Distributed fiber optic sensing system and signal processing method

Abstract

The application provides a kind of distributed optical fiber sensing system and signal processing method, belong to optical fiber sensing technical field.The distributed optical fiber sensing system light signal generating device, acoustooptic modulator, first erbium-doped fiber amplifier, circulator, first Raman amplifier, erbium-doped fiber, sensing optical fiber, coupler, photoelectric balance detector, signal acquisition device and data processing module.The application is amplified to the light signal that enters sensing optical fiber before light signal enters sensing optical fiber by first erbium-doped fiber amplifier and first Raman amplifier, so as to improve the transmission distance of light signal in sensing optical fiber, then the transmission distance of light signal is further improved by the erbium-doped fiber added in sensing optical fiber, so that sensing optical fiber can produce backscattering light signal carrying vibration signal at a farther distance, and the backscattering light signal intensity map is obtained after the backscattering light signal is processed, so that long-distance signal monitoring is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical fiber sensing, and particularly relates to a distributed optical fiber sensing system and a signal processing method. BACKGROUND

[0002] With the continuous progress of science and technology, distributed acoustic sensing (DAS) technology is widely used in urban construction, industrial production and other fields. As a new type of passive sensing technology, DAS technology utilizes the transmission characteristics of optical fibers to realize signal transmission and measurement in the same optical fiber, and the backscattered light generated thereby can provide acoustic field information in the spatial domain. Under long distance and high time resolution, the signal will produce a serious signal-to-noise ratio drop phenomenon in the transmission process, thereby affecting the detection efficiency and accuracy of the DAS system.

[0003] In the prior art, some distributed optical fiber sensing systems extend the transmission distance by adding a relay amplification device, and the relay amplification device needs to introduce multiple high-performance optical amplifiers and filters. If the transmission distance is to be further extended, the number of relay amplification devices can be increased.

[0004] However, in the above-mentioned technology, the structure of the relay amplification device is relatively complex, and when it is introduced into the distributed optical fiber sensing system, it will significantly increase the difficulty of system production and debugging. Moreover, when more relay amplification devices are introduced to increase the detection distance, the optical fiber sensing system will become more complex. SUMMARY

[0005] In view of the problem of complex structure for long-distance signal detection existing in the prior art optical fiber sensing system, the present application aims to provide a distributed optical fiber sensing system and a signal processing method, which can realize long-distance signal detection in a simpler structure.

[0006] In a first aspect, the present application provides a distributed optical fiber sensing system, comprising: an optical signal generating device, an acousto-optic modulator, a first erbium-doped fiber amplifier, a circulator, a first Raman amplifier, an erbium-doped fiber, a sensing optical fiber, a coupler, a photoelectric balance detector, a signal acquisition device and a data processing module.

[0007] The optical signal generating device is configured to output a first continuous light beam and a second continuous light beam.

[0008] The first input end of the acousto-optic modulator receives the first continuous light beam, and is configured to modulate the first continuous light beam into a first pulsed light.

[0009] The first erbium-doped fiber amplifier is connected between the output end of the acousto-optic modulator and the first port of the circulator, and is configured to amplify the power of the first pulsed light to generate second pulsed light.

[0010] The second port of the circulator is connected to the input end of the first Raman amplifier, and the first Raman amplifier is configured to amplify the power of the second pulsed light to generate third pulsed light, and the third port of the circulator outputs a backscattered light signal carrying an external vibration signal.

[0011] The two ends of the erbium-doped fiber are connected to a sensing optical fiber, the first Raman amplifier is located at one end of the sensing optical fiber away from the erbium-doped fiber, and the first Raman amplifier inputs the third pulsed light into the sensing optical fiber.

[0012] The input end of the coupler is connected to the optical signal generating device and the third port of the circulator, and the coupler is configured to process the second continuous light beam and the backscattered light signal and output two light signals with the same power to a photoelectric balance detector, and the photoelectric balance detector is configured to convert the two light signals with the same power into an electrical signal.

[0013] The input end of the signal acquisition device is connected to the output end of the photoelectric balance detector, and the signal acquisition device is configured to convert the electrical signal into a digital signal, and the second input end of the acousto-optic modulator receives the digital signal as a trigger signal.

[0014] The data processing module is connected to the output end of the signal acquisition device and is configured to process the digital signal and output a backscattered light signal intensity map.

[0015] In a possible implementation, the optical signal generating device comprises:

[0016] A laser is configured to generate a continuous laser beam.

[0017] A beam splitter is configured to split the laser beam into a first continuous light beam and a second continuous light beam.

[0018] In a possible implementation, the beam splitter splits the laser beam into a first continuous light beam of 90% and a second continuous light beam of 10%.

[0019] In a possible implementation, a second Raman amplifier is further included, the second Raman amplifier is located at the other end of the sensing optical fiber away from the erbium-doped fiber, and is configured to amplify the power of the light signal transmitted in the reverse direction.

[0020] In a possible implementation, a second erbium-doped fiber amplifier is further included, which is connected between the input end of the coupler and the third port of the circulator, and is configured to amplify the power of the backscattered light signal.

[0021] In a second aspect, the present application further provides a signal processing method, which is applied to the system of any of the embodiments of the first aspect, and the method comprises:

[0022] The optical signal generating device outputs a first continuous light beam and a second continuous light beam;

[0023] The first input end of the acousto-optic modulator receives the first continuous light beam and modulates the first continuous light beam into a first pulsed light;

[0024] The first erbium-doped fiber amplifier amplifies the power of the first pulsed light to generate a second pulsed light;

[0025] The first Raman amplifier amplifies the power of the second pulsed light to generate a third pulsed light;

[0026] The coupler processes the second continuous light beam and the backscattered light signal carrying the external vibration signal and outputs two light signals with the same power;

[0027] The photoelectric balance detector converts the two light signals with the same power into electrical signals;

[0028] The signal acquisition device converts the electrical signals into digital signals;

[0029] The second input end of the acousto-optic modulator receives the digital signals as trigger signals;

[0030] The data processing module processes the digital signals and outputs a backscattered light signal intensity map.

