Microphone

Abstract

A microphone (1) is provided with: a light source (11) that outputs an optical signal; an optical coupler (12) for demultiplexing and multiplexing the optical signal; a transmission path (13) that includes an optical fiber (130) that transmits the demultiplexed optical signals demultiplexed by the optical coupler (12) to the optical coupler (12) in mutually opposite directions; a sensor unit (14) that is connected to the transmission path (13) and returns the demultiplexed optical signal transmitted by the transmission path (13) to the transmission path (13) via the space unit (40); and a light receiving element (15) that receives a multiplexed optical signal multiplexed by the optical coupler (12).

Description

Technical Field

[0001] This disclosure relates to a microphone that uses optical fiber to detect sound. Background Technology

[0002] In recent years, microphones that detect sound modulated by optical signals transmitted through optical fibers have been put into practical use. For example, Patent Document 1 describes an optical fiber interferometric sensor that branches off light emitted from a light source and propagates it clockwise and counterclockwise within a looped optical fiber, then demodulates the coupled light to detect sound modulated by the propagating light within the optical fiber.

[0003] However, the acoustic impedance differs significantly between the environment in which the sound is generated and the coating of the optical fiber's periphery. Therefore, in the fiber optic interferometric sensor disclosed in Patent Document 1, a portion of the sound is reflected by the periphery of the optical fiber, raising concerns about reduced sound pressure penetrating the fiber and a decreased degree of change in the fiber's refractive index. Consequently, there are concerns about the inability to detect sound with high precision.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-241431 Summary of the Invention

[0007] This disclosure was made to solve such a problem, and its purpose is to provide a microphone capable of detecting sound with high precision using optical fiber.

[0008] -Methods for solving problems-

[0009] A microphone according to one aspect of this disclosure comprises: a light source for outputting an optical signal; an optical coupler for splitting and combining the optical signal; a transmission path including an optical fiber, the optical fiber transmitting the split optical signals obtained by the optical coupler in opposite directions to the optical coupler; a sensor unit connected to the transmission path, which returns the split optical signals transmitted by the transmission path to the transmission path via a spatial unit; and a light-receiving element for receiving the combined optical signal obtained by the optical coupler. Attached Figure Description

[0010] Figure 1 This is a diagram showing the overall structure of the microphone in Embodiment 1.

[0011] Figure 2 This is a diagram showing the structure of the sensor unit in Embodiment 2.

[0012] Figure 3This is a diagram showing a modified structure of the sensor section in Embodiment 2.

[0013] Figure 4 This is a diagram showing the structure of the sensor unit in Embodiment 3.

[0014] Figure 5 This is a diagram illustrating an example of the structure of an existing Sagnac interference microphone. Detailed Implementation

[0015] (The understanding that forms the basis of this disclosure)

[0016] In recent years, microphones that detect the modulation of optical signals based on the amplitude, frequency, or phase of the optical signal transmitted by optical fiber have been put into practical use as measuring devices for sound generated in the air and water, as well as AE (Acoustic Emission) sensors.

[0017] For example, such as Figure 5 As shown, in the Sagnac interferometer microphone 100 described in Patent Document 1, etc., the driver 90 causes a light source 91, such as an LED (Light Emitting Diode) or SLD (Super Luminescent Diode), to emit an optical signal. An optical coupler 92 splits the optical signal emitted from the light source 91. The split optical signal in the optical coupler 92 is transmitted in opposite directions through a looped optical fiber 93.

[0018] A sound-receiving sensor unit 94 is configured at a position different from the midpoint of optical fiber 93. The sensor unit 94 is positioned in the environment (hereinafter referred to as the sound field) where the sound of the detected object is generated. Furthermore, the sound field includes air and water, etc. When sound is generated in the sound field, the sound penetrates into the optical fiber 93 that constitutes the sensor unit 94, and the refractive index of the optical fiber 93 changes according to the sound pressure. As a result, the phase of the optical signal is modulated. Because the sensor unit 94 is configured at a position different from the midpoint of optical fiber 93, the timing of the modulation of the clockwise transmitted optical signal (hereinafter referred to as CW light) and the counterclockwise transmitted optical signal (hereinafter referred to as CCW light) by the sensor unit 94 is different.

