A dual fiber microphone system based on coherent combining technique

Abstract

The application discloses a kind of double optical fiber microphone systems based on coherent synthesis technology, belong to optical fiber sensing field, comprising: light source, for emitting fixed wavelength monochromatic light;With light source connection light guide unit, for the monochromatic light is split, obtains multiple beam optical signal;With the light guide unit connection pickup module, using high melting point passive element, the pickup module includes: double optical fiber and reflective film, the pickup module is used to collect sound information, based on double optical fiber and reflective film, obtains multiple beam coherent light signal containing sound information;The light guide unit is also used to interfere and synthesize single beam optical signal by coherent synthesis technology to multiple beam coherent light signal;With light guide unit connection photoelectric detection module, for single beam optical signal is converted into electrical signal, and electrical signal is restored to sound signal by code.The application can be used for the monitoring of sound pressure, vibration and other parameters in extreme environment, and can also improve the sensitivity, signal-to-noise ratio and stability of microphone.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber sensing, and particularly relates to a dual optical fiber microphone system based on coherent synthesis technology. BACKGROUND

[0002] Sound wave detection has wide applications in industrial manufacturing, aerospace, traffic noise monitoring and pipeline leakage monitoring. A microphone is a device for converting sound wave signals into electric signals. At present, a widely used microphone is a condenser microphone, which uses an extremely thin metal film as one pole of a capacitor and forms a capacitor with another fixed electrode. The principle is that sound waves cause the vibration of the metal film, thereby causing the distance between the two poles of the capacitor to change. To maintain the electric potential between the two poles of the capacitor, the sound wave vibration will cause the change of the storage capacity of the capacitor, and the microphone relies on the change of the capacity to realize the conversion. As can be known from the working principle, the electric microphone contains an active device, is very susceptible to electromagnetic interference and is not moisture-proof, and thus is not suitable for working in an environment with strong electromagnetic interference and moisture.

[0003] Optical fiber microphones have attracted widespread attention due to their advantages of anti-electromagnetic interference, corrosion resistance, small size, high sensitivity and long-distance signal transmission. However, the existing optical fiber microphones cannot improve the precision, signal-to-noise ratio and sound pressure sensitivity of sound wave detection in complex environments, and finally cannot accurately measure the sound wave parameters. SUMMARY

[0004] The application provides a dual optical fiber microphone system based on coherent synthesis technology, which uses a novel dual optical fiber structure to collect sound pressure signals, so as to solve the technical problem that the existing technology cannot accurately measure sound wave parameters.

[0005] To achieve the above object, the application provides a dual optical fiber microphone system based on coherent synthesis technology, which comprises:

[0006] A light source is configured to emit monochromatic light of a fixed wavelength.

[0007] A light guide unit connected with the light source is configured to split the monochromatic light to obtain a plurality of light signals.

[0008] A pickup module connected with the light guide unit is configured to collect sound information, and comprises a dual optical fiber and a reflective film. The pickup module is configured to obtain a plurality of coherent light signals containing sound information based on the dual optical fiber and the reflective film.

[0009] The light guide unit is further configured to interfere and synthesize the plurality of coherent light signals into a single light signal by using coherent synthesis technology.

[0010] A photoelectric detection module connected with the light guide unit, used for converting the single-beam light signal into an electric signal, and restoring the electric signal into a sound signal through a code.

[0011] Preferably, the lengths of the double optical fibers are equal, and the double optical fibers are placed in parallel on the same horizontal plane, the distances between the end faces of the double optical fibers and the reflecting film are equal, and the double optical fibers and the reflecting film constitute two identical F-P interference cavities.

[0012] Preferably, the reflecting film is detachable and is made of a thin film material with a small thermal expansion coefficient.

[0013] Preferably, the light guide unit comprises a plurality of ports, and the ports are used for splitting a single-beam light into a plurality of beams of light and for synthesizing a plurality of beams of light into a single-beam light.

[0014] Preferably, the sound pickup module further comprises a double-core optical fiber quartz sleeve and a quartz sleeve shell.

[0015] The double-core optical fiber quartz sleeve is used for fixing the double optical fibers.

[0016] The quartz sleeve shell is used for fixing the reflecting film and the double-core optical fiber quartz sleeve.

[0017] Preferably, the sound pickup module further comprises a data acquisition module and a data processing module.

[0018] The data acquisition module is used for acquiring the electric signal.

[0019] The data processing module is used for filtering the electric signal and restoring a sound signal through a code.

