Distributed optical fiber sensing system and signal processing method

Abstract

The invention provides a distributed optical fiber sensing system and a signal processing method, and belongs to the technical field of optical fiber sensing. The distributed optical fiber sensing system comprises an optical signal generation device, an acoustic optical modulator, a first erbium-doped optical fiber amplifier, a circulator, a first Raman amplifier, an erbium-doped optical fiber, a sensing optical fiber, a coupler, a photoelectric balance detector, a signal acquisition device and a data processing module. Before an optical signal enters the sensing optical fiber, the optical signal entering the sensing optical fiber is amplified through the first erbium-doped optical fiber amplifier and the first Raman amplifier, so that the transmission distance of the optical signal in the sensing optical fiber is increased, and then the transmission distance of the optical signal is further increased through the erbium-doped optical fiber additionally arranged in the sensing optical fiber; therefore, the sensing optical fiber can generate a back scattering light signal carrying a vibration signal at a farther distance, and the back scattering light signal is correspondingly processed to obtain a back scattering light signal intensity graph, so that remote signal monitoring is realized.

Description

Technical Field

[0001] The present application belongs to the field of optical fiber sensing technology, and specifically, relates to a distributed optical fiber sensing system and a signal processing method. Background Art

[0002] With the continuous advancement of science and technology, Distributed Acoustic Sensing (DAS) has been widely used in urban construction, industrial production and other fields. As a new type of passive sensing technology, DAS technology uses the transmission characteristics of optical fiber to achieve signal transmission and measurement in the same optical fiber. The resulting backscattered light can provide sound field information in the spatial domain. Under long distances and high temporal resolution, DAS technology will produce a serious signal-to-noise ratio drop during signal transmission, thus 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 amplifier, and the relay amplifier needs to introduce multiple high-performance optical amplifiers and filters. If the transmission distance is to be further extended, the number of relay amplifiers can be increased.

[0004] However, in the above technology, the structure of the relay amplifier device is relatively complex. When it is introduced into the distributed fiber optic sensing system, the difficulty of system production and debugging will be significantly increased. Moreover, when more relay amplifier devices are introduced to increase the detection distance, the fiber optic sensing system will become more complex. Summary of the invention

[0005] In view of the problem of complex structure of long-distance signal detection in existing fiber optic sensing systems, the present application aims to provide a distributed fiber optic sensing system and a signal processing method, which can achieve long-distance signal detection with 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 fiber, a coupler, a photoelectric balanced detector, a signal acquisition device, and a data processing module;

[0007] The optical signal generating device is used 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 used to modulate the first continuous light beam into a first pulse 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 the first erbium-doped fiber amplifier is used to amplify the power of the first pulse light to generate a second pulse light;

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

[0011] Both ends of the erbium-doped optical fiber are connected to the sensing optical fiber, the first Raman amplifier is located at one end of the sensing optical fiber away from the erbium-doped optical fiber, and the first Raman amplifier inputs the third pulse 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, the coupler is used to process the second continuous light beam and the backscattered light signal and output two optical signals with the same power to the photoelectric balanced detector, and the photoelectric balanced detector is used to convert the two optical signals with the same power into electrical signals;

[0013] The input end of the signal acquisition device is connected to the output end of the photoelectric balance detector, the signal acquisition device is used 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 used to process the digital signal and output a backscattered light signal intensity graph.

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

[0016] A laser for generating a continuous laser beam;

[0017] The beam splitter is used to split the laser beam into a first continuous beam and a second continuous beam.

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

[0019] In a possible implementation manner, 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 optical fiber and is used to amplify the power of the reversely transmitted optical signal.

[0020] In a possible implementation manner, a second erbium-doped fiber amplifier is further included, 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 to amplify the power of the backscattered optical signal.

