JP2008261684A - Vibration detecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibration detecting apparatus capable of improving detection sensitivity when optical detection of digital vibrations is performed. <P>SOLUTION: A laser beam Lout from a laser light source 10 is made to separately travel through two optical paths OP1 and OP2 in a two-beam interferometer. A diffracted light Ld1 which has traveled through the optical path OP1 and been diffracted by a diffraction element 151 on a vibrating membrane 14 and a diffracted light Ld2 which has traveled through the optical path OP2 and been diffracted by the diffraction element 151 are made to interfere with each other to form interference fringes. On the basis of the interference fringes, vibrations of the vibrating membrane 14 are quantized and detected. Vibrations of the vibrating membrane 14 are thereby optically and digitally detected. The diffraction pitch of the diffraction element 151 is set in such a way as to have approximately the same length as that of the pitch of the interference fringes F1 when the vibrating membrane 14 is in a stationary state. Since the directions of diffraction of the diffracted lights Ld1 and Ld2 approximately match each other, displacements of the vibrating membrane 14 are amplified and detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vibration detection apparatus that optically detects displacement of a vibrating body.

  In recent years, a recording system using SACD (Super Audio Compact Disc), sampling of 24 bits-96 kHz, and the like have been used, and higher sound quality is becoming mainstream. Under such circumstances, the conventional analog microphone device has a limit in recording high-frequency audio particularly at 20 kHz or higher, so let's record content by taking advantage of the high-frequency reproduction characteristic of the above recording method. And if it was a bottleneck.

  Also, the dynamic range does not reach the 144 dB that is possible by the 24-bit recording that is the feature of the recording method, and the wide dynamic range cannot be fully utilized.

  Furthermore, at recording sites, with conventional analog microphone devices, noise increases due to long-distance routing with analog cables, or phantom power must be supplied from the mixing console to the condenser microphone. It was an obstacle to all-digitalization in the recording / production system.

  In recent years, several digital microphone devices have been proposed (for example, Patent Documents 1 and 2).

JP-A-10-308998 JP-A-11-178099

  In Patent Document 1, a digital sound signal is output by detecting vibration of a diaphragm using a laser light source and a Mach-Zehnder interferometer.

  On the other hand, in Patent Document 2, a ΔΣ (delta sigma) modulator including a laser light source and a diaphragm is configured. Therefore, it is considered that the 1-bit digital audio signal can be obtained with a simple configuration by the action of the ΔΣ modulator, and the noise of the audio signal in the audible band can be reduced by using the noise shaving effect. .

  However, these Patent Documents 1 and 2 have a problem that the detection sensitivity cannot be increased so much because the wavelength of the laser beam is about 0.6 μm. Therefore, it is effective when the vibration of the diaphragm is large, but it is difficult to detect the vibration of the diaphragm when applied to a high sensitivity microphone that requires vibration detection of about several pm, There was room for improvement.

  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 digital vibration.

  The vibration detection apparatus of the present invention includes a light source that emits laser light, an interferometer, and detection means. Here, the interferometer is configured to include a vibrating body having a diffraction element capable of diffracting the laser light, and the laser light emitted from the light source is separated into the first and second optical paths and travels. An interference fringe formed by causing the first diffracted light diffracted by the diffraction element to travel along the first optical path and the second diffracted light traveled along the second optical path and diffracted by the diffraction element to interfere with each other It is. The detecting means quantizes and detects the vibration of the vibrating body based on the formed interference fringes. The diffraction pitch of the diffraction element is set to be the same as or an integral multiple of the interference fringe pitch when the vibrating body is stationary. Note that “same” and “integer multiple” are not limited to literally the same or integer multiples, but also mean substantially identical or substantially integer multiples due to manufacturing variations.

  In the vibration detection apparatus of the present invention, the laser light emitted from the light source travels while being separated into two optical paths (first and second optical paths) within the interferometer. At this time, the first diffracted light that travels along the first optical path and is diffracted by the diffraction element of the vibrating body, and the second diffracted light that travels along the second optical path and is diffracted by the diffraction element are They interfere with each other and form interference fringes. Based on the interference fringes, the vibration of the vibrating body is quantized and detected. In addition, since the diffraction pitch of the diffraction element is set to be the same or an integral multiple of the pitch of the interference fringes when the vibrating body is stationary, the displacement of the vibrating body is amplified and detected. .

  In the vibration detection device of the present invention, the diffraction pitch of the diffraction element is the same length as the pitch of the interference fringes when the vibration body is stationary, and the extending direction of the interference fringes when the vibration body is stationary You may set so that it may become parallel. In this case, the first-order diffracted light of the first diffracted light and the first-order diffracted light of the second diffracted light travel to the second optical path side, respectively, and the first-order diffracted light of the first diffracted light and the second diffracted light The 0th-order diffracted light of the diffracted light travels toward the first optical path. In addition, since only the 0th-order diffracted light and the 1st-order diffracted light are generated in the first and second diffracted lights, the intensity of these diffracted lights is increased and the detection accuracy is improved. “Parallel” is not limited to literally parallel, but also means substantially parallel due to manufacturing variation or the like.

  In the vibration detection apparatus of the present invention, the diffraction pitch of the diffraction element is twice as long as the pitch of the interference fringes when the vibration body is stationary, and the interference fringes extend when the vibration body is stationary. You may set so that it may become parallel to a direction. When configured in this way, the first-order diffracted light of the first diffracted light and the first-order diffracted light of the second diffracted light travel in the normal direction of the vibrator. Accordingly, the first and second diffracted lights can be configured not to travel to the first or second optical path side, respectively, and generation of return light to the laser light source can be avoided, and the first and second optical paths can be prevented. There is no possibility that the light beam will be hindered by the detection means. Note that the term “double” is not limited to literally double, but also means a case of approximately double due to manufacturing variation or the like. The “perpendicular direction” is not limited to the literal normal direction, but also means a substantially normal direction.

