JP2006067219A - Optical microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturized and highly sensitive optical microphone by efficiently increasing an acoustic wave detection sensitivity in a limited region. <P>SOLUTION: An optical microphone 1 includes a cylinder mirror 4 of a cylinder shape having a mirror surface on the inside wall, with a notch 4k or a hole 4a provided in a portion of the wall surface for inputting/outputting a laser beam 8. By reflecting the laser beam 8 being output from a laser light generator 2 for a plurality of times in an acoustic signal detection field 9 inside the cylinder mirror 4, a light path of star and polygonal shape is formed. Since an acoustic wave inside the acoustic signal detection field 9 produces the laser beam 8 being modulated approximately as many as the number of reflection times, as compared with the case of a linear optical path, a photoelectric converter 6 detects the modulation amount produced in the light beam so as to output an electric signal. An opening surface of the cylinder mirror 4 is provided with a horn 21 with the diameter of a throat 21ma slightly longer than the outer diameter of a ring-shaped region 11 and an equalizer 22 with the diameter of a bottom 22t slightly shorter than the inner diameter of the ring-shaped region 11 having high light path density and high acoustic signal detection sensitivity to thereby concentrate acoustic waves on the ring-shaped region 11. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical microphone that detects sound waves using a light beam, and more particularly to an optical microphone that includes sound wave concentrating means for concentrating sound waves.

A microphone that is a device that converts sound waves into an electrical signal is generally a dynamic or condenser microphone that uses a diaphragm. On the other hand, there has been proposed a microphone that detects sound waves using a light beam such as laser light without using a diaphragm (see, for example, Patent Documents 1 and 2).
JP 2002-78093 A JP 2003-230196 A

  Many conventional microphones using a light beam use refraction or diffraction due to a change in the refractive index of air as a sound wave detection principle. However, since the effects of refraction and diffraction are very small, the conventional optical microphone has a very low detection sensitivity, and it has been difficult to obtain sufficient detection sensitivity. In general, in an optical microphone, in order to detect sound waves, the optical path length of the light beam is set according to its size, and the sound waves from the sound source have different phases depending on the position of the light beam on the optical path. Therefore, the modulation of the light beam by the sound wave has a different magnitude and polarity depending on the position on the optical path. Therefore, the modulation for the same light beam has different sizes and polarities in each part, and the detection sensitivity is lowered. End up. This effect becomes more pronounced when the ratio of the wavelength of the sound wave and the optical path length of the light beam used for sound wave detection is larger when the optical path of the light beam is a linear optical path, and the optical path of the light beam is expanded in a two-dimensional space. In such a case, the larger the area of the sound wave detection region, the more prominent. With conventional optical microphones, the device is large and the detection area of sound waves tends to be wide, so the frequency at which the sensitivity begins to decrease due to the suppression effect falls within the audible band, and sufficient frequency characteristics as an acoustic microphone Cannot be obtained, or extreme detection directivity is generated only in a sound source on a specific axis that does not produce a suppression effect on the light beam, making it difficult to put it to practical use.

  Therefore, an object of the present invention is to provide a small and highly sensitive optical microphone in which the detection sensitivity of sound waves is efficiently increased without increasing the detection area of sound waves, and the frequency characteristics and directivity are improved.

  The present invention has the following configuration as means for solving the above problems.

(1) a light beam output means for outputting a light beam;
The light beam output from the light beam output means is reflected a plurality of times to form an optical path whose shape when viewed from one direction is a star polygon, and an acoustic signal detection field that is an area including this optical path is defined as the optical path. Is formed by a central region where no sound is present, a ring-shaped region having a high optical path density outside the central region and a high acoustic signal detection sensitivity, and a region having a low acoustic detection sensitivity outside and passing through the acoustic signal detection field. Optical path forming means for modulating the light beam of the star-shaped polygon with sound waves to
A sound wave concentrating means for concentrating the sound wave passing through the acoustic signal detection field in a circular shape or an annular shape and guiding it within the ring-shaped region;
A light beam detecting means for detecting a modulation amount of the light beam emitted from the optical path forming means and outputting an electrical signal corresponding to the modulation amount;
It is provided with.

