Asymmetric laser interferometer long-range probing demodulation system and disturbance positioning method

Abstract

The application discloses a kind of asymmetric laser interferometer type long-distance detection demodulation system and disturbance positioning method, including two lasers, Mach-Zehnder fiber interferometer, data acquisition card and industrial computer, two lasers provide the narrow linewidth light source of different central wavelength;Two light sources enter Mach-Zehnder fiber interferometer in clockwise and counterclockwise direction respectively, two signal lights share the same sensing fiber link when detecting;A phase modulator introduces high-frequency carrier signal on a sensing fiber, and the corresponding sensing light signal is modulated with high-frequency carrier;Subsequently two sensing interference light signals enter industrial computer after erbium-doped fiber amplifier, dense wave division multiplexer, photodetector, data acquisition card, two interference sensing light signals are demodulated into phase information introduced by disturbance event by corresponding improved phase generation carrier algorithm respectively, and the specific position information of disturbance event acting on fiber link is analyzed by cross-correlation time delay estimation theory.

Description

Technical Field

[0001] This invention relates to the field of sensing and detection technology, and in particular to an asymmetric Mach-Zehnder fiber laser interferometer-type long-distance distributed fiber optic disturbance location detection and demodulation system and disturbance location method. Background Technology

[0002] Distributed fiber optic disturbance sensing technology utilizes coherent optical detection to achieve continuous and accurate sensing and measurement of target disturbance events within its corresponding monitoring range through a single fiber optic link. Compared to traditional electromagnetic and discrete fiber optic disturbance sensing technologies, this type of sensing technology has significant advantages such as high positioning accuracy, large monitoring range, fast response speed, and easy installation. Based on the coherent optical detection structure and principle, distributed fiber optic disturbance sensing technology is mainly divided into backscattered interferometer type and forward interferometer type. Among them, the backscattered interferometer type can achieve specific analysis of the target disturbance event by demodulating the intensity or phase of backscattered light such as Rayleigh scattering and Brillouin scattering in the sensing fiber. Furthermore, this type of distributed fiber optic disturbance sensing system can effectively adjust the spatial resolution between corresponding disturbance events by appropriately adjusting the width of the laser pulse light entering the sensing fiber. However, due to factors such as fiber transmission loss and backscattered light intensity, this type of sensing system usually suffers from shortcomings such as low signal-to-noise ratio and small monitoring range without repeaters when conducting long-distance sensing and monitoring. Forward-fiber interferometer-type distributed fiber optic disturbance sensing systems achieve precise detection of disturbance events on the target object by constructing specific types of fiber laser interferometers, such as Mach-Zehnder interferometers, Michelson interferometers, and Sagnac interferometers. Because this type of distributed fiber optic disturbance sensing system uses the interference of forward signal light emitted from a light source to achieve the sensing, detection, and transmission of disturbance events on the target object, it offers advantages over backscattered light interferometer-type distributed fiber optic sensing systems. These advantages include a larger, repeater-free monitoring range, wider detection frequency response, and simpler sensing structure, making it more suitable for the precise sensing and measurement of target disturbance events over long distances.

[0003] Forward interferometer-type distributed fiber optic disturbance sensing systems use linearly polarized light emitted from a laser for forward transmission and coherent optical interference via a specific type of fiber optic interferometer to sense, detect, and demodulate the disturbance event. Therefore, this type of distributed fiber optic disturbance sensing system cannot directly demodulate and analyze the specific location of the disturbance event using a single forward interferometric sensing light signal. Consequently, forward interferometer-type distributed fiber optic disturbance sensing systems typically require the design of specific types of bidirectional symmetrical fiber optic interferometers, such as dual Mach-Zehnder interferometers and dual Michelson interferometers, and further analysis of the specific disturbance location information using cross-correlation time delay estimation theory. Although the aforementioned bidirectional symmetrical fiber optic interferometers can demodulate the specific location information of the disturbance event acting on the sensing fiber optic link, their signal-to-noise ratio is severely degraded during long-distance sensing due to the backscattered Rayleigh light generated by the forward light transmission, thus severely limiting their accurate sensing and measurement of disturbance events under long-distance monitoring conditions. Furthermore, although quantitative demodulation of disturbance information can be achieved by introducing a 3×3 coupler linear phase demodulation scheme at the detection and demodulation output end of a bidirectional symmetrical fiber interferometer, its demodulation output is still affected by nonlinear factors such as interference light intensity fluctuations and laser frequency shifts. Moreover, at least four detection channels are required during the sensing process to achieve demodulation and analysis of disturbance events.