  In the vibration detection apparatus of the present invention, the vibrating body may be arranged so that the incident angles of the light traveling in the first and second optical paths with respect to the diffraction element are different from each other. When configured in this manner, the traveling directions of the first and second diffracted lights can be adjusted according to the respective incident angles, so that it is possible to avoid the generation of return light to the laser light source and to detect it. The degree of freedom of arrangement of means is improved.

  According to the vibration detection apparatus of the present invention, the laser beam from the light source is separated into two optical paths (first and second optical paths) in the interferometer, and travels along the first optical path to have a diffraction element included in the vibrator. The first diffracted light diffracted by the light and the second diffracted light diffracted by the diffractive element through the second optical path are caused to interfere with each other to form interference fringes, and vibration is generated based on the interference fringes Since the vibration of the body is quantized and detected, the vibration of the vibrating body can be optically digitally detected. In addition, since the diffraction pitch of the diffraction element is set to be equal to or an integral multiple of the pitch of the interference fringes when the vibration body is stationary, the displacement of the vibration body can be amplified and detected. Therefore, it is possible to improve detection sensitivity when optically detecting digital vibration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 shows a configuration of a vibration detection device (optical microphone device 1) according to a first embodiment of the present invention. This microphone device 1 outputs a binarized audio signal Sout using a vibrating membrane (vibrating membrane 14 to be described later) that vibrates in response to a sound wave Sw, and includes a laser light source 10 and a diffraction grating on the surface. 151 includes a two-beam interferometer including the vibration film 14 formed with 151 and a detection unit that outputs an output signal (audio signal Sout) that is a digital signal.

  The laser light source 10 emits laser light Lout. For example, a multi-mode (Fabry-Perot type) laser light source (for example, an edge-emitting semiconductor laser light source) or a single-mode laser light source (for example, a surface-emitting type) A semiconductor laser light source, a DFB (Distributed FeedBack) laser, and the like).

<Configuration of interferometer>
The interferometer (two-beam interferometer) includes the beam splitter 11, two lenses 121 and 122, two reflection mirrors 131 and 132, and the vibrating film 14 having the diffraction grating 151 formed on the surface. ing.

  The beam splitter 11 converts the laser light Lout emitted from the laser light source 10 into two optical paths, that is, an optical path OP1 (first optical path) on the reflection mirror 131 side and an optical path OP2 (second optical path) on the reflection mirror 132 side. It is for separating and advancing.

  The lenses 121 and 122 are collimator lenses that collect light traveling on the optical paths OP1 and OP2. The focal points of these lenses 121 and 122 are set on the reflecting mirrors 131 and 132, respectively.

  The reflection mirror 131 is a mirror for reflecting the light traveling in the optical path OP1 and guiding it in the direction of the vibration film 14 (diffraction grating 151). Similarly, the reflection mirror 132 is a mirror for reflecting the light traveling in the optical path OP2 and guiding it in the direction of the vibration film 14 (diffraction grating 151). The light reflected by the reflecting mirrors 131 and 132 is directed toward the vibration film 14 (diffraction grating 151) while being diffused thereafter, as indicated by the dotted lines in FIG.

  The vibration film 14 is displaced according to the sound wave Sw, and is formed of a vibration film whose surface is gold-deposited, for example, similar to that used for a capacitor microphone. The vibration film 14 is disposed on a virtual plane including an intersection of central rays (shown by solid lines in FIG. 1) of light beams traveling in the optical paths OP1 and OP2 in a stationary state. A diffraction grating (grating) 151 having a predetermined diffraction pattern is formed on the surface of the vibration film 14 where light from the optical paths OP1 and OP2 is incident.

  The diffraction pitch of the diffraction grating 151 is substantially the same as the pitch of interference fringes described later when the vibrating membrane 14 is in a stationary state (when it is on the virtual plane) (first-order grating (GRT)). And is set to be substantially parallel to the extending direction of the interference fringes at that time. The vibrating membrane 14 is arranged so that the incident angles of light traveling on the optical paths OP1 and OP2 with respect to the diffraction grating 151 are substantially the same (incident angle θ) as shown in the figure. Further, even when the vibration film 14 is displaced as indicated by the arrows in the drawing, the light rays of the light beams from the optical paths OP1 and OP2 are always incident on the diffraction grating 151.

  With such an arrangement, in the interferometer of the present embodiment, the laser light Lout emitted from the laser light source 10 travels while being separated into two optical paths (first and second optical paths). Specifically, an optical path OP1 (first optical path) from the beam splitter 11 through the reflection mirror 131 to the diffraction grating 151, and an optical path OP2 (second optical path) from the beam splitter 11 to the diffraction grating 151 through the reflection mirror 132. And the light path). At this time, the light traveling on the optical paths OP1 and OP2 is diffracted by the diffraction grating 151, and diffracted lights Ld1 (first diffracted light) and Ld2 (second diffracted light) are generated on the optical path OP2 side. These diffracted beams Ld1 and Ld2 interfere with each other, and interference fringes are formed. Details of the diffracted lights Ld1 and Ld2 will be described later.

<Configuration of detection unit>
The detection unit includes two photoelectric conversion elements 161 and 162 and a digital count unit 17.

  The photoelectric conversion elements 161 and 162 detect interference fringes formed by the interference between the diffracted lights Ld1 and Ld2, perform photoelectric conversion, and output the output signals Sx and Sy, respectively. In this embodiment, the optical path OP2 is used. Arranged on the side. These photoelectric conversion elements 161 and 162 are configured by, for example, PD (Photo Diode).