  As is well known, sound waves are vibration components of the density of air, and in the space in which sound waves are propagated, a large or small distribution of the optical refractive index of air occurs depending on the degree of density, and this distribution is accompanied by the propagation of sound waves. Moving. Therefore, when a light beam is passed through a space where sound waves are propagated, the light beam is modulated according to the gradient of the refractive index of air at the passing point, and the amount of modulation changes as the refractive index distribution moves. Therefore, this light beam is subjected to modulation correlated with sound waves. In this configuration, the optical microphone outputs a light beam from the light beam output means, and the light beam output from the light beam output means by the optical path forming means is within an acoustic signal detection field that is a region for detecting sound waves. By reflecting the light beam multiple times so as to form a star-shaped polygonal optical path, the light beam is modulated in the acoustic signal detection field by the number of times of reflection in the case of a straight optical path. Then, the modulated light beam is guided to a light beam detecting means having a photoelectric conversion function, a modulation amount of the light beam corresponding to the gradient of the refractive index of the sound wave is detected, and an electric signal corresponding to the modulation amount is output. . Therefore, it is possible to effectively increase the detection sensitivity of sound waves in a limited space.

  The optical path forming unit reflects the light beam output from the light beam output unit a plurality of times, and forms an optical path in the acoustic signal detection field having a star polygon when viewed from one direction. Since the light beam does not pass through the central region of the acoustic signal detection field, the acoustic signal detection field has no acoustic signal detection sensitivity. In the immediate outer periphery, the optical path is concentrated so as to surround a central region that does not have acoustic signal detection sensitivity, and a region with high optical path density, which is the number of optical paths per unit region, is formed in a ring shape. Is done. Further, the outside is a region with low optical path density and low acoustic signal detection sensitivity. Sound waves are concentrated in a circular shape or an annular shape by the sound wave concentration means, and are guided into a ring-shaped region where the optical path density of the acoustic signal detection field is high and the acoustic signal detection sensitivity is high. Therefore, since the modulation of the light beam by the sound wave is performed around the ring-shaped region having a high optical path density and high acoustic signal detection sensitivity, the sound wave detection sensitivity in a limited space can be further increased.

  (2) The sound wave concentration means is characterized by comprising a horn or a horn and an equalizer.

  In this configuration, since the horn and the equalizer are used to concentrate the sound wave propagating from the sound source, the sound wave can be efficiently concentrated in a circular shape or an annular shape.

  The optical microphone of the present invention outputs a light beam from the light beam output means, and the light path forming means reflects the light beam output from the light beam output means a plurality of times to detect a star-shaped polygonal optical path as an acoustic signal. Form in the field. Thereby, the frequency | count that a sound wave modulates a light beam can be increased efficiently, without expanding the area | region which detects a sound wave, and an acoustic signal detection sensitivity can be improved. Also, since the acoustic signal detection field can be made small, it is possible to set the frequency at which the suppression effect starts to occur higher than the audible band, and it is possible to prevent having extreme directivity within the audible band, which is good for acoustic use This makes it possible to manufacture an optical microphone with a good frequency characteristic and directivity.

  Further, the optical microphone of the present invention concentrates the sound wave in a circular shape or an annular shape by the sound wave concentrating means, and guides it to the ring-shaped region having a high optical path density and high acoustic signal detection sensitivity formed by the light beam. A strong sound field can be generated in a ring-shaped region where the optical path density of the beam is high, and the detection sensitivity of sound waves can be further increased.

  FIG. 1 is a configuration diagram illustrating an outline of an optical microphone according to an embodiment of the present invention, where (A) is a top view seen from the sound source side, (B) is a side view, and (C) is a cylinder. It is a top view at the time of using a polygonal column mirror instead of a mirror. The optical microphone 1 includes a laser beam generation unit 2 and a light source system lens unit 3 which are light beam output units, a cylindrical mirror 4 which is an optical path forming unit, and a detection system lens unit 5 and a photoelectric conversion unit 6 which are light beam detection units. I have.

  The laser beam generator 2 includes a semiconductor laser element and a laser drive circuit (not shown) and emits a laser beam 7. The generation source of the laser light 7 is not limited to the semiconductor laser element, and a generation device such as a solid laser, a liquid laser, or a gas laser may be used.

  The light source system lens unit 3 condenses the laser beam 7 emitted from the laser beam generator 2 and converts it into a laser beam 8 that is a substantially parallel beam with a predetermined spot diameter. The light source system lens unit 3 may be a single lens or a combination lens, and is a compound optical system such as a combination of a collimator that creates parallel light from divergent light and a beam expander that narrows the beam diameter of the parallel light. There may be.

