CN117664310A

CN117664310A - Dual-wavelength distributed optical fiber sensing demodulation system and method and security monitoring equipment

Info

Publication number: CN117664310A
Application number: CN202311650871.3A
Authority: CN
Inventors: 吴军
Original assignee: Agricultural Bank of China
Current assignee: Agricultural Bank of China
Priority date: 2023-12-04
Filing date: 2023-12-04
Publication date: 2024-03-08

Abstract

The application discloses a dual-wavelength distributed optical fiber sensing demodulation system and method and security monitoring equipment, wherein a light source module is used for generating a wavelength lambda ₁ And lambda (lambda) ₂ The dual-wavelength narrow pulse optical signals are output to a sensing module, reflected by a plurality of fiber bragg grating pairs which are sequentially connected in series by sensing fibers in the sensing module, output to an interference module, form dual-wavelength interference signals in the interference module, output to a demodulation module, perform photoelectric conversion in the demodulation module to generate corresponding electric signals, and perform phase demodulation and winding on the electric signals by utilizing a dual-wavelength linear regression phase unwrapping algorithm to obtain corresponding distributed vibration information, so that distributed acoustic sensing with high signal-to-noise ratio and high dynamic range is realized, the sensing device is applied to perimeter security monitoring of bank business points, and effectively improves bank businessAnd the perimeter security of the network points protects the national asset security.

Description

Dual-wavelength distributed optical fiber sensing demodulation system and method and security monitoring equipment

Technical Field

The application relates to the technical field of security protection, in particular to a dual-wavelength distributed optical fiber sensing demodulation system and method and security protection monitoring equipment.

Background

The bank business outlets are places where banks are business to the outside, are important departments for intensively storing and keeping a large amount of important articles such as foreign currency cash, securities, noble metals and the like, and are national financial security key precaution units. The banking business outlets are usually arranged in necessary places such as dense population, economy, developed traffic and the like, and various factors such as frequent population flow, high and new invasion means, complex in-out activities and the like bring great security challenges to the security and normal operation of the banking business outlets.

At present, most of banking business sites still adopt a mode of combining manual duty with traditional means such as video and infrared to finish site perimeter security monitoring, so that the monitoring difficulty is large, the monitoring range is small, the sensitivity is low, and the cost of manpower, material resources and financial resources is also higher. Meanwhile, the video or infrared means are required to be installed at the visible positions of the entrances and exits of the bank business outlets, the concealment is poor, the visual positions are easily damaged by lawbreakers, and the aesthetic property of the image construction of the bank business outlets is affected. In extreme severe environments such as the night, storm, sand storm and the like, the monitoring means have obvious failure rate and limitation, and the perimeter security of the bank business outlets under emergency conditions can be greatly reduced.

Disclosure of Invention

In order to solve the technical problems, the embodiment of the application provides a dual-wavelength distributed optical fiber sensing demodulation system and method and security monitoring equipment, so as to solve the various practical problems of large monitoring difficulty, small monitoring range, low sensitivity, high cost, poor concealment, poor attractiveness, high failure rate and the like in the conventional security of the periphery of a bank business website and effectively improve the operation safety of the bank business website.

In order to achieve the above purpose, the embodiment of the present application provides the following technical solutions:

a dual-wavelength distributed optical fiber sensing demodulation system comprises a light source module, a sensing module, an interference module and a demodulation module;

the light source module is used for generating a wavelength lambda ₁ And lambda (lambda) ₂ The dual-wavelength narrow pulse optical signal is output to the sensing module;

the sensing module comprises a plurality of fiber bragg grating pairs which are sequentially connected in series by sensing fibers, wherein the fiber bragg grating pairs are formed by Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ The optical fiber gratings are connected to form the optical fiber grating, and the intervals between any two adjacent optical fiber grating pairs are equal; each of the fiber grating pairs in the sensing module is configured to reflect the dual wavelengths The narrow pulse optical signal generates a reflected dual-wavelength narrow pulse optical signal and outputs the reflected dual-wavelength narrow pulse optical signal to the interference module;

the interference module is used for forming a dual-wavelength interference signal by the dual-wavelength narrow pulse optical signal reflected by the previous fiber bragg grating pair and the dual-wavelength narrow pulse optical signal reflected by the next fiber bragg grating pair in the sensing module, and outputting the dual-wavelength interference signal to the demodulation module;

the demodulation module is used for carrying out photoelectric conversion on the dual-wavelength interference signals to generate corresponding electric signals, and carrying out phase demodulation and unwrapping on the electric signals by utilizing a dual-wavelength linear regression analysis phase unwrapping algorithm to obtain corresponding distributed vibration information.

Optionally, the light source module includes:

a first narrow band laser for generating a wavelength lambda and a first polarization controller ₁ The narrow-band laser of (2) is output after polarization modulation by the first polarization controller;

a second narrow band laser for generating a wavelength lambda and a second polarization controller ₂ The narrow-band laser of (2) is output after polarization modulation by the second polarization controller;

a first dense wavelength division demultiplexer for outputting the first narrow band laser with wavelength lambda ₁ And the wavelength of the output of the second narrow-band laser is lambda ₂ Is mixed with the narrow-band laser to form dual-wavelength mixed laser;

a semiconductor optical amplifier for modulating the dual-wavelength mixed laser output by the first dense wavelength division multiplexing device into dual-wavelength narrow optical pulses with high extinction ratio;

the erbium-doped optical fiber amplifier is used for amplifying the dual-wavelength narrow optical pulse output by the semiconductor optical amplifier, and outputting amplified wavelength lambda ₁ And lambda (lambda) ₂ Is a dual wavelength narrow pulse optical signal.

Optionally, the light source module further comprises a three-port optical circulator and a dual-wavelength matching fiber bragg grating pair;

the first end of the three-port optical circulator is connected with the output end of the erbium-doped fiber amplifier, the second end of the three-port optical circulator is connected with the input end of the sensing template, and the third end of the three-port optical circulator is connected with the dual-wavelength matching fiber grating pair;

the dual-wavelength matching fiber grating pair is formed by a Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ Is formed by connecting fiber gratings;

when the dual-wavelength narrow pulse optical signal amplified by the erbium-doped fiber amplifier passes through the three-port optical circulator, the dual-wavelength matching fiber grating pair filters out broadband spontaneous radiation noise of the dual-wavelength narrow pulse optical signal, and the broadband spontaneous radiation noise is further output to the sensing module.

