Distributed optical fiber sensing system and method

Abstract

The invention belongs to the technical field of optical fiber sensing, and discloses a distributed optical fiber sensing system and method. A narrow linewidth laser is used for emitting continuous laser, a coupler is used for dividing the continuous laser into two paths, one path serves as a local oscillator signal to be input into a receiving unit, and the other path serves as a detection signal to be input into a second modulation unit; the first modulation unit is used for generating an electric modulation signal, and the second modulation unit introduces random phase coding under the action of the electric modulation signal, modulates the amplitude and phase of a detection signal and outputs pulsed light; the amplified pulsed light is output to an optical fiber through a circulator, and a Rayleigh backscattering signal generated by the optical fiber is output to a receiving unit; performing beat frequency on the local oscillator signal and the Rayleigh backscattering signal by using a receiving unit to generate an electric signal; and the data acquisition unit is used for acquiring sensing information. The system has the capability of measuring the power and phase distribution of Rayleigh backscattering signals at the same time, and functions which can be completed by two sets of systems originally can be completed by one set of system.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and more specifically, relates to a distributed optical fiber sensing system and method. Background Art

[0002] Optical fiber communication networks are a key component and supporting base of my country's digital infrastructure. With the continuous growth of data transmission demand, the management of large-scale optical fiber networks requires more intelligent monitoring technology. Real-time perception and regulation of link status during data transmission has become a new research trend and hot spot. Distributed optical fiber sensing technology uses optical fiber as the transmission medium and sensing unit of the signal. By detecting the changes in the intensity, phase, polarization state and other parameters of the optical signal in the optical fiber under the action of the external field, it realizes the continuous distributed measurement of external parameters along the optical fiber, thus becoming the most ideal non-destructive health monitoring technology in optical communication networks.

[0003] Distributed fiber optic sensing technology can be divided into several types according to its principles or monitoring parameters. The more common types used in optical communication networks are optical time-domain reflectometer (OTDR), coherent optical time-domain reflectometer (COTDR) and phase-sensitive optical time-domain reflectometer (φ-OTDR).

[0004] OTDR and COTDR mainly measure the power distribution curve of Rayleigh Backscattering Signal (RBS) in optical fiber, which can reflect the attenuation coefficient of optical fiber and the location of events such as optical fiber breakage, joints, and bends. The measurement time is relatively long (minutes level) and can only reflect the current quality of optical fiber. Compared with OTDR, COTDR uses slightly different light sources and receivers, so it has higher performance and can be applied to long-distance optical fiber communication systems, such as submarine optical cables. OTDR and COTDR have been deployed and applied in current optical communication systems.

[0005] φ-OTDR mainly measures the phase distribution curve of RBS. By differentiating the curves measured at different times, it calculates the impact of external disturbances (such as vibration and temperature) on the optical fiber. Its measurement time is short (millisecond level), and it can understand the environmental disturbance of the optical fiber link in real time. Studies have shown that this ability can help predict whether and when the optical cable will be cut. Due to cost constraints, φ-OTDR has not yet been deployed on a large scale in current optical communication systems and is still under research, but it has great application potential.

[0006] It can be seen that OTDR / COTDR and φ-OTDR provide two different monitoring capabilities for optical communication systems, and both are desired by network managers. The latter can provide predictive capabilities and improve network reliability through active operation and maintenance. The former can accurately locate the location of the accident after it occurs, providing reliable information support for rapid repair. If you want to have both the power and phase of the Rayleigh backscattered signal in the optical fiber, it usually means that you need to deploy two systems, but this undoubtedly increases the cost and management complexity. How to use a system to simultaneously measure the power and phase of the Rayleigh backscattered signal in the optical fiber to reduce costs and management complexity is a topic of concern and research in this field. Summary of the invention

[0007] The present invention provides a distributed optical fiber sensing system and method to solve the problem in the prior art that it is difficult to simultaneously measure the power and phase of a Rayleigh backscattering signal in an optical fiber through a set of systems.

