Patent Translate Powered by EPO and Google 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 JP2008275515 An object of the present invention is to provide a vibration detection device capable of improving detection sensitivity when vibration detection is optically performed. A laser beam Lout from a light source 10 is separated into two light paths (a reference light path and a reflected light path) in an interferometer. In addition, interference fringes are formed by causing the reference light reflected by the reflection plate 141 in the reference light path and the reflection light reflected by the diaphragm 131 and the half mirror 142 in the reflected light path to interfere with each other. Then, the vibration of the vibrating film 131 is detected based on the interference pattern. Thereby, the vibration of the vibrating film 131 is optically detected. In addition, the reflected light is made to be multi-reflected between the vibrating film 131 and the half mirror 142 in the reflected light path. The optical path difference between the reference light and the reflected light becomes large, and the displacement of the vibrating film 131 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 sampling have been used, and high sound quality has become mainstream. 05-05-2019 1 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, in Patent Document 1, a digital audio signal is obtained by performing signal conversion and digital signal processing of interference fringes caused by displacement of a microphone diaphragm in an interferometer such as the Mach-Zehnder method. It has been proposed to obtain an output. Further, for example, in Patent Document 2, in the Michelson-type interferometer, a change in interference fringes caused by displacement of the microphone diaphragm is converted by a photoelectric conversion element and a bit stream signal is binarized by this value. It has been proposed to have a diaphragm driving means for moving the microphone diaphragm as a feedback path for constructing a so-called delta sigma (delta sigma) modulator. [0006] 05-05-2019 2 JP-A-10-308998 JP-A-11-178099 [0007] In Patent Document 1 described above, a digital audio signal is output by detecting the vibration of the diaphragm using a Mach-Zehnder interferometer or a Michelson interferometer. [0008] On the other hand, in Patent Document 2 described above, a ΔΣ (delta sigma) modulator including 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 effective to detect the vibration of the diaphragm when it is applied to a high sensitivity microphone for which detection of vibration of several pm to several tens of pm is required. It was difficult and 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 optically detecting vibration. [0011] 05-05-2019 3 The vibration detection device of the present invention comprises a light source for emitting a laser beam, an interferometer, and a detection means. Here, the interferometer includes a vibrator and a first reflector capable of reflecting laser light, and a second reflector capable of at least partially reflecting laser light, and is emitted from a light source. Separates the laser beam into the first and second optical paths and advances the reference light reflected by the first reflector in the first optical path, and the vibrator and the second reflector in the second optical path And the reflected light that has been multi-reflected between them to interfere with each other to form an interference pattern. Further, the detection means detects the vibration of the vibrator based on the formed interference fringes. [0012] In the vibration detection device of the present invention, laser light emitted from the light source travels while being separated into two optical paths (first and second optical paths) in the interferometer. At this time, the reference light reflected by the first reflector in the first light path and the reflected light reflected by the vibrator and the second reflector in the second light path interfere with each other to form interference fringes. Be done. Then, the vibration of the vibrator is detected based on the interference fringes. Here, since the reflected light is multiply reflected between the vibrating body and the second reflector in the second light path, the displacement of the vibrating body is added for the number of reflections, and the reference light and the reflected light are added. Thus, the displacement of the vibrating body is amplified and detected. [0013] In the vibration detection device of the present invention, the second reflector may be configured by a half mirror that partially reflects and partially transmits the laser light. [0014] In this case, when the reflected light is constituted by a plurality of types of reflection components having different numbers of reflections due to multiple reflections between the oscillator and the second reflector, among the plurality of types of reflection components having different numbers of reflections It is preferable to set the optical path length in the second 05-05-2019 4 optical path by the reflection component of the desired number of reflections to be equal to the optical path length of the first optical path. In this configuration, the visibility (intelligibility) of the interference fringes formed due to interference is maximized, and thus selective interference between the reflection component of the desired number of reflections and the reference light becomes possible. . Note that "equal" is not limited to the case of being literally equal, but also means the case of being