[0004] In summary, designing a laser interferometer-type distributed fiber optic disturbance sensing system capable of long-distance, precise sensing and detection, and able to accurately locate and analyze disturbance events, has significant theoretical and practical value for enhancing its in-depth application in the field of disturbance sensing and detection. Summary of the Invention

[0005] To better achieve accurate sensing and detection in long-distance distributed fiber optic disturbance sensing systems, and to more accurately analyze disturbance information acting on the sensing fiber optic link, this invention provides an asymmetric laser interferometer-based long-distance detection and demodulation system and a disturbance localization method. The system is based on an asymmetric Mach-Zehnder fiber optic interferometer-based distributed fiber optic disturbance sensing system combining clockwise and counterclockwise directions to effectively suppress the dominant frequency backscattering Rayleigh noise in the sensing signal and effectively improve the system's sensing signal-to-noise ratio. It utilizes an improved phase-generating carrier demodulation technique, unaffected by interference light intensity and modulation depth, to effectively demodulate the corresponding phase information of the two disturbance sensing signals. Finally, through cross-correlation delay estimation theory, the location information of the disturbance event acting on the sensing fiber optic link is further precisely demodulated.

[0006] The first aspect of this invention is to provide an asymmetric laser interferometer-type long-distance detection and demodulation system to overcome the bottleneck of the rapidly deteriorating signal-to-noise ratio of sensing and detection with increasing sensing distance, thereby achieving accurate perception and high-sensitivity detection of disturbance events. The demodulation system includes a first laser, a second laser, a Mach-Zehnder fiber interferometer, a data acquisition card, and an industrial control computer. The first laser provides a narrow linewidth light source with a center wavelength of λ1, and the second laser provides a narrow linewidth light source with a center wavelength of λ2.

[0007] Linearly polarized light from the first laser enters the Mach-Zehnder fiber interferometer in a clockwise direction, while linearly polarized light from the second laser enters it in a counterclockwise direction. Both signal beams share the same sensing fiber link during detection. Furthermore, a phase modulator is installed on the sensing fiber of the Mach-Zehnder fiber interferometer, introducing a high-frequency carrier signal onto one of its sensing fibers to modulate the corresponding sensing light signal. The sensing interference light signal output from the clockwise direction is a superposition of sensing light with a center wavelength of λ2 and backscattered Rayleigh noise light with a center wavelength of λ1. The sensing interference light signal output from the counterclockwise direction is a superposition of sensing light with a center wavelength of λ1 and Rayleigh scattering noise interference light with a center wavelength of λ2.

[0008] Subsequently, the two sensing interference optical signals are first amplified by erbium-doped fiber amplifiers, and then filtered by corresponding dense wavelength division multiplexers (with center bandwidths of λ2±0.2 nm and λ1±0.2 nm, respectively) to remove the dominant frequency Rayleigh scattering noise superimposed on the sensing signal light, thereby effectively improving the signal-to-noise ratio of the sensing signal. The sensing interference optical signal without Rayleigh scattering noise is received by a photodetector, and then converted from analog to digital and acquired by a data acquisition card before being processed by an industrial control computer. The industrial control computer uses a single-frequency modulation phase-generating carrier module to demodulate the phase information introduced by the disturbance event in the two sensing signals, and analyzes the specific location information of the disturbance event acting on the fiber optic link through cross-correlation time delay estimation theory.

[0009] Furthermore, the single-frequency modulation phase generation carrier module includes:

[0010] High-pass filter: Used to filter out the DC component in the sensor's optical signal and provide an effective AC signal component;

[0011] carrier signal cos(w) c t): High-frequency carrier modulation is performed on one of the sensing signals in the Mach-Zehnder fiber interferometer, and the signal is directly multiplied with it to obtain a hybrid modulation signal;

[0012] First low-pass filter: used to obtain the sine term part containing the product of the first-order Bessel function term and the phase information of the disturbance signal to be measured;

[0013] Second low-pass filter: used to obtain the cosine term part containing the product of the zero-order Bessel function term and the phase information of the disturbance signal to be measured;

[0014] Differentiator: Used to perform differentiation operations on the signal terms after passing through the first low-pass filter / second low-pass filter, so as to realize the conversion between corresponding trigonometric functions;

[0015] Inverter: Used to invert a signal term to obtain the corresponding target output signal term;

[0016] Multiplier: Used to perform product operations on signal terms to obtain the corresponding target output signal term;

[0017] Divider: Used to perform division operations on signal items to obtain the corresponding target output signal item;

[0018] Square root operator: Used to perform square root operations on signal items to obtain the corresponding target output signal item;

[0019] Arctangent operator: Used to perform arctangent operation on the signal to obtain the phase signal introduced by the disturbance signal under test;

[0020] Cross-correlation operator: Used to perform cross-correlation operations on the two acquired phase signals to obtain time delay information.