[0020] Preferably, the voltage value of the electric signal is used for reflecting the vibration frequency and the vibration amplitude of the reflecting film.

[0021] Compared with the prior art, the sound pickup system has the following advantages and technical effects:

[0022] The sound pickup system based on the coherent synthesis technology can eliminate signal distortion caused by phase change, make the signal more stable and pure, improve the sensitivity, signal-to-noise ratio and stability of the sound pickup, and has the advantages of low cost, good real-time performance and good applicability.

[0023] The sound pickup system can be developed into an integrated device, so that the sound wave measuring equipment is miniaturized and convenient for actual field application.

[0024] The microphone system has strong fault tolerance, if a problem occurs in one of the two optical fibers, the other optical fiber can still maintain normal sound pressure collection, thereby enhancing the reliability of the microphone system.

[0025] The pickup module of the microphone system adopts passive elements and has high melting point, and is suitable for measurement of sound pressure, vibration and other parameters in extreme environments such as strong electromagnetic interference, high temperature, high pressure and strong corrosion.

[0026] The reflective film of the microphone system can be replaced according to requirements in different test scenes, for example, when there are different requirements for parameters such as frequency response range and sound pressure sensitivity, the reflective film can be replaced conveniently and quickly, and the microphone system is easy to assemble. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of this application, and their

[0028] Figure 1 It is a schematic diagram of the double optical fiber microphone system of the embodiment of the application;

[0029] Figure 2 It is a structure diagram of the pickup module of the embodiment of the application;

[0030] Figure 3 It is a structure diagram of the double F-P interference cavity of the embodiment of the application;

[0031] Figure 4 It is a whole experiment flowchart of the embodiment of the application;

[0032] Figure 5 It is a waveform diagram and a spectrum diagram of the detected low-frequency sinusoidal sound pressure signal of the reflective film of the embodiment of the application under different frequency vibration conditions;

[0033] Figure 6 It is a waveform diagram and a spectrum diagram of the detected high-frequency sinusoidal sound pressure signal of the reflective film of the embodiment of the application under different frequency vibration conditions;

[0034] Figure 7 It is a relationship diagram between the voltage signal and the sound pressure amplitude of the embodiment of the application;

[0035] 1-laser, 2-light guide unit, 3-first single-mode optical fiber, 4-second single-mode optical fiber, 5-pickup module, 6-optoelectronic detection module, 7-data acquisition module, 8-data processing module, 9-reflective film, 10-double-core optical fiber quartz sleeve, 11-quartz sleeve shell. DETAILED DESCRIPTION

[0036] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0037] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described herein can be executed in a different order.

[0038] Embodiment one

[0039] As Figure 1 shown, the present embodiment provides a dual-fiber microphone system based on coherent synthesis technology, which adopts a dual-beam sound wave structure fiber microphone, including:

[0040] a laser 1 capable of emitting a fixed wavelength; a light guide unit 2 as a light transmission medium and realizing a light splitting function; a sound vibration sensing pickup module 5 composed of two single-mode optical fibers 3, 4 and a reflective film 9; a photoelectric detection module 6 for converting optical signals into electrical signals; a data acquisition module 7 for realizing signal acquisition function; a data processing module 8 for processing the collected signals;

[0041] The monochromatic light emitted by the laser 1 enters the light guide unit 2 from port I of the light guide unit 2, divides a beam of light into two identical beams of light, and emits the dual-beam light from ports II and III of the light guide unit 2 at the same time. The two beams of light enter the microphone pickup module 5 through the two optical fibers 3 and 4, respectively form two identical F-P cavities with the reflective film 9, and are subjected to sound vibration sensing. The F-P interference light enters the light guide unit 2 from ports II and III of the light guide unit 2, and then exits from port IV of the light guide unit 2 to enter the photoelectric detection module 6 to convert the optical signals into electrical signals. Then the data acquisition module 7 acquires and transmits the signals to the data processing module 8 to display the time domain signal and the frequency domain signal in real time through software, and restores the sound through code.

[0042] In the present embodiment, the light guide unit 2 is a 2x2 optical fiber coupler, and the light splitting ratio is 50:50;

[0043] The photoelectric detection module 6 is an InGaAs photodiode;

[0044] The laser 1 adopts a DFB laser, and the wavelength of the light emitted by the DFB laser is 1550nm, and the power is set to 1-5mw;

[0045] The diameters of the single-mode optical fibers 3 and 4 are 125μm.