[0021] In a second aspect, the present application further provides a signal processing method, which is applied to the system described in any implementation manner of the first aspect, and the method includes:

[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 pulse light;

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

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

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

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

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

[0029] The second input terminal of the acousto-optic modulator receives the digital signal as a trigger signal;

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

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

[0032] Performing wavelet decomposition on the digital signal to obtain wavelet coefficients;

[0033] Determining a noise threshold of a digital signal according to the statistical information of the wavelet coefficients;

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

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

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

[0037] Obtaining a 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] The noise threshold of the digital signal is determined 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 includes a second erbium-doped optical fiber amplifier, and the second erbium-doped optical fiber amplifier is connected between the input end of the coupler and the third port of the circulator; the method further includes:

[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 includes a second Raman amplifier, and the second Raman amplifier is located at the other end of the sensing optical fiber away from the erbium-doped optical fiber; the method further includes:

[0043] The second Raman amplifier amplifies the power of the reversely transmitted optical signal.

[0044] The present application provides a distributed optical fiber sensing system and a signal processing method, wherein the distributed optical fiber sensing system includes: an optical signal generating device, an acousto-optic modulator, a first erbium-doped optical fiber amplifier, a circulator, a first Raman amplifier, an erbium-doped optical fiber, a sensing optical fiber, a coupler, a photoelectric balanced detector, a signal acquisition device and a data processing module. Before the optical signal enters the sensing optical fiber, the present application amplifies the optical signal entering the sensing optical fiber through the first erbium-doped optical fiber amplifier and the first Raman amplifier, so that the optical signal still has a certain intensity when it is transmitted to 75km. Since the present application also adds a section of erbium-doped optical fiber between the sensing optical fibers, the erbium ions excited in the erbium-doped optical 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 undergo Rayleigh scattering at the farthest transmission distance and return a backscattered optical signal carrying a vibration signal. After the backscattered optical signal is processed accordingly, a backscattered optical signal intensity graph is obtained, thereby realizing long-distance signal monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

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

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

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

[0049] Figure 4 A flowchart of a signal processing method provided in an embodiment of the present application;

[0050] Figure 5 A flowchart of a signal processing method for a data processing module provided in an embodiment of the present application;

[0051] Figure 6 for Figure 2 A graph of the intensity of backscattered light signals received by the data processing module in the illustrated embodiment;

[0052] Figure 7 for Figure 5 A comparison diagram of single frequency signals before and after signal processing in the illustrated embodiment;

[0053] Figure 8 for Figure 7 The image of the single frequency signal after FFT restoration;

[0054] Fig. 9 for Figure 5 A diagram showing the signal restoration effect of the distributed optical fiber sensing system of the illustrated embodiment.

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

[0056] Description of reference numerals:

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

[0058] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0059] In the embodiments of the present application, words such as "first" and "second" are used to distinguish the same or similar items with substantially the same functions and effects. Those skilled in the art can understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit the difference.

[0060] It should be noted that in the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a concrete way. In the embodiments of the present application, "at least one" refers to one or more, and "more than one" refers to two or more.

[0061] It should be noted that the “at…” in the embodiments of the present application may be the instant when a certain situation occurs, or may be a period of time after the occurrence of a certain situation, and the embodiments of the present application do not specifically limit this.

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

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

[0064] Circulator: A circulator is a multi-port device that transmits the incident wave entering any port to the next port in the order determined by the static bias magnetic field. Generally, a circulator is a three-port device. When the signal enters from the first port in the direction determined by the static bias magnetic field, the signal will be output from the second port; when the signal enters from 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 advancement of science and technology, distributed fiber optic acoustic wave sensing technology has been widely used in urban construction, industrial production and other fields. As a new type of passive sensing technology, distributed fiber optic acoustic wave sensing technology uses the transmission characteristics of optical fiber to realize signal transmission and measurement in the same optical fiber. The resulting backscattered light signal can provide sound field information in the spatial domain. However, under long distances and high temporal resolution, the distributed fiber optic acoustic wave sensing technology will produce a serious signal-to-noise ratio drop during the transmission process, thereby affecting the detection efficiency and accuracy of the distributed fiber optic acoustic wave sensing system. In some existing technologies, the distributed fiber optic sensing system will introduce at least one relay amplifier to increase the signal transmission distance, and the structure of the relay amplifier is mostly complex, which will make the production and debugging process of the equipment more difficult, and correspondingly increase the detection cost.