Optionally, the interference module includes a 3×3 optical fiber coupler, a first interference arm and a second interference arm, where the first interference arm is provided with a delay optical fiber and a first faraday rotation mirror, the second interference arm is provided with a second faraday rotation mirror, and the length of the delay optical fiber is equal to the interval between two adjacent fiber bragg grating pairs in the sensing module;

the dual-wavelength narrow pulse optical signals output from the sensing module and reflected by the fiber bragg grating pairs are divided into three paths of reflected dual-wavelength narrow pulse optical signals after passing through the 3×3 fiber coupler, wherein the first path of reflected dual-wavelength narrow pulse optical signals pass through the first interference arm, the second path of reflected dual-wavelength narrow pulse optical signals pass through the second interference arm, and therefore the dual-wavelength narrow pulse optical signals reflected by the previous fiber bragg grating pair and the dual-wavelength narrow pulse optical signals reflected by the next fiber bragg grating pair in the sensing module form dual-wavelength interference signals, and the 3×3 fiber coupler divides the dual-wavelength interference signals into three paths of interference light with preset phase differences.

Optionally, the demodulation module includes a second dense wave decomposition multiplexer, a third dense wave decomposition multiplexer, a fourth dense wave decomposition multiplexer, six photoelectric converters, a multichannel data acquisition card and a processor;

The second dense wave demultiplexer is used for the second dense wave demultiplexerThe first path of interference light output by the 3X 3 optical fiber coupler is subjected to wave division multiplexing to obtain a first group of wavelength lambda ₁ And lambda (lambda) ₂ Is a light source for the light beam;

the third dense wavelength division multiplexer is used for performing wavelength division multiplexing on the second path of interference light output by the 3×3 optical fiber coupler to obtain a second group of wavelengths lambda ₁ And lambda (lambda) ₂ Is a light source for the light beam;

the fourth dense wavelength division multiplexer is configured to perform wavelength division multiplexing on the third interference light output by the 3×3 optical fiber coupler to obtain a third group of wavelengths lambda ₁ And lambda (lambda) ₂ Is a light source for the light beam;

each group has a wavelength lambda ₁ And lambda (lambda) ₂ The two paths of interference light of the multi-channel data acquisition card respectively pass through the photoelectric converter to be subjected to photoelectric conversion to form corresponding electric signals, and the corresponding electric signals are acquired by the multi-channel data acquisition card;

the processor is used for utilizing a dual-wavelength linear regression phase unwrapping algorithm to acquire each group of wavelengths lambda of the multichannel data acquisition card ₁ And lambda (lambda) ₂ And (3) carrying out phase demodulation and winding on the electric signals corresponding to the two paths of interference light to obtain corresponding distributed vibration information.

Optionally, the dual-wavelength distributed optical fiber sensing demodulation system further comprises a dual-channel pulse program generator;

The first output channel of the dual-channel pulse program generator is connected with the control signal input end of the semiconductor optical amplifier to modulate the semiconductor optical amplifier; and a second output channel of the two-channel pulse program generator is connected with a synchronous acquisition control end of the multi-channel acquisition card so as to synchronously acquire.

Optionally, the dual-wavelength distributed optical fiber sensing demodulation system further comprises a four-port optical circulator;

the first end of the four-port optical circulator is connected with the output end of the sensing module, the second end of the four-port optical circulator is connected with the input end of the sensing module, the third end of the four-port optical circulator is connected with the communication end of the 3 x 3 optical fiber coupler in the interference module and the demodulation module, and the fourth end of the four-port optical circulator is connected with the input end of the second dense wavelength division multiplexing device in the demodulation module.

A dual-wavelength distributed optical fiber sensing demodulation method comprises the following steps:

generating a wavelength lambda ₁ And lambda (lambda) ₂ Is a dual wavelength narrow pulse optical signal;

with wavelength lambda ₁ And lambda (lambda) ₂ The dual-wavelength narrow pulse optical signal of the optical fiber is transmitted to a plurality of fiber bragg grating pairs which are connected in series in sequence by a sensing optical fiber, and the fiber bragg grating pairs have the Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ The optical fiber gratings are connected to form the optical fiber grating, and the intervals between any two adjacent optical fiber grating pairs are equal to each other, so that the dual-wavelength narrow pulse optical signals reflected by the optical fiber grating pairs are obtained;

forming a dual-wavelength interference signal by the dual-wavelength narrow pulse optical signal reflected by the former fiber bragg grating pair and the dual-wavelength narrow pulse optical signal reflected by the latter fiber bragg grating pair;

and performing photoelectric conversion on the dual-wavelength interference signal to generate a corresponding electric signal, and performing phase demodulation and unwrapping on the electric signal by utilizing a dual-wavelength linear regression analysis phase unwrapping algorithm to obtain corresponding distributed vibration information.

Optionally, the electric signal is subjected to phase demodulation and unwrapping by using a dual-wavelength linear regression analysis phase unwrapping algorithm to obtain corresponding distributed vibration information:

based on the electric signal corresponding to the dual-wavelength interference signal, winding phases under dual wavelengths after phase demodulation are obtained, and the winding phases under dual wavelengths satisfy the following conditions:

wherein d (n) is the optical path difference between the signal arm and the reference arm, θ ₁ w (n) and θ ₂ w (n) is the phase change, θ, caused by the same vibration signal at two different wavelengths ₁ (n) and θ ₂ (n) the same vibration signal is lambda at the wavelength ₁ And lambda (lambda) ₂ Digital phase variation, k, under laser light ₁ (n) and k ₂ (n) represents λ at each time of n ₁ And lambda (lambda) ₂ Phase winding integers for two wavelengths;

according to the same optical fiber strain or optical path difference change corresponding to different wavelengths under the same acoustic wave vibration, establishing a linear relationship between dual-wavelength phases, wherein the linear relationship between the dual-wavelength phases satisfies the following conditions:

at a point in time n, linearly traverse k ₁ (n) calculating a regression error function e [ k ] ₂ (n)]K under optimal least squares solution ₁ (n) and k ₂ (n) the regression error function e [ k ] ₂ (n)]The method meets the following conditions:

wherein round [ k ] ₁ (n)]Representation pair k ₁ Rounding of (n);

using k obtained by solving ₁ (n) and k ₂ (n) recovering the real phase corresponding to the moment;

and demodulating each moment independently to acquire all phases of each moment, and further obtaining corresponding distributed vibration information.

The security monitoring equipment comprises the dual-wavelength distributed optical fiber sensing demodulation system.

