Asymmetric laser interferometer type long-distance detection demodulation system and disturbance positioning method

Abstract

The invention discloses an asymmetric laser interferometer type long-distance detection demodulation system and a disturbance positioning method, the system comprises two lasers, a Mach-Zehnder fiber interferometer, a data acquisition card and an industrial personal computer, and the two lasers provide narrow linewidth light sources with unequal central wavelengths; the two paths of light sources enter the Mach-Zehnder optical fiber interferometer clockwise and anticlockwise respectively, and the two paths of signal light share the same sensing optical fiber link during detection; a phase modulator introduces a high-frequency carrier signal on one path of sensing optical fiber, and performs high-frequency carrier modulation on a corresponding sensing optical signal; then the two paths of sensing interference optical signals enter an industrial personal computer after respectively passing through an erbium-doped optical fiber amplifier, a dense wavelength division multiplexer, a photoelectric detector and a data acquisition card, and phase information introduced by a disturbance event is demodulated by the two paths of interference sensing optical signals respectively through respective corresponding improved phase generation carrier algorithms; and specific position information of the disturbance event acting on the optical fiber link is analyzed through a cross-correlation time delay estimation theory.

Description

Technical Field

[0001] The present 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 disturbance positioning detection demodulation system and a disturbance positioning method. Background Art

[0002] Distributed fiber-optic disturbance sensing technology utilizes coherent light detection to achieve continuous and precise sensing and measurement of target disturbance events within its monitoring range through a single optical fiber link. Compared to traditional electromagnetic and discrete fiber-optic disturbance sensing technologies, this type of sensing offers significant advantages, including high positioning accuracy, a wide monitoring range, fast response speed, and easy installation. Based on the coherent light detection structure and principle, distributed fiber-optic disturbance sensing technologies are primarily categorized as backscattered light interferometers and forward light interferometers. The backscattered light interferometer type specifically analyzes the target disturbance event by demodulating the intensity or phase of backscattered light, such as Rayleigh and Brillouin scattered light, within the sensing fiber. Furthermore, this type of distributed fiber-optic disturbance sensing system effectively adjusts the spatial resolution between disturbance events by appropriately adjusting the width of the laser pulses entering the sensing fiber. However, due to factors such as fiber transmission loss and backscattered light intensity, this type of sensing system often suffers from low signal-to-noise ratio and a limited unrelayed monitoring range when used for long-distance sensing and monitoring. Forward-light interferometer-based distributed fiber optic disturbance sensing systems achieve precise detection of disturbance events on the target under test 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 by a light source to achieve sensing, detection, and transmission of disturbance events on the target under test, compared to backscattered light interferometer-based distributed fiber optic disturbance sensing systems, forward-light interferometer-based distributed fiber optic disturbance sensing systems offer advantages such as a large, relay-free monitoring range, a wide detection frequency response, and a simpler sensing structure. These systems are more suitable for accurately sensing and measuring disturbance events on targets over long-distance monitoring ranges.

[0003] Forward-beam interferometer-based distributed fiber optic disturbance sensing systems use linearly polarized light emitted by a laser for forward transmission and coherent optical interference through a specific type of fiber optic interferometer to detect and demodulate the disturbance event to be measured. Therefore, this type of distributed fiber optic disturbance sensing system cannot directly demodulate and analyze the specific location of the disturbance event through a single forward interferometer sensing light signal. In view of this, forward-beam interferometer-based distributed fiber optic disturbance sensing systems usually require the design of specific types of bidirectional symmetric fiber optic interferometers, such as dual Mach-Zehnder fiber interferometers and dual Michelson fiber interferometers, and further analyze the specific disturbance location information based on cross-correlation delay estimation theory. Although such bidirectional symmetric fiber optic interferometers can demodulate the specific location information of disturbance events acting on the sensing fiber link, their signal-to-noise ratio will be severely degraded during long-distance sensing and monitoring due to the influence of backward Rayleigh scattered light generated by the forward light transmission, which seriously restricts their accurate perception and measurement of disturbance events under long-distance monitoring conditions. In addition, 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 the bidirectional symmetric fiber interferometer, its demodulation output result is still affected by nonlinear factors such as interference light intensity fluctuations and laser frequency shift, and at least four-way detection is required during the sensing process to realize the demodulation and analysis of disturbance events.