substantially equal due to manufacturing variations and the like. [0015] Further, when the reflected light is constituted by a plurality of types of reflection components having different numbers of reflections due to multiple reflections between the vibrator and the second reflector, interference fringes due to the plurality of types of reflection components having different numbers of reflections It is preferable to set the optical path length of the first optical path so that the intelligibility peaks do not interfere with each other. In such a configuration, it is easy to independently detect the intelligibility peak of each interference fringe. [0016] According to the vibration detection device of the present invention, the laser light from the light source is split into two light paths (first and second light paths) in the interferometer, and the light is reflected by the first reflector in the first light path. The interference light is formed by causing the reference light and the reflected light reflected by the vibrator and the second reflector to interfere with each other in the second optical path, and the vibration of the vibrator is detected based on the interference fringes. Therefore, the vibration of the vibrating body can be detected optically. Further, since the reflected light is multiply reflected between the vibrating body and the second reflector in the second optical path, the optical path difference between the reference light and the reflected light is increased, and the vibration is caused. Body displacement can be amplified and detected. Therefore, it is possible to improve the detection sensitivity when performing vibration detection optically. [0017] Hereinafter, embodiments of the present invention will be described in detail with reference to 05-05-2019 5 the drawings. [0018] First Embodiment FIG. 1 shows a configuration of a vibration detection apparatus (optical microphone apparatus 1) according to a first embodiment of the present invention. The microphone device 1 outputs an audio signal Sout using a diaphragm (a diaphragm 131 described later) that vibrates according to the sound wave Sw, and the laser light source 10, the diaphragm 131, the reflection plate 141, and the half A Michelson interferometer including a mirror 142 and a detection unit for outputting an output signal (audio signal Sout) which is a digital signal are provided. [0019] The laser light source 10 emits a laser light Lout, and for example, a self-pulsation type semiconductor laser with low coherence is used. In order to reduce the coherence, a semiconductor laser modulated at a high frequency may be used. [0020] The lens 11 is a lens (collimator lens) for collimating the laser beam Lout from the laser light source 10. [0021] <Interferometer Configuration> The interferometer includes a polarization beam splitter 12, a vibrating film 131, a reflector 141, a half mirror 142, three λ / 4 plates 151 to 153, a beam splitter 16, and two polarizations. It is comprised from board 171,172. [0022] The polarization beam splitter 12 transmits two light paths, that is, a reflected light path (first light path) on the vibrating film 131 side and a reference light path on the reflecting plate 141 05-05-2019 6 side (laser light Lout emitted from the laser light source 10 and passing through the lens 11). And the second optical path). Specifically, although the details will be described later, in this polarization beam splitter 12, the P-polarization component p0 of the laser light Lout travels to the reflected light path side, and the S-polarization component s0 of the laser light Lout travels to the reference light path side. It is set. The laser beam Lout is separated into approximately 50% each by the P-polarization component p0 and the S-polarization component s0. [0023] The vibrating film 131 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 the case of, for example, a capacitor microphone. The vibrating film 131 is configured to be able to reflect the laser beam Lout (specifically, the S polarization component s0) with a high reflectance, and is accommodated in the microphone capsule 13 as shown in FIG. It is supposed to be Further, as shown in FIG. 1, the distance between the vibrating film 131 and the polarization beam splitter 12 is previously set to L1. A detailed configuration example of the microphone capsule 13 will be described later. [0024] The reflection plate 141 is configured to be able to reflect the laser light Lout (specifically, the Ppolarization component p0), which is the reference light, with a high reflectance. The distance between the reflection plate 141 and the polarization beam splitter 12 is set to L0 as shown in FIG. 1, and the distance L0 can be adjusted as described later. [0025] The half mirror 142 is disposed on the reflection light path, specifically, between the polarization beam splitter 12 and the vibrating film 13. The distance between the half mirror 142 and the vibrating film 131 is set to be L2 in advance as shown in FIG. The half mirror 142 partially 05-05-2019 7 reflects and partially transmits the laser light Lout (specifically, the S-polarization component s0) (for example, 50% and 50% of the laser light Lout) Thus, as shown in FIG. 1, multiple reflection of the laser beam Lout is possible between the vibrating film 131 and the half mirror 142 (multiple reflected light Lr is generated). . [0026] The λ / 4 plate 151 is disposed on the reflected light path, specifically, between the polarization beam splitter 12 and the half mirror 142. The λ / 4 plate 152 is disposed on the