Method for processing FP cavity of EFPI optical microphone with long cavity length and EFPI optical microphone

Abstract

The invention provides a processing method of an EFPI optical microphone FP cavity with a long cavity length, and also provides the EFPI optical microphone, which breaks through the limitation of the traditional process on the processing of a structure with a long cavity length, so that the processed FP cavity can enable the EFPI optical microphone to have better fineness and remarkably improve the sound pressure detection sensitivity; the problems that a traditional EFPI optical microphone mostly adopts a short-cavity-length structure, and low-noise and broadband acoustic detection requirements are difficult to meet in the aspects of long-cavity-length construction, environment robustness and integration precision are solved. When the FP cavity is processed, firstly, the length of a glass sleeve is determined, the glass sleeve is processed through a 3D additive manufacturing technology, in the 3D additive manufacturing process, a vibrating diaphragm and a reflecting mirror are oppositely arranged and form the FP cavity with part of the glass sleeve, and the opposite surfaces of the vibrating diaphragm and the reflecting mirror are two reflecting surfaces of the FP cavity respectively.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of optical microphones, in particular to a processing method of an EFPI optical microphone FP cavity with a long cavity length and the EFPI optical microphone. BACKGROUND

[0002] An EFPI (Extrinsic Fabry-Perot Interferometer) optical microphone changes the optical path difference of an interference cavity through diaphragm vibration caused by sound pressure, resulting in changes in reflected light phase and intensity, and the sound signal is recovered after the electric signal converted by a photoelectric detector. Its advantages include anti-electromagnetic interference, wide frequency response (20Hz~20kHz) and high sensitivity, and it is suitable for professional audio recording, industrial monitoring, medical treatment and scientific research and other fields.

[0003] The FP cavity (Fabry-Perot cavity) of the traditional EFPI optical microphone adopts a short cavity length structure, and there are problems in long cavity length construction, environmental robustness and integration accuracy, which cannot meet the low noise and wide frequency acoustic detection requirements. SUMMARY

[0004] In view of the above problems, the application provides a processing method of an EFPI optical microphone FP cavity with a long cavity length, and also provides the EFPI optical microphone, which breaks through the limitation of traditional process on long cavity length structure processing, so that the FP cavity processed can make the EFPI optical microphone have better fineness and significantly improve the sound pressure detection sensitivity.

[0005] The technical scheme is as follows: the processing method of the EFPI optical microphone FP cavity with a long cavity length, characterized by determining the length of the glass sleeve, processing the glass sleeve through a 3D additive manufacturing technology, in the 3D additive manufacturing process, the diaphragm and the reflector are oppositely arranged and form a FP cavity with part of the glass sleeve, and the opposite surfaces of the diaphragm and the reflector are respectively two reflecting surfaces of the FP cavity.

[0006] Further, the specific steps of processing the glass sleeve through the 3D additive manufacturing technology include: step 1, designing and establishing a three-dimensional model of the glass sleeve through software;

[0007] Step 2, optimizing the model geometry and adding a support structure for supporting the corresponding part of the glass sleeve in the 3D additive manufacturing process;

[0008] Step 3, selecting appropriate consumables for glass sleeve forming;

[0009] Step 4, decoding the model file, checking its integrity and geometric errors, repairing holes or overlapping surfaces, adjusting the size ratio, simplifying details, optimizing the support structure to reduce forming defects;

[0010] Step 5, start the 3D additive forming device, the control system drives the consumable pressure control unit to form the glass sleeve.

[0011] Further, before the 3D additive forming in step 5, the diaphragm is placed in the 3D additive forming area as the base of the 3D additive manufacturing; the mirror is added in the 3D additive forming process to be integrally formed with the glass sleeve.

[0012] Further, the diaphragm is deposited with a silicon-based thin film to constitute one side surface of the FP cavity; the mirror is coated with graphene to constitute one side surface of the FP cavity.

[0013] Further, during the 3D additive forming in step 5, the thickness of each layer of material is precisely controlled to the nanometer level to ensure the geometric shape and surface quality of the structure.

[0014] Further, the cavity length of the FP cavity is 5 mm, and the parallelism error of the two reflecting surfaces is less than 10 -4 rad, and the surface roughness Ra is less than 10 nm.

[0015] An EFPI optical microphone characterized in that the FP cavity is made by the above processing method.