[0008] The present invention provides a distributed optical fiber sensing system, comprising: a narrow linewidth laser, a coupler, a first modulation unit, a second modulation unit, a first erbium-doped optical fiber amplifier, a circulator, an optical fiber, a receiving unit and a data acquisition unit; the continuous laser emitted by the narrow linewidth laser is divided into two paths after passing through the coupler, one path is input into the receiving unit as a local oscillator signal, and the other path is input into the second modulation unit as a detection signal; the first modulation unit generates an electrical modulation signal and transmits it to the second modulation unit; the second modulation unit introduces random phase encoding under the action of the electrical modulation signal, modulates the amplitude and phase of the detection signal, and outputs pulse light; the first erbium-doped optical fiber amplifier amplifies the pulse light; the amplified pulse light is input into the first port of the circulator, and output to the optical fiber through the second port of the circulator, the Rayleigh backscattering signal generated by the optical fiber is transmitted to the second port of the circulator, and output to the receiving unit through the third port of the circulator, the receiving unit performs beat frequency on the local oscillator signal and the Rayleigh backscattering signal to generate an electrical signal; the data acquisition unit collects the electrical signal to obtain sensing information.

[0009] Preferably, the second modulation unit adopts an IQ modulator, or the second modulation unit adopts a cascaded intensity modulator and a phase modulator; the intensity modulator adopts an acousto-optic modulator or a Mach-Zehnder modulator, and the phase modulator adopts an electro-optic modulator.

[0010] Preferably, when the second modulation unit introduces random phase coding, a set coding scheme is used to make the phase within a pulse vary within the range of -π to π and obey specific distribution characteristics; the phases of pulses emitted at different times are the same; the set coding scheme is one of uniform distribution, Gaussian distribution, Bernoulli distribution, pseudo-random sequence coding, and Golay coding.

[0011] Preferably, the distributed optical fiber sensing system further comprises: a second erbium-doped optical fiber amplifier; the second erbium-doped optical fiber amplifier is arranged between the circulator and the receiving unit, and the second erbium-doped optical fiber amplifier is used to amplify the Rayleigh backscattering signal.

[0012] Preferably, the first modulation signal unit adopts an arbitrary waveform generator; the receiving unit adopts a dual-polarization integrated coherent receiver or a polarization diversity receiver; and the data acquisition unit adopts an oscilloscope.

[0013] Preferably, the distributed optical fiber sensing system further comprises: a data processing unit; the data processing unit performs calculations based on the received sensing information to obtain the power distribution and phase distribution of the Rayleigh backscattering signal along the optical fiber.

[0014] Preferably, the data processing unit performs the following operations to obtain the power distribution:

[0015] Calculate the total power of the two polarization states and obtain the power matrix P MxN ;

[0016] The total power is calculated using the following formula:

[0017] P=|XI+jXQ| 2 +|YI+jYQ| 2

[0018] In the formula, the electrical signal generated by the receiving unit includes four electrical signals, which are recorded as XI, XQ, YI and YQ respectively. X and Y represent two polarization states, I and Q represent the real part and imaginary part of the signal; P represents the total power, j represents the imaginary number, || represents the absolute value; M represents the number of pulses, N represents the number of sampling points, and the power matrix P MxN The rows represent the time dimension, and the columns represent the space dimension;

[0019] For the power matrix P MxN Averaging along the spatial and temporal directions to obtain an averaged power matrix;

[0020] The averaged power matrix is ​​normalized to obtain the power distribution of the Rayleigh backscattered signal along the optical fiber.

[0021] Preferably, the data processing unit performs the following operations to obtain the phase distribution:

[0022] Calculate complex signals of two polarization states and record them as a first complex signal SX and a second complex signal SY;

[0023] The complex signal is calculated using the following formula:

[0024] SX=XI+jXQ

[0025] SY=YI+jYQ

[0026] In the formula, the electrical signal generated by the receiving unit includes four electrical signals, which are respectively recorded as XI, XQ, YI and YQ, X and Y represent two polarization states, I and Q represent the real part and imaginary part of the signal; j represents an imaginary number;

[0027] Calculate a rotation vector RVS based on the first complex signal SX and the second complex signal SY;

[0028] Calculating the phase of the rotation vector and RVS;

[0029] The phase is unwound to obtain the phase distribution of the Rayleigh backscattered signal along the optical fiber.

