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JP2008128910

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DESCRIPTION JP2008128910
The present invention provides a vibration detection device capable of providing a vibration
detection device capable of improving detection sensitivity when performing digital vibration
detection optically. A laser light Lout from a laser light source 10 is separated into two optical
paths OP1 and OP2 in an interferometer configured according to a Mach-Zehnder
interferometer. Interference light is formed on the beam splitter 12 by causing the reference
light from the optical path OP2 and the reflected light from the optical path OP1 to interfere with
each other. Then, based on the interference fringes, the vibration of the vibrating film 11 is
quantized and detected. Further, the reference light is reflected by the beam splitter 12 and the
reflection mirror 13 in one optical path OP2 (reference optical path) of the two optical paths OP1
and OP2. In the other optical path OP1 (reflected optical path), the reflected light is multiply
reflected by the vibrating film 11 and the beam splitter 12. The optical path difference between
the reference light and the reflected light becomes large, and the displacement of the diaphragm
11 is amplified and detected. [Selected figure] Figure 1
Vibration detection device
[0001]
The present invention relates to a vibration detection device that optically detects displacement
of a vibrating body.
[0002]
In recent years, recording methods using SACD (Super Audio Compact Disc) and 24 bit-96 kHz
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sampling have been used, and high sound quality has become mainstream.
In such a flow, the microphone device of the conventional analog system has a limitation in
recording of the high frequency of 20 kHz or more, so let's record the content by making use of
the reproduction of the high frequency which is the feature of the above recording method And
when it was, it was a bottleneck.
[0003]
In addition, with regard to the dynamic range, it has not reached 144 dB which is possible by the
24-bit bit recording which is the feature of the above recording system, and the wide dynamic
range has not been fully utilized.
[0004]
Furthermore, at the recording site, in the conventional analog microphone device, noise increases
due to the long distance routing with the analog cable, and phantom power must be supplied to
the condenser microphone from the mixing console. It has been an obstacle to all digitization in
recording and production systems.
[0005]
Therefore, in recent years, several digital microphone devices have been proposed (for example,
Patent Documents 1 and 2).
[0006]
JP-A-10-308998 JP-A-11-178099
[0007]
In the patent document 1, a digital audio signal is output by detecting the vibration of the
diaphragm using a laser light source and a Mach-Zehnder interferometer or Michelson
interferometer.
[0008]
On the other hand, in Patent Document 2 described above, a ΔΣ (delta sigma) modulator
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including a laser light source and a diaphragm is configured.
Therefore, it is considered that a 1-bit digital audio signal can be obtained with a simple
configuration by the action of the ΔΣ modulator, and noise reduction of the audio signal in the
audible band can be achieved using the noise shaving effect. .
[0009]
However, in these patent documents 1 and 2, since the wavelength of a laser beam is about 0.6
micrometer, there existed a problem that detection sensitivity could not be improved very much.
Therefore, although it is effective when the vibration of the diaphragm is large, it is difficult to
detect the vibration of the diaphragm when it is applied to a high sensitivity microphone that
requires a vibration detection of about several pm, There was room for improvement.
[0010]
The present invention has been made in view of such problems, and an object thereof is to
provide a vibration detection device capable of improving detection sensitivity when performing
digital vibration detection optically.
[0011]
The first vibration detection apparatus according to the present invention includes a light source
for emitting a laser beam, a vibrator capable of reflecting the laser beam, and a beam splitter, and
splits the laser beam into two optical paths and advances them. Interference occurs by causing
the reference light reflected by the beam splitter in one of the two optical paths and the reflected
light multiply reflected by the oscillator and the beam splitter in the other of the two optical
paths to interfere with each other It comprises an interferometer that forms a stripe, and a
detection unit that quantizes and detects the vibration of the vibrating body based on the formed
interference pattern.
[0012]
In the first vibration detection apparatus of the present invention, the laser light emitted from the
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light source is split into two light paths in the interferometer, and the reference light is a beam
splitter in one of these two light paths (reference light path). In the other light path (reflected
light path), the reflected light is multiply reflected by the vibrator and the beam splitter.
Then, the reference light and the reflected light interfere with each other to form an interference
fringe, and based on the formed interference fringe, the vibration of the vibrator is quantized and
detected.
Here, in the interferometer, the reflected light is multi-reflected, so that the optical path
difference between the reference light and the reflected light becomes large, and as a result, the
displacement of the vibrating body is amplified and detected.
[0013]
In the first vibration detection apparatus of the present invention, the interferometer has a
reflector capable of reflecting laser light, the beam splitter is disposed between the vibrator and
the reflector, and the one optical path is a reflector It is possible to form so as to be formed
between the beam splitter and the other light path formed between the oscillator and the beam
splitter.
In this configuration, the reference light is reflected by the beam splitter and the reflector in one
of the optical paths, and the reflected light is multiply reflected by the vibrator and the beam
splitter in the other optical path.
[0014]
Further, the vibrator and the beam splitter are disposed to face each other, and the one light path
is formed inside the beam splitter and the other light path is formed between the vibrator and the
beam splitter. It is possible.
In such a configuration, in one of the optical paths, the reference light is reflected by the end face
in the beam splitter, and in the other optical path, the reflected light is multiply reflected by the
vibrator and the beam splitter.
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[0015]
In addition, the interferometer has a pair of reflectors capable of reflecting laser light, and the
oscillator doubles as a beam splitter and is disposed between the pair of reflectors, and the one
optical path is a pair of reflections. The light path is formed between one of the reflectors of the
body and the vibrator, and the other light path is formed between the reflector of the other of the
pair of reflectors and the vibrator. It is possible.
When configured in this manner, the reference light is reflected by one reflector and the vibrator
in one of the light paths, and the reflected light is reflected by the other reflector and the vibrator
in the other light path.
[0016]
In this case, the light source, the interferometer, and the detection means are integrated on a
semiconductor substrate, and the area of at least one of the pair of reflectors is smaller than the
area of the vibrator on the semiconductor substrate. It is preferable to When configured in this
manner, a part of the wave traveling toward the vibrating body can reach the vibrating body
without passing through the reflector. Further, the reflector is more preferably elongated in the
direction along the projection component on the substrate surface in the traveling direction of
the laser beam. In such a configuration, the wave directed to the vibrating body can more easily
reach the vibrating body without passing through the reflector.
[0017]
In the first vibration detection apparatus of the present invention, it is preferable that the
reference light be multiply reflected by the beam splitter in the one optical path. In such a
configuration, the distance between the beam splitter and the oscillator can be reduced without
changing the optical path length of the one optical path (reference optical path), and the
interferometer can be miniaturized. Preferably, at least one of the reference light and the
reflected light is reflected such that the sum of the incident angle and the reflection angle is an
acute angle. In such a configuration, the optical path difference between the reference light and
the reflected light is further increased, so that the vibration detection sensitivity is further
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enhanced.
[0018]
A second vibration detection apparatus according to the present invention includes a light source
for emitting a laser beam, and a vibrator and a beam splitter which can reflect the laser beam so
that the sum of the incident angle and the reflection angle becomes an acute angle. A reference
beam reflected by the beam splitter in one of the two optical paths, and a vibrator and a beam in
the other of the two optical paths, while the laser beam is split and traveled in the two optical
paths; The interferometer includes an interferometer that causes the reflected light reflected by
the splitter to interfere with each other to form an interference pattern, and a detection unit that
quantizes and detects the vibration of the vibrator based on the formed interference pattern.
[0019]
In the second vibration detection apparatus of the present invention, the laser beam emitted from
the light source is split into two light paths in the interferometer, and the reference light is a
beam splitter in one of these two light paths (reference light path). In the other light path
(reflected light path), the reflected light is reflected by the vibrator and the beam splitter.
