A simulation modeling method for distributed fiber optic acoustic sensing system

Abstract

A simulation modeling method for a distributed optical fiber acoustic sensor system relates to the field of distributed monitoring technology, comprising: based on Simulink modules, a laser model, a beam splitter model, an acousto-optic modulator model, an erbium-doped optical fiber amplifier and attenuator model, a sensing optical fiber model, a photodetector model, an external disturbance model and an optical fiber coupler model are respectively constructed and packaged respectively; according to an optical path diagram of the distributed optical fiber acoustic sensor system, corresponding functional modules are added to a Simulink workspace; using signal lines, an input signal of a module is connected with an output signal of another module having the same name; the Simulink modeling of the distributed optical fiber acoustic sensor system is completed for simulation operation; an intuitive basis is provided for debugging, installation, fault diagnosis and system optimization of the distributed optical fiber acoustic sensor system; and the problem of no Simulink modeling method and system for the distributed optical fiber acoustic sensor system is solved.

Description

Technical Field

[0001] The invention relates to the technical field of distributed monitoring, and in particular to a simulation modeling method for a distributed optical fiber acoustic sensor system. Background Art

[0002] Distributed fiber acoustic sensing (DAS) system is one of the fastest-growing fiber sensing technologies in the past decade. The system is based on the principle of phase-sensitive time-domain reflectometry (φ-OTDR). A narrow linewidth laser injects narrow pulse light into the optical fiber, and detects the vibration wave field at various positions on the optical fiber by extracting the phase difference between the backscattered Rayleigh scattered light signals at different times in the optical fiber. The distributed fiber acoustic sensing (DAS) system can realize continuous full-scale distributed monitoring in real space, and has the advantages of long monitoring distance, multiple measurement parameters, high sensitivity, fast response speed, good signal-to-noise ratio, no need for external power supply, and anti-electromagnetic interference. It is a technology urgently needed in the current fields of national defense, earthquake, petroleum, and electricity.

[0003] Distributed fiber acoustic sensing (DAS) systems involve many optical devices, most of which are modular devices, expensive, and high-precision. If the parameters of the purchased optical devices are not matched properly, it will affect the system performance and even burn the devices, thereby increasing the experimental cost and R&D cycle. Therefore, it is necessary to carry out modeling and simulation research based on the actual characteristics of optical devices. In addition, based on system simulation, it is also easy to obtain the optical phenomena after the optical signal passes through different optical devices, which is important for the debugging, installation, fault diagnosis, and system optimization of distributed fiber acoustic sensing (DAS) systems. At present, there is no report on the Simulink modeling method and system of distributed fiber acoustic sensing (DAS) systems. Summary of the invention

[0004] The embodiment of the present invention provides a simulation modeling method for a distributed optical fiber acoustic sensor system. Based on the mathematical model and instruction manual of the optoelectronic device of the distributed optical fiber acoustic sensor system, a device model is built, and a Simulink device module is formed after packaging, and a device module library is formed: a user selects a suitable device module from the device module library, and can freely build a distributed optical fiber acoustic sensor system structure required by the user; the device module built according to the device module can simulate the influence of the device parameter on the system operation, and can verify and optimize the user's design scheme; in the output signal part of the device module, it is easy to connect to To Workspace, and obtain the optical phenomenon of the optical signal after passing through different optical devices after the system is running, so as to provide an intuitive basis for the debugging, installation, fault diagnosis and system optimization of the distributed optical fiber acoustic sensor system, and solve the problem of no Simulink modeling method and system for the distributed optical fiber acoustic sensor system.

[0005] A simulation modeling method for a distributed optical fiber acoustic sensing system comprises the following steps:

[0006] Step 1: According to the laser mathematical model, based on the Simulink module, a laser model is constructed and packaged into a laser module;

[0007] Step 2, according to the beam splitter mathematical model, based on the Simulink module, construct the beam splitter model and encapsulate it into a beam splitter module;

[0008] Step 3, according to the mathematical model of the acousto-optic modulator, based on the Simulink module, construct the acousto-optic modulator model and encapsulate it into an acousto-optic modulator module;

[0009] Step 4, according to the mathematical model of the erbium-doped fiber amplifier and the mathematical model of the attenuator, based on the Simulink module, construct the erbium-doped fiber amplifier and attenuator models, and encapsulate them into an erbium-doped fiber amplifier module;

