Novel optical fiber Fabry-Perot cavity acoustic vibration sensor

Abstract

The invention provides a novel optical fiber Fabry-Perot cavity acoustic vibration sensor, and relates to the technical field of optical fiber sensing. Comprising a dual-light TOSA used for generating first incident laser and second incident laser, an optical fiber circulator used for combining the first incident laser and the second incident laser to obtain combined laser, an optical fiber Fabry-Perot cavity sensing probe used for receiving the combined laser and carrying out interference to obtain returned laser after interference, and an optical fiber Fabry-Perot cavity sensing probe used for receiving the returned laser after interference. The optical fiber circulator is further used for transmitting the returned laser after interference to the double-detection ROSA, and the double-detection ROSA is used for receiving the returned laser after interference, carrying out light splitting to obtain first returned laser and second returned laser, and converting the first returned laser and the second returned laser to obtain a first electric signal and a second electric signal. The signal processing system is used for preprocessing the first electric signal and the second electric signal to obtain corresponding amplitude signals. The Fabry-Perot cavity sensor solves the problems of inaccurate accuracy and sensitivity of the Fabry-Perot cavity sensor in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, in particular to a novel optical fiber Fabry-Perot cavity acoustic vibration sensor. Background Art

[0002] With the rapid development of fiber optic sensing technology, fiber optic sensors are widely used in online detection of high-voltage cable equipment and highway bridges due to their advantages such as high sensitivity, good multiplexing, and strong anti-electromagnetic interference. As an important part of the sensor family, the fiber optic Perot cavity sensor is more in line with the current social sensing technology needs in terms of sensitivity, anti-interference ability, and transmission distance compared to traditional sensors, and has therefore received widespread attention from domestic and foreign researchers. In addition, the fiber optic Perot cavity sensor probe is tiny and can be used as a point sensor. It can be easily installed in some key parts of the cable and is one of the commonly used sensors. The present application involves the use of the Perot cavity sensor to measure the amplitude of the object to be measured.

[0003] The signal light transmitted by the fiber-optic Fabry-Perot cavity sensor contains the cavity length information to be measured. The intensity demodulation technology generally uses a narrowband light source with a long coherence length. The wavelength of the light source is a fixed value, which is to extract the corresponding Fabry-Perot cavity length from the interference light intensity. This technology is the method originally used by the Fabry-Perot cavity sensor, which has the advantages of being simple, direct and fast in response. The cavity length of the Fabry-Perot cavity is the decisive factor in determining the sensitivity of the Fabry-Perot cavity. However, due to the fluctuation of the excitation light source wavelength or the external temperature in the intensity demodulation, the demodulated cavity length result will be inaccurate, which in turn affects the accuracy and sensitivity of the Fabry-Perot cavity sensor. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a novel optical fiber Fabry-Perot cavity acoustic vibration sensor, which solves the problem of inaccurate accuracy and sensitivity of the Fabry-Perot cavity sensor in the prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A novel optical fiber Fabry-Perot cavity acoustic vibration sensor, comprising:

[0007] Dual-optical TOSA, dual-detection ROSA, fiber optic circulator, fiber optic Fabry-Perot cavity sensor probe and signal processing system;

[0008] The dual-light TOSA is connected to the first port of the optical fiber circulator, the optical fiber Fabry-Perot cavity sensor probe is connected to the second port of the optical fiber circulator, the dual-detection ROSA is connected to the third port of the optical fiber circulator, and the dual-detection ROSA is connected to the signal processing system;

[0009] The dual-wavelength TOSA is used to generate a first incident laser and a second incident laser. The fiber optic circulator is used to combine the first incident laser and the second incident laser to obtain a combined laser and transmit the combined laser to the fiber optic Fabry-Perot cavity sensing probe. The fiber optic Fabry-Perot cavity sensing probe is used to receive the combined laser and perform interference to obtain a returned laser after interference. The fiber optic circulator is also used to transmit the returned laser after interference to the dual-detection ROSA. The dual-detection ROSA is used to receive the returned laser after interference, perform beam splitting to obtain a first returned laser and a second returned laser, and convert the first returned laser and the second returned laser to obtain a first electrical signal and a second electrical signal. The signal processing system is used to preprocess the first electrical signal and the second electrical signal to obtain corresponding amplitude signals.

[0010] Preferably, the signal processing system includes:

[0011] a preamplification module, a differential amplification module, an A / D acquisition module, a single-chip microcomputer, and a background computer;

[0012] The preamplification module is used to preamplify the first electrical signal and the second electrical signal. The differential amplification module is used to differentially amplify the preamplified signal. The A / D acquisition module is used to acquire the differentially amplified signal and transmit it to the single-chip microcomputer.

