Optical microphone and sound wave detection method

Abstract

The invention provides an optical microphone and a sound wave detection method. The optical microphone includes: an MEMS structural member configured to generate a vibration displacement in response to a sound wave; the laser device is configured to emit laser to the MEMS structural member and receive reflected light of the MEMS structural member, so that self-mixing interference is formed in the MEMS structural member, and the emergent light intensity of the laser device linearly changes along with the vibration displacement; and the photoelectric detector is configured to convert the emergent light intensity into a current signal reflecting the sound wave. Linear conversion between sound wave vibration and an electric signal is realized by regulating and controlling a feedback intensity factor, and a complex demodulation process is omitted; by adopting the compact integration or split type optical path design of the MEMS structure, the laser and the detector, the system has the advantages of high sensitivity, high environmental adaptability, easiness in mass production and the like.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of optical acoustic detection, and in particular to an optical microphone and an acoustic detection method. BACKGROUND

[0002] With the growing demand for human-computer voice interaction in application scenarios such as intelligent terminals and vehicle-mounted systems, the importance of microphones as core sensors is increasingly prominent. Traditional electret microphones (ECM) have been difficult to meet the performance requirements of modern intelligent devices due to problems such as large size, low sensitivity, poor anti-interference performance, and poor temperature resistance.

[0003] How to realize a microphone with small size, simple structure, and good performance has become a technical problem to be solved. SUMMARY

[0004] Embodiments of the present disclosure provide an optical microphone, an acoustic detection method, and an assembly method of an optical microphone.

[0005] In a first aspect, embodiments of the present disclosure provide an optical microphone, comprising: a MEMS structure configured to generate a vibration displacement in response to an acoustic wave; a laser configured to emit laser light to the MEMS structure and receive reflected light thereof, to form a self-mixing interference inside, so that an outgoing light intensity of the laser changes linearly with the vibration displacement; and a photodetector configured to convert the outgoing light intensity into a current signal reflecting the acoustic wave.

[0006] In some embodiments, the optical path parameters between the laser and the MEMS structure are configured to cause the self-mixing interference to be in a linear operating region so that the outgoing light intensity and the vibration displacement are in a linear relationship.

[0007] In some embodiments, the feedback intensity factor of the self-mixing interference corresponding to the linear operating region satisfies an interval of 1 to 2.

[0008] In some embodiments, the laser is a laser diode outputting a single-mode laser with a steady-state wavelength; the photodetector is a photodiode, and an output current signal thereof is in a linear proportional relationship with the outgoing light intensity received from the laser.

[0009] In some embodiments, the laser diode and the photodiode are integrated in a TO package base; and the MEMS structure is connected to the TO package base through a support positioning structure.

[0010] In some embodiments, the optical microphone further comprises: a fiber beam splitter disposed at an outgoing end of the laser and configured to split a part of the outgoing light intensity after the self-mixing interference and guide it to the photodetector.

[0011] In some embodiments, the optical microphone further comprises: a micro-mirror arranged between the laser and the MEMS structure, configured to reflect the laser emitted by the laser to the MEMS structure, and reflect the laser reflected by the MEMS structure back to the laser cavity along the original light path to achieve self-mixing interference.

[0012] In some embodiments, the MEMS structure is any one of a MEMS membrane, a MEMS sheet, a MEMS beam, or a MEMS spherical shell.

[0013] In some embodiments, the optical microphone further comprises: a laser driving module configured to provide constant current power supply to the laser; a current signal processing circuit configured to amplify and convert the current signal output by the photodetector into a voltage signal; and a signal acquisition device configured to acquire the voltage signal.

[0014] In a second aspect, the embodiments of the present disclosure provide a self-mixing interference-based acoustic wave detection method, comprising: generating a vibration displacement in response to an external acoustic wave by a MEMS structure; emitting laser to the MEMS structure by a laser and receiving reflected light thereof, the reflected light returning to the laser cavity and forming self-mixing interference with the laser field in the cavity, so that the outgoing light intensity of the laser changes linearly with the vibration displacement; receiving the outgoing light intensity by a photodetector and converting it into a current signal reflecting the acoustic wave.

[0015] In some embodiments, the step of emitting laser to the MEMS structure by a laser and receiving reflected light thereof, the reflected light returning to the laser cavity and forming self-mixing interference with the laser field in the cavity, so that the outgoing light intensity of the laser changes linearly with the vibration displacement, comprises: emitting single-mode laser of a steady-state wavelength by the laser; the laser irradiating to the surface of the MEMS structure and reflecting back to the laser cavity along the original path; the reflected light forming self-mixing interference with the laser field in the cavity; and configuring the optical path parameters between the laser and the MEMS structure so that the self-mixing interference is in a linear working region to make the outgoing light intensity and the vibration displacement have a linear relationship.

[0016] In some embodiments, the acoustic wave detection method further comprises: converting and amplifying the current signal into a voltage signal by a current signal processing circuit; and inputting the voltage signal into a signal acquisition device for analysis to obtain the sound pressure amplitude and frequency characteristics of the acoustic wave.

[0017] In a third aspect, the embodiments of the present disclosure provide an assembly method of an optical microphone, comprising: providing a MEMS structure piece that generates a vibration displacement in response to an external sound wave; arranging a laser and a photodetector to form an optical unit for laser emission and light intensity detection; constructing an optical path between the MEMS structure piece and the optical unit, so that the laser emitted by the laser is reflected back to the laser cavity through the MEMS structure piece, forming a self-mixing interference in the cavity, so that the outgoing light intensity of the laser changes linearly with the vibration displacement, and the photodetector receives the outgoing light intensity of the laser and converts it into a current signal reflecting the sound wave.

[0018] In some embodiments, wherein the optical path between the MEMS structure piece and the optical unit is constructed, comprising: integrating the laser and the photodetector in a TO package base; mounting the MEMS structure piece on the TO package base through a support positioning structure to realize optical axis alignment with the laser outgoing direction.

[0019] In some embodiments, wherein the optical path between the MEMS structure piece and the optical unit is constructed, comprising: providing a fiber splitter at the laser outgoing end; guiding the laser emitted by the laser to the MEMS structure piece through the fiber splitter, and making the reflected light return to the laser cavity through the original path; guiding the outgoing light intensity to the photodetector through the fiber splitter.

[0020] In some embodiments, wherein the optical path between the MEMS structure piece and the optical unit is constructed, comprising: providing a micro-mirror between the laser and the MEMS structure piece, wherein the micro-mirror reflects the laser emitted by the laser to the surface of the MEMS structure piece, and guides the reflected light to return to the laser cavity along the original path.

