WO2012127808A1 - 光マイクロホン - Google Patents
光マイクロホン Download PDFInfo
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- WO2012127808A1 WO2012127808A1 PCT/JP2012/001675 JP2012001675W WO2012127808A1 WO 2012127808 A1 WO2012127808 A1 WO 2012127808A1 JP 2012001675 W JP2012001675 W JP 2012001675W WO 2012127808 A1 WO2012127808 A1 WO 2012127808A1
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- WIPO (PCT)
- Prior art keywords
- light wave
- order diffracted
- wave
- diffracted light
- photoelectric conversion
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R23/00—Transducers other than those covered by groups H04R9/00 - H04R21/00
- H04R23/008—Transducers other than those covered by groups H04R9/00 - H04R21/00 using optical signals for detecting or generating sound
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
Definitions
- the present application relates to an optical microphone that receives an acoustic wave propagating in a gas such as air and converts the received acoustic wave into an electric signal using the light wave.
- a microphone is known as a device that receives a sound wave and converts it into an electric signal.
- Many microphones represented by dynamic microphones and condenser microphones have a diaphragm. In these microphones, sound waves are received by vibrating the diaphragm, and the vibrations are taken out as electrical signals. Since this type of microphone has a mechanical vibration part, there is a possibility that the characteristics of the mechanical vibration part may be changed by repeatedly using the microphone many times. Further, if a very powerful sound wave is detected by the microphone, the vibration part may be destroyed.
- Patent Document 1 and Patent Document 2 do not have a mechanical vibration part, and an acoustic wave is generated by using a light wave.
- An optical microphone for detection is disclosed.
- Patent Document 1 discloses a method of detecting an acoustic wave by modulating light with an acoustic wave and detecting a modulation component of the light. Specifically, as shown in FIG. 29, laser light shaped using the output optical component 111 is applied to the acoustic wave 1 propagating in the air to generate diffracted light. At this time, two diffracted light components whose phases are inverted from each other are generated. After adjusting the diffracted light by the light receiving optical component 112, only one of the two diffracted light components is received by the photodiode 113 and converted into an electric signal to detect the acoustic wave 1.
- Patent Document 2 discloses a method of detecting an acoustic wave by propagating the acoustic wave in the medium and detecting a change in the optical characteristics of the medium.
- the acoustic wave 1 propagating in the air is taken in from the opening 201 and travels through the acoustic waveguide 202 in which at least a part of the wall surface is formed from the photoacoustic propagation medium unit 203.
- a sound wave traveling through the acoustic waveguide 202 is taken into the photoacoustic propagation medium unit 203 and propagates therethrough.
- the refractive index changes with the propagation of the sound wave.
- Patent Document 2 discloses that the acoustic wave in the waveguide can be taken into the photoacoustic propagation medium unit 203 with high efficiency by using silica dry gel as the photoacoustic propagation medium unit 203.
- a laser Doppler vibrometer is used.
- the laser Doppler vibrometer is large because it requires a complex optical system including an optical frequency shifter such as an acousto-optic element and a large number of mirrors, beam splitters, lenses, and the like. For this reason, there exists a subject that the whole measuring apparatus disclosed by patent document 2 will become large.
- An object of the present application is to solve at least one of the problems of the prior art and to provide an optical microphone in which the frequency dependence of the acoustic wave of sensitivity is suppressed.
- the optical microphone disclosed in the present application is an optical microphone that detects an acoustic wave propagating through an environmental fluid using a light wave, and the propagation medium unit that propagates the acoustic wave and the propagation medium unit that propagates in the propagation medium unit.
- a light source that emits a light wave that passes through the propagation medium part across the acoustic wave, a reflection part that retroreflects the light wave that has passed through the propagation medium part, reflected by the reflection part, and transmitted through the propagation medium part
- a photoelectric conversion unit that receives the light wave and outputs an electrical signal, wherein the light wave emitted from the light source passes through the propagation medium unit and is generated along with the propagation of the acoustic wave in the propagation path.
- a 0th-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated by the refractive index distribution, and the 0th-order diffracted light wave generated in the forward path is reflected by the reflection unit to A zero-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated by a refractive index distribution of the propagation medium portion generated along with the propagation of the acoustic wave in the return path that passes through the carrying medium portion, and the photoelectric conversion
- the interference light between the + 1st order diffracted light wave generated on the forward path and the -1st order diffracted light wave generated on the return path, and the + 1st order generated on the -1st order diffracted light wave generated on the forward path and the return path At least one of the interference light with the folding light wave is detected.
- an optical microphone having a small and simple structure can be realized. Further, by retroreflecting the light wave transmitted through the propagation medium part, the light wave is transmitted through the propagation medium part in the forward path and the return path, and the + 1st order diffracted light wave generated in the forward path and the ⁇ 1st order diffracted light wave generated in the return path, or in the forward path
- the diffraction directions of the ⁇ 1st order diffracted light wave generated and the + 1st order diffracted light wave generated in the return path can be made the same. Therefore, the area of the portion where the two diffracted light waves overlap and interfere with each other can be made constant regardless of the frequency of the acoustic wave, and an optical microphone in which the sensitivity hardly varies depending on the frequency can be realized.
- (A)-(d) is a figure which shows a mode that a diffracted light wave produces
- FIG. 1A It is a figure which shows the example which used the reversal mirror as a reflection part in the optical microphone shown to FIG. 1A. It is a figure which shows the positional relationship of the diffracted light wave in the optical microphone shown to FIG. 1A.
- FIG. 1B is a diagram showing an example in which the 0th-order diffracted light wave is blocked and the diffracted light wave is received by a photoelectric conversion unit in the optical microphone shown in FIG. 1A.
- FIG. 1A it is a figure which shows the example which has arrange
- 1B is a diagram showing an example in which a light receiving lens system having an enlargement ratio distribution is arranged on a light receiving surface of a photoelectric conversion unit in the optical microphone shown in FIG. 1A.
- FIG. It is a figure which shows the diffracted light wave produced
- 1B is a diagram showing a diffracted light wave generated or observed in the return path of a light wave in the optical microphone shown in FIG. 1A.
- FIG. 1A It is a figure which shows the positional relationship when a 0th-order diffracted light wave and a 1st-order diffracted light wave interfere.
- (A) to (c) are output from the incident acoustic wave, the light wave detected by the photoelectric detector, the electrical signal output from the photoelectric detector, and the frequency converter in the optical microphone shown in FIG. 1A, respectively.
- (A)-(d) is a figure which shows a mode that a diffracted light wave produces
- (A) And (b) is a figure which shows the relationship between the propagation direction of an acoustic wave, and the diffraction direction of a light wave. It is a figure which shows the propagation medium part by which the propagation direction of the acoustic wave was restrict
- (A) is a figure which shows the structure of 4th Embodiment of the optical microphone by this invention
- (b) is a schematic diagram which shows the other form of a photoelectric conversion element array. It is a figure explaining the sound source localization using the optical microphone by 4th Embodiment. It is a figure which shows the structure of embodiment of the flaw detection apparatus by this invention. It is a figure which shows schematically the structure of the conventional optical microphone. It is a figure which shows the structure of the other conventional optical microphone.
- the optical microphone disclosed in the present application is an optical microphone that detects an acoustic wave propagating through an environmental fluid using a light wave, and the propagation medium unit that propagates the acoustic wave and the propagation medium unit that propagates in the propagation medium unit.
- a light source that emits a light wave that passes through the propagation medium part across the acoustic wave, a reflection part that retroreflects the light wave that has passed through the propagation medium part, reflected by the reflection part, and transmitted through the propagation medium part
- a photoelectric conversion unit that receives the light wave and outputs an electrical signal, wherein the light wave emitted from the light source passes through the propagation medium unit and is generated along with the propagation of the acoustic wave in the propagation path.
- a 0th-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated by the refractive index distribution, and the 0th-order diffracted light wave generated in the forward path is reflected by the reflection unit to A zero-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated by a refractive index distribution of the propagation medium portion generated along with the propagation of the acoustic wave in the return path that passes through the carrying medium portion, and the photoelectric conversion
- the interference light between the + 1st order diffracted light wave generated on the forward path and the -1st order diffracted light wave generated on the return path, and the + 1st order generated on the -1st order diffracted light wave generated on the forward path and the return path At least one of the interference light with the folding light wave is detected.
- the optical microphone further includes a beam splitter positioned between the light source and the propagation medium unit, and the beam splitter includes the + 1st order diffracted light wave generated by the forward path and the backward path, and A minus first-order diffracted light wave is emitted in a direction different from that of the light source.
- the reflecting portion has retroreflectivity in a plane including at least the propagation direction of the acoustic wave in the propagation medium portion and the propagation direction of the light wave emitted from the light source.
- the reflecting section is a reversal mirror, and the symmetry axis of the reversal mirror is perpendicular to the propagation direction of the acoustic wave and the propagation direction of the light wave.
- the reflecting portion is a corner cube mirror.
- the photoelectric conversion unit has a light receiving surface, and the photoelectric conversion unit generates the 0 0 generated in the return path so that the 0th-order diffracted light wave generated in the return path does not enter the light receiving surface.
- the second diffracted light wave is arranged shifted in a predetermined direction.
- the photoelectric conversion unit has a light receiving surface
- the optical microphone is configured such that the 0th-order diffracted light wave generated in the return path is the light-receiving surface so that the 0th-order diffracted light wave does not enter the light-receiving surface.
- a light-shielding portion that shields the light from entering.
- the optical microphone further includes a light receiving lens system disposed on the propagation medium side with respect to the light shielding part on the return optical path and having a diverging action.
- the optical microphone further includes a light receiving lens system that is disposed closer to the propagation medium than the light blocking portion on the return optical path and has a distribution in which an enlargement ratio decreases from the center toward the outside.
- the propagation medium part is constituted by silica dry gel.
- the light wave is laser light.
- the optical microphone further includes a frequency conversion unit that converts the frequency of the electrical signal obtained by the photoelectric conversion unit to 1/2.
- the acoustic wave detection method disclosed in the present application is an acoustic wave detection method for detecting an acoustic wave propagating through an environmental fluid using a light wave, and the step (A) of propagating the acoustic wave in a propagation medium portion
- a light wave is transmitted across the acoustic wave propagating in the propagation medium portion, and a zero-order diffracted light wave, a + 1st order diffracted light wave, and a refractive index distribution of the propagation medium portion generated along with the propagation of the acoustic wave
- the reflected 0th-order diffracted light wave so as to cross the acoustic wave propagating through
- step (-1) for generating -1st order diffracted light wave, and interference between the + 1st order diffracted light wave generated in step (B) and retroreflected, and the -1st order diffracted light wave generated in step (D).
- the optical microphone disclosed in the present application is an optical microphone that detects an acoustic wave using a light wave, and crosses the propagation medium part in which the acoustic wave propagates and the acoustic wave that propagates in the propagation medium part.
- a light source that emits a light wave that passes through the propagation medium part, a reflection part that retroreflects the light wave that has passed through the propagation medium part, and the light wave that is reflected by the reflection part and transmitted through the propagation medium part
- a photoelectric conversion element array having a plurality of photoelectric conversion elements that output electrical signals, and the propagation that occurs with the propagation of the acoustic wave in the forward path through which the light wave emitted from the light source passes through the propagation medium section
- a zero-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated from the light wave by the refractive index distribution of the medium part, and the 0th-order diffracted light wave generated in the forward path is
- the 0th order diffracted light wave and the + 1st order diffraction are generated from the 0th order diffracted light in the forward path
- a light wave and a ⁇ 1st order diffracted light wave are generated, and the photoelectric conversion element array has a first interference obtained by interference between the + 1st order diffracted light wave generated in the forward path and the ⁇ 1st order diffracted light wave generated in the return path.
- At least one of a light wave and a ⁇ 1st order diffracted light wave generated on the forward path and a + 1st order diffracted light wave generated on the return path is a part of the plurality of photoelectric conversion elements. Detect with.
- the propagation direction of the acoustic wave is specified based on the position of the partial photoelectric conversion element that detects at least one of the first interference light wave and the second interference light wave in the photoelectric conversion element array. .
- the acoustic waves are separated and detected according to frequency by independently detecting at least one of the first interference light wave and the second interference light wave by the plurality of photoelectric conversion elements.
- each of the plurality of photoelectric conversion elements has a fan-shaped light receiving unit, and the light receiving unit has different orientations in a circle centered on a position irradiated with the 0th-order diffracted light wave on the return path.
- the acoustic wave propagation direction is specified by an orientation in the circle of the light receiving portions of the partial photoelectric conversion elements that are arranged and detect at least one of the first interference light wave and the second interference light wave.
- the propagation medium section is located in a direction perpendicular to the propagation direction of the light wave emitted from the light source from the azimuth of 180 ° or more around the point where the light wave intersects the vertical surface.
- each of the plurality of photoelectric conversion elements has a ring-shaped light receiving unit having an inner diameter and an outer diameter different from each other, and the light receiving unit of the plurality of photoelectric conversion elements is a zero-order diffracted light wave in the return path.
- the light receiving unit of the plurality of photoelectric conversion elements is a zero-order diffracted light wave in the return path.
- each of the plurality of photoelectric conversion elements has a light receiving portion, and the light receiving portion is arranged at least one dimension around a position irradiated with the 0th-order diffracted light wave on the return path, and At least one of the first interference light wave and the second interference light wave is independently detected by the plurality of photoelectric conversion elements.
- the acoustic wave is separated and detected in different frequency bands according to the size of the light receiving portions of the plurality of photoelectric conversion elements and the distance from the center.
- the light receiving unit is two-dimensionally arranged in the one-dimensional arrangement direction and in a direction non-parallel to the one-dimensional arrangement direction, and at least of the first interference light wave and the second interference light wave.
- the propagation direction of the acoustic wave is further specified by the azimuth around the center of the light receiving portions of the part of the photoelectric conversion elements that have detected one.
- each of the plurality of photoelectric conversion elements has a partial ring-shaped light receiving portion, and the light receiving portion has a radius within a circle centered on a position irradiated with the 0th-order diffracted light wave on the return path.
- the light receiving portion has a radius within a circle centered on a position irradiated with the 0th-order diffracted light wave on the return path.
- the acoustic wave is separated and detected according to frequency by two or more photoelectric conversion elements, and the propagation direction of the acoustic wave is specified from the circumferential direction around the center.
- the optical microphone further includes a light receiving lens system having a diverging action, which is provided closer to the propagation medium portion than the photoelectric conversion element array.
- the optical microphone further includes a light receiving lens system that is disposed closer to the propagation medium than the light blocking portion on the return optical path and has a distribution in which an enlargement ratio decreases from the center toward the outside.
- the propagation medium part is constituted by silica dry gel.
- the light wave is laser light.
- the optical microphone further includes a frequency conversion unit that converts the frequency of the electrical signal obtained by the photoelectric conversion element array to 1/2.
- the flaw detection apparatus disclosed in the present application emits a light wave that passes through the subject across a sound source that excites an acoustic wave in the subject and a reflected wave of the acoustic wave caused by a defect in the subject.
- a light source a reflection unit that retroreflects a light wave that has passed through the subject, a photoelectric unit that includes a plurality of photoelectric conversion elements that receive the light wave reflected by the reflection unit and pass through the subject and output an electrical signal.
- a zero-order diffracted light wave from the light wave due to the refractive index distribution of the object that occurs as the reflected wave propagates in the forward path through which the light wave emitted from the light source passes through the object.
- + 1st order diffracted light wave and ⁇ 1st order diffracted light wave are respectively generated, and the 0th order diffracted light wave generated in the forward path passes through the subject by reflection at the reflecting portion, and the anti-reflection
- a zero-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated from the 0th-order diffracted light in the forward path by the refractive index distribution of the subject generated along with wave propagation.
- At least one of the second interference light waves obtained by interference with the generated + 1st order diffracted light wave is detected by a part of the plurality of photoelectric conversion elements, and at least one of the first interference light wave and the second interference light wave
- the propagation direction of the reflected wave is specified based on the position in the photoelectric conversion element array of the part of the photoelectric conversion elements detected, and the first interference light wave and the photoelectric conversion element array are detected by the photoelectric conversion element array.