Compared with the prior art, the technical scheme has the following advantages:

the dual-wavelength distributed optical fiber sensing demodulation system provided by the embodiment of the application comprises a light source module and a sensing modeA block, an interference module and a demodulation module; the light source module is used for generating a wavelength lambda ₁ And lambda (lambda) ₂ The dual-wavelength narrow pulse optical signals are output to the sensing module; the sensing module comprises a plurality of fiber bragg grating pairs which are sequentially connected in series by sensing optical fibers, wherein the fiber bragg grating pairs have Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ The optical fiber gratings are connected to form the optical fiber grating, and the intervals between any two adjacent optical fiber grating pairs are equal; each fiber grating pair in the sensing module is used for reflecting the dual-wavelength narrow pulse optical signal, generating a reflected dual-wavelength narrow pulse optical signal and outputting the reflected dual-wavelength narrow pulse optical signal to the interference module; the interference module is used for forming a dual-wavelength interference signal by the dual-wavelength narrow pulse optical signal reflected by the previous fiber bragg grating pair and the dual-wavelength narrow pulse optical signal reflected by the next fiber bragg grating pair in the sensing module, and outputting the dual-wavelength interference signal to the demodulation module; the demodulation module is used for carrying out photoelectric conversion on the dual-wavelength interference signals to generate corresponding electric signals, and carrying out phase demodulation and unwrapping on the electric signals by utilizing a dual-wavelength linear regression phase unwrapping algorithm to obtain corresponding distributed vibration information; the dual-wavelength distributed optical fiber sensing demodulation system has the following advantages:

1. the new generation optical fiber sensing technology is introduced into a security monitoring system for the perimeter of a bank business in the financial security field, so that the property security of the bank business is further improved, and the national property security is ensured;

2. The dual-wavelength distributed optical fiber sensing demodulation system is an interference type optical fiber distributed acoustic sensing system, has high sensitivity, and can meet the effective data acquisition of various monitoring targets such as personnel, machinery, animals and the like;

3. the dual-wavelength distributed optical fiber sensing demodulation system carries out phase demodulation and unwrapping by adopting a dual-wavelength linear regression phase unwrapping algorithm, so that the dynamic range of the sensing system is ensured, and the reliability of the monitoring system is improved;

4. the sensing module in the dual-wavelength distributed optical fiber sensing demodulation system is composed of a plurality of fiber bragg grating pairs with sensing fibers connected in series in sequence, and a single linear sensing module can monitor important positions or places such as a business outlet entrance of a bank, a counter, a safe, a storehouse and the like at the same time, so that compared with the traditional multi-sensor monitoring, a great amount of cost can be saved;

5. the sensing module in the dual-wavelength distributed optical fiber sensing demodulation system can be laid in an embedded mode, can be buried and laid in the underground or material of each place of a bank business website, and can realize super-concealed sensing, so that on one hand, the alertness of criminals is reduced, and on the other hand, the overall image attractiveness of the website can be improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a prior art interferometric fiber bragg grating distributed acoustic sensing system;

FIG. 2 is a schematic diagram of a path matching interference of the distributed acoustic sensing system of the interferometric fiber bragg grating of FIG. 1;

FIG. 3 is an interference schematic diagram of the interferometric fiber grating distributed acoustic sensing system shown in FIG. 1;

fig. 4 is a schematic structural diagram of a dual-wavelength distributed optical fiber sensing demodulation system according to an embodiment of the present application;

fig. 5 is a schematic flow chart of a dual-wavelength distributed optical fiber sensing demodulation method according to an embodiment of the present application;

fig. 6 is a schematic distribution diagram of a security monitoring device according to an embodiment of the present application.

Detailed Description

The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, but the present application may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present application is not limited to the specific embodiments disclosed below.

To facilitate understanding of the present application, fiber optic sensing technology and existing distributed fiber optic sensing demodulation systems will be described first.

The optical fiber sensing technology is a novel sensing technology which is researched by people after the first global communication optical fiber is drawn by Corning corporation in the United states of America in 1970, and utilizes the transmission and sensing characteristics of the optical fiber, when the physical quantity of the external environment changes, the intensity, phase, wavelength, frequency and other characteristics of the transmitted light of the optical fiber also change correspondingly, and the change of the physical quantity of the external environment can be known through photoelectric conversion and characteristic analysis.

Since the advent of optical fiber sensing technology, optical fiber sensing technology has been studied in depth and widely used in the related fields of the military and civilians by virtue of its numerous absolute advantages. The optical fiber sensor has more stable sensing performance and wider application field than the traditional electromagnetic sensor by virtue of the advantages of electric insulation, intrinsic safety and extremely high light wave frequency of the optical fiber, which are not interfered by external common electromagnetic waves, and is widely applied to perimeter security detection in important places such as aerospace, petroleum power, ship bridges, civil and water conservancy and the like.

Distributed acoustic sensing (Distributed Acoustic Sensing, DAS) systems are one of the most important technologies with dynamic monitoring and application prospects among fiber optic distributed sensing technologies. The sound waves are often indistinguishable from vibration density, and safety and health monitoring, natural disasters, early warning of other various abnormal events and the like of a structure to be detected can be effectively realized by detecting vibration feedback conditions of related structures.

Among various optical fiber sensing modulation forms including intensity, wavelength, frequency, polarization state and the like, the phase modulation-based interference type optical fiber distributed acoustic sensing technology has extremely high sensitivity, senses external acoustic wave information according to the phase change of backward Rayleigh scattered light in a sensing optical fiber, and generally has long coherence length of a narrow line width light source used by a system, which can reach thousands of kilometers at maximum, and is extremely easy to generate interference effect, so the optical fiber distributed acoustic sensing technology is a sensing mode with extremely high detection sensitivity and is widely applied to the fields of microstrain measurement or acoustic sensing, such as structural health monitoring, perimeter security, optical fiber hydrophone, seismic wave monitoring and the like. The interference type fiber bragg grating is used as a reflecting element, and interference signals with signal to noise ratio 2-3 orders of magnitude higher than Rayleigh scattered light can be obtained through narrow light pulse dislocation interference, so that the interference type fiber bragg grating is a preferred technology for sensing with high sensitivity, high signal to noise ratio and high dynamic range.