[0019] Optical coupler 92 combines CW light and CCW light modulated at different timings and emits an optical signal representing the interference light between the CW and CCW light to a light-receiving element 95, such as a photodiode. The light-receiving element 95 converts the optical signal received from optical coupler 92 into an electrical signal and outputs it. Therefore, by demodulating the output signal of the light-receiving element 95 using signal processing circuitry or the like, sound generated in the sensor section 94 can be detected.

[0020] However, the acoustic impedance of the sound field generated by the sound of the object being detected differs significantly from that of the coating material constituting the periphery of the optical fiber 93. Therefore, in existing Sagnac interferometer microphones 100, a portion of the sound is reflected by the periphery of the optical fiber 93, raising concerns about reduced sound pressure penetrating into the fiber 93 and a decreased degree of change in the refractive index of the fiber 93. Consequently, there are concerns about the accuracy of sound detection.

[0021] Therefore, the inventors conducted in-depth research on microphones capable of detecting sound with high precision using optical fibers, and thus conceived of the various embodiments of this disclosure as shown below.

[0022] (1) A microphone according to one aspect of the present disclosure includes: a light source for outputting an optical signal; an optical coupler for splitting and combining the optical signal; a transmission path including an optical fiber, wherein the optical fiber transmits the split optical signal obtained by the optical coupler in opposite directions to the optical coupler; a sensor section connected to the transmission path for returning the split optical signal transmitted by the transmission path to the transmission path via a spatial section; and a light-receiving element for receiving the combined optical signal obtained by the optical coupler.

[0023] In this structure, the wavelength-splitting optical signal obtained by the optical coupler is transmitted through the optical fiber in opposite directions to the optical coupler, and then returns to the transmission path via the sensor section and the spatial section. Therefore, if sound is generated in the spatial section, the refractive index of the medium through which the wavelength-splitting optical signal passes can be directly changed without passing through the surface of the optical fiber. Thus, based on the combined optical signal received by the light-receiving element, the phase change of the optical signal caused by the sound generated in the spatial section can be clearly determined. As a result, the sound can be detected with high precision.

[0024] (2) The microphone described in (1) above may also include a pair of lenses disposed at both ends of the space.

[0025] In this structure, since a pair of lenses are provided at both ends of the spatial section, the degree of attenuation of the wavelength division optical signal in the spatial section can be reduced when the wavelength division optical signal returns to the transmission path through the spatial section.

[0026] (3) In the microphone described in (1) above, the sensor part may also include an optical waveguide for guiding the wavelength division optical signal, and the spatial part is disposed in the middle of the optical waveguide.

[0027] In this structure, since a space section is provided in the middle of the optical waveguide included in the sensor section, the wavelength-divided optical signal transmitted through the transmission path can be returned to the transmission path via the space section simply by using the optical waveguide to guide the wavelength-divided optical signal transmitted through the transmission path.

[0028] (4) In the microphone described in (3) above, the optical waveguide may also include multiple branch paths, and the spatial portion is disposed in the middle of the multiple branch paths.

[0029] In this structure, the optical waveguide includes multiple branch paths with spatial sections disposed along its length. Therefore, when guiding a wavelength-divided optical signal transmitted via the transmission path through this optical waveguide, the optical path length for the wavelength-divided optical signal to propagate within the spatial sections can be increased. This, in turn, enhances the degree to which the refractive index of the medium through which the wavelength-divided optical signal passes is directly altered by sound generated within the spatial sections.

[0030] (5) In the microphone described in (3) or (4) above, the optical fiber may also include a first optical fiber and a second optical fiber, one end of the optical waveguide is connected to the first optical fiber, and the other end of the optical waveguide is connected to the second optical fiber.