[0030] On the other hand, the present invention provides a distributed optical fiber sensing method, which is implemented by using the above-mentioned distributed optical fiber sensing system, and the distributed optical fiber sensing method comprises the following steps:

[0031] A narrow linewidth laser is used to emit continuous laser light, and a coupler is used to divide the continuous laser light into two paths, one path is input to a receiving unit as a local oscillator signal, and the other path is input to a second modulation unit as a detection signal;

[0032] The first modulation unit generates an electrical modulation signal and transmits it to the second modulation unit. The second modulation unit introduces random phase coding under the action of the electrical modulation signal, modulates the amplitude and phase of the detection signal, and outputs pulsed light.

[0033] The pulse light is amplified by a first erbium-doped fiber amplifier, the amplified pulse light is input through a first port of a circulator, and output to an optical fiber through a second port of the circulator, a Rayleigh backscattering signal generated by the optical fiber is transmitted to the second port of the circulator, and output to a receiving unit through a third port of the circulator;

[0034] Using the receiving unit to beat the local oscillator signal and the Rayleigh backscattered signal to generate an electrical signal;

[0035] The electrical signal is collected by a data collection unit to obtain sensing information.

[0036] Preferably, the distributed optical fiber sensing method further comprises the following steps:

[0037] The sensing information is received by a data processing unit, and calculation is performed according to the sensing information to obtain the power distribution and phase distribution of the Rayleigh backscattering signal.

[0038] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0039] The present invention uses a narrow linewidth laser to emit continuous laser light, and uses a coupler to divide the continuous laser light into two paths, one path is input to a receiving unit as a local oscillator signal, and the other path is input to a second modulation unit as a detection signal; the first modulation unit generates an electrical modulation signal and transmits it to the second modulation unit, and the second modulation unit introduces random phase coding under the action of the electrical modulation signal, modulates the amplitude and phase of the detection signal, and outputs pulse light; the first erbium-doped fiber amplifier is used to amplify the pulse light, and the amplified pulse light is input through the first port of the circulator, and output to the optical fiber through the second port of the circulator, and the Rayleigh backscattering signal generated by the optical fiber is transmitted to the second port of the circulator, and output to the receiving unit through the third port of the circulator; the receiving unit beats the local oscillator signal and the Rayleigh backscattering signal to generate an electrical signal; the data acquisition unit is used to collect the electrical signal to obtain sensing information. The present invention improves the phase-sensitive optical time domain reflectometer φ-OTDR, so that it has the ability to simultaneously measure the power and phase distribution of the Rayleigh backscattering signal, and uses one system to complete the functions that originally could only be completed by two systems, thereby reducing the system cost and the system failure rate. The present invention can also achieve a good effect of suppressing fading by introducing random phase coding. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of a distributed optical fiber sensing system provided in Example 1 of the present invention;

[0041] Figure 2 is a schematic diagram of the amplitude and phase of pulsed light; Figure 2 (a) is a schematic diagram of the amplitude of pulse light. Figure 2 (b) is a phase diagram of pulse light;

[0042] Figure 3 A flow chart of data processing performed by a data processing unit in a distributed optical fiber sensing system provided in Example 1 of the present invention;

[0043] Figure 4 is the experimental result diagram; Figure 4 (a) is the power trajectory curve measured when the pulse width is set to 100ns. Figure 4(b) is the power trajectory curve measured when the pulse width is set to 200ns. Figure 4 (c) is the power trajectory curve measured when the pulse width is set to 500ns. Figure 4 (d) is the power trajectory curve measured when the pulse width is set to 1000ns. Figure 4 (e) is the differential phase trajectory curve measured using a 100ns pulse. Figure 4 (f) in the figure is the curve of the phase change of the vibration position over time.