[0066] In order 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 includes: 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. Before the optical signal enters the sensing fiber, the optical signal entering the sensing fiber is amplified by the first erbium-doped fiber amplifier and the first Raman amplifier, so that the optical signal can be transmitted over a longer distance for detection. Since the present application also adds a section of erbium-doped fiber between the sensing fibers, the erbium ions excited in the erbium-doped fiber interact with the optical signal with enhanced power, thereby 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 undergo Rayleigh scattering at the farthest transmission distance and return a backscattered optical signal carrying a vibration signal. After the backscattered optical signal is processed accordingly, a backscattered optical signal intensity graph is obtained, thereby realizing long-distance signal monitoring.

[0067] Figure 1 FIG. 1 is a schematic diagram of the structure of the first distributed optical fiber sensing system according to an embodiment of the present application. 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 balanced detector 107, a signal acquisition device 108 and a data processing module 109.

[0068] Among them, the optical signal generating device 101 is used to output a first continuous light beam and a second continuous light beam; the first input end of the acousto-optic modulator 102 receives the first continuous light beam and is used to modulate the first continuous light beam into a first pulse light; the first erbium-doped fiber amplifier 103 is connected between the output end of the acousto-optic modulator 102 and the first port of the circulator 104, and the first erbium-doped fiber amplifier 103 is used to amplify the power of the first pulse light to generate a second pulse light; the second port of the circulator 104 is connected to the input end of the first Raman amplifier 105, and the first Raman amplifier 105 is used to amplify the power of the second pulse light to generate a third pulse light, and 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, and the first Raman amplifier 105 is located at the sensing fiber 110 away from the erbium-doped fiber 111. One end of the optical fiber 111, and the first Raman amplifier 105 inputs the third pulse light into the sensing optical 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 is used to process the second continuous light beam and the backscattered light signal and output two optical signals with the same power to the photoelectric balanced detector 107, the photoelectric balanced detector 107 is used to convert the two optical signals with the same power into electrical signals; the input end of the signal acquisition device 108 is connected to the output end of the photoelectric balanced detector 107, the signal acquisition device 108 is used to convert the electrical signal into a digital signal, and 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 is used to process the digital signal and output a backscattered light signal intensity map.

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

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

[0071] In the embodiment of the present application, the acousto-optic modulator 102 is used to modulate the first continuous light beam into a first pulse light of a certain detection frequency, and the detection frequency and power of the first pulse light can be adjusted. Specifically, the acousto-optic modulator 102 may include an acousto-optic modulation module and an acousto-optic modulation driving module, wherein the acousto-optic modulation driving module is used to provide a periodic radio frequency (RF) signal to the acousto-optic modulation module to control the opening and closing of the first continuous light beam, thereby controlling the width of the pulse generation. By adjusting the period of the RF signal, the frequency of the final output of the first pulse light can be adjusted.

[0072] In the embodiment of the present application, the first erbium-doped fiber amplifier 103 amplifies the first pulse light output by the acousto-optic modulator 102, thereby enhancing the signal strength so that the optical signal can be transmitted over a longer distance.

[0073] In the embodiment of the present application, the circulator 104 is operated in the order of the first port, the second port, and the third port. The second pulse 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 pulse light is output from the second port of the circulator 104, and is transmitted to the input end of the first Raman amplifier 105. The first Raman amplifier 105 is used to further enhance the power intensity of the optical signal, thereby outputting the third pulse light.

[0074] In the embodiment of the present application, the third pulse light reaching a certain power enters the sensing optical fiber 110 for transmission. In the sensing system without the first Raman amplifier 105, the intensity of the optical signal will generally be significantly weakened at 75 km of the sensing optical fiber 110. In the present embodiment, since the first Raman amplifier 105 is added, the optical signal transmission still has a certain intensity at 75 km. At this time, in order to further increase the transmission distance, the present embodiment considers adding a section of erbium-doped optical fiber of several meters at 74 km of the forward transmission of the sensing optical fiber 110 to connect to the next section of the sensing optical fiber 110. When the third pulse light output by the first Raman amplifier 105 enters the erbium-doped optical fiber, the power intensity of the third pulse light can excite the erbium ions in the erbium-doped optical fiber, causing it to transition from the ground state (low energy level) to the excited state (high energy level), and the interaction between the optical signal and the excited erbium ions is stimulated emission, generating new photons with the same phase and frequency as the incident signal light (the third pulse light). These newly generated photons form a coherent superposition with the incident signal light, thereby enhancing the intensity of the signal light and further increasing the transmission distance of the optical signal.