[0016] Further, the glass sleeve includes an FP cavity section for forming the FP cavity and a collimator mounting section for mounting a collimator, an optical fiber is connected with the collimator, the collimator is perpendicular to the mirror, a photodetector is further mounted at one end of the mirror away from the FP cavity, and the photodetector is used to receive reflected light and complete optical / electric conversion.

[0017] Further, in use, the light signal emitted by the laser is transmitted through the optical fiber, enters the FP cavity in the glass sleeve through the collimator, in the cavity, the light signal is reflected multiple times between the diaphragm and the mirror to form an interference signal, at this time, due to the slight vibration of the diaphragm caused by external sound pressure, the cavity length of the FP cavity changes, which directly affects the phase and intensity of the interference light intensity, so that the reflected light signal is modulated, the modulated light signal after reflection is received and processed by the photodetector, and the received light signal is converted into an electric signal, the phase change information caused by the sound pressure is embedded in the electric signal, which reflects the characteristics of the diaphragm vibration, the converted electric signal is transmitted to a data processing system for further analysis, and the original sound signal waveform is restored by extracting the phase change in the interference signal to obtain a measurement result.

[0018] Further, the glass sleeve further sequentially mounts a filter perpendicular to the optical axis, which is used to filter stray light and improve signal purity.

[0019] A convex lens is used to focus light signals and reduce light energy loss;

[0020] Concave lenses are used to optimize optical path distribution and ensure uniform optical signal.

[0021] Beneficial effects: The FP cavity processing method provided by this invention uses 3D additive manufacturing technology (such as two-photon polymerization and fused deposition modeling) to directly manufacture intrigued Fabry-Perot cavities with a cavity length of up to 5mm. At the same time, the EFPI optical microphone breaks through the processing limitations of traditional processes for long cavity and long structure. The specially made glass sleeve integrates a flexible diaphragm and a plane mirror respectively. By precisely controlling the additive layer thickness (nanoscale) and the coefficient of thermal expansion of the material, the cavity length accuracy error is ensured to be ≤±0.5%, and the surface roughness Ra inside the cavity is <10nm, reducing light scattering loss. This solves the problem that traditional EFPI optical microphones mostly use short cavity and long structure, which makes it difficult to meet the requirements of low noise and wideband acoustic testing in terms of long cavity construction, environmental robustness and integration accuracy. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the EFPI optical microphone.

[0023] Figure 2 This is a schematic diagram of part of the optical path system. Detailed Implementation

[0024] like Figure 1 The method for fabricating the long-cavity EFPI optical microphone FP cavity shown is as follows: the length of the glass sleeve 1 is determined, and the glass sleeve 1 is fabricated by 3D additive manufacturing technology. During the 3D additive manufacturing process, the diaphragm 4 and the reflector 5 are arranged opposite to each other and together with part of the glass sleeve 1 to form the FP cavity 3 (Fabry-Perot cavity). The opposite surfaces of the diaphragm 4 and the reflector 5 are the two reflecting surfaces of the FP cavity 3.

[0025] Specifically, the steps for processing glass sleeves using 3D additive manufacturing technology include: Step 1, designing and creating a three-dimensional model of the glass sleeve using SolidWorks software;

[0026] The extrinsic Fabry-Perot cavity has a cavity length of 5 mm, a diaphragm 4 diameter of 3 mm and a thickness of 50 μm, a reflector 5 diameter of 3 mm, a collimator mounting area inner diameter of 3.02 mm, an outer diameter of 5 mm, a length of 6 mm, and a total length of 16 mm.

[0027] Step 2: Optimize the model geometry and add support structures. Set the layer height to 0.1mm and the forming speed to 10mm / s to support the corresponding part of the glass sleeve 1 during the 3D additive manufacturing process.

[0028] Step 3, select the appropriate consumables for glass sleeve forming, for example, high borosilicate glass melting line (consumable box 10A) can be selected.

[0029] Step 4, decode the model file, check its integrity and geometric errors using Netfabb, repair holes or overlapping surfaces, adjust the size ratio, simplify details, and optimize support structures to reduce forming defects.

[0030] Step 5, start the 3D additive forming device, control the system to drive the consumable pressure control unit, deposit high borosilicate glass to form a glass sleeve, and use nanoscale additive layer thickness control to match the material thermal expansion coefficient during the forming process to ensure that the cavity length precision error is ≤±0.5% and the inner surface roughness Ra<10nm, reducing light scattering loss while improving interference efficiency.

