Integrated Michelson interference type optical microphone and acoustic detection system

Abstract

The invention belongs to the technical field of photoacoustic spectrum detection and analysis, and particularly relates to an integrated Michelson interference type optical microphone and an acoustic detection system. The optical microphone comprises a vibrating diaphragm and a waveguide, the vibrating diaphragm comprises a wafer and a beam structure, the wafer is provided with a first side face and a second side face which are opposite in the first direction, the wafer is provided with a through hole penetrating through the first side face and the second side face, the beam structure is matched with the through hole, one side of the beam structure is connected with the wafer, and the other side portions of the beam structure and the wafer are arranged in a spaced mode. The beam structure is provided with a third side face and a fourth side face which are opposite in the first direction, and the fourth side face is recessed in the second side face. The waveguides are arranged on one side of the second side face of the wafer at intervals in the first direction, the first reflection ends of the waveguides face the second side face, and the second reflection ends face the fourth side face. According to the invention, the sound pressure can be effectively converted into the optical path change of the sensing arm, the detection capability of weak sound signals is improved, the device size is greatly reduced, and the integration level of the sensor is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoacoustic spectrum detection and analysis, and particularly relates to an integrated Michelson interference type optical microphone and an acoustic detection system. BACKGROUND

[0002] Weak acoustic signal detection has great application value in the fields of military reconnaissance, industrial nondestructive testing, medical diagnosis and environmental monitoring, etc. For example, in transformer fault gas detection, trace characteristic gas generates a weak acoustic signal, which usually has the characteristics of extremely small amplitude, extremely low signal-to-noise ratio (SNR) and is easily overwhelmed by environmental noise, thereby putting forward extremely high requirements for the sensitivity and stability of the sensing technology.

[0003] Traditional electrical microphones (such as capacitive and piezoelectric types) have inherent disadvantages such as being susceptible to electromagnetic interference, requiring power supply, short signal transmission distance and poor stability in harsh environments. Optical microphones have become an ideal choice for weak acoustic signal detection due to their high sensitivity, intrinsic safety, resistance to electromagnetic interference and suitability for long-distance transmission. Among them, the research on interference type optical fiber acoustic sensors is the most extensive. The mechanical sensitivity of the common transduction structure based on a thin film or an elastic column is restricted by the geometric size of the transduction unit. In comparison, the single-end fixed free-end cantilever beam transduction structure has higher mechanical sensitivity. The traditional discrete optical fiber interference system is bulky, and the reference arm and the sensing arm are easily disturbed by environmental temperature and vibration, resulting in phase drift, which degrades the noise level of the sensor and makes it difficult to reduce the minimum detectable sound pressure. SUMMARY

[0004] Based on the above technical problems, the application provides an integrated Michelson interference type optical microphone and an acoustic detection system, aiming to at least partially solve the technical problems of poor mechanical sensitivity and large volume in the related art.

[0005] The application is implemented by the following technical solutions: In a first aspect of the application, an integrated Michelson interference type optical microphone is provided, which comprises: a diaphragm comprising a wafer and a beam structure, the wafer having a first side and a second side opposite to each other along a first direction, the wafer being provided with a through hole penetrating through the first side and the second side, the beam structure being matched with the through hole, one side of the beam structure being connected to the wafer, and the remaining side of the beam structure being spaced apart from the wafer, the beam structure having a third side and a fourth side opposite to each other along the first direction, the fourth side being recessed inwardly from the second side; and a waveguide being spaced apart from the second side of the wafer along the first direction, the waveguide having an incident end, a first reflection end, a second reflection end, a first emission end and a second emission end, the first reflection end being directed toward the second side, and the second reflection end being directed toward the fourth side.

[0006] In some embodiments, the wafer comprises a top layer, a substrate, and a buried oxide layer, the top layer and the substrate are oppositely arranged, and the buried oxide layer is arranged between the top layer and the substrate; wherein: the beam structure and the top layer are integrally formed, and the second side and a side of the top layer facing the substrate are flush.

[0007] In some embodiments, the waveguide comprises a substrate, the substrate is provided with a first waveguide channel, a second waveguide channel, and a third waveguide channel arranged in sequence along a second direction, the first direction and the second direction are perpendicular to each other, the first waveguide channel, the second waveguide channel, and the third waveguide channel have an overlapping region to form a coupling region, wherein: the first waveguide channel, the second waveguide channel, and the third waveguide channel each have a first end and a second end, the first end of the first waveguide channel, the first end of the second waveguide channel, and the first end of the third waveguide channel are located on a first side of the coupling region, the second end of the first waveguide channel, the second end of the second waveguide channel, and the second end of the third waveguide channel are located on a second side of the coupling region, the first end of the first waveguide channel is the incident end, the second end of the first waveguide channel is the first reflection end, the second end of the third waveguide channel is the second reflection end, the first end of the second waveguide channel is the first exit end, and the first end of the third waveguide channel is the second exit end.