[0075] In the embodiment of the present application, when the optical signal enters the sensing optical fiber 110, a backscattered optical signal carrying a 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 in the reverse direction. 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 present 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 balanced detector 107, the photoelectric effect is used to convert the optical signal into an electrical signal proportional to the light intensity. It should be noted that the two optical signals with the same power output by the coupler 106 enter the photoelectric balanced detector 107 for differential detection, which is conducive to suppressing common mode noise and improving the sensitivity and signal-to-noise ratio of the optical signal, which is very important in optical fiber sensing.

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

[0078] In the embodiment of the present application, the digital signal is the far-end vibration signal detected in the optical fiber sensing system. In order to analyze the vibration signal, it is necessary to process the digital signal through the data processing module 109 to output the backscattered light signal intensity diagram corresponding to the vibration signal.

[0079] It should be noted that the sensing optical fiber of the present application adopts single-mode optical fiber, which can reduce the transmission loss of optical signals and increase the transmission distance. In addition, single-mode optical fiber has low cost and is a widely used standard optical fiber.

[0080] In the above embodiment, the optical signal is amplified by the first erbium-doped fiber amplifier 103 and the first Raman amplifier 105 before entering the sensing optical fiber 110, so that the optical signal still has a certain intensity when it is transmitted to 75 km. Since a section of erbium-doped optical fiber 111 is added between the sensing optical fiber 110, the erbium ions excited in the erbium-doped optical fiber 111 interact with the optical signal with enhanced power, thereby enhancing the intensity of the optical signal, thereby further improving the transmission distance of the optical signal. At this time, the optical signal can also undergo Rayleigh scattering at the farthest transmission distance and transmit back the backscattered optical signal carrying the vibration signal. After the backscattered optical signal is processed accordingly, a backscattered optical signal intensity graph is obtained, thereby realizing long-distance signal monitoring. Figure 1 In the illustrated embodiment, the distributed optical fiber sensing system is capable of effectively detecting vibration signals at a distance of 125 km.

[0081] Figure 2 FIG. 1 is a schematic diagram of the structure of a second distributed optical fiber sensing system according to an embodiment of the present application. Figure 1 Improvements are made based on the embodiments shown. Figure 2 As shown, a distributed optical fiber sensing system, which Figure 1 The embodiment 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 optical fiber 111 and is used to amplify the power of the reversely transmitted optical signal. Figure 1 The functions of the embodiments shown are the same and will not be described in detail here.

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

[0083] In the above embodiment, when the optical signal is sent from the far end of the sensing optical fiber 110, the second Raman amplifier 112 can amplify it. This reverse amplification can compensate for the loss of the signal when it is transmitted in the sensing optical fiber 110, improve the signal-to-noise ratio of the signal, and thus extend the transmission distance of the optical signal. Figure 2 In the illustrated embodiment, the distributed optical fiber sensing system is capable of effectively detecting vibration signals over 150 km, significantly breaking through the limitations of traditional detection distances.

[0084] Figure 6 for Figure 2The backscattered light signal intensity diagram received by the data processing module 109 in the embodiment shown. It can be seen that after adding 5m of erbium-doped optical fiber 111 after 74km in the embodiment of the present application, the first Raman amplifier 105 is started, and the signal intensity near 74km is significantly improved. It can be seen that the maximum value that can be detected by the signal acquisition device 108 is significantly increased; after adding the second Raman amplifier 112 at the end of the sensing optical fiber 110, the signal amplitude at 150km is significantly enhanced and is equivalent to the signal amplitude at 110km.

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

[0086] Figure 3 FIG. 1 is a schematic diagram of the structure of a third distributed optical fiber sensing system according to an embodiment of the present application. Figure 2 Improvements are made based on the embodiments shown. Figure 3 As shown, a distributed optical fiber sensing system, which Figure 2 The embodiment further includes a second erbium-doped fiber amplifier 113, which is connected between the input end of the coupler 106 and the third port of the circulator 104, and is used to amplify the power of the backscattered optical signal. Figure 2 The functions of the embodiments shown are the same and will not be described in detail here.