[0021] The present disclosure provides a MEMS optical microphone based on the principle of optical self-mixing interference and a sound wave detection method. The microphone can integrate an optical path for vibration measurement inside a small size probe. The generated electrical signal does not need complex modulation and demodulation, and can be read out only through simple amplification processing, thereby effectively simplifying the system structure. The microphone has the characteristics of compact structure, simple manufacturing process and low cost, and can realize high-precision spatial acoustic signal pickup and measurement, and has good integration and commercial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a block diagram of an optical microphone according to an embodiment of the present disclosure;

[0023] Figure 2 is a flowchart of a sound wave detection method based on self-mixing interference according to an embodiment of the present disclosure;

[0024] Figure 3 is a flowchart of an assembly method of an optical microphone according to an embodiment of the present disclosure;

[0025] Figure 4 is an installation embodiment of an optical microphone according to an embodiment of the present disclosure;

[0026] Figure 5 is a structural diagram of an experimental device for verifying Figure 4 the feasibility of the system;

[0027] Figure 6 A in is the voltage output result of the optical microphone according to an embodiment of the present disclosure under different sound pressure conditions, and B is the voltage output waveform of the optical microphone according to an embodiment of the present disclosure under 800Hz, 100mPa sound pressure excitation;

[0028] Figure 7 is a structural schematic diagram of an optical microphone according to an embodiment of the present disclosure under different MEMS structure forms;

[0029] Figure 8 is a structural schematic diagram of an optical microphone according to an embodiment of the present disclosure adopting a fiber beam splitting configuration;

[0030] Figure 9 is a structural schematic diagram of an optical microphone according to an embodiment of the present disclosure adopting a micro mirror auxiliary optical path configuration. DETAILED DESCRIPTION

[0031] In order for those skilled in the art to better understand the technical solutions of the present disclosure, the technical solutions of the present disclosure will be described in detail below with reference to the drawings.

[0032] In the following, the example embodiments will be described more fully with reference to the accompanying drawings, in which, however, the example embodiments can be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, the purpose of the embodiments is to explain the present disclosure fully and to provide those skilled in the art with a full understanding of the scope of the present disclosure.

[0033] The embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0034] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0036] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an overly literal or overly formal sense unless expressly so defined herein.

[0037] In the present disclosure, the following technical terms should be understood as follows, unless otherwise specified:

[0038] Self-Mixing Interference (SMI), also known as Optical Feedback Interference (OFI), refers to a phenomenon that the laser emitted by a laser is reflected by an external reflecting surface (such as a MEMS structure) and re-coupled into the laser cavity, and interacts with the light field in the cavity to cause modulation of the outgoing light intensity. The intensity is quantified by the feedback strength factor.

[0039] The feedback strength factor (C) is a dimensionless parameter that characterizes the degree of influence of external feedback light on the working state of the laser.

[0040] MEMS is an acoustic sensitive structure based on micro-electro-mechanical system technology, which converts acoustic pressure signals into mechanical vibration displacement.

[0041] Optical path parameters refer to designable variables that affect the feedback strength of self-mixing interference.

[0042] MEMS (Micro-electro mechanical system) microphones have advantages of small size, easy integration, high sensitivity and strong robustness. In a MEMS microphone, a structure based on an optical sensing principle has significant advantages in sensitivity and signal-to-noise ratio compared with a microphone based on a capacitive, inductive or other principle. In some related technologies, a fiber-optic interference type structure of an optical MEMS microphone can achieve a millimeter-level probe, but relies on a complex interference demodulation algorithm and a large number of large equipment, and has problems such as fiber polarization fading, which limits the signal long-distance transmission capability. A grating interference type MEMS microphone has strong performance, but the manufacturing process is complex and the cost is high, which is difficult to be widely applied. In summary, the existing MEMS microphone based on optical sensing still has limitations in sensitivity, signal demodulation complexity, structure size, integration difficulty and manufacturing cost to different degrees.

[0043] The present disclosure aims to overcome the problems of existing optical MEMS microphones, such as complex structure, difficult signal demodulation and high manufacturing cost, and provides a MEMS optical microphone based on self-mixing interference principle, which has advantages of simple structure, small size, low cost and convenient signal processing, and is suitable for high-precision detection of various spatial acoustic signals.

[0044] The present disclosure provides an optical microphone based on self-mixing interference, which converts the vibration of a MEMS under the excitation of a sound wave into an electrical signal output by using the self-mixing interference principle. The sound causes the MEMS structure to vibrate slightly, changes the optical path length of the external cavity of the laser, induces interference between the reflected light and the laser in the cavity, and changes the outgoing light intensity with the displacement. The photodetector receives the change in light intensity and outputs a current signal, and the overall system maintains linear response without the need for demodulation to directly obtain the sound waveform. The present disclosure integrates the MEMS element, the laser and the detector in a millimeter-level probe, has advantages of compact structure, sensitive response, strong anti-interference and no need for complex signal processing, and is suitable for high-precision and miniaturized sound signal detection scenarios.

[0045] The MEMS optical microphone based on self-mixing interference of the present disclosure converts the movement of a MEMS excited by a sound signal into an electrical signal output by using the self-mixing interference principle, and realizes extremely high sensitivity sound signal detection.

[0046] Figure 1 is a block diagram of an optical microphone according to an embodiment of the present disclosure.

[0047] In a first aspect, referring to Figure 1 The present disclosure provides an optical microphone, which comprises:

[0048] The MEMS structure 101 is configured to generate a vibration displacement in response to a sound wave.

[0049] a laser 102 configured to emit laser light to the MEMS structure and receive reflected light therefrom to form self-mixing interference inside the laser, so that an output light intensity of the laser varies linearly with the vibration displacement;

[0050] a photodetector 103 configured to convert the output light intensity into an electrical current signal reflecting the acoustic wave.

[0051] In embodiments of the present disclosure, as shown in Figure 1 The present disclosure provides an optical microphone based on the principle of self-mixing interference, which includes a MEMS structure 101, a laser 102, and a photodetector 103.

[0052] The MEMS structure 101 is a micro-electro-mechanical system element that is driven to vibrate when a spatial acoustic wave signal acts on its structure, thereby generating a continuously changing vibration displacement x in the time dimension. This displacement changes the length of the propagation path of the laser in the external cavity, causing the laser to experience an optical path change of 2x during propagation.

[0053] The laser 102 emits laser light to the MEMS structure 101, which is reflected from the MEMS surface back to the cavity of the laser from the light emission direction, and coupled with the original laser in the cavity to form a self-mixing interference phenomenon. This interference effect modulates the MEMS vibration displacement into the output light intensity of the laser. Under the medium feedback conditions designed in the present disclosure (for example, the feedback strength factor is controlled between 1 and 2), the change of the output light intensity is linearly related to the vibration displacement of the MEMS structure, thereby realizing linear modulation output of the interference signal and ensuring the simplicity of signal processing without the need for large-scale instrument measurement equipment.

[0054] The photodetector 103 receives the output light of the laser and can convert the received light intensity change into a corresponding electrical current signal. This electrical current signal carries the vibration information of the MEMS responding to the acoustic wave, and thus can be used for subsequent extraction of sound features or acoustic analysis.