reference light path, specifically, between the polarization beam splitter 12 and the reflector 141. [0027] As described later, the beam splitter 16 divides the S-polarization component s1 (reflected light) and the P-polarization component p1 (reference light) of the laser light Lout incident through the polarization beam splitter 12 into an optical path and polarization of the polarizing plate 171 side. The light path on the side of the plate 172 is separated by about 50% and advanced. [0028] The polarizing plates 171 and 172 are polarizing plates having polarization axes in directions respectively inclined 45 degrees from the polarization direction of the incident S-polarization component s1 (reflected light) and the polarization direction of the P-polarization component p1 (reference light). Although the details will be described later according to such a configuration, in these polarizing plates 171 and 172, the S polarization component s1 and the P polarization component p1 interfere with each other to form interference fringes. The λ / 4 plate 153 is disposed on the optical path between the beam splitter 16 and the polarizing plate 171. [0029] With such an arrangement, in the interferometer of the present embodiment, the laser light Lout emitted from the laser light source 10 is split into two light paths (first and second light paths) 05-05-2019 8 and travels. Specifically, the polarization beam splitter 12, the λ / 4 plate 151, the half mirror 142, the vibrating film 131, the half mirror 142, the λ / 4 plate 151, the polarization beam splitter 12, the beam splitter 16, the polarization plates 171 and 172, and λ Second light path (reflected light path) passing through the 1⁄4 plate 153, the polarization beam splitter 12, the λ / 4 plate 152, the reflection plate 141, the λ / 4 plate 152, the polarization beam splitter 12, the beam splitter 16, the polarization plate 171, It travels separately to a first optical path (reference optical path) passing through 172 and λ / 4 plate 153. At this time, light reflected by the vibrating film 131 through the λ / 4 plate 151 in the reflection light path (S-polarized component s1, reflected light) and reflected by the reflection plate 141 through the λ / 4 plate 152 in the reference light path Interference light (P-polarized light component p1, reference light) interferes with each other in the polarizing plates 171 and 172 to form interference fringes. [0030] <Structure of Detection Unit> The detection unit includes two photoelectric conversion elements 181 and 182 and a digital signal processing unit 19. [0031] The photoelectric conversion elements 181 and 182 detect interference fringes formed on the polarizing plates 171 and 172, perform photoelectric conversion, and output output signals Sx and Sy, respectively. The photoelectric conversion elements 181 and 182 are configured by, for example, PD (Photo Diode). [0032] The digital signal processing unit 19 AD (analog / digital) converts the output signals Sx and Sy output from the photoelectric conversion elements 181 and 182, and outputs an output signal (audio signal Sout) that is a digital signal. . Such digital counting method will be described in detail later. [0033] 05-05-2019 9 Next, with reference to FIG. 2 and FIG. 3, a detailed configuration example of the microphone capsule 13 shown in FIG. 1 will be described. FIGS. 2 and 3 show cross-sectional configurations of the microphone capsules 13A and 13B, which are detailed configuration examples of the microphone capsule 13. FIG. [0034] The microphone capsule 13A shown in FIG. 2 includes a housing 130, a diaphragm 131, a back electrode 132, a back plate 133, and a transparent member 134, and functions as an omnidirectional microphone capsule. The vibrating film 131 is disposed on the side (front side) on which the sound wave Sw is incident, and the back electrode 132 is disposed on the back side. The back plate 133 is not provided with an opening or the like for sealing the microphone capsule, but a part of the back plate 133 is a transparent member 134 made of glass, transparent resin or the like on which an anti-reflection (AR) film is formed. It has become. With such a configuration, in the microphone capsule 13A, the laser light Lout is transmitted through the transparent member 134 on the back side without interfering with the incidence of the sound wave Sw while maintaining the sealed structure for forming the omnidirectional microphone capsule. Thus, it is possible to make the light enter the vibrating membrane 131. [0035] On the other hand, the microphone capsule 13B shown in FIG. 3 includes the housing 130, the diaphragm 131, the back electrode 132, the back plate 133, and the opening 135, and functions as a unidirectional microphone capsule. ing. In this microphone capsule 13B, an opening for obtaining appropriate directivity by displacing the diaphragm 131 in a part of the back plate 133 by the difference between the sound pressure applied to the front of the diaphragm 131 and the sound pressure on the back side. The portion 135 is provided, and the laser beam Lout can be incident on the vibrating film 131 through the opening 135. With such a configuration, in the microphone capsule 13B, the laser light Lout is made to enter the diaphragm 131 without blocking the incidence of the sound wave Sw by using the opening portion 135 for forming a single directional microphone capsule. Is possible. [0036] 05-05-2019 10 Here, the vibrating film 131 corresponds to one specific example of the vibrator in the present invention, the reflecting plate 141 corresponds to one