[0087] In the embodiment of the present application, although the distributed optical fiber sensing system can form a backscattered optical signal from a distant vibration signal for backtransmission, in order to further improve the power intensity of the backscattered optical signal, the present embodiment sets a second erbium-doped optical fiber amplifier 113 at the output end of the third port of the circulator 104, so as to amplify the backscattered optical signal carrying the external vibration signal. After the amplified backscattered optical signal undergoes photoelectric conversion and analog-to-digital conversion, a more obvious digital signal can be obtained, which is conducive to further processing and analysis at a later stage.

[0088] Figure 4 A flow chart of a signal processing method provided in an embodiment of the present application. Figure 4 As shown, a signal processing method is applied to any of the distributed optical fiber sensing systems in the above embodiments. Figure 1 Taking the distributed optical fiber sensing system shown in FIG. as an example, the signal processing method includes:

[0089] S401: The optical 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 used to output two continuous light beams, wherein the first continuous light beam is used as a detection light, and the second continuous light beam is used as a local light. Specifically, the optical signal generating device 101 may include a laser and a beam splitter, wherein the laser is used to generate a continuous laser beam; and the beam splitter is used to split the laser beam into a first continuous light beam and a second continuous light beam. In this 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 detection distances.

[0091] S402: 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 pulse 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 used to provide a periodic radio frequency (RF) signal to control the opening and closing of the first continuous light beam, thereby controlling the width of the pulse generation. By adjusting the period of the RF signal, the frequency of the final output of the first pulse light can be adjusted.

[0093] S403: The first erbium-doped fiber amplifier amplifies the power of the first pulse light to generate a second pulse light.

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

[0095] S404: The first Raman amplifier amplifies the power of the second pulse light to generate a third pulse light.

[0096] In the embodiment of the present application, the first Raman amplifier 105 is disposed at the output end of the second port of the circulator 104, and is used to amplify the power of the second pulse light to obtain the third pulse light, so as to input the third pulse light into the sensing optical fiber 110. After entering the sensing optical fiber 110, the third pulse light can generate a backscattered light signal through Rayleigh scattering, enter the second port of the circulator 104, and then be output from the third port of the circulator 104.

[0097] In one 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 optical fiber 111. In this case, the signal processing method further includes: the second Raman amplifier 112 amplifies the power of the reversely transmitted optical signal. The second Raman amplifier 112 can directional 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 thus 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 optical signals with the same power.

[0099] In the embodiment of the present application, the coupler 106 is a 50:50 coupler 106, which outputs two optical signals with the same power after receiving the backscattered optical signal output by the third port of the circulator 104 and the second continuous optical beam output by the optical signal generating device 101. After the two optical signals with the same power enter the photoelectric balanced detector 107, the photoelectric effect is used to convert the optical signals into electrical signals proportional to the light intensity.

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

[0101] S406: The photoelectric balanced detector converts two optical signals of equal power into electrical signals.

[0102] In the embodiment of the present application, after two optical signals with the same power enter the photoelectric balance detector 107, the photoelectric effect is used to convert the optical signals into electrical signals proportional to the light intensity.

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

[0104] In the embodiment of the present application, the electrical signal output by the photoelectric balance detector 107 is still only an analog signal, so it is necessary to use the signal acquisition device 108 to perform analog-to-digital conversion to generate a digital signal.

[0105] S408: The second input terminal of the AOM receives the digital signal as a trigger signal.

[0106] In the embodiment of the present application, the digital signal output by the signal acquisition device 108 is output to the acousto-optic modulation driving module as a trigger signal, thereby controlling the output of the acousto-optic modulation module.

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

[0108] In the embodiment of the present application, the digital signal is also output to the data processing module 109, so as to process the digital signal and output a backscattered light signal intensity map corresponding to the vibration signal.

[0109] In the above embodiment, through the coordinated action of various modules of the distributed optical fiber sensing system, long-distance detection of vibration signals can be achieved, and the vibration signals can be output in the form of backscattered light signal intensity diagrams, so that the characteristic information of the vibration signals can be understood more intuitively.

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

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

[0112] Figure 5 Flow chart of the signal processing method of the data processing module provided in the embodiment of the present application. Figure 5 As shown, the data processing module 109 processes the digital signal to output a backscattered light signal intensity graph, and may also include:

[0113] S510: Perform wavelet decomposition on the digital signal to obtain wavelet coefficients.