[0055] In some embodiments, the optical path parameters between the laser and the MEMS structure are configured such that the self-mixing interference is in a linear operating region to make the output light intensity linearly related to the vibration displacement.

[0056] In some embodiments, the feedback strength factor of the self-mixing interference corresponding to the linear operating region satisfies the interval of 1 to 2.

[0057] In the embodiments of the present disclosure, the feedback intensity factor of the self-mixing interference is controlled by reasonably designing the optical path parameters between the laser 102 and the MEMS structure 101, so that the change of the outgoing light intensity caused by the change of the optical path and the vibration displacement of the MEMS structure 101 are in a proportional relationship. The optical path parameters include but are not limited to the distance (external optical path length) from the laser 102 to the MEMS structure 101, the reflectivity of the MEMS surface, the model and structural parameters of the laser, etc. The above multiple optical path parameters need to be designed comprehensively to ensure that the feedback intensity factor of the self-mixing interference is between 1 and 2, and the feedback level (i.e. feedback regime) is in the medium feedback interval. The feedback intensity factor is a parameter for measuring the degree of influence of the return light on the field in the laser cavity, and when it is in this interval, the output response curve of the self-mixing interference is approximately linear, and the outgoing light intensity changes linearly with the change of the optical path (or displacement).

[0058] Under this design condition, the outgoing light intensity of the laser 102 is proportional to the displacement x, which satisfies: E = E0 + K * 2x

[0059] Wherein, E0 is the outgoing light intensity of the laser 102 in the undisturbed state; K is the change coefficient of the outgoing light intensity of the laser diode caused by the change of the optical path and the self-mixing interference; x is the vibration displacement of the MEMS structure 101 caused by the external sound driving, that is, half of the change of the optical path of the light reflected back to the laser diode after the laser exits through the MEMS structure 101, and x = 0 when there is no external disturbance.

[0060] The photodetector 103 receives the outgoing light intensity and converts it into a current signal:

[0061] I pd = N * (E0 + K * 2x)

[0062] Which can also be expressed as:

[0063] I pd = I0 + N * K * 2x

[0064] Wherein, N represents the proportional coefficient of the photodiode for converting the outgoing light intensity of the LD into the photocurrent; I0 = N·E0 is the photocurrent of the photodiode under the outgoing light intensity of the laser 102 in the undisturbed state.

[0065] Since the displacement of the MEMS structure 101 and the change of the light intensity are in a linear relationship, and the photodetector 103 has a linear response characteristic, the final output current signal is proportional to the vibration displacement x of the MEMS structure 101, realizing the linear conversion from the sound wave to the electrical signal. This mechanism significantly simplifies the signal processing process, without the need for a phase-locked amplifier or complex demodulation algorithm, but through a simple circuit to output the original sound waveform signal, which is suitable for various types of signal acquisition devices.

[0066] Further, the vibration displacement of the MEMS structure 101 under the acoustic wave excitation at a single frequency can be expressed as:

[0067] x = A * sin(2πft)

[0068] where t is time, A is the vibration amplitude of the MEMS structure 101 affected by sound, and f is the vibration frequency of the MEMS structure 101 affected by sound, which is basically equivalent to the sound frequency.

[0069] In some embodiments, the laser is a laser diode outputting a single-mode laser at a steady wavelength; and the photodetector is a photodiode, and the output current signal of the photodiode is linearly proportional to the received outgoing light intensity from the laser.

[0070] In the embodiments of the present disclosure, the laser 102 is a laser diode (such as a Fabry-Perot laser diode or a vertical cavity surface emitting laser (VCSEL)), which emits a single-mode laser at a steady wavelength λ to ensure the formation of a stable self-mixing interference signal. After the laser is emitted through the light outlet, it irradiates the reflecting surface of the MEMS structure 101 and is reflected back to the light path, and finally returns to the inside of the laser cavity, and is coupled with the in-cavity laser field to form a self-mixing interference phenomenon.

[0071] In the preferred embodiments, to simplify the optical path structure and improve the feedback efficiency, the reflecting surface of the MEMS structure 101 is preferably arranged perpendicularly to the light emission direction of the laser 102, so that the outgoing light can be reflected vertically back to the laser cavity. However, the present disclosure does not limit the perpendicular arrangement relationship. The reflecting mirror can also be arranged to deflect the light path, so that the laser irradiates the surface of the MEMS structure arranged obliquely, and the final path of the laser returning to the laser diode cavity is realized by means of auxiliary optical devices such as interference mirrors, to ensure the formation of an effective self-mixing interference signal.

[0072] In the embodiments of the present disclosure, the photodetector 103 is preferably a photodiode, which receives the outgoing light from the laser diode, and the output current signal of the photodiode is linearly proportional to the outgoing light intensity. That is, when the outgoing light intensity of the laser 102 changes due to the vibration of the MEMS structure 101, the photodiode can linearly respond to the change of the light intensity and generate a current signal proportional thereto. The current signal output by the photodetector is linearly related to the vibration displacement x of the MEMS structure. This linear relationship is due to the modulation relationship between the light intensity and the vibration displacement (through the linear interval at a medium feedback level of the feedback intensity control) and the linear photoelectric conversion characteristics of the photodiode.

[0073] In some embodiments, the laser diode and the photodiode are integrated in a TO package base;

[0074] The MEMS structure 101 is connected to the TO package base through a support positioning structure.

[0075] In the embodiments of the present disclosure, the laser diode and the photodiode are integrated in the same package base, for example, in the form of a TO package. The MEMS structure is connected to the package base through a support positioning structure, thereby realizing coaxial integration and stable alignment of the laser 102, the MEMS structure 101 and the photodetector 103. This structure helps to improve the overall compactness, assembly precision and batch processing consistency of the system, and is suitable for the packaging requirements of miniaturized sensor modules.

[0076] In some embodiments, the optical microphone further comprises:

[0077] An optical fiber beam splitter is arranged at the exit end of the laser and configured to split a part of the exit light intensity after self-mixing interference and guide it to the photodetector.

[0078] In the embodiments of the present disclosure, the optical microphone further comprises an optical fiber beam splitter arranged at the exit end of the laser, for splitting a part of the exit light intensity after self-mixing interference and guiding it to the photodetector for light intensity monitoring. This structure allows the laser and the photodetector to be arranged away from the MEMS structure, which is suitable for occasions where the MEMS probe needs to be inserted into a narrow space or a high interference environment, thereby enhancing the applicability and environmental robustness of the system.

[0079] In some embodiments, the optical microphone further comprises:

[0080] A miniature mirror is arranged between the laser and the MEMS structure and configured to reflect the laser emitted by the laser to the MEMS structure and reflect the laser reflected by the MEMS structure back to the laser cavity along the original light path to realize self-mixing interference.