[0046] As Figure 2As shown in the figure, the microphone pickup module 5 comprises a reflecting film 9 for receiving sound wave signals, optical fibers 3, 4 for transmitting light, a double-core optical fiber quartz sleeve 10 for fixing the optical fibers, and a quartz sleeve shell 11 for fixing the reflecting film 9 and the double-core optical fiber sleeve 10, wherein the reflecting film 9 is mounted at the front end of the quartz sleeve shell 11, the double-core optical fiber quartz sleeve 10 is mounted in the accommodating cavity of the quartz sleeve shell 11, the two optical fibers 3, 4 in the double-core optical fiber quartz sleeve 10 are parallel, and the optical fiber end faces are in the same horizontal plane, and the optical fiber end faces and the reflecting film 9 form two identical F-P cavities.

[0047] The fixing needs to ensure that the two optical fibers 3, 4 are inserted into the double-core optical fiber quartz sleeve 10, so that the two optical fibers 3, 4 remain parallel and the end faces are in the same horizontal plane. After the optical fibers are fixed, the double-core optical fiber quartz sleeve 10 is inserted into the accommodating cavity of the quartz sleeve shell 11, the reflecting film 9 is fixed at the end face of the quartz sleeve shell 11, then the distance between the optical fibers 3, 4 and the inner surface of the reflecting film 9 is adjusted to ensure that the two optical fibers 3, 4 are symmetrically perpendicular to the center position of the inner surface of the reflecting film 9, and the quartz sleeve shell 11 and the double-core optical fiber quartz sleeve 10 are fixed. At the same time, the distance between each component is appropriate.

[0048] In this embodiment, the pickup module 5 uses passive components with high melting points, which are suitable for measuring sound pressure, vibration and other parameters in extreme environments such as strong electromagnetic interference, high temperature, high pressure and strong corrosion.

[0049] As shown in the figure, the double-F-P cavity structure comprises two single-mode optical fibers 3, 4 and a reflecting film 9 for receiving sound wave signals. Figure 3

[0050] In this embodiment, the reflecting film 9 is a high-reflectivity thin film such as an aluminum film, a nickel film, a titanium film or a stainless steel film; the thickness of the reflecting film 9 is 0.1-10 μm, and the radial dimension is 0.1-20 mm.

[0051] The embodiment provides a double-fiber microphone system based on coherent synthesis technology, which uses optical fibers as a medium for transmitting light and a diaphragm as a transducer for detecting sound wave signals. The distance between the sensing area of the optical fiber end face and the diaphragm is several microns to several tens of microns, the structure is compact and small, the sensitivity is high and controllable. The purpose of the embodiment is to use a novel double-beam structure for measuring sound waves to improve the measurement accuracy and signal stability of the microphone.

[0052] ​The basic principle of the extrinsic F-P interference type fiber-optic microphone is that the optical fibers 3, 4 are perpendicular to the center of the reflecting film 9, the optical fiber end face and the inner surface of the reflecting film maintain a certain distance, and an F-P interference cavity is formed. When there is external sound pressure, the reflecting film 9 vibrates to produce elastic deformation, which causes the distance between the optical fiber end face and the center of the film to change, and the sound pressure signal can be restored by detecting this change. The optical signal carrying sound information is converted into an electrical signal after photoelectric conversion, and the pickup and restoration of the sound by the fiber-optic microphone are realized by collecting and processing the electrical signal. The sound pressure sensitivity and frequency response range of the reflecting film 9 are mainly determined by the material, diameter and thickness. By changing these three parameters and replacing different reflecting films, sound wave measurement with different sound pressure sensitivity and frequency width can be realized, which is suitable for sound wave measurement in harsh environments such as strong electromagnetic interference and humidity.

[0053] The reflecting film 9 sensitive to pressure is one of the important components of the fiber-optic microphone, and the microphone perceives the change of external sound pressure through the reflecting film 9. For example, as described in the non-patent document ("Flat and corrugated diaphragm design handbook", Mechanical Engineering New York Based Marcel Dekker, 1982.), for the extrinsic F-P interference type fiber-optic sensor, the center positions of the optical fibers 3, 4 and the inner surface of the reflecting film 9 form an F-P cavity, so only the deformation of the center position of the diaphragm needs to be considered. The deformation equation of the center position of the circular diaphragm is:

[0054]

[0055] Where y is the deformation of the center position of the reflecting film, p is the sound pressure, E is the Young's modulus, h is the thickness of the reflecting film, a is the radius of the reflecting film, and v is the Poisson's ratio.