[0044] Among them, 1-narrow linewidth laser, 2-coupler, 3-first modulation unit, 4-second modulation unit, 5-first erbium-doped fiber amplifier, 6-circulator, 7-optical fiber, 8-second erbium-doped fiber amplifier, 9-receiving unit, 10-data acquisition unit. DETAILED DESCRIPTION

[0045] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0046] Embodiment 1:

[0047] Embodiment 1 provides a distributed optical fiber sensing system, see Figure 1 , mainly including: a narrow linewidth laser 1, a coupler 2, a first modulation unit 3, a second modulation unit 4, a first erbium-doped fiber amplifier 5, a circulator 6, an optical fiber 7, a receiving unit 9 and a data acquisition unit 10.

[0048] The continuous laser light emitted by the narrow linewidth laser 1 is divided into two paths after passing through the coupler 2, one path is input into the receiving unit 9 as a local oscillator signal, and the other path is input into the second modulation unit 4 as a detection signal; the first modulation unit 3 generates an electrical modulation signal and transmits it to the second modulation unit 4; the second modulation unit 4 introduces random phase encoding under the action of the electrical modulation signal, modulates the amplitude and phase of the detection signal, and outputs pulse light; the first erbium-doped fiber amplifier 5 amplifies the pulse light; the amplified pulse light is input through the first port of the circulator 6, and output to the optical fiber 7 through the second port of the circulator 6, the Rayleigh backscattering signal generated by the optical fiber 7 is transmitted to the second port of the circulator 6, and output to the receiving unit 9 through the third port of the circulator 6, the receiving unit 9 beats the local oscillator signal and the Rayleigh backscattering signal to generate an electrical signal; the data acquisition unit 10 acquires the electrical signal to obtain sensing information.

[0049] Among them, the narrow linewidth laser 1 can emit continuous laser with high coherence, so it has better performance and is more suitable for application in long-distance fiber-optic communication systems; but on the other hand, due to the use of a narrow linewidth light source with high coherence, there will be serious coherent fading noise in the system, which is manifested as a very large amplitude jitter in the received optical power trajectory curve, which will have a significant impact on the system. The present invention can effectively suppress coherent fading noise and solve the above problems by performing random phase modulation on the transmitted pulse light. In addition, compared with the solution of suppressing coherent fading noise by sweeping the light source, the present invention does not need to perform a sweep operation on the light source, which solves the problems caused by the sweep operation. Specifically, sweeping the light source will increase the complexity and hardware cost of the light source, and the introduction of sweeping will reduce the performance of the sensing system to a certain extent, and it is impossible to achieve the optimal state of both the power measurement and the phase measurement functions at the same time.

[0050] The coupler 2 may be a polarization-maintaining coupler, and the first modulation signal unit 3 may be an arbitrary waveform generator.

[0051] The second modulation unit 4 adopts an IQ modulator, or the second modulation unit 4 adopts a cascaded intensity modulator and a phase modulator. The intensity modulator adopts an acousto-optic modulator AOM or a Mach-Zehnder modulator MZM, and the phase modulator adopts an electro-optic modulator EOM.

[0052] For example, the present invention utilizes an arbitrary waveform generator to generate an electrical signal and applies it to an IQ modulator, and utilizes the IQ modulator to simultaneously adjust the phase and amplitude of light to generate the pulse light we desire.

[0053] When the second modulation unit 4 introduces random phase coding, a set coding scheme is used to make the phase within a pulse vary within the range of -π to π and obey specific distribution characteristics; the phases of pulses emitted at different times are the same; the set coding scheme includes but is not limited to uniform distribution, Gaussian distribution, Bernoulli distribution, pseudo-random sequence coding, and Golay coding.

[0054] Traditional COTDR and φ-OTDR systems only modulate the amplitude of light, turning continuous light into pulsed light, and the phase within the light pulse is continuous. However, the present invention not only modulates the amplitude of light, but also modulates the phase of light by introducing random phase encoding, so the phase within the generated light pulse is random. Figure 2 As shown, Figure 2 (a) is a schematic diagram of the amplitude of pulse light. Figure 2 (b) is a phase diagram of pulsed light, where τ pis the pulse width, T is the time interval between pulses, the phase within a pulse is random, varying between -π and π, and the phases of pulses emitted at different times are the same.

[0055] The receiving unit 9 adopts a dual-polarization integrated coherent receiver or a polarization diversity receiver, and the data acquisition unit 10 can adopt an oscilloscope.