[0031] In addition, the FP cavity 3 can be processed by integral molding, specifically, the diaphragm 4 is placed in the 3D additive forming area as the base of 3D additive manufacturing before Step 5 of 3D additive manufacturing; the mirror 5 is added during the 3D additive manufacturing process to form a long-cavity-length interference structure with the glass sleeve.

[0032] The reason why the EFPI optical microphone with long cavity length can have higher detection sensitivity is that the linear relationship between sound pressure and Fabry-Perot cavity transmission light intensity, the greater the slope of the linear region of the Fabry-Perot cavity transmission characteristic curve, the more sensitive the Fabry-Perot cavity to the refractive index change caused by the sound wave, and the higher the sensor sound detection sensitivity. But at the same time, the dynamic range of the sensor is negatively related to the cavity length, the longer the cavity length, the smaller the dynamic range, the narrower the range of sound pressure that can be detected, and it is easy to appear high sound pressure signal saturation, distortion. The dynamic range of the sensor limits the Fabry-Perot cavity length cannot be infinitely long. In actual application scenarios, the dynamic range of the sensor is generally 200Pa (140dB), so the final calculation of 5mm cavity length is the best. In addition, regarding the fineness, the fineness refers to the maximum number of distinguishable stripes between two adjacent stripes of the Fabry-Perot cavity, the greater the stripe fineness, the finer and sharper the stripe, the better the wavelength locking, and the fineness can be solved by the following formula:

[0033]

[0034] In the formula:

[0035] F represents the fineness of the interferometer;

[0036] R represents the reflectivity of the Fabry-Perot cavity;

[0037] n represents the refractive index of the medium in the Fabry-Perot cavity;

[0038] d represents Fabry-Perot cavity length / m;

[0039] represents the optical loss coefficient.

[0040] According to the relationship between the Fabry-Perot cavity length and the fineness of the Fabry-Perot cavity in the above formula, it can be obtained that the longer the Fabry-Perot cavity length is, the greater the fineness of the interferometer is, the finer the stripe is, and the better the wavelength locking is. Therefore, by adopting the long cavity length structure, the fineness of the interferometer is higher.

[0041] On the basis of the above, the specific structure of the EFPI optical microphone is introduced as follows:

[0042] In combination with Figure 1 , the EFPI optical microphone comprises a glass sleeve 1, an optical fiber 2, an FP cavity 3, a diaphragm 4, a mirror 5, an optical path system 6, and a photodetector 7.

[0043] The glass sleeve 1 comprises an FP cavity section for forming the FP cavity 3 and a collimator mounting section for mounting the collimator 8. When the length of the glass sleeve 1 is determined, a length for forming the collimator mounting section is reserved, and the long cavity length interferometric structure can be customized by using the above processing method.

[0044] The optical fiber 2 extends from one end of the collimator mounting section and can adopt an SMF-28 single-mode optical fiber with a core diameter of 9 μm, a cladding diameter of 125 μm, and a working wavelength of 1550 nm. The end face of the optical fiber is polished to a plane, and the reflectivity is about 4%, which ensures the stable input of the optical signal. The optical fiber is fixed to the collimator mounting section of the glass sleeve 1 by a high-precision ceramic ferrule (outer diameter 3 mm), and the center deviation is controlled to be less than 0.1°, thereby ensuring the alignment of the optical path.

[0045] The FP cavity 3 is formed by the reflecting surface of the diaphragm 4 and the reflecting surface of the mirror 5, and the cavity length is 5 mm. The FP cavity 3 is integrally formed in the glass sleeve by 3D additive manufacturing technology, so that the parallelism error of the two reflecting surfaces is less than 10 -4 rad, and the surface roughness Ra is less than 10 nm. The long cavity length structure makes the fineness (Finesse) of the interferometer exceed 100, thereby significantly improving the sound pressure detection sensitivity.

[0046] The diaphragm 4 is fixed to one end of the cavity and serves as one of the reflecting surfaces. The diaphragm 4 can be used as the base for 3D additive manufacturing during the processing of the FP cavity 3. The diaphragm 4 is deposited with a silicon-based thin film on one side surface of the FP cavity 3, and the thickness and diameter of the thin film are 50 μm and 3 mm, respectively. The tension control makes the resonance frequency greater than 20 kHz, and the sound pressure sensitivity is about 1 nm / Pa.