[0008] In some embodiments, the first end of the first waveguide channel and the first end of the third waveguide channel respectively extend away from the second waveguide channel, and the second end of the first waveguide channel and the second end of the third waveguide channel respectively extend away from the second waveguide channel.

[0009] In some embodiments, at least part of the first waveguide channel and the third waveguide channel on the first side of the coupling region are in a first arc shape, and at least part of the first waveguide channel and the third waveguide channel on the second side of the coupling region are in a second arc shape.

[0010] In some embodiments, the middle part of the first waveguide channel and the third waveguide channel are in a third arc shape, and the two ends of the third arc shape are respectively the same as the corresponding first arc shape and the second arc shape.

[0011] In some embodiments, along the first direction, the second end of the first waveguide channel to the coupling region has a first distance, the second end of the second waveguide channel to the coupling region has a second distance, and the third end of the second waveguide channel to the coupling region has a third distance; wherein the first distance and the second distance are both greater than the third distance.

[0012] In some embodiments, the method for producing the diaphragm comprises: making a mask on the surface of the wafer to form a mask for the beam structure; etching on the wafer to form an air slit on the wafer; depositing a silicon nitride layer on the surface of the wafer; performing backside lithography on the wafer after frontside etching to form a back cavity on the back of the wafer; and removing the silicon nitride layer and the buried oxide layer at the bottom of the back cavity groove.

[0013] In some embodiments, the method for producing the waveguide comprises: providing and cleaning the surface of a substrate to obtain an ultraclean surface on the substrate; processing the obtained ultraclean surface to prepare a lower cladding layer; processing a waveguide groove on the surface of the prepared lower cladding layer; filling silica in the processed waveguide groove as a waveguide core, the refractive index of the silica in the waveguide groove being greater than the refractive index of the substrate; and depositing an upper cladding layer on the surface of the lower cladding layer to wrap the waveguide core.

[0014] In the second aspect of the present application, an acoustic detection system is provided, comprising: a detection light source, the optical microphone of the first aspect, a photodetector, and a signal demodulation processor; wherein: the detection light source is connected with the incident end, the photodetector is provided with two, the two photodetectors are respectively connected with the first exit end and the second exit end, and the two photodetectors are connected with the signal demodulation processor. The integrated Michelson interference optical microphone provided by the present application has the following advantages: on the one hand, the wafer of the diaphragm is provided with a through hole penetrating through the first side surface and the second side surface, the beam structure is matched with the through hole, one side of the beam structure is connected with the wafer, the remaining side of the beam structure is arranged in a gap of the wafer, the beam structure has a third side surface and a fourth side surface opposite to each other in the first direction, and the fourth side surface is concave in the second side surface, so that the beam structure and the wafer are fixed on one side, the beam structure forms a cantilever posture, the free side of the beam structure has higher mechanical sensitivity relative to the transducing structure such as the diaphragm and the elastic column, and the problems of low response to weak signals and poor linearity of the conventional transducing structure are overcome, the sound pressure can be effectively converted into the change of the optical path of the sensing arm, and the detection capability for weak sound signals is improved.

[0015] In addition, since the waveguide is arranged on one side of the second side of the wafer along the first direction, and the waveguide has an incident end, a first reflection end, a second reflection end, a first emission end and a second emission end, the first reflection end faces the second side, the second reflection end faces the fourth side, and the second side and the fourth side are reflection surfaces of the diaphragm, in use, light is input through the incident end and output from the first reflection end and the second reflection end, wherein the light output from the first reflection end is reflected by the second side, the light output from the second reflection end is reflected by the fourth side and then incident to the waveguide again, and then emitted from the first emission end and the second emission end and collected to obtain relevant parameters, thereby realizing weak sound signal detection. Since the first reflection end and the second reflection end of the waveguide are arranged separately from the reflection surfaces of the diaphragm, air propagation can be realized, and the phenomenon of large device size caused by the connection of the first reflection end and the second reflection end of the waveguide with the reflection surfaces of the diaphragm through the optical fiber is avoided, thereby greatly reducing the device size and improving the integration of the sensor while ensuring the complete construction of the Michelson interference structure. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the following embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort.