[0056] In addition, the distributed optical fiber sensing system may further include: a second erbium-doped optical fiber amplifier 8; the second erbium-doped optical fiber amplifier 8 is arranged between the circulator 6 and the receiving unit 9, and the second erbium-doped optical fiber amplifier 8 is used to amplify the Rayleigh backscattering signal.

[0057] The distributed optical fiber sensing system may further include: a data processing unit; the data processing unit performs calculations based on the received sensing information to obtain the power distribution and phase distribution of the Rayleigh backscattering signal along the optical fiber.

[0058] The electrical signal generated by the receiving unit 9 includes four electrical signals, which are respectively recorded as XI, XQ, YI and YQ, where X and Y represent two polarization states, and I and Q represent the real part and imaginary part of the signal. The four electrical signals enter the data acquisition unit 10, and after the data is collected, the data processing unit can perform corresponding analysis and calculation to obtain the power and phase distribution trajectory of the Rayleigh backscattering signal.

[0059] For details, see Figure 3 , the data processing unit performs the following operations to obtain the power distribution:

[0060] Step 1: Calculate the total power of the two polarization states and obtain the power matrix P MxN .

[0061] The total power is calculated using the following formula:

[0062] P=|XI+jXQ| 2 +|YI+jYQ| 2

[0063] In the formula, P represents the total power, j represents an imaginary number, || represents the absolute value; M represents the number of pulses, N represents the number of sampling points, and the power matrix P MxN The rows represent the time dimension and the columns represent the space dimension.

[0064] That is, assuming that M measurements are taken (M pulses are sent), and each signal has N sampling points each time, a power matrix P can be obtained. MxN , the rows represent the time dimension (the i-th row represents the trajectory measured by the i-th pulse), and the columns represent the space dimension (the j-th column represents the j-th sampling point, which is related to the optical fiber distance).

[0065] Step 2: For the power matrix P MxN The average is performed along the spatial direction and the temporal direction to obtain the averaged power matrix.

[0066] Specifically, the step 2 includes:

[0067] Step 201: Perform block averaging on the power along the spatial direction (specifically, the distance direction). Assuming that the block size is B, the columns of the matrix can be divided into n groups, each group having a total of B data points. For example, the kth group P k+1 ,P k+2 ,…,P k+B , after averaging, P_k=1 / B×(P k+1 +P k+2 +…P k+B ), n=floor(N / B), which is the largest integer not greater than N / B. After averaging, the dimension of the power matrix changes from M×N to M×n.

[0068] In order not to affect the spatial resolution of the sensor system, the block size B is selected to be less than or equal to τ p ×RSR, where RSR is the sampling rate at the receiving end.

[0069] Step 202: average the power along the time direction, that is, average the trajectory data obtained at different times, and the dimension of the power matrix after averaging changes from M×n to 1×n.

[0070] Step 3: normalize the averaged power matrix to obtain the power distribution of the Rayleigh backscattered signal along the optical fiber.

[0071] The normalization process includes calculating the noise power and subtracting the noise power from the obtained 1×n trace.

[0072] After the above operations, the power distribution trajectory of the RBS along the optical fiber can be obtained. The averaging operation effectively reduces the power jitter caused by fading and can be used to accurately estimate events such as optical fiber loss.

[0073] For details, see Figure 3 , the data processing unit performs the following operations to obtain the phase distribution:

[0074] Step 1: Calculate the complex signals of two polarization states and record them as a first complex signal SX and a second complex signal SY;

[0075] The complex signal is calculated using the following formula:

[0076] SX=XI+jXQ

[0077] SY=YI+jYQ

[0078] Here we only consider one trajectory, that is, the data obtained by sending one pulse, so the data dimension is 1×N.

[0079] Step 2: Calculate the rotation vector RVS based on the first complex signal SX and the second complex signal SY.