  The cylindrical mirror 4 has a cylindrical shape and the entire inner wall surface is a mirror surface 4m. A cutout 4k or a hole 4a is formed in a part of the wall surface, and the incident laser beam 8 is reflected a plurality of times to modulate sound waves with respect to the light beam. Is performed multiple times. Here, in the following description, it is assumed that the cutout 4k is formed in the cylindrical mirror 4. The cylindrical mirror 4 is arranged so that the laser beam 8 incident on the acoustic signal detection field 9 inside thereof is reflected a plurality of times by the mirror surface 4 m to form a star-shaped polygonal optical path. That is, the laser beam 8 output from the laser beam generator 2, the circle inscribed in the mirror surface 4m (shown by a dotted line in FIGS. 1A and 1C), and the normal line at the intersection of the laser beam 8 are formed. It arrange | positions so that the incident angle ∠A may become a predetermined angle. As a result, at each reflection point of the laser beam 8 on the mirror surface 4m, the laser beam 8 is incident on the normal line at the reflection point on the mirror surface 4m at an incident angle 、 A and is reflected at the reflection angle ∠A.

  FIG. 1 shows a case where the incident angle ∠A to the cylindrical mirror 4 is 6 degrees. In the present embodiment, as shown in FIG. 1B, the optical path of the laser beam 8 is formed on substantially the same plane. In the following description, a plane on which the optical path of the laser beam 8 is formed is referred to as an XY plane, and an axis perpendicular to the XY plane is referred to as a Z axis.

  When the cylindrical mirror 4 is provided with the cutout 4k and the hole 4a, if the laser beam 8 passes through with certainty, depending on the arrangement position of the laser light generation unit 2 and the photoelectric conversion unit 6 with respect to the cylindrical mirror 4, the incident beam May be provided independently from the output holes and cutouts, or a common one may be provided. For example, when the cylindrical mirror 4 is provided with a notch 4k and a hole 4a that are used for both input and output, a sector ring having a narrow angle (center angle) of 2a when the maximum incident angle of the laser beam 8 is a. The shape of the mold is such that the center of the fan-shaped ring is positioned inside the cylindrical mirror 4 from the intersection of the laser beam 8 output from the laser light generator 2 and the circle inscribed in the mirror surface 4m. good.

  Further, as shown in FIG. 1C, instead of the cylindrical mirror 4, a polygonal column mirror 14 having a polygonal opening surface and an inner wall surface as a mirror surface, and a cutout 14k or a hole 14a formed in part is provided. It is also possible to use it. The polygonal column mirror 14 reflects the laser beam 8 on each surface of the inner wall corresponding to each side of the polygon of the opening surface according to the incident angle ∠A (the definition of the incident angle is the same as that of the cylindrical mirror 4). Set the number of corners of the aperture surface. For example, when the incident angle ∠A of the laser beam 8 is 6 degrees, a polygonal prism mirror having a regular 15-sided opening surface is used.

  The detection system lens unit 5 condenses the laser beam 8 that is repeatedly reflected by the cylindrical mirror 4 and converges it on a detection element (not shown) that constitutes the photoelectric conversion unit 6. At this time, the detection system lens unit 5 may be a single lens or a combination lens.

  The photoelectric conversion unit 6 detects the modulation amount of the laser beam 8 converged on a detection element (not shown) by the detection system lens unit 5, and outputs an electric signal corresponding to the modulation amount.

  The modulation of the laser beam (light beam) 8 by the sound wave can be detected by several methods, but the modulation is detected as a change in the position of the received laser spot due to a change in the gradient of the refractive index according to the density of the air due to the sound wave. , A method of detecting the absolute position of the received laser spot on the PSD using an optical position detector (PSD: Position Sensitive Detector) and converting it to an electrical signal, or a change in the position of the received laser spot on the multi-segment photoelectric conversion element The sound wave can be detected by a method of converting the signal into an electric signal by analog or digital arithmetic processing.

