CN113970368A - Distributed optical fiber vibration acoustic wave sensing system for realizing optical down-conversion based on series connection of double acousto-optic modulators - Google Patents
Distributed optical fiber vibration acoustic wave sensing system for realizing optical down-conversion based on series connection of double acousto-optic modulators Download PDFInfo
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Abstract
The invention relates to the technical field of optical time domain reflectometers, in particular to a distributed optical fiber vibration sound wave sensing system for realizing optical down-conversion based on series connection of double acousto-optic modulators, which comprises a demodulation circuit board and a down-conversion light path module, wherein the demodulation circuit board comprises a main control unit, an AD module, a photoelectric detector module, a driving signal conditioning module, a network port module and a serial port module, and the down-conversion light path module comprises a narrow-linewidth light source, an optical fiber beam splitter, an acousto-optic modulator combination, an optical fiber amplifier, an optical fiber circulator and an optical fiber beam combiner.
Description
Technical Field
The invention relates to the technical field of optical time domain reflectometers, in particular to a distributed optical fiber vibration acoustic wave sensing system for realizing optical down-conversion based on series connection of double acousto-optic modulators.
Background
The optical time domain reflectometer is a measuring instrument based on backward Rayleigh scattering light signals, can directly measure optical fiber vibration signals on the basis of the backward Rayleigh scattering theory, and can reflect the optical loss change condition of the whole optical fiber circuit. When an optical pulse propagates in the optical fiber, a backward rayleigh scattered signal generated by the pulse along the whole sensing optical fiber path is received by the optical detector, and a continuous distributed intensity signal arranged according to time sequence is formed, namely, any position in the sensing optical fiber has a backward rayleigh scattered light intensity corresponding to the position. According to the theory, by monitoring the intensity of the returned backward Rayleigh scattering optical signals, the optical fiber loss condition distributed along the optical fiber circuit can be reflected by the change of the detection light intensity, so that the parameter information of the optical fiber disturbance position, such as temperature, pressure, vibration, sound and the like, can be further obtained, and the disturbance information can be accurately positioned by calculating the round trip time of the optical pulse. The technology has the advantages of distributed optical fiber sensing measurement, has the characteristics of high detection sensitivity, high positioning precision and the like, and is widely applied to the fields of petrochemical natural gas conveying pipeline early warning, bridge and tunnel large-scale public facility safety monitoring, long-distance perimeter security and protection, power cable structure health monitoring and the like.
In a distributed optical fiber vibration/acoustic wave sensing system which is generally used at present, a demodulation light path of the distributed optical fiber vibration/acoustic wave sensing system is that continuous light generated by a narrow-linewidth laser is divided into two paths through an optical fiber beam splitter, one path is used as local light, and the other path is modulated through an acoustic optical modulator to carry out frequency shift and optical pulse generation on probe light. The returned signal light and the local light enter the optical fiber coupler for beat frequency, and the difference frequency signal enters the data acquisition system. In the scheme, because the spatial resolution and the attributes of the acousto-optic crystal are considered, an acousto-optic modulator with the frequency shift of 200MHz is generally adopted, so that certain requirements are provided for the sampling rate of system data acquisition and signal post-processing and the performance index of data parallel processing hardware. According to the nyquist sampling theorem, disturbance signals are required to be well restored, the sampling rate of an acquisition card needs to be at least 400MHz, the very strict requirement is provided for the design of a hardware circuit, the noise suppression of a phase noise measurement system is not facilitated, the data processing at the rear end of the system is too bulky, and the real-time performance of the system is reduced.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a distributed optical fiber vibration/sound wave sensing system for realizing optical down-conversion based on the series connection of double acousto-optic modulators, which realizes optical down-conversion in an optical path through optical conversion and time delay control, reduces the requirements of the system on data acquisition and signal post-processing, reduces the data processing magnitude of the system, and increases the real-time performance of phase demodulation of the system.