Fig. 1 shows a schematic structural diagram of a conventional interference type fiber grating distributed acoustic sensing system, as shown in fig. 1, where the distributed acoustic sensing system mainly comprises a narrow linewidth laser, a semiconductor optical amplifier (Semiconductor Optical Amplifier, SOA), an Erbium-doped fiber amplifier (Erbium-Doped Fiber Amplifier, EDFA), an isotactic weak fiber grating (Fiber Bragg Grating, FBG) array (hereinafter referred to as a fiber grating array), an unbalanced michelson interferometer (Unbalanced Michelson Interferometer, UMI), three-port optical circulators C1, C2, and modules (such as photoelectric converters PD1, PD2, PD3, and digital acquisition cards) for photoelectric receiving and processing. In the fiber grating array, the central wavelength, 3dB bandwidth, reflectivity and other device parameters of each fiber grating (FBG#1, FBG#2, FBG#3 …) are basically consistent, and the distance between any two adjacent fiber gratings is equal, wherein in fig. 1, the distance is 5m; the unbalanced Michelson interferometer mainly comprises a 3×3 coupler, two Faraday gyros (Faraday Rotator Mirror, FRM1 and FRM2 in fig. 1) and two interference arms with unequal lengths, wherein the arm length difference of the two interference arms is a delay optical fiber with the length difference of 5m, namely, the arm length difference of the two interference arms of the unbalanced Michelson interferometer is equal to the distance between two adjacent fiber gratings in a fiber grating array, and the Faraday gyros compensate the fiber birefringence effect introduced by the fact that the two interference arms in the interferometer are common single-mode fibers by utilizing 45-degree optical rotation characteristics.

In fig. 1, the full weak fiber bragg grating array forms a Fizeou type interference structure, each fiber bragg grating in the fiber bragg grating array is an array reflection element, and a sensing fiber between every two adjacent fiber bragg gratings is an independent acoustic wave sensing area.

Fig. 2 shows a path matching interference schematic diagram of the interference type optical fiber grating distributed acoustic sensing system shown in fig. 1, and in combination with fig. 1 and fig. 2, it can be known that, in specific operation, a narrow pulse optical signal emitted by a narrow linewidth laser device arrives at an identical weak optical fiber grating array through a semiconductor optical amplifier SOA, an erbium-doped optical fiber amplifier EDFA and a three-port optical circulator C1, each optical fiber grating in the identical weak optical fiber grating array reflects the narrow pulse optical signal to form a reflection pulse sequence, the reflection pulse sequence is transmitted to an unbalanced michelson interferometer, and because the arm length difference of two interference arms is equal to the distance between two adjacent optical fiber gratings in the optical fiber grating array, the narrow optical pulse reflected by the former optical fiber grating and the narrow optical pulse reflected by the latter optical fiber grating are just overlapped in time, so as to form an interference optical pulse sequence, the interference optical pulse sequence passes through a 3×3 coupler to form three paths, and is respectively subjected to photoelectric conversion and finally acquired by a digital acquisition card, and finally converted into a time domain signal, so as to obtain distributed vibration information, and the sound wave sensing is performed independently between any two adjacent optical fiber gratings.

Fig. 3 shows an interference schematic diagram of an interference type optical fiber grating distributed acoustic sensing system, and referring to fig. 3, pulse light passes through each optical fiber grating to form a reflected narrow pulse, and according to Fizeau interference theory, it is assumed that the light intensities input to the optical fiber gratings fbg#1 and fbg#2 are I respectively _s1 And I _s2 The corresponding reflected light intensity is I _r1 And I _r2 Then I _r1 And I _r2 Coherent light interference and reflected light I will occur at the unbalanced Michelson interferometer _r1 And I _r2 The electric field strengths of (2) can be expressed as:

E ₁ ＝I _r1 exp{-2j(knz ₀ )} (1)

E ₂ ＝I _r2 exp{-2j[kn(z ₀ +z)]} (2)

where k is the wavenumber of the light wave and k=2pi/λ ₀ ，λ ₀ Is the wavelength of the light wave and n is the core refractive index of the fiber. When I _r1 And I _r2 After interference occurs, the intensity of the returned interference pulse is as follows:

I _R ＝(E ₁ +E ₂ )(E ₁ +E ₂ ) ^* ＝I _r1 ² +I _r2 ² +2I _r1 I _r2 cos(knz) (3)

from equation (3), it is known that the reflected interference signal is only related to the pitch z of the fiber grating and the core refractive index n of the fiber. When the surrounding environment of the fiber grating changes, the change of the fiber grating spacing and the refractive index of the fiber core is caused, so that the change is perceived, wherein the refractive index of the fiber core is usually negligible in the actual environment.

Equation (3) analyzes the acoustic wave sensing mechanism from the interference angle, and the analysis is performed from the phase angle.

Let the length of the optical fiber be L ₀ The phase delay phi generated after the light passes through is:

Wherein n represents the refractive index of the fiber core, lambda represents the wavelength of light, k ₀ Representing the wavenumber of light in vacuum, β represents the propagation constant of light, which can be calculated by equation (5):

β＝k ₀ n (5)

according to the strain sensing mathematical model of the optical fiber, the change of the optical wave phase delay caused by the change of external physical quantity (temperature, stress strain and the like) is as follows:

in the formula (6), the three terms of the right formula respectively represent different stress-strain effects: the leader represents the phase change caused by the change in the length of the fiber, called strain effect; the intermediate term represents the phase change caused by the change of the refractive index of the optical fiber, and is called photoelastic effect or optical gap effect; the tail represents the phase change caused by the change in the radius of the fiber, known as the poisson effect. This is a mathematical model of the stress-strain of the fiber, where the acoustic wave causes very little, usually negligible, change in the fiber radius.

For the refractive index of the optical fiber, the refractive index change of the optical fiber caused by sound waves can be described by using the optical index B parameter, and if the optical fiber material is uniform and isotropic, the three axial optical index change delta B of the optical fiber material is stressed in a non-axial direction _i And strain epsilon corresponding to three directions _i The mathematical relationship in equation (7) can be satisfied:

Wherein B is _i ＝1/n _i ² Elastic light matrix { P } _ij And is a symmetric matrix in which matrix coefficients P ₁₁ And P ₁₂ And are related to the optical fiber material, and P ₃₃ ＝(P ₁₁ -P ₁₂ )/2，ε ₁ And epsilon ₂ Are all representative of the transverse (and radial) strain, ε, of the fiber ₃ Representing the longitudinal (axial) strain of the fibre, i.e. DeltaL/L ₀ 。

Differentiating the two sides of the formula (7) respectively to obtain a formula (8):

according to elastic mechanics, the refractive index change under three-direction strain of an optical fiber has the following relationship:

generally, optical fiber distributed sound in the kHz and below frequency bandsThe optical sensing system mainly measuring axial strain of the optical fibre, i.e. epsilon ₃ Thus, ε can be reduced ₁ Substituting 0 and formula (9) into formula (6) to obtain the optical wave phase delay change delta phi and the axial strain epsilon of the optical fiber caused by the change of external physical quantity (temperature, stress strain and the like) ₃ The following relationship is satisfied:

wherein G is _ε ＝(1-0.5n ² P ₁₂ ) Referred to as strain factor, is typically at a level of 0.7 to 0.8 in common single mode fibers.