Then, the reference light and the reflected light interfere with each other to form an interference
fringe, and based on the formed interference fringe, the vibration of the vibrator is quantized and
detected. Here, in this interferometer, the laser beam is reflected by the oscillator and the beam
splitter so that the sum of the incident angle and the reflection angle becomes an acute angle, so
the optical path difference between the reference beam and the reflected beam becomes large. As
a result, the displacement of the vibrator is amplified and detected.
[0020]
According to the first vibration detection apparatus of the present invention, the laser light from
the light source is split into two light paths in the interferometer, and the reference light is
divided by the beam splitter in one of these two light paths (reference light path). Since the
reflected light is reflected by the vibrator and the beam splitter in the other light path (reflected
light path) while being reflected, the light path difference between the reference light and the
reflected light is increased, and the displacement of the vibrator is amplified and detected. can
do. Further, since the vibration of the vibrating body is quantized and detected based on the
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interference fringes formed by the reference light and the reflected light interfering with each
other, the vibration of the vibrating body can be optically digitally detected. . Therefore, it is
possible to improve detection sensitivity when performing digital vibration detection optically.
[0021]
Further, according to the second vibration detection apparatus of the present invention, the laser
light from the light source is separated into two optical paths in the interferometer, and the
reference light is beamed in one of these two optical paths (reference optical path) The reflected
light is reflected by the splitter and the other light path (reflected light path) so that the reflected
light is reflected by the vibrating body and the beam splitter so that the sum of the incident angle
and the reflected angle becomes an acute angle when they are reflected. It is possible to increase
the optical path difference between the light source and the reflected light, and amplify and
detect the displacement of the vibrating body. Further, since the vibration of the vibrating body is
quantized and detected based on the interference fringes formed by the reference light and the
reflected light interfering with each other, the vibration of the vibrating body can be optically
digitally detected. . Therefore, it is possible to improve detection sensitivity when performing
digital vibration detection optically.
[0022]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings.
[0023]
First Embodiment FIG. 1 shows a cross-sectional configuration of a vibration detection apparatus
(optical microphone apparatus 1) according to a first embodiment of the present invention.
The microphone device 1 outputs a binarized audio signal Sout using a vibrating film (a vibrating
film 11 described later) that vibrates according to the sound wave Sw, and the laser light source
10, the vibrating film 11, and , A beam splitter 12, a reflection mirror 13, a pair of photoelectric
conversion elements 141 and 142, and a digital count unit 15.
[0024]
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The laser light source 10 irradiates the vibrating film 11 with the laser light Lout, and for
example, a multi-mode (Fabry-Perot type) laser light source (for example, an edge emitting type
semiconductor laser light source) or a single mode laser light source (For example, a surfaceemitting semiconductor laser light source, a DFB (Distributed FeedBack) laser, etc.) or the like.
[0025]
The vibrating film 11 is displaced according to the sound wave Sw, and is formed of a vibrating
film or the like on the surface of which gold is vapor-deposited, as in, for example, those used for
a condenser microphone.
The vibrating film 11 can reflect the laser beam Lout with a reflectance of approximately 100%.
[0026]
The beam splitter 12 is disposed between the vibrating film 11 and the reflecting mirror 13, and
total reflection on the central portions of the upper and lower surfaces of the beam splitter 12 is
capable of reflecting the laser light Lout with a reflectance of approximately 100%. Films 12A
and 12B are formed. On the other hand, on both ends of the upper surface and the lower surface
of the beam splitter 12, a semi-transmissive film (not shown) capable of reflecting the laser light
Lout with a reflectance of about 50% and transmitting the remaining light is formed. There is.
With such a configuration, the beam splitter 12 emits the laser beam Lout emitted from the laser
light source 10 and reflected by the vibrating film 11, for example, an optical path OP1
(reflection on the vibrating film 11 side (reflected light side) The light path is separated into the
light path OP2 (transmission light path) on the reflection mirror 13 side (reference light side),
and the light (reflection light) from the reflection light path OP1 and the transmission light path
OP2 at the point P22 in the figure, for example. Light (reference light) is superimposed again and
functions as an optical element for causing interference with each other, and is made of, for
example, quartz glass or the like. Although details will be described later, such interference in the
beam splitter 12 causes interference fringes to be formed at the point P22 in accordance with
the phase difference between the reference light and the reflected light.
[0027]
The reflection mirror 13 is a mirror configured to be able to reflect the laser light Lout with a
reflectance of approximately 100%.
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[0028]
Although the details will be described later, an interferometer based on a so-called Mach-Zehnder
interferometer is configured by the reflection mirror 13, the beam splitter 12, and the vibrating
film 11.
[0029]
The photoelectric conversion elements 141 and 142 detect interference fringes formed on the
beam splitter 12 (specifically, point P22), perform photoelectric conversion, and output output
signals Sx and Sy, respectively.
The photoelectric conversion elements 141 and 142 are configured by, for example, PD (Photo
Diode).
[0030]
The digital counting unit 15 quantizes the output signals Sx and Sy output from the photoelectric
conversion elements 141 and 142, for example, by counting at a predetermined count timing
described later using a Lissajous figure as shown in FIG. And an output signal (audio signal Sout)
which is a digital signal.
A digital counting method using such a Lissajous figure will be described in detail later.
[0031]
Next, with reference to FIGS. 3 to 6, an exemplary configuration in the case where the
microphone device 1 of the present embodiment is integrated on a semiconductor substrate will
be described. Here, FIG. 3 shows a cross-sectional configuration when the microphone device 1
shown in FIG. 1 is integrated on a semiconductor substrate, and FIG. 4 shows the microphone
device 1 shown in FIG. FIG. 5 schematically shows the form of the interference fringes formed on
the beam splitter 12, and FIG. 6 shows a plan configuration (corresponding to the plan
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configuration shown in FIG. 4) in the case where the microphone device 1 shown in FIG. 4 is
housed in a package section (package 18 described below).
[0032]
In the microphone device 1 shown in FIGS. 3 and 4, the surface emitting laser light source 10A as
a laser light source and the pinhole portion 140 are formed on a silicon (Si) substrate 16, and
photoelectric conversion is performed in the Si substrate 16. A conversion IC (Integrated Circuit)
150 functioning as the conversion elements 141 and 142 and the digital count unit 15 is formed.
The surface of the Si substrate 16 is mirror-finished to function as a reflection mirror 13. The
beam splitter 12 is supported at its both ends by a pair of beam splitter supporting posts 121
and 122.
[0033]
The surface-emitting laser light source 10A is a so-called vertical cavity surface (VCSEL; Vertical
Cavity Surface Emitting Laser) laser light source, and has a single mode. A collimator lens 10B for
condensing the laser light Lout is disposed above the surface-emitting laser light source 10A, and
the periphery of the collimator lens 10B is supported by the lens support 10C. There is.
[0034]
The pinhole portion 140 is formed above the photoelectric conversion elements 141 and 142,
and for example, the interference fringes formed on the beam splitter 12 are configured as
shown in FIG. 5 (the bright line Fw and the dark line Fb alternate) If the photoelectric conversion
elements 141 and 142 detect the phases of the interference fringes different from each other by
90 °, as indicated by points P140A and 140B in FIG. Note that, instead of such a pinhole
portion, a slit portion extending in the direction along the interference fringes may be provided.
[0035]
The calculation IC 150 is an IC that functions as the digital count unit 15 as described above, and
specifically an area (area other than the area where the optical path is formed) deviated from the
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area where the optical path of the laser light Lout is formed. For example, as shown in FIG. 4, it is
formed in the region between the electrode pad 17A described later and the beam splitter
support column 121 (or the region between the electrode pad 17B described later and the beam
splitter support column 122). preferable. This is because when the laser light Lout is reflected by
the surface of the Si substrate 16, the possibility of disturbance of reflection due to the presence
of the computing IC 150 is avoided.