- the distance at which the reflected wave propagates through the subject is calculated from the time at which at least one of the second interference light waves is detected and the excitation time of the acoustic wave in the subject, and the specified propagation direction and the calculated
- the position of the defect in the subject is estimated from the distance.
- the acoustic wave detection method disclosed in the present application is an acoustic wave detection method for detecting an acoustic wave using a light wave, the step (A) of propagating the acoustic wave in the propagation medium section, and the propagation medium section.
- a light wave is transmitted so as to cross the acoustic wave propagating through the acoustic wave, and a 0th-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated by the refractive index distribution of the propagation medium portion generated along with the propagation of the acoustic wave.
- a propagation direction of the acoustic wave is specified based on a position in the photoelectric conversion element array of the partial photoelectric conversion elements detected by the element array and detecting at least one of the first interference light wave and the second interference light wave.
- Another acoustic wave detection method disclosed in the present application is an acoustic wave detection method for detecting an acoustic wave using a light wave, the step (A) of propagating the acoustic wave in a propagation medium section, and the propagation medium A light wave is transmitted across the acoustic wave propagating through the part, and a zero-order diffracted light wave, a + 1st-order diffracted light wave, and a ⁇ 1st-order diffracted light wave are generated by the refractive index distribution of the propagation medium part generated along with the propagation of the acoustic wave.
- a step (B) for generating light waves a step (C) for retroreflecting the 0th-order diffracted lightwave, the + 1st-order diffracted lightwave and the ⁇ 1st-order diffracted lightwave generated in step (B), By transmitting the folding light wave so as to cross the acoustic wave propagating through the propagation medium portion, the + 1st order diffracted light wave and the ⁇ 1 next order are generated by the refractive index distribution of the propagation medium portion generated along with the propagation of the acoustic wave.
- FIG. 1A shows the configuration of the main part of the optical microphone 101 of this embodiment.
- the optical microphone 101 is a microphone that detects the acoustic wave 1 propagating through the environmental fluid as an electrical signal using the light wave 4.
- environmental fluid refers to a fluid existing in the external space of the optical microphone 101.
- the environmental fluid is air.
- the optical microphone 101 includes a propagation medium unit 2, a light source 3, a photoelectric conversion unit 5, and a reflection unit 6.
- the acoustic wave 1 propagating through the environmental fluid enters the propagation medium unit 2.
- the light wave 4 emitted from the light source 3 enters the propagation medium unit 2.
- the light wave 4 incident on the propagation medium part 2 passes through the propagation medium part 2, it acts on the acoustic wave 1 and reaches the reflection part 6.
- the light wave 4 is reflected by the reflecting portion 6 and enters the propagation medium portion 2 again.
- the light wave 4 incident on the propagation medium part 2 again passes through the propagation medium part 2 it reacts with the acoustic wave 1 again toward the light source 3.
- the optical microphone 101 may include a beam splitter 7 between the light source 3 and the propagation medium unit 2 in order to detect the light wave 4 transmitted through the propagation medium unit 2 twice by the photoelectric conversion unit 5.
- the light wave 4 enters the propagation medium unit 2 from the light source 3 via the beam splitter 7, is reflected by the reflection unit 6, then passes through the propagation medium unit 2 again and reaches the beam splitter 7.
- the light wave 4 that has reached the beam splitter 7 is reflected by the beam splitter 7 and enters the photoelectric conversion unit 5.
- the optical path where the light wave 4 emitted from the light source 3 reaches the propagation medium unit 2 and the optical path where the light wave 4 reaching the beam splitter 7 reaches the photoelectric conversion unit 5 can be adjusted in different directions. For this reason, the photoelectric conversion part 5 can be arrange
- the photoelectric conversion unit 5 can be disposed behind or around the light source 3.
- the projected area on the light receiving surface of the photoelectric conversion unit 5 of the light source 3 is made small so that the photoelectric conversion unit 5 can receive the light wave 4 with a sufficient amount of light, and the area where the light wave 4 is blocked is made as small as possible. May be.
- an isolator may be provided on the propagation medium portion 2 side of the light source in order to prevent the operation of the light source 3 from becoming unstable due to the reflected light entering the light source 3.
- the photoelectric conversion unit 5 outputs an electrical signal including a component having a frequency twice that of the acoustic wave 1. For this reason, as shown in FIG. 1A, the photoelectric conversion unit 5 is connected to the frequency conversion unit 21, and the frequency conversion unit 21 converts the frequency of the input signal to 1 ⁇ 2, thereby generating a component of the acoustic wave 1. An electrical signal containing is obtained.
- each component of the optical microphone 101 will be described specifically, and then the operation of the optical microphone 101 will be described.
- coordinates are set as shown in FIG. 1A. Specifically, the direction in which the acoustic wave 1 propagates is taken on the x axis, and the direction in which the light wave 4 propagates is taken on the z axis. Also, the direction orthogonal to the x-axis and z-axis is taken as the y-axis.
- the acoustic wave 1 that can be detected by the optical microphone 101 of the present embodiment is an audible wave or an ultrasonic wave of approximately 20 Hz to 20 MHz.
- the acoustic wave 1 may be a continuous wave whose frequency changes with time, such as voice or music, or may be a continuous wave of a single frequency sine wave. Alternatively, it may be a temporally discontinuous acoustic wave such as a single pulse burst signal.
- the acoustic wave 1 propagating through the environmental fluid is incident on the propagation medium section 2 and propagates in the x direction inside the propagation medium section 2 as shown in FIGS.
- the density of the material constituting the propagation medium portion 2 changes, and this causes a change in refractive index.
- the acoustic wave 1 is a longitudinal wave, the refractive index distribution is generated in the propagation direction (x-axis) of the acoustic wave 1. Almost no distribution occurs on the plane perpendicular to the propagation direction of the acoustic wave 1.
- the refractive index distribution of the propagation medium portion 2 generated by the acoustic wave 1 functions as a diffraction grating.
- the propagation medium part 2 is constituted by a solid propagation medium and may have a sound velocity smaller than that of air. Further, the light wave 4 emitted from the light source 3 may be translucent. Specifically, the sound speed of the propagation medium unit 2 may be smaller than 340 m / sec, which is the sound speed of air.
- a material having a low sound velocity has a relatively low density, so that reflection at the boundary between an environmental fluid such as air and the propagation medium unit 2 is small, and an acoustic wave is taken into the propagation medium unit 2 with relatively high efficiency. Can do.
- a silica dry gel may be used as the propagation medium of the propagation medium unit 2.
- the silica dry gel has the property that the difference in acoustic impedance with air is small, and the acoustic wave 1 propagating in the air can be efficiently taken into the propagation medium portion 2 composed of the silica dry gel.
- the sound velocity of the silica dry gel is 50 m / sec or more and 150 m / sec or less, smaller than the sound velocity in air, 340 m / sec, and the density is as small as about 70 kg / m 3 or more and 280 kg / m 3 .
- the acoustic wave in air can be taken in efficiently inside.
- silica dry gel having a sound velocity of 50 m / sec and a density of 100 kg / m 3 is used, the reflection at the interface with air is 70%, and about 30% of the energy of the acoustic wave is not reflected at the interface and enters the inside. It is captured. Further, this silica dry gel has a feature that the refractive index change amount ⁇ n of the light wave is large.
- the refractive index change ⁇ n of air is 2.0 ⁇ 10 ⁇ 9 for a sound pressure change of 1 Pa, whereas the refractive index change ⁇ n for a 1 Pa sound pressure change of the silica dry gel is 1.0. ⁇ 10 -7 and so on. Therefore, sufficient sensitivity can be obtained without preparing a large propagation medium exceeding 10 cm.
- the light source 3 emits a light wave 4, and the emitted light wave 4 passes through the propagation medium unit 2 as shown in FIGS. 1A, 1B and 2 (a) to 2 (d).
- the wavelength and intensity of the light wave 4 are not particularly limited, and a wavelength and intensity at which the photoelectric conversion unit 5 can detect the light wave 4 with good sensitivity are selected. However, a wavelength that is not so much absorbed by the propagation medium unit 2 may be selected.
- the light wave 4 may be coherent light or incoherent light. However, when coherent light such as laser light is used, diffracted light waves are more likely to interfere with each other and signals can be extracted more easily.
- the diameter of the light wave 4 is, for example, not less than 0.01 mm and not more than 20 mm.
- An optical path through which the light wave 4 emitted from the light source 3 passes through the propagation medium unit 2 is referred to as a forward path.
- the light wave 4 emitted from the light source 3 enters the propagation medium unit 2 and acts on the acoustic wave 1 in the propagation medium unit 2 as shown in FIG. Specifically, due to the propagation of the acoustic wave 1, a density distribution of the propagation medium is generated in the propagation medium unit 2, and a refractive index distribution of the propagation medium is generated thereby.
- the refractive index distribution of the propagation medium functions as a diffraction grating for the light wave 4 and diffracts the light wave 4. For this reason, as shown in FIG.
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c of the light wave 4 by the acoustic wave 1 are generated.
- the 0th-order diffracted light wave 4 a that travels straight in the direction of incidence without being diffracted by the acoustic wave 1 is also emitted from the propagation medium portion 2.
- the refractive index distribution moves with the propagation of the acoustic wave 1, the frequency of the diffracted light wave is shifted by the Doppler effect.
- the propagation directions of the + 1st order diffracted light wave 4 b and the ⁇ 1st order diffracted light wave 4 c are located on a plane including the propagation direction of the light wave 4 emitted from the light source 3 and the propagation direction of the acoustic wave 1.
- the propagation directions of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c form angles ⁇ and ⁇ , respectively, with respect to the 0th order diffracted light wave 4a on this plane.
- the phases of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c are inverted from each other.
- the angle is based on the propagation direction of the light wave 4 toward the reflecting portion 6 and the angle in the positive direction of the X axis is positive.
- the + 1st order diffracted light wave 4b is diffracted in the positive direction of the x axis at an angle ⁇ with respect to the 0th order diffracted light wave 4a
- the ⁇ 1st order diffracted light wave 4c is the 0th order diffracted light wave. Diffracts in the negative x-axis direction at an angle - ⁇ with respect to 4a. If the sound pressure of the acoustic wave 1 propagating through the environmental fluid is large enough to be measured by a normal microphone, the diffracted light wave produced is dominated by the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c.
- the diffracted light wave beyond the next order is negligible.
- the sound pressure of the acoustic wave 1 it may be considered that a second-order or higher order diffracted light component is generated.
- the second or higher order diffracted light component may be optically or electrically removed.
- the propagation direction of the light wave 4 and the propagation direction of the acoustic wave 1 are not parallel, that is, the acoustic wave 1 may propagate so as to cross the light wave 4.
- the propagation direction of the acoustic wave 1 and the propagation direction of the light wave 4 are perpendicular to the xz plane, the highest diffraction efficiency is obtained and the sensitivity as a microphone is increased.
- the reflection unit 6 retroreflects the light wave 4. Retroreflection means that incident light is reflected in the same direction as the incident direction. That is, the incident direction of the light wave 4 incident on the reflecting portion 6 is parallel to the emitting direction of the light wave 4 reflected and emitted from the reflecting portion 6. By using the reflection part 6 that retroreflects, the light wave 4 can be reflected and transmitted through the propagation medium part 2 twice.
- the + 1st order diffracted light wave (or ⁇ 1st order diffracted light wave) generated when the light is transmitted through the propagation medium part 2 for the first time (return path) by retroreflection can be reflected in the same direction as the incident direction.
- the + 1st order diffracted light wave (or ⁇ 1st order diffracted light wave) generated in the forward path and the ⁇ 1st order diffracted light wave (or + 1st order diffracted light wave) generated in the second pass through the propagation medium section 2 (return path)
- the diffraction directions of the two diffracted light waves can be made coincident with each other, and a substantially constant intensity interference light wave can be obtained regardless of the frequency change of the acoustic wave.
- the optical axis of the 0th-order diffracted light wave 4 a emitted from the reflecting unit 6 may be coincident with the optical axis of the 0th-order diffracted light wave 4 a that is transmitted through the propagation medium unit 2 and incident on the reflecting unit 6.
- this allows the light wave 4 in the forward path and the 0th-order diffracted light wave 4 a in the return path to be affected at the same position from the acoustic wave 1 in the propagation medium section 2. Therefore, it is possible to suppress the time difference between the acoustic wave 1 that contacts the forward path and the return path, and to contact (act) the light wave 4 and the acoustic wave 1 twice at substantially the same time.
- the positions of the + 1st order diffracted light wave 4b and ⁇ 1st order diffracted light wave 4c emitted from the reflecting unit 6 are the same as the 0th order diffracted light wave 4a emitted from the reflecting unit 6. In contrast, it is reversed. Specifically, the + 1st-order diffracted light wave 4b incident on the reflection unit 6 is positioned on the positive side of the x axis with respect to the light wave 4 incident on the reflection unit 6, but is emitted from the reflection unit +1. The next-order diffracted light wave 4b is located on the negative side of the x-axis with respect to the 0th-order diffracted light wave 4a emitted from the reflecting portion 6.
- the ⁇ 1st-order diffracted light wave 4c incident on the reflecting portion 6 is located on the negative side of the x-axis with respect to the light wave 4 incident on the reflecting portion 6, whereas it is emitted from the reflecting portion ⁇ 1.
- the next-order diffracted light wave 4c is located on the positive side of the x axis with respect to the 0th-order diffracted light wave 4a emitted from the reflecting portion 6.
- the + 1st order diffracted light wave 4b incident on the reflection unit 6 propagates in the positive region of the x axis
- the + 1st order diffracted light wave 4b emitted from the reflection unit 6 is x Propagates the negative region of the axis.
- the ⁇ 1st order diffracted light wave 4c incident on the reflecting portion 6 propagates in the negative region of the x axis
- the ⁇ 1st order diffracted light wave 4c emitted from the reflecting portion 6 propagates in the positive region of the x axis.
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c are diffracted by the angle ⁇ with respect to the 0th order diffracted light wave 4a and propagate.
- the distance between the propagation medium unit 2 and the reflection unit 6 is L1
- the + 1st order diffracted light wave 4b is L1 ⁇ ⁇ from the 0th order diffracted light wave 4a in the positive direction of the x axis.
- the ⁇ 1st-order diffracted light wave 4c is located away from the 0th-order diffracted light wave 4a by L1 ⁇ ⁇ in the negative x-axis direction.
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c reflected by the reflecting unit 6 may not be separated from the 0th order diffracted light wave 4a reflected by the reflecting unit 6.
- L1 may be small. More specifically, L1 may be 5 mm or less, for example. Further, the thickness of the propagation medium portion in the direction in which the light wave 4 is transmitted may be small.
- a corner cube mirror 8 shown in FIG. 3 can be used as the reflection unit 6, for example.
- the corner cube mirror 8 is a combination of three plane mirrors at a right angle.
- the incident light wave is reflected three times by the plane mirror, and the light wave is emitted in a direction parallel to the incident direction.
- FIG. 4 shows a state in which the light wave 4 is reflected on the xz section by the corner cube mirror 8.
- the corner cube mirror 8 is shown to have two orthogonal reflecting surfaces in the xz section.
- the 0th-order diffracted light wave 4a, the + 1st-order diffracted light wave 4b, and the -1st-order diffracted light wave 4c incident on the corner cube mirror 8 are reflected in the emission direction parallel to the incident direction. That is, as shown in FIG. 4, the + 1st order diffracted light wave 4 b incident on the corner cube mirror 8 and the 0th order diffracted light wave (z axis) form an angle ⁇ , and the + 1st order diffracted light wave emitted from the corner cube mirror 8. 4b also forms an angle ⁇ with the z-axis.
- the ⁇ 1st order diffracted light wave 4c incident on the corner cube mirror 8 and the z axis form an angle ⁇
- the ⁇ 1st order diffracted light wave 4c emitted from the corner cube mirror 8 also forms an angle ⁇ with the z axis. .
- the positional relationship of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c with respect to the 0th order diffracted light wave 4a is inverted in the x-axis direction, and the light wave 4 is inverted in the x-axis direction and reflected.