[0013] Preferably, the wavelength difference between the first incident laser and the second incident laser is an odd multiple of half the period of the Fabry-Perot cavity interference spectrum.

[0014] Preferably, the fiber optic Fabry-Perot cavity sensing probe includes:

[0015] One end of the single-mode fiber is provided with the fiber optic connector, and the other end is stripped to expose the bare fiber, which passes through the ceramic ferrule and is fixed with ultraviolet curable glue. The fiber end face is parallel to the vibrating plate. The vibrating plate is adhesively bonded to the quartz bracket and the ceramic ferrule with ultraviolet curable glue. The vibrating plate, the quartz bracket, and the ceramic ferrule together form a sensing module. The quartz bracket is placed in the U-shaped groove of the ceramic base and adhesively bonded with ultraviolet curable glue. The ceramic housing is buckled on the ceramic base and adhesively bonded with epoxy resin glue to enclose the sensing module in the ceramic housing and the ceramic base.

[0016] The single-mode fiber is used to transmit optical signals, and the vibrating plate is used to perform interference modulation on the received signals.

[0017] Preferably, the zirconia ceramic housing is made of zirconia ceramic material.

[0018] Preferably, the quartz base fixes the probe bracket by gluing.

[0019] Preferably, both the quartz base and the probe bracket are made of quartz material.

[0020] Preferably, the matching frequency range corresponding to the shape, thickness, and effective length of the vibrating piece is 300 Hz - 2000 Hz.

[0021] Preferably, the size of the vibrating piece is:

[0022] 15 mm in length, 5 mm in width, and 0.05 mm in thickness.

[0023] The present invention discloses the following technical effects:

[0024] The present invention provides a novel fiber optic Fabry - Perot cavity acoustic vibration sensor, including a dual - optical TOSA, a dual - detector ROSA, an optical fiber circulator, an optical fiber Fabry - Perot cavity sensing probe, and a signal processing system; the dual - optical TOSA is connected to the first port of the optical fiber circulator, the optical fiber Fabry - Perot cavity sensing probe is connected to the second port of the optical fiber circulator, the dual - detector ROSA is connected to the third port of the optical fiber circulator, and the dual - detector ROSA is connected to the signal processing system; the dual - optical TOSA is used to generate a first incident laser and a second incident laser, the optical fiber circulator is used to combine the first incident laser and the second incident laser to obtain a combined laser and transmit the combined laser to the optical fiber Fabry - Perot cavity sensing probe, the optical fiber Fabry - Perot cavity sensing probe is used to receive the combined laser and perform interference to obtain an interfered returned laser, the optical fiber circulator is further used to transmit the interfered returned laser to the dual - detector ROSA, the dual - detector ROSA is used to receive the interfered returned laser and perform beam splitting to obtain a first returned laser and a second returned laser and convert the first returned laser and the second returned laser to obtain a first electrical signal and a second electrical signal, and the signal processing system is used to pre - process the first electrical signal and the second electrical signal to obtain corresponding amplitude signals. In the dual - wavelength intensity - demodulated fiber optic Fabry - Perot cavity sensor of the present invention, due to the use of two lasers with different wavelengths, after being modulated by the fiber optic Fabry - Perot cavity, interference light intensity values are detected by two photodetectors, and differential amplification is performed, so that when meeting the requirements of the intensity - demodulated fiber optic Fabry - Perot cavity sensor, the sensitivity of the sensor is constant after fitting the two interference light intensity values. Thus, the inevitable influence of temperature drift in the intensity - demodulated Fabry - Perot cavity is solved, thereby improving the detection sensitivity and accuracy. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1Schematic diagram of a novel fiber optic Fabry - Perot cavity acoustic vibration sensor structure provided by an embodiment of the present invention;

[0027] Figure 2 Cross - sectional view of the Fabry - Perot cavity provided by an embodiment of the present invention;

[0028] Figure 3 Schematic diagram of the interference spectrum of the laser by the Fabry - Perot cavity provided by an embodiment of the present invention;

[0029] Figure 4 Coordinate diagram of the interference spectrum of the Fabry - Perot cavity provided by an embodiment of the present invention.