  The digital count unit 18 quantizes the output signals Sx and Sy output from the photoelectric conversion elements 161 and 162, for example, by counting them at a predetermined count timing to be described later using a Lissajous figure as shown in FIG. An output signal (audio signal Sout) that is a digital signal is output. A digital counting method using such a Lissajous figure will be described in detail later.

  Here, the vibrating membrane 14 corresponds to a specific example of “a vibrating body” in the invention, and the diffraction grating 151 corresponds to a specific example of “a diffraction element” in the invention. The reflection mirror 131 corresponds to a specific example of “first reflector” in the present invention, and the reflection mirror 132 corresponds to a specific example of “second reflector” in the present invention. Further, the photoelectric conversion elements 161 and 162 correspond to a specific example of “two photoelectric conversion elements” in the present invention, and the photoelectric conversion elements 161 and 162 and the digital count unit 17 are specific examples of “detecting means” in the present invention. Corresponding to the example, the digital count unit 17 corresponds to a specific example of “graphic generation means” and “counter” in the present invention.

  Next, with reference to FIG. 3 and FIG. 4 in addition to FIG. 1 and FIG. 2, the operation of the microphone device 1 of the present embodiment will be described in detail.

  In the microphone device 1, the laser light Lout is emitted from the laser light source 10 and enters the beam splitter 11 as shown in FIG. Then, the incident laser beam Lout is separated by the beam splitter 11 into an optical path OP1 (first optical path) on the reflection mirror 131 side and an optical path OP2 (second optical path) on the reflection mirror 132 side by about 50%. proceed.

  Next, the light traveling in the optical paths OP1 and OP2 is collected by the lenses 121 and 122, focused on the reflection mirrors 131 and 132, reflected by the reflection mirrors 131 and 132, and diffused to the diffraction grating 151. Proceed toward.

Next, the light reflected by the reflection mirrors 131 and 132 in the optical paths OP1 and OP2 is incident on the diffraction grating 151 on the vibration film 14 at an incident angle θ. Then, since the diffraction grating 151 is a first-order grating as described above, for example, as shown in FIG. 3, the incident light beam L11 (incident angle θ) from the optical path OP1 is converted into a zero-order diffracted light as an incident angle. While the diffracted light beam L12 (corresponding to the diffracted light beam Ld1) is generated with the same diffraction angle φ, the incident light beam L21 (incident angle θ) from the optical path OP2 returns to the incident direction as it is as the first-order diffracted light beam (the diffraction angle is θ Diffracted light beam L22 (corresponding to diffracted light beam Ld2) is generated. Interference fringes are formed by the interference between the diffracted beams Ld1 and Ld2. At this time, since the traveling directions of the diffracted rays L12 and L22 are substantially the same, the interference fringes F1 having a coarse pitch (close to the null frenzy) are formed as shown in the figure. Note that the interference fringe pitch P in such a stationary state is given by the following (1), where λ is the wavelength of light from the optical paths OP1 and OP2, and θ is the incident angle of these lights in the stationary state to the diffraction grating 151. ) Expression.
P = λ / (2 × sin θ) (1)

  Further, when the vibration film 14 is displaced according to the sound wave Sw, and the diffraction grating 151 is displaced upward by Δx as shown in FIG. 4, for example, as shown in FIG. 4, the incident light beam from the optical path OP1 is changed. The incident angle changes to the incident angle θ ′ as in the incident light beam L13, and the diffraction angle of the 0th-order diffracted light beam also changes to the diffraction angle φ ′ as in the diffracted light beam L14. Further, the diffraction angle of the first-order diffracted light beam with respect to the incident light beam L23 from the optical path OP2 also changes like the diffracted light beam L24. That is, since an angle is generated between the diffracted rays L14 and L24, the pitch of the interference fringes also changes as shown in the figure, and the interference fringes F2 with a fine pitch are obtained.

  Next, the formed interference fringes (light and dark patterns) are detected by the photoelectric conversion elements 161 and 162 in a state where the phases are shifted from each other by 90 degrees through a pinhole or the like (not shown). The interference fringes detected by the photoelectric conversion element 161 are converted into electrical signals and output as an output signal Sx, while the interference fringes detected by the photoelectric conversion element 162 are also converted into electrical signals and output as an output signal Sy. The

Next, in the digital count unit 17, the output signals Sx and Sy from the photoelectric conversion elements 161 and 162 are regarded as an X signal and a Y signal, respectively. For example, a circular or arc-shaped Lissajous figure as shown in FIG. Is generated. Specifically, first, by calculating the following formulas (2) and (3) using the median value of the interference fringe intensity by the (X, Y) signal as the center point C (CX, CY), X, Y) signal is converted to an (x, y) signal.
x = X-CX (2)
y = Y-CY (3)

  Then, a Lissajous figure that moves on the circumference around the center point C as shown in FIG. 2 is obtained from the movement of the signal point (x, y) by the calculation of the above equations (2) and (3). It is done. At this time, the detection point (for example, signal point P0 in the figure) detected by the photoelectric conversion elements 161 and 162 is one point on the circumference, and the circumference is displaced according to the displacement of the vibration film 14. Become. Therefore, if the number of times such a signal point P0 passes a predetermined reference point (for example, four reference points Pa to Pd on the x axis and the y axis) is counted, the intensity of the interference fringes is uniquely determined. Thus, the displacement of the vibration film 14 is detected digitally, and the counted number is output as the audio signal Sout of a digital signal that is information of the angle α. In addition, when the four reference points Pa to Pd are counted as reference points in this way, it means that the count is performed every time the interference fringes fluctuate by 90 degrees (1/4 wavelength).