[0080] Specifically, assuming that the block size is B, the data can be divided into n groups, each with B data points. Taking X polarization as an example, the kth group SX k+1 ,SX k+2 ,…,SX k+B ,RVS_X_k=1 / B×(SX k+1 SX0* k+1 / |SX0 k+1 |+SX k+2 SX0* k+2 / |SX0 k+2 |+…+SX k+B SX0* k+B / |SX0 k+B |), n = floor(N / B), which is the maximum integer not greater than N / B, where SX0 represents the data of the reference trajectory (i.e., the trajectory data measured by the first pulse light), * represents conjugation, and RVS_Y_k is calculated in the same way. Finally, RVS_k = 1 / 2×(RVS_X_k+RVS_Y_k), and the dimension of RVS is 1×n.

[0081] In order not to affect the spatial resolution of the sensor system, the block size B is selected to be less than or equal to τ p ×RSR, where RSR is the sampling rate at the receiving end.

[0082] Step 3: Calculate the phase of the rotation vector and RVS to obtain the phase trajectory, i.e., φ 1xn .

[0083] Step 4: Unwind the phase, calculate the continuously changing phase trajectory, and obtain the phase distribution of the Rayleigh backscattering signal along the optical fiber.

[0084] After the above operations, the phase distribution trajectory of RBS along the optical fiber can be obtained, and then through differential operations (conventional operations of φ-OTDR), the phase change of RBS can be calculated, thereby inferring the position and size of the vibration on the optical fiber. The introduction of random phase coding and the use of the RVS method in the present invention can greatly reduce the impact of fading noise on phase demodulation.

[0085] In addition, the present invention may also adopt other data processing schemes to modify the above data processing method, for example, replacing the block average with other average methods (such as sliding average, weighted average) and the like.

[0086] In summary, the present invention can perform data analysis through the data processing unit to draw a trajectory curve of optical power and a trajectory curve of phase.

[0087] In order to verify the effect of the present invention, relevant experiments are given and explained below.

[0088] Experimental conditions: The pulse widths were set to 100ns, 200ns, 500ns, and 1000ns, respectively, the phase modulation rate was 1G / s (the corresponding phase encoding numbers were 100, 200, 500, and 1000, respectively), the receiver sampling rate was 1GSa / s, and the fiber length was about 10km. Phase encoding used a random number uniformly distributed between -π and π.

[0089] Figure 4 is the experimental result diagram, where Figure 4 (a) is the power trajectory curve measured when the pulse width is set to 100ns. Figure 4 (b) is the power trajectory curve measured when the pulse width is set to 200ns. Figure 4 (c) is the power trajectory curve measured when the pulse width is set to 500ns. Figure 4 (d) in the figure is the power trajectory curve measured when the pulse width is set to 1000ns, that is, Figure 4 (a) to (d) in the figure correspond to the power traces measured under different pulse widths, with power jitter (Δa) of 0.17dB, 0.14dB, 0.08dB and 0.06dB, and one-way dynamic range (SWDR) of 13dB, 14.5dB, 16.9dB and 17.4dB, respectively. A total of 200 traces were used for averaging in the experiment. Theoretically, the more traces are used, the higher the SWDR will be. Ten times the number of traces can increase the SWDR by 10dB. Figure 4 (e) is the differential phase trajectory curve measured using a 100ns pulse. We added a section of optical fiber wrapped around a piezoelectric ceramic at the end of the optical fiber and used the piezoelectric ceramic to simulate the vibration source. The vibration signal is a sine wave with a frequency of 1kHz. Figure 4 In (e), we can clearly see that there is a significant peak at the end, which is the phase change caused by vibration. Figure 4 (f) in the figure is the curve of the phase change of the vibration position over time. It can be clearly seen that the phase change is positively correlated with the vibration signal.

[0090] The experiment verifies the feasibility of the present invention, which can accurately measure both power distribution and phase distribution.