[0036]
The microphone device 1 is also housed in a predetermined package 18 as shown in FIG. 6, for
example. Specifically, the plurality of electrode pads 17A and 17B formed at both ends on the Si
substrate 16 are electrically connected to the lead frames 18A and 18B of the package 18
through the metal interconnections 19, respectively. A membrane 11 is provided on top of the
package 18.
[0037]
When configured in this manner, the distance (for example, FIG. 1) between the vibrating film 11
provided in the package 18 and the Si substrate 16 (specifically, for example, the beam splitter
12) accommodated in the package 18. The distance d1) between the vibrating film 11 and the
beam splitter 12 shown is preferably configured to allow fine adjustment. As a specific
configuration in that case, for example, the package 18 is formed in a cylindrical shape, and the
height is finely adjusted by the rotation of the package 18 like a threaded ring for focusing
adjustment in the case of a camera lens. There are some that can be When configured in this
manner, it is possible to finely adjust the distance between the vibrating film 11 and the Si
substrate 16 by rotation of the ring while detecting interference fringes.
[0038]
Here, the vibrating film 11 corresponds to one specific example of the vibrator in the
present invention, the reflection mirror 13 corresponds to one specific example of the
reflector in the present invention, and the photoelectric conversion elements 141 and 142
and the digital count The part 15 corresponds to one specific example of the "detection means"
in the present invention. Also, the digital counting unit 15 corresponds to one specific example of
the "graphic generation means" and the "counter" in the present invention. The optical path OP2
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corresponds to a specific example of "one of two optical paths" in the present invention, and the
laser light Lout traveling on the optical path OP2 side is a specific example of "reference light" in
the present invention It corresponds. The optical path OP1 corresponds to a specific example of
"the other optical path of the two optical paths" in the present invention, and the laser light Lout
traveling on the optical path OP1 side is a specific example of "reflected light" in the present
invention It corresponds.
[0039]
Next, the operation of the microphone device 1 according to the present embodiment will be
described in detail with reference to FIGS. Here, FIG. 7 schematically shows the cross-sectional
configuration of a conventional general Mach-Zehnder interferometer, and FIGS. 8A to 8C show
the Mach-Zehnder interference shown in FIG. The cross-sectional structure of the interferometer
(interferometer of the structure according to a Mach-Zehnder interferometer) in the microphone
apparatus which concerns on this Embodiment which deform ¦ transformed based on the meter
is represented typically.
[0040]
First, the overall operation of the microphone device 1 of the present embodiment will be
described with reference to FIGS.
[0041]
In the microphone device 1, as shown in FIGS. 1 and 3, when the laser light Lout is emitted from
the laser light source 10 and is incident on the vibrating film 11 at an incident angle θ, it is
reflected by the vibrating film 11 and the beam splitter 12 To reach.
Then, the laser light Lout is split into reflected light and transmitted light at a point P11 on the
beam splitter 12 by the action of a semi-transmissive film (not shown), and as a result, the laser
light Lout passes through the optical path OP1 on the vibrating film 11 side (reflection Optical
path: divided into an optical path of points P11 to P12 to P22) and an optical path on the side of
the reflection mirror 13 (transmitted optical path: optical path of points P11 to P21 to P22). The
laser beam Lout on the reflected light path OP1 side is multi-reflected by the vibrating film 11
and the total reflection film 12A on the beam splitter 12, and reaches the point P22 on the beam
splitter 12 as reflected light. On the other hand, the laser light Lout (reference light) on the
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transmission light path OP2 side is multi-reflected by the total reflection film 12B on the
reflection mirror 13 and the beam splitter 12, and reaches the point P22 on the beam splitter 12.
Therefore, at this point P22, the reference light from the transmitted light path OP2 and the
reflected light from the reflected light path OP1 interfere with each other, and as shown in FIG. 5,
for example, interference fringes in which bright lines Fw and dark lines Fb are alternately
arranged. Is formed.
[0042]
Here, at the point P22 which is the terminal end of the beam splitter 12, the conditional
expression for overlapping the reference light and the reflected light is, for example, the distance
between the points P11 and P12 on the beam splitter 12 as shown in FIG. (L length on the
optical path OP1 side) L1, the distance between the points P21 and P22 on the beam splitter 12
(L length on the optical path OP2 side) L2, L1 ¦ OP1 ¦ optical path length of the optical path OP1,
optical path length of the optical path OP2 ¦ OP2 ¦, the number of times the reflected light on the
optical path OP1 is reflected by the vibrating membrane 11 is m1, the number of times the
reference light on the optical path OP2 is reflected by the reflecting mirror 13 is m2, and the
distance between the vibrating membrane 11 and the beam splitter 12 D1, the distance between
the reflecting mirror 13 and the beam splitter 12 d2, and the incident angle when the reference
light and the interference light enter the vibrating film 11 or the reflecting mirror 13 When,
based on the following (11) to (14), it is determined by the following equation (15).
[0043]
That is, the L length L1 on the optical path OP1 side, the optical path length of the optical path
OP1 ¦ OP1 ¦, the L length L2 on the optical path OP2 side, and the optical path length ¦ OP2 ¦ of
the optical path OP2 are respectively as in equations (11) to (14) Since the condition for
overlapping the reference light and the reflected light at point P22 is L1 = L2, the conditional
expression is as shown in equation (15).
[0044]
[0045]
Therefore, since this conditional expression does not depend on the incident angle θ, optical
adjustment can be easily performed.
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In addition, if the size of L length and the size of incident angle θ are predetermined, conditional
expression (15) can be obtained by appropriately selecting and setting the combination of (m1,
d1) and (m2, d2). Can meet.
For example, in the case of L1 = L2 ≒ 10 mm and θ ≒ 60 °, the combination of (m1, d1) and
(m2, d2) may be selected from Table 1 below.
[0046]
[0047]
Next, the interference fringes formed at the point P22 on the beam splitter 12 are detected by
the photoelectric conversion elements 141 and 142.
At this time, the phases of the interference fringes detected by the photoelectric conversion
elements 141 and 142 are adjusted by the pinhole section 140 as shown in FIGS. 3 and 4, and,
for example, two detection points P140A, As in 140 B, the signals are detected 90 degrees out of
phase with each other.
Then, the interference fringes detected by the photoelectric conversion element 141 are
converted into an electrical signal and output as an output signal Sx, while the interference
fringes detected by the photoelectric conversion element 142 are also converted into an
electrical signal, and are output as an output signal Sy Ru.
[0048]
Next, in the digital counting unit 15, the output signals Sx and Sy from the photoelectric
conversion elements 141 and 142 are regarded as an X signal and a Y signal, respectively. For
example, a circular or circular Lissajous figure as shown in FIG. It is generated. Specifically, first,
the central value of the intensity of the interference fringe due to the (X, Y) signal is taken as the
central point C (CX, CY), and the following equations (16) and (17) are calculated to Convert the
X, Y) signals into (x, y) signals. x=X−CX …(16) y=Y−CY …(17)
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[0049]
Then, from the movement of the signal point (x, y), a Lissajous figure moving on the
circumference centered on the central point C is obtained from the movement of the signal point
(x, y) by the calculation of the equations (16) and (17). Be At this time, the detection point (for
example, signal point P0 in the figure) detected by the photoelectric conversion elements 141
and 142 is one point on this circumference, and is displaced on the circumference according to
the displacement of the vibrating film 11. Become. Therefore, if the number of times such signal
point P0 passes through a predetermined reference point (for example, four reference points Pa
to Pd on the x-axis and y-axis) is counted, the intensity of the interference fringes is uniquely
determined. The displacement of the diaphragm 11 is detected digitally, and the counted number
of times is output as an audio signal Sout of a digital signal which is information of the angle α.