[0056] As can be seen from the above formula, the sensitivity of the circular reflecting film mainly depends on the thickness, radius and material of the reflecting film. For a reflecting film of a selected material, the sensitivity can be improved by appropriately increasing the radius of the reflecting film or reducing the thickness of the reflecting film. The selection of the reflecting film material directly affects the performance and application environment of the microphone, and is very important for the design and manufacture of the microphone. The sensitivity, repeatability and other parameters of the sensor are related to the material properties of the sensor reflecting film, such as Young's modulus, Poisson's ratio and thermal expansion coefficient. The influence of temperature on the sensitivity of the fiber-optic microphone cannot be ignored, and it is particularly important to select a material with a small enough thermal expansion coefficient as the reflecting film in order to reduce the sensitivity of the microphone to temperature.

[0057] The fiber end face and the reflecting film constitute a simple F-P cavity. Approximately, it is a double-beam interference. Taking the first fiber as an example, laser is emitted from the fiber, and at the same time, about 4% of the light beam is reflected back from the fiber end face, and the rest of the light beam is transmitted to the reflecting film surface. The reflected light carrying the sound signal reflected by the reflecting film is re-injected into the fiber, and the two beams of light interfere at the fiber end face.

[0058] The electric vectors E1 and E2 of the two beams of light r and the output light intensity I after interference out can be represented as:

[0059]

[0060]

[0061]

[0062] wherein A1 and A2 are the amplitudes of the light reflected by the reflecting film and the light reflected by the fiber end face respectively, r A1 2 and A2 2 are the squares of the amplitudes of the light reflected by the reflecting film and the light reflected by the fiber end face respectively, A1 2 and A2 2 are the squares of the amplitudes of the light reflected by the reflecting film and the light reflected by the fiber end face respectively, ω is the light frequency, and φ1 and φ2 are the phases of the light reflected by the reflecting film and the light reflected by the fiber end face respectively. The corresponding relationship between the phase of the coherent term and the F-P cavity length change can be represented as:

[0063]

[0064] wherein λ is the wavelength of the laser, and ΔL is the F-P cavity length change.

[0065] The initial distances of the two fibers to the reflecting film are equal, and are denoted as L. When the reflecting film vibrates under the action of the sound pressure, the displacement at the center of the reflecting film is ΔL, and the two F-P cavity lengths L1 and L2 can be represented as:

[0066] L1 = L + ΔL, L2 = L + ΔL (6)

[0067] According to the working principle of the fiber interferometer, the four beams of light I1, I2, Ir1 and Ir2 are received by the photoelectric detection module and interfere, wherein I1 and I2 are the light intensities of the light emitted by the two fibers and the light reflected by the reflecting film. According to the multi-beam interference principle, the interference field intensity mainly depends on the light intensity of the strongest light beam. Since the fiber end face reflected light is only about 4%, the interference signal received by the photoelectric detection module is mainly the interference between I1 and I2. The electric vectors of the two beams of light are respectively:

[0068]

[0069]

[0070] E1 and E2 are the intensity of two beams of light, ω is the frequency, A1 and A2 are the amplitudes, is the square of the amplitude A1, is the square of the amplitude A2, and is the initial phase of the vibration. The two vibrations are independent of each other, and the result of superimposed modulation is as follows:

[0071]

[0072] The amplitude A and the initial phase of the combined vibration are determined by the following formula:

[0073]

[0074] The phase difference is the phase difference of the two lights:

[0075]

[0076] The phase difference can be eliminated by ensuring that the distance between the end faces of the two optical fibers and the reflecting film is equal, and the length of the optical fiber is consistent. The light intensity is increased to twice the original, and the application of the double-beam sound wave detection technology improves the sound pressure sensitivity, signal-to-noise ratio and stability of the microphone.

[0077] The embodiment provides a double-fiber microphone system based on coherent synthesis technology, which can be applied to acoustic detection, and a flowchart of the double-fiber microphone system based on coherent synthesis technology is as shown in Figure 4 .

[0078] S100: Based on the first light signal emitted by the laser 1, the second light signal and the third light signal are obtained by splitting through the light guide unit 2, the fourth light signal and the fifth light signal are obtained by reflection through the reflecting film 9, and the fourth light signal and the fifth light signal are combined into the sixth light signal by interference.