[0010] Step 5, constructing a sensing optical fiber model based on the sensing optical fiber mathematical model and the Simulink module, and encapsulating it into a sensing optical fiber module;

[0011] Step 6, according to the mathematical model of the photodetector, based on the Simulink module, construct a photodetector model and encapsulate it into a photodetector module;

[0012] Step 7, according to the mathematical model of the external disturbance, based on the Simulink module, construct an external disturbance model and encapsulate it into an external disturbance module;

[0013] Step 8, according to the mathematical model of the optical fiber coupler, based on the Simulink module, construct the optical fiber coupler model and encapsulate it into an optical fiber coupler module;

[0014] Step 9, according to the optical path diagram of the distributed optical fiber acoustic sensing system, add the corresponding functional module to the Simulink workspace, use the signal line to connect the input signal of the module with the output signal of other modules with the same name, and connect the output signal of the module to To Workspace to complete the Simulink modeling of the distributed optical fiber acoustic sensing system;

[0015] Step 10, according to the parameters of the distributed fiber optic acoustic sensing system, calculate the simulation time and sampling interval of the Simulink system, set the parameters of each functional module of the distributed fiber optic acoustic sensing system, use a fixed step size and ode1 solution method to simulate the system, obtain the calculation data from the To Workspace of the output signal of each module, and analyze it.

[0016] Furthermore, in step 1, when the phase noise and frequency shift characteristics of the laser are considered, the light field of the amplitude-stabilized single-mode laser is:

[0017]

[0018] In the formula, E 0 is the electric field strength of the laser, P 0 is the power of the laser, ω=2πf 0 , f 0 is the laser center frequency, is the phase noise of the laser, γ is the frequency shift rate of the laser, where, It is caused by spontaneous radiation and can be considered as a Wiener process. Its increment obeys a Gaussian normal distribution with a mean of 0, that is:

[0019]

[0020] In the formula, It is a Gaussian distribution with a mean of 0 and a variance of 2πτ△f, where τ is the sampling interval and △f is the line width of the laser.

[0021] Furthermore, in step 2, the laser light field E(t) is divided into two parts after passing through the beam splitter. Assuming that the beam splitting ratio of the beam splitter is g1:g2, one part is g1 times the laser light field E(t), that is, g 1 E(t), and the other part is g2 times the laser light field E(t), that is, g 2 E(t).

[0022] Furthermore, in step 3, the light field E(t) output by the laser is modulated by the acousto-optic modulator and becomes a pulse signal with a width of w, that is, in is a rectangular function, that is, when t≤w, is 1, when t>w, is 0.

[0023] Furthermore, in step 4, assuming that the erbium-doped fiber amplifier operates in the linear amplification region and its gain is G, the output signal P of the erbium-doped fiber amplifier is o (t) and input signal P i The relationship between (t) is: o (t) = P i (t)10 G / 10 , assuming the adjustment multiple of the attenuator is At, then the output optical signal after adjustment by the attenuator is A t P o (t).

[0024] Furthermore, the calculation formula E of the sensing optical fiber electric field given in step 5 is cobs (t) The mathematical model is:

[0025]

[0026] In the formula, is the backscattered light power capture factor, n f is the refractive index of the optical fiber core, λ is the wavelength of the backscattered light, λ = c / f 0 , c is the speed of light in a vacuum, f 0 is the center frequency of the laser, r is the mode field radius of the optical fiber, α is the attenuation coefficient of light in the optical fiber, and v g =c / n f , N is the number of scatterers in the entire sensing fiber, τ i is the time delay, l i is the distance from the incident surface to the i-th scattering point, and τ i =2l i / v g , r i is the reflectivity of the ith scattering point, φ i is the phase delay of the ith scattering point, r i Satisfies the Rayleigh distribution, φ i It follows a uniform distribution in (-π,π), is a rectangular function, when hour, Otherwise, the rectangular function is 0, β is the propagation constant of light in the optical fiber,

[0027] Since the entire optical fiber is divided into N scatterers, let the pulse width w just cover n sc scatterers, the length of each scatterer is △l, then when the rising edge of the pulse reaches the i-th scatterer, the above formula is modified to the sensing fiber electric field calculation formula E cobs (t i ):