[0031] In this structure, since both ends of the optical waveguide are connected to the first optical fiber and the second optical fiber, the wavelength-divided optical signal transmitted from the first optical fiber to the optical waveguide can be transmitted to the second optical fiber, and the wavelength-divided optical signal transmitted from the second optical fiber to the optical waveguide can be transmitted to the first optical fiber. Therefore, the wavelength-divided optical signal transmitted from the transmission path containing the optical fiber to the sensor unit can be returned to the transmission path via the spatial unit.

[0032] (6) In the microphone described in (1) above, the sensor unit may also include: a pair of optical combiners and splitters for dividing the split optical signal into a group of optical signals with multiple wavelength components and combining the group of optical signals; and multiple split transmission paths for transmitting the group of optical signals obtained by splitting by one of the pair of optical combiners and splitters to the other of the pair of optical combiners and splitters via the space unit.

[0033] In this structure, when a wavelength-divided optical signal is split into multiple wavelength components by an optical combiner / splitter, these components are transmitted through multiple wavelength-divided transmission paths to another optical combiner / splitter via the space section, where they are combined. Therefore, if sound is generated in the space section, the refractive index of the medium through which each wavelength component of the optical signal passes through the signal group can change directly without passing through the surface of the optical fiber. Thus, based on the combined optical signal received by the light-receiving element, the timing of the phase changes of each wavelength component in the signal group can be determined, thereby allowing the estimation of the direction of arrival of the sound generated in the space section.

[0034] (7) In the microphone described in (6) above, the plurality of wavelength division transmission paths may also include a pair of lenses disposed at both ends of the space.

[0035] In this structure, since a pair of lenses are provided at both ends of the space portion included in each wavelength division transmission path, the degree of attenuation of each optical signal in the space portion can be reduced when each optical signal in the optical signal group returns to the transmission path via the space portion through each wavelength division transmission path.

[0036] (8) In the microphone described in (6) or (7) above, the optical fiber may also include a first optical fiber and a second optical fiber, one of the pair of optical combiners / splitters is connected to the first optical fiber, and the other of the pair of optical combiners / splitters is connected to the second optical fiber.

[0037] According to this structure, a wavelength-divided optical signal transmitted from the first optical fiber to an optical combiner / splitter can be divided into a group of optical signals with multiple wavelength components. This group of optical signals is then transmitted through multiple wavelength-divided transmission paths to another optical combiner / splitter for multiplexing before being transmitted to the second optical fiber. Furthermore, according to this structure, a wavelength-divided optical signal transmitted from the second optical fiber to the other optical combiner / splitter can be divided into a group of optical signals with multiple wavelength components. This group of optical signals is then transmitted through multiple wavelength-divided transmission paths to the first optical combiner / splitter for multiplexing before being transmitted to the first optical fiber. Thus, the wavelength-divided optical signal transmitted to the sensor unit via a transmission path including the optical fiber can be returned to the transmission path via a spatial unit.

[0038] (9) In the microphone described in (2) or (7) above, the lens may also be a collimating lens.

[0039] According to this structure, by using a collimating lens, it is possible to make the wavelength-divided optical signal or the signals contained in the group of optical signals with multiple wavelength components into parallel light for transmission in the spatial section. Therefore, it is possible to suppress the signal attenuation received by the optical element due to the diffusion of these signals in the spatial section.

[0040] Furthermore, the embodiments described below are all specific examples of this disclosure. The numerical values, shapes, structural elements, etc., shown in the following embodiments are examples and are not intended to limit this disclosure. In addition, structural elements in the following embodiments that are not described in independent technical solutions representing the highest-level concept are described as arbitrary structural elements. Furthermore, various contents can be combined in all embodiments.

[0041] (Implementation Method 1)

[0042] Figure 1 This is a diagram showing the overall structure of the microphone 1 in Embodiment 1. The microphone 1 includes: a light source 11, an optical coupler 12, a transmission path 13, a sensor unit 14, and a light-receiving element 15.

[0043] The light source 11 is connected to a driving circuit (driver) (not shown) and outputs a light signal corresponding to the driving signal output from the driving circuit. The light source 11 is, for example, constructed from an SLD (Super Luminescent Diode). However, the light source 11 is not limited to this and may also be constructed from an LED (Light Emitting Diode). Furthermore, compared to LEDs, SLDs have a higher output light signal intensity and output a light signal with higher interferometry; therefore, the light source 11 is preferably constructed from an SLD.