[0004] To sum up, the design of a laser interferometer-type distributed fiber optic disturbance sensing system with long-distance accurate perception and detection and accurate positioning and analysis of disturbance events has important theoretical value and practical significance for improving its in-depth application in the field of disturbance sensing and detection. Summary of the Invention

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

[0006] The first aspect of the present invention is to provide an asymmetric laser interferometer-based long-distance detection and demodulation system to address the bottleneck of its sensing detection signal-to-noise ratio, which deteriorates rapidly as the sensing distance increases, and achieve 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 computer. The first laser provides a narrow linewidth light source with a central wavelength of λ1, and the second laser provides a narrow linewidth light source with a central wavelength of λ2.

[0007] The linearly polarized light from the first laser enters the Mach-Zehnder fiber interferometer in a clockwise direction, and the linearly polarized light from the second laser enters the Mach-Zehnder fiber interferometer in a counterclockwise direction. The two signal lights share the same sensing fiber link during detection. A phase modulator is also provided on the sensing fiber of the Mach-Zehnder fiber interferometer. The phase modulator introduces a high-frequency carrier signal into one of the sensing fibers and performs high-frequency carrier modulation on the corresponding sensing light signal. The sensing interference light signal entering the Mach-Zehnder fiber interferometer from the clockwise direction outputs a superposition of sensing light with a central wavelength of λ2 and backward Rayleigh scattering noise light with a central wavelength of λ1. The sensing interference light signal entering the Mach-Zehnder fiber interferometer from the counterclockwise direction outputs a superposition of a sensing light signal with a central wavelength of λ2 and a Rayleigh scattering noise interference light signal with a central wavelength of λ1.

[0008] The two interfering optical sensing signals are then amplified by erbium-doped fiber amplifiers. Dense wavelength division multiplexers (with central bandwidths of λ2±0.2 nm and λ1±0.2 nm, respectively) then filter out the dominant Rayleigh scattering noise superimposed on the sensing signals, effectively improving the signal-to-noise ratio (SNR) of the sensing signals. The interfering optical sensing signals, free of Rayleigh scattering noise, are received by a photodetector. A data acquisition card then performs analog-to-digital conversion and data acquisition, sending the data to an industrial computer for processing. The industrial computer 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, through cross-correlation delay estimation theory, parse the specific location of the disturbance event on the optical fiber link.

[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 light signal and provide effective AC signal component;

[0011] Carrier signal cos(w c t): Perform high-frequency carrier modulation on one sensing signal in the Mach-Zehnder fiber interferometer and directly perform product operation with it to obtain a mixed modulated signal;

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

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

[0014] Differentiator: used to perform differential operation on the signal items passed through the first low-pass filter / the second low-pass filter to achieve conversion between corresponding trigonometric functions;

[0015] Inverter: used to perform reverse operation on the signal term to obtain the corresponding target output signal term;

[0016] Multiplier: used to perform product operations on signal items to obtain corresponding target output signal items;

[0017] Divider: used to perform division operation on the signal item to obtain the corresponding target output signal item;

[0018] Square root operator: used to perform square root operation on the signal item to obtain the corresponding target output signal item;

[0019] Inverse tangent operator: used to perform inverse tangent operation on the signal to obtain the phase signal introduced by the disturbance signal to be measured;

[0020] Cross-correlation operator: used to perform cross-correlation operation on the two acquired phase signals to obtain 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 optical fiber isolator, a first optical fiber circulator, and a first polarization controller, and then enters the Mach-Zehnder optical fiber interferometer in a clockwise direction; linearly polarized light from the second laser passes through a second optical fiber isolator, a second optical fiber circulator, and a second polarization controller, and then enters the Mach-Zehnder optical fiber interferometer in a counterclockwise direction;

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

[0023] The two modulated sensor interference optical signals then pass through an erbium-doped fiber amplifier, a dense wavelength division multiplexer, and an optoelectronic controller, before being converted into digital form and collected by a data acquisition card. The signals are then sent to an industrial computer for demodulation, thereby analyzing the specific location information of the disturbance event on the optical fiber link.