[0091] In summary, the distributed optical fiber sensing system provided in Example 1 is improved on the basis of the conventional φ-OTDR, so that it has the ability of OTDR / COTDR to measure power. Therefore, only one system needs to be deployed to complete the simultaneous measurement of the two parameters of power and phase, reducing the complexity of the sensing system and the management and operation costs. Example 1 introduces random phase coding, that is, random phase modulation of the pulse light. Since the phase within the pulse is disrupted, the transmitted pulse light can be equivalent to the sum of several independent small pulses, so it can achieve a good effect of suppressing fading. Example 1 greatly reduces the complexity of the light source by introducing random phase coding, and can effectively suppress fading noise without frequency scanning, and avoids the degradation of system performance caused by frequency scanning. Since the phase coding of Example 1 is implemented in the pulse (that is, different phases are modulated in a single pulse), a higher spatial resolution can be obtained during measurement. Since Example 1 does not need to adjust the frequency of the pulse light or control the polarization of the pulse light, the system structure is simple. Since the vibration information can only be obtained by processing the detection results obtained from pulses of the same light frequency, the solution provided in Example 1 has a larger frequency range for measuring vibration than a solution that requires adjusting the light frequency.

[0092] Embodiment 2:

[0093] Embodiment 2 provides a distributed optical fiber sensing method, which is implemented by the distributed optical fiber sensing system as described in Embodiment 1. The distributed optical fiber sensing method provided by Embodiment 2 includes the following steps:

[0094] A narrow linewidth laser is used to emit continuous laser light, and a coupler is used to divide the continuous laser light into two paths, one path is input to a receiving unit as a local oscillator signal, and the other path is input to a second modulation unit as a detection signal;

[0095] The first modulation unit generates an electrical modulation signal and transmits it to the second modulation unit. The second modulation unit introduces random phase coding under the action of the electrical modulation signal, modulates the amplitude and phase of the detection signal, and outputs pulsed light.

[0096] The pulse light is amplified by a first erbium-doped fiber amplifier, the amplified pulse light is input through a first port of a circulator, and output to an optical fiber through a second port of the circulator, a Rayleigh backscattering signal generated by the optical fiber is transmitted to the second port of the circulator, and output to a receiving unit through a third port of the circulator;

[0097] Using the receiving unit to beat the local oscillator signal and the Rayleigh backscattered signal to generate an electrical signal;

[0098] The electrical signal is collected by a data collection unit to obtain sensing information.

[0099] In addition, the distributed optical fiber sensing method provided in Example 2 may further include the following steps:

[0100] The sensing information is received by a data processing unit, and calculation is performed according to the sensing information to obtain the power distribution and phase distribution of the Rayleigh backscattering signal.

[0101] Since the steps in the distributed optical fiber sensing method provided in Example 2 correspond to the functions of the components or units in the distributed optical fiber sensing system provided in Example 1, Example 2 can be understood by referring to the description of Example 1, which will not be repeated here.

[0102] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A distributed optical fiber sensing system, characterized in that: include: A narrow linewidth laser, a coupler, a first modulation unit, a second modulation unit, a first erbium-doped fiber amplifier, a circulator, an optical fiber, a receiving unit and a data acquisition unit; the continuous laser light emitted by the narrow linewidth laser is divided into two paths after passing through the coupler, one path is input into the receiving unit as a local oscillator signal, and the other path is input into the second modulation unit as a detection signal; the first modulation unit generates an electrical modulation signal and transmits it to the second modulation unit; the second modulation unit introduces random phase encoding under the action of the electrical modulation signal, modulates the amplitude and phase of the detection signal, and outputs pulse light; the first erbium-doped fiber amplifier amplifies the pulse light; the amplified pulse light is input into the first port of the circulator, and output to the optical fiber through the second port of the circulator, the Rayleigh backscattering signal generated by the optical fiber is transmitted to the second port of the circulator, and output to the receiving unit through the third port of the circulator, and the receiving unit performs beat frequency on the local oscillator signal and the Rayleigh backscattering signal to generate an electrical signal; The data acquisition unit acquires the electrical signal to obtain sensing information.

2. The distributed optical fiber sensing system according to claim 1, characterized in that: The second modulation unit adopts an IQ modulator, or the second modulation unit adopts a cascaded intensity modulator and a phase modulator; the intensity modulator adopts an acousto-optic modulator or a Mach-Zehnder modulator, and the phase modulator adopts an electro-optic modulator.