- the corner cube mirror 8 when the corner cube mirror 8 is used as the reflecting portion 6, the zero-order diffracted light wave 4a is applied to the vertex 6a where the three plane mirrors of the corner cube mirror 8 are combined, and the three sides gathered at the vertex 6a. May be incident at an angle of 45 °.
- the optical axis of the 0th-order diffracted light wave 4a incident on the corner cube mirror 8 and the optical axis of the 0th-order diffracted light wave 4a emitted from the corner cube mirror 8 can be matched.
- the + 1st-order diffracted light wave 4b incident on the corner cube mirror 8 propagates through the positive region of the x-axis and is emitted from the corner cube mirror 8 Propagates in the negative region of the x-axis.
- the ⁇ 1st order diffracted light wave 4c incident on the corner cube mirror 8 propagates in the negative region of the x axis
- the ⁇ first order diffracted light wave 4c emitted from the corner cube mirror 8 propagates in the positive region of the x axis.
- the corner cube mirror 8 has two orthogonal reflecting surfaces in the same manner as the xz cross section in every cross section including the yz cross section. Therefore, the corner cube mirror 8 emits the light wave 4 incident from an arbitrary direction in a direction parallel to the incident direction. Further, the positional relationship of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c with respect to the 0th order diffracted light wave 4a is inverted.
- the corner cube mirror 8 when used as the reflecting portion 6, not only when the acoustic wave 1 propagates in the x direction but also in any direction on the xy plane, the reflecting portion 6
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c are reflected in a reversed relationship with respect to the 0th order diffracted light wave 4a on a plane including the propagation direction of the light wave 4 incident on the sound wave and the propagation direction of the acoustic wave 1.
- the optical microphone 101 can detect the acoustic wave 1 regardless of the propagation direction of the acoustic wave 1.
- a reversal mirror 12 may be used as the reflection unit 6 as shown in FIG.
- the reversal mirror 12 has a structure in which two plane mirrors are joined so as to be orthogonal to each other, and inverts incident light in line symmetry with a line intersecting the two mirror surfaces as a symmetry axis 13.
- the symmetry axis 13 may be arranged so as to be perpendicular to the propagation direction of the acoustic wave 1 and the propagation direction of the light wave 4.
- the 0th-order diffracted light wave 4 a may be incident on the reversal mirror 12 on the symmetry axis 13. Accordingly, the 0th-order diffracted light wave 4a, the + 1st-order diffracted light wave 4b, and the ⁇ 1st-order diffracted light wave 4c incident on the reversal mirror 12 are reflected in the emission direction parallel to the incident direction, as described with reference to FIG.
- the positional relationship of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c with respect to the 0th order diffracted light wave 4a is inverted in the x-axis direction.
- a sound insulating portion 9 may be provided in a region other than the opening 10 where the acoustic wave 1 of the propagation medium portion 2 is incident. Thereby, it is possible to suppress the acoustic wave 1 propagating in a direction other than the x direction from entering the propagation medium unit 2.
- the sound insulating portion 9 is made of a transparent material such as acrylic or glass, or when a non-transparent material is used, the light transmitting portion 11 is formed by making a hole in a portion where the light wave 4 propagates as shown in FIG. May be provided.
- the light wave 4 reflected by the reflection unit 6 is incident on the propagation medium unit 2 again, and acts on the acoustic wave 1 in the propagation medium unit 2 to generate a diffracted light wave.
- the light wave 4 emitted from the reflection unit 6 includes a 0th-order diffracted light wave 4a, a + 1st-order diffracted light wave 4b, and a -1st-order diffracted light wave 4c, and these light waves act on the acoustic wave 1 to generate a diffracted light wave.
- the intensities of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c are small, the intensities of the diffracted light waves of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c are very small. Therefore, the diffracted light waves of the first-order diffracted light wave 4b and the ⁇ 1st-order diffracted light wave 4c can be ignored, and only the diffracted light wave of the 0th-order diffracted light wave 4a needs to be considered.
- the 0th-order diffracted light wave 4a reflected by the reflecting section 6 acts on the acoustic wave 1 in the propagation medium section 2, whereby the + 1st-order diffracted light wave 4d and the -1st-order diffracted light wave 4e. Produces.
- the + 1st order diffracted light wave 4d is diffracted in the positive direction of the x axis
- the ⁇ 1st order diffracted light wave 4e is diffracted in the negative direction of the x axis.
- the 0th-order diffracted light wave 4 a ′ that has not been diffracted is emitted from the propagation medium portion 2.
- FIG. 6 is a cross-sectional view of the light wave 4 immediately before entering the beam splitter 7 through the propagation medium portion 2 again when viewed in the negative direction from the positive z-axis direction in the xy cross section.
- the forward ⁇ 1st order diffracted lightwave 4c and the backward + 1st order diffracted lightwave 4d are positioned in the positive direction of the x axis, and the forward + 1st order diffracted lightwave is positioned in the negative direction of the x axis.
- the -1st order diffracted light wave 4e on the return path are located and overlap each other.
- the light waves interfere with each other, and the light intensity changes in accordance with the acoustic wave 1 signal.
- an acoustic signal 1 can be detected by obtaining an electrical signal corresponding to a change in light intensity.
- the phase of the + 1st order diffracted light wave and the ⁇ 1st order diffracted light wave by the diffraction grating are inverted, so that even if the + 1st order diffracted light wave and the ⁇ 1st order diffracted light wave overlap, The light waves cancel each other and no interference occurs.
- the forward -1st order diffracted light wave 4c incident on the photoelectric conversion unit 5 is reflected by the reflection unit 6, the phase is reversed at the time of reflection, and is in phase with the + 1st order diffracted light wave 4d on the return path. It has become.
- the -1st order diffracted light wave 4c on the forward path and the + 1st order diffracted light wave 4d on the return path overlap, so that an interference light wave is generated in the region 14a.
- the phase of the + 1st order diffracted light wave 4b in the forward path is also reversed in phase at the reflecting portion 6, and is in phase with the -1st order diffracted light wave 4e in the return path. By overlapping 4d, an interference light wave is generated in the region 14b.
- the acoustic wave 1 can be detected by receiving one or both of the interference light wave in the region 14a and the interference light wave in the region 14b by the photoelectric conversion unit 5. Both interference light waves may be detected from the viewpoint of increasing the amount of received light and increasing the detection sensitivity. However, if at least one interference light wave is received by the photoelectric conversion unit 5, the acoustic wave 1 can be detected. it can.
- the positions of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c generated in the forward path and reflected by the reflection unit 6 are +1 next time generated in the return path.
- the positions of the folding light wave 4d and the ⁇ 1st order diffracted light wave 4e are shifted. For this reason, the area where the diffracted light wave on the forward path and the diffracted light wave on the return path overlap is reduced, and the sensitivity for detecting the acoustic wave 1 is reduced.
- the distance L1 between the propagation medium unit 2 and the reflection unit 6 is small, the area where the diffracted light wave in the forward path and the diffracted light wave in the return path overlap increases, and the sensitivity for detecting the acoustic wave 1 increases.
- the 0th-order diffracted light wave 4 a ′ does not contribute to the detection of the acoustic wave 1. For this reason, it is not necessary to receive light by the photoelectric conversion unit 5.
- the 0th-order diffracted light wave 4a ′ is shifted in the positive z-axis direction so that the 0th-order diffracted light wave 4a ′ does not enter the light receiving surface 5a.
- the photoelectric conversion unit 5 may be arranged so that only the ⁇ 1st order diffracted light wave 4c and the + 1st order diffracted light wave 4d are incident on the light receiving surface 5a.
- the photoelectric conversion unit 5 may be shifted from the 0th order diffracted light wave 4a ′ in the negative z-axis direction. Good.
- only the 0th-order diffracted light wave 4 a ′ may be shielded by the light shielding unit 14, and the 0th-order diffracted light wave 4 a ′ may not be detected by the photoelectric conversion unit 5.
- a light receiving lens system 15 having a function of diverging light including a concave lens may be disposed on the light receiving surface 5 a of the photoelectric conversion unit 5.
- the difference in propagation angle between the 0th-order diffracted light wave 4a ′ and the + 1st-order diffracted light waves 4b and 4d and the ⁇ 1st-order diffracted light waves 4c and 4e can be increased. It becomes easy to do.
- the light receiving lens system 15 may include a lens having a distribution in which the enlargement ratio decreases from the center toward the outside.
- the light receiving lens system 15 is not provided. Good. In this case, since the light wave to be detected by the light receiving lens system does not spread, the light receiving surface of the photoelectric conversion unit 5 may be small.
- the velocity Vn of the acoustic wave 1 propagating through the propagation medium part 2 is reduced, so that a large diffraction angle can be obtained. Therefore, when separating the 0th-order diffracted light wave 4a ′, the + 1st-order diffracted lightwaves 4b and 4d, and the ⁇ 1st-order diffracted lightwaves 4c and 4e, the distance from the propagation medium unit 2 to the photoelectric conversion unit 5 is shortened. Can do.
- the electrical signal generated by the photoelectric conversion unit 5 has a frequency twice that of the acoustic wave 1. For this reason, when an electrical signal having the same frequency as that of the acoustic wave 1 is obtained, the frequency conversion unit 21 converts the frequency of the electrical signal output from the photoelectric conversion unit 5 to 1 ⁇ 2.
- the frequency conversion unit 21 for example, a frequency divider constituted by an electronic circuit or the like can be used.
- FIG. 11 schematically shows how the light wave 4 acts on the acoustic wave 1 in the propagation medium portion 2 in the forward path.
- the acoustic wave 1 propagates in the direction indicated by the arrow.
- the black portion representing the acoustic wave 1 indicates a portion where the propagation medium is dense due to the displacement of the propagation medium due to the acoustic wave 1, and the white portion indicates a portion where the propagation medium is rough.
- ⁇ represents the wavelength of the acoustic wave 1 propagating through the propagation medium section 2
- f represents the frequency of the acoustic wave 1
- ⁇ represents the wavelength of the light wave 4
- f 0 represents the frequency of the light wave 4.
- the light wave 4 propagates in the z-axis direction, the acoustic wave 1 propagates in the x-axis direction, and the direction in which the acoustic wave 1 propagates is the positive direction of the x-axis. Further, the distance that the light wave 4 propagates through the propagation medium portion 2 is assumed to be l.
- the propagation medium unit 2 is a diffraction grating having a refractive index change pattern with a period ⁇ .
- the light wave 4 When the light wave 4 is incident on the propagation medium portion 2 in such a state, a diffracted light wave is generated. At this time, in the case of the acoustic wave 1 having a sound pressure in a measurable range, the second or higher order diffracted light component is small and can be ignored.
- the acoustic wave 1 is compared with the 0th-order diffracted light wave 4a that is propagated in the z-axis direction without being diffracted and the 0th-order diffracted light wave 4a.
- the + 1st order diffracted light wave 4b and 0th order diffracted light wave 4a diffracted in the positive direction of the x-axis which is the propagation direction of -1 are diffracted in the negative direction of the x-axis which is the reverse direction of the propagation of the acoustic wave 1.
- Three diffracted light waves of the folding light wave 4c are emitted.
- the frequencies of the + 1st order diffracted light wave 4 b and the ⁇ 1st order diffracted light wave 4 c are subjected to Doppler shift by the acoustic wave 1.
- the frequency of the + 1st order diffracted light wave 4b subjected to Doppler shift is f 0 + f
- the frequency of the ⁇ 1st order diffracted light wave 4c is f 0 ⁇ f.
- Frequency of 0-order diffracted light wave 4a remains of f 0.
- the diffraction angle of the + primary diffracted light wave 4b and -1 order diffracted light wave 4c theta, intensity I 1 of the zero-order diffracted light waves 4a intensity I 0 and + 1st-order diffracted light wave 4b and -1 order diffracted light wave 4c has the following formula (1 ), (2) and (3).
- ⁇ is the wavelength of the light wave 4
- ⁇ is the wavelength of the acoustic wave 1
- f is the frequency of the acoustic wave 1 in the propagation medium section 2
- I in is the intensity of the light wave 4
- ⁇ n is the amount of change in the refractive index of the propagation medium part 2 due to the propagation of the acoustic wave 1 of 1 Pa
- P is the sound pressure of the acoustic wave
- l is the distance that the light wave 4 propagates through the propagation medium part 2
- J 0 is the 0th order Bessel function J 1 represents a first-order Bessel function.
- FIG. 12 schematically shows how the light wave 4 acts on the acoustic wave 1 in the propagation medium portion 2 in the return path.
- ⁇ represents the wavelength of the acoustic wave 1 propagating through the propagation medium section 2
- f represents the frequency of the acoustic wave 1
- ⁇ represents the wavelength of the light wave 4
- f 0 represents the frequency of the light wave 4.
- the light wave 4 propagates in the direction opposite to the z-axis direction.
- the frequencies of the + 1st order diffracted light wave 4d and the ⁇ 1st order diffracted light wave 4e are subjected to Doppler shift by the acoustic wave 1.
- the frequency of the diffracted light wave 4d subjected to the Doppler shift is f 0 + f
- the frequency of the diffracted light wave 4e is f 0 ⁇ f.
- the diffraction angle ⁇ of the + 1st order diffracted light wave 4d and the ⁇ 1st order diffracted light wave 4e is expressed by Expression (1). Further, 0-order diffraction intensity and + 1st-order diffracted light wave 4d and -1 order diffracted light wave 4e 'intensity I 0 of the' optical waves 4a I 1 'is expressed by the following equation (4) and (5).
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c reflected by the reflecting part 6 also enter the propagation medium part 2. Similar to the 0th-order diffracted light wave 4a, it is considered that a diffracted light wave is generated by the action of these diffracted light wave and the acoustic wave 1, but for the acoustic wave 1 having a sound pressure in the measurement range, the + 1st-order diffracted light wave 4b and The ⁇ first-order diffracted light waves respectively generated by diffracting the ⁇ 1st-order diffracted light waves 4c are extremely small in intensity and can be ignored.
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c propagate through the propagation medium section 2 at the same angle.
- the frequency of the + 1st order diffracted light wave 4b is f 0 + f
- the frequency of the ⁇ 1st order diffracted light wave 4c remains f 0 ⁇ f.
- FIG. 6 shows the positional relationship of each diffracted light wave.
- the + 1st order diffracted light wave 4b on the forward path and the ⁇ 1st order diffracted light wave 4e on the return path overlap and interfere
- the ⁇ 1st order diffracted light wave 4c on the forward path and the + 1st order diffracted light wave 4d on the return path overlap and interfere with each other.
- the + 1st order diffracted light wave 4b or + 1st order diffracted light wave 4d having a frequency of f 0 + f interferes with the ⁇ 1st order diffracted light wave 4c or ⁇ 1st order diffracted light wave 4e having a frequency of f 0 ⁇ f.
- interference light whose intensity changes at a frequency of 2f is generated.
- the diffraction angles ⁇ of the + 1st-order diffracted light wave 4b on the forward path and the -1st-order diffracted light wave 4e on the return path are both expressed by Expression (1).
- the diffraction angles ⁇ of the ⁇ 1st-order diffracted light wave 4c in the forward path and the + 1st-order diffracted light wave 4d in the return path are also expressed by Expression (1).
- the diffraction angle ⁇ of the + 1st order diffracted light wave 4b in the forward path and the diffraction angle ⁇ of the -1st order diffracted light wave 4e in the return path are the same according to the equation (1). It means that the area of two diffracted light waves that overlap and interfere with each other does not change. Similarly, the diffraction angle ⁇ of the -1st order diffracted light wave 4c on the forward path and the diffraction angle ⁇ of the + 1st order diffracted light wave 4d on the return path change in the same manner as the frequency f of the acoustic wave 1 changes.
- the optical microphone 101 having a substantially constant detection sensitivity is realized even if the frequency f of the acoustic wave 1 fluctuates.
- the intensities of the + 1st order diffracted light waves 4b and 4d and the ⁇ 1st order diffracted light waves 4c and 4e change according to the sound pressure P of the acoustic wave 1.
- the forward + 1st order diffracted light wave 4b and the backward -1st order diffracted light wave 4e (or the forward path).