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

[0025] Step 1: When an abnormal disturbance event acts 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 the high-frequency carrier. The two modulated interference optical signals are then boosted in power and filtered for noise suppression by an erbium-doped fiber amplifier and a dense wavelength division multiplexer. After being received in real time by a photodetector, the signals are converted to digital by a data acquisition card, collected, and then processed by an industrial computer.

[0026] Step 2: At the demodulation end, the two interferometric optical signals are demodulated using their respective improved phase generation carrier algorithms to extract the phase information introduced by the disturbance event. Ultimately, the position of the disturbance acting on the sensing fiber link is accurately determined using cross-correlation delay estimation theory. Specifically, the improved phase generation carrier demodulation algorithm employed for phase information demodulation of the two interferometric optical signals received by the photodetector is consistent. This is explained below using the first interferometric optical signal as an example.

[0027] The first interference sensing light signal is filtered through a high-pass filter to remove the DC component; then it is divided into two branches for specific transmission and solution operations, one of which is connected to the high-frequency carrier signal cos(w c t) After the product is multiplied, the sine term part containing the first-order Bessel function term and the phase information of the disturbance signal to be measured is obtained through the first low-pass filter, and the other branch directly obtains the cosine term part containing the zero-order Bessel function term and the phase information of the disturbance signal to be measured through the second low-pass filter; then the sine term part and the cosine term part obtained from the first low-pass filter and the second low-pass filter are further divided into two terms for subsequent demodulation mathematical operations. Specifically, the sine term part and the cosine term part are 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 the inverse operation is performed to obtain a constant coefficient square term containing only the product of the zero-order and first-order Bessel functions, which is passed through the square root operator to obtain the corresponding first-order Bessel function result S 11 On the other hand, the sine term and cosine term output by the first low-pass filter and the second low-pass filter are directly divided to obtain the product Y of the tangent term containing the disturbance phase information and the reciprocal term of the above-mentioned Bessel function result. 22 (t), which is further negated to obtain the corresponding S 22(t). Due to S 11 Item (t) and S 22 The Bessel coefficients in term (t) are reciprocals of each other, so a direct multiplication of the two yields a tangent term containing only the perturbation phase information. This tangent term then passes through an inverse tangent operator to yield the corresponding perturbation phase information.

[0028] Similarly, the disturbance phase information of the second interference sensing light signal is obtained according to the above phase generation carrier demodulation operation process.

[0029] Step 3: Since the disturbance phase information in the first interference sensing signal contains a wave number term of λ2 / 2π, the disturbance phase information obtained in step 2 is subjected to a reverse product operation to remove the amplitude influence of the wave number term, so that its final demodulation output result f1(t) is a pure disturbance phase information term containing fixed time delay information; similarly, since the disturbance phase information in the second interference sensing signal contains a wave number term of λ1 / 2π, the disturbance phase information obtained in step 2 is subjected to a reverse product operation to remove the amplitude influence of the wave number term, so that its final demodulation output result f2(t) is a pure disturbance phase information term containing fixed time delay information; the two disturbance phase information terms are passed through a cross-correlation operator to obtain the corresponding fixed time delay value information, and then the position information acting on the sensing optical fiber link is solved through the specific relationship between the disturbance 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 new type of laser interferometer-type distributed optical fiber disturbance sensing system combined with a bidirectional central wavelength asymmetric Mach-Zehnder optical fiber interferometer, thereby achieving accurate perception and detection of disturbance events under long-distance monitoring conditions;

[0032] The demodulation system is based on the principle of clockwise and counterclockwise Mach-Zehnder interference and multiplexes the same sensing fiber link to achieve the perception, detection and analysis of disturbance events. An erbium-doped fiber amplifier and a dense wavelength division multiplexer are introduced at the detection and demodulation end to effectively improve the signal-to-noise ratio of the disturbance sensing signal to be measured.