[0044] Optical coupler 12 is connected to light source 11, light receiving element 15, and transmission path 13 via optical fiber 130. Optical coupler 12 splits the optical signal input from light source 11 into two optical signals (hereinafter referred to as split-wavelength optical signals) and outputs these two split-wavelength optical signals to transmission path 13. In addition, optical coupler 12 combines the two split-wavelength optical signals input from transmission path 13 and outputs the optical signal representing the interference of the two light signals represented by the two split-wavelength optical signals (hereinafter referred to as combined optical signal) to light receiving element 15.

[0045] The transmission path 13 is composed of optical fiber 130, which transmits the two wavelength-divided optical signals obtained by the optical coupler 12 in opposite directions to the optical coupler 12. Figure 1 An example is shown below: one of the two wavelength division multiplexing (WDM) optical signals, "CW light" (hereinafter referred to as the first WDM optical signal), is transmitted clockwise to optical coupler 12, and the other WDM optical signal, "CCW light" (hereinafter referred to as the second WDM optical signal), is transmitted counterclockwise to optical coupler 12. The transmission path 13 is housed in a housing or the like, so that the optical signal transmitted within the optical fiber 130 is not modulated by ambient sound.

[0046] Specifically, optical fiber 130 is composed of optical fiber that transmits optical signals in single-mode. However, optical fiber 130 is not limited to this and may also be composed of optical fiber that transmits optical signals in multimode. Optical fiber 130 is classified into a first optical fiber 131 and a second optical fiber 132. The first optical fiber 131 and the second optical fiber 132 have different lengths. One end of the first optical fiber 131 and the second optical fiber 132 is connected to the optical coupler 12.

[0047] The sensor unit 14 is connected to the transmission path 13 via the first optical fiber 131 and the second optical fiber 132, allowing the two wavelength-divided optical signals transmitted through the transmission path 13 to return to the transmission path 13 via the space unit 40. The sensor unit 14 is positioned in the environment (hereinafter referred to as the sound field) where the sound of the detected object is generated. The sound field includes air and water, etc.

[0048] Specifically, the other ends of the first optical fiber 131 and the second optical fiber 132 are arranged to face each other via the space portion 40. In addition, a first lens 41 is provided at the other end of the first optical fiber 131, and a second lens 42 is provided at the other end of the second optical fiber 132. Thus, a pair of first lenses 41 and second lenses 42 are provided at both ends of the space portion 40.

[0049] The first lens 41 makes the first wavelength division optical signal transmitted to the other end of the first optical fiber 131 a parallel optical signal, which is then emitted through the space portion 40 towards the second lens 42. The second lens 42 makes the second wavelength division optical signal transmitted to the other end of the second optical fiber 132 a parallel optical signal, which is then emitted through the space portion 40 towards the first lens 41. Additionally, the first lens 41 focuses the second wavelength division optical signal incident from the second lens 42 via the space portion 40 and emits it towards the other end of the first optical fiber 131. Conversely, the second lens 42 focuses the first wavelength division optical signal incident from the first lens 41 via the space portion 40 and emits it towards the other end of the second optical fiber 132.

[0050] The first lens 41 and the second lens 42 are, for example, collimating lenses. However, one or more of the first lens 41 and the second lens 42 may also be, for example, a plano-convex lens or other lens that makes the optical signal parallel light and emits it. In these cases, it is possible to suppress the attenuation of the first wavelength division optical signal and the second wavelength division optical signal transmitted to the optical coupler 12 due to diffusion between the other end of the first optical fiber 131 and the other end of the second optical fiber 132.

[0051] With the above structure, the first wavelength-divided optical signal obtained by the optical coupler 12 is transmitted to the first lens 41 of the sensor section 14 through the first optical fiber 131 of the transmission path 13. Then, the first wavelength-divided optical signal is emitted through the space section 40 via a pair of first lenses 41 and second lenses 42 to the other end of the second optical fiber 132 of the transmission path 13, and is transmitted to the optical coupler 12 through the second optical fiber 132.

