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JP2001238293

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JP2001238293
[0001]
The present invention relates to an acoustoelectric converter, and more particularly to an
acoustoelectric converter using a vertical cavity surface emitting laser diode (VCSEL) as a light
emitting element.
[0002]
2. Description of the Related Art An optical microphone device is known as a microminiature
acoustoelectric converter using a VCSEL. FIG. 6 is a view showing the basic structure of the
optical microphone device. FIG. 6A shows a cross-sectional shape, in which the electronic circuit
board 12 is placed on the bottom surface 8 of the housing 1 and the board 9 on which the light
emitting element LD and the light receiving element PD are arranged is attached. A surface
emitting laser diode LD is used as a light emitting element, and a photodiode PD is used as a light
receiving element. A circular surface emitting laser diode LD is disposed at the center of the
substrate 9, and the light receiving elements PD are disposed concentrically so as to surround the
surface emitting laser diode LD.
[0003]
FIG. 6B is an enlarged plan view showing the light emitting and receiving part of the substrate 9
on which the light emitting and receiving element shown by a dotted line in FIG. 6A is mounted.
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As shown in the figure, a circular light emitting element LD is disposed at the central portion, and
light receiving elements PD1, PD2,..., PDn are disposed concentrically so as to surround this. As
the light emitting element LD used here, a vertical cavity surface emitting laser can be used. The
light emitting element LD and the light receiving element PD can be simultaneously
manufactured on a gallium arsenide wafer by a semiconductor manufacturing process.
Accordingly, since the alignment accuracy between the light emitting element LD and the light
receiving element PD is determined by the accuracy of the mask used in the semiconductor
manufacturing process, the alignment accuracy can be made 1 μm or less. It is possible to
realize with a high accuracy of one-hundredth or less compared to the alignment accuracy.
[0004]
In general, the vertical cavity surface emitting laser light emitting element has substantially
uniform light emission intensity distribution concentrically. Therefore, the radiation light emitted
toward the diaphragm 2 at a predetermined angle from the light emitting element LD disposed at
the central portion is concentrically reflected with the same intensity, and the diaphragm 2 is
received by the sound wave 7. As a result of the vibration, the reflection angle changes and
reaches the concentric circle of the light receiving element PD. Therefore, it is possible to detect
the vibration displacement of the diaphragm 2 by detecting the change in the amount of received
light of the light receiving elements PD1 to PDn arranged concentrically, converting this into the
change of the electric signal and outputting it. Since the strength of the incident sound wave 7
can be detected by this, it can be used as an optical microphone element. An electrode 11 is
formed to drive the light emitting element LD and the light receiving element PD or to detect the
amount of incident light.
[0005]
The displacement of the diaphragm 2 is detected by amplifying the change of the electric signal
detected from the light receiving element PD with an amplifier such as a differential amplifier or
a divider. Here, if it is intended to increase the output of the amplifier to a practical level, it is
necessary to increase the amplification factor of the amplifier, which complicates the amplifier
design. Further, when the amplification factor is increased, the noise generated on the electronic
circuit is also increased accordingly, which makes it difficult to increase the signal / noise (S / N)
ratio. Therefore, in order to obtain a signal having a high S / N ratio without increasing the
amplification factor of the amplifier, it is necessary to increase the change in the movement
width of the reflected light when the light is received by the light receiving element.
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[0006]
FIG. 7 shows a structure in which the lens element 3 is disposed on the optical path between the
substrate 9 and the diaphragm 2 in order to expand the movement width of the reflected light. A
lens element 3 having a lens diameter of 0.25 mm and an enlargement magnification of 6.5 is
disposed on the optical path, with the distance (L0) between the light emitting element LD and
the diaphragm 2 being 1.3 mm. The diaphragm 2 is disposed in the vicinity of the focal position
of the lens element 3 and is used as a reference position. Point a in FIG. 7 indicates the imaging
position. Further, a point b indicates an image forming point at a position reflected by the
diaphragm 2 and folded back. The state shown in FIG. 7 is a state in which the diaphragm 2 is
recessed by high pressure sound. The angle θ is determined by the convergence angle of the
lens element 3, and in the state shown in FIG. 7, θ = 12 °. The diaphragm 2 is initially at the
position 2c, and vibrates by a predetermined amount δ of deformation by the vibration to move
to the position 2d. Further, the diameter of the reaching distance of the reflected light when the
diaphragm 2 is at rest is 2A, and the diameter of the reaching distance of the reflected light when
the diaphragm 2 is moved by the odd amount δ is 2B. In the configuration as shown in FIG. 7,
the movement width when the reflected light converged by the lens element 3 reaches the light
receiving element PD becomes large, and the light receiving sensitivity becomes high.