  When a two-part photoelectric conversion element is used for the photoelectric conversion unit 6, when the laser beam 8 is not affected by the sound wave, the light receiving laser spot is positioned at the center of the two photoelectric conversion elements. It is assumed that an electrical signal is detected by a differential calculation of the outputs of two photoelectric conversion elements with respect to a change in position of a received laser spot of the laser beam 8. In addition, a photodiode (PD) or the like is used as the photoelectric conversion element, and the diameter of the laser spot is such that the laser spot does not completely move on either detection element when modulated with the maximum expected sound wave. The area of each detection element is set larger than the area of the laser spot.

  In addition, when the cylindrical mirror 4 (optical path forming means) of the present invention is used, the modulation is detected by the laser Doppler effect as a change in sound velocity due to air density due to sound waves, or the change in the optical path length due to air density due to sound waves. In the case where detection is performed based on the phase difference from the reference light, it is possible to effectively increase the detection sensitivity of sound waves in a limited space.

  Next, the operation of the optical microphone 1 will be described. As is well known, sound waves are vibration components of the density of air, and in the space in which sound waves are propagated, a large or small distribution of the optical refractive index of air occurs depending on the degree of density, and this distribution is accompanied by the propagation of sound waves. Moving. For this reason, when a laser beam passes in a space where sound waves propagate in a direction perpendicular to the propagation direction, the laser beam is modulated according to the gradient of the refractive index at the passing point, and the refractive index distribution is moved accordingly. Since the modulation amount changes, the laser beam undergoes modulation correlated with the sound wave.

  An optical microphone 1 according to an embodiment of the present invention emits a laser beam 7 from a laser beam generator 2 and converts the laser beam 7 into a laser beam (parallel beam) 8 by a light source system lens unit 3. 4, the acoustic signal detection field 9 is reflected a plurality of times so as to form a star-shaped polygonal optical path. As a result, the modulation by the sound wave 20 is applied to the laser beam 8 within the acoustic signal detection field by approximately the number of times of reflection in the case of the straight optical path. Then, the modulated laser beam 8 is guided to the photoelectric conversion unit 6 via the detection system lens unit 5, and the modulation amount of the laser beam 8 corresponding to the inclination of the refractive index of air is detected, and the electric power corresponding to the modulation amount is detected. Output a signal.

  Further, in the acoustic signal detection field 9 in the cylindrical mirror 4, since the laser beam 8 does not pass through the central region, the central region becomes a region having no acoustic signal detection sensitivity (hereinafter referred to as the central region 10), and immediately around the outer periphery. A region having a high optical path density and a high acoustic signal detection sensitivity in which a plurality of optical paths are concentrated (intersected) is formed in a ring shape so as to surround the central region 10 having no acoustic signal detection sensitivity (hereinafter referred to as a ring). (Referred to as a region 11). Further, the outside is an area where the optical path density is low and the acoustic signal detection sensitivity is low (hereinafter referred to as the outer peripheral area 12). Thus, the acoustic signal detection sensitivity in the acoustic signal detection field 9 has a non-uniform sensitivity distribution, and the modulation of the laser beam 8 by the sound wave 20 output from the sound source 19 is performed around the ring-shaped region 11.

  Therefore, the detection area of the sound wave 20 can be made a limited space, and the number of operations of the sound wave 20 on the laser beam 8 can be efficiently performed without enlarging the acoustic signal detection field 9 that is an area for detecting the sound wave 20. Therefore, the detection sensitivity of the sound wave 20 in a limited space can be effectively increased.

  If the optical path of the laser beam 8 is substantially a star polygon when viewed from one direction, for example, in the Z-axis direction, which is the direction in which the sound waves 20 propagate, the presence or absence of crossing of the optical paths. Does not matter. Further, even if the optical paths of the laser beams 8 do not intersect at all on the same plane, the same effect can be obtained if they are different by a sufficiently small distance with respect to the wavelength of the sound wave 20 to be detected.

  Next, the incident angle of the laser beam on the cylindrical mirror will be described. 2A and 2B are top views showing optical paths of a star-shaped polygon formed in a cylindrical mirror. FIG. 2A shows a case where the incident angle ∠A is 12 degrees, and FIG. 2B shows a case where the incident angle ∠A is 24 degrees. (C) The incident angle ∠A is 48 degrees.