[0031] In a possible implementation, the data processing module processes the digital signals to output a backscattered light signal intensity map, which comprises:

[0032] Wavelet decomposition is performed on the digital signals to obtain wavelet coefficients;

[0033] According to statistical information of the wavelet coefficients, a noise threshold of the digital signals is determined;

[0034] Hard threshold processing is performed on the wavelet coefficients of each layer according to the noise threshold;

[0035] The digital signals are reconstructed according to the wavelet coefficients after the hard threshold processing to obtain a backscattered light signal intensity map.

[0036] In a possible implementation, the determining the noise threshold of the digital signal according to the statistical information of the wavelet coefficients comprises:

[0037] obtaining the noise standard deviation of the digital signal according to the statistical information of the wavelet coefficients;

[0038] determining the length of the digital signal;

[0039] determining the noise threshold of the digital signal according to the length of the digital signal and the noise standard deviation.

[0040] In a possible implementation, the distributed optical fiber sensing system further comprises a second erbium-doped fiber amplifier connected between the input end of the coupler and the third port of the circulator; and the method further comprises:

[0041] the second erbium-doped fiber amplifier amplifies the power of the backscattered light signal.

[0042] In a possible implementation, the distributed optical fiber sensing system further comprises a second Raman amplifier located at the other end of the sensing optical fiber away from the erbium-doped fiber; and the method further comprises:

[0043] the second Raman amplifier amplifies the power of the backscattered light signal.

[0044] The present application provides a distributed optical fiber sensing system and a signal processing method, wherein the distributed optical fiber sensing system comprises: an optical signal generating device, an acousto-optic modulator, a first erbium-doped fiber amplifier, a circulator, a first Raman amplifier, an erbium-doped fiber, a sensing optical fiber, a coupler, a photoelectric balance detector, a signal acquisition device and a data processing module. The present application amplifies the optical signal entering the sensing optical fiber through the first erbium-doped fiber amplifier and the first Raman amplifier before the optical signal enters the sensing optical fiber, so that the optical signal still has a certain intensity when it is transmitted to 75km. Since the present application additionally provides an erbium-doped fiber between the sensing optical fibers, the excited erbium ions in the erbium-doped fiber interact with the optical signal with enhanced power, thereby enhancing the intensity of the optical signal, thereby increasing the transmission distance of the optical signal by 125km. At this time, the optical signal can also occur Rayleigh scattering at the farthest transmission point and return the backscattered light signal carrying the vibration signal. After the backscattered light signal is processed, the backscattered light signal intensity map is obtained, thereby realizing long-distance signal monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0045] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the application.

[0046] Figure 1 A structural schematic diagram of a first distributed optical fiber sensing system provided by an embodiment of the present application is shown in the figure;

[0047] Figure 2 A structural schematic diagram of a second distributed optical fiber sensing system provided by an embodiment of the present application is shown in the figure;

[0048] Figure 3 A structural schematic diagram of a third distributed optical fiber sensing system provided by an embodiment of the present application is shown in the figure;

[0049] Figure 4 A flow chart of a signal processing method provided by an embodiment of the present application is shown in the figure;

[0050] Figure 5 A flow chart of a signal processing method of a data processing module provided by an embodiment of the present application is shown in the figure;

[0051] Figure 6 A Figure 2 A backscattering light signal intensity graph received by the data processing module in the embodiment shown in the figure;

[0052] Figure 7 A Figure 5 A single frequency signal comparison graph before and after signal processing in the embodiment shown in the figure;

[0053] Figure 8 A Figure 7 An image after the single frequency signal of the embodiment shown in the figure is restored by FFT;

[0054] Figure 9 A Figure 5 A signal restoration effect diagram of the distributed optical fiber sensing system of the embodiment shown in the figure.

[0055] The above figures have shown the specific embodiments of the present application, which will be described in more detail hereinafter. These figures and textual descriptions are not intended to limit the scope of the concept of the present application by any means, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments.

[0056] Explanation of reference signs:

[0057] 101-optical signal generating device; 102-acousto-optic modulator; 103-first erbium-doped fiber amplifier; 104-circulator; 105-first Raman amplifier; 106-coupler; 107-optical balanced detector; 108-signal collecting device; 109-data processing module; 110-sensing optical fiber; 111-erbium-doped fiber; 112-second Raman amplifier; 113-second erbium-doped fiber amplifier. DETAILED DESCRIPTION

[0058] The exemplary embodiments will be described in detail herein with reference to the attached drawings. The following description is made with reference to the accompanying drawings in which like reference numerals refer to like elements, unless the context of use indicates otherwise. The following description of exemplary embodiments is not representative of all embodiments consistent with the present application. Rather, it is merely an example of apparatus and methods consistent with some aspects of the present application as detailed in the appended claims.

[0059] In the embodiments of the present application, the terms such as "first", "second" and the like are used to distinguish different items or similar items having essentially the same function and effect. Those skilled in the art can understand that the terms such as "first", "second" and the like do not limit the quantity and execution order, and the terms such as "first", "second" and the like do not necessarily mean different.