[0007]
However, even with the structure of the improved optical microphone device shown in FIG. 7, the
sensitivity is still not necessarily high enough. Accordingly, an object of the present invention is
to provide an acoustoelectric conversion device using a lens element as shown in FIG.
[0008]
SUMMARY OF THE INVENTION According to the present invention, there is provided a
diaphragm which vibrates by sound, a light emitting element which causes light to be incident on
the diaphragm, and light which is reflected from the diaphragm and which receives light from the
diaphragm. A light receiving element which converts displacement into a change of an electric
signal and outputs the light, and converges incident light from the light emitting element and
guides it to the diaphragm, and diverges and reflects light from the vibrating body on a first focal
point on the optical axis In an acoustoelectric conversion device comprising a lens element which
converges between a position and a second focal position and guides it to the light receiving
element, the optical element is converged between the first focal position and the second focal
position. A shielding means is provided for shielding a part of the diverging reflected light.
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[0009]
In the acoustoelectric converter, the light emitting element can be provided on the optical axis
substantially at the same position as the shielding means.
Further, in the acoustoelectric conversion device, the light receiving element can be configured to
be divided into two with respect to the optical axis. Furthermore, in the acoustoelectric
conversion device, the light emitting element can be a vertical cavity surface emitting laser
element. In the acoustoelectric conversion device, the shielding means may be a knife edge
provided substantially at right angles to the optical axis.
[0010]
Further, according to the present invention, a diaphragm that vibrates by sound, a light emitting
element that causes light to be incident on the diaphragm, and light reflected from the
diaphragm are received, and the displacement of the diaphragm due to the sound is a change in
electric signal A light receiving element for converting and outputting, and incident light from the
light emitting element are converged and guided to the diaphragm, and diverging reflected light
from the vibrating body is at a first focal position and a second focal position on the optical axis
And a lens element for guiding the light to the light receiving element, and further reflecting the
diverging reflected light respectively converged on the first focal position and the second focal
position. Mirror means for guiding the light receiving element. In the acoustoelectric converter,
the light emitting element can be provided on the optical axis substantially at the same position
as the mirror means.
[0011]
Furthermore, according to the present invention, a trapezoidal vertical cavity surface emitting
laser light emitting device having a mirror surface which is substantially uniform concentrically
with the light emission intensity distribution of the light emitting surface and has a mirror
surface falling at a predetermined angle from the light emitting surface The light emitting
element is disposed on both sides of the light emitting element, d = h · tan (180−2 · α) from the
optical axis 4 provided that the light receiving element is divided into two at a distance of α> 45
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°. And a diaphragm which is disposed approximately in parallel and in close proximity to each
other and vibrates by sound, and converges incident light from the light emitting element and
guides it to the diaphragm, and diverges and reflects light from the diaphragm as an optical axis
And a lens element which is converged between the upper first focal position and the second
focal position and leads to the light receiving element, and the light emitting surface of the light
emitting element is the first focal position on the optical axis. And the convergent reflected light,
which is disposed between Is reflected by the serial mirror surface is obtained by the guided to
the light receiving element. In the acoustoelectric conversion device, the light emitting element
and the light receiving element can be manufactured on the same substrate in the same process.
In the acoustoelectric conversion device, the light emitting element and the light receiving
element can be manufactured on different substrates in different steps.