[0079] S200: The sixth light signal is photoelectrically converted to obtain the first electric signal, the data acquisition module 7 acquires the first electric signal and converts it into a digital signal and transmits it to the data processing module 8, and the time domain signal and the frequency domain signal of the sound can be displayed in real time.

[0080] S300: The first electric signal reflects the vibration frequency and amplitude of the reflecting film 9 through voltage, and based on the F-P interference principle and the intensity demodulation principle, the restoration of the sound signal is realized through the code.

[0081] In the embodiment, in the case of lower frequency vibration, the detected sinusoidal vibration signal waveform and spectrum diagram are as shown in Figure 5 .Figure 5 (a)-(d) are time domain graphs of 20Hz, 30Hz, 40Hz, 50Hz sine wave vibration signals respectively, Figure 5 (e)-(h) are frequency domain graphs of 20Hz, 30Hz, 40Hz, 50Hz sine wave vibration signals respectively. Figure 5 It can be known that the time domain signal detected by the application is consistent with the vibration waveform applied on the reflective film, and the frequency domain signal detected by the application is also consistent with the vibration frequency applied on the reflective film.

[0082] In the embodiment, the detected sine wave vibration signal waveform graph and spectrum graph under different frequency vibrations are as shown in Figure 6 Figure 6 (a)-(d) are time domain graphs of 14kHz, 16kHz, 18kHz, 20kHz sine wave vibration signals respectively, Figure 6 (e)-(h) are frequency domain graphs of 14kHz, 16kHz, 18kHz, 20kHz sine wave vibration signals respectively. Figure 6 It can be known that the time domain signal detected by the application is consistent with the vibration waveform applied on the reflective film, and the frequency domain signal detected by the application is also consistent with the vibration frequency applied on the reflective film.

[0083] In the embodiment, the relationship graph between the detected voltage signal and the sound pressure amplitude applied on the reflective film is as shown in Figure 7 It can be known that the detected voltage amplitude and the sound pressure amplitude applied on the reflective film show a good linear relationship. Figure 7

[0084] In summary, the technical scheme disclosed in the embodiment can accurately measure sound and vibration very conveniently, can be developed as an integrated device, and can be applied in the sound pressure and vibration measurement field. The device can be applied to sound pressure and vibration detection in a strong magnetic interference environment, humid and other harsh conditions, and can also measure ultrasonic waves or infrasonic waves.

[0085] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited to this. Any changes or replacements within the technical range disclosed by the present application can be easily thought of by those skilled in the art, and 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 dual-fiber microphone system based on coherent combining technology, characterized in that, include: A light source, used to emit monochromatic light of a fixed wavelength; The light guide unit connected to the light source is used to split the monochromatic light to obtain multiple light signals; The sound pickup module connected to the light guide unit uses a passive component with a high melting point. The sound pickup module includes two optical fibers and a reflective film. The sound pickup module is used to collect sound information and obtains multiple coherent light signals containing sound information based on the two optical fibers and the reflective film. The two optical fibers are of equal length and are arranged in parallel on the same horizontal plane. The end faces of the two optical fibers are equidistant from the reflective film and form two identical FP interference cavities. The light guiding unit is also used to synthesize the multiple coherent light signals into a single light signal through coherent combining technology. The photoelectric detection module connected to the light guide unit is used to convert the single beam light signal into an electrical signal, and then use code to restore the electrical signal into a sound signal.

2. The dual-fiber microphone system based on coherent combining technology according to claim 1, characterized in that, The reflective film is replaceable and is made of a thin film material with a low coefficient of thermal expansion.

3. The dual-fiber microphone system based on coherent combining technology according to claim 1, characterized in that, The light guiding unit includes several ports, which are used to split a single beam of light into multiple beams of light and to combine multiple beams of light into a single beam of light.

4. The dual-fiber microphone system based on coherent combining technology according to claim 1, characterized in that, The pickup module also includes: a dual-core fiber optic quartz sleeve and a quartz sleeve housing; The dual-core optical fiber quartz sleeve is used to fix the two optical fibers; The quartz sleeve shell is used to fix the reflective film and the dual-core optical fiber quartz sleeve.

5. The dual-fiber microphone system based on coherent combining technology according to claim 1, characterized in that, Also includes: Data acquisition module and data processing module; The data acquisition module is used to acquire electrical signals; The data processing module is used to filter the electrical signal and restore the sound signal through code.

6. The dual-fiber microphone system based on coherent combining technology according to claim 1, characterized in that, The voltage value of the electrical signal is used to reflect the vibration frequency and vibration amplitude of the reflective film.

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