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

[0034] The positioning method designs and develops an improved phase generation carrier demodulation algorithm at the demodulation end of the asymmetric laser interferometer type long-distance detection demodulation system, which is not affected by the interference light intensity and modulation depth, and is used to demodulate the phase information introduced by the disturbance event in the two sensor signals in real time to obtain the fixed time delay information between the two sensor signals;

[0035] Moreover, the positioning method designs a corresponding phase generation carrier algorithm based on the idea of ​​differential cross-division, so it has a higher linear demodulation range and stability when solving the disturbance phase signal, thereby further realizing the accurate analysis of the position information of the disturbance event to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0037] Figure 2 Schematic diagram of phase modulation of the disturbance positioning method of the system of the present invention.

[0038] in,

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

[0040] 4: first polarization controller; 5: first fiber coupler; 6: second laser;

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

[0042] 10: Second fiber coupler; 11, 12: Sensing fiber; 13: Transmitting 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 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: inverse tangent operator;

[0049] CC: Cross-correlation operator. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions, beneficial effects and significant improvements 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 in combination with the drawings provided in the examples of the present invention. Obviously, all the described embodiments are only partial embodiments of the present invention, rather than all embodiments; based on the demonstrations made in the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field based on the content, implementation methods and drawings of the present invention without making any creative work shall fall within the scope of protection of the present invention.

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

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

[0053] Based on a clockwise and counterclockwise Mach-Zehnder fiber interferometer with asymmetric working 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 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 central wavelength of λ1, which is used to construct a clockwise long-distance Mach-Zehnder fiber interferometer sensing structure;

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

[0056] The first optical fiber isolator 2 is used to unidirectionally transmit the linearly polarized light signal from the first laser 1 and isolate the return light signal from being transmitted back to the light source laser and causing damage to it; similarly, the second optical fiber isolator 7 is used to unidirectionally transmit the linearly polarized light signal from the second laser 6.

[0057] The first fiber circulator 3 and the second fiber circulator 8 are three-port fiber circulators, which are used to forward transmit the optical signals output by the two lasers to the subsequent fiber optical path structure, and simultaneously reversely transmit the sensor signal light to the rear-end demodulation end optical path structure.

[0058] The first polarization controller 4 and the second polarization controller 9 are used to dynamically adjust the polarization states of the optical signals output by the first and second lasers to ensure that the interference visibility of the sensing signal light is optimized.

[0059] The first fiber coupler 5 and the second fiber coupler 10 are both 3dB fiber couplers; the first fiber coupler 5 is used to split the signal light with a central wavelength of λ1 into two equal 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 central wavelength of λ2 into two equal 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 the backward Rayleigh scattered noise light superimposed on the counterclockwise sensing signal light to achieve an enhancement of the signal-to-noise ratio. The second dense wavelength division multiplexer 19 is used to filter out and suppress the backward Rayleigh scattered noise light superimposed on the clockwise sensing signal light to achieve an enhancement of the signal-to-noise ratio.

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

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

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

[0065] The data acquisition card 21 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] The industrial computer 22 is used to perform final demodulation processing on the two-channel sensing electrical signals output by the data acquisition card 21 to output the position information of the disturbance event to be measured.

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

[0068] The optical paths of the clockwise and counterclockwise Mach-Zehnder fiber interferometers based on the asymmetric working wavelength 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 equally divides the linearly polarized light with a central wavelength of λ1 and then performs clockwise sensing, detection, and transmission along the sensing fiber link. A phase modulator 14 located on the sensing fiber 11 modulates the sensing light with a high-frequency carrier wave, which then interferes at the first fiber coupler 5. The output of the first fiber coupler 5 is a superposition of sensing light with a central wavelength of λ2 and backward Rayleigh scattered noise light with a central wavelength of λ1. The sensor interference light signal output from the first fiber coupler 5 passes through the first polarization controller 4 and the first fiber circulator 3 before being fed into the first erbium-doped fiber amplifier 15 for power boosting and amplification. The sensor light signal with a central wavelength of λ2 and the Rayleigh scattering noise interference light signal with a central wavelength of λ1, output by the first erbium-doped fiber amplifier 15, then enter the first dense wavelength division multiplexer 16 for noise suppression and filtering. Because 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 is effectively suppressed and eliminated. After the backscattered Rayleigh scattering noise light component contained in the sensor light signal is filtered and suppressed by the first dense wavelength division multiplexer 16, the signal undergoes analog-to-digital conversion and data acquisition through the first photoelectric controller 17 and the data acquisition card 21, before entering the industrial computer 22.