  As described above, the incident angle ∠A to the cylindrical mirror 4 is defined as an angle formed by the laser beam 8 and the normal line at the intersection of the circle inscribed in the mirror surface 4 m of the cylindrical mirror 4 and the laser beam 8. As shown in FIG. 2, the shape of the star-shaped polygonal optical path pattern of the laser beam 8 formed in the acoustic signal detection field 9 changes according to the incident angle of the laser beam 8, and in a region where the optical path density is high. The diameter of a certain ring-shaped region 11 changes. Further, the detection directivity of the sound wave (acoustic signal) 20 can be changed by changing the diameter of the ring-shaped region 11.

  For example, as shown in FIG. 2A, when the incident angle is set so that the optical path is concentrated near the center of the acoustic signal detection field 9, the ring-shaped region 11 having high acoustic signal detection sensitivity is located near the center. As a result, the detection sensitivity of the peripheral region is lowered. Therefore, in the optical microphone 1, even when the sound wave 20 having a different phase is applied to the vicinity of the central portion and the peripheral portion of the acoustic signal detection field 9, the suppression effect is not significant, and the 8-shaped acoustic signal detection sensitivity. It becomes a near-bidirectional optical microphone with.

  In addition, as shown in FIGS. 2B and 2C, when the incident angle is set so that the optical path is concentrated on the peripheral portion of the acoustic signal detection field 9, a ring having high acoustic signal detection sensitivity in the peripheral portion. A region 11 is formed. In this case, when the sound source 19 is on the axis perpendicular to the optical path surface of the laser beam 8 forming the star polygon at the center of the star polygon, the sound wave 20 is phased at any part of the ring-shaped region 11 having high detection sensitivity. Since they are the same, the suppression effect does not occur. On the other hand, when the sound source 19 is located at a position away from the vertical axis, the ring-shaped region 11 with high detection sensitivity is modulated by the sound wave 20 having a different phase depending on the position. As a result, the optical microphone has a narrow directivity in both directions of the axis. Thus, in the optical microphone 1, the detection directivity of the sound wave can be changed by changing the incident angle of the laser beam 8 to the cylindrical mirror 4.

  Here, in the example shown in FIGS. 2A, 2 </ b> B, and 2 </ b> C, the number of reflections of the laser beam 8 is 29 times. When the cylindrical mirror 4 is replaced with the polygonal column mirror 14, it is preferable to use a mirror having a regular 30-side opening. In these examples, the number of modulations of the sound wave 20 with respect to the laser beam 8 is the same even if the incident angle is changed, and the acoustic signal detection sensitivity is kept substantially the same even if the detection directivity is changed.

  The incident angles at which the number of reflections is the same are 9 degrees, 27 degrees, and 63 degrees at which the laser beam 8 is reflected 19 times on the inner wall of the cylindrical mirror 4, and 7.5 degrees and 37.5 degrees at which the laser beam 8 is reflected 23 times. , 52.5 degrees, and many combinations such as 5 degrees, 25 degrees, 35 degrees, and 55 degrees reflecting 35 times.

  As described above, in the optical microphone of the present invention, the directivity can be changed without changing the detection sensitivity of the sound wave by switching a plurality of incident angles having the same number of reflections.

  Also, by changing the diameter of the cylindrical mirror 4, the size of the acoustic signal detection field 9 and the diameter of the optical path of the star polygon can be changed. If a large cylindrical mirror is used, super directivity ( It is also possible to obtain a very sharp directivity).

  FIGS. 3A and 3B are configuration diagrams showing a state in which the sound concentrator is attached to the optical microphone, where FIG. 3A is a top view, FIG. 3B is a cross-sectional view taken along line AA ′ in FIG. 3A, and FIG. FIG. 3 (A) is a cross-sectional view taken along the line BB ′, and FIG. As shown in FIG. 3, the horn 21 that is an acoustic concentrator (sound concentrating means) has a cylindrical outer shape, a circular opening 21ma called a throat is formed on one plane 21m, and the other plane 21n has a circular opening 21ma. A circular opening 21na called a mouth having a diameter larger than the throat 21ma is formed, and a trumpet-shaped through hole 21a having a paraboloid 21h connecting both the openings 21ma and 21na is formed around the axis of the cylinder. ing. The diameters of the flat surfaces 21m and 21n of the horn 21 are substantially the same as or slightly larger than the diameter of the opening surface 4f of the cylindrical mirror 4. Further, the horn 21 is disposed so as to cover the entire opening surface 4f of the cylindrical mirror 4 of the optical microphone 1 with one plane (bottom surface) 21m. Furthermore, the throat 21ma of the horn 21 has a diameter substantially the same as or slightly larger than the outer diameter of the ring-shaped region 11 which is a region having a high optical path density formed in the acoustic signal detection field 9 of the cylindrical mirror 4. It is formed at a position facing the region 11.