[0052] On the other hand, the second-wavelength-divided optical signal obtained by the optical coupler 12 is transmitted to the second lens 42 of the sensor section 14 through the second optical fiber 132 of the transmission path 13. After that, the second-wavelength-divided optical signal is emitted through the space section 40 via a pair of second lenses 42 and first lenses 41 to the other end of the first optical fiber 131 of the transmission path 13, and is transmitted to the optical coupler 12 through the first optical fiber 131.

[0053] Optical coupler 12 combines the first wavelet optical signal and the second wavelet optical signal transmitted from transmission path 13, and outputs the combined optical signal representing the interference of the two lights represented by the first wavelet optical signal and the second wavelet optical signal to the light receiving element 15.

[0054] The light-receiving element 15 receives the combined optical signal output from the optical coupler 12, converts the received combined optical signal into an electrical signal, and outputs it. The light-receiving element 15 is, for example, composed of a photodiode.

[0055] In the microphone 1 of this structure, the first and second wave-split optical signals obtained by wave splitting in the optical coupler 12 are transmitted to the optical coupler 12 in opposite directions via the optical fiber 130. Midway through this transmission, the first and second wave-split optical signals return to the optical fiber 130 via the sensor section 14 and the space section 40. Therefore, when sound is generated in the space section 40, the refractive index of the medium through which the first and second wave-split optical signals pass can be directly changed without passing through the surface of the optical fiber 130. Thus, based on the combined optical signal received by the light-receiving element 15, the phase change of the optical signal caused by the sound generated in the space section 40 can be clearly determined. As a result, the sound can be detected with high precision.

[0056] (Implementation Method 2)

[0057] The structure of the microphone 1 in Embodiment 2 of this disclosure will be described below. The microphone 1 in Embodiment 2 is similar to the sensor unit 14 in Embodiment 1. Figure 1 The structure is different. The sensor unit 14a in Embodiment 2 ( Figure 2 The feature is that it includes an optical waveguide 44 for guiding the wavelength division multiplexing (WDM) optical signal, and a spatial portion 40 is disposed in the middle of the optical waveguide 44.

[0058] Figure 2 This is a diagram showing the structure of the sensor unit 14a in Embodiment 2. Specifically, as shown... Figure 2 As shown, the sensor unit 14a includes a substrate 43 having a spatial portion 40. The spatial portion 40 is formed by cutting away a portion of the substrate 43. An optical waveguide 44 is formed in the substrate 43, which guides an optical signal from one end 431 of the substrate 43 through a first end 401 and a second end 402 that are opposed to each other in the spatial portion 40 to the other end 432 of the substrate 43. The other end of a first optical fiber 131 is connected to one end 431 of the substrate 43, and the other end of a second optical fiber 132 is connected to the other end 432 of the substrate 43. That is, one end of the optical waveguide 44 is connected to the other end of the first optical fiber 131, and the other end of the optical waveguide 44 is connected to the other end of the second optical fiber 132.

[0059] The sensor unit 14a of Embodiment 2 can transmit the first wave-splitting optical signal and the second wave-splitting optical signal from the other end of the first optical fiber 131 to the other end of the second optical fiber 132 via the space portion 40 through the optical waveguide 44 formed in the substrate 43, thus eliminating the trouble of the above-mentioned configuration.

[0060] In addition, Figure 2 In this design, the shape of the spatial portion 40 is rectangular, but the shape of the spatial portion 40 is not limited to this. For example, the shape of the spatial portion 40 can also be elliptical or other shapes. Correspondingly, the positions of the first end 401 and the second end 402, which are opposite each other in the spatial portion 40, through which the optical waveguide 44 passes can also be changed.

[0061] In addition, Figure 2 In this example, the two ends of the optical waveguide 44 are formed as opposite ends of the substrate 43a in the long side direction. However, this is not a limitation; the two ends of the optical waveguide 44 may also be located as opposite ends of the substrate 43a in the short side direction. Alternatively, one end of the optical waveguide 44 may be located at either of the opposite ends of the substrate 43a in the short side direction, and the other end of the optical waveguide 44 may be located at either of the opposite ends of the substrate 43a in the long side direction.