[0017] Figure 1 The arrangement schematic diagram of the integrated Michelson interference optical microphone 10 in one or more embodiments of the present application is shown; Figure 2 The arrangement schematic diagram of the diaphragm 100 in Figure 1 is shown; Figure 3 The structure schematic diagram of the waveguide 200 in Figure 1 is shown; Figure 4 The arrangement schematic diagram of the acoustic detection system in one or more embodiments of the present application is shown; Figure 5 The frequency response diagram finally obtained by testing the response of the acoustic signal in the range of 100-400 Hz by the acoustic detection system provided by the present application is shown; Figure 6 The frequency response diagram finally obtained by testing the response of the acoustic signal in the range of 0-1500 Hz by the acoustic detection system provided by the present application is shown; Figure 7 The linearity test diagram of the optical microphone 10 is shown; Figure 8A sequence diagram showing the output sound field calibration sound pressure under linearity test is shown.

[0018] Explanation of reference numerals: 10, optical microphone; 100, diaphragm; 110, wafer; 111, first side; 112, second side; 113, top layer; 114, substrate; 115, buried oxygen layer; 120, beam structure; 121, third side; 122, fourth side; 130, air slit; 200, waveguide; 20a, incident end; 20b, first reflection end; 20c, second reflection end; 20d, first emission end; 20e, second emission end; 20f, coupling region; 210, first waveguide channel; 220, second waveguide channel; 230, third waveguide channel; 240, substrate; 30, probe light source; 40, photodetector; 50, signal demodulation processor; Y, first direction; X, second direction; P1, reference light path; P2, sensing light path. DETAILED DESCRIPTION

[0019] In order for those skilled in the art to which the present application pertains to more clearly understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of protection of the present application.

[0020] The integrated Michelson interference optical microphone provided by the present application mainly consists of two parts, i.e., a diaphragm and a waveguide, which are arranged at intervals along a first direction. Light emitted by a probe light source is transmitted to the diaphragm 100 through the waveguide 200, and the beam structure 120 of the diaphragm 100 produces physical vibration to modulate the light signal to restore the sound.

[0021] Figure 1 An arrangement schematic diagram of the integrated Michelson interference optical microphone 10 in one or more embodiments of the present application is shown, in conjunction with Figure 1 For the convenience of description, the first direction Y used in the description of the present application is defined as Figure 1 the vertical direction shown in the figure, and the second direction X is defined as Figure 1 the horizontal direction shown in the figure. The related details of the diaphragm 100 and the waveguide 200 will be further described in conjunction with the drawings.

[0022] Figure 2It shows Figure 1 A schematic diagram of the arrangement of the diaphragm 100. (Combined with...) Figure 2 The diaphragm 100 includes a wafer 110 and a beam structure 120. The wafer 110 has a first side surface 111 and a second side surface 112 opposite to each other along a first direction Y. That is, the first side surface 111 is the top surface of the wafer 110, and the second side surface 112 is the bottom surface of the wafer 110. The wafer 110 is provided with a through hole penetrating the first side surface 111 and the second side surface 112, that is, the through hole is vertically penetrating. The beam structure 120 is adapted to the through hole. One side of the beam structure 120 is connected to the wafer 110, and the remaining sides of the beam structure 120 are connected to the wafer. The beam structure 120 is configured with a gap of 110, meaning that the remaining sides of the beam structure 120 form an air slit 130 with the wafer 110. The beam structure 120 has a third side surface 121 and a fourth side surface 122 facing away from each other along the first direction Y. That is, the third side surface 121 is located on the top surface of the beam structure 120, and the fourth side surface 122 is located on the bottom surface of the beam structure 120. The fourth side surface 122 is recessed into the second side surface 112, that is, the bottom surface of the wafer 110 forms a back cavity structure. The second side surface 112 and the fourth side surface 122 can be used as light reflecting surfaces. With this configuration, the beam structure 120 and the wafer 110 are fixed on one side, so that the beam structure 120 forms a cantilever posture. The free side of the beam structure 120 has higher mechanical sensitivity than transducer structures such as thin film and elastic column, overcoming the problems of low response and poor linearity of traditional transducer structures. It can effectively convert sound pressure into optical path change of the sensing arm and improve the detection capability of weak sound signals.

[0023] Combination Figure 1 as well as Figure 2 In some embodiments, wafer 110 includes a top layer 113, a substrate 114, and a buried oxide layer 115. The top layer 113 and substrate 114 are disposed opposite each other, and the buried oxide layer 115 is disposed between the top layer 113 and substrate 114. The beam structure 120 is integrally formed with the top layer 113, and the second side 112 is flush with the side of the top layer 113 facing the substrate 114. Specifically, the overall thickness of wafer 110 is approximately 1 mm, and the buried oxide layer 115 is a silicon dioxide layer to balance the stress within wafer 110. Specifically, the thickness of the buried oxide layer 115 can be 90-110 nm, for example, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, or any value between these values. This application does not impose any limitations on this.