  As shown in FIG. 3, for example, in the optical microphone 1, the sound wave 20 output from the sound source 19 installed in front of the opening surface 4 f of the cylindrical mirror 4 is amplified in amplitude when passing through the horn 21, The signal detection field 9 reaches the central region 10 and the ring-shaped region 11. The sound wave 20 passes through the ring-shaped region 11 and modulates the laser beam 8.

  Thus, by attaching the horn 21 to the cylindrical mirror 4 of the optical microphone 1, the sound wave 20 is concentrated on the ring-shaped region 11 where the optical path density of the laser beam 8 in the acoustic signal detection field 9 is high, thereby generating a strong sound field. Therefore, compared with the case where the horn 21 is not attached to the cylindrical mirror 4, the sound wave can be detected efficiently. In addition, the generation of the suppression effect can be further reduced, and the sound wave detection sensitivity can be increased.

  In addition, the horn 21 attached to the cylindrical mirror 4 is different in shape depending on the characteristics of the sound wave detected by the optical microphone 1 and the position of the sound source 19, so that the detection sensitivity and directivity of the optical microphone 1 are used. Can be changed. For example, the detection sensitivity and directivity of the optical microphone 1 can be changed by changing the paraboloid 21h in the through hole 21a of the horn 21 to a shape such as a conical shape, an elliptical cone shape, or a polygonal pyramid shape.

  The outer shape of the horn 21 is not limited to a cylindrical shape, and for example, the outer shape may be a trumpet type or a conical type. As shown in FIG. 2, the ring-shaped region 11 formed by the laser beam 8 in the optical microphone 1 has a diameter that matches the incident angle of the laser beam 8.

  4A and 4B are diagrams showing a configuration in which two horns are attached to an optical microphone. FIG. 4A is a top view, and FIG. 4B is a cross-sectional view taken along line AA ′ in FIG. The cylindrical mirror 4 of the optical microphone 1 includes two opening surfaces 4f and 4n, and the optical microphone 1 can detect sound waves propagated from both surfaces. Therefore, as shown in FIG. 4, the detection sensitivity and directivity of the sound wave propagating from the two directions are improved by providing the horns 21 so as to cover the entire opening surfaces 4f and 4n of the cylindrical mirror 4, respectively. be able to. Moreover, as the horn 21 attached to the two opening surfaces 4f and 4n of the cylindrical mirror 4, by attaching each of the horns 21 having different detection sensitivity and directivity characteristics, an optical microphone having directivity in two directions, An optical microphone having different detection sensitivity and directivity in each direction can be provided.

  Next, another embodiment of the acoustic concentrator will be described. As described with reference to FIG. 3, in the optical microphone 1 of the above embodiment, by using the horn 21 having the through hole 21 a that matches the size of the ring-shaped region 11 formed by the laser beam 8, the sound wave can be efficiently generated. Is detected.

  Furthermore, in this embodiment, a horn 21 having a throat 21 ma slightly larger than the outer diameter of the ring-shaped region 11 is provided on the opening surface 4 f of the cylindrical mirror 4, and an ellipse whose bottom surface 22 t is slightly smaller than the inner diameter of the ring-shaped region 11. By providing a parabolic equalizer 22 at the center of the horn 21 so as to penetrate the throat 21ma, the sound wave 20 is more efficiently applied to the ring-shaped region 11 formed in the acoustic signal detection field 9. You can concentrate well. Further, the diameter of the throat 21ma of the horn 21 and the equalizer 22 according to the incident angle of the laser beam 8 to the cylindrical mirror 4, that is, according to the shape of the star-shaped polygonal optical path pattern formed in the acoustic signal detection field 9. By changing the diameter of the bottom surface 22t, the sound wave 20 can be concentrated on the ring-shaped region 11 without passing through the central region 10 and the outer peripheral region 12.