[0081] In the embodiments of the present disclosure, the optical microphone further comprises a miniature mirror arranged between the laser 102 and the MEMS structure 101, for reflecting the laser beam emitted by the laser to the surface of the MEMS structure at a predetermined angle, while reflecting the reflected light back to the laser cavity along the original path to complete the self-mixing interference. The mirror can be a mirror formed by micro-machining, an integrated prism or a reflective coating glass component. This structure is particularly suitable for non-axial optical path design, such as lateral arrangement or flat packaging scenarios, and can further expand the application range of the optical microphone under different spatial conditions.

[0082] In some embodiments, the MEMS structure is a micro-electro-mechanical system element capable of vibrating in response to sound waves and having a reflectivity for implementing linear feedback of self-mixing interference.

[0083] In some embodiments, the MEMS structure is any one of a MEMS membrane, a MEMS sheet, a MEMS beam, or a MEMS spherical shell.

[0084] In embodiments of the present disclosure, the MEMS structure 101 can be any micro mechanical structure capable of vibrating in response to sound waves and having a suitable reflectivity for generating vibration or deformation of the optical path of the laser in response to the sound pressure of the external sound. The structure has the following basic conditions: one is capable of generating effective vibration displacement under the driving of sound waves, and the other is that the surface thereof has a suitable reflectivity to ensure that the feedback strength factor is within a reasonable range and an effective self-mixing interference signal is formed. The MEMS structure includes but is not limited to micro-electro-mechanical elements such as a MEMS membrane, a MEMS sheet, a MEMS beam, and a MEMS spherical shell. Different structure forms can be selected according to specific application scenarios to meet the requirements of frequency response range, sensitivity, or package volume and the like.

[0085] In some embodiments, the optical microphone further includes a laser driving module configured to provide constant current power supply to the laser.

[0086] In embodiments of the present disclosure, to ensure that the laser 102 works stably and reliably, the laser is powered by a constant current source provided by a laser driving module. The working mode of the commonly used laser diode requires constant current power supply.

[0087] In some embodiments, the optical microphone further includes a current signal processing circuit configured to convert the current signal output by the photodetector into a voltage signal and amplify the voltage signal.

[0088] In embodiments of the present disclosure, the current signal output by the photodetector 103 is processed by a current signal processing circuit. The circuit can adopt a transimpedance amplifier (TIA) structure to convert a weak current signal (such as μA level) into a readable voltage signal (such as hundreds of millivolts) and output to a signal acquisition module for further analysis. In other embodiments, the current signal can also be directly amplified to mA level and input into a collection device supporting current collection.

[0089] In embodiments of the present disclosure, the output voltage (or current) signal does not need to be demodulated, but can directly restore the corresponding sound wave form, and can use a short-time Fourier transform or other time-frequency algorithm to perform real-time frequency analysis on the sound. The relationship between the output signal amplitude and the actual sound pressure can be obtained through an acoustic calibration experiment.

[0090] In some embodiments, the optical microphone further comprises a signal acquisition device configured to acquire the voltage signal.

[0091] In the embodiments of the present disclosure, the signal acquisition device is a signal reading device, and its specific form can be flexibly selected according to the application scenario, and is not limited to a single device type. In the experimental, test or scientific research occasions, the signal acquisition device can be various signal acquisition devices such as an oscilloscope, a frequency meter, a lock-in amplifier (LIA) and the like. Since the laser intensity modulation link and the photoelectric conversion link in the present disclosure both maintain a linear relationship, the acquired voltage signal can not need to be demodulated, and the processing requirement of the acquisition device is further simplified.

[0092] It should be noted that the signal acquisition device is not a component of the optical microphone structure of the present application, but an optional external device according to the application scenario, which is used to further sample, digitize and perform time domain waveform or frequency domain feature analysis on the voltage signal output by the current signal processing circuit.

[0093] In some embodiments, the MEMS structure, the laser and the photodetector are integrated in a probe with a diameter of not more than 6 mm and a length of not more than 4 mm.

[0094] In the embodiments of the present disclosure, the MEMS structure 101, the laser 102 and the photodetector 103 can be integrally packaged, and in the specific implementation process, can be packaged in a probe with a size of about 6 mm in diameter x 4 mm in length.

[0095] In the embodiments of the present disclosure, the laser driving module, the current signal processing circuit and the signal acquisition device constitute a back-end processing circuit, which is independently arranged outside the probe.

[0096] The optical microphone core device proposed in the present disclosure can be integrated in a 6 mm x 4 mm micro probe; without expensive optical fiber devices and complex demodulation systems; the self-mixing interference principle makes the output signal not need to be demodulated, which is convenient for system integration; the detection method based on the laser interference principle has higher precision; and can be widely applied in the fields of intelligent voice terminal, vehicle-mounted audio, industrial acoustic detection and the like.

[0097] Figure 2 is a flowchart of a self-mixing interference-based sound wave detection method according to an embodiment of the present disclosure.

[0098] In a second aspect, referring to Figure 2 The embodiments of the present disclosure provide a self-mixing interference-based sound wave detection method, comprising:

[0099] S21, generating a vibration displacement in response to an external sound wave by a MEMS structure;

[0100] S22, emitting laser to the MEMS structure and receiving its reflected light, the reflected light returning to the laser cavity and forming self-mixing interference with the laser field in the cavity, so that the outgoing light intensity of the laser linearly changes with the vibration displacement;

[0101] S23, receiving the outgoing light intensity by the photodetector and converting it into a current signal reflecting the sound wave.

[0102] In some embodiments, the vibration displacement is generated by the MEMS structure in response to the external sound wave, comprising:

[0103] The external sound wave acts on the MEMS structure to drive it to generate vibration displacement with the sound wave frequency and amplitude, so that the optical path between the MEMS structure and the light outlet of the laser changes.

[0104] In the embodiments of the present disclosure, the external sound wave excitation acts on the MEMS structure (such as a MEMS thin film, a beam, a spherical shell, etc.), causing it to generate vibration displacement with the sound wave frequency and amplitude. The vibration of the MEMS structure causes the distance between the MEMS structure and the light outlet of the laser to change, thereby changing the optical path length of the laser propagation path. Part of the laser reflected on the surface of the MEMS structure returns to the laser, triggering the self-mixing interference effect in the cavity, so that the output light power of the laser is modulated according to the vibration state of the MEMS structure, and the mechanical vibration information is converted into the change of the outgoing light intensity. The photodetector detects the change of the outgoing light intensity of the laser and converts it into a current signal, which is processed by a current signal conditioning circuit to form a voltage signal linearly related to the sound.