- -1st order diffracted light wave 4c interferes with the return path + 1st order diffracted light wave 4d), and an interference component light wave whose intensity changes at frequency 2f is obtained.
- the intensity of the diffracted light wave in the forward path is different from that of the diffracted light wave, or a component that does not interfere with the diffracted light wave is included in the two diffracted light waves.
- a direct current component having a certain intensity is included.
- this interference component is photoelectrically converted by the photoelectric conversion unit 5 and then the direct current component is removed by a high-pass filter or the like, an electric signal having a frequency of 2f which is a difference frequency component is obtained. This is twice the frequency f of the acoustic wave 1 to be detected.
- the frequency conversion unit 21 converts the frequency of the signal output from the photoelectric conversion unit 5 to 1 ⁇ 2 times and outputs it. Thereby, the acoustic wave 1 is converted into an electric signal.
- FIG. 14B shows an example in which a large amount of DC component is mixed in the interference component of the light wave because the separation of the 0th-order diffracted light wave 4a ′ is insufficient.
- the maximum intensity of the light wave to be detected is within a range that does not exceed the maximum input level of the photoelectric conversion unit 5, it is converted into an electrical signal, and then the acoustic wave 1 is removed by removing the DC component with a high-pass filter or the like. An electric signal having the same frequency as can be obtained.
- the ratio of the component of the acoustic wave 1 in the optical signal detected by the photoelectric conversion unit 5 is relatively small with respect to the entire optical signal to be detected, the measurement accuracy is compared with that in the case of FIG. Then drop.
- the acoustic wave 1 can be detected by disposing an optical system that attenuates the amount of light waves including interference components, such as disposing an attenuator on the light receiving surface of the photoelectric conversion unit 5.
- the measurement accuracy is lower than in the case of FIG.
- the DC component in the light wave including the interference component due to the diffracted light wave obtained in the forward path and the return path is made as small as possible, and the range that does not exceed the maximum input level of the photoelectric conversion unit 5
- the acoustic wave 1 can be detected with high accuracy as shown in FIG.
- the acoustic wave is propagated to the propagation medium part through which the light wave is transmitted, and the transmitted light wave is retroreflected and transmitted again to the propagation medium part.
- the + 1st order diffracted light wave or the ⁇ 1st order diffracted light wave generated by acting on the acoustic wave in the forward path of the light wave, and the 1st order diffracted light wave or + 1st order diffracted light wave generated by acting on the acoustic wave in the return path Can interfere with each other and detect an interference component of a light wave having a frequency twice that of an acoustic wave.
- the + 1st-order diffracted light wave (or -1st-order diffracted light wave) in the forward path and the -1st-order diffracted light wave (or + 1st-order diffracted light wave) in the return path regardless of the frequency change of the acoustic wave Can be emitted in the same direction, the area where the two diffracted light waves overlap can be made almost constant, and an optical microphone can be obtained that can obtain a constant sensitivity regardless of the frequency of the acoustic wave 1 to be detected. To do.
- a small and simple optical microphone can be realized without using a special measuring instrument such as a laser Doppler vibrometer or an optical interferometer. can do.
- the optical microphone of Patent Document 1 and the method of Patent Document 2
- an acoustic wave can be detected, but the propagation direction of the acoustic wave is specified, or the acoustic wave is separated and detected according to the frequency.
- the optical microphone of the present embodiment is capable of at least one of specifying the propagation direction of acoustic waves and separating detection according to the frequency of acoustic waves.
- At least one of the first interference light wave and the second interference light wave is detected using a photoelectric conversion element array including a plurality of photoelectric conversion elements. For this reason, the direction of these interference light waves with respect to the detection position of the 0th-order diffracted light wave on the photoelectric conversion element array can be detected, and the propagation direction of the acoustic wave can be specified. Further, by detecting at least one of the first interference light wave and the second interference light wave independently with two or more photoelectric conversion elements arranged at different distances from the detection position of the 0th-order diffracted light wave, the frequency of the acoustic wave is determined. Separation detection can be performed.
- an optical microphone can be configured without using a complicated optical system such as a laser Doppler vibrometer or an interferometer, an optical microphone having a small and simple configuration can be realized.
- FIG. 15 shows the configuration of the main part of the optical microphone 102 of the second embodiment.
- the optical microphone 102 specifies the propagation direction of the acoustic wave 1 using the light wave 4. Further, the acoustic wave 1 may be detected as an electric signal.
- the acoustic wave 1 propagates through an environmental fluid such as air or a solid existing in the external space of the optical microphone 102.
- the optical microphone 102 includes a propagation medium unit 2, a light source 3, a photoelectric conversion element array 26 ⁇ / b> A, and a reflection unit 6.
- the acoustic wave 1 enters the propagation medium unit 2.
- the light wave 4 emitted from the light source 3 is incident on the propagation medium unit 2 and acts on the acoustic wave 1 when passing through the propagation medium unit 2 to reach the reflection unit 6.
- the light wave 4 is reflected by the reflection unit 6 and enters the propagation medium unit 2 again.
- the optical path from which the light wave 4 travels from the light source 3 to the reflection unit 6 is referred to as the forward path
- the optical path from the reflection unit 6 to the light source 3 refers to the return path.
- the optical microphone 102 may include a beam splitter 7 between the light source 3 and the propagation medium unit 2 in order to detect the light wave 4 transmitted twice through the propagation medium unit 2 by the photoelectric conversion element array 26A.
- the light wave 4 enters the propagation medium unit 2 from the light source 3 via the beam splitter 7, is reflected by the reflection unit 6, then passes through the propagation medium unit 2 again and reaches the beam splitter 7.
- the light wave 4 that has reached the beam splitter 7 is reflected by the beam splitter 7 and enters the photoelectric conversion element array 26A.
- the optical path where the light wave 4 emitted from the light source 3 reaches the propagation medium unit 2 and the optical path where the light wave 4 reaching the beam splitter 7 reaches the photoelectric conversion element array 26A can be adjusted in different directions. .
- the photoelectric conversion element array 26 ⁇ / b> A can be arranged in a different direction from the light source 3, and the detection of the light wave 4 becomes easy.
- the acoustic wave 1 propagating through the propagation medium unit 2 generates a density distribution of the propagation medium unit 2 that travels in the direction in which the acoustic wave 1 propagates (open arrow).
- This density distribution acts as a diffraction grating on the light wave 4 transmitted through the propagation medium portion 2, and ⁇ 1st order diffracted light waves are generated in the forward path and the return path of the light wave 4.
- the ⁇ first-order diffracted light wave is generated on a plane including the propagation direction of the light wave 4 and the propagation direction of the acoustic wave 1. Further, a 0th-order diffracted light wave that is not diffracted by the propagation medium unit 2 is also generated.
- the 0th-order diffracted light wave is incident again on the propagation medium unit 2 by the reflecting unit 6 and a ⁇ 1st-order diffracted light wave is generated again.
- the ⁇ first-order diffracted light waves generated in the forward path and the return path of the light wave 4 interfere with each other, and a first interference light wave 41 and a second interference light wave 42 are generated. Therefore, by detecting in which direction around the 0th-order diffracted light wave 4a the first interference light wave 41 and the second interference light wave 42 are generated using the photoelectric conversion element array 26A, the propagation direction of the acoustic wave Can be specified.
- the optical microphone 102 will be described for each component.
- coordinates are set as shown in FIG. Specifically, the direction in which the acoustic wave 1 propagates is taken on the x axis, and the direction in which the light wave 4 propagates is taken on the z axis.
- the plane on the light receiving portion of the photoelectric conversion element array 26A is taken as the x 'axis and the y' axis.
- the acoustic wave 1 that can be detected by the optical microphone 102 of the present embodiment is an audible wave or an ultrasonic wave of approximately 20 Hz to 20 MHz.
- the acoustic wave 1 may be a continuous wave whose frequency changes with time, such as voice or music, or may be a continuous wave of a single frequency sine wave. Alternatively, it may be a temporally discontinuous acoustic wave such as a single pulse burst signal.
- the acoustic wave 1 enters the propagation medium unit 2 from the environmental medium outside the optical microphone 102 and propagates through the propagation medium unit 2.
- FIG. 15 shows a state in which the acoustic wave 1 propagates in the positive direction of the x axis.
- the density of the material constituting the propagation medium portion 2 changes, and this causes a change in refractive index.
- the acoustic wave 1 is a longitudinal wave, the refractive index distribution is generated in the propagation direction (x-axis) of the acoustic wave 1. Almost no distribution occurs on the plane perpendicular to the propagation direction of the acoustic wave 1.
- the refractive index distribution of the propagation medium portion 2 generated by the acoustic wave 1 functions as a diffraction grating.
- the propagation medium part 2 is constituted by a solid propagation medium and may have a sound velocity smaller than that of air. Further, the light wave 4 emitted from the light source 3 may be translucent. Specifically, the sound speed of the propagation medium unit 2 may be smaller than 340 m / sec, which is the sound speed of air.
- a material having a low sound velocity has a relatively low density, so that reflection at the boundary between an environmental fluid such as air and the propagation medium unit 2 is small, and an acoustic wave is taken into the propagation medium unit 2 with relatively high efficiency. Can do.
- a silica dry gel may be used as the propagation medium of the propagation medium unit 2.
- the silica dry gel has the property that the difference in acoustic impedance with air is small, and the acoustic wave 1 propagating in the air can be efficiently taken into the propagation medium portion 2 composed of the silica dry gel.
- the sound velocity of the silica dry gel is 50 m / sec or more and 150 m / sec or less, smaller than the sound velocity in air, 340 m / sec, and the density is as small as about 70 kg / m 3 or more and 280 kg / m 3 .
- the acoustic wave in air can be taken in efficiently inside.
- silica dry gel having a sound velocity of 50 m / sec and a density of 101 kg / m 3 is used, the reflection at the interface with air is 70%, and about 30% of the energy of the acoustic wave is not reflected at the interface and enters the inside. It is captured. Further, this silica dry gel has a feature that the refractive index change amount ⁇ n of the light wave is large.
- the refractive index change ⁇ n of air is 2.0 ⁇ 10 ⁇ 9 for a sound pressure change of 1 Pa, whereas the refractive index change ⁇ n for a 1 Pa sound pressure change of the silica dry gel is 1.0. ⁇ 10 -7 and so on. Therefore, sufficient sensitivity can be obtained without preparing a large propagation medium exceeding 10 cm.
- the light source 3 emits a light wave 4, and the emitted light wave 4 passes through the propagation medium unit 2.
- the wavelength and intensity of the light wave 4 are not particularly limited, and a wavelength and intensity at which the photoelectric conversion element array 26A can detect the light wave 4 with good sensitivity are selected. However, a wavelength that is not so much absorbed by the propagation medium unit 2 may be selected.
- the light wave 4 may be coherent light or incoherent light. However, when coherent light such as laser light is used, diffracted light waves are more likely to interfere with each other and signals can be extracted more easily.
- the diameter of the light wave 4 is, for example, not less than 0.01 mm and not more than 20 mm.
- the light wave 4 emitted from the light source 3 enters the propagation medium part 2 in the forward path, and acts on the acoustic wave 1 in the propagation medium part 2 as shown in FIG. Specifically, due to the propagation of the acoustic wave 1, a density distribution of the propagation medium is generated in the propagation medium unit 2, and a refractive index distribution of the propagation medium is generated thereby.
- the refractive index distribution of the propagation medium functions as a diffraction grating for the light wave 4 and diffracts the light wave 4.
- FIG. 17 schematically shows how the light wave 4 acts on the acoustic wave 1 in the propagation medium portion 2 in the forward path.
- the acoustic wave 1 propagates in the direction indicated by the arrow.
- the black portion representing the acoustic wave 1 indicates a portion where the propagation medium is dense due to the displacement of the propagation medium due to the acoustic wave 1, and the white portion indicates a portion where the propagation medium is rough.
- ⁇ represents the wavelength of the acoustic wave 1 propagating through the propagation medium section 2
- f represents the frequency of the acoustic wave 1
- ⁇ represents the wavelength of the light wave 4
- f 0 represents the frequency of the light wave 4.
- the light wave 4 propagates in the z-axis direction, the acoustic wave 1 propagates in the x-axis direction, and the direction in which the acoustic wave 1 propagates is the positive direction of the x-axis. Further, the distance that the light wave 4 propagates through the propagation medium portion 2 is assumed to be l.
- the propagation medium unit 2 is a diffraction grating having a refractive index change pattern with a period ⁇ .
- the light wave 4 When the light wave 4 is incident on the propagation medium portion 2 in such a state, a diffracted light wave is generated. At this time, in the case of the acoustic wave 1 having a sound pressure in a measurable range, the second or higher order diffracted light component is small and can be ignored.
- the frequencies of the + 1st order diffracted light wave 4 b and the ⁇ 1st order diffracted light wave 4 c are subjected to Doppler shift by the acoustic wave 1.
- the frequency of the + 1st order diffracted light wave 4b subjected to Doppler shift is f 0 + f
- the frequency of the ⁇ 1st order diffracted light wave 4c is f 0 ⁇ f.
- Frequency of 0-order diffracted light wave 4a remains of f 0.
- the diffraction angle of the + primary diffracted light wave 4b and -1 order diffracted light wave 4c theta, intensity I 1 of the zero-order diffracted light waves 4a intensity I 0 and + 1st-order diffracted light wave 4b and -1 order diffracted light wave 4c has the following formula (1 ), (2) and (3).
- ⁇ is the wavelength of the light wave 4
- ⁇ is the wavelength of the acoustic wave 1
- f is the frequency of the acoustic wave 1
- C s is the propagation speed of the acoustic wave 1 in the propagation medium section 2
- I in is the intensity of the light wave 4
- ⁇ n is the amount of change in the refractive index of the propagation medium part 2 due to the propagation of the acoustic wave 1 of 1 Pa
- P is the sound pressure of the acoustic wave 1
- l is the distance that the light wave 4 propagates through the propagation medium part 2
- J 0 is the 0th order Bessel function J 1 represents a first-order Bessel function.
- Equation (3) the light intensities of the ⁇ first-order diffracted light waves 4b and 4c change according to the sound pressure of the acoustic wave 1.
- the directions in which the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c are generated are determined by the propagation direction of the acoustic wave 1 propagating through the propagation medium section 2. If the propagation direction of the acoustic wave 1 is the x-axis direction, the diffracted light waves 4b and 4c are generated in the x-axis direction as described above. For example, as shown in FIG. When propagating in a direction deviated from the x axis by an angle ⁇ in the xy plane perpendicular to the propagation direction z of the light wave 4, the diffracted light waves 4b and 4c are also deviated from the x axis by an angle ⁇ . To occur.
- the reflection unit 6 retroreflects the light wave 4.
- retroreflection means that incident light is reflected in the same direction as the incident direction. That is, the incident direction of the light wave 4 incident on the reflecting portion 6 is parallel to the emitting direction of the light wave 4 reflected and emitted from the reflecting portion 6.
- the + 1st order diffracted light wave (or ⁇ 1st order diffracted light wave) generated when the light is transmitted through the propagation medium unit 2 for the first time (outward path) can be reflected in the same direction as the incident direction. Therefore, the diffraction direction of the + 1st order diffracted light wave (or ⁇ 1st order diffracted light wave) generated in the forward path and the ⁇ 1st order diffracted light wave (or + 1st order diffracted light wave) generated when passing through the propagation medium unit 2 for the second time
- the two diffracted light waves can be obtained with a substantially constant intensity interference light wave regardless of the frequency change of the acoustic wave.
- the optical axis of the 0th-order diffracted light wave 4 a emitted from the reflecting unit 6 may be coincident with the optical axis of the 0th-order diffracted light wave 4 a that is transmitted through the propagation medium unit 2 and incident on the reflecting unit 6. That is, the reflection unit 6 may perform retroreflection with point symmetry with respect to the point where the 0th-order diffracted light wave 4 a is incident on the reflection unit 6.
- the light wave 4 in the forward path and the 0th-order diffracted light wave 4 a in the return path can be affected from the acoustic wave 1 in the propagation medium unit 2 at the same position. Therefore, it is possible to suppress the time difference between the acoustic wave 1 that contacts the forward path and the return path, and to contact (act) the light wave 4 and the acoustic wave 1 twice at substantially the same time.