  In this manner, in the microphone device 1 of the present embodiment, the laser light Lout emitted from the laser light source 10 travels while being separated into the two optical paths OP1 and OP2 within the two-beam interferometer. At this time, the diffracted light Ld1 diffracted by the diffraction element 151 on the vibration film 14 traveling along the optical path OP1 and the diffracted light Ld2 traveling along the optical path OP2 and diffracted by the diffraction element 151 interfere with each other, thereby causing interference fringes. Is formed. Based on the interference fringes, the vibration of the vibration film 14 is quantized and detected. Further, since the diffraction pitch of the diffraction element 151 is set to be substantially the same as the pitch of the interference fringes F1 when the vibrating membrane 14 is in a stationary state (when on the virtual plane), the diffracted light Ld1 , Ld2 are substantially matched in diffraction direction, whereby the displacement of the vibrating membrane 14 is amplified and detected.

  Next, with reference to FIG. 5, the traveling direction of the diffracted light and the amplification effect of the displacement of the vibration film 14 will be described in more detail (quantitatively).

As shown in FIG. 5, the incident light beam Lb enters the diffraction grating 151 from the point S2 on the optical path OP2 at the incident angle θ, and is diffracted at the diffraction angle φ by the diffraction grating 151 having the pitch Pg. When Lc is satisfied, the diffraction condition represented by the following equation (4) is satisfied.
Pg × (sin θ + sin φ) = m × λ (m: diffraction order) (4)

In the present embodiment, since the diffraction pitch Pg of the diffraction grating 151 is set to be approximately the same length as the pitch P of the interference fringes, the following equation (5) is established from the equation (1). Therefore, when the diffraction pitch Pg according to the equation (5) is put into the equation (4), the following equation (6) is established. Therefore, when m = 1 (first order diffraction), the diffraction angle φ = incident angle as described above. It can be seen that a diffracted light beam having θ is generated.
Pg = P = λ / (2 × sin θ) (5)
sin φ = (2m−1) × sin θ (6)

  In FIG. 5, when the pitch of interference fringes formed by interference between diffracted rays Lc and Ld by incident rays La and Lb (incident angle θ) from points S1 and S2 on the optical paths OP1 and OP2 is represented by Λ. The interference fringe pitch Λ is expressed by the following equation (7). Further, in FIG. 5, the midpoint of points S1 and S2 is P1, the intersection of incident rays La and Lb at diffraction grating 151 is P2, the distance between points S1 and P2 is l, and the distance between points P1 and P2 is x. When the distance between the points P1 and S1 is y, the following equation (8) is geometrically satisfied.

  Here, how much the pitch Λ of the interference fringes changes with respect to the displacement of the position x of the vibration film 14 is expressed by the following equation (9).

  The following formulas (10) and (11) are derived from the above formula (7). Also, from the above equation (5), the following equation (12) is derived (note that the diffraction angle φ decreases when θ increases here, so that the decoding in equation (12) is considered only minus ( A plus occurs in the case of transmission diffraction))). Further, the following equation (13) is derived from the above equation (8).

  When the formulas (10) to (13) thus derived are substituted into the formula (9) and calculated, the following formula (14) is derived.

  Here, according to the above equation (14), when the incident angle θ≈the diffraction angle φ, that is, as in the present embodiment, the diffraction pitch Pg of the diffraction grating 151 is substantially the same as the pitch P of the interference fringes. It can be seen that the second product term on the right side diverges to infinity and the third product term on the right side converges to 2. Therefore, since the rate of change of the interference fringe pitch Λ with respect to the displacement of the position x of the vibration film 14 is infinite according to the equation (14), the interference fringe pitch Λ with respect to the minute displacement of the vibration film 14 under this condition. It can be seen that the sensitivity is infinitely improved. In contrast, when the difference between the incident angle θ and the diffraction angle φ increases, the equation (14) also shows that the sensitivity of the interference fringe pitch Λ to the minute displacement of the vibration film 14 decreases.

Further, when the value of (l ² −x ² ) ^1/2 in the first product term on the right side, that is, the value of the distance y in FIG. Since the rate of change of the interference fringe pitch Λ with respect to the displacement increases, it can be seen that the sensitivity of the interference fringe pitch Λ to the minute displacement of the vibration film 14 is improved. That is, it can be seen that if the size of the entire interferometer can be reduced, the sensitivity of the pitch Λ of the interference fringes with respect to minute displacements of the vibration film 14 is improved. This is because the change in the incident angle θ increases with a minute displacement x of the vibration film 14.

  As described above, in the present embodiment, the laser light Lout from the laser light source 10 is separated into the two optical paths OP1 and OP2 within the two-beam interferometer, and travels along the optical path OP1 by the diffraction element 151 on the vibration film 14. The diffracted diffracted light Ld1 travels along the optical path OP2 and the diffracted light Ld2 diffracted by the diffraction element 151 interferes with each other to form interference fringes, and the vibration of the vibrating film 14 is quantized based on the interference fringes. Therefore, the vibration of the vibration film 14 can be optically digitally detected. In addition, since the diffraction pitch of the diffraction element 151 is set to be substantially the same as the pitch of the interference fringes F1 when the vibration film 14 is in a stationary state (when on the virtual plane), the diffraction light Ld1, Ld2 The diffraction directions can be made to substantially coincide with each other, whereby the displacement of the vibration film 14 can be amplified and detected. Therefore, it is possible to improve detection sensitivity when optically detecting digital vibration.

  In addition, the detection of interference fringes is performed using the two photoelectric conversion elements 161 and 162, and the phase differences of the interference fringes detected by the photoelectric conversion elements 161 and 162 are set to be approximately 90 degrees, A circular Lissajous figure can be formed as follows and can be easily detected.