[0105] In some embodiments, the laser is emitted by the laser to the MEMS structure and the reflected light is received, the reflected light returning to the laser cavity and forming self-mixing interference with the laser field in the cavity, so that the outgoing light intensity of the laser linearly changes with the vibration displacement, comprising:

[0106] The laser emits single-mode laser with a stable wavelength;

[0107] The laser irradiates the surface of the MEMS structure in the vertical direction and reflects back to the laser cavity along the original path;

[0108] The reflected light forms self-mixing interference with the laser field in the cavity;

[0109] The optical path parameters between the laser and the MEMS structure are configured so that the self-mixing interference is in the linear working area to make the outgoing light intensity and the vibration displacement have a linear relationship.

[0110] In the embodiments of the present disclosure, the laser preferably adopts a single-mode laser with a steady wavelength, and the outgoing light is vertically irradiated to the MEMS surface, and the reflected light returns to the laser cavity along the original path and is coupled with the laser field in the cavity to form a self-mixed interference. In order to ensure the linear relationship between the change of the outgoing light intensity and the displacement of the MEMS vibration, the optical path parameters between the laser and the MEMS are comprehensively designed. By adjusting the optical path parameters, the system is operated in the linear interference working area corresponding to the medium feedback strength (the feedback strength factor is about 1-2). Under this condition, the slight vibration of the MEMS structure linearly modulates the outgoing light intensity of the laser, which provides an ideal basis for the subsequent electric signal conversion. The modulated light intensity output by the laser is received by a photodetector. Preferably, a photodiode is used, which directly converts the change of the outgoing light intensity into an electric current signal with a corresponding amplitude. The current signal carries the information of the displacement of the MEMS vibration, that is, the acoustic characteristics such as the sound pressure size and frequency of the external sound wave signal are consistent.

[0111] In some embodiments, the sound wave detection method further comprises:

[0112] The current signal is converted into a voltage signal and amplified by a current signal processing circuit;

[0113] The voltage signal is input into a signal acquisition device for analysis to obtain the sound pressure amplitude and frequency characteristics of the sound wave.

[0114] In the embodiments of the present disclosure, the current signal is processed by a transimpedance amplifier (TIA) circuit, converted into a voltage signal with a linear proportional relationship and moderately amplified. The voltage signal is directly input into a signal acquisition device, such as an oscilloscope, a data acquisition card, a spectrum analyzer, a lock-in amplifier, etc. Through the analysis of the voltage signal, the amplitude characteristics (sound pressure size) and frequency components of the detected sound wave can be extracted, and the real-time measurement and acoustic data acquisition of the spatial sound signal can be realized. Since the interference output is a linearly modulated light intensity, no additional demodulation algorithm is needed.

[0115] In the embodiments of the present disclosure, a self-mixing interference-based acoustic wave detection method is provided, which realizes high-sensitivity detection of acoustic wave signals by introducing the vibration of a MEMS structure under external acoustic wave excitation into a laser interference path. The method specifically comprises: a MEMS structure generates a small vibration displacement under the action of an acoustic wave; a laser emits single-mode laser to the MEMS and receives the reflected light, and the outgoing light intensity is linearly changed through the self-mixing interference mechanism; and a photodetector receives the light intensity change and converts it into an electrical signal output. Since the present method ensures the linear relationship between the outgoing light intensity of the laser and the vibration displacement of the MEMS in design, the obtained electrical signal can be directly used to restore the acoustic waveform without complex signal demodulation algorithms, which greatly reduces the system processing complexity and eliminates the dependence on large signal calculation equipment.

[0116] Compared with the traditional optical fiber interference sensing method, the present method has a more compact structure and can realize high signal-to-noise ratio acoustic detection without an external demodulation module. Compared with the MEMS microphone based on grating interference, the present method has a simpler processing technology and higher device integration, is suitable for small-scale packaging and batch manufacturing, and has good application prospect and market conversion potential.

[0117] Figure 3 FIG. 1 is a flowchart of an assembly method of an optical microphone according to an embodiment of the present disclosure.

[0118] In a third aspect, referring to Figure 3 The present disclosure provides an assembly method of an optical microphone, comprising:

[0119] S31, providing a MEMS structure that generates a vibration displacement in response to an external acoustic wave;

[0120] S32, arranging a laser and a photodetector to form an optical unit for laser emission and light intensity detection;

[0121] S33, constructing an optical path between the MEMS structure and the optical unit, so that the laser emitted by the laser is reflected back to the laser cavity through the MEMS structure, self-mixing interference is formed in the cavity, the outgoing light intensity of the laser changes linearly with the vibration displacement, and the photodetector receives the outgoing light intensity of the laser and converts it into an electric current signal reflecting the acoustic wave.

[0122] In the embodiments of the present disclosure, the MEMS structure is a micro-electro-mechanical system element that can vibrate out-of-plane under acoustic wave excitation, causing optical path change and modulating the outgoing light intensity of the laser. The laser is preferably a single-mode laser that emits a steady-state wavelength, and the photodetector is preferably a photodiode with linear photoelectric response characteristics, to ensure stable detection of the interference signal and realize high-fidelity conversion of the acoustic signal.

[0123] In some embodiments, the optical path between the MEMS structure and the optical unit is constructed by:

[0124] The laser and photodetector are integrated in a TO package base.

[0125] The MEMS structure is mounted on the TO package base through a support positioning structure to achieve optical axis alignment with the laser emission direction.

[0126] In the embodiments of the present disclosure, the above packaging structure can simplify device layout and installation process, improve optical path stability and overall assembly consistency, and is especially suitable for batch and standardized manufacturing processes.

[0127] In some embodiments, the optical path between the MEMS structure and the optical unit is constructed by:

[0128] An optical fiber beam splitter is arranged at the laser emission end.

[0129] The laser emitted by the laser is guided to the MEMS structure through the optical fiber beam splitter, and the reflected light is returned to the laser cavity through the original path.

[0130] The outgoing light intensity is guided to the photodetector through the optical fiber beam splitter.

[0131] In the embodiments of the present disclosure, an optical fiber beam splitter is arranged at the laser emission end, and the laser is guided to the MEMS structure. The reflected light from the MEMS surface is returned to the laser cavity through the original path to form self-mixing interference. The beam splitter guides the modulated outgoing light signal out and to the photodetector for real-time detection. This configuration supports remote arrangement of the laser and the photodetector, and is suitable for optical microphone probe applications in narrow, humid, or electromagnetic interference environments.

[0132] In some embodiments, the optical path between the MEMS structure and the optical unit is constructed by:

[0133] A micro-mirror is arranged between the laser and the MEMS structure,

[0134] The micro-mirror reflects the laser emitted by the laser to the surface of the MEMS structure, and guides the reflected light to return to the laser cavity along the original path.

[0135] In the embodiments of the present disclosure, a micro mirror can be arranged between the laser and the MEMS structure for deflecting the laser emitted by the laser to the MEMS surface, and the laser returns to the laser cavity along the original path after being reflected and forms a self-mixing interference. The mirror can be a micro-machined silicon mirror, a coated glass, or a micro prism, which is suitable for a lateral layout or a flat packaging scenario with limited laser path direction.