[0021] In one embodiment, the asymmetric laser interferometer-type long-distance detection and demodulation system includes: a first laser and a second laser; linearly polarized light from the first laser passes through a first fiber isolator, a first fiber circulator, and a first polarization controller before entering the Mach-Zehnder fiber interferometer in a clockwise direction; linearly polarized light from the second laser passes through a second fiber isolator, a second fiber circulator, and a second polarization controller before entering the Mach-Zehnder fiber interferometer in a counterclockwise direction.

[0022] In the Mach-Zehnder fiber interferometer, linearly polarized light with different center wavelengths is sensed and transmitted in clockwise / counterclockwise directions along the sensing fiber link, and the phase modulator located on the sensing fiber modulates the sensing light with a high-frequency carrier.

[0023] Subsequently, the two modulated sensing interference optical signals are respectively passed through an erbium-doped fiber amplifier, a dense wavelength division multiplexer, and a photoelectric controller. The data acquisition card then performs analog-to-digital conversion and data acquisition, which is then sent to an industrial control computer for demodulation to extract the specific location information of the disturbance event acting on the fiber optic link.

[0024] A second aspect of the present invention is to provide a disturbance localization method for the aforementioned asymmetric laser interferometer-type long-distance detection and demodulation system, comprising:

[0025] Step 1: When an abnormal disturbance event occurs on the sensing fiber, the narrow-linewidth optical signals emitted by the first and second lasers enter the Mach-Zehnder fiber interferometer in clockwise and counterclockwise directions, respectively. The phase modulator introduces a high-frequency carrier signal into the sensing fiber, modulating the sensing light with a high-frequency carrier. The two modulated interference light signals are then enhanced and noise suppressed by an erbium-doped fiber amplifier and a dense wavelength division multiplexer, respectively. After being received in real time by a photodetector, the data acquisition card performs analog-to-digital conversion and data acquisition before the data is processed by the industrial control computer.

[0026] Step Two: At the demodulation end, the two interferometric sensing optical signals are demodulated using their respective improved phase generation carrier algorithms to extract the phase information introduced by the disturbance event. Finally, the location information of the disturbance acting on the sensing fiber link is accurately calculated using cross-correlation delay estimation theory. Specifically, the improved phase generation carrier demodulation operation process used by the two interferometric sensing optical signals received by the photodetector during phase information demodulation is consistent. Therefore, the following explanation and illustration will take the first interferometric sensing optical signal as an example.

[0027] The first interferometric sensing optical signal is filtered by a high-pass filter to remove the DC component; then it is split into two branches for specific transmission and calculation. One branch is coupled with the high-frequency carrier signal cos(w c After multiplication, the first low-pass filter yields a sine term containing a first-order Bessel function term multiplied by the phase information of the disturbance signal under test. The second branch directly passes through a second low-pass filter to obtain a cosine term containing a zero-order Bessel function term multiplied by the phase information of the disturbance signal under test. Subsequently, the sine and cosine terms obtained from the first and second low-pass filters are further divided into two terms for subsequent demodulation mathematical operations. Specifically, the sine and cosine terms are directly multiplied by their respective differentials to obtain the complete trigonometric function term Q. 11 (t) and I 11 (t), then dividing the two and performing the reverse operation yields a constant-coefficient square term containing only the product of zero-order and first-order Bessel functions. Passing this through a square root operator gives the corresponding first-order term S of the Bessel function result. 11 (t). On the other hand, the sine and cosine terms output by the first and second low-pass filters can be directly divided to obtain the product Y, which contains the perturbation phase information tangent term and the reciprocal of the above Bessel function result. 22 (t), which is further inverted to obtain the corresponding S. 22(t) term. Because S 11 (t) term and S 22 The Bessel coefficients in term (t) are reciprocals of each other; therefore, directly calculating their product yields the tangent term containing only perturbation phase information. This tangent term, after passing through an arctangent calculus, provides the corresponding perturbation phase information.

[0028] Similarly, the perturbation phase information of the second interferometric sensing optical signal is obtained based on the above phase generation carrier demodulation operation process.

[0029] Step 3: Since the perturbation phase information in the first interferometric sensing signal contains a wavenumber term of λ² / 2π, the amplitude influence of the wavenumber term is removed from the perturbation phase information obtained in Step 2 through a backward multiplication operation, so that the final demodulated output result f1(t) is a pure perturbation phase information term containing fixed time delay information; similarly, since the perturbation phase information in the second interferometric sensing signal contains a wavenumber term of λ¹ / 2π, the amplitude influence of the wavenumber term is removed from the perturbation phase information obtained in Step 2 through a backward multiplication operation, so that the final demodulated output result f2(t) is a pure perturbation phase information term containing fixed time delay information; the corresponding fixed time delay value information is obtained by solving the two perturbation phase information terms through a cross-correlation operator, and then the position information acting on the sensing fiber optic link is obtained by solving the specific relationship between the perturbation position information and the fixed time delay information.