[0060] It should be noted that in the embodiments of the present application, the words "exemplary" or "for example" are used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "for example" should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the exemplary or example embodiments are presented as a specific example of the described concept. In the embodiments of the present application, "at least one" means one or more, and "multiple" means two or more.

[0061] It should be noted that in the embodiments of the present application, "at the time of" can be at the moment when a certain condition occurs, or within a period of time after a certain condition occurs, which is not specifically limited in the embodiments of the present application.

[0062] In order to clearly describe the technical solutions of the embodiments of the present application, the following briefly introduces some terms and technologies involved in the embodiments of the present application:

[0063] Erbium-doped fiber amplifier: erbium-doped fiber amplifier (EDFA) is a device used for amplifying optical signals in optical fiber communication systems. The basic principle of erbium-doped fiber is to put an erbium-doped fiber into a laser amplifier, in which the laser signal will pass through the erbium doping and thus be amplified. The advantage of erbium-doped fiber amplifier is that it can maintain the stability of the signal in long distance transmission, and its power loss is very low, which can effectively amplify the signal and keep it in good stability during transmission.

[0064] Circulator: A circulator is a multi-port device that directs incident waves entering any of its ports to the next port in a direction determined by a static bias magnetic field. A typical circulator is a three-port device, when a signal enters the first port from the direction determined by the static bias magnetic field, the signal will be output from the second port; when a signal enters the second port, the signal will be output from the third port. The function of the circulator is to transmit high-frequency signal energy in one direction.

[0065] With the continuous progress of science and technology, distributed optical fiber acoustic wave sensing technology is widely used in urban construction, industrial production and other fields. As a new type of passive sensing technology, distributed optical fiber acoustic wave sensing technology uses the transmission characteristics of optical fiber to transmit and measure signals in the same optical fiber. The backscattered light signal generated thereby can provide acoustic field information in the spatial domain. However, under long distance and high time resolution, the signal will produce a serious signal-to-noise ratio drop during transmission, thereby affecting the detection efficiency and accuracy of the distributed optical fiber acoustic wave sensing system. In some existing technologies, at least one relay amplification device is introduced to increase the signal transmission distance, and the structure of the relay amplification device is mostly complex, which will cause the production and debugging process of the equipment to be more difficult, and the detection cost is increased accordingly.

[0066] To solve the above problems, the embodiment of the present application first provides a distributed optical fiber sensing system, wherein the distributed optical fiber sensing system comprises: an optical signal generating device, an acousto-optic modulator, a first erbium-doped fiber amplifier, a circulator, a first Raman amplifier, an erbium-doped fiber, a sensing optical fiber, a coupler, a photoelectric balance detector, a signal acquisition device and a data processing module. Before the optical signal enters the sensing optical fiber, the optical signal entering the sensing optical fiber is amplified by the first erbium-doped fiber amplifier and the first Raman amplifier, so that the optical signal can be transmitted for a longer distance for detection. Since the present application further adds an erbium-doped fiber between the sensing optical fibers, the excited erbium ions in the erbium-doped fiber interact with the enhanced power optical signal, enhancing the intensity of the optical signal, thereby further increasing the transmission distance of the optical signal. At this time, the optical signal can also occur Rayleigh scattering at the farthest transmission point and return the backscattered light signal carrying the vibration signal. After the backscattered light signal is processed, the backscattered light signal intensity map is obtained, thereby realizing long-distance signal monitoring.

[0067] Figure 1 The first distributed optical fiber sensing system of the embodiment of the present application is shown in the structure diagram. As shown in Figure 1As shown, a distributed optical fiber sensing system includes an optical signal generating device 101, an acousto-optic modulator 102, a first erbium-doped fiber amplifier 103, a circulator 104, a first Raman amplifier 105, an erbium-doped fiber 111, a sensing fiber 110, a coupler 106, a photoelectric balance detector 107, a signal acquisition device 108, and a data processing module 109.

[0068] The optical signal generating device 101 is configured to output a first continuous light beam and a second continuous light beam. The acousto-optic modulator 102 receives the first continuous light beam at a first input end and modulates the first continuous light beam into a first pulsed light. The first erbium-doped fiber amplifier 103 is connected between an output end of the acousto-optic modulator 102 and a first port of the circulator 104. The first erbium-doped fiber amplifier 103 amplifies the power of the first pulsed light to generate a second pulsed light. The second port of the circulator 104 is connected to an input end of the first Raman amplifier 105. The first Raman amplifier 105 amplifies the power of the second pulsed light to generate a third pulsed light. The third port of the circulator 104 outputs a backscattered light signal carrying an external vibration signal. The two ends of the erbium-doped fiber 111 are connected to the sensing fiber 110. The first Raman amplifier 105 is located at an end of the sensing fiber 110 away from the erbium-doped fiber 111. The first Raman amplifier 105 inputs the third pulsed light into the sensing fiber 110. The input end of the coupler 106 is connected to the optical signal generating device 101 and the third port of the circulator 104. The coupler 106 processes the second continuous light beam and the backscattered light signal and outputs two light signals with the same power to the photoelectric balance detector 107. The photoelectric balance detector 107 converts the two light signals with the same power into an electrical signal. The input end of the signal acquisition device 108 is connected to the output end of the photoelectric balance detector 107. The signal acquisition device 108 converts the electrical signal into a digital signal. The second input end of the acousto-optic modulator 102 receives the digital signal as a trigger signal. The data processing module 109 is connected to the output end of the signal acquisition device 108 and processes the digital signal to output a backscattered light signal intensity map.