specific example of the first reflector in the present invention, and the half mirror 142 is the present invention. Corresponds to one specific example of the second reflector in the above. The photoelectric conversion elements 181 and 182 correspond to one specific example of the two photoelectric conversion elements in the present invention, and the photoelectric conversion elements 181 and 182 and the digital signal processing unit 19 are one of the detection means in the present invention. The digital signal processing unit 19 corresponds to a specific example of the "graphic generation means" and the "counter" in the present invention, corresponding to the specific example. [0037] Next, the operation of the microphone device 1 of the present embodiment will be described in detail. [0038] First, the basic operation of the microphone device 1 will be described with reference to FIGS. 1 to 4. [0039] In the microphone device 1, as shown in FIG. 1, the laser light Lout is emitted from the laser light source 10, and the laser light Lout is collimated by the lens 11 and then enters the polarization beam splitter 12. Then, the incident laser beam Lout is separated and travels by about 50% each to the reflected light path (second light path) on the vibrating film 131 side and the reference light path (first light path) on the reflective plate 141 side. Thereby, the laser beam Lout is separated into the P-polarization component p0 traveling in the reflection light path and the S-polarization component s0 (reference light) traveling in the reference light path. That is, the polarization beam splitter 12 reflects the light of the S polarization component and transmits the light of the P polarization component. 05-05-2019 11 [0040] Here, when passing through the λ / 4 plate 151, the P polarization component p0 changes from linear polarization to circular polarization, and after being reflected by the vibrating film 131, it becomes circular polarization in the opposite direction, and passes through the λ / 4 plate 151 again. Is converted to the S-polarization component s1 (reflected light). Since the S-polarized component s1 is reflected by the polarization beam splitter 12 as described above, it travels in the direction of the beam splitter 16 along the reflected light path. On the other hand, the Spolarization component s0, which is the reference light, changes from linear polarization to circular polarization when passing through the λ / 4 plate 152, and then becomes circular polarization in the opposite direction when reflected by the reflection plate 141. By passing through, it is converted into a P-polarization component p1. Then, the P-polarization component p1 travels in the direction of the beam splitter 16 along the reference optical path because it passes through the polarization beam splitter 12 as described above. At this time, the Spolarization component s1 and the P-polarization component p1 traveling on the same optical path (the reflection optical path and the reference optical path) do not interfere with each other because the polarization directions thereof are different by 90 degrees. [0041] Next, the S polarized light component s1 and the P polarized light component p1 traveling in the reflected light path and the reference light path are separated by the beam splitter 16 into about 50% each in the light path on the polarizing plate 171 side and the light path on the polarizing plate 172 side. To reach the polarizing plates 171 and 172, respectively. At that time, since the λ / 4 plate 153 is inserted in the middle of the light path on the polarizing plate 171 side, the S polarized light component s1 and the P polarized light component p1 reaching the vibrating plate 171 and the S polarized light reaching the vibrating plate 172 The components of the component s1 and the P-polarized component p1 are 90 degrees out of phase with each other. The polarizing plates 171 and 172 respectively have polarization axes in directions inclined 45 degrees from the polarization direction of the S-polarization component s1 and the polarization direction of the P-polarization component p1, respectively, so the phases of the S-polarization component s1 and the P-polarization component p1 Even in the case of the present embodiment in which the S polarization components s1 and the P polarization component p1 of the reference light interfere with each other in the polarizing plates 171 and 172, interference fringes are formed. 05-05-2019 12 [0042] Next, the interference fringes formed on the polarizing plates 171 and 172 are detected by the photoelectric conversion elements 181 and 182, respectively. Here, since the phases of the Spolarization component s1 and P-polarization component p1 reaching the diaphragm 171 and the S-polarization component s1 and P-polarization component p1 reaching the diaphragm 172 differ from each other by 90 degrees, photoelectric conversion is performed. In the elements 181 and 182, the interference fringes are detected with the phases being shifted by 90 degrees. Then, the interference fringes detected by the photoelectric conversion element 181 are converted into an electrical signal and output as an output signal Sx, while the interference fringes detected by the photoelectric conversion element 182 are also converted into an electrical signal and output as an output signal Sy Ru. [0043] Next, in the digital count 19, assuming that the output signals Sx and Sy from the photoelectric conversion elements 181 and 182 are X and Y signals, for example, a circular or arc-shaped Lissajous figure as shown