[0030] The present invention has the following beneficial effects:

[0031] The asymmetric laser interferometer-type long-distance detection and demodulation system is a novel laser interferometer-type distributed fiber optic disturbance sensing system that combines a bidirectional center wavelength asymmetric Mach-Zehnder fiber interferometer, thereby achieving accurate perception and detection of disturbance events under long-distance monitoring conditions.

[0032] Moreover, the demodulation system is based on the clockwise and counterclockwise Mach-Zehnder optical interference principle, and adopts the multiplexing of the same sensing fiber link to realize the sensing, detection and analysis of disturbance events; erbium-doped fiber amplifier and dense wavelength division multiplexer are introduced at the detection demodulation end to effectively improve the signal-to-noise ratio of the disturbance sensing signal under test;

[0033] The asymmetric laser interferometer-type long-distance detection and demodulation system is based on the principle of dense wavelength division multiplexing. By constructing a bidirectional asymmetric laser interferometer distributed fiber optic disturbance sensing system, it focuses on solving the bottleneck of the rapid deterioration of the signal-to-noise ratio during long-distance sensing and monitoring.

[0034] The positioning method describes the development of an improved phase generation carrier demodulation algorithm at the demodulation end of the asymmetric laser interferometer-type long-distance detection and demodulation system. This algorithm is unaffected by interference light intensity and modulation depth and is used to demodulate the phase information introduced by disturbance events in the two sensing signals in real time, so as to obtain the fixed time delay information between the two sensing signals.

[0035] Moreover, the positioning method is based on the idea of ​​differential cross division to design the corresponding phase generation carrier algorithm. Therefore, it has a higher linear demodulation range and stability when solving the disturbance phase signal, thereby further realizing the accurate analysis of the location information of the disturbance event to be measured. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the asymmetric laser interferometer-type long-distance detection and demodulation system described in this invention;

[0037] Figure 2 This is a schematic diagram of the phase modulation method for the disturbance positioning of the system described in this invention.

[0038] in,

[0039] 1: First laser; 2: First fiber optic isolator; 3: First fiber optic circulator;

[0040] 4: First polarization controller; 5: First fiber coupler; 6: Second laser;

[0041] 7: Second fiber optic isolator; 8: Second fiber optic circulator; 9: Second polarization controller;

[0042] 10: Second fiber optic coupler; 11, 12: Sensing fiber; 13: Conducting fiber;

[0043] 14: Phase modulator; 15: First erbium-doped fiber amplifier; 16: First dense wavelength division multiplexer;

[0044] 17: First photodetector; 18: Second erbium-doped fiber amplifier;

[0045] 19: Second dense wavelength division multiplexer; 20: Second photodetector;

[0046] 21: Data acquisition card; 22: Industrial control computer; 23: Signal generator;

[0047] HPF: High-pass filter; LPF1: First low-pass filter; LPF2: Second low-pass filter;

[0048] DIFF: Differentiator; Sqrt: Square root operator; Arctan: Arctangent operator;

[0049] CC: Cross-correlation operator. Detailed Implementation

[0050] To make the objectives, technical solutions, beneficial effects, and significant advancements of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings provided in the examples of the present invention. Obviously, all the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort and in accordance with the content, implementation methods, and drawings of the present invention are within the scope of protection of the present invention.

[0051] It should also be noted that the following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0052] like Figure 1 As shown, an asymmetric laser interferometer-type long-distance detection and demodulation system is provided; specifically, it includes:

[0053] Based on clockwise and counterclockwise Mach-Zehnder fiber interferometers with asymmetric operating wavelengths, the system includes: a first laser 1, a second laser 6, a first fiber isolator 2, a second fiber isolator 7, a first fiber circulator 3, a second fiber circulator 8, a first polarization controller 4, a second polarization controller 9, a Mach-Zehnder interferometer, a phase modulator 14, a first erbium-doped fiber amplifier (EDFA) 15, a second erbium-doped fiber amplifier 18, a first dense wavelength division multiplexer 16, a second dense wavelength division multiplexer 19, a first photodetector 17, a second photodetector 20, a data acquisition card 21, an industrial control computer 22, and a signal generator 23. The Mach-Zehnder interferometer includes a first fiber coupler 5, a second fiber coupler 10, and sensing fibers 11 and 12.

[0054] Among them, the first laser 1 is a narrow linewidth laser with a center wavelength of λ1, which is used to construct a long-distance Mach-Zehnder fiber interferometer sensing structure in the clockwise direction.

[0055] The second laser 6 is a narrow-linewidth laser with a center wavelength of λ2, used to construct a long-distance Mach-Zehnder fiber interferometer sensing structure in the counterclockwise direction.