[0070] The 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. In the Mach-Zehnder interferometer, the second fiber coupler 10 equally divides the linearly polarized light with a central wavelength of λ2 and then 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 wave, which then interferes at the second fiber coupler 10. The output of the second fiber coupler 10 is a superposition of the sensing light with a central wavelength of λ1 and the backscattered Rayleigh noise light with a central wavelength of λ2. The sensor interference optical signal output from the second fiber coupler 10 passes through the transmission fiber 13, the second polarization controller 9, and the second fiber circulator 8 before entering the second erbium-doped fiber amplifier 18 for power boosting and amplification. The sensor optical signal with a central wavelength of λ1 and the Rayleigh scattering noise interference optical signal with a central wavelength of λ2 output by the second erbium-doped fiber amplifier 18 enter the dense wavelength division multiplexer DWDM2 for noise suppression and elimination. At this point, the bandwidth of the second dense wavelength division multiplexer 19 is set to λ1 ± 0.2 nm, effectively suppressing and eliminating the Rayleigh scattering noise optical signal with a wavelength of λ2 in its output optical signal. After filtering and suppressing the backward Rayleigh scattering noise component contained in the sensor signal by the second dense wavelength division multiplexer 19, the signal undergoes analog-to-digital conversion and data acquisition through the second photoelectric controller 20 and the data acquisition card 21, before entering the industrial computer 22.

[0071] The high-frequency carrier signal output by the signal generator 23 is used to perform high-frequency modulation on the disturbance event signal to be measured 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 is the carrier signal angular frequency. Then the sensing light signal received by the first photodetector 17 and the second photodetector 20 can be expressed as:

[0073] (1)

[0074] Where I PD1 (t) and I PD2(t) represents the sensor light signals received by the first photodetector 17 and the second photodetector 20, respectively. A1 and A2 represent the DC components in the two sensor signals, respectively. B1 and B2 represent the AC components in the two sensor signals, respectively. g(t) represents the phase information expression corresponding to the disturbance event introduced when it acts on the sensor fiber link. τ represents the fixed delay difference formed by the disturbance sensor signal to the two photodetectors. According to the design concept and content of the present invention, it can be seen that the two sensor detection signals shown in formula (1) are subsequently further sent to the industrial control computer to perform the disturbance positioning method, thereby accurately demodulating and calculating the specific delay information.

[0075] like Figure 2 As shown, the method in which the industrial computer demodulates the received information to obtain disturbance location detection includes:

[0076] Two-way sensor light signal I from data acquisition card 21 PD1 (t) and I PD2 (t) are respectively filtered by high-pass filters (HPF) to remove their corresponding DC components, and then divided into two paths for specific transmission operations. PD1 (t) and I PD2 (t) is exactly the same in the subsequent specific demodulation operation process. PD1 (t) as an example to derive the specific demodulation operation process.

[0077] Sensor signal I PD1 (t) is converted to I' after the DC component is removed by the high-pass filter HPF PD1 (t), then I' PD1 (t) is divided into two paths for transmission and operation, one of which is connected to the high-frequency carrier signal cos(w c The product of the two paths is sent to the first low-pass filter LPF1 for specific calculation, while the other path is directly sent to the second low-pass filter LPF2 for specific calculation. The outputs I1(t) and Q1(t) obtained after 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 self-differentiation multiplication and direct division respectively through the differentiator DIFF. 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) Direct division operation to obtain Y 11 (t), and then directly multiply it with -1 and perform square root operation to get S 11 (t):

[0082] (4)

[0083] Y in formula (3) 22 (t) is directly multiplied by -1 to get S 22 (t):

[0084] (5)

[0085] In formula (4), S 11 (t) and S in formula (5) 22 (t) Direct product operation and inverse tangent operation can be obtained:

[0086] (6)

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

[0088] (7)

[0089] According to the above derivation process, the sensor signal I PD2 (t) Figure 2 After demodulation of the single-frequency modulation phase generation carrier solution, we can get:

[0090] (8)

[0091] By performing a cross-correlation operation on the calculated outputs of formula (7) and formula (8) and calculating the horizontal coordinate value corresponding to the maximum amplitude, the specific delay value y(t) can be obtained:

[0092] (9)

[0093] Finally, the corresponding specific value can be solved based on the mathematical relationship between the delay value τ and the specific position information x of the disturbance event on the sensing fiber link in formula (9). The calculation expression for the specific position information x of the disturbance event on the sensing fiber link is:

[0094] (10)

[0095] Where 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 positioning method designed by the present invention can accurately demodulate the position information of disturbance events acting on the sensing fiber link. Therefore, the asymmetric laser interferometer-based distributed fiber disturbance sensing system designed by the present invention can achieve accurate positioning and detection of disturbance events on long-distance fiber links.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements 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 replacements made by those skilled in the art based on the contents of this specification are all within the scope of protection required by the present invention.

Claims

1. An asymmetric laser interferometer type long distance detection and demodulation system, characterized in that: The invention comprises a first laser (1), a second laser (6), a Mach-Zehnder fiber interferometer, a data acquisition card (21) and an industrial control computer (22), wherein the first laser (1) provides a narrow linewidth light source with a central wavelength of λ1, and the second laser (6) provides a narrow linewidth light source with a central wavelength of λ2; The linearly polarized light from the first laser (1) enters the Mach-Zehnder fiber interferometer in a clockwise direction, and the linearly polarized light from the second laser (6) enters the Mach-Zehnder fiber interferometer in a counterclockwise direction, and the two signal lights share the same sensing fiber link during detection; and a phase modulator (14) is further provided on the sensing fiber of the Mach-Zehnder fiber interferometer, and the phase modulator (14) introduces a high-frequency carrier signal on one of the sensing fibers and performs high-frequency carrier modulation on the corresponding sensing light signal; the sensing interference light signal entering the Mach-Zehnder fiber interferometer from the clockwise direction outputs a superposition of the sensing light with a central wavelength of λ2 and the backward Rayleigh scattering noise light with a central wavelength of λ1; the sensing interference light signal entering the Mach-Zehnder fiber interferometer from the counterclockwise direction outputs a superposition of the sensing light signal with a central wavelength of λ2 and the Rayleigh scattering noise interference light signal with a central wavelength of λ1; Subsequently, the two-way sensor interference optical signal is power-amplified by an erbium-doped fiber amplifier, and then the main frequency Rayleigh scattering noise superimposed on the sensor signal light is filtered out by the corresponding dense wavelength division multiplexer; the sensor interference optical signal without Rayleigh scattering noise is received by the corresponding photoelectric detector, and then the data acquisition card (21) completes analog-to-digital conversion and data acquisition and enters 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-way sensor signal, and analyzes the specific position information of the disturbance event acting on the optical fiber link through the cross-correlation delay estimation theory.

2. The asymmetric laser interferometer type long distance detection and demodulation system according to claim 1, characterized in that: The single-frequency modulation phase generation carrier module includes: High-pass filter (HPF): used to filter out the DC component in the sensor light signal and provide effective AC signal components; Carrier signal: Performs high-frequency carrier modulation on one sensor signal in the Mach-Zehnder fiber interferometer and directly performs product operation with it to obtain a mixed modulated signal; The first low-pass filter (LPF1): is used to obtain the sine term part containing the product operation of the first-order Bessel function term and the phase information of the disturbance signal to be measured; The second low-pass filter (LPF2) is used to obtain the cosine term part of the product operation containing the zero-order Bessel function term and the phase information of the disturbance signal to be measured; Differentiator (DIFF): used to perform differential operation on the signal items after the first low-pass filter (LPF1) / the second low-pass filter (LPF2) to achieve conversion between corresponding trigonometric functions; Inverter: used to perform reverse operation on the signal term to obtain the corresponding target output signal term; Multiplier: used to perform product operations on signal items to obtain corresponding target output signal items; Divider: used to perform division operation on the signal item to obtain the corresponding target output signal item; Square root operator (Sqrt): used to perform square root operation on the signal item to obtain the corresponding target output signal item; Arctan operator: used to perform arctan operation on the signal to obtain the phase signal introduced by the disturbance signal to be measured; Cross-correlation operator (CC): used to perform cross-correlation operation on the two acquired phase signals to obtain delay information.