  In addition, since the output signals Sx and Sy from the two photoelectric conversion elements 161 and 162 are respectively used as an X signal and a Y signal, a circular or arc-shaped Lissajous figure based on these X and Y signals is generated. The detection points of the stripes are displaced on the circumference according to the displacement of the vibration film 14, and the displacement of the vibration film 14 can be detected digitally by counting the number of times of passing through a predetermined reference point. Become.

  Further, the diffraction pitch of the diffraction grating 151 is substantially the same as the pitch of the interference fringes F1 when the vibration film 14 is in a stationary state, and is substantially the same as the extending direction of the interference fringes when the vibration film 14 is in a stationary state. Since they are parallel, only the 0th-order diffracted light and the 1st-order diffracted light are generated in the diffracted lights Ld1 and Ld2, and the intensity of the diffracted lights Ld1 and Ld2 is increased as compared with the second embodiment described below. Can do. Therefore, it is possible to clarify the distinction between the bright and dark interference fringes, improve the interference fringe detection accuracy, and improve the vibration film 14 detection accuracy.

  In the above-described embodiment and the like, the case where the photoelectric conversion elements 161 and 162 are disposed on the optical path OP2 side has been described. However, in the two-beam interferometer of the present embodiment, the 0th-order diffracted light and the diffracted light Ld2 of the diffracted light Ld1 are described. In general, the first-order diffracted light of the diffracted light travels toward the optical path OP2, and the first-order diffracted light of the diffracted light Ld1 and the 0th-order diffracted light of the diffracted light Ld2 travel toward the optical path OP1, respectively. 161 and 162 may be arranged on at least one of the optical paths OP1 and OP2.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the same thing as the component in 1st Embodiment, and description is abbreviate | omitted suitably.

  FIG. 6 illustrates a configuration of the vibration detection device (microphone device 1A) according to the present embodiment. In the microphone device 1A according to the first embodiment shown in FIG. 1, a diffraction grating 152 is provided on the surface of the vibration film 14 instead of the diffraction grating 151, and the photoelectric conversion elements 161 and 162 are respectively provided. The vibration film 14 (diffraction grating 152) is arranged in a substantially perpendicular direction.

  The diffraction grating 152 has a diffraction pitch (secondary grating (GRT)) that is approximately twice the pitch of the interference fringes when the vibrating membrane 14 is in a stationary state (when on the virtual plane). : Diffraction grating 152 diffraction pitch Pg = 2 × (interference fringe pitch P)), and is set to be substantially parallel to the extending direction of the interference fringes at that time. Further, the vibrating film 14 is arranged so that the incident angles of light traveling on the optical paths OP1 and OP2 with respect to the diffraction grating 152 are substantially the same (incident angle θ) as shown in the figure. Further, even when the vibration film 14 is displaced as indicated by the arrow in the drawing, the light rays of the light beams from the optical paths OP1 and OP2 are always incident on the diffraction grating 152. The diffraction grating 152 corresponds to a specific example of “diffraction element” in the present invention.

  With this configuration, in the microphone device 1A of the present embodiment, since the diffraction grating 152 is a second-order grating as described above, for example, as shown in FIG. Diffracted light beam L16 (corresponding to diffracted light beam Ld3 in FIG. 6) as a first-order diffracted light beam with a diffraction angle φ = 0 ° by the incident light beam L15 (incident angle θ) from the optical path OP1. At the same time, the incident light beam L25 (incident angle θ) from the optical path OP2 generates a diffracted light beam L26 (corresponding to the diffracted light beam Ld4 in FIG. 6) having a diffraction angle φ = 0 ° as the first-order diffracted light beam. Since the traveling directions of the diffracted light beams L16 and L26 are substantially the same due to the interference between the diffracted light beams Ld3 and Ld4, an interference fringe F3 having a coarse pitch (near null frenzy) is formed as shown in the figure. . Note that the first-order diffracted light beams of incident light beams L15 and L16 are generated in the direction of diffraction angle φ = 0 ° (perpendicular direction of vibration film 14), respectively, in the above equation (4), Pg = 2P = 2 × (λ / It is also derived from substituting (2 × sin θ)).

  Further, for example, as shown in FIG. 8, when the vibrating membrane 14 is displaced in response to the sound wave Sw, and the diffraction grating 152 is also displaced upward by Δx, the incident from the optical path OP1 as in the first embodiment. The incident angle of the light beam changes to the incident angle θ ′ as in the incident light beam L17, and the diffraction angle of the first-order diffracted light beam also changes to the diffraction angle φ ′ as in the diffracted light beam L18. Further, the diffraction angle of the first-order diffracted light beam with respect to the incident light beam L27 from the optical path OP2 also changes to the diffraction angle φ ′ as in the diffracted light beam L28. That is, since an angle is generated between the diffracted light beams L18 and L28, the pitch of the interference fringes also changes as shown in the figure, and the interference fringes F4 have a fine pitch.

  The interference fringes F3 and F4 thus formed are detected by the photoelectric conversion elements 161 and 162, and the same effect can be obtained by the same operation as that of the first embodiment.

  Further, in this embodiment, since the diffracted lights Ld3 and Ld4 can be prevented from traveling to the optical paths OP1 and OP2, the generation of return light to the laser light source 10 can be avoided as in the first embodiment. In addition, the light beams on the optical paths OP1 and OP2 can be prevented from being obstructed by the photoelectric conversion elements 161 and 162 as in the first embodiment.