[0056] The first fiber optic isolator 2 is used for unidirectional transmission of linearly polarized light signals from the first laser 1 and to isolate the return light signals from being transmitted back to the light source laser, thus preventing damage. Similarly, the second fiber optic isolator 7 is used for unidirectional transmission of linearly polarized light signals from the second laser 6.

[0057] The first fiber optic circulator 3 and the second fiber optic circulator 8 are three-port fiber optic circulators used to transmit the optical signals output by the two lasers in the forward direction to the subsequent fiber optic path structure, and simultaneously transmit the sensing signal light in the reverse direction to the back-end demodulation optical path structure.

[0058] The first polarization controller 4 and the second polarization controller 9 are used to dynamically adjust the polarization state of the output light signals of the first and second lasers to ensure that the interference visibility of the sensing signal light reaches the optimal level.

[0059] The first fiber coupler 5 and the second fiber coupler 10 are both 3dB fiber couplers; wherein the first fiber coupler 5 is used to split the signal light with a center wavelength of λ1 into two paths and send them into the sensing fiber for sensing detection and transmission; the second fiber coupler 10 is used to split the signal light with a center wavelength of λ2 into two paths and send them into the sensing fiber for sensing detection and transmission.

[0060] The first erbium-doped fiber amplifier 15 is used to enhance and amplify the power of the sensing interference signal light output by the counterclockwise Mach-Zehnder interferometer; the second erbium-doped fiber amplifier 18 is used to enhance and amplify the power of the sensing interference signal light output by the clockwise Mach-Zehnder interferometer.

[0061] The first dense wavelength division multiplexer (DWDM) 16 is used to filter out and suppress back Rayleigh scattering noise light superimposed on the counterclockwise sensing signal light to enhance the signal-to-noise ratio. The second dense wavelength division multiplexer 19 is used to filter out and suppress back Rayleigh scattering noise light superimposed on the clockwise sensing signal light to enhance the signal-to-noise ratio.

[0062] Phase modulator 14: used to introduce a high-frequency carrier signal onto the reference arm of the Mach-Zehnder fiber interferometer to achieve high-frequency modulation of the disturbance signal under test.

[0063] The first photodetector 17 is used to receive counterclockwise sensing light signals and convert them into corresponding sensing electrical signals, and the second photodetector 20 is used to receive clockwise sensing light signals and convert them into corresponding sensing electrical signals.

[0064] Signal generator 23 is used to generate high-frequency carrier signals and external trigger signals required for real-time acquisition by the acquisition card.

[0065] Data acquisition card 21: It has dual-channel data acquisition capability and is used to perform analog-to-digital conversion and data acquisition on the sensing electrical signals output by the first photodetector 17 and the second photodetector 20.

[0066] Industrial computer 22: Used to perform final demodulation processing on the two sensor electrical signals output by data acquisition card 21 to output the location information of the disturbance event to be measured.

[0067] The sensing optical fibers 11 and 12 are ordinary G.652D type single-mode multi-core communication optical fibers, used for sensing specific disturbance events and transmitting signals.

[0068] The optical paths of the clockwise and counterclockwise Mach-Zehnder fiber interferometers based on working wavelength asymmetry are as follows:

[0069] Linearly polarized light from the first laser 1 passes through the first fiber isolator 2, the first fiber circulator 3, and the first polarization controller 4 before entering the Mach-Zehnder interferometer in a clockwise direction. In the Mach-Zehnder interferometer, the first fiber coupler 5 divides the linearly polarized light with a center wavelength of λ1 into equal parts and then performs clockwise sensing and transmission along the sensing fiber link. The phase modulator 14 located on the sensing fiber 11 modulates the sensing light with a high-frequency carrier and performs interference at the second fiber coupler 10. The output of the first fiber coupler 5 is the superposition of the sensing light with a center wavelength of λ2 and the backscattered Rayleigh noise light with a center wavelength of λ1. The sensing interference light signal output from the first fiber coupler 5 is then sent to the first erbium-doped fiber amplifier 15 for power enhancement and amplification after passing through the first polarization controller 4 and the first fiber circulator 3. The sensing light signal with a center wavelength of λ2 and the Rayleigh scattering noise light signal with a center wavelength of λ1 output from the first erbium-doped fiber amplifier 15 are then fed into the first dense wavelength division multiplexer 16 for noise suppression and filtering. Since the bandwidth of the first dense wavelength division multiplexer 16 is set to λ2 ± 0.2 nm, the Rayleigh scattering noise light with a wavelength of λ1 in its output light signal can be effectively suppressed and eliminated. After the backscattering Rayleigh noise light component contained in its sensing signal is filtered out and suppressed by the first dense wavelength division multiplexer 16, the signal is sequentially converted from analog to digital and acquired by the first photoelectric controller 17 and the data acquisition card 21 before entering the industrial control computer 22.