3. The asymmetric laser interferometer type long distance detection and demodulation system according to claim 1, characterized in that: The demodulation system comprises: a first laser (1) and a second laser (6); linearly polarized light from the first laser (1) passes through a first optical fiber isolator (2), a first optical fiber circulator (3), and a first polarization controller (4), and then enters the Mach-Zehnder optical fiber interferometer in a clockwise direction; linearly polarized light from the second laser (6) passes through a second optical fiber isolator (7), a second optical fiber circulator (8), and a second polarization controller (9), and then enters the Mach-Zehnder optical fiber interferometer in a counterclockwise direction; In the Mach-Zehnder fiber interferometer, linearly polarized light with different central wavelengths is sensed, detected, and transmitted in clockwise / counterclockwise directions along the sensing fiber link, and a 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 transmitted through an erbium-doped fiber amplifier, a dense wavelength division multiplexer, and an optoelectronic controller, and then the analog-to-digital conversion and data acquisition are completed by a data acquisition card (21) and then sent to an industrial control computer (22) for demodulation to analyze the specific location information of the disturbance event acting on the optical fiber link.

4. The disturbance positioning method of 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 optical 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, and the phase modulator (14) introduces a high-frequency carrier signal into the sensing optical fiber to perform high-frequency carrier modulation on the sensing light; The two interfering optical signals after being modulated are respectively subjected to power enhancement and noise suppression filtering by an erbium-doped fiber amplifier and a dense wavelength division multiplexer, and then received in real time by a photoelectric detector. The signals are then converted into digital form and data is collected by a data acquisition card (21) and then sent to an industrial control computer (22) for processing. Step 2: The two interferometric sensing light signals received by the photodetector use the same phase to generate a carrier demodulation process, including: the two interferometric sensing light signals pass through a high-pass filter to remove the DC component, and then are divided into two branches for specific transmission and solution operations; One of the branches is connected to the high frequency carrier signal cos(w c t) After multiplication, the first low-pass filter (LPF1) is used to obtain the sine term part containing the first-order Bessel function term and the phase information of the disturbance signal to be measured for the product operation, and the other branch is directly passed through the second low-pass filter (LPF2) to obtain the cosine term part containing the zero-order Bessel function term and the phase information of the disturbance signal to be measured for the product operation; then the sine term part and the cosine term part obtained from the first low-pass filter (LPF1) and the second low-pass filter (LPF2) are further divided into two terms for demodulation operation; on the one hand, the sine term part and the cosine term part are directly multiplied by their respective differentials to obtain the complete trigonometric function term Q 11 (t) and I 11 (t), and then the two are divided and reversed to obtain a constant coefficient square term containing only the product of the zero-order and first-order Bessel functions, which is passed through the square root operator to obtain the corresponding first-order Bessel function result S 11 (t); On the other hand, the first low-pass filter (LPF1) and the sine term part obtained from the second low-pass filter (LPF2) and the cosine term part are directly divided to obtain the product result Y of the tangent term containing the perturbation phase information and the reciprocal term of the above Bessel function result. 22 (t), which is further negated to obtain the corresponding S 22 (t); Due to S 11 Item (t) and S 22 The Bessel coefficients in item (t) are reciprocals of each other, so the direct multiplication of the two can obtain the tangent term containing only the perturbation phase information; the tangent term is passed through the inverse tangent operator to obtain the corresponding perturbation phase information; Step 3: Since the disturbance phase information in the first interference sensing signal contains a wave number term of λ2 / 2π, the disturbance phase information obtained in step 2 is subjected to a reverse product operation to remove the amplitude influence of the wave number term, so that its final demodulation output result f1(t) is a pure disturbance phase information term containing fixed time delay information; similarly, since the disturbance phase information in the second interference sensing signal contains a wave number term of λ1 / 2π, the disturbance phase information obtained in step 2 is subjected to a reverse product operation to remove the amplitude influence of the wave number term, so that its final demodulation output result f2(t) is a pure disturbance phase information term containing fixed time delay information; the two disturbance phase information terms are passed through a cross-correlation operator to obtain the corresponding fixed time delay value information, and then the position information acting on the sensing optical fiber link is solved through the specific relationship between the disturbance position information and the fixed time delay information.

Images