[0136] The structure can significantly improve the compactness and flexibility of system assembly, support the combination packaging of different types of lasers, MEMS structures and detector modules, and is suitable for large-scale manufacturing and multi-scenario deployment.

[0137] In order for those skilled in the art to more clearly understand the technical solutions provided by the embodiments of the present disclosure, the optical microphone provided by the embodiments of the present disclosure is described in detail below through specific embodiments:

[0138] Embodiment one

[0139] Figure 4 is an installation embodiment of an optical microphone according to the present disclosure.

[0140] As shown in Figure 4 , an installation embodiment of an optical microphone includes a MEMS diaphragm, a laser diode, a photodiode, and a TO package base (i.e., a transistor outline package base).

[0141] The MEMS diaphragm is a specific implementation form of the MEMS structure used in the present embodiment. It produces a small vibration displacement that varies with frequency and amplitude under the action of external sound waves, and is a key component for realizing sound wave response.

[0142] The laser diode and the photodiode are integrally arranged in the TO package base to form a compact emission-detection unit. The TO package base is used to carry and fix the laser diode and the photodiode, thereby accurately maintaining the relative positions of the two in space and ensuring the stability of laser output and reception. Preferably, commercially available TO56 or TO46 package forms can be used; in other embodiments, custom packaging methods can also be used to achieve this function.

[0143] A support positioning ring is arranged between the MEMS diaphragm and the TO package base. This ring structure plays a role in accurate positioning and support during assembly, so that the MEMS diaphragm can be aligned with the TO package base to form a stable optical path. In actual manufacturing process, the "MEMS diaphragm-positioning ring-TO package base" structure is in the form of a sandwich, which significantly simplifies the assembly process, improves production efficiency, and is suitable for distributed manufacturing and batch assembly.

[0144] To reduce the stiffness of the MEMS thin film while enhancing the reflectivity of the thin film, in some embodiments, the MEMS thin film can adopt a composite thin film structure: taking a polyimide or silicon-based flexible material as a substrate, combining a high-reflectivity metal material (such as gold, silver, or aluminum) as a reflective layer, and laminating the two through plasma bonding or micro-nano processing, thereby having both low stiffness and high light reflection characteristics.

[0145] In the working process, a sound signal reaches the MEMS thin film, driving it to vibrate. The outgoing light of the laser diode irradiates the surface of the MEMS thin film, and part of the laser returns to the diode cavity through the laser diode light outlet, couples with the cavity laser, generates self-mixing interference, causes the outgoing light intensity of the laser diode to change, and further causes the change of the photocurrent signal generated by the photodiode.

[0146] The laser intensity change is converted into a current signal by the photodiode:

[0147] I pd = N·(E0+ K·2x)

[0148] which can also be expressed as:

[0149] I pd = I0+ N·K·2x

[0150] wherein x is the relative displacement of the vibration of the MEMS thin film driven by the external sound, that is, half of the change in the optical path of the outgoing light of the laser diode after being reflected by the MEMS thin film, and x = 0 when there is no disturbance from the outside. K is the change coefficient of the outgoing light intensity of the laser diode caused by the change in the optical path and the self-mixing interference. E0 is the outgoing light intensity of the laser diode in the undisturbed state. I0 is the photocurrent of the photodiode under the outgoing light intensity of the laser diode in the undisturbed state. N represents the proportional coefficient of the photodiode converting the outgoing light intensity of the LD into the photocurrent.

[0151] By reasonably designing the optical path parameters (such as the reflectivity of the MEMS, the distance from the laser to the MEMS, the type of the laser, etc.), the interference feedback intensity factor can be controlled in the medium feedback interval (such as 1-2), so that the change in the outgoing light intensity caused by the change in the optical path and the vibration displacement of the MEMS thin film are in a proportional relationship, thereby simplifying the subsequent signal processing.

[0152] Further, the current signal is input to a current signal processing circuit, which preferably adopts a transimpedance amplifier (TIA) structure, simultaneously realizing current-voltage conversion and voltage amplification, and outputs a voltage signal in a linear relationship with the vibration displacement of the MEMS. The final voltage signal can be collected by a signal collection card, without the need for demodulation to directly restore the sound waveform, and further frequency characteristic analysis of the sound can be realized by applying algorithms such as short-time Fourier transform.

[0153] In this embodiment, the integrated structure is highly compact, the MEMS, laser and detector are highly aligned, easy to modular packaging, with the advantages of simple structure, high positioning accuracy, short signal processing chain, etc., suitable for small-scale deployment and batch manufacturing, with good scalability and engineering application prospects.

[0154] Figure 5 is a verification Figure 4 system feasibility experimental device structure diagram.

[0155] To verify Figure 4 the feasibility of the self-mixing interference-based MEMS optical microphone shown in FIG. 1, an experimental platform as shown in FIG. 2 is constructed, an actual acoustic application scenario is simulated, and response performance tests are carried out. Figure 5

[0156] The experimental system mainly includes the following components:

[0157] A laser diode with a wavelength of 650 nm (model: QSI, QL65I7SA) is used. This device is an integrated laser, which has integrated a laser diode and a photodiode inside. The package form is TO package. This type of laser can simultaneously complete laser emission and feedback light detection functions in a compact space;

[0158] The laser diode is connected to a customized circuit board. The circuit board contains: a laser constant current driving module, which provides a stable constant current for the laser diode to ensure that the laser works in a steady-state single-mode emission condition; an integrated trans-impedance amplifier (TIA), which is used to convert current signals to voltage signals and amplify them for subsequent acquisition;

[0159] The output voltage signal is received and recorded by a data acquisition card (model: NIPCIe-6363, National Instruments). The acquisition card can achieve high-precision sampling of voltage signals at different time points and synchronous analysis with acoustic signal frequency characteristics;

[0160] A commercial loudspeaker (Canton S301) is used as a sound source, and a PC is used to control the output of test signals with different frequencies and intensities. The loudspeaker outputs the set sound waves through a digital audio interface to achieve sound field excitation.

[0161] The calibration reference device uses a sound level meter (model: Beijing Sound, MPA215), which is placed in an equivalent position parallel to the optical microphone and maintains the same direction as the sound source, to calibrate the sound pressure level actually received by the microphone. This configuration ensures the consistency of the sound field received by both devices, providing a reliable reference for subsequent linear relationship verification and error analysis.

[0162] ​The entire experiment was conducted in an anechoic chamber, which effectively suppressed ambient background noise and excess reflected sound waves, ensuring that the microphone's measurement results were not affected by external interference.