[0024] In some embodiments, the through hole can be a square hole with a length of about 3 mm, a width of about 1 mm, and a thickness of about 4 μm. The beam structure 120 can be integrally formed with the wafer 110, and the air gap 130 formed between the beam structure 120 and the wafer 110 can have a size of 2.5-3.5 μm. For example, the air gap 130 can have a size of 2.5 μm, 3.0 μm, 3.5 μm, or any value between the above two values.

[0025] The production method of the diaphragm 100 provided in the present application is as follows: A mask is made on the surface of the wafer 110. In a specific implementation, the mask is made on the surface of the top layer 113 of the wafer 110 by using a photolithography process to form a mask plate of the beam structure 120, wherein the mask pattern length is consistent with the size of the through hole. The wafer 110 is etched to form the air gap 130 on the wafer 110. In a specific implementation, the deep reactive ion etching is used to etch the air gap 130 between the beam structure 120 and the wafer 110, and the buried oxide layer 115 at the through hole is used as the etching stop and dry stripping is performed. A silicon nitride layer is deposited on the surface of the wafer 110. In a specific implementation, the low-pressure chemical vapor deposition method is used to deposit a silicon nitride layer with a certain thickness on the surface of the top layer 113 of the wafer 110 for protection, so as to prevent damage to the beam structure 120 in the subsequent production process. For example, the thickness of the silicon nitride layer can be 180-220 nm, such as 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, or any value between the above two values, which are not limited in the present application.

[0026] The wafer 110 after the front etching is backside photolithography to form a back cavity on the back of the wafer 110. In a specific implementation, the reactive ion etching method is used to etch the substrate 114 of the wafer 110 to form the back cavity, and at this time, the groove bottom of the back cavity is the fourth side surface 122. The silicon nitride layer and the buried oxide layer 115 at the groove bottom of the back cavity are removed. In a specific implementation, the silicon nitride layer and the buried oxide layer 115 at the groove bottom of the back cavity are removed by acid washing, so as to release the beam structure 120 with a thickness of 4 μm and form the air gap 130 between the beam structure 120 and the wafer 110. Thus, the diaphragm 100 in the form of a cantilever beam required for the sensing structure is prepared.

[0027] Figure 3 The structure of the waveguide 200 in Figure 1 is shown, and the waveguide 200 is combined with Figure 1 and Figure 3The waveguide 200 is arranged on one side of the second side 112 of the wafer 110 along the first direction Y, that is, the waveguide 200 is arranged on the bottom surface of the wafer 110, and the waveguide 200 has an incident end 20a, a first reflection end 20b, a second reflection end 20c, a first emission end and a second emission end. The first reflection end 20b faces the second side 112, and the second reflection end 20c faces the fourth side 122. In use, the optical microphone 10 inputs light through the incident end 20a and outputs light from the first reflection end 20b and the second reflection end 20c. The light output from the first reflection end 20b is reflected through the second side 112, and the light output from the second reflection end 20c is reflected through the fourth side 122 and then incident to the waveguide 200 again and emitted from the first emission end 20d and the second emission end 20e for collection to obtain relevant parameters and realize weak sound signal detection. Since the first reflection end 20b and the second reflection end 20c of the waveguide 200 are arranged separately from the reflecting surface of the diaphragm 100, air propagation can be realized, and the phenomenon of large device size caused by the connection of the first reflection end 20b and the second reflection end 20c of the waveguide 200 with the reflecting surface of the diaphragm 100 through an optical fiber is avoided. The device size is greatly reduced under the condition of ensuring the complete construction of the Michelson interference structure, and the integration of the sensor is improved.

[0028] In some embodiments, the waveguide 200 is a 3x3 integrated coupling waveguide 200, which is provided with a first waveguide channel 210, a second waveguide channel 220 and a third waveguide channel 230 arranged in sequence along the second direction X. The first direction Y and the second direction X are perpendicular to each other, that is, the first waveguide channel 210, the second waveguide channel 220 and the third waveguide channel 230 are arranged separately along the horizontal direction shown in the figure. The first waveguide channel 210, the second waveguide channel 220 and the third waveguide channel 230 have an overlapping region to form a coupling region 20f. The first waveguide channel 210, the second waveguide channel 220 and the third waveguide channel 230 each have a first end and a second end. The first end of the first waveguide channel 210, the first end of the second waveguide channel 220 and the first end of the third waveguide channel 230 are located on the first side of the coupling region 20f. The second end of the first waveguide channel 210, the second end of the second waveguide channel 220 and the second end of the third waveguide channel 230 are located on the second side of the coupling region 20f. The first end of the first waveguide channel 210 is the incident end 20a, and the second end of the first waveguide channel 210 is the first reflection end 20b. The first reflection end 20b faces the second side 112. The second end of the third waveguide channel 230 is the second reflection end 20c, and the second reflection end 20c faces the fourth side 122. The first end of the second waveguide channel 220 and the first end of the third waveguide channel 230 are both emission ends.