3. The distributed optical fiber sensing system according to claim 1, characterized in that: When the second modulation unit introduces random phase coding, a set coding scheme is used to make the phase within a pulse vary within the range of -π to π and obey specific distribution characteristics; the phases of pulses emitted at different times are the same; the set coding scheme is one of uniform distribution, Gaussian distribution, Bernoulli distribution, pseudo-random sequence coding, and Golay coding.

4. The distributed optical fiber sensing system according to claim 1, characterized in that: Also includes: a second erbium-doped fiber amplifier; The second erbium-doped fiber amplifier is arranged between the circulator and the receiving unit, and the second erbium-doped fiber amplifier is used to amplify the Rayleigh backscattering signal.

5. The distributed optical fiber sensing system according to claim 1, characterized in that: The first modulation signal unit adopts an arbitrary waveform generator; the receiving unit adopts a dual-polarization integrated coherent receiver or a polarization diversity receiver; and the data acquisition unit adopts an oscilloscope.

6. The distributed optical fiber sensing system according to claim 1, characterized in that: Also includes: Data processing unit; The data processing unit performs calculations based on the received sensing information to obtain the power distribution and phase distribution of the Rayleigh backscattering signal along the optical fiber.

7. The distributed optical fiber sensing system according to claim 6, characterized in that: The data processing unit performs the following operations to obtain the power distribution: Calculate the total power of the two polarization states and obtain the power matrix P MxN ; The total power is calculated using the following formula: P=|XI+jXQ| 2 +|YI+jYQ| 2 In the formula, the electrical signal generated by the receiving unit includes four electrical signals, which are recorded as XI, XQ, YI and YQ respectively. X and Y represent two polarization states, I and Q represent the real part and imaginary part of the signal; P represents the total power, j represents the imaginary number, || represents the absolute value; M represents the number of pulses, N represents the number of sampling points, and the power matrix P MxN The rows represent the time dimension, and the columns represent the space dimension; For the power matrix P MxN Averaging along the spatial and temporal directions to obtain an averaged power matrix; The averaged power matrix is ​​normalized to obtain the power distribution of the Rayleigh backscattered signal along the optical fiber.

8. The distributed optical fiber sensing system according to claim 6, characterized in that: The data processing unit performs the following operations to obtain the phase distribution: Calculate complex signals of two polarization states and record them as a first complex signal SX and a second complex signal SY; The complex signal is calculated using the following formula: SX=XI+jXQ SY=YI+jYQ In the formula, the electrical signal generated by the receiving unit includes four electrical signals, which are respectively recorded as XI, XQ, YI and YQ, X and Y represent two polarization states, I and Q represent the real part and imaginary part of the signal; j represents an imaginary number; Calculate a rotation vector RVS based on the first complex signal SX and the second complex signal SY; Calculating the phase of the rotation vector and RVS; The phase is unwound to obtain the phase distribution of the Rayleigh backscattered signal along the optical fiber.

9. A distributed optical fiber sensing method, characterized in that: The distributed optical fiber sensing method is implemented by the distributed optical fiber sensing system according to any one of claims 1 to 8, and comprises the following steps: A narrow linewidth laser is used to emit continuous laser light, and a coupler is used to divide the continuous laser light into two paths, one path is input to a receiving unit as a local oscillator signal, and the other path is input to a second modulation unit as a detection signal; The first modulation unit generates an electrical modulation signal and transmits it to the second modulation unit. The second modulation unit introduces random phase coding under the action of the electrical modulation signal, modulates the amplitude and phase of the detection signal, and outputs pulsed light. The pulse light is amplified by a first erbium-doped fiber amplifier, the amplified pulse light is input through a first port of a circulator, and output to an optical fiber through a second port of the circulator, a Rayleigh backscattering signal generated by the optical fiber is transmitted to the second port of the circulator, and output to a receiving unit through a third port of the circulator; Using the receiving unit to beat the local oscillator signal and the Rayleigh backscattered signal to generate an electrical signal; The electrical signal is collected by a data collection unit to obtain sensing information.

10. The distributed optical fiber sensing method according to claim 9, characterized in that: The following steps are also included: The sensing information is received by a data processing unit, and calculation is performed according to the sensing information to obtain the power distribution and phase distribution of the Rayleigh backscattering signal.

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