[0030] Explanation of reference numerals:

[0031] 1. Ceramic shell, 2. Quartz base, 3. Single - mode optical fiber, 4. Optical fiber connector, 5. Quartz bracket, 6. Ceramic ferrule, 7. Vibration piece, 8. Sensing module. Detailed implementation manners

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] To make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0034] As Figure 1As shown in the figure, the present invention provides a novel fiber optic Fabry-Perot cavity acoustic vibration sensor, including: a dual-light TOSA, a dual-detection ROSA, an optical fiber circulator, an optical fiber Fabry-Perot cavity sensing probe, and a signal processing system; the dual-light TOSA is connected to the first port of the optical fiber circulator, the optical fiber Fabry-Perot cavity sensing probe is connected to the second port of the optical fiber circulator, the dual-detection ROSA is connected to the third port of the optical fiber circulator, and the dual-detection ROSA is connected to the signal processing system; the dual-light TOSA is used to generate a first incident laser and a second incident laser, the optical fiber circulator is used to combine the first incident laser and the second incident laser to obtain a combined laser and transmit the combined laser to the optical fiber Fabry-Perot cavity sensing probe, the optical fiber Fabry-Perot cavity sensing probe is used to receive the combined laser and perform interference to obtain an interfered returned laser, the optical fiber circulator is further used to transmit the interfered returned laser to the dual-detection ROSA, the dual-detection ROSA is used to receive the interfered returned laser and perform beam splitting to obtain a first returned laser and a second returned laser and convert the first returned laser and the second returned laser to obtain a first electrical signal and a second electrical signal, and the signal processing system is used to preprocess the first electrical signal and the second electrical signal to obtain corresponding amplitude signals.

[0035] Further, the signal processing system includes:

[0036] a preamplification module, a differential amplification module, an A / D acquisition module, a single-chip microcomputer, and a background computer;

[0037] The preamplification module is used to preamplify the first electrical signal and the second electrical signal, the differential amplification module is used to differentially amplify the preamplified signal, and the A / D acquisition module is used to acquire the differentially amplified signal and transmit it to the single-chip microcomputer.

[0038] Specifically, through the dual-light TOSA, incident lasers L1 and L2 with different wavelengths are respectively generated.

[0039] The wavelength difference between the incident laser L1 and the incident laser L2 is an odd multiple of half the period of the Fabry-Perot cavity interference spectrum.

[0040] The two incident lasers are combined into a single laser L3 and emitted to the Fabry-Perot cavity probe.

[0041] The laser L3 is split into two lasers L1+ and L2+ with the same wavelengths as the incident lasers L1 and L2 through the dual-detection ROSA.

[0042] The lasers L1+ and L2+ are respectively converted into electrical signals P1 and P2, and the converted electrical signals are preamplified and then differentially amplified respectively.

[0043] The corresponding principle is as follows:

[0044] The reason why the FP cavity vibration sensor for optical intensity demodulation is difficult to use is that the actual light source is a DFB narrowband laser, and the interference spectrum of the FP cavity is a function of temperature.

[0045] The dual-wavelength demodulation method uses the reflected light information at two wavelengths for compensation operations, which can effectively improve the accuracy compared with single-wavelength demodulation. The light source of the system generally uses a tunable laser to output two different wavelengths of light through regulation. However, using this device of the tunable laser greatly increases the cost of the system. Therefore, in this experiment, a dual-light TOSA composed of two distributed feedback (DFB) lasers is used as the light source.

[0046] As shown in the attached Figure 3 specification, if only one light source is used, the influence of temperature drift on the interference light intensity of the Fabry-Perot cavity is huge. If a dual-wavelength laser light source is used and when making the Fabry-Perot cavity, the cavity length of the Fabry-Perot cavity is adjusted so that the wavelength difference between the two laser light sources corresponds to an odd multiple of half the period of the Fabry-Perot cavity interference spectrum, and the signals detected by the dual-detection ROSA are differentially amplified. At this time, the influence of the interference light intensity on temperature is greatly reduced. Then, through environmental temperature monitoring and compensation, the influence of the environmental temperature on the measurement results of the sensor can be basically eliminated.

[0047] As shown in the attached Figure 4 specification, assuming that the interference spectrum of the broadband light source of the F-P cavity is adjusted to a quadratic function y = -ax 2 +b, since the sensitivity of the F-P cavity sensor can be represented by the slope of the interference spectrum, the sensitivity can be represented by y' = -2ax.