[0029] In actual use, the light emitted by the probe light source is incident to the first waveguide channel 210 through the first end of the first waveguide channel 210 of the waveguide 200, and is emitted from the second end of the first waveguide channel 210 and the second end of the third waveguide channel 230 after being split in the waveguide 200, wherein the light emitted from the second end of the first waveguide channel 210 is the reference light beam, and the light emitted from the second end of the first waveguide channel 210 is the sensing light beam. The reference light beam is emitted through the second side surface 112 and incident to the first waveguide channel 210 through the second end of the first waveguide channel 210, the sensing light beam is reflected through the fourth side surface 122 and then incident to the third waveguide channel 230 through the second end of the fourth waveguide channel 200, and the reflected light is coupled and interfered again in the first waveguide channel 210 and the third waveguide channel 230 through the coupling area 20f and then split again, and is output from the first end of the second waveguide channel 220 and the first end of the third waveguide channel 230, respectively. An elliptical fitting algorithm is used to demodulate the two interference light beams with a fixed phase difference to obtain the to-be-measured acoustic wave signal.

[0030] In some embodiments, the first end of the first waveguide channel 210 and the first end of the third waveguide channel 230 extend away from the second waveguide 200, and the second end of the first waveguide channel 210 and the second end of the third waveguide channel 230 extend away from the second waveguide channel 220. That is, the first end of the first waveguide channel 210 and the first end of the third waveguide channel 230 are arranged opposite to each other, and the second end of the first waveguide channel 210 and the second end of the third waveguide channel 230 are also arranged opposite to each other. In this way, the phenomenon of crosstalk and interference of light outside the coupling area 20f during the propagation of the light in the waveguide 200 can be avoided to some extent, so that the light can react in the coupling area 20f as much as possible.

[0031] In some embodiments, at least part of the first waveguide channel 210 and the third waveguide channel 230 on the first side of the coupling area 20f is in a first arc shape, and at least part of the first waveguide channel 210 and the third waveguide channel 230 on the second side of the coupling area 20f is in a second arc shape. The centers of the first arc shape and the second arc shape are located on the inner side of the first waveguide channel 210 and the third waveguide channel 230. In this way, the above-mentioned opposite arrangement technical solution can be achieved.

[0032] In some embodiments, the middle part of the first waveguide channel 210 and the third waveguide channel 230 is in a third arc shape, and the two ends of the third arc shape are connected with the corresponding first arc shape and second arc shape respectively. In addition, the center of the third arc shape of the first waveguide channel 210 is located outside the first waveguide channel 210, and the center of the third arc shape of the third waveguide channel 230 is located outside the third waveguide channel 230. In this way, the first waveguide channel 210 and the third waveguide channel 230 as a whole are in a curved shape, and the bending degree of the curved shape can be reduced, and the full radius of the curved shape can be increased, so as to reduce the loss of light in the waveguide 200 and avoid escape.

[0033] For example, the radius of the first arc shape, the second arc shape and the third arc shape can be 2mm-5mm. If the radius is too small, the light transmission loss of the first arc shape and the second arc shape will be too large. If the radius is too large, due to the influence of the overall size of the waveguide, the bending radius of the third arc shape will be compressed, causing the light transmission loss of the third arc shape to be too large. For example, the radius of the first arc shape, the second arc shape and the third arc shape can be 2mm, 3mm, 4mm, 5mm or any value between the above two values, which is not limited in the present application.

[0034] In specific implementation, along the first direction Y, the first waveguide channel 210, the second waveguide channel 220 and the third waveguide channel 230 all have a first segment, a second segment and a third segment arranged in the direction of the wafer 110 in turn, and the second segment of the first waveguide channel 210, the second segment of the second waveguide channel 220 and the second segment of the third waveguide channel 230 are arranged in a stack to form the coupling area 20f. In addition, the first segment of the first waveguide channel 210 and the first segment of the third waveguide channel 230 are both in an arc shape, and the center of the first segment of the first waveguide channel 210 and the first segment of the third waveguide channel 230 is located on the side of the first segment of the first waveguide channel 210 and the first segment of the third waveguide channel 230, i.e. between the first segment of the first waveguide channel 210 and the first segment of the third waveguide channel 230. In addition, the third segment of the first waveguide channel 210 and the third segment of the third waveguide channel 230 are both in an arc shape, and the center of the third segment of the first waveguide channel 210 and the third segment of the third waveguide channel 230 is located on the side of the third segment of the first waveguide channel 210 and the third segment of the third waveguide channel 230, i.e. between the third segment of the first waveguide channel 210 and the third segment of the third waveguide channel 230. In addition, the second segment of the first waveguide channel 210 and the second segment of the third waveguide channel 230 are also in an arc shape, and the center of the second segment of the first waveguide channel 210 and the second segment of the third waveguide channel 230 is located on the side of the second segment of the first waveguide channel 210 and the second segment of the third waveguide channel 230, i.e. on the outside of the second segment of the first waveguide channel 210 and the second segment of the third waveguide channel 230.