[0047] The mirror 5 is coated with graphene and fixed at the other end of the cavity to enhance the interference contrast. It is kept 5mm apart from the diaphragm during the FP cavity 3 processing and fixed at the other end of the FP cavity 3 with a parallelism deviation of <0.5°. It constitutes the graphene deposition on one side of the FP cavity 3 with a diameter of 3mm.

[0048] The optical path system 6 is used to optimize the optical signal transmission and is combined with Figure 2 It specifically includes a collimator 8, a filter 9, a convex lens 10, and a concave lens 11.

[0049] The collimator 8 is used to collimate the divergent light beam output by the optical fiber 2 to reduce the beam divergence angle. Its inner diameter is 3.02mm and it is fixed in the collimator mounting section of the glass sleeve 1. The exit center is perpendicular to the mirror 5 with a deviation of <0.1°. The collimator 8 and the mirror 5 are vertically aligned through the pre-set collimator mounting area (inner diameter tolerance ±1μm) with an optical axis offset of <500nm.

[0050] The filter 9 is used to filter out stray light to improve signal purity. The convex lens 10 is used to focus the optical signal to reduce light energy loss. The concave lens 11 is used to optimize the optical path distribution to ensure uniformity of the optical signal.

[0051] The photodetector 7 is used to receive reflected light and complete the optical / electrical conversion. It can use an InGaAs ring photodiode with a bandwidth of 30kHz and a noise equivalent power of <10pW / √Hz (less than 10 picowatts per square root hertz of bandwidth). It is installed in a ring shape on the back of the mirror 5, which can shorten the optical signal transmission path to improve coupling efficiency.

[0052] A stable extrinsic Fabry-Perot interferometric cavity is formed by constructing a glass sleeve 1 to support and fix the optical fiber 2, diaphragm 4 and mirror 5 using 3D additive manufacturing technology, with a cavity length set to 5 millimeters. The optical fiber 2 is fixed in the collimator mounting area of the glass sleeve 1 through a high-precision ceramic ferrule, ensuring that the optical path is aligned without deviation. The diaphragm 4 and mirror 5 are installed at both ends of the cavity, ensuring that their parallelism deviation with the end face of the optical fiber 2 is controlled within 0.5 degrees to ensure accurate transmission of the optical signal. The optical path system 6, including the collimator 8, filter 9, convex lens 10 and concave lens 11, is installed inside the glass sleeve 1, perpendicular to the optical axis, for optimizing the transmission quality of the optical signal. The photodetector 7 is then bonded to the back of the mirror 5, ready to receive the reflected light signal. The system is calibrated to check the optical path alignment and the accuracy of the cavity length, ensuring that the microphone is in the best working condition, laying the foundation for subsequent sound signal measurement. The long-cavity high-precision EFPI optical microphone is connected to a 1550nm distributed feedback (DFB) laser with a power of 3mW, a relative intensity noise (RIN) of <-140dB / Hz and a wavelength stability of <0.01nm. The laser light signal is transmitted through the optical fiber 2, enters the extrinsic Fabry-Perot cavity inside the glass sleeve 1 through the collimator 8. In the cavity, the light signal is reflected multiple times between the diaphragm 4 and the mirror 5, forming an interference signal. At this time, due to the external sound pressure causing the diaphragm 4 to vibrate slightly, the cavity length changes, which directly affects the phase and intensity of the interference light intensity, causing the reflected light signal to be modulated. The modulated light signal after reflection is received and processed by the photodetector 7. The photodetector 7 uses an InGaAs ring photodiode with high bandwidth (30 kilohertz) and low noise (noise equivalent power less than 10 picowatts / √hertz) characteristics, which can efficiently convert the received optical signal into an electrical signal. This electrical signal embeds the phase change information caused by the sound pressure, reflecting the characteristics of the diaphragm 4 vibration. Due to the effect of the sound signal, the refractive index of the light signal in the cavity changes, which in turn affects the characteristics of the interference signal, and the high sensitivity of the photodetector 7 ensures the accuracy of this conversion process. The converted electrical signal is transmitted to the data processing system for further analysis. By extracting the phase change in the interference signal, the original sound signal waveform is recovered. Users can view the measurement results such as sound pressure intensity, frequency response and other parameters through the interface of the control system.