[0028]

[0029] In the formula, m = i-n + 1,

[0030] From this, the power P of the backscattered Rayleigh light can be obtained cobs (t) is:

[0031]

[0032] When the light source is an incoherent light source, the mathematical model of the sensing fiber and the mathematical model of the backscattered Rayleigh light power are considered. The incoherent light source power P can be obtained obs(t) is:

[0033]

[0034] Where n sc is the number of scatterers covered by the pulse light,

[0035] Compare the optical power P of the time domain reflectometer mobs (t):

[0036] P mobs (t)=0.5P 0 exp(-αv g t)Sα s v g w

[0037] It can be seen that

[0038]

[0039] In the formula, α s is the Rayleigh scattering coefficient, w represents the optical pulse width;

[0040] The random number generation function rand based on Matlab can realize Rayleigh distribution and uniform distribution, among which Rayleigh distribution is r is is the Rayleigh distribution coefficient,

[0041] The Rayleigh distribution coefficient r is determined by is :

[0042]

[0043] In the formula, mean{-2r is log[1-rand(1,N)]} represents the logarithm of -2r is log[1-rand(1,N)] performs average calculation. rand(1,N) is the random number generation function of Matlab, which means that N random numbers in the range of (0,1) are generated.

[0044] Consider the coordinate l i There is an external disturbance ε(l i ), the refractive index is,

[0045]

[0046] The standard p in the formula 12 The photoelastic constant is p 12 =0.270, t i =2l i / v g ;

[0047] n fc (l i ) into the electric field calculation formula E of the sensing optical fiber cobs (t i ) can realize the perception of external disturbance signals;

[0048] According to the electric field calculation formula E of the sensing optical fiber cobs (t i ), the power of the backscattered Rayleigh light P cobs (t), incoherent light source power P obs (t), optical power P of the time domain reflectometer mobs (t), write the Sensingfiber.m file function based on the S-function module to implement the calculation of the above formula. The input quantities in the Sensingfiber.m module are the system parameter vector fParam, the array length N1, the fiber incident electric field signal EAOM and the disturbance signal Epsilon, and the output quantities are the power P of the back Rayleigh scattered light. cobs (t), optical power P of the time domain reflectometer mobs (t), incoherent light source power P obs (t), the discrete value of optical fiber length l and the calculation formula of the electric field of the sensing optical fiber E cobs (t i ), since historical data cannot be used in simulink calculations, a persistent variable (i.e., persistent variable) counter is introduced to construct a complex array EAOMa to record historical data. At the same time, the random reflectivity ri and phase delay phii of the scattering points are also defined as persistent variables. In the first calculation, the random reflectivity and phase delay of all scattering points are calculated.

[0049] Outside the S-function module, 11 fiber parameter constant modules are converted into system parameter vector fParam through VectorConcatenate, and the input of array length N is generated through the constant module named N and the value is zeros(1,N). Among them, the 11 fiber parameter modules are: laser intensity named P0 and the value is P0, fiber length named L0 and the value is L0, laser wavelength named lambda and the value is lambda, light speed named c and the value is c, and nf and the value is nf. The core refractive index, the pulse cover with the name nsc and the value nsc is the number of units, the attenuation coefficient of light in the optical fiber with the name alpha and the value alphas, the Rayleigh scattering coefficient with the name alphas and the value alphas, the light pulse width with the name w and the value w, the Rayleigh distribution coefficient with the name ris and the value ris and the mode field radius of the optical fiber with the name rfiber and the value rfiber, the above model is encapsulated to form a fiber optic sensing module, namely the Fiber module, and 11 fiber parameters and the array length N are set as cover parameters.