In order to achieve the purpose, the invention provides the following technical scheme: a distributed optical fiber vibration acoustic wave sensing system based on optical down-conversion is realized by connecting double acousto-optic modulators in series is characterized in that: comprises a demodulation circuit board (1) and a down-conversion optical path module (2),
the demodulation circuit board (1) comprises a main control unit (3), an AD module (4), a photoelectric detector module (5), a driving signal conditioning module (6), a network port module (7) and a serial port module (8),
the down-conversion light path module (2) comprises a narrow-linewidth light source (9), an optical fiber beam splitter (10), an acousto-optic modulator assembly (11), an optical fiber amplifier (12), an optical fiber circulator (13) and an optical fiber beam combiner (14),
the light source end of the narrow-linewidth light source (9) corresponds to the receiving end of the optical fiber beam splitter (10), one output end of the optical fiber beam splitter (10) corresponds to the receiving end of the acousto-optic modulator combination (11), the other output end of the optical fiber beam splitter (10) corresponds to the receiving end of the optical fiber beam combiner (14), the output end of the acousto-optic modulator combination (11) corresponds to the receiving end of the optical fiber amplifier (12), the output end of the optical fiber amplifier (12) corresponds to the receiving end of the optical fiber circulator (13), the output end of the optical fiber circulator (13) corresponds to the receiving end of the photoelectric detector module (5), the output end of the photoelectric detector module (5) is connected with the receiving end of the AD module (4), the output end of the AD module (4) is connected with the input end of the main control unit (1), and the network port module (7) and the serial port module (8) are both connected with the output end of the main control module (1), the receiving end of the driving signal conditioning module (6) is connected with the output end of the main control module (1), and the output end of the driving signal conditioning module (6) is respectively connected with the acousto-optic modulator assembly (11) and the control end of the optical fiber amplifier (12).
2. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 1, wherein: the optical fiber beam splitter (10) is a 1 x 2 optical fiber beam splitter.
3. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 2, wherein: the narrow line width light source (9) is a signal light source with the wavelength of 1550.12 nm.
4. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 3, wherein: the optical fiber combiner (14) is a 2 x 2 optical fiber combiner.
5. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 4, wherein: the main control unit (1) is an FPGA.
6. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 5, wherein: the specific working process of the sensing system is as follows:
1) a narrow linewidth laser light source emits signal light, the wavelength of the light source is 1550.12nm, and the signal light enters a 1 x 2 optical fiber beam splitter;
2) the optical fiber beam splitter divides the signal light into two beams, the optical signal 1 enters the acousto-optic modulator combination for optical modulation, and the optical signal 2 enters the optical fiber coupler as local light;
3) the FPGA controls the acousto-optic modulators to output driving signals by driving the acousto-optic modulators to be homologous according to set parameters, wherein the driving signals comprise respective frequency shift amount and repetition frequency of the two acousto-optic modulators;
4) the optical signal 1 after the modulator is a pulse optical signal at this time, has a certain pulse width and repetition frequency, and then enters an erbium-doped fiber amplifier for laser amplification;
5) the amplified signal light enters the optical fiber circulator, and is output and transmitted to the vibration optical cable from the port 2 of the circulator;
6) rayleigh scattering occurs in the vibration optical cable under the signal light, and a backward-propagated Rayleigh scattering signal is output through a port 3 of the circulator;
7) one end of the 2 x 2 optical fiber beam combiner is connected with signal light 1 emitted by the laser, and the other end is connected with a Rayleigh scattering signal returned from the vibrating optical cable, wherein the Rayleigh scattering signal light carries a vibrating signal on the vibrating optical cable. The two optical signals are subjected to optical beat frequency in the coupler to generate a difference frequency signal and a sum frequency signal, and then the difference frequency signal and the sum frequency signal are divided into two beams to enter a balance detector;
8) the two paths of signals of the balanced detector are subjected to differential processing, phase noise in a part of optical path systems is differentiated in the differential process, and then the signals enter an AD data acquisition system;
9) the FPGA receives data from the AD module and performs phase demodulation processing.
Compared with the prior art, the invention has the beneficial effects that: the sensing system consists of a light path module and a circuit module, wherein the light path module is used for modulating and outputting a sensing light signal, the circuit module is used for acquiring the light signal, the data processing module is used for preprocessing and phase demodulating a vibration signal, and optical down-conversion is realized in the light path module through the series connection and the control of the double acousto-optic modulators, so that the harsh requirements of the rear-end data acquisition system on the indexes such as the sampling rate of a high-speed acquisition card and the parallel calculation data throughput are greatly relieved, the real-time performance of the system is further improved, and the harsh limitation on the system performance index caused under the condition of high sampling rate is avoided;
A. the invention adds the acousto-optic modulator combination to carry out combined modulation on the detection light, and realizes optical down-conversion under the condition of not influencing the spatial resolution of the system;
B. the invention reduces the pressure of a hardware system for data acquisition and data demodulation at the back end of the system, and better realizes the real-time performance of the demodulation system;
the invention adopts the serial connection of the acousto-optic modulators as the modulator unit of the signal light in the light path system, and has the advantages of optical down-conversion, reduction of the requirement of the system on the sampling rate of the acquisition card and higher real-time performance of system vibration information processing. .
