All-quartz double-membrane structure optical microphone prepared from microstructure optical fiber and preparation method thereof

Abstract

The invention discloses an all-quartz double-film structure optical microphone prepared from a microstructure optical fiber and a preparation method thereof, and the all-quartz double-film structure optical microphone is formed by welding a first single-mode optical fiber, a waveguide diaphragm and a sensing circular diaphragm in sequence. The welding surface of the first single-mode fiber and the waveguide diaphragm is a first reflecting surface of Fabry-Perot interference; and the welding surface of the sensing circular diaphragm and the waveguide diaphragm is a second reflecting surface of the Fabry-Perot interference so as to form a Fabry-Perot interference effect. The all-quartz double-film structure optical microphone can keep stability and reliability under extremely harsh environmental conditions, and is suitable for various high-temperature tests and other high-voltage electromagnetic monitoring occasions.

Description

Technical Field

[0001] The invention belongs to the field of acoustic measurement, and in particular relates to an all-quartz double-membrane optical microphone prepared by microstructure optical fiber. Background Art

[0002] With the continuous advancement of sensor technology, acoustic pressure sensors that use diaphragms as transducer elements, such as acoustic detection devices such as microphones and hydrophones, play a key role in information collection. These acoustic detectors are widely used in many fields such as national defense, medical care, and economy. However, traditional capacitive sound pressure sensors are often large in size, have low voltage sensitivity, a narrow frequency response range, and are susceptible to electromagnetic interference. In contrast, fiber optic sound pressure sensors have shown their excellent application potential in acoustic imaging, ocean monitoring, and other fields, such as high sensitivity, low noise, and immunity to electromagnetic interference. The manufacturing process of these sensors not only pursues performance improvement, but also places special emphasis on stability and reliability in practical applications. Therefore, in-depth research and improvement of sensor manufacturing technology is crucial to promoting the advancement of future acoustic sensing technology.

[0003] Most of the existing optical microphones are based on Michelson interferometers, Mach-Zehnder interferometers, and diaphragm sensors prepared by the Fabry-Perot interference principle. Compared with the previous two interference methods, the FP interference structure has a more compact sensing structure and higher sensitivity, and can detect smaller sound signals. However, the sensing sensitivity and frequency response range of the FP interference structure sensor are limited by the material properties of the sensing diaphragm, so the dynamic range is limited, resulting in a situation where sensitivity and frequency response range cannot be taken into account. That is, if a material with high sensitivity is selected, its Young's modulus will be relatively low, so its frequency response range will be relatively reduced, or reducing the diaphragm thickness and increasing the diaphragm area in order to increase sensitivity will make the sensor very fragile and the sensor size larger, which is easily affected by the external environment. At the same time, the thinner the diaphragm, the more certain conditions will be imposed on the sensor preparation technology, resulting in difficulties in sensor preparation and an increase in preparation costs.

[0004] The sensitivity of existing optical microphones is limited by the vibration range of the diaphragm. Under low-frequency or small-amplitude sound pressure signals, the sensitivity of the sensor is insufficient, making it difficult to achieve accurate sound pressure measurement. Summary of the invention

[0005] The technical problem to be solved by the present invention is: how to improve the sensitivity and broadband response of the optical microphone sound pressure sensor by combining the microstructured optical fiber with the optical fiber.

[0006] In order to solve the above technical problems, the present invention provides an all-quartz double-membrane structure optical microphone prepared by microstructured optical fiber, which is formed by sequentially welding a first single-mode optical fiber, a waveguide diaphragm and a sensing circular diaphragm, wherein the welding surface between the first single-mode optical fiber and the waveguide diaphragm is the first reflection surface of Fabry-Perot interference; the welding surface between the sensing circular diaphragm and the waveguide diaphragm is the second reflection surface of Fabry-Perot interference, so as to form a Fabry-Perot interference effect.

[0007] The aforementioned all-quartz double-membrane optical microphone made of microstructured optical fiber, the waveguide diaphragm is composed of a suspended fiber core 2, a hollow layer, and an outer cladding from the inside to the outside.