[0012]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a principle view for explaining the
configuration of the present invention. In the present invention, a shielding means is provided
between the lens element 3 and the light receiving element PD for shielding a part of the
diverging reflected light converged. In the example shown in FIG. 1, a knife edge 10 is provided
as a shielding means. The reflected light reflected and diverged by the diaphragm 2 is converged
by the lens element 3 and condensed so as to converge to two focal positions f1 and f2 on the
optical axis 4. Therefore, in the present invention, the knife edge 10 is provided between the
short focus position f1 and the long focus position f2. As a result, the return light from the
diaphragm 3 is blocked by the light flux on one side, and the light flux before and after focusing
is divided into areas A and B divided into two with respect to the optical axis of the light
receiving element PD. Therefore, by taking the difference signal between the light signal detected
from the A region and the light signal detected from the B region, the light reception modulation
with higher sensitivity is performed as compared with the structure as shown in FIG. Can. By
changing the distance Δ between the knife edge 10 and the light receiving element PD, the
optimum size and sensitivity of the light receiving element can be obtained.
[0013]
FIG. 2 is a diagram for explaining the operation principle of the configuration shown in FIG. In
the example shown in FIG. 2A, the return light from the lens 3 is converged to the short focus
position f1 with respect to the knife edge 10. In this case, return light from the upper side of the
lens 3 is not blocked by the knife edge 10 and does not reach the B area of the light receiving
element PD, and the return light from the lens element 3 is irradiated only to the A area. In the
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case of FIG. 2B, the return light from the lens 3 converges to the position of the knife edge 10
between the short focus position f1 and the long focus position f2. In this example, the amount of
light received by the region A of the light receiving element PD is equal to the amount of light
received by the region B. In the example of FIG. 2C, the return light converges to the long focus
position f2 with respect to the knife edge 10. In this case, only the return light from the upper
side of the lens 3 is received in the B region of the light receiving element PD. By extracting the
magnitudes of the light signals received in the A area and the B area of the light receiving
element PD as a difference signal, a large difference signal can be obtained as compared with the
case shown in FIG.
[0014]
The diagrams shown in FIGS. 1 (a) to 1 (c) are diagrams showing how the return light is received
by the light receiving element PD, and correspond to FIGS. 2 (a) to 2 (c), respectively. In the
embodiment shown in FIG. 1, the distance between the knife edge 10 and the light receiving
element PD is Δ, the vibration displacement of the diaphragm 2 is ± δ, and the distance
between the light emitting element LD and the diaphragm is 1 Assuming that the lens diameter is
0.25 mm and the magnification is 6.5, the distance L between the light emitting element LD and
the lens is 1.2 mm, and the distance F between the lens 3 and the diaphragm 2 is 0.19 mm.
Become. In the example shown in FIG. 1, the light emitting element LD is on the optical axis 4
and at the same position as the installation position of the knife edge 10. Furthermore, the
displacement d of the diaphragm 2 is an offset amount from the reference position. Furthermore,
when Hap is the luminous flux height of the return light on the lens, luminous flux heights A and
B on the light receiving element PD due to displacement ± δ of the diaphragm 2 are shown, and
the results shown in Table 1 are obtained.
[0016]
FIG. 3 is a view showing another embodiment of the present invention. In this embodiment,
instead of shielding one return light using a shielding means as shown in FIG. Mirror means 20a
and 20b are provided to reflect and guide the light to the light receiving element. The return light
converged to the short focus position f1 by the mirror means 20a and 20b is reflected and
guided by the light receiving elements A1 and A2, and the return light converged to the long
focus position f2 is guided to the light reception elements B1 and B2. The light beam of the
return light is separated into two light receiving elements and received by such mirror means.
Therefore, the received light amount modulation can be amplified and output by taking the sum
of the difference signals of the light receiving elements on both sides. That is, in the example
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shown in FIG. 3, the light reception output signal can be extracted as a sum signal of the
difference between the light receiving elements A1 and B1 and the difference between A2 and
B2. The mirror means 20a and 20b are arranged symmetrically with respect to the optical axis 4
at a predetermined angle. The light emitting element can be installed on the optical axis 4 at the
tip of the mirror means 20a, 20b. In the example shown in FIG. 3, the light emitting element LD
is disposed on the optical axis 4 so as to be located between the short focus position f1 and the
long focus position f2. Further, they are located at the apexes of the mirror means 20a and 20b,
thereby forming a substantially trapezoidal shape.