In addition, when four reference points Pa to Pd are counted as the reference points in this way,
it means that the interference fringes are counted every 90 degrees (1⁄4 wavelength) fluctuation.
[0050]
Next, with reference to FIGS. 8A to 8C, the conventional general interferometer (Mach) shown in
FIG. 7 has the function of enlarging the optical path difference in the interferometer of the
microphone device of the present embodiment.・ We explain while comparing with Zenda
interferometer).
[0051]
First, in the conventional general Mach-Zehnder interferometer shown in FIG. 7, the laser light
emitted from the laser light source 110 vibrates with the reference light on the reflection mirror
M101 side (optical path OP102 side) in the beam splitter BS101. The light is separated into the
reflection light on the reflection mirror M102 side (the optical path OP101 side) which also
serves as a film, and after the reference light and reflection light are reflected on these reflection
mirrors M101 and M102, the reference light and reflection light are overlapped again on the
beam splitter BS102. In the beam splitter BS102, for example, interference fringes are formed as
indicated by reference numerals F101 and F102.
At this time, in the reflection mirrors M101 and M102, the reference light and the reflection light
are reflected at right angles (so that the sum of the incident angle and the reflection angle is 90
°).
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[0052]
On the other hand, in the interferometer of the microphone device of the present embodiment
shown in FIGS. 8A to 8C (interferometer having a configuration conforming to the Mach-Zehnder
interferometer), the laser light emitted from the laser light source 11 The laser beam is split by
the beam splitter BS into the reference beam on the reflecting mirror M1 side (optical path OP12
side) and the reflected beam on the reflecting mirror M2 side (optical path OP11 side) which also
serves as a vibrating film, and these reflecting mirrors M1 and M2 After the reference light and
the reflected light are reflected in the beam splitter BS, the reference light and the reflected beam
are superimposed again in the beam splitter BS, and in the beam splitter BS, interference fringes
as shown by, for example, the symbols F1 and F2 are formed. Further, in the reflection mirrors
M1 and M2, the reference light and the reflection light are reflected at acute angles (so that the
sum of the incident angle and the reflection angle becomes an acute angle). That is, in this
interferometer, since the reference light and the reflected light are reflected at acute angles by
the reflection mirrors M1 and M2, respectively, it can be configured by a single beam splitter BS.
[0053]
Specifically, the interferometer shown in FIG. 8A is the Mach-Zehnder interferometer shown in
FIG. The sum of reflection angle and reflection angle β1, B2 is reflected so that each has an
acute angle (0 <β1 <90 °, 0 <β2 <90 °), and this makes up a single beam splitter BS It is
intended to Here, the amount of change in the optical path difference between the optical paths
OP11 and OP12 (specifically, the amount of change in the optical path length of the optical path
OP11) when the reflection mirror M2 also serving as the diaphragm is displaced by Δd is It is
expressed as Therefore, the amount of change in the optical path difference between the optical
paths OP101 and OP102 (specifically, the amount of change in the optical path length of the
optical path OP101) in the Mach-Zehnder interferometer of FIG. As a result, the displacement Δd
of the reflection mirror M2 is amplified and detected.
[0054]
[0055]
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Further, in the interferometer shown in FIG. 8 (A), the interferometer shown in FIG. 8 (B) brings
the position of the reflection mirror M2 closer to the beam splitter BS side, and reflects the
reflection mirror M2 (the optical path OP21). The light is made to be multi-reflected by the
reflecting mirror M2 and the beam splitter BS.
Here, considering the configuration shown in FIG. 1, the change amount ΔL of the L length
difference of the optical paths OP11 and OP12 and the change amount ΔOP of the optical path
difference between the optical paths OP11 and OP12 (optical path OP21 in FIG. 8B) 22
corresponding to the amount of change in the optical path difference between 22) are expressed
as the following equations (20) and (21), respectively, so that the reflection that doubles as the
vibrating film in vibrating film 11 (FIG. The amount of change in ΔL and ΔOP when the mirror
M2 is displaced by Δd (when the distance d1 between the diaphragm 11 and the beam splitter
12 slightly changes) is given by the following equations (22) and (23) It is expressed as
Therefore, according to equation (23), the amount of change in the optical path difference
between the reference light and the reflected light when the vibrating film 11 or the reflecting
mirror M2 is slightly displaced is the reflected light reflected by the vibrating film 11 or the
reflecting mirror M2. As a result, it can be understood that the displacement Δd of the vibrating
film 11 and the reflection mirror M2 is further amplified and detected. Further, in the
interferometer of FIG. 8B, since the position of the reflection mirror M2 is closer to the beam
splitter BS as compared with the interferometer of FIG. 8A, the size of the interferometer
becomes smaller, The overall size of the microphone device is also reduced.
[0056]
[0057]
For example, assuming that the maximum sound pressure of the sound wave Sw is 120 dB, the
displacement Δd of the diaphragm 11 at that time is 1 μm, the incident angle θ = 60 °, and
the number of times the reflected light is reflected by the diaphragm 11 m1 = 10 From equations
(22) and (23), ¦ d (ΔL) ¦ = 11.5 μm, ¦ d (ΔOP) ¦ = 23.1 μm, and the values of these variations
have no effect on the formation of interference fringes. It turns out that there is no such thing.
[0058]
Further, in the interferometer shown in FIG. 8C, the reflection mirror M2 is disposed closer to the
beam splitter BS as compared with the interferometer shown in FIG. 8B, and the displacement
Δd of the reflection mirror M2 is further increased. In addition to amplification and detection,
05-05-2019
17
the reflection mirror M1 on the reference light side is disposed close to the beam splitter BS side.
Here, according to the equations (22) and (23), the amount of change in ΔL and ΔOP when the
vibrating film 11 and the reflection mirror M2 are minutely displaced (when d1 is minutely
changed) is equal to that of the reflection mirror 13 or Because it does not depend on the
number m2 of reflections of the reference light by the reflection mirror M1, when the reflection
mirror M1 on the reference light side is also disposed close to the beam splitter BS side, the
amount of change in the optical path difference is not affected. It can be seen that the
interferometer, and thus the entire microphone device, is more compact.
[0059]
Thus, in the interferometer (interferometer conforming to the Mach-Zehnder interferometer) in
the microphone device of the present invention shown in FIGS. 8A to 8C, the reflection mirror
M2 (the vibration in FIG. 1) which functions as a vibrating film Since the reflected light on the
side corresponding to the film 11 is reflected at an acute angle by the beam splitter BS, the
amount of change in the optical path difference between the optical paths OP11 and OP12 when
the reflection mirror M2 is displaced by .DELTA. The value is larger than the amount of change in
the optical path difference between the optical paths OP101 and OP102 in the interferometer,
and as a result, the displacement Δd of the reflection mirror M2 is amplified and detected.
[0060]
In particular, in the interferometers shown in FIGS. 8B and 8C, since the reflected light on the
reflection mirror M2 side is multiply reflected by the beam splitter BS and the reflection mirror
M2, the reflection mirror M2 is displaced by Δd. The amount of change of the optical path
difference between the optical paths OP11 and OP12 at this time is larger than that of the
interferometer shown in FIG. 8A. As a result, the displacement Δd of the reflection mirror M2 is
also amplified and detected.
[0061]
As shown in FIG. 1, FIG. 3, FIG. 8 (B) and FIG. 8 (C), when the reflected light on the vibrating film
11 side or the reflection mirror M2 side is multiply reflected, the change amount of the optical
path difference by itself It does not necessarily have to be reflected at an acute angle, such as
being reflected at a right angle, for example.