[0035] Exemplarily, the first segment, the second segment and the third segment of the first waveguide channel 210 and the third waveguide channel 230 have consistent radii, so that the first waveguide channel 210 and the third waveguide channel 230 can smoothly transition. In addition, the first segment and the third segment of the first waveguide channel 210 are arranged symmetrically with respect to the center line of the second segment, and the first segment and the third segment of the third waveguide channel 230 are arranged symmetrically with respect to the center line of the second segment. In this way, the first end of the first waveguide channel 210 and the first end of the third waveguide channel 230 can be flush, and the second end of the first waveguide channel 210 and the second end of the third waveguide channel 230 can be flush. In other arrangements, the first end of the first waveguide channel 210 and the first end of the third waveguide channel 230 are not flush, and the second end of the first waveguide channel 210 and the second end of the third waveguide channel 230 are not flush, which are not limited in the present application.

[0036] In the first direction Y, the second end of the first waveguide channel 210 to the coupling region 20f has a first distance, the second end of the second waveguide channel 220 to the coupling region 20f has a second distance, and the third end of the second waveguide channel 220 to the coupling region 20f has a third distance. The first distance and the second distance are both greater than the third distance. In this way, the length between the second end of the second waveguide channel 220 and the coupling region 20f can be reduced. This is because the second end of the second waveguide channel 220 is a redundant port, which is not used in actual applications to avoid wasting light energy. As described above, the first distance and the second distance can be consistent or inconsistent, which are not limited in the present application.

[0037] The production method of the waveguide 200 provided by the present application includes: providing and cleaning the surface of the substrate 240 to obtain an ultra-clean surface on the substrate 240. In specific implementation, the substrate 240 is a silicon dioxide substrate, which can be square and has a thickness of about 1 mm. The ultra-clean surface on the substrate 240 can be obtained by megasonic cleaning. processing the obtained ultra-clean surface to prepare a lower cladding layer. In specific implementation, the lower cladding layer can be formed on the substrate 240 by reactive ion etching. processing the surface of the prepared lower cladding layer to form a waveguide groove. In specific implementation, spin-on photoresist can be performed on the surface of the lower cladding layer, and then exposure and development are performed to define a waveguide structure pattern on the photoresist. Then, the pattern is transferred to the lower cladding layer by reactive ion etching to form a waveguide groove with an etching depth of about 10 μm. The waveguide trench is filled with silicon dioxide as the core of the waveguide 200. In the implementation, the waveguide trench can be filled with silicon dioxide by low pressure chemical vapor deposition, and the surface can be planarized by chemical mechanical polishing. In addition, the refractive index of the silicon dioxide filled in the waveguide trench is greater than the refractive index of the substrate 240, and the difference between the two refractive indexes can be 2%-5%, for example, 2%, 3%, 4%, 5% and any value between the above two values, so as to constrain the propagation path of light and avoid the escape of light in the waveguide 200. The upper cladding layer is deposited on the surface of the lower cladding layer to wrap the core of the waveguide 200. In the implementation, a layer of low refractive index silicon dioxide is again deposited as the upper cladding layer to completely wrap the core of the waveguide 200, thereby forming a complete embedded optical waveguide 200 structure on the silicon dioxide silicon substrate 114.

[0038] In combination Figure 1 The diaphragm 100 of the present application has two forming surfaces, i.e. the second side surface 112 and the fourth side surface 122. The second side surface 112 cooperates with the waveguide 200 to form a reference light path P1 for constructing a Michelson interference structure, and the fourth side surface 122 cooperates with the waveguide 200 to form a sensing light path P2 for constructing a Michelson interference. There is a fixed optical path difference between the reference light path 16 and the sensing light path 14, and the optical path difference is formed by the etching depth difference between the second side surface 112 and the fourth side surface 122 of the diaphragm 100. For example, the etching depth difference in the present application is 996 μm.

[0039] In the second aspect of the present application, the present application further provides an acoustic detection system. Figure 4 The arrangement of the acoustic detection system in one or more embodiments of the present application is shown, in combination Figure 4 The acoustic detection system includes a detection light source 20, the optical microphone 10 of the first aspect, a photodetector 30 and a signal demodulation processor 40. The detection light source 20 is connected with the incident end 20a. The photodetector 30 is provided with two photodetectors 30, and the two photodetectors 30 are respectively connected with the first exit end and the second exit end. In addition, the two photodetectors 30 are connected with the signal demodulation processor 40.