Assuming that the wavelength lambda=1550 nm of the incident light wave, the refractive index n=1.4682@1550nm of the fiber core is the strain factor G _ε By equation (10), the axial strain sensitivity of the ordinary fiber can be calculated to be about 4.64 rad/(με·m), and it is calculated that a 5m length fiber carrying 1 με axial strain in an interferometric fiber bragg grating distributed acoustic sensing system will produce a phase delay of 46.42rad, i.e., 0.046rad/nε@5m or 21.65nε/rad@5m. Therefore, the phase modulation can realize extremely high detection sensitivity, which is incomparable with modulation schemes such as wavelength modulation, light intensity modulation and the like.

From equation (10), the phase change Δφ caused by the acoustic wave and the axial strain ε of the optical fiber ₃ In good linear relation, quantitative linear test on sound waves can be realized by utilizing the phase, and the formula (10) is simplified as follows:

wherein θ (n) is the actual phase at the nth time, d (n) is the change in optical path difference in the optical fiber caused by the disturbance of the optical fiber, λ is the laser wavelength, θ _w (n) is the main value after phase winding at this time, satisfying θ _w (n) ε (-pi, pi), k (n) is a 2 pi weighting factor, also known as the phase wrapping factor.

In the prior art, for the electric signals collected by the data acquisition card after the interference signals are subjected to photoelectric conversion, one is a single-wavelength phase unwrapping algorithm, and the other is a dual-wavelength synthetic wavelength phase unwrapping algorithm.

The single-wavelength phase unwrapping algorithm is mainly based on pi phase principle, and phase unwrapping is achieved through compensation of the wrapping coefficient in the formula (11). The compensation rule of the winding coefficient k (n) is shown in the following formula (12), on the premise that the real phase to be detected meets the pi phase principle, the standard of the winding coefficient compensation is to compare the winding phase conditions of two adjacent sampling points, if the winding phase conditions are smaller than pi, the winding coefficient at the current moment is added with 1 on the basis of the previous moment, if the winding phase conditions are larger than pi, the winding coefficient is subtracted by 1, and if the winding phase conditions are between pi and pi, the winding coefficient at the current moment and the previous moment are kept consistent.

From the above analysis, it can be seen that the single-wavelength phase unwrapping algorithm depends on pi phase principle, and when the real phase signal does not satisfy pi phase principle, such as the amplitude difference between adjacent phase values is not less than 3 pi or not greater than-3 pi, the single-wavelength phase unwrapping algorithm fails, and the real phase cannot be tracked quickly.

The two-wavelength synthesized wavelength phase unwrapping algorithm is a phase unwrapping algorithm derived from the inverse relationship between wavelength and phase in equation (11), by using two different wavelengths (assuming λ respectively) ₁ And lambda (lambda) ₂ And lambda is ₁ <λ ₂ ) As can be seen from the formula (10), the variation of the retardation phase of the light wave and the axial strain ε of the acoustic wave ₃ The optical path difference changes are always the same under the same acoustic disturbance at different wavelengths, namely the acoustic signals perceived in the same optical fiber are represented. Thus, the interference phase at dual wavelengths is:

differentiating the formula (13) and the formula (14) to obtain a formula (15):

Λ=λ in the above ₁ λ ₂ /(λ ₂ -λ ₁ ) Known as the composite wavelength (or composite wavelength), is also the name of the phase unwrapping algorithm. As can be seen from the comparison between the formulas (11) and (15), the synthesized wavelength is far greater than any one of the original dual wavelengths, so that the range of the winding phase value at the synthesized wavelength is greatly increased compared with that of the single wavelength, and the dynamic range is improved to a certain extent. However, in the above differential operation, the phase noise of the system is not effectively subtracted, but noise superposition occurs, resulting in further amplification of the phase noise of the dual-wavelength system.

Therefore, the existing optical fiber distributed acoustic sensing system adopts a single-wavelength phase unwrapping algorithm to rely on pi phase principle, when a real phase signal does not meet pi phase principle, such as the amplitude difference of adjacent phase values is not smaller than 3 pi or not larger than-3 pi, the single-wavelength phase unwrapping algorithm is invalid and cannot timely track the rapid change of a real phase, and the phase noise of the system is further amplified by adopting a dual-wavelength synthesized wavelength unwrapping algorithm.

In view of this, the embodiment of the present application provides a dual-wavelength distributed optical fiber sensing demodulation system, and fig. 4 shows a schematic structural diagram of the dual-wavelength distributed optical fiber sensing demodulation system provided in the embodiment of the present application, and as shown in fig. 4, the dual-wavelength distributed optical fiber sensing demodulation system includes a light source module 100, a sensing module 200, an interference module 300 and a demodulation module 400;

wherein the light source module 100 is used for generating a wavelength lambda ₁ And lambda (lambda) ₂ Is output to the sensing module 200;

the sensing module 200 includesThe plurality of fiber grating pairs (fbgp#1, fbgp#2, fbgp#3, fbgp#4, fbgp#5 …) connected in series in sequence by the sensing fibers (sensor#1, sensor#2, sensor#3, sensor#4 … in fig. 4) are shown as an enlarged view of the fiber grating pairs in fig. 4, and the fiber grating pairs are shown as bragg wavelengths lambda ₁ Has a Bragg wavelength lambda ₂ The optical fiber gratings of the optical fiber grating pair are connected, and the intervals between any two adjacent optical fiber grating pairs are equal, for example, 5m marked in fig. 4; each fiber grating pair in the sensing module 200 is used for reflecting the dual-wavelength narrow pulse optical signal, generating a reflected dual-wavelength narrow pulse optical signal, and outputting the reflected dual-wavelength narrow pulse optical signal to the interference module 300;

the interference module 300 is configured to form a dual-wavelength interference signal from the dual-wavelength narrow pulse optical signal reflected by the previous fiber bragg grating pair and the dual-wavelength narrow pulse optical signal reflected by the next fiber bragg grating pair in the sensing module 200, and output the dual-wavelength interference signal to the demodulation module 400;

the demodulation module 400 is configured to perform photoelectric conversion on the dual-wavelength interference signal, generate a corresponding electrical signal, and perform phase demodulation and unwrapping on the electrical signal by using a dual-wavelength linear regression analysis phase unwrapping algorithm, so as to obtain corresponding distributed vibration information.