  Specifically, the sound concentrator may be shaped as described below. FIG. 5 is a diagram showing the shapes of the horn and the equalizer corresponding to the optical path pattern of the laser beam. In FIG. 5, each figure is arranged in a matrix. When the first row (A) has an incident angle of 12 degrees, the second row (B) has an incident angle of 24 degrees, the third row. (C) shows the case where the incident angle is 48 degrees. In addition, the upper stage is a star-shaped polygonal optical path pattern of the laser beam formed in the acoustic signal detection field, the middle stage is a top view of the sound pressure concentrator, and the lower stage is a cross-sectional view of the acoustic concentrator and cylindrical mirror at AA ′. It is.

  The horn 21 and the equalizer 22 which are acoustic concentrators are disposed so as to face the opening surface 4f of the cylindrical mirror 4 and the centers of the horn 21 and the equalizer 22 are aligned with the center of the ring-shaped region 11, thereby improving the detection sensitivity in the acoustic signal detection field. The high ring-shaped region and the region where the sound pressure is increased by the horn 21 can be matched.

  Further, the equalizer 22 is preferably arranged so as to penetrate the acoustic signal detection field 9 of the cylindrical mirror 4. Thereby, it is possible to prevent the sound wave 20 concentrated in the vicinity of the ring-shaped region 11 from being diffracted into the non-light path region and the detection sensitivity of the sound wave 20 from being lowered.

  As described above, according to the optical microphone according to the embodiment of the present invention, even when there is a ring-shaped region having a high detection sensitivity in the acoustic signal detection field, the acoustic concentrator efficiently increases the detection sensitivity of the sound wave. An enhanced optical microphone can be obtained.

  Here, the laser beam patterns in the acoustic signal detection field at the three types of incident angles shown in FIG. 5 can be realized simply by adjusting the incident angle of the laser beam to the acoustic signal detection field in the optical microphone having the same structure. It is. Further, as shown in FIG. 5, if the angle of reflection of the laser beam 8 at each incident angle is selected to be substantially the same when the incident angle is changed, the respective detection sensitivities can be made comparable. Therefore, the design of the acoustic concentrator is not limited from the cylindrical mirror 4 side of the optical microphone except for the diameter of the throat 21ma of the horn 21 and the diameter of the bottom surface 22t of the equalizer 22, and the aperture ratio and paraboloid of the horn 21 are not limited. The curvature of the curve and the shape of the equalizer 22 can be designed with a high degree of freedom. For this reason, it is possible to change the detection directivity characteristic by changing the horn 21 and the equalizer 22 and adjusting the incident angle of the laser beam 8 with almost no change in the structure and sensitivity of the entire optical microphone 1. Thus, according to the optical microphone of the present invention, the directivity can be changed with a high degree of freedom.

It is a block diagram which shows the outline of the optical microphone which concerns on embodiment of this invention. It is a top view which shows the optical path of the star-shaped polygon formed in the cylindrical mirror. It is a block diagram which shows the state which attached the acoustic concentrator to the optical microphone. It is a figure which shows the structure which attached two horns to the optical microphone. It is the figure which showed the shape of the horn and equalizer according to the optical path pattern of a laser beam.

Explanation of symbols

1-Optical microphone 2-Laser light generation unit 3-Light source lens unit 4-Cylinder mirror 5-Detection system lens unit 6-Photoelectric conversion unit 7-Laser beam 8-Laser beam 9-Acoustic signal detection field 10-Center region 11 -Ring region 12-Peripheral region 14-Polygonal prism 19-Sound source 20-Sound wave 21-Horn 22-Equalizer

Claims (2)

A light beam output means for outputting a light beam;
The light beam output from the light beam output means is reflected a plurality of times to form an optical path whose shape when viewed from one direction is a star polygon, and an acoustic signal detection field that is an area including this optical path is defined as the optical path. Is formed by a central region where no sound is present, a ring-shaped region having a high optical path density outside the central region and a high acoustic signal detection sensitivity, and a region having a low acoustic detection sensitivity outside and passing through the acoustic signal detection field. Optical path forming means for modulating the light beam of the star-shaped polygon with sound waves to
A sound wave concentrating means for concentrating the sound wave passing through the acoustic signal detection field in a circular shape or an annular shape and guiding it within the ring-shaped region;
A light beam detecting means for detecting a modulation amount of the light beam emitted from the optical path forming means and outputting an electrical signal corresponding to the modulation amount;
Optical microphone with   The optical microphone according to claim 1, wherein the sound wave concentration means includes a horn or a horn and an equalizer.

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