Drawings
Fig. 1 is an overall framework diagram of the system of the present invention.
In the figure: 1. a demodulation circuit board; 2. a down-conversion optical path module; 3. a main control unit; 4. an AD module; 5. a photodetector module; 6. a drive signal conditioning module; 7. a network port module; 8. a serial port module; 9. a narrow line light source; 10. an optical fiber beam splitter; 11. an acousto-optic modulator assembly; 12. an optical fiber amplifier; 13. a fiber optic circulator; 14. an optical fiber combiner.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the present invention provides a technical solution: a distributed optical fiber vibration acoustic wave sensing system for realizing optical down-conversion based on the series connection of double acousto-optic modulators comprises a demodulation circuit board 1 and a down-conversion optical path module 2,
the demodulation circuit board 1 comprises a main control unit 3, an AD module 4, a photoelectric detector module 5, a driving signal conditioning module 6, a network port module 7 and a serial port module 8,
the down-conversion light path module 2 comprises a narrow linewidth light source 9, an optical fiber beam splitter 10, an acousto-optic modulator assembly 11, an optical fiber amplifier 12, an optical fiber circulator 13 and an optical fiber beam combiner 14,
the light source end of the narrow-linewidth light source 9 corresponds to the receiving end of the optical fiber beam splitter 10, one output end of the optical fiber beam splitter 10 corresponds to the receiving end of the acousto-optic modulator assembly 11, the other output end of the optical fiber beam splitter 10 corresponds to the receiving end of the optical fiber beam combiner 14, the output end of the acousto-optic modulator assembly 11 corresponds to the receiving end of the optical fiber amplifier 12, the output end of the optical fiber amplifier 12 corresponds to the receiving end of the optical fiber circulator 13, the output end of the optical fiber circulator 13 corresponds to the receiving end of the photoelectric detector module 5, the output end of the photoelectric detector module 5 is connected with the receiving end of the AD module 4, the output end of the AD module 4 is connected with the input end of the main control unit 1, the network interface module 7 and the serial port module 8 are both connected with the output end of the main control module 1, the receiving end of the driving signal conditioning module 6 is connected with the output end of the acousto-optic modulator assembly 11 and the control end of the optical fiber amplifier 12.
The optical fiber beam splitter 10 is a 1 x 2 optical fiber beam splitter, the optical fiber beam splitter divides an optical signal emitted by a laser into two beams, namely an optical signal 1 and an optical signal 2, the optical signal 1 enters an acousto-optic modulation combination for modulation, and a detection light after the modulator enters an erbium-doped optical fiber amplifier for laser amplification; the amplified optical signal 1 is transmitted into the vibration optical cable through the port 2 of the optical fiber circulator; the optical signal 2 is beat-frequency in the optical fiber combiner as a local light and a return signal, and is finally received by the photodetector.
The narrow line width light source 9 is a signal light source with the wavelength of 1550.12 nm.
The optical fiber combiner 14 is a 2 x 2 optical fiber combiner.
The main control unit 1 is an FPGA.
The circuit part comprises a photoelectric detector, an AD module, a driving signal conditioning module, a serial port module, a network port module, an FPGA module and the like.
The photoelectric detector uses a balanced photoelectric detector, and a receiving end consists of two paths, wherein one path is local light divided by the laser, and the other path is signal light returned from the detection optical fiber, so that an optical signal is converted into an electric signal;
the AD module converts the analog electric signal into a digital signal for subsequent data processing;
the driving signal conditioning module realizes the function of generating driving signals required by the optical path part;
the network port module and the serial port module are used as a command parameter input interface and a data output interface of the system, wherein the network port is used for outputting intermediate data during vibration signal phase demodulation so as to facilitate a tester to carry out data analysis and make corresponding parameter adjustment; the serial port is used for commanding parameter input and a demodulated wavelength value, and the two interfaces are controlled by the FPGA;
the FPGA module is a core control device of the system and realizes the functions of data acquisition, dynamic gain control, driving signal output and dynamic adjustment, network port control, serial port control, phase demodulation algorithm and the like.
In order to realize the phase demodulation of the optical fiber vibration signal and the real-time performance of the demodulation signal, the invention not only dynamically adjusts the monitoring and feedback of each state through the FPGA, but also optimizes the optical path module, and uses the acousto-optic modulator combination to replace the traditional single acousto-optic modulator to realize the down-conversion of the optical frequency in the optical path.
The data demodulation processing algorithm is realized in the FPGA, and mainly processes the acquired data by frequency mixing, differential phase, dephase winding and the like, so as to realize the demodulation and transmission of the system vibration signal phase information.