Specifically, as shown in fig. 4, the light source module 100 includes:

a first narrow-band laser TL1 and a first polarization controller PC1, the first narrow-band laser TL1 for generating a wavelength lambda ₁ The narrow-band laser of (2) is output after polarization modulation by a first polarization controller PC 1;

a second narrow-band laser TL2 and a second polarization controller PC2, the second narrow-band laser TL2 for generating a wavelength lambda ₂ The narrow-band laser of (2) is output after polarization modulation by a second polarization controller PC 2;

a first dense wavelength division multiplexer DWDM1 for outputting the first narrow-band laser TL1 with a wavelength lambda ₁ The wavelength of the narrowband laser light outputted from the second narrowband laser TL2 is lambda ₂ Is mixed with the narrow-band laser to form dual-wavelength mixed laser;

a semiconductor optical amplifier SOA for modulating the dual-wavelength mixed laser output by the first dense wavelength division multiplexing device DWDM1 into dual-wavelength narrow optical pulses with high extinction ratio;

the erbium-doped optical fiber amplifier EDFA is used for amplifying the dual-wavelength narrow optical pulse output by the semiconductor optical amplifier SOA, and the wavelength after output amplification is lambda ₁ And lambda (lambda) ₂ Is a dual wavelength narrow pulse optical signal.

The first and second narrowband lasers TL1 and TL2 may be Tunable Lasers (TL) with a wavelength λ ₁ And lambda (lambda) ₂ Can be 1535.048nm and 1564.954nm respectively, the line width can be 500kHz and 100kHz respectively, and the corresponding synthetic wavelength is 80.328 μm.

The output ends of the first narrow-band laser TL1 and the second narrow-band laser TL2 are respectively and correspondingly connected with polarization controllers (PC 1 and PC 2) for controlling the polarization of the laser output light to suppress polarization induced fading caused by polarization change of sensing fibers in the grating fiber array; the polarization-adjusted dual-wavelength laser realizes dual-wavelength mixed transmission through a first dense wavelength division multiplexing (DWDM 1) (Dense Wavelength Division Multiplexer, DWDM), is modulated into a narrow optical pulse with high extinction ratio (> 50 dB) through a Semiconductor Optical Amplifier (SOA), and is effectively amplified by an erbium-doped fiber amplifier (EDFA) and then output to the sensing module 200.

Optionally, as shown in fig. 4, the light source module 100 further includes a three-port optical circulator CIR1 and a dual-wavelength matching fiber grating pair CM;

the first end of the three-port optical circulator CIR1 is connected with the output end of the erbium-doped fiber amplifier EDFA, the second end of the three-port optical circulator CIR1 is connected with the input end of the sensing template 200, and the third end of the three-port optical circulator CIR1 is connected with the dual-wavelength matching fiber grating pair CM;

the dual-wavelength matching fiber grating CM pair is characterized by Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ Is formed by connecting fiber gratings;

when the dual-wavelength narrow pulse optical signal amplified by the erbium-doped fiber amplifier EDFA passes through the three-port optical circulator CIR1, the dual-wavelength matching fiber grating pair CM filters out broadband spontaneous radiation noise, and then the broadband spontaneous radiation noise is output to the sensing module 200.

In this embodiment, the dual-wavelength narrow pulse optical signal amplified by the erbium-doped fiber amplifier EDFA is filtered by the dual-wavelength matching fiber grating pair CM with high reflectivity, whose broadband spontaneous emission noise is filtered, and is incident into the sensing module 200,

as shown in fig. 4, the sensing module 200 is formed by sequentially connecting a plurality of fiber grating pairs (fbgp#1, fbgp#2, fbgp#3, fbgp#4, fbgp#5 … in fig. 4) in series by sensing fibers (sensor#1, sensor#2, sensor#3, sensor#4, … in fig. 4), that is, forming a fiber grating array, and in the sensing module 200, each fiber grating pair forms a reflection surface for reflecting a dual wavelength light pulse. The number of fiber grating pairs is not limited, and is specifically determined according to the situation.

Alternatively, each fiber grating pair has a Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ The spacing of the adjacent ends of the fiber gratings may be 2mm and the spacing of the spaced apart ends may be 6mm.

As shown in fig. 4, the interference module 300 may be an unbalanced michelson interferometer UMI, and specifically includes a 3×3 optical fiber coupler CP, a first interference arm and a second interference arm, where one of the first interference arm and the second interference arm is used as a signal arm, the other is used as a reference arm, the first interference arm is provided with a delay optical fiber DF and a first faraday rotation mirror FRM1, the second interference arm is provided with a second faraday rotation mirror FRM2, and the length DF of the delay optical fiber is equal to the distance between two adjacent fiber grating pairs in the sensor module 200, for example, both the lengths DF and the distances between two adjacent fiber grating pairs are 5m;

the dual-wavelength narrow pulse optical signals output from the sensing module 200 and reflected by the respective fiber grating pairs are divided into three paths of reflected dual-wavelength narrow pulse optical signals after passing through the 3×3 fiber coupler CP, wherein the first path of reflected dual-wavelength narrow pulse optical signals pass through the first interference arm, the second path of reflected dual-wavelength narrow pulse optical signals pass through the second interference arm, and the third path of reflected dual-wavelength narrow pulse optical signals are cut off due to no effect on interference, so that the dual-wavelength narrow pulse optical signals reflected by the previous fiber grating pair and the dual-wavelength narrow pulse optical signals reflected by the next fiber grating pair in the sensing module 200 are formed into dual-wavelength interference signals, and the 3×3 fiber coupler CP divides the dual-wavelength interference signals into three paths of interference light with preset phase differences.

In the fiber grating array of the sensing module 200, the two-wavelength narrow pulse optical signal reflected by the former fiber grating pair and the two-wavelength narrow pulse optical signal reflected by the latter fiber grating pair are just overlapped in time, so that a two-wavelength interference signal is formed in the unbalanced michelson interferometer UMI, and the two-wavelength lasers are respectively interfered and are not mutually influenced, and the 3×3 fiber coupler CP performs the beam splitting treatment on the two-wavelength interference light, and outputs three paths of interference light with preset phase differences.

As shown in fig. 4, the demodulation module 400 includes a second DWDM2, a third DWDM3, a fourth DWDM4, six photoelectric converters PD, a multi-channel data acquisition card DAQ, and a processor PRO;

the second dense wavelength division multiplexer DWDM2 is configured to perform wavelength division multiplexing on the first path of interference light output by the 3×3 optical fiber coupler CP to obtain a first group of wavelengths lambda ₁ And lambda (lambda) ₂ Is a light source for the light beam;

the third dense wavelength division multiplexer DWDM3 is configured to perform wavelength division multiplexing on the second interference light output by the 3×3 optical fiber coupler CP to obtain a second group of wavelengths lambda ₁ And lambda (lambda) ₂ Is a light source for the light beam;

the fourth dense wavelength division multiplexer DWDM4 is configured to perform wavelength division multiplexing on the third interference light output by the 3×3 optical fiber coupler CP to obtain a third group of wavelengths lambda ₁ And lambda (lambda) ₂ Is a light source for the light beam;

each group has a wavelength lambda ₁ And lambda (lambda) ₂ The two paths of interference light of the optical fiber pass through a photoelectric converter PD to be subjected to photoelectric conversion respectively to form corresponding electric signals, and the corresponding electric signals are collected by a multichannel data collection card DAQ;

the processor PRO is used for utilizing a dual-wavelength linear regression phase unwrapping algorithm to acquire each group of wavelengths lambda of the multichannel data acquisition card DAQ ₁ And lambda (lambda) ₂ And (3) carrying out phase demodulation and winding on the electric signals corresponding to the two paths of interference light to obtain corresponding distributed vibration information.