- the positions of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c emitted from the reflecting part 6 by the retroreflection action of the reflecting part 6 are as follows. It is inverted with respect to the 0th-order diffracted light wave 4a emitted from. Specifically, the + 1st-order diffracted light wave 4b incident on the reflection unit 6 is positioned on the positive side of the x axis with respect to the light wave 4 incident on the reflection unit 6, but is emitted from the reflection unit +1.
- the next-order diffracted light wave 4b is located on the negative side of the x-axis with respect to the 0th-order diffracted light wave 4a emitted from the reflecting portion 6.
- the ⁇ 1st-order diffracted light wave 4c incident on the reflecting portion 6 is located on the negative side of the x-axis with respect to the light wave 4 incident on the reflecting portion 6, whereas it is emitted from the reflecting portion ⁇ 1.
- the next-order diffracted light wave 4c is located on the positive side of the x axis with respect to the 0th-order diffracted light wave 4a emitted from the reflecting portion 6.
- the + 1st order diffracted light wave 4b incident on the reflection unit 6 propagates in the positive region of the x axis
- the + 1st order diffracted light wave 4b emitted from the reflection unit 6 is x Propagates the negative region of the axis.
- the ⁇ 1st order diffracted light wave 4c incident on the reflecting portion 6 propagates in the negative region of the x axis
- the ⁇ 1st order diffracted light wave 4c emitted from the reflecting portion 6 propagates in the positive region of the x axis.
- the reflection unit 6 may be a corner cube mirror.
- the corner cube mirror is a combination of three plane mirrors at a right angle.
- the incident light wave is reflected three times by the plane mirror, and the light wave is emitted in a direction parallel to the incident direction.
- FIG. 18 shows a state in which the light wave 4 is reflected on the xz cross section by the reflecting portion 6 formed of a corner cube mirror.
- the corner cube mirror constituting the reflecting unit 6 is shown to have two orthogonal reflecting surfaces in the xz section.
- the 0th-order diffracted light wave 4a, the + 1st-order diffracted light wave 4b, and the -1st-order diffracted light wave 4c incident on the corner cube mirror (reflecting unit 6) are reflected in the emission direction parallel to the incident direction. That is, as shown in FIG. 18, the + 1st order diffracted light wave 4b incident on the corner cube mirror and the 0th order diffracted light wave (z axis) form an angle ⁇ , and the + 1st order diffracted light wave 4b emitted from the corner cube mirror is also It forms an angle ⁇ with the z axis.
- the ⁇ 1st order diffracted light wave 4c incident on the corner cube mirror and the z axis form an angle ⁇
- the ⁇ first order diffracted light wave 4c emitted from the corner cube mirror also forms an angle ⁇ with the z axis.
- the positional relationship of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c with respect to the 0th order diffracted light wave 4a is inverted in the x-axis direction, and the light wave 4 is inverted in the x-axis direction and reflected.
- the zero-order diffracted light wave 4a is 45 with respect to the three sides gathered at the vertex 6a at the vertex 6a where the three plane mirrors of the corner cube mirror are combined. It may be incident at an angle of °.
- the optical axis of the 0th-order diffracted light wave 4a incident on the corner cube mirror can be matched with the optical axis of the 0th-order diffracted light wave 4a emitted from the corner cube mirror.
- the + 1st-order diffracted light wave 4b incident on the corner cube mirror 8 propagates through the positive region of the x-axis and is emitted from the corner cube mirror 8 Propagates in the negative region of the x-axis.
- the ⁇ 1st order diffracted light wave 4c incident on the corner cube mirror 8 propagates in the negative region of the x axis
- the ⁇ first order diffracted light wave 4c emitted from the corner cube mirror 8 propagates in the positive region of the x axis.
- the corner cube mirror has two orthogonal reflecting surfaces in the same manner as the xz cross section in every cross section including the yz cross section. For this reason, the corner cube mirror emits the light wave 4 incident from an arbitrary direction in a direction parallel to the incident direction. Further, the positional relationship of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c with respect to the 0th order diffracted light wave 4a is inverted.
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c can be reflected in an inverted relationship with respect to the 0th order diffracted light wave 4a. it can.
- the light wave 4 reflected by the reflection unit 6 is incident on the propagation medium unit 2 again, and acts on the acoustic wave 1 in the propagation medium unit 2 to generate a diffracted light wave.
- the light wave 4 emitted from the reflection unit 6 includes a 0th-order diffracted light wave 4a, a + 1st-order diffracted light wave 4b, and a -1st-order diffracted light wave 4c, and these light waves act on the acoustic wave 1 to generate a diffracted light wave.
- the intensities of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c are smaller than the 0th order diffracted light wave 4a, and the diffracted light waves of the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c have further intensities. small. Therefore, the diffracted light waves of the first-order diffracted light wave 4b and the ⁇ 1st-order diffracted light wave 4c can be ignored, and only the diffracted light wave of the 0th-order diffracted light wave 4a needs to be considered.
- the 0th-order diffracted light wave 4a reflected by the reflecting section 6 acts on the acoustic wave 1 in the propagation medium section 2, whereby the + 1st-order diffracted light wave 4d and the ⁇ 1st-order diffracted light wave 4e. Produces.
- the + 1st order diffracted light wave 4d is diffracted in the positive direction of the x axis
- the ⁇ 1st order diffracted light wave 4e is diffracted in the negative direction of the x axis.
- the 0th-order diffracted light wave 4 a ′ that has not been diffracted is emitted from the propagation medium portion 2.
- FIG. 19 schematically shows how the light wave 4 acts on the acoustic wave 1 in the propagation medium portion 2 in the return path.
- ⁇ represents the wavelength of the acoustic wave 1 propagating through the propagation medium unit 2
- f represents the frequency of the acoustic wave 1
- ⁇ represents the wavelength of the light wave 4
- f 0 represents the frequency of the light wave 4.
- the light wave 4 propagates in the direction opposite to the z-axis direction.
- the frequencies of the + 1st order diffracted light wave 4d and the ⁇ 1st order diffracted light wave 4e are subjected to Doppler shift by the acoustic wave 1.
- the frequency of the diffracted light wave 4d subjected to the Doppler shift is f 0 + f
- the frequency of the diffracted light wave 4e is f 0 ⁇ f.
- the diffraction angles of the + 1st order diffracted light wave 4d and the ⁇ 1st order diffracted light wave 4e are expressed by Expression (1). Since the wavelength ⁇ of the 0th-order diffracted light wave 4a, the wavelength ⁇ of the acoustic wave 1, the frequency f of the acoustic wave 1, and the propagation speed C s of the acoustic wave 1 in the propagation medium part 2 do not change before and after the reflection at the reflecting unit 6. With respect to the 0th-order diffracted light wave 4a ′, the + 1st-order diffracted light wave 4d and the ⁇ 1st-order diffracted light wave 4e are diffracted at the same diffraction angles ⁇ and ⁇ .
- the diffraction angles of the + 1st order diffracted light wave 4b and -1st order diffracted light wave 4c generated in the forward path and the diffraction angles of the + 1st order diffracted light wave 4d and -1st order diffracted light wave 4e generated in the return path vary. These coincide with each other regardless of the frequency of the acoustic wave 1.
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c reflected by the reflecting unit 6 also enter the propagation medium unit 2. Similar to the 0th-order diffracted light wave 4a, it is considered that a diffracted light wave is generated by the action of these diffracted light wave and the acoustic wave 1, but for the acoustic wave 1 having a sound pressure in the measurement range, the + 1st-order diffracted light wave 4b and The ⁇ first-order diffracted light waves respectively generated by diffracting the ⁇ 1st-order diffracted light waves 4c are extremely small in intensity and can be ignored.
- the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c propagate through the propagation medium section 2 at the same angle.
- the frequency of the + 1st order diffracted light wave 4b is f 0 + f
- the frequency of the ⁇ 1st order diffracted light wave 4c remains f 0 ⁇ f.
- FIG. 20 shows the positional relationship among the + 1st order diffracted light waves 4b, 4d, the ⁇ 1st order diffracted light waves 4c, 4de and the 0th order diffracted light wave 4a ′ included in the light wave 4 in a cross section perpendicular to the propagation direction of the light wave 4. is there.
- the positional shift distance can be expressed as sin ⁇ ⁇ L2.
- the 0th-order diffracted lightwave 4a ′ and the + 1st-order diffracted lightwaves 4b and 4d and the ⁇ 1st-order diffracted lightwaves 4c and 4e are partially in the range of sin ⁇ ⁇ L2 ⁇ w. Overlapping. As will be described below, in the optical microphone 101, interference light waves generated in a region where the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4e overlap and a region where the + 1st order diffracted light wave 4d and the ⁇ 1st order diffracted light wave 4c overlap.
- the + 1st order diffracted light waves 4b, 4d and the ⁇ 1st order diffracted light waves 4c, 4e do not overlap with the 0th order diffracted light wave 4a ′ on the light receiving surface of the photoelectric conversion element array 26A, that is, sin ⁇ ⁇ L2 > W.
- the distance L2 may be sufficiently long. However, if L2 is lengthened, the optical mylophone 101 becomes larger.
- the optical microphone 102 may include a light receiving lens system 15 having a diverging action. By including the light receiving lens system 15, the + 1st order diffracted light waves 4b and 4d and the ⁇ 1st order diffracted light waves 4c and 4e can be separated from the 0th order diffracted light wave 4a ′ without lengthening L2.
- FIG. 21 shows the positional relationship between the + 1st order diffracted light waves 4b and 4d, the ⁇ 1st order diffracted light waves 4c and 4e, and the 0th order diffracted light wave 4a ′ included in the light wave 4 on the light receiving surface of the photoelectric conversion element array 26A. .
- the forward ⁇ 1st order diffracted lightwave 4c and the backward + 1st order diffracted lightwave 4d are positioned in the positive direction of the x axis, and the forward + 1st order diffracted lightwave is positioned in the negative direction of the x axis.
- 4b and the -1st order diffracted light wave 4e on the return path are located and overlap each other. In the overlapping region (shown by oblique lines), the light waves interfere with each other, and the first interference light wave 41 and the second interference light wave 42 whose light intensity changes according to the acoustic wave 1 signal are generated.
- the interference light wave has a frequency twice that of the acoustic wave 1 ((f 0 + f) ⁇ (f 0 ⁇ f)).
- the diffraction angle of the + 1st order diffracted light wave 4b generated in the forward path and the ⁇ 1st order diffracted light wave 4c generated in the return path, and the + 1st order diffracted light wave 4d generated in the return path and generated in the forward path ⁇ The diffraction angle of the first-order diffracted light wave 4 e changes and matches regardless of the frequency of the acoustic wave 1.
- the area where the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4c overlap and the area where the + 1st order diffracted light wave 4d and ⁇ 1st order diffracted light wave 4e overlap do not change even if the frequency of the acoustic wave 1 changes.
- the intensities of the first interference light wave 41 and the second interference light wave 42 are substantially constant regardless of the frequency of the acoustic wave 1. However, since the diffraction angle ⁇ changes according to the frequency f of the acoustic wave 1 as shown in the equation (1), the positions of the first interference light wave 41 and the second interference light wave 42 also change.
- the positional deviation distance D (distance between optical axes of the diffracted light wave) of the + 1st order diffracted light wave 4b generated on the forward path and the ⁇ 1st order diffracted light wave 4c generated on the return path, and the + 1st order diffracted light wave 4d generated on the return path and the forward path
- the distance D of the positional shift of the generated ⁇ 1st order diffracted light wave 4e is approximately 2 ⁇ sin ⁇ ⁇ L1 using the diffraction angle ⁇ and the distance L1 between the propagation medium section 2 and the reflection section 6 (FIG. 16A). It can be shown.
- the positional deviation distance D of the ⁇ 1st order diffracted light wave 4e generated in the forward path becomes large.
- the cross-sectional areas perpendicular to the propagation directions of the first interference light wave 41 and the second interference light wave are reduced, and the strengths of the first interference light wave 41 and the second interference light wave 42 are reduced.
- the sensitivity of the microphone 101 also decreases.
- the positional deviation D becomes larger than the spot diameter of the light wave 4c, no acoustic wave can be detected because no interference light wave is generated. Further, since the distance D also depends on the diffraction angle ⁇ , the distance D also increases depending on the wavelength of the light wave 4 and the wavelength of the acoustic wave 1. For this reason, the distance L between the propagation medium part 2 and the reflection part 6 may be made as small as possible, and the distance D may be made small.
- the optical microphone 102 of the present embodiment detects the direction in which the first interference light wave 41 and the second interference light wave 42 are emitted around the 0th-order diffracted light wave 4a ′ by the photoelectric conversion element array 26A.
- the propagation direction of the wave 1 is specified.
- a method for specifying the propagation direction of the acoustic wave 1 will be described with reference to FIG.
- the direction in which the light wave 4 propagates is defined as the z ′ axis, and the x ′ axis and the y ′ axis in the plane perpendicular to z ′. Determine.
- the x ′ axis and the y ′ axis are directions in which the x axis and the y axis are mapped onto the light receiving surface via the beam splitter 7.
- the directions in which the + 1st order diffracted light waves 4b and 4d and the ⁇ 1st order diffracted light waves 4c and 4e are generated are determined by the propagation direction of the acoustic wave 1. Therefore, when the acoustic wave 1 propagates in the x-axis direction, as shown in FIG. 22A, the first interference light wave 41 by the + 1st order diffracted light wave 4b and the ⁇ 1st order diffracted light wave 4e, and the + 1st order diffracted light wave.
- the second interference light wave 42 by the light wave 4d and the ⁇ 1st order diffracted light wave 4c is emitted to a position shifted with respect to the zeroth order diffracted light wave 4a in the negative and positive directions of the x ′ axis.
- the first interference light wave 41 and the second interference light wave 42 are x 'It appears at a position shifted in a direction rotated by an angle ⁇ from the axis.
- the photoelectric conversion element array 26A detects in which direction around the 0th-order diffracted light wave 4a ′ the first interference light wave 41 and the second interference light wave 42 are emitted, in which angle direction the acoustic wave 1 is It is possible to specify whether or not it is propagating.
- the photoelectric conversion element array 26A includes a plurality of photoelectric conversion elements 5a, 5b,... 5y, 5x.
- the number of photoelectric conversion elements 5a, 5b,... 5y, 5x is, for example, 24 as shown in FIG.
- Each photoelectric conversion element has a fan-shaped light receiving portion, and is arranged in different orientations around the position irradiated with the 0th-order diffracted light wave 4a '. If the central angle of the fan-shaped light receiving portion is 15 °, the photoelectric conversion elements are arranged in different orientations shifted by 15 ° around the position irradiated with the 0th-order diffracted light wave 4a ′.
- a circular light receiving surface can be formed as the entire array 26A.
- the first interference light wave 41 and the second interference light wave 42 irradiate the photoelectric conversion element array 26A, the first interference light wave 41 or the second interference among the plurality of photoelectric conversion elements 5a, 5b,.
- the photoelectric conversion element that receives the light wave 42 outputs an electrical signal. That is, some of the plurality of photoelectric conversion elements detect the first interference light wave 41 or the second interference light wave 42. Therefore, the first interference light wave 41 and the second interference light wave 42 depend on where the photoelectric conversion element that has detected the first interference light wave 41 or the second interference light wave 42 is located on the circular light receiving surface of the photoelectric conversion element array 26A. Can be specified by the photoelectric conversion element array 26A in which direction around the 0th-order diffracted light wave 4a ′.
- the xy coordinates in the propagation medium portion 2 correspond to the x′-y ′ coordinates on the light receiving surface of the photoelectric conversion element array 26A.
- the + 1st order diffracted light waves 4b and 4d and the ⁇ 1st order diffracted light waves 4c and 4e are diffracted in the propagation direction of the acoustic wave 1 in the xy coordinates of the propagation medium section 2, and therefore the diffracted light waves
- the emission directions of the first interference light wave 41 and the second interference light wave 42 with respect to the 0th-order diffracted light wave 4 a ′ also coincide with the propagation direction of the acoustic wave 1.