The specific working process of the sensing system is as follows:
1) a narrow linewidth laser light source emits signal light, the wavelength of the light source is 1550.12nm, and the signal light enters a 1 x 2 optical fiber beam splitter;
2) the optical fiber beam splitter divides the signal light into two beams, the optical signal 1 enters the acousto-optic modulator combination for optical modulation, and the optical signal 2 enters the optical fiber coupler as local light;
3) the FPGA controls the acousto-optic modulators to output driving signals by driving the acousto-optic modulators to be homologous according to set parameters, wherein the driving signals comprise respective frequency shift amount and repetition frequency of the two acousto-optic modulators;
4) the optical signal 1 after the modulator is a pulse optical signal at this time, has a certain pulse width and repetition frequency, and then enters an erbium-doped fiber amplifier for laser amplification;
5) the amplified signal light enters the optical fiber circulator, and is output and transmitted to the vibration optical cable from the port 2 of the circulator;
6) rayleigh scattering occurs in the vibration optical cable under the signal light, and a backward-propagated Rayleigh scattering signal is output through a port 3 of the circulator;
7) one end of the 2 x 2 optical fiber beam combiner is connected with signal light 1 emitted by the laser, and the other end is connected with a Rayleigh scattering signal returned from the vibrating optical cable, wherein the Rayleigh scattering signal light carries a vibrating signal on the vibrating optical cable. The two optical signals are subjected to optical beat frequency in the coupler to generate a difference frequency signal and a sum frequency signal, and then the difference frequency signal and the sum frequency signal are divided into two beams to enter a balance detector;
8) the two paths of signals of the balanced detector are subjected to differential processing, phase noise in a part of optical path systems is differentiated in the differential process, and then the signals enter an AD data acquisition system;
9) the FPGA receives data from the AD module and performs phase demodulation processing.
The method for realizing the optical down-conversion is to realize the optical down-conversion by combining and connecting two acousto-optic modulators in series and controlling the frequency shift direction of the acousto-optic modulators through the driving of an amplifier, so as to reduce the pressure of large difference frequency component of optical beat frequency on a rear end data acquisition and analysis system and increase the real-time performance of phase demodulation of the system. The distributed optical fiber vibration/sound wave sensing system for realizing optical down-conversion based on the series connection of the double sound-light modulators comprises the following steps:
the laser outputs continuous signal light with an optical frequency of ω + Δ ω, where Δ ω is the frequency noise generated by the laser;
the optical fiber beam splitter divides an optical signal output by the laser into two paths of signal light, wherein the first path of optical signal is used as local light, and the beat frequency is carried out on the rear surface of the first path of optical signal and a returned Rayleigh scattering optical signal; the second path of optical signal is modulated by two acousto-optic modulators connected in series, and the optical frequency of the modulated signal is changed into omega + delta omega + f1-f2。
By controlling the drive of the acousto-optic modulator, the modulated signal light not only has changed frequency, but also has corresponding pulse width and repetition frequency; the modulated signal light is incident into an erbium-doped fiber amplifier for laser amplification so as to meet the requirement of long-distance detection of a system;
the amplified signal light is incident into a detection optical fiber through an optical fiber circulator, Rayleigh scattering occurs in the detection optical fiber, the Rayleigh scattering belongs to elastic collision, the frequency of the signal light is not changed by a backward-propagating Rayleigh scattering light signal, and the backward-propagating Rayleigh scattering light carries vibration information in the detection optical fiber;
the returned Rayleigh scattered light is converged at the 2 x 2 optical fiber beam combiner through the port 3 of the optical fiber circulator and the local light of the laser, optical frequency is generated, the signal light after beat frequency is captured by the photoelectric detector, and an optical signal is converted into an electric signal and transmitted into a rear-end data acquisition and analysis system.
And the data acquisition and processing system performs phase demodulation on the acquired electric signals to obtain vibration signals of the detection optical fibers.
Specifically, two acousto-optic modulators connected in series are forward shifted by one frequency f by controlling the drive of an acousto-optic modulator amplifier1An inverse frequency shift f2Total amount of frequency shift is f1-f2Realizing optical down-conversion; of the frequency components of the beat frequency of the back end, the difference frequency signal is f1-f2Controlling f according to the actual demand of the system1、f2Can be determined according to the difference frequency component f1-f2Is matched instead of f1And matching is carried out, so that the processing capacity of the data acquisition and processing system is greatly reduced, and the system performance is improved.