[0070] Linearly polarized light from the second laser 6 passes through the second fiber isolator 7, the second fiber circulator 8, and the second polarization controller 9 before entering the Mach-Zehnder interferometer in a counterclockwise direction. Within the Mach-Zehnder interferometer, the second fiber coupler 10 divides the linearly polarized light with a center wavelength of λ2 into equal parts and then senses and transmits it counterclockwise along the sensing fiber link. The phase modulator 14, located on the sensing fiber 11, modulates the sensing light with a high-frequency carrier and performs interference at the second fiber coupler 10. The output of the second fiber coupler 10 is a superposition of the sensing light with a center wavelength of λ1 and the backscattered Rayleigh noise light with a center wavelength of λ2. The sensing interference light signal output from the second fiber coupler 10 passes through the transmission fiber 13, then through the second polarization controller 9 and the second fiber circulator 8, before being sent to the second erbium-doped fiber amplifier 18 for power enhancement and amplification. The sensing light signal with a center wavelength of λ1 and the Rayleigh scattering noise light signal with a center wavelength of λ2 output from the second erbium-doped fiber amplifier 18 interfere with each other and enter the dense wavelength division multiplexer (DWDM2) for noise suppression and elimination. Correspondingly, the bandwidth of the second DWDM2 is set to λ1 ± 0.2 nm at this time, so the Rayleigh scattering noise light signal with a wavelength of λ2 in its output light signal can be effectively suppressed and eliminated. After the backscattering Rayleigh noise light component in its sensing signal is filtered out and suppressed by the second DWDM29, it passes through the second optoelectronic controller 20 and the data acquisition card 21 to complete analog-to-digital conversion and data acquisition, and then enters the industrial control computer 22.

[0071] The high-frequency carrier signal output by the signal generator 23 is used to achieve high-frequency modulation of the disturbance event signal under test through the phase modulator 14.

[0072] If the high-frequency carrier signal applied by the signal generator 23 to the phase modulator 14 is Ccos(w c t), where C is the modulation depth, w c Let be the angular frequency of the carrier signal. Then, the sensing light signal received by the first photodetector 17 and the second photodetector 20 at this time can be expressed as:

[0073] (1)

[0074] In the formula I PD1 (t) and I PD2(t) represents the sensing optical signals received by the first photodetector 17 and the second photodetector 20, respectively; A1 and A2 represent the DC components of the two sensing signals, respectively; B1 and B2 represent the AC components of the two sensing signals, respectively; g(t) represents the phase information expression introduced when the disturbance event acts on the sensing fiber link; and τ represents the fixed time delay difference formed by the disturbance sensing signal to the two photodetectors. According to the design concept and content of this invention, the two sensing detection signals shown in formula (1) are further sent to the industrial control computer for disturbance localization method to perform precise demodulation and calculation of specific time delay information.

[0075] like Figure 2 As shown, the method for the industrial control computer to demodulate the received information to obtain disturbance location detection includes:

[0076] Two sensor light signals I from data acquisition card 21 PD1 (t) and I PD2 (t) The corresponding DC components are removed by high-pass filters (HPF) respectively, and then split into two paths for specific transmission operations. Since the sensing optical signal I... PD1 (t) and I PD2 (t) is exactly the same in the subsequent specific demodulation operation. The following will use the sensor signal I as an example. PD1 Taking (t) as an example, we can derive its specific demodulation operation process.

[0077] Sensing signal I PD1 (t) becomes I' after its DC component is removed by a high-pass filter (HPF). PD1 (t), and then I' PD1 (t) is divided into two paths for transmission and computation, one of which is connected to the high-frequency carrier signal cos(w c The product of the two inputs (t and Q) is fed into the first low-pass filter LPF1 for specific calculations, while the other input is directly fed into the second low-pass filter LPF2 for specific calculations. The outputs I1(t) and Q1(t) obtained after passing through the first low-pass filter LPF1 and the second low-pass filter LPF2, respectively, can be expressed as:

[0078] (2)

[0079] In formula (2), I1(t) and Q1(t) are obtained by performing self-differential multiplication and direct division operations through the differentiator DIFF, respectively. 11 (t), Q 11 (t) and Y 22 (t) can be expressed as:

[0080] (3)

[0081] Q in formula (3) 11 (t) and I 11 (t) After direct division, we get Y 11 (t), and then its direct product with -1 followed by a square root operation yields S. 11 (t):

[0082] (4)

[0083] Y in formula (3) 22 (t) can be directly multiplied by -1 to obtain S. 22 (t):

[0084] (5)