[0050] Furthermore, in step 6, the function of the photodetector is to convert the optical power signal P(t) into an electrical signal VP(t) that can be collected by the data acquisition card. Without relying on filtering characteristics, the mathematical model of the photodetector is:

[0051]

[0052] Where P min is the minimum detection power, k p is the conversion gain, a p is the adjustment factor, P s is the saturated input power, b p is the nonlinear coefficient, c p is the attenuation coefficient, when P(t)=2P s When So we can get c p =0.0465, b p From P = a p P s The continuity at b is determined, that is, p =k p / c p ,

[0053] When the overall output noise voltage is considered, the above equation is expressed as:

[0054] VP(t)=VP'(t)+u n (t)

[0055] In the formula, u n(t) = 2u 0 ·rand-u 0 , used to simulate the generation of ±u 0 The noise voltage, rand is a standard uniform distribution random function in the interval (0,1);

[0056] The minimum measurable power P can be obtained by multiplying the noise equivalent power in the photodetector manual by the square root of the bandwidth. min The conversion gain k is obtained by multiplying the detector responsivity and the quartz resistance gain. p , and assume a p =1.34, and then according to the saturated input power in the manual, the calculation of the mathematical model of the photodetector can be realized;

[0057] When the detector is a double-balanced detector, there is a positive power input P p (t) and negative power input P n (t), combined with the mathematical model of the photodetector and the noise voltage, the mathematical model of the double-balanced detector output is:

[0058] VP(t)=VP p (t)-VP n (t)

[0059] Among them, VP p (t) = VP′ p (t)+u np (t), VP n (t) = VP' n (t)+u nn (t), it should be noted that when the negative power input P n When (t) is 0, u nn (t) is also zero.

[0060] Furthermore, in step 7, when only the pulse disturbance is considered, ε(t)=ε 0 δ(tt 0 ), when t = t 0 When δ(tt 0 )=1,

[0061] According to the above relationship, a step module named Step1, a parameter Steptime value of llong*ts, an Initialvalue value of eps0, a Finalvalue value of 0, and a Sampletime value of ts, a step module named Step2, a parameter Steptime value of (llong-1)*ts, an Initialvalue value of 0, a Finalvalue value of eps0, and a Sampletime value of ts, and a multiplication module are used to generate a pulse disturbance ε(t), and the output is EpsilonOut, where t0=llong*ts,

[0062] The above model is encapsulated to form an external disturbance module, namely the Epsilonp module, and the number of disturbance position points llong and the time interval ts are set as cover parameters.

[0063] Furthermore, in step 8, for the input light E In1 (t) and input light E In2 (t) After passing through the fiber coupler, two paths of light are generated:

[0064]

[0065] After the above four-way light is mixed, two beat frequency signals are formed:

[0066]

[0067] When received by the photodetector, it is converted into an optical power signal:

[0068]

[0069] In the formula, the real() function represents the real part of the complex number.

[0070] Furthermore, in step 10, the simulation time and sampling interval are calculated as follows:

[0071] The simulation time is:

[0072] T=2L 0 / v g

[0073] The number of scatterer units is:

[0074] N = fix (T / 2w), fix() means taking an integer for the calculation result

[0075] The sampling interval is:

[0076] t x =T / (N-1).

[0077] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0078] The invention builds a device model based on a mathematical model and a user manual of an optoelectronic device of a distributed optical fiber acoustic sensor system, forms a Simulink device module after packaging, and forms a device module library: a user selects a suitable device module from the device module library, and can freely build a distributed optical fiber acoustic sensor system structure required by the user; the device module built according to the device module can simulate the influence of the device parameter on the system operation, and can verify and optimize the user's design scheme; in the output signal part of the device module, it is easy to connect to To Workspace, obtain the optical phenomenon of the optical signal after passing through different optical devices after the system is running, provide an intuitive basis for the debugging, installation, fault diagnosis and system optimization of the distributed optical fiber acoustic sensor system, and solve the problem of no Simulink modeling method and system for the distributed optical fiber acoustic sensor system.

[0079] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0080] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0082] Figure 1 A schematic flow chart of a simulation modeling method for a distributed optical fiber acoustic sensing system disclosed in an embodiment of the present invention;

[0083] Figure 2 A schematic diagram of the structure of the laser module in step 1 disclosed in an embodiment of the present invention;

[0084] Figure 3 A schematic diagram of the structure of the beam splitter module in step 2 disclosed in an embodiment of the present invention;

[0085] Figure 4 A schematic diagram of the structure of the acousto-optic modulator module in step 3 disclosed in an embodiment of the present invention;

[0086] Figure 5 It is a schematic structural diagram of the erbium-doped fiber amplifier module in step 4 disclosed in an embodiment of the present invention;

[0087] Figure 6A schematic diagram of the structure of the sensing optical fiber module in step 5 disclosed in an embodiment of the present invention;