[0053] Through this complete process, the long-cavity high-precision EFPI optical microphone realizes efficient conversion from sound signal capture to result output. The entire process relies on precise component design and system cooperation to ensure the accuracy and reliability of the measurement results, providing users with a high-quality acoustic detection experience.

[0054] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method of processing an EFPI optical microphone FP cavity with a long cavity length, characterized by, The steps include determining the length of the glass sleeve, processing the glass sleeve by 3D additive manufacturing technology, and arranging the diaphragm and the mirror opposite to each other and forming an FP cavity with part of the glass sleeve in the 3D additive manufacturing process, and the opposite surfaces of the diaphragm and the mirror are the two reflecting surfaces of the FP cavity.

2. The method of claim 1, wherein the long-cavity EFPI optical microphone FP cavity is processed by: The specific steps of processing the glass sleeve by 3D additive manufacturing technology include: step 1, designing and establishing a three-dimensional model of the glass sleeve by software; Step 2, optimize the model geometry and add support structure for supporting the corresponding part of the glass sleeve during 3D additive manufacturing process; Step 3, select appropriate consumables for glass sleeve forming; Step 4, decode the model file, check its integrity and geometric errors, repair holes or overlapping surfaces, adjust size ratio, simplify details, optimize support structure to reduce forming defects; Step 5, start the 3D additive forming device, and control the system to drive the consumable pressure control unit to form the glass sleeve.

3. The method of claim 2, wherein the long-cavity EFPI optical microphone FP cavity is processed by: Before the 3D additive forming in step 5, the diaphragm is placed in the 3D additive forming area as the base of 3D additive manufacturing; and the mirror is added during the 3D additive forming process to make it integrally formed with the glass sleeve.

4. The method of claim 3, wherein the long-cavity EFPI optical microphone FP cavity is processed by: The diaphragm deposits a silicon-based thin film on one side surface of the FP cavity; and the mirror is coated with graphene on one side surface of the FP cavity.

5. The method of claim 2, wherein the long-cavity EFPI optical microphone FP cavity is processed by: During the 3D additive forming in step 5, the thickness of each layer of material is precisely controlled to the nanometer level, ensuring the geometric shape and surface quality of the structure.

6. The method of claim 1, wherein the long-cavity EFPI optical microphone FP cavity is processed by: The cavity length of the FP cavity is 5mm, and the parallelism error of the two reflecting surfaces is less than 10 -4 rad, surface roughness Ra<10nm.

7. An EFPI optical microphone characterized by: The FP cavity is made by using the processing method of any one of claims 1-6.

8. The EFPI optical microphone according to claim 7, characterized in that: The glass sleeve includes an FP cavity section for forming the FP cavity and a collimator mounting section for mounting a collimator, an optical fiber is connected with the collimator, the collimator is perpendicular to the mirror, and a photodetector is further mounted at one end of the mirror away from the FP cavity, and the photodetector is used to receive reflected light and complete optical / electrical conversion.

9. An EFPI optical microphone according to claim 8, characterized in that: In use, the optical signal emitted by the laser is transmitted through the optical fiber, enters the FP cavity in the glass sleeve through the collimator, and in the cavity, the optical signal is reflected multiple times between the diaphragm and the mirror to form an interference signal. At this time, due to the external sound pressure, the diaphragm vibrates slightly, causing the cavity length of the FP cavity to change, which directly affects the phase and intensity of the interference light intensity, so that the reflected light signal is modulated. The modulated light signal after reflection is received and processed by the photodetector, and the received optical signal is converted into an electrical signal. The phase change information caused by the sound pressure is embedded in the electrical signal, reflecting the characteristics of the diaphragm vibration. The converted electrical signal is transmitted to a data processing system for further analysis. By extracting the phase change in the interference signal, the original sound signal waveform is restored and the measurement result is obtained.

10. The EFPI optical microphone of claim 8, wherein: The glass sleeve further sequentially installs a filter perpendicular to the optical axis for filtering stray light and improving signal purity, a convex lens for focusing light signals and reducing light energy loss, and a concave lens for optimizing light path distribution and ensuring uniform light signals. ​ ​

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