[0008] In the aforementioned all-quartz double-membrane optical microphone made of microstructured optical fiber, a processing hole is respectively opened at the upper part and the lower part of the outer cladding.

[0009] The aforementioned all-quartz double-membrane optical microphone made of microstructured optical fiber has four processing holes opened along the circumference of the outer cladding 33 .

[0010] The aforementioned all-quartz double-membrane optical microphone made of microstructured optical fiber, the waveguide diaphragm is processed by microstructured optical fiber, and the microstructured optical fiber is selected from three-hole optical fiber or endless single-mode photonic crystal optical fiber.

[0011] The aforementioned all-quartz double-membrane structure optical microphone made of microstructured optical fiber, the first single-mode optical fiber includes a core and a cladding.

[0012] The aforementioned all-quartz double-membrane optical microphone made of microstructured optical fiber has a coating outer diameter of 242±5μm, a cladding outer diameter of 125±0.7μm, and a core diameter of 9±0.5μm for a single-mode optical fiber.

[0013] In the aforementioned all-quartz double-diaphragm optical microphone made of microstructured optical fiber, the cladding diameter of the sensing circular diaphragm is the same as the cladding diameter of the first single-mode optical fiber.

[0014] The aforementioned all-quartz double-diaphragm optical microphone made of microstructured optical fiber has a sensing circular diaphragm thickness of 10 μm.

[0015] The aforementioned all-quartz double-membrane optical microphone made of microstructured optical fiber has a coating diameter of 270±10 μm and an outer cladding diameter of 125±7 μm.

[0016] A method for preparing an all-quartz double-membrane structure optical microphone prepared by microstructure optical fiber comprises the following steps: Step 1, welding the first single-mode optical fiber, the microstructure optical fiber, and the second single-mode optical fiber in sequence to form a single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure; Step 2, preparing the microstructured optical fiber in the single-mode-microstructured optical fiber-single-mode Fabry-Perot interferometer sensing structure into a cylindrical waveguide membrane; Step 3, processing the second single-mode optical fiber in the single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure obtained in step 2 to prepare a sensing circular diaphragm.

[0017] The method for preparing the aforementioned all-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber comprises, in step 1: Step 11, stripping the coating layer of one end of the first single-mode optical fiber and the microstructure optical fiber, and removing the residual coating layer; Step 12, cutting one end of the first single-mode optical fiber and the microstructure optical fiber flat with a cutting knife, and using a fusion splicer to fusion-splice the cut surfaces of the first single-mode optical fiber and the microstructure optical fiber; Step 13, connecting the other end of the first single-mode optical fiber with the pigtail connector to the optical spectrum analyzer; Step 14, placing the single-mode-microstructure optical fiber structure obtained in step 12 on a high-precision translation stage, starting the high-precision translation stage, controlling the stepping accuracy, and cutting the remaining microstructure optical fiber. During the cutting process, the interference spectrum of the spectrum analyzer described in step 13 is observed to obtain the optimal Fabry-Perot interferometer cavity length and spectrum contrast; Step 15, fusing the other end of the microstructured optical fiber to the second single-mode optical fiber, and making the fusion joint flat, to form a single-mode-microstructured optical fiber-single-mode Fabry-Perot interferometer sensing structure.

[0018] In the aforementioned method for preparing an all-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber, in step 11, the discharge power and discharge time parameters of the fusion splicer are adjusted to achieve smooth fusion splicing of the microstructure optical fiber and the first single-mode optical fiber end face.

[0019] The aforementioned method for preparing an all-quartz double-membrane optical microphone made of a microstructured optical fiber requires a discharge power of 3-10 bits and a discharge time of 30-50ms.

[0020] In the aforementioned method for preparing an all-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber, in step 14, the required length of the microstructure optical fiber is 200-300 μm.

[0021] In the aforementioned method for preparing an all-quartz double-membrane structure optical microphone made of a microstructured optical fiber, in step 14, the required spectral contrast is >10dB.