[Modification]
Next, modified examples of the first and second embodiments will be described. Note that in this modification, the same components as those in the above embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  FIG. 9 illustrates a configuration of a vibration detection device (microphone device 1B) according to this modification. This microphone device 1B is the same as the microphone device 1 of the first embodiment shown in FIG. 1 except that the vibrating membrane 14 is rotated by an angle β as shown by an arrow in the figure (tilted with respect to a virtual plane). The incident angles of light from the optical paths OP1 and OP2 with respect to the diffraction grating 151 are made different from each other, and the photoelectric conversion elements 161 and 162 are arranged in directions different from the optical paths OP1 and OP2, respectively.

  With this configuration, in this modification, for example, as shown in FIG. 10, the diffraction angles of the diffracted beams Ld5 and Ld6 in FIG. In addition, since the pitch P of the interference fringes represented by the above-described equation (1) also changes (becomes larger) due to the rotation of the vibration film 14, the diffraction pitch of the vibration film 14 is increased accordingly. Shall.

At this time, if the interference fringe pitch P ′ is expressed by the following equation (15), and the diffraction pitch Pg ′ of the diffraction grating 151 is also substantially equal in length, the incidence of the incident light beam Lb shown in FIG. Since the angle is (θ + β), the following equation (16) is derived when m = 1 (first-order diffraction) by the diffraction condition of the above equation (4).
P ′ = λ / (2 × sin θ × cos β) (15)
P ′ × (sin (θ + β) + sinφ) = λ (16)

Here, when the calculation is performed by substituting the above equation (15) into the above equation (16), the following equation (17) is derived. This means that the incident light beam Lb is diffracted at an angle of (θ-2β) (first-order diffracted light beam Ld ′ (corresponding to the diffracted light beam Ld6)) when viewed from the original x coordinate shown in FIG. Thus, the light beam is equiangular and parallel to the diffraction angle of the 0th-order diffracted light beam Lc ′ (corresponding to the diffracted light beam Ld5) of the incident light beam La. Therefore, due to the interference between the diffracted beams Ld5 and Ld6, interference fringes with a coarse pitch (close to the null frenzy) are formed as in the first and second embodiments.
sin φ = sin θ × cos β−cos θ × sin β = sin (θ−β) (17)

  Thus, in this modification, the diaphragm 14 and the diffraction grating 151 are rotated (tilted with respect to the virtual plane) so that the incident angles of light from the optical paths OP1 and OP2 with respect to the diffraction grating 151 are different from each other. Even in such a case, since the null fringe condition and the maximum sensitivity condition in the first embodiment do not change, the same effect can be obtained by the same action.

  Further, since the traveling directions of the diffracted lights Ld5 and Ld6 can be arbitrarily adjusted according to the respective incident angles, generation of return light to the laser light source 10 as in the first embodiment is avoided. In addition, the degree of freedom of arrangement of the photoelectric conversion elements 161 and 162 can be improved.

  In this modification, the modification to the microphone device 1 of the first embodiment shown in FIG. 1 has been described, but the modification is applied to the microphone device 1A of the second embodiment shown in FIG. May be. For example, the microphone device 1C shown in FIG. 11 is applied to the microphone device 1A of the second embodiment, and a part of the beam splitter 11 is missing as indicated by reference numeral P3 in the drawing. Thus, the vibrating film 14 and the diffraction grating 152 are rotated (tilted with respect to the virtual plane) so that the incident angles of the light from the optical paths OP1 and OP2 with respect to the diffraction grating 152 are different from each other. In the figure, 10A and 10B represent predetermined lenses.

  Although the present invention has been described with reference to the first and second embodiments and their modifications, the present invention is not limited to these embodiments and the like, and various modifications are possible. .

  For example, in the vibration detection apparatus described in the above embodiment and the like, for example, diffraction grating formation patterns as shown in FIGS. 12A to 12D are conceivable. Specifically, for example, the vibration film 14A shown in FIG. 12A is a basic example in which the diffraction grating 15A is uniformly formed on the entire surface of the vibration film 14A. In order to form such a diffraction grating 15A, for example, a film-like thin film coated with a photosensitive agent may be exposed to the shape of the diffraction grating and developed. Note that the diffraction pitch is about 0.55 μm (in the case of the primary grating) according to the above equation (1), for example, considering a two-beam optical system with a laser beam of λ = 780 nm and an incident angle θ = 45 °. 1.1 μm (in the case of a secondary grating), which can be sufficiently formed in view of the current semiconductor exposure process (and is at a level that does not cause any problems if an EB (electron beam) exposure method is used). ).

  Further, in the vibration detection apparatus of the above-described embodiment and the like, it is not necessary to irradiate the entire vibration film with a laser beam. Therefore, in the vibration film 14B shown in FIG. 12B, the diffraction element 15B is a part of the surface of the vibration film 14B. It is formed only in the vicinity of the region irradiated with the laser beam and the center region where vibration is detected, and other portions of the surface of the vibration film 14B are applied in black so that stray light can be avoided. . Furthermore, if this method is further advanced, the diffraction grating formation area is limited to a very small area, so that pinholes on the photoelectric conversion element side are eliminated, and diffracted light from only the minute diffraction grating formation area is detected. You may make it do.

  For example, in the vibration film 14C shown in FIG. 12C, two types of diffraction gratings 15C1 and 15C2 are formed on the surface of the vibration film 14C, and the diffraction pitches or phases of the diffraction gratings 15C1 and 15C2 are different from each other. It is like that. A laser beam formed in a slightly vertically long shape is applied to the diffraction gratings 15C1 and 15C2 thus configured to detect interference fringes formed by these two diffraction gratings, and at the same time, interference fringes formed by one diffraction grating. When the light is bright, the interference fringes formed by the other diffraction grating show an interference fringe having a phase shift of approximately 90 degrees. In this way, when the interference fringes formed by the diffraction gratings 15C1 and 15C2 are detected by two photoelectric conversion elements, the output signals from the two photoelectric conversion elements can maintain a 90-degree phase difference from each other. It is possible to reduce detection errors.