The invention adopts two acousto-optic modulators to be connected in series, realizes optical down-conversion by controlling the drive of the acousto-optic modulators, and reduces the frequency of beat frequency signals, thereby relieving the rigorous requirements of a rear-end data acquisition system on the indexes such as the sampling rate of a high-speed acquisition card and the throughput of parallel calculation data, further improving the real-time property of the system, and avoiding the rigorous limit on the performance index of the system caused under the condition of high sampling rate.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (6)
1. A distributed optical fiber vibration acoustic wave sensing system based on optical down-conversion is realized by connecting double acousto-optic modulators in series is characterized in that: comprises a demodulation circuit board (1) and a down-conversion optical path module (2),
the demodulation circuit board (1) comprises a main control unit (3), an AD module (4), a photoelectric detector module (5), a driving signal conditioning module (6), a network port module (7) and a serial port module (8),
the down-conversion light path module (2) comprises a narrow-linewidth light source (9), an optical fiber beam splitter (10), an acousto-optic modulator assembly (11), an optical fiber amplifier (12), an optical fiber circulator (13) and an optical fiber beam combiner (14),
the light source end of the narrow-linewidth light source (9) corresponds to the receiving end of the optical fiber beam splitter (10), one output end of the optical fiber beam splitter (10) corresponds to the receiving end of the acousto-optic modulator combination (11), the other output end of the optical fiber beam splitter (10) corresponds to the receiving end of the optical fiber beam combiner (14), the output end of the acousto-optic modulator combination (11) corresponds to the receiving end of the optical fiber amplifier (12), the output end of the optical fiber amplifier (12) corresponds to the receiving end of the optical fiber circulator (13), the output end of the optical fiber circulator (13) corresponds to the receiving end of the photoelectric detector module (5), the output end of the photoelectric detector module (5) is connected with the receiving end of the AD module (4), the output end of the AD module (4) is connected with the input end of the main control unit (1), and the network port module (7) and the serial port module (8) are both connected with the output end of the main control module (1), the receiving end of the driving signal conditioning module (6) is connected with the output end of the main control module (1), and the output end of the driving signal conditioning module (6) is respectively connected with the acousto-optic modulator assembly (11) and the control end of the optical fiber amplifier (12).
2. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 1, wherein: the optical fiber beam splitter (10) is a 1 x 2 optical fiber beam splitter.
3. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 2, wherein: the narrow line width light source (9) is a signal light source with the wavelength of 1550.12 nm.
4. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 3, wherein: the optical fiber combiner (14) is a 2 x 2 optical fiber combiner.
5. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 4, wherein: the main control unit (1) is an FPGA.
6. The distributed optical fiber vibration acoustic wave sensing system for realizing optical down conversion based on the series connection of the two acousto-optic modulators according to claim 5, wherein: the specific working process of the sensing system is as follows:
1) a narrow linewidth laser light source emits signal light, the wavelength of the light source is 1550.12nm, and the signal light enters a 1 x 2 optical fiber beam splitter;
2) the optical fiber beam splitter divides the signal light into two beams, the optical signal 1 enters the acousto-optic modulator combination for optical modulation, and the optical signal 2 enters the optical fiber coupler as local light;
3) the FPGA controls the acousto-optic modulators to output driving signals by driving the acousto-optic modulators to be homologous according to set parameters, wherein the driving signals comprise respective frequency shift amount and repetition frequency of the two acousto-optic modulators;
4) the optical signal 1 after the modulator is a pulse optical signal at this time, has a certain pulse width and repetition frequency, and then enters an erbium-doped fiber amplifier for laser amplification;
5) the amplified signal light enters the optical fiber circulator, and is output and transmitted to the vibration optical cable from the port 2 of the circulator;
6) rayleigh scattering occurs in the vibration optical cable under the signal light, and a backward-propagated Rayleigh scattering signal is output through a port 3 of the circulator;
7) one end of the 2 x 2 optical fiber beam combiner is connected with signal light 1 emitted by the laser, and the other end is connected with a Rayleigh scattering signal returned from the vibrating optical cable, wherein the Rayleigh scattering signal light carries a vibrating signal on the vibrating optical cable. The two optical signals are subjected to optical beat frequency in the coupler to generate a difference frequency signal and a sum frequency signal, and then the difference frequency signal and the sum frequency signal are divided into two beams to enter a balance detector;
8) the two paths of signals of the balanced detector are subjected to differential processing, phase noise in a part of optical path systems is differentiated in the differential process, and then the signals enter an AD data acquisition system;
9) the FPGA receives data from the AD module and performs phase demodulation processing.
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