[0022] The aforementioned method for preparing a full-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber comprises, in step 2: Step 21, etching processing holes on the upper surface and the lower surface of the side wall of the microstructured optical fiber by a laser subtractive processing method; Step 22, using a corrosive solution to penetrate into the microstructure optical fiber through the processing hole, selectively corroding the inside of the microstructure optical fiber, retaining the core part inside the microstructure optical fiber, removing the outer cladding and the rest outside the core, and finally obtaining the desired waveguide membrane; Step 23, placing the structure obtained in step 22 in deionized water and performing ultrasonic cleaning to dissolve the residual corrosive solution, thereby completing the preparation of the waveguide membrane.

[0023] In the aforementioned method for preparing an all-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber, in step 21, a processing hole is opened on the side wall of the microstructure optical fiber by laser-assisted processing, and the shape of the processing hole is rectangular, square or circular.

[0024] The aforementioned method for preparing a full-quartz double-membrane structure optical microphone prepared by a microstructured optical fiber, in step 21, through the laser subtractive processing process, a laser path is drawn in the set software, and the laser path can be square, circular or rectangular, including: Step 211, the sample prepared in the early stage is accurately placed on the three-dimensional mobile platform, and each axis of the three-dimensional mobile platform is driven by a stepper motor or a servo motor to achieve micrometer-level or even nanometer-level precise movement; the moving speed is controlled to be 2-5um / s during the process of moving the product driven by the three-dimensional mobile platform; Step 212, the control system receives the processing instruction, and adjusts the three-dimensional position of the three-dimensional moving platform in real time according to the predetermined processing path and parameters, so that the laser beam is accurately aligned with the sample surface; In step 213, the femtosecond laser source focuses the laser beam onto the sample surface through a focusing lens. The laser beam scans the sample surface along the three-dimensional coordinate axis. The focus of the laser beam changes position as the three-dimensional moving platform moves, thereby achieving local etching of the sample.

[0025] In the aforementioned method for preparing an all-quartz double-membrane structure optical microphone prepared by a microstructured optical fiber, in step 22, the corrosive solution can be selected as a hydrofluoric acid solution or a sodium hydroxide solution; the selective corrosion is carried out in a constant temperature water bath, the corrosion temperature is set to 20-30°C, and the required constant temperature water bath corrosion time is 30-50s.

[0026] The aforementioned method for preparing a full-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber comprises, in step 3: Step 31, cutting the other end of the second single-mode optical fiber to a set thickness by a laser subtractive process; Step 32, placing the second single-mode optical fiber downward into the optical fiber clamp, and fixing the optical fiber clamp vertically on the optical fiber grinder; Step 33, using a grinder to gradually move the entire structure downward, and using optical fiber grinding sandpaper to grind the end face of the second single-mode optical fiber to the micron level; Step 34, placing the polished structure under a microscope, and measuring the thickness of the second single-mode optical fiber through the microscope to see whether it meets the set requirements. If so, the sensing circular diaphragm is manufactured.

[0027] In the aforementioned method for preparing an all-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber, in step 33, the rotation speed of the optical fiber grinder is set at 3000-5000 rpm, and the grinding time is 40-60 min.

[0028] Beneficial effects achieved by the present invention: The all-quartz double-membrane structure optical microphone prepared by microstructure optical fiber of the present invention adopts an acoustic sensor made of all-quartz material. Due to the chemical and physical properties and stability of quartz material, it can maintain excellent stability and reliability under extremely harsh environmental conditions, and is suitable for a variety of high-temperature tests and other high-voltage electromagnetic monitoring occasions. The double-membrane structure design prepared by different microstructure optical fibers proposed in the present invention has a very wide frequency response band, so that the acoustic sensor can detect and measure sound pressure signals in a wide frequency band, meet acoustic applications with diverse frequency requirements, and effectively transmit environmental sound wave signals to the waveguide diaphragm. At the same time, the sensor can achieve high sensitivity and wide-band detection of sound signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of an all-quartz double-membrane microphone prepared with a microstructured optical fiber in Example 1 of the present invention; Figure 2 is a preparation flow chart of Example 3 of the present invention; Figure 3 Schematic diagram of a single-mode optical fiber in Embodiment 3 of the present invention; Figure 4 This is a schematic diagram of a microstructured optical fiber before corrosion in Example 3 of the present invention; Figure 5 Schematic diagram of different microstructure optical fibers that can be used in Example 3 of the present invention; Figure 6 Schematic diagram of the frequency response of the double membrane structure simulated by COMSOL in Example 3 of the present invention; Figure 7 This is the interference spectrum diagram of the double film structure described in Example 3 of the present invention.