[0048] Assume that the amplitude of the actual vibration signal received by the sensing probe is A. Since there is a difference in the receiving sensitivity of the sensor between the measured vibration signal amplitude and the actual vibration signal amplitude received by the F-P cavity sensing probe, the amplitudes of the two measured vibration signals can be expressed as:

[0049] P1 = Ay1' = -2Aax1

[0050] P2 = Ay2' = -2Aax2

[0051] In the above formula, P1 and P2 are the intensities of the first and second measured signals, A is the signal amplitude, a and b are coefficients related to the interference spectrum period, and x and y are the horizontal and vertical coordinates.

[0052] To ensure that the signal received by the sensing probe is independent of temperature T, the phase difference between the interference spectra corresponding to the two wavelengths of 1490 nm and 1550 nm needs to be an integer multiple of, then:

[0053]

[0054] At this time, the difference between the amplitudes of the two measured vibration signals is:

[0055]

[0056] It can be seen from the above formula that when N takes a certain value, the differential signal value of the amplitudes of the two measured signals is only related to the value of ab.

[0057] Since the present invention uses high-purity quartz as the bracket, with a thermal expansion coefficient of 0.5 ppm, it is less affected by temperature. After actual measurement, from 20 degrees to 70 degrees, the interference period of the Fabry-Perot cavity for the C-band broadband light only decreases by 0.5 nm. We adjust the interference period of the Fabry-Perot cavity for the C-band broadband light to 4.44 nm at room temperature, ensuring that the two DFB narrowband light sources at 1490 nm and 1550 nm are respectively located at the interference maximum and interference minimum. In addition, the spectral adjustment range of the DFB filter is 1.6 nm, and the spectral adjustment ranges of the two DFB narrowband light sources at 1490 nm and 1550 nm are 3.2 nm, which is greater than 2.47 nm ((4.44 + 0.5) / 2)). Therefore, as long as the values of ab are calibrated according to the ambient temperature, the differential signal of the amplitudes of the two measured signals becomes a true value that is not affected by temperature.

[0058] In this embodiment, the processing of the electrical signals P1 and P2 adopts differential amplification operation, which can be implemented by a circuit. Finally, the electrical signal output by the differential amplification operation circuit is converted into a digital signal suitable for the controller through analog-to-digital conversion for output. The controller can be a single-chip microcomputer or a computer, etc. In this application, it can be understood that the signal output by the differential amplification circuit can be used as the measurement result, that is, p1 + p2. The subsequent controller processing and analog-to-digital conversion are to organize the measurement result according to the actual circuit selection and output it to the outside through a serial port to achieve human-computer interaction.

[0059] Furthermore, the fiber optic Fabry-Perot cavity sensing probe includes:

[0060] One end of the single-mode fiber 3 is provided with the fiber connector 4, and the other end is stripped to expose the bare fiber, which passes through the ceramic ferrule 6 and is fixed with ultraviolet curable glue. The fiber end face is parallel to the vibrating piece 7; the vibrating piece 7 is bonded to the quartz bracket 5 and the ceramic ferrule 6 with ultraviolet curable glue; the vibrating piece 7, the quartz bracket 5, and the ceramic ferrule 6 together form a sensing module 8; the quartz bracket 5 is placed in the U-shaped groove of the ceramic base 2 and bonded with ultraviolet curable glue, and the ceramic shell 1 is buckled on the ceramic base 2 and bonded with epoxy resin glue to enclose the sensing module 8 in the ceramic shell 1 and the ceramic base 2.

[0061] The single-mode fiber 3 is used to transmit optical signals, and the vibrating piece 7 is used to perform interference modulation on the received signals.

[0062] Further, the zirconia ceramic housing 1 is made of zirconia ceramic material.

[0063] Further, the quartz base 2 fixes the probe holder by gluing.

[0064] Further, the production materials of both the quartz base 2 and the probe holder are quartz materials.

[0065] Further, the matching frequency range corresponding to the shape, thickness and effective length of the vibrating piece 7 is 300 Hz - 2000 Hz.

[0066] Further, the dimensions of the vibrating piece 7 are:

[0067] Length 15 mm, width 5 mm, thickness 0.05 mm.

[0068] Specifically, as shown in the attached Figure 2 description, a Fabry-Perot cavity sensor structure, which is applied to a new type of fiber optic Fabry-Perot cavity acoustic vibration sensor, forms an F-P cavity sensor through several components. Among them, the holder, housing, base, and vibrating piece 7 are fixed by gluing. Since repeated disassembly and assembly are not considered, using slow-curing resin glue can ensure both accuracy and stability.

[0069] Applying this method, the greatest effect is that the measured output quantity is only related to the amplitude, can directly reflect the amplitude, and is independent of external environmental parameters. Therefore, it is not affected by factors such as temperature, and the measurement result is stable.