[0069] In the embodiment, the optical signal generating device 101 is configured to output two continuous light beams, where the first continuous light beam is used as a probe light, and the second continuous light beam is used as a local light. Specifically, the optical signal generating device 101 can include a laser and a beam splitter. The laser is configured to generate a continuous laser beam. The beam splitter is configured to split the laser beam into the first continuous light beam and the second continuous light beam. The optical signal generating device with the above structure can adjust the intensity ratio of the probe light and the local light according to the selection of the beam splitter.

[0070] In an embodiment, the beam splitter divides the laser beam into the first continuous light beam and the second continuous light beam in different proportions according to different detection distances. For example, the beam splitter divides the laser beam into 90% of the first continuous light beam and 10% of the second continuous light beam, and the embodiment can transmit the optical signal to a detection range of 150 km.

[0071] In the embodiment, the acousto-optic modulator 102 is configured to modulate the first continuous light beam into the first pulsed light with a detection frequency, and the detection frequency and power of the first pulsed light can be adjusted. Specifically, the acousto-optic modulator 102 can include an acousto-optic modulation module and an acousto-optic modulation driving module. The acousto-optic modulation driving module is configured to provide a periodic radio frequency (RF) signal to the acousto-optic modulation module, so as to control the opening and closing of the first continuous light beam, thereby controlling the width of the pulse generation. Adjusting the period of the RF signal can adjust the frequency of the final output of the first pulsed light.

[0072] In the embodiment, the first erbium-doped fiber amplifier 103 amplifies the first pulsed light output by the acousto-optic modulator 102, thereby enhancing the signal strength to transmit the optical signal to a farther distance.

[0073] In the embodiment, the circulator 104 is configured to follow the order of the first port, the second port, and the third port. The second pulsed light output by the first erbium-doped fiber amplifier 103 is input from the first port of the circulator 104. According to the characteristics of the circulator 104, the second pulsed light is output from the second port of the circulator 104, and is thereby transmitted to the input end of the first Raman amplifier 105. The first Raman amplifier 105 is configured to further enhance the power intensity of the optical signal, and thereby output the third pulsed light.

[0074] In the embodiment, the third pulsed light reaching a certain power is transmitted in the sensing fiber 110. In a sensing system without the first Raman amplifier 105, the intensity of the optical signal is generally significantly weakened at a position of 75 km in the transmission of the sensing fiber 110. In the embodiment, the first Raman amplifier 105 is additionally provided, and the optical signal has a certain intensity when transmitted to the position of 75 km. In order to further improve the transmission distance, the embodiment considers adding a segment of erbium-doped fiber to connect the next segment of the sensing fiber 110 at the position of 74 km in the forward transmission of the sensing fiber 110. When the third pulsed light output by the first Raman amplifier 105 enters the erbium-doped fiber, the power intensity of the third pulsed light can excite the erbium ions in the erbium-doped fiber, so that the erbium ions are transitioned from the ground state (low energy level) to the excited state (high energy level). The interaction between the optical signal and the excited erbium ions is stimulated emission, which generates new photons with the same phase and frequency as the incident signal light (third pulsed light). The newly generated photons and the incident signal light form coherent superposition, thereby enhancing the intensity of the signal light and further improving the transmission distance of the optical signal.

[0075] In the embodiment of the application, when the optical signal enters the sensing optical fiber 110, a backscattered optical signal carrying the vibration signal will be generated due to Rayleigh scattering. The farther the optical signal is transmitted in the sensing optical fiber 110, the farther the backscattered optical signal will carry the vibration signal for reverse transmission. At this time, the backscattered optical signal will be input from the second port of the circulator 104 along the transmission optical fiber. Due to the irreversible characteristics of the circulator 104, the backscattered optical signal can only be output from the third port of the circulator.

[0076] In the embodiment of the application, the coupler 106 is a 50:50 coupler, which outputs two optical signals with the same power after receiving the backscattered optical signal output from the third port of the circulator 104 and the second continuous light beam output from the optical signal generating device 101. After the two optical signals with the same power enter the photoelectric balance detector 107, the optical signals are converted into electrical signals proportional to the light intensity by using the photoelectric effect. It should be noted that the two optical signals with the same power output from the coupler 106 enter the photoelectric balance detector 107 for differential detection, thereby facilitating the suppression of common-mode noise and improving the sensitivity and signal-to-noise ratio of the optical signal, which is very important in fiber sensing.

[0077] In the embodiment of the application, the electrical signal output from the photoelectric balance detector 107 is still an analog signal, so it is necessary to use the signal acquisition device 108 for analog-to-digital conversion to generate a digital signal, which can be used as a trigger signal of the acousto-optic modulator 102. Specifically, the digital signal is output to the acousto-optic modulation driving module as a trigger signal to control the output of the acousto-optic modulation module.

[0078] In the embodiment of the application, the digital signal is the remote vibration signal detected in the fiber sensing system. In order to analyze the vibration signal, the data processing module 109 is needed to process the digital signal to output the backscattered optical signal intensity diagram corresponding to the vibration signal.

[0079] It should be noted that the sensing optical fiber of the application uses a single-mode optical fiber, which can reduce the transmission loss of the optical signal, improve the transmission distance, and has low cost, belonging to a widely used standard optical fiber.

[0080] In the above embodiment, since the optical signal is amplified by the first erbium-doped fiber amplifier 103 and the first Raman amplifier 105 before entering the sensing fiber 110, the optical signal still has a certain intensity when it is transmitted to a distance of 75 km. Since the erbium-doped fiber 111 is additionally arranged between the sensing fiber 110, the excited erbium ions in the erbium-doped fiber 111 interact with the optical signal with enhanced power, thereby enhancing the intensity of the optical signal, and further improving the transmission distance of the optical signal. At this time, the optical signal can also occur Rayleigh scattering at the farthest transmission point, and the backscattered optical signal carrying the vibration signal is returned. After corresponding processing, the backscattered optical signal intensity diagram is obtained, thereby realizing long-distance signal monitoring. Figure 1 In the embodiment shown in the figure, the distributed optical fiber sensing system can effectively detect a vibration signal of 125 km.