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

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

[0116]

[0117] Among them, j is the number of decomposition levels and k is the location parameter.

[0118] Wavelet transform decomposes digital signals into different frequency scales, and then performs threshold processing at different scales, which can remove noise and retain useful information in the original signal.

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

[0120] In the embodiment of the present application, the wavelet coefficients are decomposed into a roughly normal distribution. In order to estimate the noise threshold of the digital signal, the embodiment first obtains the noise standard deviation of the digital signal based on the statistical information of the wavelet coefficients.

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

[0122]

[0123] Among them, median(|C j,k |) represents the wavelet coefficient C j,k The median in absolute value, 0.6745 is the conversion factor from median to standard deviation.

[0124] Next, determine the length N of the digital signal, and determine the noise threshold λ of the digital signal based on 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 more quickly 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 present application, after the noise threshold λ is determined, for each layer of wavelet coefficients C j,k , using the hard threshold method to obtain the processed wavelet coefficients The calculation method is as follows:

[0129]

[0130] This step uses VisuShrink adaptive filtering, which can use the noise level of the digital signal to adaptively adjust the noise threshold, and can further optimize the filtering effect, so that the processing of the digital signal can automatically adjust the filtering strength according to the characteristics of the signal, thereby maximally maintaining the original characteristics of the signal while removing noise.

[0131] S540: Reconstruct the digital signal according to the wavelet coefficients after hard threshold processing to obtain a backscattered light signal intensity map.

[0132] In the embodiment of the present application, the processed wavelet coefficients obtained in 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 the noise threshold is estimated according to the noise level, and the wavelet coefficients are threshold processed according to the noise threshold, and finally the denoised signal is reconstructed by inverse wavelet transform. This embodiment combines wavelet threshold filtering and VisuShrink adaptive filtering, which has strong robustness and flexibility, and is particularly suitable for processing signals with highly nonlinear and non-stationary characteristics, 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 the distributed fiber optic sensing system is analyzed below.

[0136] Figure 7 for Figure 5 A comparison diagram of single frequency signals after signal processing in the illustrated embodiment. Figure 7 This is a single-frequency signal diagram of 1.4 Hz at 153.5 km. The blue line is the original signal curve and the red line is the curve after signal processing.

[0137] The following first introduces the structural similarity index. The structural similarity index (SSIM) is an indicator for measuring image quality, which takes into account the brightness, contrast and structural information of the image. The closer the SSIM value is to 1, the better the denoising effect is. The calculation formula is:

[0138]

[0139] Among them, μ x and are the means of the original image and the denoised image, σ x and is their standard deviation, is their covariance, c1 and c2 are constants.

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

[0141] Figure 8 for Figure 7 The image after the single frequency signal is restored by FFT. Figure 8The image shows the 1.4 Hz single-frequency signal at 153.5 km after FFT restoration. The blue curve is the original spectrum signal and the red curve is the filtered spectrum signal.

[0142] The following introduces the signal-to-noise ratio. The signal-to-noise ratio (SNR) is an important indicator for measuring the denoising effect, which represents 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 good.

[0143] After analysis, it is found that the signal amplitude only decreases by 2.6% after filtering, while the signal-to-noise ratio is significantly improved by about 75.67%, from 12.41dB to 21.80dB. Therefore, the above signal processing method can significantly improve the signal-to-noise ratio.

[0144] Fig. 9 for Figure 5 The digital signal restoration effect diagram of the embodiment shown is after signal processing. Fig. 9 It shows that the signal maintains high quality after long distance transmission. Fig. 9 The left side of the picture (a) shows a black and white vertical stripe pattern that clearly shows the periodic changes of the signal. Fig. 9 The figure on the middle right (b) shows that the phase change curve presents a regular sinusoidal wave shape, which indicates that the signal not only maintains good periodicity and consistency during long-distance transmission, but also has high signal quality at the end without significant distortion or interference.