in FIG. It is supposed to generate. Specifically, assuming that the amplitudes of the interference light from the two optical paths are A and B, the optical path difference is ΔL, and the wavelength is λ, the intensities Ix and Iy of the interference light are respectively (1) to (3) below. It is expressed as a formula. The output signals Sx and Sy output signals X and Y corresponding to the intensities Ix and Iy of the interference light, respectively, and a DC component signal CX corresponding to A <2> + B <2> which is a DC term of the light intensity. The x and y signals are obtained by canceling CY and passing an amplifier (not shown) having a gain G ′ corresponding to the light intensity gain G represented by the following equation (4). Thus, the (x, y) signal is obtained from the (X, Y) signal by performing the following equations (5) and (6). Ix = A <2> + B <2> + 2AB cos θ (1) Iy = A <2> + B <2> +2 AB sin θ (2) θ = (2π × ΔL) / λ (3) G = 1 / (2 AB) ... (4) x = (X-CX) x G '= cos theta (5) y = (Y-CY) x G' = sin theta (6) [0044] 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 (5) Be At this time, the detection points (for example, signal point P0 in the figure) detected by the photoelectric conversion elements 181 and 182 are 05-05-2019 13 one point on this circumference, and are displaced on the circumference according to the displacement of the vibrating film 11 become. Therefore, the angle θ is uniquely determined by the values of x and y in the angular range (range of −π / 2 to + π / 2) by θ = arctan (y / x), and exceeds the upper limit of this range In the case, 1 is added to the accumulator value, and 1 is subtracted if the lower limit is exceeded. Then, the counted number is output as an audio signal Sout of a digital signal which is information of the angle θ. [0045] Next, with reference to FIG. 5 to FIG. 7 in addition to FIG. 1 to FIG. 4, the operation of the characteristic part of the present invention (multiple reflection between the diaphragm 131 and the half mirror 142) will be described in detail. . [0046] First, in FIG. 1, the intensity I of the interference fringes due to the interference between the reference light and the reflected light is expressed as the following equation (7) according to the equations (1) to (3) described above. Further, since ΔL in the equation (3) represents the displacement of the optical path difference between the reference light and the reflected light, the displacement ΔL of the optical path difference is δ, which is the displacement of the diaphragm 131 by the sound wave Sw. Assuming that the incident angle of the laser beam Lout with respect to the vibrating film 131 is θ, the following equation (8) is given. I = A <2> + B <2> +2 AB cos ((2π × ΔL) / λ) (7) ΔL = 2 × δ × cos θ (8) [0047] Here, in the interferometer of the present embodiment, a part of the reflected light reflected by the vibrating film 131 is reflected by the half mirror 142 and returned in the direction of the vibrating film 131, as shown in FIG. Multiple reflected light Lr is generated. Therefore, the incident angle to the diaphragm 131 due to such multiple reflected light Lr can be θ1 (incident angle at the first reflection), θ2 (incident angle at the second reflection),. The displacement ΔL of the optical path difference is expressed by the following equation (9). According to the equation (9), when the incident angle is around 0 ° (when the laser beam is incident almost perpendicularly to the vibrating film 131), cos θ 1 = cos θ 2 =. The displacement ΔL of the 05-05-2019 14 difference is expressed by the following equation (10), which is approximately equal to the product of the number of multiple reflections n between the vibrating film 131 of the laser light Lout and the half mirror 142 (the displacement ΔL of the optical path difference is Approximately n times the size). Accordingly, it can be seen that the optical path difference is increased due to the multiple reflection between the vibrating film 131 and the half mirror 142, and the displacement of the vibrating film 131 is also amplified and detected. Δ L = 2 × δ × (cos θ 1 + cos θ 2 + ... + cos θ n) (9) Δ L 2 2 × δ × n (10) [0048] Further, when using a laser light source 10 that emits low coherence light, such as a selfpulsation type semiconductor laser, in particular, the visibility (intelligibility) of the interference fringes can be referred to, for example, as shown in FIG. The optical path difference between the light and the reflected light is maximized when the optical path difference is zero and is rapidly reduced when the optical path difference occurs. The visibility (intelligibility) of the interference fringes is defined as the following equation (11), where Imax is the maximum value of the intensity I of the interference fringes and Imin is the minimum value of the intensity I of the interference fringes. Visibility (intelligibility) of interference fringes = (Imax-Imin) / (Imax + Imin) (11) [0049] Here, assuming that the number of multiple reflections between the oscillation film 131 of the laser light Lout and the half mirror 142 is n as described above, interference formed by the interference between the n-time reflection light reflected n times and the reference light The distance L0 between the beam splitter 12 and the reflection plate 141 when the visibility of the stripes is maximized is L1, the distance between the beam splitter 12 and the diaphragm 131 as described above, and the diaphragm 131 and the half mirror 142 And the distance between L and L is expressed by the following equation (12). Therefore, for