- the detection directions of the first interference light wave 41 and the second interference light wave 42 around the 0th-order diffracted light wave 4a ′ in the x′-y ′ coordinates of the light receiving surface of the photoelectric conversion element array 26A are set to xy of the propagation medium unit 2.
- the coordinates coincide with the propagation direction of the acoustic wave 1 with the light wave 4 as an axis. For this reason, it is detected by the photoelectric conversion element array 26A.
- the directions of the first interference light wave 41 and the second interference light wave 42 around the 0th-order diffracted light wave 4 a ′ coincide with the propagation direction of the acoustic wave 1 in the propagation medium portion 2. In this way, the propagation direction of the acoustic wave can be determined by the orientation of the photoelectric conversion element that has detected the first interference light wave 41 and the second interference light wave 42.
- the x axis is determined in an arbitrary direction on a plane perpendicular to the incident light wave 4, and the acoustic wave 1 is propagated in the determined x axis direction.
- a straight line connecting the first interference light wave 41 and the second interference light wave 42 irradiated on the light receiving surface of the conversion element array 26A can be determined as the x ′ axis.
- the x′-y ′ coordinates on the light receiving surface of the photoelectric conversion element array 26A are merely mapped by reflecting the xy coordinates in the propagation medium unit 2 with the beam splitter 7.
- the horizontal direction in the propagation medium unit 2 can be set as the x axis
- the horizontal direction of the light receiving surface of the photoelectric conversion element array 26A can be set as the x ′ axis.
- the photoelectric conversion element array 26A outputs the same detection result when the acoustic wave 1 propagates through the propagation medium portion 2 in the positive direction of the x axis and when propagates in the negative direction of the x axis.
- the direction in which the acoustic wave 1 propagates may be limited to 180 ° or less in advance.
- the acoustic wave 1 in the air is taken into the propagation medium unit 2 and the propagation direction of the acoustic wave 1 is specified.
- two surfaces 2 a perpendicular to the z-axis direction and surfaces parallel to the z-axis are positioned in a negative direction in the y-axis direction than the propagation position of the light wave 4.
- a sound insulating portion 9 for blocking the acoustic wave 1 is provided on the surface 2b to be operated.
- an opening through which the acoustic wave 1 is incident is formed on a surface 2c of the surface of the propagation medium portion 2 parallel to the z-axis and positioned in the positive direction in the y-axis direction relative to the propagation position of the light wave 4. .
- the propagation direction of the acoustic wave 1 at the position where it acts with the light wave 4 in the propagation medium portion 2 has a negative vector of the y-axis. Therefore, the propagation direction of the acoustic wave 1 can be limited to 180 °.
- the sound insulation part 9 is made of a transparent material such as glass or acrylic so that the light wave 4 can be transmitted, or the propagation part of the light wave 4. You may provide the translucent hole 31 in this.
- the optical microphone 102 may further include a propagation direction determination unit 45.
- the propagation direction determination unit 45 receives electrical signals from the photoelectric conversion elements 5a to 5x of the photoelectric conversion element array 26A, and outputs a signal representing the propagation direction of the acoustic wave 1 by an angle ⁇ from the reference direction.
- the propagation direction determination unit 45 includes a memory in which data in which such photoelectric conversion elements are associated with orientations is recorded.
- the propagation direction determination unit 45 receives the output from the photoelectric conversion element array 26A, refers to the memory, and among the photoelectric conversion elements 5a to 5x, the direction corresponding to the photoelectric conversion element that outputs an electrical signal having a predetermined intensity or more. Output ⁇ '. Thereby, the azimuth ⁇ ′ of the first interference light wave 41 and the second interference light wave 42 around the 0th-order diffracted light wave 4a ′ is output.
- the azimuth ⁇ ′ in the x′-y ′ coordinate is x It coincides with the direction ⁇ in the y coordinate. Therefore, the azimuth ⁇ ′ output from the propagation direction determining unit 45 indicates the propagation direction ⁇ of the acoustic wave 1 propagating through the propagation medium unit 2.
- output signals from the two or more photoelectric conversion elements by the first interference light wave 41 or the second interference light wave 42 are output. May be obtained. This occurs, for example, when the first interference light wave 41 or the second interference light wave 42 irradiates near the boundary between the photoelectric conversion element 5a and the photoelectric conversion element 5b.
- ⁇ ′ may be determined using the outputs of the photoelectric conversion elements 5a to 5x.
- the average phi 'm with 2' orientation phi 1 and the second interference light wave 42 'azimuth phi of the first interference light wave 41 is obtained by performing the calculation shown in the following equation.
- ⁇ ′ m (0 ⁇ Ia + 15 ⁇ Ib + ⁇ + 345 ⁇ Ix) / (Ia + Ib + ⁇ + Ix)
- the orientation of the first interference light wave 41 phi '1 and azimuth phi of the second interference light wave 42' 2, phi 'm +90 and phi' is m -90.
- the photoelectric conversion elements 5a to 5x constituting the photoelectric conversion element array 26A may not receive the 0th-order diffracted light wave 4a '. This is because the 0th-order diffracted light wave 4 a ′ does not contribute to the determination of the propagation direction of the acoustic wave 1.
- the angular resolution of the propagation direction of the acoustic wave 1 of the optical microphone 102 is determined by the fan-shaped center angle of the light receiving unit in the photoelectric conversion elements 5a to 5x, the performance of the light receiving lens system 15, the distance of the photoelectric conversion element array 26A, and the like. . High angular resolution by reducing the sector angle of the light receiving section, increasing the number of photoelectric conversion elements 5a to 5x, adjusting the positions of the light receiving lens system 15 and the photoelectric conversion element array 26A, and enlarging the light wave 4 Is obtained.
- the 15 may be configured by a plurality of photoelectric conversion elements.
- outputs from a plurality of photoelectric conversion elements constituting one fan-shaped light receiving unit may be added and used for detection of the first interference light wave 41 and the second interference light wave 42.
- the optical microphone 102 may further include a frequency conversion unit 46.
- the frequency conversion unit 46 receives the outputs of the photoelectric conversion elements 5a to 5x from the photoelectric conversion element array 26A or from the propagation direction determination unit 45, and converts the frequency of the received electrical signal to 1 ⁇ 2.
- a frequency conversion unit 46 for example, a frequency divider constituted by an electronic circuit or the like can be used. As a result, an electrical signal corresponding to the acoustic wave 1 is output from the frequency converter 46.
- the optical microphone of the present embodiment at least one of the first interference light and the second interference light is detected by the photoelectric conversion element array, and based on the position of the detected photoelectric conversion element in the photoelectric conversion element array, The propagation direction of the acoustic wave can be specified.
- a small and simple optical microphone can be realized without using a special measuring instrument such as a laser Doppler vibrometer or an optical interferometer. can do.
- FIG. 24 shows the configuration of the main part of the optical microphone 103 of the present embodiment.
- the optical microphone 103 separates and detects the acoustic wave 1 according to the frequency using the light wave 4.
- the optical microphone 103 includes a propagation medium unit 2, a light source 3, a photoelectric conversion element array 26 ⁇ / b> B, a reflection unit 6, a beam splitter 7, and a light receiving lens system 15.
- the configuration other than the photoelectric conversion element array 26B is the same as that of the optical microphone 102 of the second embodiment.
- the photoelectric conversion element array 26B includes a plurality of photoelectric conversion elements 15a, 15b,.
- Each photoelectric conversion element has a plurality of ring-shaped light receiving portions having different inner and outer diameters, and the light receiving portions are arranged concentrically around the position irradiated with the 0th-order diffracted light wave 4a '. The distances from the position irradiated with the 0th-order diffracted light wave 4a 'of the light receiving portion of each photoelectric conversion element are different from each other.
- the diffraction angles ⁇ of the + 1st order diffracted light wave 4b, the ⁇ 1st order diffracted light wave 4c, the + 1st order diffracted light wave 4d, and the ⁇ 1st order diffracted light wave 4e on the forward path can be expressed by the following equation (1).
- ⁇ represents the wavelength of the light wave 4
- ⁇ represents the wavelength of the acoustic wave 1
- f represents the frequency of the acoustic wave 1
- Cs represents the speed of sound in the propagation medium unit 2.
- L2 is the propagation distance of the light wave 4 from the propagation medium section 2 to the light receiving lens system 15
- the distance between the 0th-order diffracted light wave 4a and the + 1st-order diffracted light waves 4b and 4d and the -1st-order diffracted light waves 4c and 4e is sin ⁇ .
- ⁇ L2 can be expressed. From this, it can be seen that the distance between the 0th-order diffracted light wave 4 a ′ and the position where the first interference light wave 41 and the second interference light wave 42 are generated increases as the frequency of the acoustic wave 1 increases.
- the light wave 4 incident on the photoelectric conversion element array 26B is enlarged in the light receiving lens system 15, and the distance between the 0th-order diffracted light wave 4a, the first interference light wave 41, and the second interference light wave 42 is also changed in frequency.
- Dependent When the light receiving lens system 15 expands the light wave 4 at a constant magnification regardless of the positional relationship, the distance r between the 0th-order diffracted light wave 4a ′, the first interference light wave 41, and the second interference light wave 42 is expressed by the following equation (6) ).
- the first interference light wave 41 and the second interference light wave 42 are generated by any one of the plurality of photoelectric conversion elements 15a, 15b,. Detected.
- the frequency f of the acoustic wave 1 increases, the distance r between the 0th-order diffracted light wave 4a ', the first interference light wave 41, and the second interference light wave 42 increases.
- the acoustic wave 1 includes a plurality of different frequency components, the first interference light wave 41 and the second interference light wave 42 are independently detected by two or more of the photoelectric conversion elements 15a, 15b,. The components of the acoustic wave 1 can be detected separately for each frequency.
- the acoustic wave 1 depends on which one of the photoelectric conversion elements 15a, 15b,... 15h detects the first interference light wave 41 and the second interference light wave 42.
- Frequency f or frequency band can be specified. Since each photoelectric conversion element has a uniform light receiving portion in the circumferential direction, the frequency can be specified regardless of the propagation direction of the acoustic wave 1. Corresponding frequencies may be performed by calculation, or by inputting an acoustic wave 1 having a known frequency and recording the intensity distribution of output signals obtained from the photoelectric conversion elements 15a, 15b,. May be attached.
- the optical microphone 103 of the present embodiment may include a frequency specifying unit 47 that receives an electrical signal from the photoelectric conversion element array 26B and outputs a signal indicating the frequency or frequency band of the acoustic wave 1.
- the frequency specifying unit 47 may be configured such that the frequency f or frequency band of the acoustic wave 1 and the photoelectric conversion elements 15a, 15b,... 15h (or the distance r from the position irradiated with the 0th-order diffracted light wave 4a ′ of the light receiving unit). And a memory in which the correspondence relationship is recorded.
- the frequency specifying unit 47 receives the output from the photoelectric conversion element array 26B, refers to the memory, and among the photoelectric conversion elements 5a to 5x, the frequency band f2 corresponding to the photoelectric conversion element that outputs an electrical signal having a predetermined intensity or more. ⁇ F3 etc. are output.
- the frequency band may be determined by calculation using all electric signals of the photoelectric conversion elements 5a to 5x.
- the acoustic wave 1 may include components having a plurality of different frequencies.
- the photoelectric conversion element array 26B separates and detects the components of two or more acoustic waves 1 included in the first interference light wave 41 and the second interference light wave 42 for each frequency band described above.
- the photoelectric conversion element array 26 ⁇ / b> B can separately detect components of different frequencies of the acoustic wave 1 included in the first interference light wave 41 and the second interference light wave 42.
- the optical microphone 103 may further include a frequency conversion unit 46.
- the frequency conversion unit 46 receives the outputs of the photoelectric conversion elements 5a to 5x from the photoelectric conversion element array 26B or the frequency specifying unit 47, and converts the frequency of the received electrical signal to 1 ⁇ 2.
- the acoustic wave 1 includes a plurality of components having different frequencies, the frequency is converted by separating each of the frequency bands described above.
- a plurality or a single photoelectric conversion element designed with an arbitrary radius and width according to the frequency band to be separated may be arranged.
- the acoustic wave 1 can be detected separately for each frequency component, but also it can function as a frequency filter by not receiving light of unnecessary frequency component signals.
- the frequency range of the acoustic wave 1 detected by each photoelectric conversion element can also be arbitrarily set by giving the magnification of the light receiving lens system 15 a distribution from the center of the light wave 4 in the radial direction.
- the photoelectric conversion element array 26B may include a plurality of photoelectric conversion elements arranged in a one-dimensional manner.
- An optical microphone 103 ′ illustrated in FIG. 25 includes a photoelectric conversion element array 25 ⁇ / b> C including a plurality of photoelectric conversion elements 25 in which light receiving portions are arranged one-dimensionally instead of the photoelectric conversion element array 26 ⁇ / b> B.
- the frequency band of the acoustic wave 1 is specified as described above by the position r of the photoelectric conversion element that detects the first interference light wave 41 and the second interference light wave 42 from the irradiation position of the 0th-order diffracted light wave 4a ′. can do.
- the acoustic wave 1 includes a plurality of frequency components, the frequency component of the acoustic wave 1 can be detected separately for each frequency band.
- the optical microphone of the present embodiment depending on which photoelectric conversion element detects the first interference light wave or the second interference light wave without analyzing the frequency of the electric signal generated by the photoelectric conversion element, the frequency of the acoustic wave can be specified. Therefore, the frequency of the acoustic wave can be specified with a simple configuration. In addition, when a plurality of frequency components are included, these can be detected separately.
- FIG. 26A shows the configuration of the main part of the optical microphone 104 of the present embodiment.
- the optical microphone 104 specifies the propagation direction of the acoustic wave 1 using the light wave 4 and separates and detects the acoustic wave 1 according to the frequency.
- the optical microphone 103 includes a propagation medium unit 2, a light source 3, a photoelectric conversion element array 26D, a reflection unit 6, a beam splitter 7, and a light receiving lens system 15.
- the configuration other than the photoelectric conversion element array 26D is the same as that of the optical microphone 102 of the first embodiment.
- the photoelectric conversion element array 26D includes a plurality of photoelectric conversion elements 5a1, 5a2, ... 5a8, 5b1, 5b2, ... 5b8, ... 5x1, 5x2, ... 5x8.
- Each photoelectric conversion element has a partial ring-shaped light receiving portion, and the light receiving portion is two-dimensional in a radial direction and a circumferential direction in a circle centered on a position irradiated with the 0th-order diffracted light wave 4a ′. Is arranged. That is, photoelectric conversion elements 5a1, 5a2,... 5a8, photoelectric conversion elements 5b1, 5b2,... 5b8 are arranged in different radial directions in the same direction, and photoelectric conversion elements 5a1, 5b1, 5c1,.
- photoelectric conversion elements 5a2, 5b2, 5c2,... 5 ⁇ 2, etc. are arranged along the circumferential direction at the same radial position.
- the photoelectric conversion elements 5a1, 5a2,... 5a8 are arranged in the same direction ⁇ ′ with respect to the position irradiated with the 0th-order diffracted light wave 4a ′.
- the photoelectric conversion elements 5b1, 5b2,... 5b8 are also arranged in the same direction ⁇ ′.
- the photoelectric conversion elements 5a1, 5b1, 5c1,... 5x1 are arranged concentrically at the radial position closest to the position irradiated with the 0th-order diffracted light wave 4a ′, and the photoelectric conversion elements 5a8, 5b8, 5c8,. 5 ⁇ 8 is concentrically arranged at a radial position farthest from the position irradiated with the 0th-order diffracted light wave 4a ′.
- the light receiving unit of the photoelectric conversion element that detects the first interference light 41 and the second interference light 42 The frequency of the acoustic wave can be specified by the distance r in the radial direction centered on the position irradiated by the zeroth-order diffracted light wave 4a ′, and the propagation direction of the acoustic wave can be specified from the center direction azimuth ⁇ ′.
- the optical microphone 104 may include a propagation direction / frequency specifying unit 48 that receives an electrical signal from the photoelectric conversion element array 26D and outputs a signal indicating the propagation direction and frequency band of the acoustic wave 1.