[0081] Figure 2 FIG. 2 is a structural schematic diagram of a second distributed optical fiber sensing system according to an embodiment of the present application. The embodiment improves the embodiment shown in the figure. As shown in the figure, a distributed optical fiber sensing system comprises a first erbium-doped fiber amplifier 103, a first Raman amplifier 105, a sensing fiber 110, an erbium-doped fiber 111, and a second Raman amplifier 112. Figure 1 The embodiment improves the embodiment shown in the figure. As shown in the figure, a distributed optical fiber sensing system comprises a first erbium-doped fiber amplifier 103, a first Raman amplifier 105, a sensing fiber 110, an erbium-doped fiber 111, and a second Raman amplifier 112. Figure 2 The embodiment improves the embodiment shown in the figure. As shown in the figure, a distributed optical fiber sensing system comprises a first erbium-doped fiber amplifier 103, a first Raman amplifier 105, a sensing fiber 110, an erbium-doped fiber 111, and a second Raman amplifier 112. Figure 1 The embodiment improves the embodiment shown in the figure. As shown in the figure, a distributed optical fiber sensing system comprises a first erbium-doped fiber amplifier 103, a first Raman amplifier 105, a sensing fiber 110, an erbium-doped fiber 111, and a second Raman amplifier 112. Figure 1 The embodiment improves the embodiment shown in the figure. As shown in the figure, a distributed optical fiber sensing system comprises a first erbium-doped fiber amplifier 103, a first Raman amplifier 105, a sensing fiber 110, an erbium-doped fiber 111, and a second Raman amplifier 112.

[0082] In the embodiment of the present application, the sensing fiber 110 at the near end can be selected as 74 km, the erbium-doped fiber 111 is 5 m, and the sensing fiber 110 at the far end is 79.5 km. At this time, the second Raman amplifier 112 is about 153.5 km away from the first Raman amplifier 105 at the far end.

[0083] In the above embodiment, when the optical signal is sent at the far end of the sensing fiber 110, the second Raman amplifier 112 can amplify it. This reverse amplification can compensate for the loss of the optical signal during transmission in the sensing fiber 110, improve the signal-to-noise ratio of the signal, and thereby prolong the transmission distance of the optical signal. In the embodiment shown in the figure, Figure 2 In the embodiment shown in the figure, the distributed optical fiber sensing system can effectively detect a vibration signal of 150 km+, which significantly breaks through the limitation of the traditional detection distance.

[0084] Figure 6 In the embodiment shown in the figure, Figure 2The backscattering light signal strength diagram received by the data processing module 109 in the embodiment is shown. As can be seen, after the 5m erbium-doped optical fiber 111 is added at 74km, the first Raman amplifier 105 is started, and the signal strength near 74km is significantly improved, and the maximum value that can be detected by the signal acquisition device 108 is obviously increased. After the second Raman amplifier 112 is added at the end of the sensing optical fiber 110, the signal amplitude at 150km is significantly enhanced and is comparable to the signal amplitude at 110km.

[0085] In the embodiment, the frequency response is as low as 1.4Hz and as high as 325Hz at a distance of 150km. This extension enables the optical fiber sensing system to capture a wider band of acoustic signals, and provides strong technical support for complex application scenarios such as earthquake monitoring and environmental noise analysis.

[0086] Figure 3 Fig. 3 is a structural schematic diagram of a third distributed optical fiber sensing system according to an embodiment of the present application. The embodiment is improved on the basis of the embodiment shown in Fig. 1. Figure 2 Figure 3 As shown in Fig. 4, a distributed optical fiber sensing system is provided, which is improved on the basis of the embodiment shown in Fig. 1. Figure 2 The embodiment further includes a second erbium-doped optical fiber amplifier 113 connected between the input end of the coupler 106 and the third port of the circulator 104, for amplifying the power of the backscattering light signal. The functions of other same components are the same as those of the embodiment shown in Fig. 1, and will not be repeated here. Figure 2

[0087] In the embodiment, although the distributed optical fiber sensing system can form a backscattering light signal of a vibration signal from a remote place and return it, in order to further improve the power intensity of the backscattering light signal, the second erbium-doped optical fiber amplifier 113 is arranged at the output end of the third port of the circulator 104, so as to amplify the backscattering light signal carrying the external vibration signal. After the amplified backscattering light signal is optoelectronically converted and analog-to-digital converted, a more obvious digital signal can be obtained, which is beneficial to further processing and analysis in the later stage.

[0088] Figure 4 Fig. 5 is a flowchart of a signal processing method according to an embodiment of the present application. As shown in Fig. 5, a signal processing method is provided, which is applied to any one of the distributed optical fiber sensing systems in the above embodiments. Figure 4 Figure 1 The signal processing method includes the following steps.

[0089] S401: The light signal generating device outputs a first continuous light beam and a second continuous light beam.

[0090] ​​​In the embodiment of the present application, the optical signal generating device 101 is configured to output two continuous light beams, wherein the first continuous light beam is used as probe light, and the second continuous light beam is used as local light. Specifically, the optical signal generating device 101 can include a laser and a beam splitter, wherein the laser is configured to generate a continuous laser beam; and the beam splitter is configured to split the laser beam into the first continuous light beam and the second continuous light beam. In the embodiment, the beam splitter splits the laser beam into the first continuous light beam and the second continuous light beam in different proportions according to different probe distances.