example, when the interference light peak and the side peak of the interference light peak when the visibility of the interference fringe is maximum are expressed as the distance L0 between the beam splitter 12 and the reflector 141 on the horizontal axis, for example, It becomes like FIG. 6 (A) and (B). L0=L1+(n−1)×L2 …(12) [0050] That is, for reflected light in the reflected light path, a plurality of types of reflection components 05-05-2019 15 (for example, n = 1, n = 2, n = in FIG. 6) having different numbers of reflections due to multiple reflection between the diaphragm 131 and the half mirror 142 Since each reflection component (3),... Is included, if the distance L0 between the beam splitter 12 and the reflection plate 141 is set to L0 expressed by the above (12), In other words, if the distance L0 (and the distances L1 and L2) is set so that the optical path length in the reflected light path by the reflection component of the desired number of reflections and the optical path length of the reference optical path become substantially equal, While selective interference between the reflected component and the reference light is possible, the visibility of the interference fringes due to the interference is maximized. [0051] For example, as shown in FIG. 6A, when L2 >> d (d: the distance between the peaks of the intelligibility of the individual interference fringes), the interference fringes are clearly identified by a plurality of types of reflection components having different numbers of reflections. Since the power peaks appear at positions separated from each other with respect to the distance L0, they do not affect each other due to interference between the clearness peaks of the interference fringes. However, for example, as shown in FIG. 6B, when L2 ≒ d, the peaks of the intelligibility of interference fringes due to a plurality of types of reflection components having different numbers of reflections appear at positions close to each other with respect to the distance L0. As a result, it becomes difficult to detect selective interference between the reflection component of the desired number of reflections and the reference light, because the peaks of the intelligibility of interference fringes interfere with each other as it is. [0052] Therefore, in such a case, for example, as shown in FIG. 7, by setting the distance L2 such that L2 ≒ (d / n), interference fringes due to a plurality of types of reflection components having different numbers of reflections can be obtained. Interference effects between intelligibility peaks are minimized. As a result, it becomes easy to independently detect the peak of the intelligibility of each interference fringe, so that the detection accuracy of the displacement of the diaphragm 131 is improved. 05-05-2019 16 [0053] Thus, in the microphone device 1 of the present embodiment, the laser beam Lout emitted from the light source 10 is split into two light paths (reference light path and reflected light path) by the polarization beam splitter 12 in the interferometer, and S It travels as wave component s0 and P wave component p0. At this time, the reference light (P wave component p1) reflected by the reflecting plate 141 in the reference light path and the reflected light (S wave component s1) reflected by the diaphragm 131 and the half mirror 142 in the reflected light path interfere with each other. Interference fringes are formed on the polarizing plates 171 and 172. Then, based on the interference fringes, the light source conversion elements 181 and 182 and the digital signal processing unit 19 detect the vibration of the diaphragm 131 as the quantized audio signal Sout. Here, since the reflected light is multi-reflected between the vibrating film 131 and the half mirror 142 in the reflected light path, the optical path difference between the reference light and the reflected light becomes large. The displacement is amplified and detected. [0054] As described above, in the present embodiment, the laser light Lout from the light source 10 is separated into two optical paths (reference optical path and reflected optical path) in the interferometer, and the reference light and reflection reflected by the reflector 141 in the reference optical path In the optical path, the reflected light reflected by the vibrating film 131 and the half mirror 142 is made to interfere with each other to form an interference pattern, and the vibration of the vibrating film 131 is detected based on the interference pattern. Can be detected optically. Further, since the reflected light is multiply reflected between the vibrating film 131 and the half mirror 142 in the reflected light path, the optical path difference between the reference light and the reflected light is increased, and The displacement can be amplified and detected. Therefore, it is possible to improve the detection sensitivity when performing vibration detection optically. [0055] In addition, it can be realized with a small and simple configuration using a Michelson interferometer. Therefore, it is possible to miniaturize the vibration detecting device (microphone device) that optically detects digital vibration. 