- the propagation direction / frequency specifying unit 48 has a memory that records the correspondence between the frequency band of the acoustic wave 1 and the propagation direction ⁇ ′ and the photoelectric conversion element as shown in Table 3.
- the propagation direction / frequency specifying unit 48 receives the output from the photoelectric conversion element array 26D, and refers to the memory, and outputs the azimuth and frequency band corresponding to the photoelectric conversion element from which an electric signal having a predetermined intensity or more is output.
- the sound sources 1a, 1b, and 1c output from the plurality of sound sources 32a, 32b, and 32c can be detected and the sound source can be localized. Since the acoustic wave 1a output from the sound source 32a and the acoustic wave 1b output from the sound source 32b have different propagation directions, the first interference light wave on the light receiving surface of the photoelectric conversion element array 26D with respect to the two acoustic waves 1a and 1b. 41 and the second interference light wave 42 are generated at different positions in the ⁇ ′ direction.
- the first interference light wave 41 and the second interference light wave 42 are received by the photoelectric conversion elements having different directions, the propagation directions are specified, and sound source localization can be performed.
- the acoustic waves 1b and 1c output from the sound source 32b and the sound source 32c have the same propagation direction but have different frequencies from f2 and f3. Therefore, since the first interference light wave 41 and the second interference light wave 42 are received by the photoelectric conversion elements having the same azimuth ⁇ ′ direction but different radial distances r, the frequencies of the two acoustic waves 1b and 1c are previously obtained. If f2 and f3 are known, these two acoustic waves can be distinguished and detected.
- the photoelectric conversion element array 26D has a structure in which the photoelectric conversion elements having the partial ring-shaped light receiving portions are arranged in the radial direction and the circumferential direction.
- a photoelectric conversion element array in which a plurality of photoelectric conversion elements having rectangular light receiving portions are arranged in two non-parallel directions, for example, two orthogonal directions may be used.
- FIG. 26B schematically shows the arrangement of the light receiving surfaces of such a photoelectric conversion element array.
- This photoelectric conversion element array includes a plurality of photoelectric conversion elements 5a1, 5a2, ... 5a9, 5b1, 5b2, ... 5b9, ... 5i1, 5i2, ... 5i9.
- Each photoelectric conversion element has a rectangular light receiving part, and the photoelectric conversion element array is arranged so that the light receiving part of the photoelectric conversion element 5e5 is irradiated with the 0th-order diffracted light wave 4a '. Since each photoelectric conversion element in this photoelectric conversion element array is not arranged in the circumferential direction and the radial direction, except for a specific positional relationship, an orientation centered on a position irradiated with the 0th-order diffracted light wave 4a ′. The distance from the center to the light receiving unit is different.
- the optical microphone of the present embodiment it is possible to specify a plurality of acoustic waves propagating from different directions.
- the frequency of the acoustic wave is known in advance, it is possible to specify a plurality of acoustic waves that propagate from the same direction.
- FIG. 28 shows a configuration of a main part of the flaw detection apparatus 105 of the present embodiment.
- the flaw detection apparatus 105 can find a defect in the subject such as a transparent material without destroying the subject.
- the flaw detection apparatus 105 is the same as the optical microphone 102 of the second embodiment except that it uses a subject 33 that performs defect inspection instead of the propagation medium unit 2 and includes a sound source 32 that generates the acoustic wave 1. It has a structure.
- the subject 33 may be transparent to the light wave 4 emitted from the light source 3.
- the subject 33 made of glass or acrylic can be inspected.
- emitted from the sound source 32 may be sufficient.
- the use of a high frequency such as an ultrasonic wave as the acoustic wave 1 provides a higher resolution, so that the defect 34 can be identified with high accuracy.
- a piezoelectric element or the like can be used as the sound source 32 that outputs ultrasonic waves.
- a sound source 32 is brought into contact with one end of the subject 33, for example, and the sound source 32 is driven to excite and propagate the acoustic wave 1 into the subject 33.
- the light wave 4 emitted from the light source 3 may irradiate the subject 33 at a position other than the propagation path of the acoustic wave 1 excited by the sound source 32.
- a reflected wave 35 of the acoustic wave 1 is generated at the defect 34.
- the direction in which the defect 34 exists can be specified by the reflected wave 35 crossing the light wave 4 transmitted through the subject 33.
- the propagation time t prop that the acoustic wave 1 propagates through the subject 33 can be known.
- the propagation speed of the acoustic wave 1 in the subject 33 is V n
- the distance from the sound source 32 to the defect 34 is l in
- the distance from the defect 34 to the light wave 4 is l out
- l in + l out t prop ⁇ the relationship of V n is established. Therefore, if the propagation direction of the reflected wave 35 is specified, the distance from the position where the light wave 4 is transmitted to the defect 34 is obtained from the propagation time t prop . Therefore, the position of the defect 34 can be specified.
- the position of the internal defect can be estimated without destroying the subject 33.
- the reflection of the acoustic wave 1 also occurs when there is a material different from the material constituting the subject 33 or when a physical structural defect occurs in the material constituting the subject 33. It is possible for the painter to detect the defect 34 and estimate its position.
- the optical microphone disclosed in this application is useful as a small ultrasonic sensor or an audible microphone. Further, it can be applied as an ultrasonic wave reception sensor used for an ambient environment system using ultrasonic waves.
- the optical microphone disclosed in this application is useful as a small ultrasonic sensor or an audible microphone. Further, it can be applied as an ultrasonic wave reception sensor used for an ambient environment system using ultrasonic waves. It can also be applied as a flaw detector.
Abstract
Description
本実施形態の光マイクロホン101で検出可能な音響波1は、おおよそ20Hz以上20MHz以下の可聴波または超音波である。音響波1は、音声や音楽など時間に伴い周波数が変化する連続波であってもよいし、単一周波数の正弦波による連続波であってもよい。また、単一パルスのバースト信号のような時間的に不連続な音響波であってもよい。
環境流体を伝搬する音響波1は伝搬媒質部2に入射され、図2(a)から(d)に示すように伝搬媒質部2の内部をx方向に伝搬する。音響波1の伝搬に伴って、伝搬媒質部2を構成している物質の密度が変化し、これによって屈折率の変化が生じる。音響波1は縦波であるため、屈折率の分布は音響波1の伝搬方向(x軸)に生じる。音響波1の伝搬方向に垂直な面には分布はほとんど生じない。音響波1によって生じた伝搬媒質部2の屈折率分布は、回折格子として機能する。
光源3は光波4を出射し、出射した光波4は、図1A、図1Bおよび図2(a)から(d)に示すように、伝搬媒質部2を透過する。光波4の波長および強度に特に制限はなく、光電変換部5が良好な感度で光波4を検出することのできる波長および強度が選択される。ただし、伝搬媒質部2にあまり吸収されない波長を選択してもよい。光波4としてはコヒーレントな光を用いても、インコヒーレントな光を用いてもよい。しかし、レーザー光のようなコヒーレントな光を用いたほうが、回折光波が干渉しやすく、信号が取り出しやすい。光波4の直径は例えば0.01mm以上20mm以下である。
光源3から出射した光波4が伝搬媒質部2を透過する光路を往路と呼ぶ。光源3から出射された光波4は、伝搬媒質部2に入射し、図2(a)に示すように、伝搬媒質部2中で音響波1と作用する。具体的には、音響波1の伝搬によって、伝搬媒質部2に伝搬媒質の密度分布が生じ、これによる伝搬媒質の屈折率分布が生じる。伝搬媒質の屈折率分布は、光波4に対して回折格子として機能し、光波4を回折させる。このため、図2(b)に示すように、音響波1による光波4の+1次回折光波4bおよび-1次回折光波4cが生じる。また、音響波1によって回折されずに、入射時の方向へ直進する0次回折光波4aも伝搬媒質部2から出射する。以下において説明するように、屈折率分布は音響波1の伝搬に伴い移動するため、回折光波の周波数はドップラー効果により、シフトしている。+1次回折光波4bおよび-1次回折光波4cの伝搬方向は、光源3から出射した光波4の伝搬方向と音響波1の伝搬方向を含む平面上に位置している。+1次回折光波4bおよび-1次回折光波4cの伝搬方向は、この平面上において、0次回折光波4aに対してそれぞれ角度θおよび-θをなしている。また、+1次回折光波4bおよび-1次回折光波4cの位相は互いに反転している。角度は、光波4が反射部6へ向かう伝搬方向を基準とし、X軸の正方向への角度を正にとっている。
伝搬媒質部2を透過した0次回折光波4a、+1次回折光波4bおよび-1次回折光波4cを含む光波4は、反射部6に到達する。反射部6は、光波4を再帰反射させる。再帰反射とは、入射した光が入射方向と同じ方向へ反射することを言う。つまり、反射部6へ入射する光波4の入射方向と、反射部6において反射し、出射する光波4の出射方向は平行である。再帰反射する反射部6を用いることによって、光波4を反射させて、伝搬媒質部2に光波4を2回透過させることができる。また、再帰反射によって1回目に伝搬媒質部2を透過する際(往路)に生成する+1次回折光波(または-1次回折光波)を入射方向と同じ方向へ反射させることができる。このため、往路で生成した+1次回折光波(または-1次回折光波)と2回目に伝搬媒質部2を透過する際(復路)に生成する-1次回折光波(または+1次回折光波)との回折方向を一致させ、2つの回折光波を音響波の周波数変化に関わらず、概ね一定の強度干渉光波を得ることができる。
反射部6で反射された光波4は、再び伝搬媒質部2に入射し、伝搬媒質部2中で音響波1と作用することによって回折光波が生じる。反射部6から出射する光波4は、0次回折光波4a、+1次回折光波4bおよび-1次回折光波4cを含み、これらの光波はそれぞれ音響波1と作用して、回折光波を生成する。しかし、+1次回折光波4bおよび-1次回折光波4cの強度は小さいため、+1次回折光波4bおよび-1次回折光波4cの回折光波の強度は非常に小さい。よって1次回折光波4bおよび-1次回折光波4cの回折光波は無視することができ、0次回折光波4aの回折光波のみを考慮すればよい。
光電変換部5は、光源3から出射し、伝搬媒質部2を2度透過した光波4を検出する。図6は、伝搬媒質部2を再度透過しビームスプリッタ7に入射する直前の光波4をx-y断面でz軸の正の方向から負の方向を見た断面図である。0次回折光波4a'に対して、x軸の正の向きに往路の-1次回折光波4cおよび復路の+1次回折光波4dが位置し、x軸の負の向きに往路の+1次回折光波4bおよび復路の-1次回折光波4eが位置しており、それぞれ重なりあっている。重なり合った領域14a、14bにおいては各光波が干渉し、音響波1の信号に応じて光強度の変化が生じる。この干渉光波を光電変換部5で受光すると、光強度の変化に応じた電気信号が得られることにより、音響波1を検出することができる。
光電変換部5によって生成する電気信号は、音響波1の2倍の周波数を有する。このため、音響波1と同じ周波数の電気信号を得る場合には、周波数変換部21によって、光電変換部5から出力される電気信号の周波数を1/2に変換する。周波数変換部21としては、例えば、電子回路などで構成する分周器などを用いることができる。
次に、光マイクロホン101の動作を説明する。