[0091] In S402, the first input end of the acousto-optic modulator receives the first continuous light beam and modulates the first continuous light beam into the first pulsed light.

[0092] In the embodiment of the present application, the acousto-optic modulator 102 includes an acousto-optic modulation module and an acousto-optic modulation driving module, wherein the acousto-optic modulation driving module is configured to provide a periodic radio frequency (RF) signal for controlling the opening and closing of the first continuous light beam, thereby controlling the width of the pulse generation. Adjusting the period of the radio frequency signal can adjust the frequency of the final output of the first pulsed light.

[0093] In S403, the first erbium-doped fiber amplifier amplifies the power of the first pulsed light to generate the second pulsed light.

[0094] In the embodiment of the present application, the first erbium-doped fiber amplifier 103 amplifies the first pulsed light output by the acousto-optic modulator 102, thereby enhancing the signal strength to enable the optical signal to be transmitted over a longer distance.

[0095] In S404, the first Raman amplifier amplifies the power of the second pulsed light to generate the third pulsed light.

[0096] In the embodiment of the present application, the first Raman amplifier 105 is arranged at the second port output end of the circulator 104, and is configured to amplify the power of the second pulsed light to obtain the third pulsed light, thereby inputting the third pulsed light into the sensing optical fiber 110. After entering the sensing optical fiber 110, the third pulsed light can generate a backscattered optical signal through Rayleigh scattering, and the backscattered optical signal enters the second port of the circulator 104, and then is output from the third port of the circulator 104.

[0097] In an embodiment, the distributed optical fiber sensing system further includes a second Raman amplifier 112, which is located at the other end of the sensing optical fiber 110 away from the erbium-doped fiber 111. At this time, the signal processing method further includes: the second Raman amplifier 112 amplifies the power of the back-propagating optical signal. The second Raman amplifier 112 can amplify the signal at the far end of the sensing optical fiber 110, which can compensate for the loss of the signal during transmission in the sensing optical fiber 110, improve the signal-to-noise ratio of the signal, and thereby extend the transmission distance of the optical signal.

[0098] S405: The coupler processes the second continuous light beam and the backscattered light signal carrying the external vibration signal and outputs two light signals with the same power.

[0099] In the embodiment, the coupler 106 is a 50:50 coupler 106, which outputs two light signals with the same power after receiving the backscattered light signal output by the third port of the circulator 104 and the second continuous light beam output by the light signal generating device 101. The two light signals with the same power are converted into electrical signals proportional to the light intensity by using the photoelectric effect after entering the photoelectric balance detector 107.

[0100] In another embodiment, the distributed optical fiber sensing system further comprises a second erbium-doped fiber amplifier 113 connected between the input end of the coupler 106 and the third port of the circulator 104, and the signal processing method further comprises: the second erbium-doped fiber amplifier amplifies the power of the backscattered light signal. The second erbium-doped fiber amplifier can further amplify the backscattered light signal, which can improve the intensity of the digital signal generated, and thus facilitate subsequent signal processing and analysis.

[0101] S406: The photoelectric balance detector converts the two light signals with the same power into electrical signals.

[0102] In the embodiment, the two light signals with the same power are converted into electrical signals proportional to the light intensity by using the photoelectric effect after entering the photoelectric balance detector 107.

[0103] S407: The signal acquisition device converts the electrical signals into digital signals.

[0104] In the embodiment, the electrical signals output by the photoelectric balance detector 107 are still analog signals, so the signal acquisition device 108 is needed to perform analog-to-digital conversion to generate digital signals.

[0105] S408: The second input end of the acousto-optic modulator receives the digital signals as trigger signals.

[0106] In the embodiment, the digital signals output by the signal acquisition device 108 are output to the acousto-optic modulation driving module as trigger signals, so as to control the output of the acousto-optic modulation module.

[0107] S409: The data processing module processes the digital signals and outputs the backscattered light signal intensity map.

[0108] In the embodiment, the digital signals are also output to the data processing module 109, so as to process the digital signals and output the backscattered light signal intensity map corresponding to the vibration signal.

[0109] In the above embodiment, through the cooperative action of each module of the distributed optical fiber sensing system, remote detection of the vibration signal can be realized, so that the vibration signal is output in the form of a backscattered light signal intensity diagram, and the characteristic information of the vibration signal can be more intuitively understood.

[0110] Since the digital signal obtained after the backscattered light signal is converted has the characteristics of high nonlinearity and non-stationarity, it is not conducive to the identification of the vibration signal in the later stage. Therefore, the data processing module 109 will preprocess the familiar signal, such as removing noise in the digital signal by noise reduction. However, the threshold setting method of the traditional filter is relatively fixed, and it is difficult to adapt to complex and changeable signal processing.

[0111] In order to solve the above problems, the embodiment of the application also gives a corresponding processing method for the processing process of the data processing module 109 on the digital signal.

[0112] Figure 5 The flowchart of the signal processing method of the data processing module provided by the embodiment of the application is shown in FIG. 10. Figure 5 As shown in FIG. 10, the data processing module 109 processes the digital signal to output the backscattered light signal intensity diagram, and can also include:

[0113] S510: Wavelet decomposition is performed on the digital signal to obtain wavelet coefficients.

[0114] In the embodiment of the application, the digital signal is obtained by sampling the analog signal according to a preset sampling frequency by the signal acquisition module 109. Assuming that the time length of the analog signal is T and the preset sampling frequency is f, then the length of the digital signal is N=Txf.