05-05-2019 17 [0056] In addition, since non-contact sensing can be performed by light, the size and lightness of the vibrating film 131 can be freely selected, and the dynamic range and frequency characteristics can be changed to conventional analog methods such as dynamic method and capacitor method. It can be scaled up. [0057] Furthermore, since the digital signal can be directly taken out by counting the interference fringes, the S / N ratio can be easily reduced and noise reduction of the audio signal Sout to be output can be realized by raising the angle detection accuracy. . In addition, since digital signals can be obtained directly from the microphone device 1, digital transmission can be easily realized, and even in the case of drawing long lines from the microphone device 1, the influence of noise or the like can be eliminated. [0058] In the present embodiment, as an example of the second reflector capable of at least partially reflecting the laser light Lout, a half mirror 142 capable of partially reflecting and partially transmitting the laser light Lout. For example, as shown in FIGS. 8A and 8B, a total reflection mirror for totally reflecting the laser light Lout (total reflection mirrors 143A and 143B shown in FIG. 8A). Alternatively, the interferometer may be configured using the total reflection mirrors 144A and 144B or the like shown in FIG. In such a configuration, the decrease in light intensity at the time of reflection is suppressed, so that the detection accuracy of the interference fringes can be improved and the detection accuracy of the diaphragm 131 can be improved in addition to the effects in the above embodiment. It becomes. [0059] Second Embodiment Next, a second embodiment of the present invention will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be appropriately omitted. 05-05-2019 18 [0060] FIG. 9 shows a configuration of a vibration detection apparatus (microphone apparatus 1A) according to the present embodiment. In this microphone device 1A, an interferometer is configured by a Mach-Zehnder interferometer. Specifically, the microphone device 1A includes a laser light source 10, a Mach-Zehnder interferometer, and a detection unit including two photoelectric conversion elements 181 and 182 and a digital signal processing unit 19. Further, this Mach-Zehnder interferometer is composed of a beam splitter 161, two reflecting mirrors 145 and 146, three prisms 111 to 113, a corner cube prism 114, and a beam splitter 162. [0061] The beam splitter 161 splits the laser light Lout emitted from the laser light source 10 into a first light path OP1 (reference light path) on the prism 111 side and a second light path OP2 (reflected light path) on the reflection mirror 145 side. It is for. [0062] The reflection mirror 145 is disposed on the optical path OP2, and reflects the laser light Lout traveling on the optical path OP2 to the side of the prism 112. [0063] The prism 111 is disposed on the optical path OP1, and reflects the laser beam Lout (reference light) traveling from the side of the beam splitter 161 on the optical path OP1 to the side of the corner cube prism 114, and a corner on the optical path OP1. The laser light Lout (reference light) traveling from the cube prism 114 side is reflected to the reflection mirror 146 side. [0064] The prism 112 reflects the laser beam Lout reflected by the reflection mirror 145 to the side of the prism 113 and the vibrating film 131, and the beam splitter 162 reflects the reflected light multiply reflected by the vibrating film 131 and the prism 113 as described below. It reflects on the side of the [0065] The prism 113 is a reflective surface by metal deposition or the like on the surface on the vibrating film 131 side, and is for multiple reflection of the laser beam Lout traveling through the 05-05-2019 19 optical path OP2 between the vibrating film 131 and the prism 113. It is. [0066] The corner cube prism 114 is disposed on the optical path OP1 and is for reflecting the laser light Lout (reference light) reflected by the prism 111 and for causing the laser light Lout (reference light) to travel to the side of the prism 111 again. The corner cube prism 114 is arbitrarily displaceable as indicated by the arrow in FIG. 9, whereby the optical path length of the reference optical path is arbitrarily adjusted as in the first embodiment. It can be done. [0067] The reflection mirror 146 is disposed on the optical path OP1 and reflects the laser light Lout (reference light) reflected by the prism 111 to the side of the beam splitter 162. [0068] The beam splitter 146 splits the reference light incident from the optical path OP1 and the reflected light (multiple reflected light) incident from the optical path OP2 into an optical path on the photoelectric conversion element 181 side and an optical path on the photoelectric conversion element 182 side to travel. belongs to. [0069] Here, the corner cube prism 114 corresponds to a specific example of the first reflector in the present invention, and the prism 113 corresponds to a specific example of the second reflector and the total reflection mirror in the present invention. It corresponds. [0070] With such an arrangement, in the interferometer of the present embodiment, the laser beam Lout emitted from the laser light source 10 is split into two optical paths OP1 and OP2 by the beam splitter 161 and travels. 