[0062]
05-05-2019
18
As described above, in the present embodiment, the laser light Lout from the laser light source
10 is split into two optical paths OP1 and OP2 in an interferometer configured according to the
Mach-Zehnder interferometer, and the two optical paths OP1 and OP2 The reference beam is
reflected by the beam splitter 12 and the reflecting mirror 13 in one of the optical paths OP2
(reference optical path), and the reflected light is multiply reflected by the vibrating film 11 and
the beam splitter 12 in the other optical path OP1 (reflected optical path) Since the optical path
difference between the reference light and the reflected light is increased, the displacement of
the vibrating film 11 can be amplified and detected.
In addition, since the vibration of the vibrating film 11 is quantized and detected based on the
interference fringes formed on the beam splitter 12 because the reference light and the reflected
light interfere with each other, the vibration of the vibrating film 11 is optically detected. Can be
detected digitally.
Therefore, when performing digital vibration detection optically, it becomes possible to improve
detection sensitivity.
[0063]
In addition, since detection sensitivity at the time of performing digital vibration detection can be
improved, it is possible to widen a sound range that can be digitally detected by the microphone
device.
[0064]
In addition, since the reflection mirror (reflection mirror 13 or reflection mirror M2) on the
reflected light side is disposed close to the beam splitter (beam splitter 12 or beam splitter BS)
side, the size of the interferometer becomes smaller, and the microphone It is possible to
miniaturize the entire apparatus.
[0065]
Further, since the reference light on the reflection mirror 13 side is multi-reflected by the beam
splitter 12 and the reflection mirror 13, the optical path difference between the reference light
and the reflected light is further increased, and the displacement of the diaphragm 11 is further
05-05-2019
19
amplified. Can be detected.
Therefore, it is possible to further improve the detection sensitivity when performing digital
vibration detection optically.
In addition, since the vibrating film 11 on the reference light side is disposed close to the beam
splitter 12 side, the interferometer, and hence the entire microphone device can be further
miniaturized without affecting the change amount of the optical path difference. Is possible.
[0066]
When the reflected light on the vibrating film 11 side is reflected at an acute angle by the beam
splitter 12, the optical path difference between the reference light and the reflected light is
further increased, and the displacement of the vibrating film 11 is further amplified and detected.
be able to.
Therefore, in such a configuration, it is possible to further improve the detection sensitivity when
performing digital vibration detection optically.
[0067]
In addition, when configured so as to satisfy a predetermined conditional expression (Expression
(15)), it is possible to set in advance the optical path difference between the two optical paths
OP1 and OP2 to be zero when the diaphragm 11 is in a stationary state.
Therefore, the clarity (visibility) of the interference fringes can be easily improved.
[0068]
In addition, since the interferometer having the configuration according to the Mach-Zehnder is
used as the interferometer, as in the case of the Mach-Zehnder interferometer, the return light of
the laser light Lout to the laser light source 10 is not generated. It is possible to avoid noise
generation in the laser light source 10.
05-05-2019
20
[0069]
In addition, since non-contact sensing can be performed by light, the size and lightness of the
vibrating film 11 can be freely selected, and the dynamic range and frequency characteristics can
be changed to conventional analog methods such as the dynamic method and capacitor method.
In contrast, it can be expanded almost infinitely.
[0070]
Further, since the digital signal can be directly taken out by counting the interference fringes, the
S / N ratio can be reduced, and noise reduction of the audio signal Sout to be output can be
realized.
Therefore, since minute vibrations can be taken out, even in the case of drawing a long line from
the microphone device 1, the influence of noise or the like can be eliminated.
[0071]
In addition, the interference fringes are detected using the two photoelectric conversion elements
141 and 142, and the phase difference between the interference fringes detected by these two
photoelectric conversion elements is set to be approximately 90 degrees to each other. The
Lissajous figure can be formed as follows, and detection can be easily performed.
[0072]
Furthermore, since the output signals Sx and Sy from the two photoelectric conversion elements
141 and 142 are X and Y signals, respectively, and a circular or arc-shaped Lissajous figure is
generated based on these X and Y signals, interference occurs. The detection point of the stripes
is displaced on the circumference according to the displacement of the vibrating membrane 11,
and it is possible to detect the displacement of the vibrating membrane 11 in digital by counting
the number of times of passing through the predetermined reference point .
[0073]
In the present embodiment, the case where the vibrating film 11 is provided in the package
05-05-2019
21
portion 18 as illustrated in FIG. 6 has been described, but, for example, as in the microphone
device 1A illustrated in FIG. A vibrating membrane support column 110 for supporting the
vibrating membrane 11 may be provided, and the vibrating membrane 11 may be provided on
the vibrating membrane support column 110.
In such a configuration, for example, as shown in FIGS. 10A and 10B (corresponding to the crosssectional view along the line III-III in FIG. 9), the vibrating film 11 is against the surface of the Si
substrate Can be made slidable for each of the diaphragm supporting columns 110A and 110B,
in which case the distance between the Si substrate 16 and the diaphragm 11 (corresponding to
the distance d1 in FIG. 1) can be As shown in FIG. 10B, it is possible to change from D1 to D2,
and it becomes possible to easily adjust the height.
[0074]
Further, in the present embodiment, since the optical path difference between the optical path
OP1 and the optical path OP2 can be set to 0 beforehand, instead of the surface emitting laser
light source 10A as shown in FIG. 3, FIG. 4 and FIG. For example, as in the microphone device 1B
shown in FIG. 11, the end face is a multimode laser light source that emits a laser beam having a
short coherence length as compared with a single mode laser light source such as a surface
emitting laser light source or a DFB laser light source A light emitting laser light source 10D can
be used.
In the microphone device 1B, the edge-emitting laser light source 10D is formed on the mount
10G, and the laser light Lout emitted from the edge-emitting laser light source 10D is a
collimator lens 10E supported by the lens support 10H. , And is reflected by the reflection mirror
10F to reach the vibrating film 12 via the beam splitter 12.
With such a configuration, the configuration in the case of integration can be simplified as
compared with the case of using a surface emitting laser light source, and in particular, the
configuration can be made cheaper than the case of using a DFB laser light source. Can.
[0075]
Second Embodiment Next, a second embodiment of the present invention will be described. The
05-05-2019
22
same components as those in the first embodiment are denoted by the same reference numerals,
and the description thereof will be appropriately omitted.
[0076]
FIG. 12 shows a cross-sectional configuration of a vibration detection apparatus (microphone
apparatus 2) according to the present embodiment. In the microphone device 1 of the first
embodiment shown in FIG. 1, the microphone device 2 is configured not to provide the reflection
mirror 13 and to form an optical path on the reference light side inside the beam splitter 12. It is
[0077]
Specifically, the optical path OP3 of the reflected light is formed between the vibrating film 11
and the beam splitter 12, and the optical path OP4 of the reference light is formed inside the
beam splitter 12. The laser beam Lout on the side of the optical path OP3 is multi-reflected by
the vibrating film 11 and the total reflection film 12A on the beam splitter 12, and the laser
beam Lout on the side of the optical path OP4 is totally reflected by the total reflection films 12A
and 12B inside the beam splitter 12. It is designed to be multi-reflected.
[0078]
When the microphone device 2 of the present embodiment is integrated on a semiconductor
substrate, as in the first embodiment, for example, the edge-emitting laser 10D is used as in the
microphone device 2 shown in FIG. It can be configured like the one using the surface emitting
laser 10A as the microphone device 2A shown in FIG. In the microphone device 2A shown in FIG.
14, the surface emitting laser light source 10A is formed on the Si substrate 161, and the Si
substrate 162 for forming the photoelectric conversion elements 141 and 142 and the
calculation IC 150 is provided. It is supposed to be
[0079]
With such a configuration, in the microphone device of the present embodiment, when the laser
light Lout is emitted from the laser light source 10, the laser light Lout is refracted at the point
05-05-2019
23
P41 on the beam splitter 12 and is not shown at the point P31 on the beam splitter 12 as well.