[0115] In an embodiment, for the input digital signal x(t), the wavelet basis function Ψ j,k (t) is used to decompose the digital signal into wavelet components of different frequencies to obtain wavelet coefficients C j,k , and the formula is:

[0116]

[0117] Wherein, j is the decomposition layer number, and k is the position parameter.

[0118] Wavelet transform decomposes the digital signal into different frequency scales, so that threshold processing can be performed on different scales to remove noise and retain useful information in the original signal.

[0119] S520: Determine the noise threshold of the digital signal according to the statistical information of the wavelet coefficients.

[0120] In the embodiment of the application, the wavelet coefficients are decomposed and approximately normally distributed. In order to estimate the noise threshold of the digital signal, the embodiment first obtains the noise standard deviation of the digital signal according to the statistical information of the wavelet coefficients.

[0121] The noise standard deviation can be directly calculated according to the definition or estimated according to the normal distribution characteristics of the wavelet coefficients. In the embodiment of the application, the median absolute deviation is used to estimate the noise standard deviation σ, and the calculation method is as follows:

[0122]

[0123] Wherein, median(|C j,k |) represents the median of the absolute value of the wavelet coefficient C j,k , and 0.6745 is the conversion coefficient of the median converted into the standard deviation.

[0124] Then, the length N of the digital signal is determined, and the noise threshold λ of the digital signal is determined according to the length of the digital signal and the noise standard deviation. The specific calculation method is as follows:

[0125]

[0126] Compared with the traditional direct calculation method, the median absolute deviation method can estimate the noise standard deviation faster and improve the signal processing speed.

[0127] S530: Perform hard threshold processing on the wavelet coefficients of each layer according to the noise threshold.

[0128] In the embodiment of the application, after the noise threshold λ is determined, the hard threshold method is used to process each layer of wavelet coefficients C j,k , so as to obtain the processed wavelet coefficients The calculation method is as follows:

[0129]

[0130] The VisuShrink adaptive filtering is used in this step, which can adaptively adjust the noise threshold according to the noise level of the digital signal, further optimize the filtering effect, and automatically adjust the filtering strength according to the characteristics of the signal, so that the original characteristics of the signal can be maximally maintained while denoising.

[0131] S540: Reconstruct the backscattering light signal intensity map according to the wavelet coefficients processed by the hard threshold.

[0132] In the embodiment of the application, the processed wavelet coefficients obtained by S530 are used to reconstruct the denoised digital signal The calculation method is as follows:

[0133]

[0134] In the above embodiment, the digital signal is first decomposed into wavelet coefficients of different scales by wavelet transform, then a noise threshold is estimated according to the noise level, and the wavelet coefficients are thresholded according to the noise threshold, and finally the denoised signal is reconstructed by inverse wavelet transform. This embodiment jointly uses wavelet threshold filtering and VisuShrink adaptive filtering, has strong robustness and flexibility, and is particularly suitable for processing signals with high nonlinearity and non-stationarity, such as in the fields of submarine cable monitoring, oil well exploration, biomedical signal processing, seismic data analysis, etc.

[0135] The performance of the above signal processing method applied to a distributed optical fiber sensing system is analyzed below.

[0136] Figure 7 For Figure 5 The single frequency signal processed by the signal processing method in the above embodiment is shown in the comparative diagram. Figure 7 The single frequency signal of 1.4 Hz at 153.5 km is shown in the diagram, where the blue line is the original signal curve diagram, and the red line is the curve diagram after signal processing.

[0137] First, the structural similarity index is introduced. The structural similarity index (SSIM) is an index for measuring image quality, which considers the brightness, contrast and structural information of the image. The closer the value of SSIM is to 1, the better the denoising effect is. The calculation formula is:

[0138]

[0139] Where μ x and are the mean values of the original image and the denoised image, σ x and are their standard deviations, is their covariance, and c1 and c2 are constants.

[0140] After calculation, Figure 7 the SSIM value of the curve after signal processing in the above embodiment is 0.98, which is very close to 1, indicating that the signal after filtering processing successfully retains the main features of the original signal.

[0141] Figure 8 For Figure 7 the image after FFT restoration of the single frequency signal. Figure 8The image after the FFT reduction of the 1.4Hz single frequency signal at 153.5km, wherein the blue curve is the original frequency spectrum signal and the red curve is the filtered frequency spectrum signal.

[0142] The following introduces the signal to noise ratio, signal to noise ratio (SNR) is an important indicator to measure the effect of denoising, indicating the ratio of signal power to noise power. After denoising, if the signal to noise ratio is improved, it means that the denoising effect is better.

[0143] After analysis, the signal amplitude after filtering processing only decreased by 2.6%, while the signal to noise ratio was significantly improved by about 75.67%, from 12.41dB to 21.80dB, therefore, the above signal processing method can obviously improve the signal to noise ratio.

[0144] Figure 9 For Figure 5 The digital signal restoration effect diagram of the embodiment shown in the figure after signal processing. Figure 9 It shows that the signal still maintains high quality after long distance transmission. Figure 9 The left side (a) of the figure shows that the black and white vertical bar pattern clearly shows the periodic change of the signal, Figure 9 The right side (b) of the figure shows that the phase change curve presents a regular sinusoidal waveform, which shows that the signal maintains good periodicity and consistency during long distance transmission, and the end signal quality is high, without significant distortion or interference.