[0062] Figure 3 This is a diagram showing a modified structure of the sensor section 14a in Embodiment 2. Additionally, for example, as... Figure 3 As shown, the first end 401 ( Figure 2 It includes multiple first branch ends 401a, second ends 402 ( Figure 2 The optical waveguide 44 includes multiple second branch ends 402a opposite to multiple first branch ends 401a. Thus, the optical waveguide 44 ( Figure 2 It can also contain multiple branch optical waveguides 44a (branch paths).

[0063] Figure 3 Optical waveguide 44 is shown. Figure 2 An example containing six branch optical waveguides 44a. That is, the six branch optical waveguides 44a are respectively formed to guide optical signals from one end 431a of the substrate 43a through the first branch end 401a and the second branch end 402a that are opposite to each other in the space portion 40 to the other end 432a of the substrate 43a.

[0064] This structure and Figure 2 Compared to the structure of the sensor section 14a shown, the optical path lengths for the first and second wavelet-division optical signals transmitted in the space section 40 are increased. Therefore, it is possible to improve the degree to which the refractive index of the medium through which the first and second wavelet-division optical signals pass is directly changed by the sound generated in the space section 40.

[0065] (Implementation Method 3)

[0066] The structure of the microphone 1 in Embodiment 3 of this disclosure will be described below. The microphone 1 in Embodiment 3 is similar to the sensor unit 14 in Embodiments 1 and 2. Figure 1 , Figure 2 , Figure 3 The structures are different. Figure 4 This is a diagram showing the structure of the sensor unit 14b in Embodiment 3.

[0067] like Figure 4 As shown, the sensor unit 14b of Embodiment 3 ( Figure 4 It has a pair of first optical splitter 451 and second optical splitter 452 that are opposite each other via the space section 40, and multiple split transmission paths 460.

[0068] The first optical combiner / splitter 451 is connected to the other end of the first optical fiber 131. The first optical combiner / splitter 451 splits the first wavelength-divided optical signal transmitted to the other end of the first optical fiber 131 into a group of optical signals with multiple distinct wavelength components. The second optical combiner / splitter 452 is connected to the other end of the second optical fiber 132. The second optical combiner / splitter 452 splits the second wavelength-divided optical signal transmitted to the other end of the second optical fiber 132 into a group of optical signals with the same wavelength components as the first optical combiner / splitter 451.

[0069] Multiple wavelength division multiplexing transmission paths 460 transmit optical signal groups obtained by demultiplexing from one of the first optical combiner / demultiplexer 451 and the second optical combiner / demultiplexer 452 via the space section 40 to the other of the first optical combiner / demultiplexer 451 and the second optical combiner / demultiplexer 452. That is, multiple wavelength division multiplexing transmission paths 460 transmit optical signal groups obtained by demultiplexing from the first optical combiner / demultiplexer 451 via the space section 40 to the second optical combiner / demultiplexer 452, and on the other hand, transmit optical signal groups obtained by demultiplexing from the second optical combiner / demultiplexer 452 via the space section 40 to the first optical combiner / demultiplexer 451.

[0070] Specifically, the multiple wavelength division transmission paths 460 each have a pair of third lenses 461 and fourth lenses 462 disposed at both ends of the spatial section 40.

[0071] The third lens 461 and the fourth lens 462 are configured to face each other via the space section 40. The third lens 461 is connected to the first optical combiner / splitter 451 via optical fiber 130. The third lens 461 makes the optical signal of one wavelength component obtained by the first optical combiner / splitter 451 into a parallel optical signal, and emits it through the space section 40 toward the fourth lens 462. The fourth lens 462 is connected to the second optical combiner / splitter 452 via optical fiber 130. The fourth lens 462 makes the optical signal of one wavelength component obtained by the second optical combiner / splitter 452 into a parallel optical signal, and emits it through the space section 40 toward the third lens 461.