As shown in fig. 4, the dual-wavelength distributed optical fiber sensing demodulation system provided in the embodiment of the present application further includes a dual-channel pulse generator (Program Pulse Generator, PPG), where a first output channel of the dual-channel pulse generator PPG is connected to a control signal input end of the semiconductor optical amplifier SOA, and modulates the semiconductor optical amplifier SOA; the second output channel of the PPG of the two-channel pulse program generator is connected with the synchronous acquisition control end of the multichannel acquisition card DAQ so as to synchronously acquire.

As shown in fig. 4, the dual-wavelength distributed optical fiber sensing demodulation system provided in the embodiment of the present application further includes a four-port optical circulator CIR2; the first end of the four-port optical circulator CIR2 is connected with the output end of the light source module 100, the second end of the four-port optical circulator CIR2 is connected with the input end of the sensing module 200, the third end of the four-port optical circulator CIR2 is connected with the communication end connected with the 3×3 optical fiber coupler CP in the interference module 300 and the demodulation module 400, and the fourth end of the four-port optical circulator CIR2 is connected with the input end of the second dense wavelength division multiplexer DWDM2 in the demodulation module 400.

The sampling rate of the multichannel data acquisition card DAQ is up to 250MHz, the sampling depth is 14bits, and powerful conditions are provided for high-speed and high-precision acquisition of narrow-pulse interference optical signals.

The fiber grating array in the sensing module 200 is formed by inscribing two adjacent narrow-band weak fiber gratings to form a pair of dual-wavelength weak fiber gratings, wherein the center wavelengths of the two narrow-band weak fiber gratings are 1535.0nm and 1565.5nm respectively, the grating length is 2mm, and the reflectivity is designed to be 0.1%. In order to avoid crosstalk generated on adjacent fiber gratings in the writing process of the mask, the distance between two narrow-band weak fiber gratings is correspondingly controlled within 2 mm.

How the processor PRO uses the Dual-wavelength linear regression phase unwrapping algorithm (Dual-wavelength Linear Regression Phase Unwrapping,2λ -LRPU) to acquire the respective set of wavelengths λ for the multichannel data acquisition card DAQ in conjunction with FIG. 5 ₁ And lambda (lambda) ₂ And (3) carrying out phase demodulation and winding on the electric signals corresponding to the two paths of interference light to obtain corresponding distributed vibration information for explanation.

Firstly, based on an electric signal corresponding to a dual-wavelength interference signal, winding phases under dual wavelengths after phase demodulation are obtained, and the winding phases under the dual wavelengths are obtained by deforming the formula (13) and the formula (14) in the prior art, wherein the winding phases under the dual wavelengths satisfy the following relation:

secondly, according to the identity of optical fiber acoustic sensing under the dual wavelength, namely that the optical fiber strain or optical path difference change corresponding to different wavelengths under the same acoustic vibration is the same, the combination equality of the formula (16) and the formula (17) can be obtained:

from equation (18), a linear relationship between the phases of the two wavelengths, i.e., the phase wrapping coefficient k at the two wavelengths, can be further established ₁ (n) and k ₂ A constraint relationship between (n), said dual wavelength inter-phase linear relationship satisfying:

wherein k is ₁ (n) and k ₂ And (n) are phase winding coefficients under the dual wavelengths respectively, and are all of integer types.

Thus, the regression error function e [ k ] can be located ₂ (n)]The method meets the following conditions:

e[k ₂ (n)]＝{k ₁ (n)-round[k ₁ (n)]} ² (20)

wherein round [ k1 (n)]Representation pair k ₁ Rounding of (n).

Further, for the regression error function e [ k ] ₂ (n)]At a point in time n, by linear traversal k ₁ (n) calculating a regression error function e [ k ] by combining a least squares optimization algorithm ₂ (n)]K under optimal least squares solution ₁ (n) and k ₂ (n), i.e. solving for k corresponding to true phase ₁ (n) and k ₂ (n)。

Then, the obtained k is used for solving ₁ (n) and k ₂ (n) recovering the true phase corresponding to the point in time.

And finally, independently demodulating each moment to acquire all phases of each moment, and further obtaining corresponding distributed vibration information.

Therefore, the dual-wavelength distributed optical fiber sensing demodulation system provided by the embodiment of the application utilizes a phase unwrapping algorithm with a higher dynamic range, which is based on the dual-wavelength interference demodulation technology, uses a dual-wavelength linear regression idea and combines a least square optimal solution, breaks the phase principle limitation in the traditional single-wavelength and composite wavelength phase demodulation, and realizes digital phase demodulation with a high dynamic range irrelevant to the sampling rate, namely, the fiber grating array distributed acoustic sensing system consisting of array elements by the dual-wavelength weak fiber gratings provided by the embodiment of the application not only improves the dynamic range of a DAS system, but also reduces the sampling rate requirement and the system noise.

Correspondingly, the embodiment of the application also provides a dual-wavelength distributed optical fiber sensing demodulation method, as shown in fig. 5, which comprises the following steps:

s100: generating a wavelength lambda ₁ And lambda (lambda) ₂ Is a dual wavelength narrow pulse optical signal;

s200: with wavelength lambda ₁ And lambda (lambda) ₂ The dual-wavelength narrow pulse optical signal of the optical fiber is transmitted to a plurality of fiber bragg grating pairs which are connected in series in sequence by a sensing optical fiber, and the fiber bragg grating pairs have the Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ The optical fiber gratings are connected to form the optical fiber grating, and the intervals between any two adjacent optical fiber grating pairs are equal to obtain the dual-wavelength narrow pulse optical signals reflected by each optical fiber grating pair;

s300: forming a dual-wavelength interference signal by the dual-wavelength narrow pulse optical signal reflected by the former fiber bragg grating pair and the dual-wavelength narrow pulse optical signal reflected by the latter fiber bragg grating pair;

s400: photoelectric conversion is carried out on the dual-wavelength interference signals to generate corresponding electric signals, and phase demodulation and phase unwrapping are carried out on the electric signals by utilizing a dual-wavelength linear regression analysis phase unwrapping algorithm to obtain corresponding distributed vibration information.