[0040] In a specific implementation, before the test system is built, the working state of the optical microphone 10 is adjusted by building a debugging light path, the prepared diaphragm 100 is fixed in the special packaging shell, and the waveguide 200 is fixed through the adjusting frame, so that the first emitting end and the second reflecting end 20c are accurately opposite to the diaphragm 100, the above-mentioned Michelson interference structure is constructed, the light emitted by the light source 20 is connected to the incident end 20a of the waveguide 200, the first emitting end and the second emitting end of the waveguide 200 are respectively connected to a photodetector 30, and the photodetector 30 is output to an oscilloscope. The relative position and parallelism of the waveguide 200 and the diaphragm 100 are finely adjusted until a clear ellipse with a large eccentricity and a thin curve is observed on the oscilloscope, indicating that the contrast of the interference light path is optimal and the phase difference of the two signals is close to 2π / 3, and the system is in the best working state.

[0041] The signal demodulation processor 40 is used to perform an EF-DCM demodulation algorithm, which fits the elliptical parameters through the elliptical phase relationship between the first waveguide channel 210 and the second waveguide channel 220, eliminates the influence of external environmental factors such as coupling phase difference changes and optical power fluctuations on the static working point, demodulates the frequency and amplitude of the phase change of the interference arm through the DCM algorithm, and obtains the information of the sound signal to be measured.

[0042] The acoustic detection system provided in the present application is used to test the response of the sound signal in the range of 100-400 Hz, and the final frequency response obtained in the experiment is as shown in Figure 5 From the measurement results, the optical microphone 10 has a relatively flat sensitivity curve between 100-400 Hz, the fluctuation range of the sensitivity is between 16.03-17.44 dBre1µm / Pa, the sensitivity change is less than 1.5 dB, the frequency response is relatively flat when measuring low-frequency sound signals, the sensitivity is greatly improved compared with the thin-film microphone, and the detection demand of weak signals can be met.

[0043] Meanwhile, in order to further analyze the frequency characteristics of the optical microphone 10, the frequency range of the sound signal is further expanded, the frequency response of the optical microphone 10 is tested in 0-1500 Hz, and the position of the resonance frequency is found. The measured frequency domain characteristics of the designed optical microphone 10 are as shown in Figure 6 From Figure 6 it can be seen that the resonance frequency of the optical microphone 10 is about 1100 Hz, which is smaller than the theoretical calculation value at the design time, but still has a relatively flat sensitivity interval in the low-frequency interval.

[0044] After analyzing the frequency domain response of the entire optical microphone 10, the linearity of the optical microphone 10 is also tested, the sound signal with a frequency of 200 Hz and a sound pressure size from 0.01 Pa to 0.11 Pa is selected for testing, and the test result is as shown inFigure 7 The output sound field calibration sound pressure sequence under linearity test is shown in Table 2 after multiple experimental tests are performed. Figure 8 It can be seen from the test results that the linearity of the designed optical microphone 10 is 0.9986 at a frequency of 200 Hz, and it can stably work under a sound signal of 0.01 Pa~0.11 Pa, the fitting sensitivity is 7.486 µm / Pa, the corresponding logarithmic unit is 17.485 dBre1µm / Pa, the light source with a wavelength of 1550 nm used in the experiment is tested, and the calculated phase sensitivity is 60.86 rad / Pa, the sensitivity is measured by 1 rad / µPa, and the converted logarithmic unit is-84 dBre1rad / µPa. The common sensitivity of the phase modulation type optical microphone 10 using the thin film and elastic column transduction structure is about-100~-130 dB re 1 rad / µPa. It can be seen that the cantilever beam developed as the transduction structure of the optical microphone 10 has a significant advantage in sensitivity, and the phase and sound pressure have a good linear relationship in the working frequency band.

[0045] In the present application, unless specifically defined and limited otherwise, the first feature is "on" or "under" the second feature, which can include direct contact between the first and second features, or indirect contact between the first and second features through another feature therebetween. Moreover, the first feature "on", "above" and "over" the second feature includes the first feature directly above and obliquely above the second feature, or only indicates that the first feature is higher in horizontal height than the second feature. The first feature "under", "below" and "under" the second feature includes the first feature directly below and obliquely below the second feature, or only indicates that the first feature is lower in horizontal height than the second feature.

[0046] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0047] In the present application, unless specifically defined otherwise and limited, the terms "connected", "fixed", and the like should be construed as being broad, for example, "fixed" can be fixed connection, or detachable connection, or integrated; can be mechanical connection, or electrical connection; can be direct connection, or indirect connection through intermediate medium; can be internal connection of two elements, or interaction relationship of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0048] In addition, in the present application, the description such as "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically defined.