ここで、λは光波4の波長、Λは音響波1の波長、fは音響波1の周波数、Vnは伝搬媒質部2中の音響波1の伝搬速度、Iinは光波4の強度、Δnは1Paの音響波1の伝搬による伝搬媒質部2の屈折率変化量、Pは音響波1の音圧、lは光波4が伝搬媒質部2中を伝搬する距離、J0は0次のベッセル関数、J1は1次のベッセル関数を表している。式(1)から、音響波1の周波数fが高くなればなるほど、回折角θが大きくなることがわかる。
以下、図面を参照しながら、本発明による光マイクロホンの第2の実施形態を説明する。特許文献1の光マイクロホンや特許文献2の方法では、音響波を検出することができるが、音響波の伝搬方向を特定したり、音響波を周波数に応じて分離して検出したりすることはできない。これに対し、本実施形態の光マイクロホンは、音響波の伝搬方向の特定および音響波の周波数に応じた分離検出の少なくとも一方が可能である。
本実施形態の光マイクロホン102で検出可能な音響波1は、おおよそ20Hz以上20MHz以下の可聴波または超音波である。音響波1は、音声や音楽など時間に伴い周波数が変化する連続波であってもよいし、単一周波数の正弦波による連続波であってもよい。また、単一パルスのバースト信号のような時間的に不連続な音響波であってもよい。
音響波1は、本実施形態では光マイクロホン102の外部の環境媒体から伝搬媒質部2に入射し、伝搬媒質部2内を伝搬する。図15は、音響波1がx軸の正方向へ伝搬している様子を示している。音響波1の伝搬に伴って、伝搬媒質部2を構成している物質の密度が変化し、これによって屈折率の変化が生じる。音響波1は縦波であるため、屈折率の分布は音響波1の伝搬方向(x軸)に生じる。音響波1の伝搬方向に垂直な面には分布はほとんど生じない。音響波1によって生じた伝搬媒質部2の屈折率分布は、回折格子として機能する。
光源3は光波4を出射し、出射した光波4が伝搬媒質部2を透過する。光波4の波長および強度に特に制限はなく、光電変換素子アレイ26Aが良好な感度で光波4を検出することのできる波長および強度が選択される。ただし、伝搬媒質部2にあまり吸収されない波長を選択してもよい。光波4としてはコヒーレントな光を用いても、インコヒーレントな光を用いてもよい。しかし、レーザー光のようなコヒーレントな光を用いたほうが、回折光波が干渉しやすく、信号が取り出しやすい。光波4の直径は例えば0.01mm以上20mm以下である。
光源3から出射された光波4は、往路において、伝搬媒質部2に入射し、図16(a)に示すように、伝搬媒質部2中で音響波1と作用する。具体的には、音響波1の伝搬によって、伝搬媒質部2に伝搬媒質の密度分布が生じ、これによる伝搬媒質の屈折率分布が生じる。伝搬媒質の屈折率分布は、光波4に対して回折格子として機能し、光波4を回折させる。
ここで、λは光波4の波長、Λは音響波1の波長、fは音響波1の周波数、Csは伝搬媒質部2中の音響波1の伝搬速度、Iinは光波4の強度、Δnは1Paの音響波1の伝搬による伝搬媒質部2の屈折率変化量、Pは音響波1の音圧、lは光波4が伝搬媒質部2中を伝搬する距離、J0は0次のベッセル関数、J1は1次のベッセル関数を表している。式(1)から、音響波1の周波数fが高くなればなるほど、回折角θが大きくなることがわかる。また、式(3)から±1次回折光波4b、4cの光強度は音響波1の音圧に応じて変化することがわかる。
伝搬媒質部2を透過した0次回折光波4a、+1次回折光波4bおよび-1次回折光波4cを含む光波4は、反射部6に到達する。反射部6は、光波4を再帰反射させる。第1の実施形態でも説明したように、再帰反射とは、入射した光が入射方向と同じ方向へ反射することを言う。つまり、反射部6へ入射する光波4の入射方向と、反射部6において反射し、出射する光波4の出射方向は平行である。再帰反射する反射部6を用いることによって、光波4を反射させて、伝搬媒質部2に光波4を2回透過させることができる。また、再帰反射によって、1回目に伝搬媒質部2を透過する際(往路)に生成する+1次回折光波(または-1次回折光波)を入射方向と同じ方向へ反射させることができる。このため、往路で生成した+1次回折光波(または-1次回折光波)と2回目に伝搬媒質部2を透過する際に生成する-1次回折光波(または+1次回折光波)との回折方向を一致させ、2つの回折光波を音響波の周波数変化に関わらず、概ね一定の強度干渉光波を得ることができる。
反射部6で反射された光波4は、再び伝搬媒質部2に入射し、伝搬媒質部2中で音響波1と作用することによって回折光波が生じる。反射部6から出射する光波4は、0次回折光波4a、+1次回折光波4bおよび-1次回折光波4cを含み、これらの光波はそれぞれ音響波1と作用して、回折光波を生成する。しかし、+1次回折光波4bおよび-1次回折光波4cの強度は0次回折光波4aに比較して小さく、+1次回折光波4bおよび-1次回折光波4cの回折光波の強度はこれよりも更に小さい。よって1次回折光波4bおよび-1次回折光波4cの回折光波は無視することができ、0次回折光波4aの回折光波のみを考慮すればよい。
伝搬媒質部2を再度透過した光波4は、ビームスプリッタ7により、往路の光波4とは異なる方向に伝搬する。図20は、光波4に含まれる+1次回折光波4b、4d、-1次回折光波4c、4deおよび0次回折光波4a’の位置関係を光波4の伝搬方向に垂直な断面で見たものである。この断面の伝搬媒質部2からの距離をL2、回折角度をθとすると、0次回折光波4aと、復路の+1次回折光波4dおよび-1次回折光波4eの0次回折光波4a’からの位置ずれ距離は、sinθ×L2と表せる。0次回折光波4a’のビーム半径をwとすると、sinθ×L2<wの範囲では、0次回折光波4a’と+1次回折光波4b、4dおよび-1次回折光波4c、4eとが部分的に重なる。以下において説明するように、光マイクロロホン101では、+1次回折光波4bと-1次回折光波4eとが重なる領域および+1次回折光波4dと-1次回折光波4cとが重なる領域に生じる干渉光波を検出することによって音響波1の伝搬方向および音響波1の周波数の少なくとも一方を特定する。このため、ある態様では、光電変換素子アレイ26Aの受光面上において、+1次回折光波4b、4dおよび-1次回折光波4c、4eは0次回折光波4a’と重ならない、つまり、sinθ×L2>wである。
図21は、光電変換素子アレイ26Aの受光面上における、光波4に含まれる+1次回折光波4b、4d、-1次回折光波4c、4eおよび0次回折光波4a’の位置関係を示している。
光マイクロホン102は、さらに伝搬方向決定部45を備えていてもよい。伝搬方向決定部45は、光電変換素子アレイ26Aの光電変換素子5a~5xからの電気信号を受け取り、音響波1の伝搬方向を基準方向からの角度φで表す信号を出力する。
φ’=(0×Ia+15×Ib)/(Ia+Ib)
φ’m=(0×Ia+15×Ib+・・+345×Ix)/(Ia+Ib+・・+Ix)
この場合、第1干渉光波41の方位φ’1と第2干渉光波42の方位φ’2は、φ’m+90およびφ’m-90である。
光マイクロホン102は、さらに周波数変換部46を備えていてもよい。周波数変換部46は、光電変換素子アレイ26Aから、または、伝搬方向決定部45から、光電変換素子5a~5xの出力を受け取り、受け取った電気信号の周波数を1/2に変換する。周波数変換部46としては、例えば、電子回路などで構成する分周器などを用いることができる。これにより、周波数変換部46から音響波1に対応した電気信号が出力される。
図24は、本実施形態の光マイクロホン103の主要部の構成を示している。光マイクロホン103は、光波4を用いて音響波1をその周波数に応じて分離して検出する。このために、光マイクロホン103は、伝搬媒質部2と、光源3と、光電変換素子アレイ26Bと、反射部6と、ビームスプリッタ7と、受光レンズ系15とを備える。光電変換素子アレイ26B以外の構成は、第2の実施形態の光マイクロホン102と同じである。
図26(a)は、本実施形態の光マイクロホン104の主要部の構成を示している。光マイクロホン104は、光波4を用いて音響波1の伝搬方向を特定し、かつ、音響波1をその周波数に応じて分離して検出する。このために、光マイクロホン103は、伝搬媒質部2と、光源3と、光電変換素子アレイ26Dと、反射部6と、ビームスプリッタ7と、受光レンズ系15とを備える。光電変換素子アレイ26D以外の構成は、第1の実施形態の光マイクロホン102と同じである。
本発明による探傷装置の実施形態を説明する。図28は、本実施形態の探傷装置105の主要部の構成を示している。探傷装置105は、透明材料などの被検体の中の欠陥を、被検体を破壊することなく見つけることができる。探傷装置105は、伝搬媒質部2の換わりに欠陥検査を行う被検体33を用い、音響波1を生成する音源32を備えている点を除いて、第2の実施形態の光マイクロホン102と同じ構造を備えている。
2 伝搬媒質部
3 光源
4 光波
4a 往路の0次回折光波
4a'復路の0次回折光波
4b 往路の+1次回折光波
4c 往路の-1次回折光波
4d 復路の+1次回折光波
4e 復路の-1次回折光波
5 光電変換部
5a~5x 光電変換素子
6 反射部
7 ビームスプリッタ
8 コーナーキューブミラー
9 遮音部
10 開口部
11 光透過部
12 リバーサルミラー
13 対称軸
14 遮光部
15 受光レンズ系
21 周波数変換部
26A,26B、26C、26D 光電変換素子アレイ
31 透光孔
32、32a、32b、32c 音源
33 被検体材料
34 欠陥
35 反射波
101、102、103、104 光マイクロホン
105 探傷装置
111 出射系光学部品
112 受光系光学部品
113 光ダイオード
201 開口部
202 音響導波路
203 光音響伝搬媒質部
204 レーザードップラー振動計
Claims (20)
- 光波を用いて、環境流体を伝搬する音響波を検出する光マイクロホンであって、
前記音響波が伝搬する伝搬媒質部と、
前記伝搬媒質部中を伝搬する前記音響波を横切って、前記伝搬媒質部を透過する光波を出射する光源と、
前記伝搬媒質部を透過した光波を再帰反射させる反射部と、
前記反射部で反射し、前記伝搬媒質部を透過した前記光波を受光し、電気信号を出力する光電変換部とを備え、
前記光源から出射する前記光波が前記伝搬媒質部を透過する往路において、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、0次回折光波、+1次回折光波および-1次回折光波がそれぞれ生成し、
前記往路において生成した前記0次回折光波が、前記反射部における反射によって前記伝搬媒質部を透過する復路において、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、0次回折光波、+1次回折光波および-1次回折光波が生成し、
前記光電変換部は、前記往路で生成した+1次回折光波と前記復路で生成した前記-1次回折光波との干渉光、および、前記往路で生成した-1次回折光波と前記復路で生成した前記+1次回折光波との干渉光の少なくとも一方を検出する光マイクロホン。 - 前記光源と前記伝搬媒質部との間に位置しているビームスプリッタをさらに備え、
前記ビームスプリッタは、前記往路および前記復路によって生成した前記+1次回折光波および-1次回折光波を前記光源とは異なる方向に出射させる請求項1に記載の光マイクロホン。 - 前記反射部は、少なくとも前記伝搬媒質部における前記音響波の伝搬方向および前記光源から出射する前記光波の伝搬方向を含む平面において再帰反射性を有する請求項1または2に記載の光マイクロホン。
- 前記反射部は、リバーサルミラーであり、
前記リバーサルミラーの対称軸が、前記音響波の伝搬方向および前記光波の伝搬方向に垂直である請求項3に記載の光マイクロホン。 - 前記反射部はコーナーキューブミラーである請求項3に記載の光マイクロホン。
- 前記光電変換部は受光面を有し、
前記0次回折光波が前記受光面に入射しないように、前記復路で生成した前記0次回折光波が前記受光面へ入射するのを遮る遮光部をさらに備える請求項1から5のいずれかに記載の光マイクロホン。 - 前記復路の光路上において、前記遮光部よりも伝搬媒質側に配置されており、発散作用を有する受光レンズ系をさらに備える請求項6に記載の光マイクロホン。
- 前記光電変換部は、前記反射部で反射し、前記伝搬媒質部を透過した前記光波を受光し、電気信号を出力する複数の光電変換素子を有する光電変換素子アレイであって、
前記光電変換素子アレイは、前記往路で生成した+1次回折光波と前記復路で生成した前記-1次回折光波とが干渉することにより得られる第1干渉光波、および、前記往路で生成した-1次回折光波と前記復路で生成した前記+1次回折光波とが干渉することにより得られる第2干渉光波の少なくとも一方を前記複数の光電変換素子の一部で検出し、
前記第1干渉光波および前記第2干渉光波の少なくとも一方を検出した前記一部の光電変換素子の前記光電変換素子アレイにおける位置に基づき、前記音響波の伝搬方向を特定する請求項1に記載の光マイクロホン。 - 前記光電変換部は、前記反射部で反射し、前記伝搬媒質部を透過した前記光波を受光し、電気信号を出力する複数の光電変換素子を有する光電変換素子アレイであって、
前記光電変換素子アレイは、前記往路で生成した+1次回折光波と前記復路で生成した前記-1次回折光波とが干渉することにより得られる第1干渉光波、および、前記往路で生成した-1次回折光波と前記復路で生成した前記+1次回折光波とが干渉することにより得られる第2干渉光波の少なくとも一方を前記複数の光電変換素子の一部で検出し、
前記第1干渉光波および前記第2干渉光波の少なくとも一方を前記複数の光電変換素子によって独立して検出することにより、前記音響波を周波数に応じて分離検出する請求項1に記載の光マイクロホン。 - 前記複数の光電変換素子のそれぞれは、受光部を有し、
前記複数の光電変換素子の前記受光部は、前記復路の0次回折光波が照射する位置を中心として配置されており、
前記複数の光電変換素子の受光部の大きさおよび前記中心からの距離によって前記音響波を異なる周波数帯域で分離して検出する請求項9に記載の光マイクロホン。 - 前記複数の光電変換素子の受光部は、第1の配置方向および前記第1の配置方向と非平行な第2の方向に、2次元に配置されており、
前記第1干渉光波および前記第2干渉光波の少なくとも一方を検出した前記一部の光電変換素子の受光部の前記中心周りの方位によって、前記音響波の伝搬方向をさらに特定する請求項10に記載の光マイクロホン。 - 前記複数の光電変換素子のそれぞれは、部分リング状の受光部を有し、前記受光部は、前記復路の0次回折光波が照射する位置を中心とする円内において、半径方向および円周方向において、2次元に配置されており、
前記第1干渉光波および前記第2干渉光波の少なくとも一方を、前記円周方向の同じ方位であって、半径方向に異なる位置にある2つ以上の光電変換素子によって、前記音響波を周波数に応じて分離検出し、
前記中心周り前記円周方向方位から前記音響波の伝搬方向を特定する請求項8または9に記載の光マイクロホン。 - 前記光電変換部より前記伝搬媒質部側に設けられた、発散作用を有する受光レンズ系をさらに備える請求項1から12のいずれかに記載の光マイクロホン。
- 前記復路の光路上に配置されており、中心から外側に向かって拡大率が小さくなる分布を有する受光レンズ系をさらに備える請求項1から13のいずれかに記載の光マイクロホン。
- 前記伝搬媒質部がシリカ乾燥ゲルによって構成されている請求項1から14のいずれかに記載の光マイクロホン。
- 前記光電変換部で得られた電気信号の周波数を1/2倍に変換する周波数変換部をさらに備える請求項1から15のいずれかに記載の光マイクロホン。
- 被検体内に音響波を励起する音源と、
前記被検体中の欠陥によって生じた前記音響波の反射波を横切って、前記被検体を透過する光波を出射する光源と、
前記被検体を透過した光波を再帰反射させる反射部と、
前記反射部で反射し、前記被検体を透過した前記光波を受光し、電気信号を出力する複数の光電変換素子を有する光電変換素子アレイとを備え、
前記光源から出射する前記光波が前記被検体を透過する往路において、前記反射波の伝搬に伴って生じる前記被検体の屈折率分布により、前記光波から、0次回折光波、+1次回折光波および-1次回折光波がそれぞれ生成し、
前記往路において生成した前記0次回折光波が、前記反射部における反射によって前記被検体を透過する復路において、前記反射波の伝搬に伴って生じる前記被検体の屈折率分布により、前記往路の0次回折光から、0次回折光波、+1次回折光波および-1次回折光波が生成し、
前記光電変換素子アレイは、前記往路で生成した+1次回折光波と前記復路で生成した前記-1次回折光波とが干渉することにより得られる第1干渉光波、および、前記往路で生成した-1次回折光波と前記復路で生成した前記+1次回折光波とが干渉することにより得られる第2干渉光波の少なくとも一方を前記複数の光電変換素子の一部で検出し、
前記第1干渉光波および前記第2干渉光波の少なくとも一方を検出した前記一部の光電変換素子の前記光電変換素子アレイにおける位置に基づき、前記反射波の伝搬方向を特定し、
前記光電変換素子アレイによる、前記第1干渉光波および前記第2干渉光波の少なくとも一方を検出した時刻および、前記被検体内における音響波の励起時刻から、前記反射波が前記被検体を伝搬する距離を算出し、
前記特定した伝搬方向および前記算出した距離から前記被検体内における欠陥の位置を推定する探傷装置。 - 光波を用いて、環境流体を伝搬する音響波を検出する音響波の検出方法あって、
伝搬媒質部中に音響波を伝搬させるステップ(A)と、
前記伝搬媒質部中を伝搬する前記音響波を横切るように光波を透過させ、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、0次回折光波、+1次回折光波および-1次回折光波をそれぞれ生成させるステップ(B)と、
前記ステップ(B)で生成した0次回折光波、+1次回折光波および-1次回折光波を再帰反射させるステップ(C)と、
前記再帰反射した0次回折光波が前記伝搬媒質部中を伝搬する前記音響波を横切るように透過することによって、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、+1次回折光波および-1次回折光波をそれぞれ生成させるステップ(D)と、
前記ステップ(B)で生成し、再帰反射した+1次回折光波と、前記ステップ(D)で生成した-1次回折光波との干渉光、および、前記ステップ(B)で生成し、再帰反射した-1次回折光波と、前記ステップ(D)で生成した+1次回折光波との干渉光の少なくとも一方を検出するステップ(E)と、
を包含する音響波の検出方法。 - 光波を用いて、音響波を検出する音響波の検出方法あって、
伝搬媒質部中に音響波を伝搬させるステップ(A)と、
前記伝搬媒質部中を伝搬する前記音響波を横切るように光波を透過させ、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、0次回折光波、+1次回折光波および-1次回折光波をそれぞれ生成させるステップ(B)と、
前記ステップ(B)で生成した0次回折光波、+1次回折光波および-1次回折光波を再帰反射させるステップ(C)と、
前記再帰反射した0次回折光波が前記伝搬媒質部中を伝搬する前記音響波を横切るように透過することによって、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、+1次回折光波および-1次回折光波をそれぞれ生成させるステップ(D)と、
前記ステップ(B)で生成し、再帰反射した+1次回折光波と、前記ステップ(D)で生成した-1次回折光波との第1干渉光波、および、前記ステップ(B)で生成し、再帰反射した-1次回折光波と、前記ステップ(D)で生成した+1次回折光波との第2干渉光波の少なくとも一方を、複数の光電変換素子を有する光電変換素子アレイによって検出し、前記第1干渉光波および前記第2干渉光波の少なくとも一方を検出した前記一部の光電変換素子の前記光電変換素子アレイにおける位置に基づき、前記音響波の伝搬方向を特定するステップ(E)と
を包含する音響波の検出方法。 - 光波を用いて、音響波を検出する音響波の検出方法あって、
伝搬媒質部中に音響波を伝搬させるステップ(A)と、
前記伝搬媒質部中を伝搬する前記音響波を横切るように光波を透過させ、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、0次回折光波、+1次回折光波および-1次回折光波をそれぞれ生成させるステップ(B)と、
前記ステップ(B)で生成した0次回折光波、+1次回折光波および-1次回折光波を再帰反射させるステップ(C)と、
前記再帰反射した0次回折光波が前記伝搬媒質部中を伝搬する前記音響波を横切るように透過することによって、前記音響波の伝搬に伴って生じる前記伝搬媒質部の屈折率分布により、+1次回折光波および-1次回折光波をそれぞれ生成させるステップ(D)と、
前記ステップ(B)で生成し、再帰反射した+1次回折光波と、前記ステップ(D)で生成した-1次回折光波との第1干渉光波、および、前記ステップ(B)で生成し、再帰反射した-1次回折光波と、前記ステップ(D)で生成した+1次回折光波との第2干渉光波の少なくとも一方を、複数の光電変換素子を有する光電変換素子アレイによって独立して検出することにより、前記音響波を周波数に応じて分離検出するステップ(E)と、を包含する音響波の検出方法。
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