As a result, the laser beam Lout is split into the optical path OP3 on the vibrating film 11 side
and the optical path OP4 inside the beam splitter 12, as described above. The laser beam Lout on
the optical path OP1 side is multi-reflected by the vibrating film 11 and the total reflection film
12A on the beam splitter 12, and reaches a point P32 on the beam splitter 12 as reflected light.
On the other hand, the laser beam Lout (reference beam) on the optical path OP4 side is multireflected by the total reflection films 12A and 12B inside the beam splitter 12 and reaches a
point P32 on the beam splitter 12. Therefore, at the point P32 and the subsequent point P42, the
reference light from the optical path OP4 and the reflected light from the optical path OP3
interfere with each other, and interference fringes are formed as in the first embodiment.
[0080]
In the same manner as in the first embodiment, the interference fringes formed at point P42 on
the beam splitter 12 are detected by the photoelectric conversion elements 141 and 142 with
their phases shifted by 90 degrees from each other. It is output as the output signals Sx and Sy.
Then, the digital count unit 15 generates a Lissajous figure based on the output signals Sx and
Sy. As a result, the displacement of the diaphragm 11 is detected digitally, and is output as an
audio signal Sout which is a digital signal.
[0081]
Here, as in the first embodiment, the conditional expression for overlapping the reference light
and the reflected light at the point P 32 on the beam splitter 12 is, for example, an optical path
between the points P 31 and P 32 on the beam splitter 12. The L length on the OP3 side is L3,
the L length on the optical path OP4 side between the points P31 and P32 on the beam splitter
12 is L4, the optical path length of the optical path OP3 is ¦ OP3 ¦, the optical path length of the
optical path OP4 is ¦ OP4 ¦, the optical path OP3 The number of times the reflected light on the
side is reflected by the vibrating film 11 is m3, the number of times the reference light on the
optical path OP4 is reflected by one end face (total reflection film 12B) inside the beam splitter
12 is m4, and the refractive index of the beam splitter 12 , The distance between the vibrating
film 11 and the beam splitter 12 is d3, the thickness of the beam splitter 12 is d4, and the laser
light Lout from the beam splitter 12 is Assuming that the angle obtained by subtracting the
incident angle at the time of emission as reflected light from 90 degrees is φ and the angle
obtained by subtracting the refraction angle at that time from 90 degrees is θ, the following
equations (24) to (27) Based on the equation (28) and (29),
[0082]
05-05-2019
24
That is, the L length L3 on the optical path OP3 side, the optical path length of the optical path
OP3 ¦ OP3 ¦, the L length L4 on the optical path OP4 side, and the optical path length ¦ OP4 ¦ of
the optical path OP4 are respectively as in Eqs. (24) to (27) Since the condition for overlapping
the reference light and the reflected light at point P42 is L3 = L4, the conditional expressions are
as shown in equations (28) and (29).
Equation (29) represents Snell's law.
[0083]
[0084]
In the interferometer of this embodiment, the reflected light propagates in the air, while the
reference light propagates in the beam splitter. Therefore, unlike the first embodiment, the
equations (28) and (29) Even if the equation (1) is satisfied, the optical path difference between
the reference light and the reflected light can not be made zero.
If the size of the angle θ and the refractive index n are determined in advance, the size of the
angle φ is determined by the equation (29). If the size of the L length is further set in advance,
(m3 The conditional expression (28) can be satisfied by appropriately selecting and setting the
combination of, d3) and (m4, d4). For example, in the case of θ ≒ 60 °, n = 1.5, φ ≒ 70.5 °,
L3 = L4 ≒ 10 mm, combinations of (m3, d3) and (m4, d4) are shown in Table 2 below. The
combination of (m3, d3) and (m4, d4) may be any combination other than the same row.
[0085]
[0086]
In the interferometer of the present embodiment, as described above, the optical path difference
between the reference light and the reflected light can not be set to 0 beforehand, so it is
preferable to use laser light with a long coherence length.
05-05-2019
25
Therefore, for example, a surface emitting laser light source 10A as shown in FIG. 14 or a DFB
laser light source as shown in FIG. 14 such as an edge emitting laser light source 10D shown in
FIG. Preferably, the laser light source is In this single-mode configuration, the coherence length
of the laser light is long, so even if the optical path difference between the reference light and the
reflected light is not 0 in advance, the phase difference of the interference fringes is increased to
improve the clarity. It can be easily enhanced.
[0087]
As described above, also in the present embodiment, the laser light Lout from the laser light
source 10 is split into two optical paths OP3 and OP4 in the interferometer configured according
to the Mach-Zehnder interferometer, and these two optical paths OP3 and OP4. The reference
light is reflected inside the beam splitter 12 in one of the optical paths OP4 (reference optical
path), and the reflected light is multiply reflected by the vibrating film 11 and the beam splitter
12 in the other optical path OP3 (reflected optical path). Therefore, the optical path difference
between the reference light and the reflected light can be increased, and the displacement of the
vibrating film 11 can be amplified and detected. Therefore, as in the first embodiment, it is
possible to improve the detection sensitivity when performing digital vibration detection
optically.
[0088]
Further, since the reflection mirror 13 need not be provided, the device configuration can be
simplified and the size can be further reduced as compared with the microphone device 1 of the
first embodiment shown in FIG.
[0089]
Further, since the reference light is multi-reflected inside the beam splitter 12, the optical path
difference between the reference light and the reflected light is further increased as in the first
embodiment, and the displacement of the vibrating film 11 is further amplified. Can be detected.
Therefore, it is possible to further improve the detection sensitivity when performing digital
vibration detection optically.
05-05-2019
26
[0090]
When the reflected light on the vibrating film 11 side is reflected at an acute angle by the beam
splitter 12, the optical path difference between the reference light and the reflected light is
further increased as in the first embodiment, and the vibrating film 11 is Displacement can be
further amplified and detected. Therefore, in such a configuration, it is possible to further
improve the detection sensitivity when performing digital vibration detection optically.
[0091]
Further, if it is configured so as to satisfy the predetermined conditional expressions (Equation
(28) and (29)), the optical paths of the two optical paths OP3 and OP4 in the stationary state of
the diaphragm 11, unlike the first embodiment. Although the difference can not be set to 0
beforehand, the light from the optical paths OP3 and OP4 can be superimposed on the points
P32 and P42 on the beam splitter 12. Therefore, if these conditional expressions are satisfied, it
is possible to actually form interference fringes.
[0092]
Third Embodiment Next, a third embodiment of the present invention will be described. The same
components as those in the first or second embodiment are denoted by the same reference
numerals, and the description will not be repeated.
[0093]
FIG. 15 shows a cross-sectional configuration of a vibration detection apparatus (microphone
apparatus 3) according to the present embodiment. In the microphone device 1 of the first
embodiment shown in FIG. 1, this microphone device 3 is provided with a vibrating film 11 as
well as a beam splitter-cum-diaphragm 112 which is so thin that its thickness can be almost
ignored instead of the beam splitter 12. In order not to do so, the beam splitter / vibration film
112 is configured to be sandwiched between a pair of reflection mirrors 131 and 132 capable of
reflecting the laser light Lout. The reflecting mirrors 131 and 132 correspond to one specific
05-05-2019
27
example of the pair of reflectors in the present invention, and the reflecting mirror 132
corresponds to one specific example of the one reflector in the present invention, The
reflecting mirror 131 corresponds to a specific example of the other reflector in the present
invention.