[0049] Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and purposes of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. An integrated Michelson interferometer optical microphone, characterized by, The optical microphone comprises: a diaphragm comprising a wafer and a beam structure, the wafer having a first side and a second side opposite to each other along a first direction, the wafer being provided with a through hole penetrating the first side and the second side, the beam structure being adapted to the through hole, one side of the beam structure being connected to the wafer, the rest of the beam structure being spaced apart from the wafer, the beam structure having a third side and a fourth side opposite to each other along the first direction, the fourth side being recessed in the second side; a waveguide being spaced apart from the second side of the wafer along the first direction, the waveguide having an incident end, a first reflection end, a second reflection end, a first emission end and a second emission end, the first reflection end being directed to the second side, the second reflection end being directed to the fourth side.

2. The integrated Michelson-interferometric optical microphone of claim 1, wherein The wafer comprises a top layer, a substrate and a buried oxygen layer, the top layer and the substrate being oppositely arranged, the buried oxygen layer being arranged between the top layer and the substrate; wherein: the beam structure and the top layer are integrally formed, the second side and the side of the top layer directed to the substrate are flush.

3. The integrated Michelson-interferometric optical microphone of claim 1, wherein The waveguide comprises a substrate, the substrate being provided with a first waveguide channel, a second waveguide channel and a third waveguide channel arranged in sequence along a second direction, the first direction and the second direction being perpendicular to each other, the first waveguide channel, the second waveguide channel and the third waveguide channel having an overlapping region to form a coupling region, wherein: the first waveguide channel, the second waveguide channel and the third waveguide channel each have a first end and a second end, the first end of the first waveguide channel, the first end of the second waveguide channel and the first end of the third waveguide channel are located at a first side of the coupling region, the second end of the first waveguide channel, the second end of the second waveguide channel and the second end of the third waveguide channel are located at a second side of the coupling region, the first end of the first waveguide channel is the incident end, the second end of the first waveguide channel is the first reflection end, the second end of the third waveguide channel is the second reflection end, the first end of the second waveguide channel is the first emission end, and the first end of the third waveguide channel is the second emission end.

4. The integrated Michelson-interferometric optical microphone of claim 3, wherein The first end of the first waveguide channel and the first end of the third waveguide channel respectively extend away from the second waveguide channel, and the second end of the first waveguide channel and the second end of the third waveguide channel respectively extend away from the second waveguide channel.

5. The integrated Michelson-interferometric optical microphone of claim 4, wherein At least part of the first waveguide channel and the third waveguide channel located at the first side of the coupling region are in a first arc shape; At least part of the first waveguide channel and the third waveguide channel located at the second side of the coupling region are in a second arc shape.

6. The integrated Michelson-interferometric optical microphone of claim 5, wherein The middle part of the first waveguide channel and the third waveguide channel are in a third arc shape, and the two ends of the third arc shape are respectively the same as the first arc shape and the second arc shape.

7. The integrated Michelson-interferometric optical microphone of claim 3, wherein In the first direction, the second end of the first waveguide channel to the coupling region has a first distance, the second end of the second waveguide channel to the coupling region has a second distance, and the third end of the second waveguide channel to the coupling region has a third distance; wherein, The first distance and the second distance are both greater than the third distance.

8. The integrated Michelson-interferometric optical microphone according to any one of claims 1 to 7, characterized in that The method for producing the diaphragm comprises: Making a mask on the surface of the wafer to form a mask plate of the beam structure; Etching on the wafer to form air slits on the wafer; Depositing a silicon nitride layer on the surface of the wafer; After the wafer is etched on the front surface, backside lithography is performed to form a back cavity on the back surface of the wafer; The silicon nitride layer and the buried oxygen layer at the bottom of the back cavity groove are removed.

9. The integrated Michelson-interferometric optical microphone according to any one of claims 1 to 7, characterized in that The method for producing the waveguide comprises: Providing and cleaning the surface of a substrate to obtain an ultra-clean surface on the substrate; Processing the obtained ultra-clean surface to prepare a lower cladding layer; Processing a waveguide groove on the surface of the prepared lower cladding layer; Filling silica in the processed waveguide groove as a waveguide core, the refractive index of the silica in the waveguide groove being greater than the refractive index of the substrate; Depositing an upper cladding layer on the surface of the lower cladding layer to wrap the waveguide core.

10. An acoustic detection system, characterized in that The acoustic detection system comprises a detection light source, the optical microphone according to any one of claims 1-9, a photodetector, and a signal demodulation processor; wherein: The detection light source is connected with the incident end, the photodetector is provided with two, the two photodetectors are respectively connected with the first exit end and the second exit end, and the two photodetectors are both connected with the signal demodulation processor.

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