[0030] Figure numerals: 1. first single-mode optical fiber; 2. microstructure optical fiber; 3. waveguide diaphragm; 4. sensing circular diaphragm; 11. core one; 12. cladding; 31. core two; 32. hollow layer; 33. outer cladding; 34. processing hole; 5. second single-mode optical fiber. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] Example 1 like Figure 1 As shown, this embodiment provides an all-quartz double-membrane structure optical microphone prepared by microstructured optical fiber, which is formed by sequentially welding a first single-mode optical fiber 1, a waveguide diaphragm 3 and a sensing circular diaphragm 4, wherein the welding surface between the first single-mode optical fiber and the waveguide diaphragm 3 is the first reflection surface of Fabry-Perot interference; the welding surface between the sensing circular diaphragm 4 and the waveguide diaphragm 3 becomes the second reflection surface of Fabry-Perot interference to form a Fabry-Perot interference effect, and the interference spectrum, i.e., a sine wave, can be seen in the interference spectrum.

[0034] The waveguide membrane comprises a suspended fiber core 2 31, a hollow layer 32, and an outer cladding 33 from the inside to the outside. A processing hole 34 is respectively opened at the upper and lower parts of the outer cladding 33 to facilitate the entry of the etching solution to etch away the parts except the waveguide membrane.

[0035] The waveguide diaphragm is processed by selecting different microstructure optical fibers according to different requirements. The microstructure optical fiber can be selected from three-hole optical fiber, non-cutoff single-mode photonic crystal optical fiber, etc.

[0036] The first single-mode optical fiber 1 includes a core 11 and a cladding 12.

[0037] The cladding diameter of the sensing circular diaphragm 4 is the same as the diameter of the first single-mode optical fiber. The thickness of the sensing circular diaphragm is usually in the micrometer range, 10 μm in this embodiment, and is used to sense external sound signals. The sensing film vibrates, driving the internal waveguide film to bend and deform.

[0038] When external sound pressure acts on the sensing circular diaphragm 4, the mechanical vibration of the sensing circular diaphragm at the end surface will force the waveguide diaphragm 3 to deform, thereby causing the second reflection surface of the Fabry-Perot interference structure to move. Due to the elastic effect of the waveguide diaphragm, the refractive index of the interferometer also changes, resulting in a corresponding change in the output light intensity. When the waveguide diaphragm 3 is axially bent and deformed, the effective refractive index of the waveguide diaphragm changes. According to formula (1), (1) in, represents the distribution of the original effective refractive index in the straight waveguide, Represents the longitudinal distance between the test point and the fiber axis, is the waveguide cross section and The tilt angle of the plane, Represents the bending radius.

[0039] Example 2 The present embodiment provides an all-quartz double-membrane structure optical microphone made of microstructured optical fiber, which is formed by sequentially welding a first single-mode optical fiber 1, a waveguide diaphragm 3 and a sensing circular diaphragm 4. The welding surface between the first single-mode optical fiber and the waveguide diaphragm 3 is the first reflection surface of Fabry-Perot interference; the welding surface between the sensing circular diaphragm 4 and the waveguide diaphragm 3 becomes the second reflection surface of Fabry-Perot interference to form a Fabry-Perot interference effect.

[0040] The waveguide membrane comprises, from the inside to the outside, a suspended fiber core 2 31 , a hollow layer 32 , and an outer cladding 33 . Four processing holes 34 are opened along the circumference of the outer cladding 33 to facilitate the entry of the corrosion solution.