Further, in step S400, the electric signal is phase demodulated and unwrapped by using a dual-wavelength linear regression analysis phase unwrapping algorithm, so as to obtain corresponding distributed vibration information:

S410: based on the electric signal corresponding to the dual-wavelength interference signal, winding phases under dual wavelengths after phase demodulation are obtained, and the winding phases under dual wavelengths satisfy the following conditions:

wherein d (n) is the optical path difference between the signal arm and the reference arm, θ ₁ w (n) and θ ₂ w (n) is the phase change induced by the same vibration signal at two different wavelengths,θ ₁ (n) and θ ₂ (n) the same vibration signal is lambda at the wavelength ₁ And lambda (lambda) ₂ Digital phase variation, k, under laser light ₁ (n) and k ₂ (n) represents λ at each time of n ₁ And lambda (lambda) ₂ Phase winding integers for two wavelengths;

s420: according to the same optical fiber strain or optical path difference change corresponding to different wavelengths under the same acoustic wave vibration, establishing a linear relationship between dual-wavelength phases, wherein the linear relationship between dual-wavelength phases satisfies the following conditions:

s430: at a point in time n, linearly traverse k ₁ (n) calculating a regression error function e [ k ] ₂ (n)]K under optimal least squares solution ₁ (n) and k ₂ (n) regression error function e [ k ] ₂ (n)]The method meets the following conditions:

e[k ₂ (n)]＝{k ₁ (n)-round[k ₁ (n)]} ² (20)

wherein round [ k ] ₁ (n)]Representation pair k ₁ Rounding of (n);

s440: using k obtained by solving ₁ (n) and k ₂ (n) recovering the real phase corresponding to the moment;

s450: and demodulating each moment independently to acquire all phases of each moment, and further obtaining corresponding distributed vibration information.

The dual-wavelength distributed optical fiber sensing demodulation method provided by the embodiment of the application corresponds to the dual-wavelength distributed optical fiber sensing demodulation device, and the dual-wavelength distributed optical fiber sensing demodulation device has been described in detail, which is not repeated here.

The embodiment of the application also provides a security monitoring device, as shown in fig. 6, which can be security monitoring devices of banking business outlets, and the security monitoring device comprises the dual-wavelength distributed optical fiber sensing demodulation system (shown in a DAS instrument and a connecting line area thereof in fig. 6) provided by any embodiment. It can be seen that the dual-wavelength distributed optical fiber sensing demodulation system can be buried and laid at important positions or places such as a bank business outlet entrance, a financial counter, financial machines, a safe, a warehouse and the like, the optical fiber grating array can utilize a space division multiplexing technology to realize the function of simultaneously monitoring multiple targets of the bank business outlet system by a single linear sensor array, can realize high concealment by adopting an embedded layout mode, enhances the overall attractiveness, and can effectively monitor the perimeter security of the bank business outlet through further data acquisition and data analysis.

Since the dual-wavelength distributed optical fiber sensing demodulation apparatus has been described in detail above, a detailed description thereof will be omitted.

In summary, for various practical problems such as large monitoring difficulty, small monitoring range, low sensitivity, high cost, poor concealment, unattractive appearance, high failure rate and the like in the conventional perimeter security protection of the bank business sites, the dual-wavelength distributed optical fiber sensing demodulation system and the method thereof, and the security protection monitoring equipment provided by the embodiment of the application have the following advantages:

In the description, each part is described in a parallel and progressive mode, and each part is mainly described as a difference with other parts, and all parts are identical and similar to each other.

The features described in the various embodiments of the present disclosure may be interchanged or combined with one another in the description to enable those skilled in the art to make or use the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The dual-wavelength distributed optical fiber sensing demodulation system is characterized by comprising a light source module, a sensing module, an interference module and a demodulation module;

the sensing module comprises a plurality of fiber bragg grating pairs which are sequentially connected in series by sensing fibers, wherein the fiber bragg grating pairs are formed by Bragg wavelength lambda ₁ Has a Bragg wavelength lambda ₂ The optical fiber gratings are connected to form the optical fiber grating, and the intervals between any two adjacent optical fiber grating pairs are equal; each fiber grating pair in the sensing module is used for reflecting the dual-wavelength narrow pulse optical signal to generate a reflected dual-wavelength narrow pulse optical signalOutputting to the interference module;

2. The dual wavelength distributed optical fiber sensing demodulation system of claim 1 wherein the light source module comprises:

3. The dual wavelength distributed optical fiber sensing demodulation system of claim 2 wherein the light source module further comprises a three port optical circulator and a dual wavelength matched fiber grating pair;

4. The dual wavelength distributed optical fiber sensing demodulation system according to claim 2 or 3 wherein the interference module comprises a 3 x 3 optical fiber coupler, a first interference arm and a second interference arm, the first interference arm is provided with a delay optical fiber and a first faraday rotation mirror, the second interference arm is provided with a second faraday rotation mirror, and the length of the delay optical fiber is equal to the distance between two adjacent pairs of optical fiber gratings in the sensing module;

5. The dual wavelength distributed optical fiber sensing demodulation system of claim 4 wherein the demodulation module comprises a second dense wavelength division demultiplexer, a third dense wavelength division demultiplexer, a fourth dense wavelength division demultiplexer, six optical-to-electrical converters, a multichannel data acquisition card, and a processor;

the second dense wavelength division multiplexer is used for performing wavelength division multiplexing on the first path of interference light output by the 3×3 optical fiber coupler to obtain a first group of wavelengths lambda ₁ And lambda (lambda) ₂ Is a light source for the light beam;

6. The dual wavelength distributed optical fiber sensing demodulation system of claim 5 further comprising a dual channel pulse program generator;

7. The dual wavelength distributed optical fiber sensing demodulation system of claim 5 further comprising a four port optical circulator;

8. The dual-wavelength distributed optical fiber sensing demodulation method is characterized by comprising the following steps of:

9. The method for dual wavelength distributed optical fiber sensing demodulation according to claim 8, wherein the electrical signal is phase demodulated and demodulated by using a dual wavelength linear regression analysis phase unwrapping algorithm to obtain corresponding distributed vibration information:

e[k ₂ (n)]＝{k ₁ (n)-round[k ₁ (n)]} ²

wherein round [ k ] ₁ (n)]Representation pair k ₁ Rounding of (n);

10. A security monitoring device comprising the dual wavelength distributed optical fiber sensing demodulation system of any one of claims 1-7.