[0145] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A distributed optical fiber sensing system, characterized by, The application relates to a kind of optical signal detection devices and methods. The application comprises: An optical signal generating device, an acousto-optic modulator, a first erbium-doped fiber amplifier, a circulator, a first Raman amplifier, an erbium-doped fiber, a sensing fiber, a coupler, a photoelectric balance detector, a signal acquisition device, and a data processing module. The optical signal generating device is configured to output a first continuous light beam and a second continuous light beam. A first input end of the acousto-optic modulator receives the first continuous light beam and is configured to modulate the first continuous light beam into a first pulsed light. The first erbium-doped fiber amplifier is connected between an output end of the acousto-optic modulator and a first port of the circulator, and is configured to amplify the power of the first pulsed light to generate a second pulsed light. A second port of the circulator is connected to an input end of the first Raman amplifier, and the first Raman amplifier is configured to amplify the power of the second pulsed light to generate a third pulsed light. A third port of the circulator outputs a backscattered light signal carrying an external vibration signal. The erbium-doped fiber is connected in series in the sensing fiber, the first Raman amplifier is located at an input end of the sensing fiber, and the first Raman amplifier inputs the third pulsed light into the sensing fiber. The erbium-doped fiber is arranged at a position 74 km away from the first Raman amplifier in the sensing fiber and has a length of 5 meters. The erbium-doped fiber is configured to enhance the intensity of the light signal through stimulated emission. The three-stage amplification structure of the first erbium-doped fiber amplifier, the first Raman amplifier, and the erbium-doped fiber enables the light signal to be transmitted in the sensing fiber for more than 125 km. An input end of the coupler is connected to the optical signal generating device and the third port of the circulator. The coupler is configured to process the second continuous light beam and the backscattered light signal and output two light signals with the same power to the photoelectric balance detector. The photoelectric balance detector is configured to convert the two light signals with the same power into electrical signals. An input end of the signal acquisition device is connected to an output end of the photoelectric balance detector. The signal acquisition device is configured to convert the electrical signals into digital signals. A second input end of the acousto-optic modulator receives the digital signals as a trigger signal to control the output of the acousto-optic modulator. A data processing module is connected to an output end of the signal acquisition device. The data processing module is configured to process the digital signals and output a backscattered light signal intensity map. The data processing module adopts a joint processing mode of wavelet threshold filtering and VisuShrink adaptive filtering to perform noise reduction processing on the digital signals. The data processing module performs wavelet decomposition on the digital signals to obtain wavelet coefficients, determines a noise threshold of the digital signals according to statistical information of the wavelet coefficients, performs hard threshold processing on the wavelet coefficients of each layer according to the noise threshold, and reconstructs the digital signals according to the wavelet coefficients after the hard threshold processing to obtain the backscattered light signal intensity map.

2. The distributed optical fiber sensing system of claim 1, wherein, The optical signal generating device comprises a laser configured to generate a continuous laser beam and a beam splitter configured to split the continuous laser beam into a first continuous light beam and a second continuous light beam. The beam splitter splits the continuous laser beam into a first continuous light beam with a power of 90% and a second continuous light beam with a power of 10%.

3. The distributed optical fiber sensing system of claim 1, wherein, The second Raman amplifier is located at the other end of the sensing fiber away from the erbium-doped fiber, and is used for amplifying the power of the backward transmission optical signal.

4. The distributed optical fiber sensing system of claim 1, wherein, The second erbium-doped fiber amplifier is connected between the input end of the coupler and the third port of the circulator, and is used for amplifying the power of the backscattered optical signal.

5. A signal processing method characterized by, The method is applied to the distributed optical fiber sensing system according to any one of claims 1 to 4, and the method comprises: The optical signal generating device outputs a first continuous light beam and a second continuous light beam, wherein the optical signal generating device comprises: a laser for generating a continuous laser beam; and a beam splitter for splitting the laser beam into the first continuous light beam and the second continuous light beam; The first input end of the acousto-optic modulator receives the first continuous light beam and modulates the first continuous light beam into a first pulsed light; The first erbium-doped fiber amplifier amplifies the power of the first pulsed light to generate a second pulsed light; The first Raman amplifier amplifies the power of the second pulsed light to generate a third pulsed light; The coupler processes the second continuous light beam and the backscattered optical signal carrying the external vibration signal and outputs two optical signals with the same power; The photoelectric balance detector converts the two optical signals with the same power into electrical signals; The signal acquisition device converts the electrical signals to obtain digital signals; The second input end of the acousto-optic modulator receives the digital signals as a trigger signal for controlling the output of the acousto-optic modulator; The data processing module processes the digital signals and outputs a backscattered optical signal intensity map, wherein the data processing module adopts a joint processing mode of wavelet threshold filtering and VisuShrink adaptive filtering to perform noise reduction processing on the digital signals, including: performing wavelet decomposition on the digital signals to obtain wavelet coefficients, determining a noise threshold of the digital signals according to statistical information of the wavelet coefficients, performing hard threshold processing on the wavelet coefficients of each layer according to the noise threshold, and reconstructing the digital signals according to the wavelet coefficients after the hard threshold processing to obtain the backscattered optical signal intensity map.

6. The signal processing method of claim 5, wherein, The determination of the noise threshold of the digital signals according to the statistical information of the wavelet coefficients comprises: obtaining a noise standard deviation of the digital signals according to the statistical information of the wavelet coefficients; determining the length of the digital signals; determining the noise threshold of the digital signals according to the length of the digital signals and the noise standard deviation.

7. The signal processing method of claim 5, wherein, The distributed optical fiber sensing system further comprises a second Raman amplifier located at the other end of the sensing fiber away from the erbium-doped fiber; and the method further comprises: The second Raman amplifier amplifies the power of the backward transmission optical signal.

8. The signal processing method of claim 5, wherein, The distributed optical fiber sensing system further comprises a second erbium-doped fiber amplifier connected between the input end of the coupler and the third port of the circulator; and the method further comprises: The second erbium-doped fiber amplifier amplifies the power of the backscattered optical signal.

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