[0094]
To describe the configuration of the microphone device 3 more specifically, the optical path OP5
of the reflected light is formed between the reflection mirror 131 and the beam splitter /
vibration film 112, and between the reflection mirror 132 and the beam splitter / vibration film
112. The optical path OP6 of the reference light is formed. The laser beam Lout on the side of
the optical path OP5 is multi-reflected by the total reflection film 112A on the reflecting mirror
132 and the beam splitter combined vibrating film 112, and the laser beam Lout on the side of
the optical path OP6 is combined with the reflecting mirror 132 and the beam splitter combined
vibrating film It is designed to be multi-reflected by the total reflection film 112 B on 112.
[0095]
The microphone device 3 according to the present embodiment also uses the edge-emitting laser
10D as in the microphone device 3 shown in FIG. 16, for example, as in the first and second
embodiments, and FIG. Like the microphone device 3A shown in the above, it can be configured
as one using the surface emitting laser 10A. In the microphone device 3A shown in FIG. 17, the
prism 10I supported by the lens support 10C is provided on the collimator lens 10B, and the
laser beam Lout refracted by the prism 10I is reflected by the reflection mirror 131. (Incidence
angle: θ) is to reach a point P51 on the beam splitter / vibration film 112.
[0096]
When the microphone device is integrated on the semiconductor substrate as described above, it
is preferable that the area of at least one of the reflection mirrors 131 and 132 be smaller than
the area of the beam splitter / vibration film 112. In such a configuration, a part of the sound
wave Sw directed to the beam splitter / vibration membrane 112 can reach the beam splitter /
vibration membrane 112 without passing through, for example, the reflection mirror 131. Also,
in that case, the reflection mirror 131 is elongated in the direction along the projection
component on the surface of the Si substrate 16 in the traveling direction of the laser light Lout
05-05-2019
28
(the traveling direction of the optical paths OP5 and OP6) as shown in FIG. Is more preferable. In
such a configuration, the sound wave Sw directed to the beam splitter / vibration membrane 112
can more easily reach the beam splitter / vibration membrane 112 without passing through the
reflection mirror 131.
[0097]
With such a configuration, in the microphone device 3 of the present embodiment, when the
laser light Lout is emitted from the laser light source 10, the laser light Lout reaches a point P51
on the diaphragm for beam / splitter 112. Then, at this point P51, the light is separated into the
reflected light and the transmitted light by the action of the semi-transparent film (not shown),
and as a result, the laser light Lout is, as described above, It is divided into an optical path OP6.
The laser beam Lout on the optical path OP5 side is multi-reflected by the total reflection film
112A on the reflection mirror 131 and the beam splitter / vibration film 112, and reaches point
P52 on the beam splitter / vibration film 112 as reflected light. On the other hand, the laser light
Lout (reference light) on the optical path OP6 side is multi-reflected by the total reflection film
112B on the reflection mirror 132 and the beam splitter / vibration film 112, and reaches the
point P52 on the beam splitter / vibration film 112. Therefore, at this point P52, the reference
light from the optical path OP6 and the reflected light from the optical path OP5 interfere with
each other, and interference fringes are formed as in the first and second embodiments.
[0098]
Here, in the present embodiment, as described above, the beam splitter / vibrator diaphragm 112
functioning as a diaphragm is provided between the reflection mirrors 131 and 132 and is
sandwiched between the two optical paths OP5 and OP6. Therefore, for example, when the
diaphragm for beam splitter 112 is displaced upward, the optical path length of the optical path
OP5 becomes short and the optical path length of the optical path OP6 becomes long, and
thereby the optical path difference between them becomes larger. There is. Therefore, the optical
path difference between the reference light and the reflected light becomes larger compared to
the first and second embodiments, and the displacement of the diaphragm is amplified and
detected.
[0099]
05-05-2019
29
After that, as in the first and second embodiments, the interference fringes formed at the point
P52 on the beam splitter combined vibrating film 112 are 90 degrees out of phase with each
other in the photoelectric conversion elements 141 and 142. It is detected in the state and is
output as the output signals Sx and Sy, respectively. Then, the digital count unit 15 generates a
Lissajous figure based on the output signals Sx and Sy. As a result, the displacement of the
diaphragm 11 is detected digitally, and is output as an audio signal Sout which is a digital signal.
[0100]
The conditional expression for overlapping the reference light and the reflected light at a point
P52 which is the terminal end of the beam splitter / vibration film 112 is, for example, the
number of times the reflected light on the optical path OP5 is reflected by the reflection mirror
131 The number of times the reference light on the side of the optical path OP6 is reflected by
the reflection mirror 132 is m6, the distance between the reflection mirror 131 and the vibrating
membrane 112 for beam splitter is d5, and the distance between the reflecting mirror 132 and
the vibrating membrane 112 for beam splitter Assuming that d6, as in the first embodiment, it is
obtained as in the following equation (30). (m5)×(d5)=(m6)×(d6)
……(30)
[0101]
Therefore, since this conditional expression does not depend on the incident angle θ, optical
adjustment can be easily performed as in the first embodiment. Further, if the size of the L length
(the distance between the points P51 and P52 on the beam splitter / cumbing diaphragm 112)
and the size of the incident angle θ are predetermined, (m5, as in the first embodiment)
Conditional expression (30) can be satisfied by appropriately selecting and setting the
combination of d5) and (m6, d6). Strictly speaking, although the optical path length of the optical
path OP6 is larger than the optical path length of the optical path OP5 by the thickness of the
beam splitter / oscillator 112, the thickness of the beam splitter / oscillator 112 is almost as
described above. Because it is negligibly thin (for example, about several μm), the difference in
optical path has almost no effect on the clarity of the interference fringes.
[0102]
As described above, also in the present embodiment, the laser light Lout from the laser light
05-05-2019
30
source 10 is split into two optical paths OP5 and OP6 in the interferometer configured according
to the Mach-Zehnder interferometer, and these two optical paths OP5 and OP6 The reference
light is reflected by the reflecting mirror 132 and the total reflection film 112B on the beam
splitter combined vibrating film 112 in one of the optical paths OP6 (reference optical path), and
the reflected light is reflected in the other optical path OP5 (reflected optical path) Since the
multiple reflection is performed on the total reflection film 112A on the beam splitter / vibration
membrane 112, the optical path difference between the reference light and the reflected light is
increased, and the displacement of the beam splitter / vibration membrane 112 is amplified and
detected. be able to. Therefore, as in the first and second embodiments, it is possible to improve
the detection sensitivity when performing digital vibration detection optically.
[0103]
In addition, since the beam splitter / vibration film 112 is sandwiched between the two optical
paths OP5 and OP6, the optical path difference between the optical paths OP5 and OP6 can be
further increased. Therefore, as compared with the first and second embodiments, the optical
path difference between the reference light and the reflected light can be made larger, and the
displacement of the beam splitter / vibration film 112 can be further amplified and detected. It is
possible to further improve the detection sensitivity when performing digital vibration detection.
[0104]
In addition, since the reference light on the side of the optical path OP6 is multiply reflected by
the reflection mirror 132 and the beam splitter / vibration film 112, the optical path difference
between the reference light and the reflected light is the same as in the first and second
embodiments. The displacement of the beam splitter / vibration membrane 112 can be amplified
and detected. Therefore, it is possible to further improve the detection sensitivity when
performing digital vibration detection optically.
[0105]
When the reflected light on the side of the optical path OP5 is reflected at an acute angle by the
beam splitter / vibration film 112, the optical path difference between the reference light and the
reflected light is further increased as in the first and second embodiments. The displacement of
the beam splitter / vibration membrane 112 can be further amplified and detected. Therefore, in
05-05-2019
31
such a configuration, it is possible to further improve the detection sensitivity when performing
digital vibration detection optically.
