. 4 is a schematic view of an optical microphone according to a second
embodiment of the present invention, in which (A) is a front view, (B) and (D) are side views, and
(C) , (E) is a top view, and shows the case of ∠ C = 45 degrees.
4B and 4C show the case where the incident angle 入射 A of the laser beam 8 to the cylindrical
mirror 4 is set to 6 degrees as an example, and FIGS. 4D and 4E show the same. The case where
the incident angle ∠A of the laser beam 8 to the cylindrical mirror 4 is set to 48 degrees is
shown.
Since the optical microphone 1b shown in FIG. 4 has substantially the same configuration as the
optical microphone 1a shown in FIG. 3, only different portions will be described in detail. In the
following description of the second embodiment, a plane on which the star-shaped polygonal
optical path of the laser beam 8 is formed is referred to as an XY plane, and an axis
perpendicular to the XY plane is referred to as a Z axis. Further, in FIG. 4, the incident angle is an
angle between the laser beam 8 and the normal to the mirror 4m at the reflection point of the
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laser beam 8 on the mirror 4m.
[0034]
As shown in FIG. 4, the optical microphone 1b has a configuration in which a shielding plate 17
is provided on the side of the opening surface 4f of the cylindrical mirror 4 of the optical
microphone 1a shown in FIG. The shielding plate 17 is formed with a non-air-permeable light
transmitting portion 18 through which the laser beam 8 passes and air does not flow. The light
transmitting portion 18 is formed by filling a light transmitting member such as glass or resin in
a hole provided in the shielding plate 17 or providing a notch or a hole in the shielding plate 17
to form the notch or the hole. It is also possible to fit in the light transmitting member molded
into the above, or to form the whole of the shielding plate 17 by the light transmitting member.
[0035]
For example, as shown in FIG. 4E, when the maximum incident angle of the laser beam 8 is a, the
light transmitting portion 18 provided on the shielding plate 17 emits light between narrow
angles (central angles) which are 2a. It is good to form with a permeable member.
[0036]
In addition, it is desirable to coat the surface of the light transmitting portion 18 of the shielding
plate 17 with a dielectric multi-layered film that prevents a decrease in transmittance due to
surface reflection.
As a result, it is possible to prevent the reflection of the laser beam 8 incident on the light
transmission unit 18.
[0037]
Here, although FIG. 4 shows an embodiment in which the shielding plate 17 having air tightness
is provided on the back side of the cylindrical mirror 4, the present invention is not limited to
this. For example, in the case of a configuration in which the cylindrical mirror 4 is housed in a
housing, light transmission is provided between the space on the back of the acoustic signal
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detection field 9 and the space in which the electronic components and the like in the housing
are installed. By providing the case, the same effect as providing the shielding plate 17 can be
obtained. Further, the shielding plate 17 and the case provided on the back surface of the
cylindrical mirror 4 are not limited to those having perfect air tightness, and holes or slits may be
provided for sound wave introduction.
[0038]
As described above, by providing a shielding plate or a case having light permeability in the back
space of the acoustic signal detection field 9 and designing it so that the acoustic impedance is
optimal, the degree of freedom in light path design is high, It is possible to obtain a highperformance optical microphone in which the acoustic impedance nonuniformity is eliminated.
Moreover, it is also possible to perform directivity control by introducing a sound wave from the
outside into the back space.
[0039]
It is a block diagram which shows the basic composition of the optical microphone which
concerns on embodiment of this invention. It is a top view which shows the light path of the starshaped polygon formed in the cylindrical mirror. It is a schematic block diagram of the optical
microphone concerning a 2nd embodiment of the present invention. It is a schematic block
diagram of the optical microphone which concerns on 3rd Embodiment of this invention.
Explanation of sign
[0040]
1, 1a, 1b, 1c-optical microphone 2-laser light generation unit 3-light source system lens unit 4cylindrical mirror 5-detection system lens unit 6 photoelectric conversion unit 7 laser light 8laser beam 9 acoustic signal detection Field 10-central area 11-ring area 12-sound wave 13sound source 15, 18-light transmission part 16-plane mirror 17-cover
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