  In FIG. 12C, two types of diffraction gratings are formed in the longitudinal direction of the vibration film. However, separation of the diffraction regions in the lateral direction can also cause a phase shift and obtain the same effect. it can. For example, in the vibrating membrane 14D shown in FIG. 12D, the diffraction grating 15D is formed in a two-dimensional direction in the plane, and the diffraction pitch is made different between the vertical direction and the horizontal direction. The difference may be detected. In this case, the configuration of the interferometer is obtained by adding an interferometer in a direction perpendicular to the paper surface to the interferometer described in the above embodiment and the like, and becomes a three-dimensional interferometer.

  Further, two-beam interference may be performed using one type of diffraction grating and two types of laser beams having different wavelengths, and two interference fringes generated by the respective wavelengths may be detected by a plurality of photoelectric conversion elements. . In such a configuration, since a plurality of maximum sensitivity points can be provided, it is possible to compensate for a decrease in sensitivity accompanying an increase in the displacement of the diffraction grating position.

  In the above-described embodiment, etc., the case where the diffraction pitch of the diffraction grating is approximately the same as or approximately twice as long as the pitch of the interference fringes when the diaphragm is stationary is described. The diffraction pitch of the diffraction grating may be set to be approximately the same as or substantially an integral multiple of the pitch of the interference fringes when the diaphragm is stationary.

  In the above-described embodiment and the like, the case has been described where four reference points Pa to Pd are provided on the Lissajous figure to perform digital counting. However, the number of reference points is not limited to this, and for example, as shown in FIG. In addition to the four reference points Pa to Pd, for example, reference lines E to H may be used, and the reference points may be set finely and increased. In such a configuration, the number of counts can be increased, so that the value of the output signal Sout can be increased and the detection sensitivity can be further improved.

  In the above embodiments and the like, the semiconductor laser has been described as the light source that emits the laser light Lout. However, for example, a gas laser, a fixed laser, or the like may be used.

  In the above-described embodiment and the like, a diffraction grating (grating) has been described as an example of a diffraction element, but other diffraction elements may be used in addition to this.

  In addition, the vibration detection device according to the above-described embodiment or the like can detect optical vibration with high sensitivity, but on the contrary, it is sensitive to environmental temperature because of high sensitivity. Therefore, for example, when applied to a microphone device, fluctuations of about 10 Hz or less, which are almost unrelated to sound, are cut (use of a high-pass filter), or temperature fluctuation is cut by controlling the temperature of the entire system with a Peltier element or the like. By doing so, you may make it suppress the drift of the Lissajous figure resulting from such a temperature fluctuation. In order to compensate for this by detecting a slow fluctuation of the Lissajous figure of about 10 Hz or less, a method of suppressing a drift by causing a wavelength change by controlling an injection current to the laser light source is also conceivable.

  In the above-described embodiment and the like, as an example of the vibration detection device of the present invention, the vibration body is a vibration film (vibration film 14) that vibrates in response to sound waves, and the vibration of the vibration film 14 is detected as an audio signal Sout. However, the vibration detection device of the present invention is not limited to this, and may be configured to detect other vibrations. Specifically, for example, the vibration sensor 1D shown in FIG. 14 is configured as a vibration sensor that detects displacement and vibration of the region 80 to be inspected, so that the region 80 to be inspected is hard and heavy, for example. In addition, the displacement and vibration of the inspected site 80 can be accurately detected in a non-contact manner. Further, as shown in the figure, if the vibration sensor 1D is connected to the actuator 81 via the wiring 82, it is possible to suppress the vibration of the inspected site 80 relative to the reference object.

  Furthermore, the vibration detection device (microphone device) of the present invention is, for example, as shown in FIG. 15, the microphone device 1 shown in FIG. 1 (or the microphone device 1A shown in FIG. 6 and the microphone device shown in FIG. 1B or the microphone device 1C shown in FIG. 11), a transmission format encoder 2 that encodes the audio signal Sout output from the microphone device 1, and the transmission format encoder 2 and a digital transmission path (for example, an optical fiber) ), The 1-bit stream system recorder 4 and the PCM (Pulse Code Modulation) recorder 6, the 1-bit system recording medium 51, the PCM system recording medium 71, and the playback equipment amplifier speakers 52 and 72. Applied to an audio signal recording and playback system consisting of It is possible. In the audio signal recording / reproducing system having such a configuration, since the binarized audio signal Sout can be transmitted, it is possible to easily transmit a long distance compared to the case of transmitting an analog audio signal. Become.