[0041] Other technical features are the same as those of Example 1.

[0042] Example 3 like Figure 2 As shown, this embodiment provides a method for preparing an all-quartz double-membrane structure optical microphone prepared by a microstructure optical fiber, comprising the following steps: Step 1, sequentially fusing the first single-mode optical fiber 1, the microstructure optical fiber 2, and the second single-mode optical fiber 5 to form a single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure, including: Step 11, stripping the coating layer of one end of the first single-mode optical fiber and the microstructure optical fiber, and wiping the optical fiber with alcohol to remove the residual coating layer; In step 11, the discharge power and discharge time parameters of the fusion splicer are adjusted to achieve smooth fusion splicing of the microstructured optical fiber and the first single-mode optical fiber end face, the required discharge power is 3-10 bits, and the discharge time is 30-50ms; Step 12, cutting one end of the first single-mode optical fiber and the microstructure optical fiber flat with a cutting knife, and using a fusion splicer to fuse the cut surfaces of the first single-mode optical fiber and the microstructure optical fiber. During the fusion splicing process, the signal loss of the fusion splicer is controlled to be less than 0.1 dB to ensure the signal transmission distance of the prepared microphone and the stability of the system; Step 13, connecting the other end of the first single-mode optical fiber with the pigtail connector to the optical spectrum analyzer; Step 14, placing the single-mode-microstructured optical fiber structure obtained in step 12 on a high-precision translation stage, starting the high-precision translation stage, controlling the stepping accuracy to 1 μm, cutting the remaining microstructured optical fiber, and obtaining the optimal Fabry-Perot interferometer cavity length and spectral contrast by observing the interference spectrum of the spectrum analyzer described in step 13 during the cutting process, such as Figure 7 As shown; In step 14, according to the spectrum analyzer, the required length of the microstructured optical fiber is 200-300 μm to achieve maximum interference intensity and vibration sensing characteristics; In step 14, according to the spectrum analyzer, the required spectral contrast is >10dB; Step 15, welding the other end of the microstructure fiber to the second single-mode fiber, and making the welding point smooth, the welding loss of the welding machine is less than 0.1dB, to form a single-mode-microstructure fiber-single-mode Fabry-Perot interferometer sensing structure.

[0043] Figure 3 Schematic diagram of a single-mode optical fiber used in this embodiment, wherein (a) is a cross-sectional view of the actual object, and (b) is a simplified structural diagram; Figure 4 The structure diagram of the microstructured optical fiber used in this embodiment before corrosion, where (a) is a cross-sectional view of the actual object and (b) is a simplified structural diagram. The single-mode optical fiber has a complete solid structure, and the inner core is tightly wrapped by the cladding; in this embodiment, the outer diameter of the coating layer of the first single-mode optical fiber 1 is 242±5μm, the outer diameter of the cladding is 125±0.7μm, and the core is 9±0.5μm.

[0044] The core of the microstructured optical fiber is surrounded by honeycomb-like air holes, so that the core can be fixed in the center of the optical fiber, so that the corroded waveguide membrane can be located in the center of the sensing membrane to obtain the maximum deformation, that is, to obtain the maximum sensing sensitivity. The coating diameter of the microstructured optical fiber 2 is 270±10μm, and the outer cladding diameter is 125±7μm, which is used to protect the waveguide membrane 3. The diameter of the waveguide membrane 3 is 4.7±0.1μm, and the end face is a flat and smooth surface.

[0045] Figure 5Schematic diagram of different types of microstructure optical fibers in this embodiment, where (a) is a three-hole suspended core microstructure optical fiber, (b) is a supercontinuum photonic crystal microstructure optical fiber, and (c) is an endless single-mode photonic crystal microstructure optical fiber. The common feature is that the fiber core is surrounded by different structures. Therefore, different waveguide film sizes can be obtained by different etching times to meet the application requirements of different scenarios.