[0106]
Further, as in the first embodiment, the optical path difference between the optical path OP5 and
the optical path OP6 can be set to approximately 0 in advance, so only with a single mode laser
light source such as a surface emitting laser light source or a DFB laser light source. Instead, a
multi-mode laser light source (for example, an edge-emitting laser light source) that emits a laser
beam having a shorter coherence length than these can be used. When the multimode laser light
source is used as described above, the structure when integrated on a semiconductor substrate
can be simplified as compared with the case where a surface emitting laser light source is used.
In particular, a DFB laser light source can be used. Compared with the case where it uses, it can
be set as a cheap structure.
[0107]
Furthermore, when the area of at least one of the reflection mirrors 131 and 132 is made smaller
than the area of the beam splitter / vibration film 112 in the case of integration on a
semiconductor substrate, part of the acoustic wave Sw is, for example, the reflection mirror 131.
The beam splitter / vibration membrane 112 can be made to reach without passing through.
Therefore, it is possible to prevent the sound pressure Sw from being completely blocked by the
reflection mirror and reducing the sound pressure, and to further improve the detection
sensitivity. Further, as shown in FIG. 18, for example, the reflecting mirror 131 is elongated in
the direction along the projection component on the surface of the Si substrate 16 in the
traveling direction of the laser light Lout (the traveling direction of the optical paths OP5 and
OP6). In this case, the sound wave Sw can more easily reach the beam splitter / vibration
membrane 112 without passing through the reflecting mirror 131. Therefore, in that case, the
portion where the sound wave Sw is blocked by the reflection mirror can be made smaller, and
the detection sensitivity can be further improved.
[0108]
The present invention has been described above by the first to third embodiments. However, the
present invention is not limited to these embodiments, and various modifications can be made.
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[0109]
For example, although the above embodiment has described the case where digital reference is
performed by providing four reference points Pa to Pd on the Lissajous figure, the number of
reference points is not limited to this and, for example, as shown in FIG. For example, using the
reference lines E to H in addition to the four reference points Pa to Pd, the reference points may
be set finely and increased.
With such a configuration, the count number can be increased, so that the value of the output
signal Sout can be increased to further improve the detection sensitivity.
[0110]
Moreover, although the semiconductor laser was mentioned as a light source which emits the
laser beam Lout in the said embodiment and demonstrated, you may make it use a gas laser,
fixed laser, etc. besides this.
[0111]
Further, in the above embodiment, as an example of the vibration detection device of the present
invention, the vibration body is the vibration film (the vibration film 11) that vibrates according
to the sound wave, and the vibration of the vibration film 11 is detected as the audio signal Sout.
Although the optical microphone device has been described, the vibration detection device of the
present invention is not limited thereto, and may be configured to detect another vibration.
[0112]
Furthermore, the vibration detection device (microphone device) of the present invention is, for
example, as shown in FIG. 20, the microphone device 1 shown in FIG. 1 (or the microphone
device 1A shown in FIG. 1B, the microphone device 2 shown in FIG. 12, the microphone device
2A shown in FIG. 14, the microphone device 3 shown in FIG. 15, etc.), and a transmission format
for encoding the audio signal Sout output from the microphone device 1 An encoder 4, an editing
device 5 connected to the transmission format encoder 4 via a digital transmission path (for
example, an optical fiber), a 1 bit stream recorder 6, a PCM (Pulse Code Modulation) recorder 8,
1 bit recording Media 71, PCM recording media 91, playback equipment It can be applied to the
audio signal recording and reproducing system composed of a speaker 72 and 92 Metropolitan.
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In the audio signal recording and reproducing system having such a configuration, since the
binarized audio signal Sout can be transmitted, it is possible to easily perform long distance
transmission as compared with the case of transmitting an analog audio signal. Become.
[0113]
FIG. 1 is a cross-sectional view illustrating an entire configuration of a vibration detection device
according to a first embodiment of the present invention.
It is a figure showing an example of the Lissajous figure created in the digital count part shown
in FIG. FIG. 6 is a cross-sectional view illustrating an example of the case where the vibration
detection device according to the first embodiment is integrated on a semiconductor substrate. It
is a top view showing the principal part structure of the vibration detection apparatus shown in
FIG. It is a schematic diagram for demonstrating the detection point by two photoelectric
conversion elements in an interference fringe. It is a top view showing the principal part
structure at the time of packaging the vibration detection apparatus shown in FIG. It is sectional
drawing showing the structure of the conventional common Mach Zehnder interferometer. It is
sectional drawing showing the principal part structure of the interferometer of the structure
which followed the Mach-Zehnder interferometer which concerns on 1st Embodiment. FIG. 16 is
a top view illustrating a configuration of a vibrator detection device integrated on a
semiconductor substrate according to a modification of the first embodiment. FIG. 10 is a crosssectional view for explaining a sliding operation of a vibrating membrane in the vibrating body
detection device shown in FIG. FIG. 7 is a cross-sectional view illustrating a configuration of a
vibrator detection device integrated on a semiconductor substrate according to a modification of
the first embodiment. It is sectional drawing showing the whole structure of the vibration
detection apparatus which concerns on the 2nd Embodiment of this invention. It is sectional
drawing showing an example at the time of integrating the vibration detection apparatus which
concerns on 2nd Embodiment on a semiconductor substrate. FIG. 16 is a cross-sectional view
illustrating a configuration of a vibration detection device integrated on a semiconductor
substrate according to a modification of the second embodiment. It is sectional drawing showing
the whole structure of the vibration detection apparatus which concerns on the 3rd Embodiment
of this invention. It is sectional drawing showing an example at the time of integrating the
vibration detection apparatus which concerns on 3rd Embodiment on a semiconductor substrate.
FIG. 18 is a cross-sectional view showing a configuration of a vibration detection device
integrated on a semiconductor substrate according to a modification of the third embodiment.
FIG. 16 is a schematic top view showing an example of the arrangement of the reflection mirror
and the beam splitter / vibration membrane in the vibrator detection device shown in FIG. 15; It
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is a figure showing an example of the Lissajous figure concerning the modification of the present
invention. It is a block diagram showing the example of composition of the sound recording and
reproducing system provided with the vibration detecting device shown in FIG.
Explanation of sign
[0114]
1, 1A, 1B, 2, 2A, 3, 3A: microphone device, 10: laser light source, 10A: surface emitting laser light
source, 10B, 10E: collimator lens, 10C, 10H: lens supporting portion, 10D: end surface light
emitting type Laser light source, 10F: reflection mirror, 10G: Si submount, 10I: prism, 11:
diaphragm, 110: diaphragm support column, 112: beam splitter and diaphragm, 12: beam
splitter, 12A, 12B, 112A, 112B ... total reflection film, 121, 122 ... beam splitter support column,
13, 131, 132 ... reflection mirror, 140 ... pinhole section, 141, 142 ... photoelectric conversion
element, 15 ... digital count section, 150 ... IC for operation, 16, 161, 162 ... Si substrate, 17A,
17B ... electrode pad, 18 ... package, 18A, 18 ... lead frame, 19 ... metal wiring, 4 ... transmission
format encoder, 5 ... editing device, 6 ... 1 bit stream recorder, 71 ... 1 bit recording media, 72, 92
... playback device amplifier speaker, 8 ... PCM method recorder 91: PCM recording medium, Sw:
sound wave, Sx, Sy: output signal from photoelectric conversion element, Sout: audio signal, Lout:
laser light, OP1, OP2, OP11, OP11, OP12, OP21, OP22, OP22, OP31, OP32,. Optical path, C:
central point, P0: signal point, Pa to Pd: reference point, E to H: reference line, Fb: dark line, Fw:
bright line, F2, F2: interference fringe, M1, M2: reflective mirror, BS ... beam splitter.
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