It is a figure showing the whole structure of the vibration detection apparatus which concerns on the 1st Embodiment of this invention. It is a figure showing an example of the Lissajous figure created in the digital count part shown in FIG. It is a figure for demonstrating an example of the diffracted light and interference fringe which arise with the diffraction grating shown in FIG. It is a figure for demonstrating an example of the diffracted light and interference fringe when a diaphragm is displaced in FIG. It is a figure for demonstrating the advancing direction of the diffracted light in 1st Embodiment. It is a figure showing the whole structure of the vibration detection apparatus which concerns on 2nd Embodiment. It is a figure for demonstrating an example of the diffracted light and interference fringe which arise with the diffraction grating shown in FIG. FIG. 8 is a diagram for explaining an example of diffracted light and interference fringes when the vibration film is displaced in FIG. 7. It is a figure showing the whole structure of the vibration detection apparatus which concerns on the modification of this invention. It is a figure for demonstrating the advancing direction of the diffracted light in the modification of FIG. It is sectional drawing showing the structure of the vibration detection apparatus which concerns on the other modification of this invention. It is a top view showing the diaphragm and diffraction grating which concern on the modification of this invention. It is a figure showing an example of the Lissajous figure concerning the modification of the present invention. It is a perspective view showing the application example of the vibration detection apparatus which concerns on the other modification of this invention. It is a block diagram showing the example of a structure of the audio | voice recording / reproducing system provided with the vibration detection apparatus of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1A-1C ... Microphone apparatus, 1D ... Vibration sensor, 10 ... Laser light source, 10A, 10B ... Lens, 11 ... Beam splitter, 121, 122 ... Lens, 131, 132 ... Reflection mirror, 14, 14A-14D ... Vibration Membrane, 151, 152, 15A, 15B, 15C1, 15C2, 15D ... Diffraction grating (grating), 161, 162 ... Photoelectric conversion element, 17 ... Digital count unit, 2 ... Transmission format encoder, 3 ... Editing equipment, 4 ... 1 Bit stream system recorder, 51... 1 bit system recording medium, 52, 72... Reproduction equipment amplifier speaker, 6 .. PCM system recorder, 71... PCM system recording medium, 80. ... sound wave, OP1, OP2 ... light path, Sx, Sy ... from photoelectric conversion element Force signal, Sout ... audio signal, Lout ... laser light, Ld1-Ld6 ... diffracted light, L11-L18, L21-L28, La-Ld, Lc ', Ld' ... light, F1-F4 ... interference fringes, θ, θ '... incident angle, φ, φ' ... diffraction angle, β ... displacement (rotation) angle of vibrating membrane (diffraction grating), Δx ... diffraction grating displacement, C ... center point, P0 ... signal point, Pa to Pd ... Reference point, EH ... reference line.

Claims (11)

A light source that emits laser light;
The laser beam is configured to include a vibrating body having a diffraction element capable of diffracting the laser beam, and the laser beam emitted from the light source travels while being separated into first and second optical paths, and travels along the first optical path. An interferometer that forms interference fringes by causing the first diffracted light diffracted by the diffractive element and the second diffracted light diffracted by the diffractive element to travel along the second optical path to interfere with each other. ,
Detection means for quantizing and detecting vibrations of the vibrator based on the formed interference fringes,
The vibration detection apparatus, wherein the diffraction pitch of the diffraction element is set to be equal to or an integral multiple of the pitch of interference fringes when the vibrating body is stationary. The interferometer is
A beam splitter that separates the laser light into first and second optical paths;
A first reflector disposed on the first optical path;
The vibration detection device according to claim 1, further comprising a second reflector disposed on the second optical path. The diffraction pitch of the diffractive element is the same length as the pitch of interference fringes when the vibrating body is stationary, and is parallel to the extending direction of the interference fringes when the vibrating body is stationary. The vibration detection device according to claim 1, wherein the vibration detection device is set. The detection means is
Two photoelectric conversion elements that detect the interference fringes in a state in which the phases are shifted from each other by 90 degrees;
Considering the output signals from the two photoelectric conversion elements as signal points, figure generating means for generating a Lissajous figure having a circular or arc shape on a plane;
A counter that counts the number of times a signal point passes a predetermined reference point on the generated Lissajous figure,
The vibrating body is disposed so that incident angles of light traveling in the first and second optical paths with respect to the diffraction element are the same,
The vibration detection apparatus according to claim 3, wherein the photoelectric conversion element is disposed on at least one side of the first and second optical paths. The diffraction pitch of the diffractive element is twice as long as the pitch of interference fringes when the vibrating body is stationary, and is parallel to the extending direction of the interference fringes when the vibrating body is stationary. The vibration detection device according to claim 1, wherein The detection means is
Two photoelectric conversion elements that detect the interference fringes in a state in which the phases are shifted from each other by 90 degrees;
Considering the output signals from the two photoelectric conversion elements as signal points, figure generating means for generating a Lissajous figure having a circular or arc shape on a plane;
A counter that counts the number of times a signal point passes a predetermined reference point on the generated Lissajous figure;
The vibrating body is disposed so that incident angles of light traveling in the first and second optical paths with respect to the diffraction element are the same,
The vibration detection device according to claim 5, wherein the photoelectric conversion element is arranged in a direction perpendicular to the vibrating body. The vibration detection device according to claim 1, wherein the vibrating body is arranged so that incident angles of light traveling in the first and second optical paths with respect to the diffraction element are different from each other. . The diffraction pitch of the diffractive element is the same length as the pitch of interference fringes when the vibrating body is stationary, and is parallel to the extending direction of the interference fringes when the vibrating body is stationary. Set,
The detection means is
Two photoelectric conversion elements that detect the interference fringes in a state in which the phases are shifted from each other by 90 degrees;
Considering the output signals from the two photoelectric conversion elements as signal points, figure generating means for generating a Lissajous figure having a circular or arc shape on a plane;
A counter that counts the number of times a signal point passes a predetermined reference point on the generated Lissajous figure,
The vibration detection device according to claim 1, wherein the photoelectric conversion element is arranged in a direction different from the directions on the first and second optical paths. The vibration detection apparatus according to claim 1, wherein the diffraction element is formed only on a part of the surface of the vibrating body, and the other part of the surface of the vibrating body is coated in black. The two diffractive elements are formed on the surface of the vibrating body, and the phases of interference fringes formed by the diffracted light from each diffractive element are 90 degrees different from each other. The vibration detection apparatus described. The said vibrating body is a vibrating membrane which vibrates according to a sound wave, It is comprised as an optical microphone apparatus which detects the vibration of this vibrating membrane as a quantized audio | voice signal. Vibration detection device.

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