[0046] Step 2, preparing the microstructured optical fiber in the single-mode-microstructured optical fiber-single-mode Fabry-Perot interferometer sensing structure into a cylindrical waveguide membrane, comprising: Step 21, etching processing holes on the upper surface and the lower surface of the side wall of the microstructured optical fiber by a laser subtractive processing method; Step 22, using a corrosive solution to penetrate into the microstructure optical fiber through the processing hole, selectively corroding the inside of the microstructure optical fiber, retaining the core part inside the microstructure optical fiber, removing the outer cladding and the rest outside the core, and finally obtaining the desired waveguide membrane; The corrosive solution can be a hydrofluoric acid solution or a sodium hydroxide solution; Selective corrosion is carried out in a constant temperature water bath, and the corrosion temperature is set to 20-30°C to obtain better corrosion effect. The required constant temperature water bath corrosion time is 30-50s; Step 23, placing the structure obtained in step 22 in deionized water and performing ultrasonic cleaning to dissolve the residual corrosive solution, thereby completing the preparation of the waveguide membrane; In step 21, a processing hole is opened on the side wall of the microstructured optical fiber by laser-assisted processing. The processing hole shape can be rectangular, square, circular, etc., and the window size is 10×10μm. The larger the window size, the more hydrofluoric acid enters, so it is necessary to control the hole size and etching time, otherwise it is easy to cause structural damage; During laser subtractive processing, the laser power is controlled to 3-8mW to avoid damaging the optical fiber structure; During laser subtractive processing, the laser path is drawn in the set software. The laser path can be square, circular or rectangular, including: Step 211, the sample prepared in the previous step is precisely placed on a three-dimensional moving platform, and each axis of the three-dimensional moving platform is driven by a stepper motor or a servo motor to achieve micrometer-level or even nanometer-level precise movement; When the product is moved by the three-dimensional mobile platform, the moving speed is controlled to be 2-5um / s; Step 212, the control system receives the processing instruction, and adjusts the three-dimensional position of the three-dimensional moving platform in real time according to the predetermined processing path and parameters, so that the laser beam is accurately aligned with the sample surface; Step 213, the femtosecond laser source focuses the laser beam onto the sample surface through a focusing lens, and the laser beam scans the sample surface along the three-dimensional coordinate axis. The focus of the laser beam changes position as the three-dimensional moving platform moves, thereby achieving local etching of the sample. The diameter of the fiber core 31 in the etched waveguide film is 3-5 μm.

[0047] Step 3, processing the second single-mode optical fiber in the single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure obtained in step 2 to prepare a sensing circular diaphragm, including: Step 31, cutting the other end of the second single-mode optical fiber to a set thickness by a laser subtractive process; Step 32, placing the second single-mode optical fiber downward into the optical fiber clamp, and fixing the optical fiber clamp vertically on the optical fiber grinder; Step 33, using a grinder to gradually move the entire structure downward, using special optical fiber grinding sandpaper to grind the end face of the second single-mode optical fiber to the micrometer level, and monitoring the grinding process through an optical camera at the same time, so that if the second single-mode optical fiber is found to be broken or damaged during the grinding process, the grinding is stopped; In step 33, the speed of the optical fiber grinder is set at 3000-5000 rpm to prevent the optical fiber from being damaged by excessive speed, and the grinding time is 40-60 min; Step 34, placing the polished structure under a microscope, and measuring the thickness of the second single-mode optical fiber through the microscope to see whether it meets the set requirements. If so, the sensing circular diaphragm is manufactured.

[0048] like Figure 6 As shown, the all-quartz dual-diaphragm structure optical microphone of this embodiment has a very wide frequency response band, so that the acoustic sensor can detect and measure sound pressure signals within a wide frequency band, meet acoustic applications with diverse frequency requirements, and effectively transmit ambient sound wave signals to the waveguide diaphragm.