[0085] In formula (4), S 11 (t) and S in formula (5) 22 (t) After direct multiplication and taking the arctangent, we get:

[0086] (6)

[0087] Finally, by directly multiplying S1(t) in formula (6) with the constant term λ2 / 2π, we can obtain:

[0088] (7)

[0089] Based on the above derivation process, the sensing signal I... PD2 (t) Figure 2 After demodulation, the single-frequency modulation phase-generated carrier scheme yields:

[0090] (8)

[0091] By performing cross-correlation on the calculation outputs of formulas (7) and (8) and calculating the abscissa value corresponding to their maximum amplitude, the specific time delay value y(t) can be obtained:

[0092] (9)

[0093] Finally, the specific value can be calculated based on the mathematical relationship between the time delay value τ and the specific location information x of the disturbance event acting on the sensing fiber optic link in formula (9). The calculation expression for the specific location information x of the disturbance event acting on the sensing fiber optic link is as follows:

[0094] (10)

[0095] In the formula, L is the total length of the sensing fiber link, c represents the speed of light in a vacuum, and n represents the effective refractive index of the sensing fiber. According to formula (10), the disturbance localization method designed in this invention can accurately demodulate the location information of disturbance events acting on the sensing fiber link. Therefore, the asymmetric laser interferometer-type distributed fiber optic disturbance sensing system designed in this invention can achieve accurate localization and detection of disturbance events on long-distance fiber optic links.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. Non-essential improvements, adjustments or substitutions made by those skilled in the art based on the content of this specification are all within the scope of protection claimed by the present invention.

Claims

1. An asymmetric laser interferometer-type long-distance detection and demodulation system, characterized in that, Includes a first laser (1), a second laser (6), a Mach-Zehnder fiber interferometer, a data acquisition card (21) and an industrial control computer (22). The first laser (1) provides a narrow linewidth light source with a center wavelength of λ1, and the second laser (6) provides a narrow linewidth light source with a center wavelength of λ2. Linearly polarized light from the first laser (1) enters the Mach-Zehnder fiber interferometer in a clockwise direction, and linearly polarized light from the second laser (6) enters the Mach-Zehnder fiber interferometer in a counterclockwise direction. The two signal lights share the same sensing fiber link during detection. Furthermore, a phase modulator (14) is provided on the sensing fiber of the Mach-Zehnder fiber interferometer. The phase modulator (14) introduces a high-frequency carrier signal on one of its sensing fibers and modulates the corresponding sensing light signal with a high-frequency carrier. The sensing interference light signal output from the clockwise direction entering the Mach-Zehnder fiber interferometer is a superposition of sensing light with a center wavelength of λ2 and backscattered Rayleigh noise light with a center wavelength of λ1. The sensing interference light signal output from the counterclockwise direction entering the Mach-Zehnder fiber interferometer is a superposition of sensing light with a center wavelength of λ1 and Rayleigh scattering noise interference light with a center wavelength of λ2. λ1 is not equal to λ2. Subsequently, the two sensing interference optical signals are amplified by erbium-doped fiber amplifiers, and then the corresponding dense wavelength division multiplexers filter out the dominant frequency Rayleigh scattering noise superimposed on the sensing signal light. The sensing interference optical signals without Rayleigh scattering noise are received by the corresponding photodetectors, and then the data acquisition card (21) performs analog-to-digital conversion and data acquisition before entering the industrial control computer (22) for processing. The industrial control computer (22) uses a single-frequency modulation phase generation carrier module to demodulate the phase information introduced by the disturbance event in the two sensing signals, and analyzes the specific location information of the disturbance event acting on the optical fiber link through the cross-correlation time delay estimation theory. The single-frequency modulation phase generation carrier module includes: High-pass filter: Used to filter out the DC component in the sensor's optical signal and provide an effective AC signal component; Carrier signal: A high-frequency carrier is used to modulate one of the sensing signals in the Mach-Zehnder fiber interferometer, and the signal is directly multiplied with the carrier signal to obtain a hybrid modulation signal; First low-pass filter: used to obtain the sine term part containing the product of the first-order Bessel function term and the phase information of the disturbance signal to be measured; Second low-pass filter: used to obtain the cosine term part containing the product of the zero-order Bessel function term and the phase information of the disturbance signal to be measured; Differentiator: Used to perform differentiation operations on the signal terms after passing through the first low-pass filter / second low-pass filter, so as to realize the conversion between corresponding trigonometric functions; Inverter: Used to invert a signal term to obtain the corresponding target output signal term; Multiplier: Used to perform product operations on signal terms to obtain the corresponding target output signal term; Divider: Used to perform division operations on signal items to obtain the corresponding target output signal item; Square root operator: Used to perform square root operations on signal items to obtain the corresponding target output signal item; Arctangent operator: Used to perform arctangent operation on the signal to obtain the phase signal introduced by the disturbance signal under test; Cross-correlation unit: Used to perform cross-correlation operations on the acquired two phase signals to obtain time delay information.