[0163] In this experimental system, a speaker controlled by a PC emits sound signals of different frequencies and sound pressure levels, exciting the MEMS structure to produce minute vibrations. Laser output light illuminates the MEMS reflective surface and returns to the cavity, forming a self-mixing interference that modulates the emitted light intensity. An integrated photodiode detects this intensity change and outputs a current signal, which is then converted by a transimpedance circuit and acquired by a data acquisition card. By comparing the results with those of a sound level meter, the proposed optical microphone system's response sensitivity, linear range, and frequency characteristics to different sound intensities can be evaluated, verifying the feasibility and effectiveness of achieving high-precision sound signal reconstruction without demodulation.

[0164] Figure 6 A and Figure 6 B in this disclosure shows the optical microphone in Figure 5 The response output results of the experimental platform shown are used to verify its detection performance under different sound pressure and frequency conditions. Among them, Figure 6 A in the figure shows the voltage output signal of the optical microphone under different sound pressure excitations to reflect its response to changes in sound pressure amplitude; Figure 6 Figure B shows the voltage waveform output by the microphone system under sound pressure conditions of 800Hz and 100mPa. The waveform is close to an ideal sine wave, indicating that the system has good frequency fidelity.

[0165] The voltage signal described above is the response signal output by the optical microphone system after processing by a transimpedance amplifier and finally input to the signal acquisition card. It directly reflects the interference result corresponding to the tiny vibration displacement of the MEMS structure under acoustic excitation. This electrical signal allows for direct reconstruction of the acoustic waveform without a demodulation algorithm, further verifying the high sensitivity, linear response capability, and real-time signal output characteristics of the proposed system.

[0166] Experimental results show that the proposed optical microphone based on the self-mixing interference principle exhibits good linear response characteristics at all three tested frequencies. As the sound pressure level increases, the vibration amplitude generated by the MEMS structure increases synchronously, reflected in the output voltage signal; that is, the voltage amplitude is directly proportional to the sound pressure level, and the linear relationship is significant.

[0167] Under sound pressure excitation conditions of 800Hz and 100mPa, the output voltage waveform exhibits a regular sinusoidal shape, indicating that the designed self-mixing interference system has high phase fidelity and low distortion response capability to periodic vibrations, and can accurately reproduce the shape of external sound waves.

[0168] In the experiment, no additional interference demodulation algorithm is introduced, and the acquisition card can directly obtain the voltage signal equivalent to the shape of the sound wave, further verifying that the linear correspondence between the output signal and the MEMS vibration displacement can be realized by controlling the interference feedback strength factor to be in the linear region (about 1 to 2).

[0169] In summary, Figure 6 The experimental data shown sufficiently demonstrate that the MEMS optical microphone based on self-mixing interference of the present disclosure can: sensitively detect the structure vibration caused by a small sound pressure; realize linear output of an electrical signal; not rely on an external demodulation algorithm; and have good frequency adaptability and waveform fidelity. The test results further verify the practicability and superiority of the system structure and signal processing mechanism proposed by the present disclosure in the field of spatial sound signal acquisition.

[0170] Embodiment Two

[0171] Figure 7 is a structural schematic diagram of an optical microphone of an embodiment of the present disclosure under different MEMS structure forms, which shows the installation structures of MEMS spherical shells and MEMS beams as sound wave response elements, respectively.

[0172] In the present embodiment, the MEMS structure is not limited to a MEMS thin film, but can be replaced by other types of MEMS structures, such as a MEMS spherical shell or a MEMS beam, as long as it can produce a vibration displacement perpendicular to the surface direction of the device (i.e., out-of-plane vibration) under the excitation of a sound wave; the surface has the ability to reflect laser light and is suitable for wide-band sound signal detection to realize self-mixing interference between the outgoing light and the reflected light of a laser diode.

[0173] As Figure 7 shown, the upper part shows the installation structure of a MEMS spherical shell as a sound wave response element. This structure can produce a vertical vibration displacement under the excitation of a sound wave, which helps to improve the sensitivity and dynamic range of the microphone. Specifically, this structure can effectively constrain sound waves, enhance sound energy collection efficiency, and help to further improve the sensitivity and minimum measurable sound pressure of the microphone. The lower part shows an optical microphone using a MEMS beam structure. In this structure, multiple beam-shaped units are distributed in a ring or radial shape, and produce periodic out-of-plane vibration under the action of a sound wave, which is suitable for the optimization design of sound response in a specific frequency band, and has high structural stability.

[0174] In the configuration of the two MEMS structures, the laser diode still emits laser towards the MEMS structure, the reflected light returns to the laser cavity via the same path to induce the self-mixing interference phenomenon, and the photodetector detects the change of the outgoing light intensity to output the current signal. The introduction of different MEMS structures can adjust and optimize the parameters such as response frequency range, sensitivity, dynamic range, etc. according to the actual application requirements, and further improve the applicability and performance of the method in different scenarios.

[0175] Embodiment three

[0176] Figure 8 is a system structure schematic diagram of an optical microphone of the embodiment of the present disclosure using a fiber beam splitting configuration, which shows the signal transmission and interference measurement path between the laser, photodetector and MEMS structure.

[0177] The embodiment provides an optical microphone system, which is different from the integrated packaging mode of embodiment one. As shown in Figure 8 The laser diode (LD) and photodiode (PD) are not directly integrated with the MEMS structure, but are spatially separated by the optical path structure realized by fiber coupling and beam splitter.

[0178] The laser diode can adopt a packaging form with a fiber pigtail, or the output laser can be coupled into the fiber through a later process. After the outgoing laser is transmitted through the fiber, it irradiates the MEMS structure (such as a MEMS film, beam or spherical shell), which vibrates out of the plane under the action of external sound, thereby modulating the optical path of the laser. The reflected light returns to the laser diode cavity through the same optical path and forms self-mixing interference with the laser field in the cavity, resulting in a change in the output light intensity of the laser. In order to realize the detection of this light intensity change, the outgoing end of the laser is configured with a fiber beam splitter for splitting a modulated laser output to a photodiode for real-time monitoring. The photodiode can be set at the end of the optical path by free space end reception, or can adopt a packaging form with a fiber pigtail to be directly coupled to the output end of the fiber beam splitter.

[0179] The laser diode, photodiode and MEMS structure are spatially decoupled, which is convenient for distributed arrangement; it can also allow a smaller volume of MEMS film, so that the MEMS film and the probe of the fiber pigtail can measure in some extreme environments (such as narrow, humid, strong electromagnetic interference, etc.), further avoiding the interference of the laser diode and the photodiode, which is conducive to the stability of the system; it is suitable for smaller MEMS structures, which is convenient for improving the sensitivity and spatial adaptability of the probe.

[0180] Embodiment four

[0181] Figure 9 This is a schematic diagram of an optical microphone with a micro-mirror-assisted optical path configuration according to an embodiment of the present disclosure. It shows the path design where the laser beam changes its propagation direction after passing through the mirror, illuminates the MEMS structure, and then returns to the laser cavity through the reflection path to achieve self-mixing interference.