05-05-2019 20 Specifically, the first light path (reference light path) passing through the beam splitter 161, the prism 111, the corner cube prism 114, the prism 111, the reflecting mirror 146 and the beam splitter 162, the beam splitter 161, the reflecting mirror 145, the prism 112, The light beam travels while being separated into a second optical path (reflected optical path) passing through the diaphragm 131, the prism 113, the prism 112, and the beam splitter 162. At this time, the reflected light reflected by the vibrating film 131 and the prism 113 in the reflected light path and the reference light reflected by the corner cube prism 114 in the reference light path interfere with each other in the beam splitter 162 to form interference fringes. Thus, based on the interference fringes, the photoelectric conversion elements 181 and 182 and the digital signal processing unit 19 detect the vibration of the diaphragm 131 as the quantized audio signal Sout as in the first embodiment. [0071] Further, since the reflected light is multi-reflected between the vibrating film 131 and the prism 113 in the reflected light path, the optical path difference between the reference light and the reflected light becomes large, whereby the displacement of the vibrating film 131 Amplified and detected [0072] Therefore, also in this embodiment, the same effect can be obtained by the same action as that of the first embodiment. That is, it is possible to improve the detection sensitivity when optically performing vibration detection. [0073] Further, since the Mach-Zehnder interferometer is used as the interferometer, return light of the laser light Lout is not generated with respect to the laser light source 10 without using expensive optical components such as a wavelength plate and a polarization beam splitter. It is possible to 05-05-2019 21 avoid the noise generation in the laser light source 10 at low cost. [0074] Although the present invention has been described above by the first and second embodiments, the present invention is not limited to these embodiments, and various modifications are possible. [0075] For example, even if the count number of angle division is increased with respect to an angle uniquely determined in the range of-(π / 2) <θ <+ (π / 2) of the Lissajous figure described in the above embodiment. Good. When configured in this manner, it is possible to improve the detection sensitivity by increasing the angular resolution. [0076] 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. [0077] Further, in the above embodiment, as an example of the vibration detection device of the present invention, the vibration body is the vibration film (vibration film 131) that vibrates according to the sound wave, and the vibration of the vibration film 131 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. [0078] Furthermore, in the above embodiment, the case where digital detection is performed using the digital count unit 19 as the signal Sout in which the vibration of the vibrating film 131 is quantized, but the vibration of the vibrating film is directly output as an analog signal You may 05-05-2019 22 Specifically, for example, by using the output signals Sx and Sy from the photoelectric conversion elements 181 and 182 in a region where the change in interference light intensity changes linearly, it is possible to obtain an electric signal substantially proportional to the diaphragm displacement. This signal may be output as an analog audio signal as it is. According to a well-known method, the optical path length on the reference light side can be moved by a piezo element or the like, and the DC component of the output signal can be controlled to the position of the linear region by applying negative feedback to the piezo element is there. [0079] BRIEF DESCRIPTION OF THE DRAWINGS It is a figure showing the whole structure of the vibration detection apparatus which concerns on the 1st Embodiment of this invention. It is sectional drawing showing an example of a detailed structure of the microphone capsule shown in FIG. It is sectional drawing showing the other example of a detailed structure of the microphone capsule shown in FIG. It is a figure showing an example of the Lissajous figure created in the digital signal processing part shown in FIG. It is a characteristic view which shows the general relationship of the optical path difference and visibility in an interferometer. It is a characteristic view showing the relation between the interference light peak and visibility by a plurality of kinds of reflection components in a 1st embodiment. It is a characteristic view for explaining interference of interference light peaks by a plurality of kinds of reflection components. It is sectional drawing showing the aspect of the multiple reflection which concerns 05-05-2019 23 on the modification of 1st Embodiment. It is a figure showing the whole structure of the oscillation detection instrument concerning a 2nd embodiment. Explanation of sign [0080] 1, 1A: microphone device, 10: laser light source, 11: lens, 111 to 113: prism, 114: corner cube prism, 12: polarization beam splitter, 13, 13A, 13B: microphone capsule, 130: housing, 131: Vibrating film, 132: back electrode, 133: back plate, 134: transparent member, 135: opening, 141: reflecting plate, 142: half mirror, 143A, 143B, 144A, 144B: total reflection mirror, 145, 146: reflection Mirror, 151, 152, 153 ... λ / 4 plate, 16, 161, 162 ... beam splitter, 171, 172 ... polarizing plate, 181, 182 ... photoelectric conversion element, 19 ... digital signal processing unit, Sw ... sound wave, s0, s0 s1 ... S polarization component, p0, p1 ... P polarization component, OP1, OP2 ... optical path, Sx, Sy ... from the photoelectric conversion element Output signal, Sout: voice signal, Lout: laser light, Lr: multiple reflection light, L0: distance between polarization beam splitter and reflector, L1: distance between polarization beam splitter and diaphragm, L2: half Distance between mirror and diaphragm, d distance between diffracted light peaks, C center point P0 signal point Pa to Pd reference point E to H reference line. 05-05-2019 24
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