[0070] On the other hand, this application only requires one Fabry-Perot cavity probe to interfere with the combined laser L3, and there is no probe error. Generally, in the prior art, two Fabry-Perot cavity probes are required to interfere with two beams of lasers respectively, and it is difficult to make the Fabry-Perot cavity probes completely consistent, so errors are inevitable.

[0071] In the third aspect, this application only requires one Fabry-Perot cavity probe and one circulator, while in the prior art, each of the two beams of lasers requires one circulator. Since the Fabry-Perot cavity probe and the circulator are costly, applying this device and method can reduce costs.

[0072] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other.

[0073] In this article, specific examples are used to illustrate the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A novel fiber optic Fabry-Perot cavity acoustic vibration sensor, characterized in that, Including: Dual-wavelength TOSA, dual-detection ROSA, optical fiber circulator, fiber Fabry-Perot cavity sensing probe and signal processing system; The dual-wavelength TOSA is connected to the first port of the optical fiber circulator, the fiber Fabry-Perot cavity sensing probe is connected to the second port of the optical fiber circulator, the dual-detection ROSA is connected to the third port of the optical fiber circulator, and the dual-detection ROSA is connected to the signal processing system; The dual-wavelength TOSA is used to generate a first incident laser and a second incident laser. The optical fiber circulator is used to combine the first incident laser and the second incident laser to obtain a combined laser and transmit the combined laser to the fiber Fabry-Perot cavity sensing probe. The fiber Fabry-Perot cavity sensing probe is used to receive the combined laser and perform interference to obtain an interfered return laser. The optical fiber circulator is also used to transmit the interfered return laser to the dual-detection ROSA. The dual-detection ROSA is used to receive the interfered return laser, perform beam splitting to obtain a first return laser and a second return laser, and convert the first return laser and the second return laser to obtain a first electrical signal and a second electrical signal. The signal processing system is used to perform differential amplification and AD acquisition on the first electrical signal and the second electrical signal, and then transmit an alarm signal and amplitude to the background according to a set amplitude threshold and perform local storage.

2. The novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 1, characterized in that, The signal processing system includes: Pre-amplification module, differential amplification module, A / D acquisition module, single-chip microcomputer, 485 communication module, background computer; The pre-amplification module is used to pre-amplify the first electrical signal and the second electrical signal. The differential amplification module is used to perform differential amplification on the pre-amplified signal. The A / D acquisition module is used to acquire the differentially amplified signal and transmit it to the single-chip microcomputer, and then transmit it to the background computer through the 485 communication module. The background computer is used to store the differentially amplified signal.

3. A novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 1, characterized in that, The wavelength difference between the first incident laser and the second incident laser is an odd multiple of half the period of the Fabry-Perot cavity interference spectrum.

4. The novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 1, characterized in that, The fiber Fabry-Perot cavity sensing probe includes: Ceramic shell, ceramic base, single-mode optical fiber, fiber optic connector, quartz bracket, ceramic ferrule, vibrating plate, sensing module; One end of the single-mode optical fiber is provided with the fiber optic connector, and the other end is stripped to expose the bare fiber, which passes through the ceramic ferrule and is fixed with ultraviolet curing glue. The fiber end face is parallel to the vibrating plate. The vibrating plate is bonded to the quartz bracket and the ceramic ferrule with ultraviolet curing glue. The vibrating plate, quartz bracket, and ceramic ferrule together form a sensing module. The quartz bracket is placed in the U-shaped groove of the ceramic base and bonded with ultraviolet curing glue. The ceramic shell is buckled on the ceramic base and bonded with epoxy resin glue to enclose the sensing module in the ceramic shell and ceramic base. The single-mode optical fiber is used to transmit optical signals, and the vibrating plate is used to perform interference modulation on the received signals.

5. A novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 4, characterized in that, The zirconia ceramic shell is made of zirconia ceramic material.

6. The novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 5, characterized in that, The quartz base fixes the probe bracket by gluing.

7. A novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 6, characterized in that, Both the quartz base and the probe bracket are made of quartz material.

8. A novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 7, characterized in that, The matching frequency range corresponding to the shape, thickness, and effective length of the vibrating plate is 300Hz - 2000Hz.

9. A novel fiber optic Fabry-Perot cavity acoustic vibration sensor according to claim 7, characterized in that, The dimensions of the vibrating piece are as follows: Length: 15 mm, width: 5 mm, thickness: 0.05 mm.

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