[0182] This embodiment provides an optical microphone system based on a reflective micromirror structure. The difference lies in using a reflector to achieve a non-axial optical path design, which optimizes the optical path arrangement and enhances the compatibility and flexibility of the system packaging. For example... Figure 9 As shown, the laser beam emitted by the laser diode first illuminates a miniature mirror set at a specific angle θ; the mirror reflects the laser beam onto the surface of a MEMS structure (such as a thin film, beam, or spherical shell); the MEMS vibrates vertically under the action of the acoustic wave (out-of-plane vibration), thereby modulating the round-trip optical path of the laser; the modulated reflected light returns along the original path, and after being reflected again by the mirror, it is coupled back to the laser cavity, generating a self-mixing interference effect with the optical field inside the laser cavity; subsequently, the output light is detected by a photodetector, realizing the conversion of the acoustic signal into an electrical signal.

[0183] In the embodiments of this disclosure, the reflector can be fabricated in various forms, including: silicon-based micromirrors formed by micromachining; integrated microprisms; or optical components such as reflective coated glass.

[0184] This structure is suitable for non-axial layouts, such as flat packaging and side-mounted detectors; it effectively expands the degree of freedom in light distribution between lasers and MEMS, improving the overall system design compatibility and integration flexibility; it is particularly suitable for industrial or consumer applications where space is limited or there are special requirements for package size.

[0185] The optical microphone disclosed herein has the following beneficial effects:

[0186] 1) This disclosure is based on the principle of self-mixing interferometric vibration measurement, using laser interference signals to reflect minute vibration displacements under acoustic excitation, thus avoiding the problem of traditional electret microphones and condenser, piezoelectric, and piezoresistive MEMS microphones being susceptible to interference in electromagnetic environments. It achieves the technical effect of high sensitivity and high signal-to-noise ratio spatial acoustic signal pickup and recording.

[0187] 2) The present disclosure uses a laser diode (such as FP-LD, VCSEL) based on Fabry-Perot cavity or vertical cavity surface emitting structure as a laser, combined with miniaturized optical path design, avoiding the problem of bloated system structure of traditional solid or gas laser. In the optical path design, the reflection path is shortened (for example, shortened to within 1 mm), and a highly integrated package (such as TO56, TO46, or a custom package solution) is used to realize the miniaturization of the entire measurement probe. At the same time, the present disclosure does not limit the packaging method of the laser or whether the photodiode is integrated, and can support integrated and separated structures, enhancing the flexibility of system design.

[0188] 3) The present disclosure realizes the linear relationship between MEMS vibration displacement and laser exit light intensity, and based on the linear photoelectric conversion characteristics of the photodetector, the final output current signal is in direct proportion to the MEMS vibration displacement caused by the acoustic wave. This linear conversion of acoustic wave to electrical signal can significantly simplify the signal processing system, without the need for complex algorithms such as homodyne demodulation, heterodyne demodulation, phase unwrapping, etc. The voltage signal can be directly output by the transimpedance amplifier for conventional signal acquisition equipment (such as oscilloscope, data acquisition card, frequency meter), thereby realizing the miniaturization of the whole device, effectively reducing the system implementation difficulty and cost.

[0189] 4) The present disclosure converts spatial sound signals into MEMS motion by responding to external sound waves through acoustically sensitive MEMS, unlike existing fiber Fabry-Perot microphones. The present method can measure the motion state of MEMS in real time, realizing the technical effects of high precision, low power consumption, miniaturization, and easy processing of sound signal detection.

[0190] Those skilled in the art should understand that the present method emphasizes the physical working mechanism of the laser (FP / VCSEL), rather than a specific package form (TO56 / TO46); the photodiode and the laser diode can be integrated or physically separated, both of which are within the protection scope of the present disclosure; the miniaturized structure is reflected in that the probe size can be controlled to be below 6mm x 4mm, only integrating the core measurement unit, and the back-end circuit can be designed as an external modular.

[0191] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0192] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. An optical microphone comprising: a MEMS structure configured to generate a vibration displacement in response to an acoustic wave; a laser configured to emit laser light to the MEMS structure and receive reflected light therefrom to form self-mixing interference inside the laser, such that an outgoing light intensity of the laser linearly varies with the vibration displacement; a photodetector configured to convert the outgoing light intensity into an electrical current signal reflecting the acoustic wave.

2. The optical microphone of claim 1, wherein, An optical path parameter between the laser and the MEMS structure is configured such that the self-mixing interference is in a linear operation region to make the outgoing light intensity linearly related to the vibration displacement.

3. The optical microphone of claim 2, wherein, A feedback intensity factor of the self-mixing interference corresponding to the linear operation region satisfies an interval of 1 to 2.

4. The optical microphone of claim 3, wherein, The laser is a laser diode outputting single-mode laser light of a steady-state wavelength. The photodetector is a photodiode, and an output electrical current signal thereof is linearly proportional to the outgoing light intensity received from the laser. 5.The optical microphone of claim 4, wherein the laser diode and the photodiode are integrated in a TO package base; the MEMS structure is connected to the TO package base through a support positioning structure. 6.The optical microphone of claim 4, further comprising: a fiber beam splitter disposed at an outgoing end of the laser and configured to split the outgoing light intensity after self-mixing interference and guide it to the photodetector. 7.The optical microphone of claim 4, further comprising: a micro-mirror disposed between the laser and the MEMS structure and configured to reflect the laser light emitted by the laser to the MEMS structure and reflect the laser light reflected by the MEMS structure back to the laser cavity along the original light path to achieve self-mixing interference.

8. The optical microphone of any of claims 1-7, wherein, The MEMS structure is any one of a MEMS membrane, a MEMS sheet, a MEMS beam, or a MEMS spherical shell. 9.A method for detecting an acoustic wave, comprising: generating a vibration displacement by a MEMS structure in response to an external acoustic wave; emitting laser light to the MEMS structure by a laser and receiving reflected light therefrom, the reflected light returning to a laser cavity and forming self-mixing interference with a cavity laser field, such that an outgoing light intensity of the laser linearly varies with the vibration displacement; receiving the outgoing light intensity by a photodetector and converting it into an electrical current signal reflecting the acoustic wave.

10. The acoustic wave detection method of claim 9, wherein, emitting laser light to the MEMS structure by a laser and receiving reflected light therefrom, the reflected light returning to a laser cavity and forming self-mixing interference with a cavity laser field, such that an outgoing light intensity of the laser linearly varies with the vibration displacement, comprising: emitting single-mode laser light of a steady-state wavelength by the laser; the laser light irradiating a surface of the MEMS structure and reflecting back to the laser cavity along the original path; the reflected light forming self-mixing interference with the cavity laser field; configuring an optical path parameter between the laser and the MEMS structure such that the self-mixing interference is in a linear operation region to make the outgoing light intensity linearly related to the vibration displacement.

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