2. The asymmetric laser interferometer-type long-distance detection and demodulation system according to claim 1, characterized in that, The demodulation system includes: a first laser (1) and a second laser (6); linearly polarized light from the first laser (1) passes through a first fiber isolator (2), a first fiber circulator (3), and a first polarization controller (4) before entering the Mach-Zehnder fiber interferometer in a clockwise direction; linearly polarized light from the second laser (6) passes through a second fiber isolator (7), a second fiber circulator (8), and a second polarization controller (9) before entering the Mach-Zehnder fiber interferometer in a counterclockwise direction; In the Mach-Zehnder fiber interferometer, linearly polarized light with different center wavelengths is sensed and transmitted in clockwise / counterclockwise directions along the sensing fiber link. The phase modulator (14) located on the sensing fiber modulates the sensing light with a high-frequency carrier. Subsequently, the two modulated sensing interference optical signals are respectively passed through an erbium-doped fiber amplifier, a dense wavelength division multiplexer, and a photoelectric controller. The data acquisition card (21) completes analog-to-digital conversion and data acquisition, and enters the industrial control computer (22) for demodulation, thereby resolving the specific location information of the disturbance event acting on the fiber optic link.

3. A perturbation localization method, which utilizes the asymmetric laser interferometer-type long-distance detection and demodulation system according to claim 1, comprising: Step 1: When an abnormal disturbance event acts on the sensing fiber, the narrow linewidth optical signals emitted by the first laser (1) and the second laser (6) enter the Mach-Zehnder fiber interferometer in clockwise and counterclockwise directions, respectively. The phase modulator (14) introduces a high-frequency carrier signal on the sensing fiber and modulates the sensing light with a high-frequency carrier. After being modulated, the two interference light signals are enhanced and noise suppressed by an erbium-doped fiber amplifier and a dense wavelength division multiplexer, respectively. After being received in real time by a photodetector, they are converted from analog to digital and acquired by a data acquisition card (21) and then processed by an industrial control computer (22). Step 2: The two interferometric sensing optical signals received by the photodetector are subjected to the same phase-generated carrier demodulation process, including: the two interferometric sensing optical signals are filtered by a high-pass filter to remove the DC component, and then split into two branches for specific transmission and calculation. One of the branches is related to the high-frequency carrier signal cos(w) c After multiplication, the first low-pass filter yields a sine term containing a first-order Bessel function term multiplied by the phase information of the disturbance signal under test. The other branch directly passes through a second low-pass filter to obtain a cosine term containing a zero-order Bessel function term multiplied by the phase information of the disturbance signal under test. Subsequently, the sine and cosine terms obtained from the first and second low-pass filters are further divided into two items for demodulation. The sine and cosine terms are then directly multiplied by their respective differentials to obtain the complete trigonometric function term Q. 11 (t) and I 11 (t), then the two are divided and reversed to obtain a constant coefficient square term containing only the product of zero-order and first-order Bessel functions. This term is then passed through a square root operator to obtain the first-order term S of the corresponding Bessel function result. 11 (t); On the other hand, the product Y, which is the product of the tangent term containing perturbation phase information and the reciprocal of the above-mentioned Bessel function result, is obtained by directly dividing the sine term obtained from the first low-pass filter and the cosine term obtained from the second low-pass filter. 22 (t), which is further inverted to obtain the corresponding S. 22 (t) term; due to S 11 (t) term and S 22 The Bessel coefficients in term (t) are reciprocals of each other, so the direct product of the two can be used to obtain the tangent term containing only perturbation phase information; the tangent term is then passed through an arctangent calculus to obtain the corresponding perturbation phase information; Step 3: Since the perturbation phase information in the first interferometric sensing signal contains a wavenumber term of λ² / 2π, the amplitude influence of the wavenumber term is removed from the perturbation phase information obtained in Step 2 through a backward multiplication operation, so that the final demodulated output result f1(t) is a pure perturbation phase information term containing fixed time delay information; similarly, since the perturbation phase information in the second interferometric sensing signal contains a wavenumber term of λ¹ / 2π, the amplitude influence of the wavenumber term is removed from the perturbation phase information obtained in Step 2 through a backward multiplication operation, so that the final demodulated output result f2(t) is a pure perturbation phase information term containing fixed time delay information; the corresponding fixed time delay value information is obtained by solving the two perturbation phase information terms through a cross-correlation operator, and then the position information acting on the sensing fiber optic link is obtained by solving the specific relationship between the perturbation position information and the fixed time delay information.

Images