[0145] Obviously, those skilled in the art can make various changes and modifications 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 equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A distributed optical fiber sensing system, characterized in that: include: 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 balanced detector, a signal acquisition device and a data processing module; The optical signal generating device is used to output a first continuous light beam and a second continuous light beam; The first input end of the acousto-optic modulator receives the first continuous light beam, and is used to modulate the first continuous light beam into a first pulse light; 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 the first erbium-doped fiber amplifier is used to amplify the power of the first pulse light to generate a second pulse light; The second port of the circulator is connected to the input end of the first Raman amplifier, the first Raman amplifier is used to amplify the power of the second pulse light to generate a third pulse light, and the third port of the circulator outputs a backscattered light signal carrying an external vibration signal; Both ends of the erbium-doped optical fiber are connected to the sensing optical fiber, the first Raman amplifier is located at one end of the sensing optical fiber away from the erbium-doped optical fiber, and the first Raman amplifier inputs the third pulse light into the sensing optical fiber; The input end of the coupler is connected to the optical signal generating device and the third port of the circulator, the coupler is used to process the second continuous light beam and the backscattered light signal and output two optical signals with the same power to the photoelectric balanced detector, and the photoelectric balanced detector is used to convert the two optical signals with the same power into electrical signals; The input end of the signal acquisition device is connected to the output end of the photoelectric balance detector, the signal acquisition device is used 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; The data processing module is connected to the output end of the signal acquisition device and is used to process the digital signal and output a backscattered light signal intensity graph.

2. The distributed optical fiber sensing system according to claim 1, characterized in that: The optical signal generating device comprises: A laser for generating a continuous laser beam; The beam splitter is used to split the laser beam into a first continuous beam and a second continuous beam.

3. The distributed optical fiber sensing system according to claim 2, characterized in that: The beam splitter splits the laser beam into 90% of a first continuous beam and 10% of a second continuous beam.

4. The distributed optical fiber sensing system according to claim 1, characterized in that: It also includes a second Raman amplifier, which is located at the other end of the sensing optical fiber away from the erbium-doped optical fiber and is used to amplify the power of the reversely transmitted optical signal.

5. The distributed optical fiber sensing system according to claim 1, characterized in that: It also includes a second erbium-doped fiber amplifier, which is connected between the input end of the coupler and the third port of the circulator and is used to amplify the power of the backscattered optical signal.

6. A signal processing method, characterized in that: Applied to the distributed optical fiber sensing system according to any one of claims 1 to 5, the method comprises: The optical signal generating device outputs a first continuous light beam and a 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 pulse light; The first erbium-doped fiber amplifier amplifies the power of the first pulse light to generate a second pulse light; The first Raman amplifier amplifies the power of the second pulse light to generate a third pulse light; The coupler processes the second continuous light beam and the backscattered light 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 signal into a digital signal; The second input terminal of the acousto-optic modulator receives the digital signal as a trigger signal; The data processing module processes the digital signal and outputs a backscattered light signal intensity graph.

7. The signal processing method according to claim 6, characterized in that: The data processing module processes the digital signal to output a backscattered light signal intensity graph, including: Performing wavelet decomposition on the digital signal to obtain wavelet coefficients; Determining a noise threshold of a digital signal according to the statistical information of the wavelet coefficients; Hard threshold processing is performed on the wavelet coefficients of each layer according to the noise threshold; The digital signal is reconstructed according to the wavelet coefficients after hard threshold processing to obtain the backscattered light signal intensity map.

8. The signal processing method according to claim 7, characterized in that: Determining the noise threshold of the digital signal according to the statistical information of the wavelet coefficients includes: Obtaining a noise standard deviation of the digital signal according to the statistical information of the wavelet coefficients; determining the length of the digital signal; The noise threshold of the digital signal is determined according to the length of the digital signal and the noise standard deviation.

9. The signal processing method according to claim 6, characterized in that: The distributed optical fiber sensing system further comprises a second Raman amplifier, wherein the second Raman amplifier is located at the other end of the sensing optical fiber away from the erbium-doped optical fiber; the method further comprises: The second Raman amplifier amplifies the power of the reversely transmitted optical signal.

10. The signal processing method according to claim 6, characterized in that: The distributed optical fiber sensing system further comprises a second erbium-doped optical fiber amplifier, wherein the second erbium-doped optical fiber amplifier is connected between the input end of the coupler and the third port of the circulator; the method further comprises: The second erbium-doped fiber amplifier amplifies the power of the backscattered light signal.

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