[0049] Example 4 A method for preparing an all-quartz double-membrane structure optical microphone prepared by microstructure optical fiber comprises the following steps: Step 1, welding the first single-mode optical fiber, the microstructure optical fiber, and the second single-mode optical fiber in sequence to form a single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure; Step 2, preparing the microstructured optical fiber in the single-mode-microstructured optical fiber-single-mode Fabry-Perot interferometer sensing structure into a cylindrical waveguide membrane; Step 3, processing the second single-mode optical fiber in the single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure obtained in step 2 to prepare a sensing circular diaphragm.

[0050] In step 2, include: Step 21, etching processing holes on the upper surface, the lower surface, and both sides of the side wall of the microstructure optical fiber by a laser subtractive processing method; Step 22, using a corrosive solution to penetrate into the microstructure optical fiber through the processing hole, selectively corroding the inside of the microstructure optical fiber, retaining the core part inside the microstructure optical fiber, removing the outer cladding and the rest outside the core, and finally obtaining the desired waveguide membrane; Step 23, placing the structure obtained in step 22 in deionized water and performing ultrasonic cleaning to dissolve the residual corrosive solution, thereby completing the preparation of the waveguide membrane.

[0051] Other technical features are the same as those of Example 1.

[0052] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An all-quartz double-membrane optical microphone made of microstructured optical fiber, characterized in that: It is formed by sequentially welding a first single-mode optical fiber, a waveguide diaphragm and a sensing circular diaphragm, wherein the welding surface between the first single-mode optical fiber and the waveguide diaphragm is the first reflection surface of Fabry-Perot interference; the welding surface between the sensing circular diaphragm and the waveguide diaphragm is the second reflection surface of Fabry-Perot interference, so as to form a Fabry-Perot interference effect.

2. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 1, characterized in that: The waveguide membrane comprises, from inside to outside, a suspended fiber core 2, a hollow layer, and an outer cladding.

3. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 1, characterized in that: A processing hole is respectively formed at the upper part and the lower part of the outer cladding layer.

4. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 3, characterized in that: Four processing holes are opened along the circumference of the outer cladding.

5. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 3, characterized in that: The waveguide membrane is made of microstructured optical fiber, and the microstructured optical fiber is made of three-hole optical fiber or non-cutoff single-mode photonic crystal optical fiber.

6. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 1, characterized in that: The first single-mode optical fiber includes a core and a cladding.

7. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 1, characterized in that: The outer diameter of the coating layer of the first single-mode optical fiber is 242±5 μm, the outer diameter of the cladding layer is 125±0.7 μm, and the core is 9±0.5 μm.

8. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 1, characterized in that: The cladding diameter of the sensing circular diaphragm is the same as the cladding diameter of the first single-mode optical fiber.

9. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 1, characterized in that: The thickness of the sensing circle diaphragm is 10μm.

10. The all-quartz double-membrane optical microphone made of microstructured optical fiber according to claim 5, characterized in that: The coating diameter of the microstructured optical fiber is 270±10μm, and the outer cladding diameter is 125±7μm.

11. A method for preparing an all-quartz double-membrane optical microphone made of microstructured optical fiber, characterized in that: The following steps are involved: Step 1, welding the first single-mode optical fiber, the microstructure optical fiber, and the second single-mode optical fiber in sequence to form a single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure; Step 2, preparing the microstructured optical fiber in the single-mode-microstructured optical fiber-single-mode Fabry-Perot interferometer sensing structure into a cylindrical waveguide membrane; Step 3, processing the second single-mode optical fiber in the single-mode-microstructure optical fiber-single-mode Fabry-Perot interferometer sensing structure obtained in step 2 to prepare a sensing circular diaphragm.

12. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 11, characterized in that: In step 1, include: Step 11, stripping the coating layer of one end of the first single-mode optical fiber and the microstructure optical fiber, and removing the residual coating layer; Step 12, cutting one end of the first single-mode optical fiber and the microstructure optical fiber flat with a cutting knife, and using a fusion splicer to fusion-splice the cut surfaces of the first single-mode optical fiber and the microstructure optical fiber; Step 13, connecting the other end of the first single-mode optical fiber with the pigtail connector to the optical spectrum analyzer; Step 14, placing the single-mode-microstructure optical fiber structure obtained in step 12 on a high-precision translation stage, starting the high-precision translation stage, controlling the stepping accuracy, and cutting the remaining microstructure optical fiber. During the cutting process, the interference spectrum of the spectrum analyzer described in step 13 is observed to obtain the optimal Fabry-Perot interferometer cavity length and spectrum contrast; Step 15, fusing the other end of the microstructured optical fiber to the second single-mode optical fiber, and making the fusion joint flat, to form a single-mode-microstructured optical fiber-single-mode Fabry-Perot interferometer sensing structure.

13. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 12, characterized in that: In step 11, the discharge power and discharge time parameters of the fusion splicer are adjusted to achieve smooth fusion splicing of the end faces of the microstructure optical fiber and the first single-mode optical fiber.

14. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 13, characterized in that: The required discharge power is 3-10bit and the discharge time is 30-50ms.

15. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 12, characterized in that: In step 14, the required length of the microstructured optical fiber is 200-300 μm.

16. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 12, characterized in that: In step 14, the required spectral contrast is >10dB.

17. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 11, characterized in that: In step 2, include: Step 21, etching processing holes on the upper surface and the lower surface of the side wall of the microstructured optical fiber by a laser subtractive processing method; Step 22, using a corrosive solution to penetrate into the microstructure optical fiber through the processing hole, selectively corroding the inside of the microstructure optical fiber, retaining the core part inside the microstructure optical fiber, removing the outer cladding and the rest outside the core, and finally obtaining the desired waveguide membrane; Step 23, placing the structure obtained in step 22 in deionized water and performing ultrasonic cleaning to dissolve the residual corrosive solution, thereby completing the preparation of the waveguide membrane.

18. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 17, characterized in that: In step 21, a processing hole is opened on the side wall of the microstructure optical fiber by laser-assisted processing, and the shape of the processing hole is rectangular, square or circular.

19. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 17, characterized in that: In step 21, during the laser subtractive processing, a laser path is drawn in the set software. The laser path can be a square, a circle or a rectangle, including: Step 211, the sample prepared in the early stage is accurately placed on the three-dimensional mobile platform, and each axis of the three-dimensional mobile platform is driven by a stepper motor or a servo motor to achieve micrometer-level or nanometer-level movement; during the process of moving the product driven by the three-dimensional mobile platform, the moving speed is controlled to be 2-5um / s; Step 212, the control system receives the processing instruction, and adjusts the three-dimensional position of the three-dimensional moving platform in real time according to the predetermined processing path and parameters, so that the laser beam is accurately aligned with the sample surface; In step 213, the femtosecond laser source focuses the laser beam onto the sample surface through a focusing lens. The laser beam scans the sample surface along the three-dimensional coordinate axis. The focus of the laser beam changes position as the three-dimensional moving platform moves, thereby achieving local etching of the sample.

20. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 17, characterized in that: In step 22, the corrosive solution is selected from hydrofluoric acid solution or sodium hydroxide solution; the selective corrosion is carried out in a constant temperature water bath, the corrosion temperature is set to 20-30°C, and the required constant temperature water bath corrosion time is 30-50s.

21. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 11, characterized in that: In step 3, include: Step 31, cutting the other end of the second single-mode optical fiber to a set thickness by a laser subtractive process; Step 32, placing the second single-mode optical fiber downward into the optical fiber clamp, and fixing the optical fiber clamp vertically on the optical fiber grinder; Step 33, using a grinder to gradually move the entire structure downward, and using optical fiber grinding sandpaper to grind the end face of the second single-mode optical fiber to the micron level; Step 34, placing the polished structure under a microscope, and measuring by the microscope whether the thickness of the second single-mode optical fiber meets the set requirements. If so, the sensing circular diaphragm is manufactured.

22. The method for preparing a full quartz double-membrane structure optical microphone prepared by a microstructure optical fiber according to claim 21, characterized in that: In step 33, the rotation speed of the optical fiber grinder is set at 3000-5000 rpm, and the grinding time is 40-60 min.

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