[0017]
FIG. 4 is a diagram for explaining the detailed operation principle of the second embodiment
shown in FIG. A trapezoidal vertical resonator type surface emitting laser light emitting element
LD having mirror surfaces 20a and 20b that descend from the light emitting surface at a
predetermined angle α is disposed in the center, and optical axes 4 to d are provided on both
sides of this light emitting element LD. A substrate on which the light receiving elements A1 and
B1 divided by a distance of h = tan (180−2 · α) (where α> 45 °) are disposed is used. Here, h
is the height of the trapezoid, and the ends of the mirror surfaces 20a and 20b are extended with
the inclination α and are the height from the intersection with the optical axis 4 to the substrate.
Further, d is the distance from the optical axis 4 to the division point of the light receiving
element divided into two. The return light from the lens 3 along the optical axis 4 has an incident
angle and a reflection angle of α, and the relationship of d = h · tan (180−2 · α) is established.
FIG. 2 (d) is a view showing a reflection state of return light when such mirror means 20a and
20b are used.
[0018]
FIG. 5 is a view for explaining a method of manufacturing the light emitting element and the
mirror means in the embodiment shown in FIG. 3. (a) shows a method of manufacturing the light
emitting / receiving element and the mirror means in the same step on a gallium arsenide
substrate. (B) shows a method of combining a complex of a light emitting element and a mirror
means, which are separately formed, with the light receiving element after producing the light
receiving element on a silicon substrate.
[0019]
Although the method of manufacturing in the same process shown in FIG. 5A can reduce the
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number of processes, it has the disadvantage that the gallium arsenide substrate is expensive.
In this method, a gallium arsenide substrate is prepared (step 40), and the periphery is etched
away with the portion where the light emitting element is to be formed in the center (step 41).
Next, crystal growth is performed on the entire surface (step 42). Then, the side wall of the light
emitting element LD formed in the central portion is etched at a predetermined angle to form an
inclined surface (step 43). Next, mirror coating is performed on this slope to form a mirror means
so that light is reflected.
[0020]
In the manufacturing method according to FIG. 5A, since the light emitting element, the light
receiving element and the mirror means are integrally formed on the same substrate, it is
possible to realize an ultra-compact acoustoelectric transducer with high accuracy. However, as
described above, since the gallium arsenide substrate is expensive, there is a disadvantage that
the cost increases. In the method shown in FIG. 5 (b), only the light receiving element is formed
using a low cost silicon substrate, and the light emitting element and the mirror means are
formed on an expensive gallium arsenide substrate and integrally formed by die bonding. It is a
thing.
[0021]
As shown in step 50, a silicon substrate is prepared, and substrate etching and crystal growth are
performed (steps 51 and 52) to form a light receiving element portion. On the other hand, a
gallium arsenide substrate is prepared, and crystal growth is performed thereon (steps 60 and
61) to form a light emitting element. Then, an inclined surface is formed at a predetermined
angle on the crystal plane formed in step 61, and mirror coating is performed on this inclined
surface (step 62) to form a light emitting element and a mirror means integrated with the light
emitting element. . Next, this is separated by dicing (step 63), and a chip consisting of the
separated light emitting element and mirror means is bonded to a light receiving element
consisting of a silicon substrate by die bonding (step 53), a light receiving / emitting element and
mirror means Form Although this manufacturing method increases the number of steps, the cost
of the device can be reduced because the silicon substrate is less expensive than the gallium
arsenide substrate.
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[0022]
As described above in detail based on the above embodiments, in the present invention, by
providing a shielding means for shielding a part of the return light or a mirror means for further
reflecting the return light, the present invention can Since the difference between the detection
signals becomes large or the movement width of the return light can be greatly increased, a high
S / N reproduced sound can be realized. Needless to say, the present invention can be used not
only for an optical microphone device but also for an acoustic sensor or the like.
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