[0072] Furthermore, the third lens 461 focuses the light signal incident from the fourth lens 462 via the spatial section 40, and transmits the focused light signal to the first optical combiner / splitter 451 via the optical fiber 130. The fourth lens 462 focuses the light signal incident from the third lens 461 via the spatial section 40, and transmits the focused light signal to the second optical combiner / splitter 452 via the optical fiber 130.

[0073] The third lens 461 and the fourth lens 462 are, for example, collimating lenses. However, one or more of the third lens 461 and the fourth lens 462 may also be, for example, a plano-convex lens or other lens that makes the optical signal parallel and emits it. In these cases, it is possible to suppress the diffusion of the optical signal group with multiple wavelength components obtained by splitting by one of the first optical combiner / splitter 451 and the second optical combiner / splitter 452 in the spatial section 40, thereby preventing the attenuation of the optical signal group transmitted to the other of the first optical combiner / splitter 451 and the second optical combiner / splitter 452.

[0074] When the optical signal group with multiple wavelength components obtained by the second optical combiner / splitter 452 is transmitted through the fourth lens 462, the spatial section 40, and the third lens 461, the first optical combiner / splitter 451 further combines the optical signal group and outputs the combined optical signal to the other end of the first optical fiber 131. Similarly, when the optical signal group with multiple wavelength components obtained by the first optical combiner / splitter 451 is transmitted through the third lens 461, the spatial section 40, and the fourth lens 462, the second optical combiner / splitter 452 further combines the optical signal group and outputs the combined optical signal to the other end of the second optical fiber 132.

[0075] In this structure, the refractive index of the medium through which the light signals of each wavelength component transmitted in the space section 40 pass does not change directly via the surface of the optical fiber 130, thus, based on the combined light signal received by the light receiving element 15, the timing of the phase change of the light signal of each wavelength component can be determined, thereby estimating the direction of arrival of the sound generated in the space section 40.

[0076] The microphone disclosed herein is capable of detecting sound with high precision using optical fiber, and is therefore useful as a meter for sound generated in the air and water, as well as an AE sensor.

Claims

1. A microphone, comprising: Light source, outputs light signal; An optical coupler is used to split and combine the optical signal. The transmission path includes an optical fiber, which transmits the wavelength-divided optical signals obtained by the optical coupler in opposite directions to the optical coupler. The sensor unit, connected to the transmission path, returns the wavelength division optical signal transmitted by the transmission path to the transmission path via the space unit; and The light-receiving element receives the combined optical signal obtained by the optical coupler.

2. The microphone according to claim 1, wherein, The microphone includes a pair of lenses disposed at both ends of the space.

3. The microphone according to claim 1, wherein, The sensor unit includes an optical waveguide for guiding the wavelength division optical signal. The spatial portion is located in the middle of the optical waveguide.

4. The microphone according to claim 3, wherein, The optical waveguide includes multiple branch paths. The space section is located in the middle of the multiple branch roads.

5. The microphone according to claim 3, wherein, The optical fiber includes a first optical fiber and a second optical fiber. One end of the optical waveguide is connected to the first optical fiber. The other end of the optical waveguide is connected to the second optical fiber.

6. The microphone according to claim 1, wherein, The sensor unit includes: A pair of optical combiners and splitters are used to split the wavelength-demultiplexed optical signal into a group of optical signals with multiple wavelength components and to combine the optical signal groups. and Multiple wavelength division transmission paths transmit the optical signal group obtained by wavelength division by one of the pair of optical combiners / demultiplexers to the other of the pair of optical combiners / demultiplexers via the spatial section.

7. The microphone according to claim 6, wherein, The multiple wavelength division transmission paths each include a pair of lenses disposed at both ends of the spatial section.

8. The microphone according to claim 6, wherein, The optical fiber includes a first optical fiber and a second optical fiber. One of the pair of optical combiners / demultiplexers is connected to the first optical fiber. The other of the pair of optical splitters is connected to the second optical fiber.

9. The microphone according to claim 2 or 7, wherein, The lens is a collimating lens.

Images