[0088] Figure 7 A schematic diagram of the structure of the photoelectric detector module in step 6 disclosed in an embodiment of the present invention;

[0089] Figure 8 It is a structural schematic diagram of the external disturbance module in step 7 disclosed in an embodiment of the present invention;

[0090] Fig. 9 It is a structural schematic diagram of the optical fiber coupler module in step 8 disclosed in an embodiment of the present invention;

[0091] Fig.10 Schematic diagram of the structure of the direct detection distributed optical fiber acoustic sensing system model disclosed in Example 1 of the present invention;

[0092] Fig.11 A schematic diagram of a power curve of scattered optical power of an optical fiber obtained by simulation disclosed in Example 1 of the present invention;

[0093] Fig.12 Schematic diagram of the output voltage curve of the photodetector obtained by simulation disclosed in Example 1 of the present invention;

[0094] Fig.13 It is a schematic diagram of a curve of a difference voltage output by a photodetector after disturbance disclosed in Example 1 of the present invention;

[0095] Fig.14 It is a structural schematic diagram of the heterodyne detection type distributed optical fiber acoustic sensing system model disclosed in Example 2 of the present invention;

[0096] Fig.15 A schematic diagram of a photodetector output voltage curve obtained by simulation disclosed in Example 2 of the present invention;

[0097] Fig.16 Schematic diagram of the output difference voltage curve of the photodetector after disturbance disclosed in Example 2 of the present invention. DETAILED DESCRIPTION

[0098] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0099] like Figure 1-9 As shown, an embodiment of the present invention provides a simulation modeling method for a distributed optical fiber acoustic sensing system, comprising the following steps:

[0100] Step 1: According to the laser mathematical model, based on the Simulink module, a laser model is constructed and packaged into a laser module;

[0101] When considering the phase noise and frequency shift characteristics of the laser, the optical field of the amplitude-stabilized single-mode laser is:

[0102]

[0103] In the formula, E 0 is the electric field strength of the laser, P 0 is the power of the laser, ω=2πf 0 , f 0 is the laser center frequency, is the phase noise of the laser, γ is the frequency shift rate of the laser, where, It is caused by spontaneous radiation and can be considered as a Wiener process. Its increment obeys a Gaussian normal distribution with a mean of 0, that is:

[0104]

[0105] In the formula, It is a Gaussian distribution with a mean of 0 and a variance of 2πτ△f, where τ is the sampling interval and △f is the line width of the laser;

[0106] According to the above formula, the modeling method of the laser model based on the Simulink module is as follows: the electric field intensity E of the laser is generated by using a constant module named E0 and a variable value of E0. 0 The constant module named omega and the variable value omega, the constant module named gamma and the variable value gamma, and the addition module are used to generate (ω+γ). The clock module and the constant module named t0 and the variable value t0, and the addition module are used to generate (t+t 0 ), and then use the multiplication module to generate (ω+γ)(t+t 0 ). The phase noise of the laser is generated by using a constant module named fs with a variable value of fs, a white noise module, a multiplication module, a constant module named phi0 with a variable value of phi0, and a block integration module. The Noisepower parameter value in the white noise module is ts*(2*pi*ts*fw), the Sampletime parameter is ts, and the seed parameter is

[23341] . 0 )and Generated by adding modules The electric field strength E of the laser 0 As a complex mode, the laser (ω+γ)(t+t0 ) as the argument, and the laser light field is generated based on the Magnitude-AngletoComplex module The output interface is the light field output Ecout and the phase output phi. The above model is encapsulated to form a laser module, namely the Laser module, and the electric field intensity E0, laser center frequency omega, frequency shift rate gamma, sampling interval ts, line width fw, start time t0 and initial phase phi0 are set as cover parameters.

[0107] Step 2, according to the beam splitter mathematical model, based on the Simulink module, construct the beam splitter model and encapsulate it into a beam splitter module;

[0108] The laser light field E(t) is divided into two parts after passing through the beam splitter. Assuming the beam splitting ratio of the beam splitter is g1:g2, then one part is g1 times the laser light field E(t), that is, g 1 E(t), and the other part is g2 times the laser light field E(t), that is, g 2 E(t);

[0109] According to the above relationship, a proportional module named Gain1 with a variable value of g1 is used to generate a beam splitting of g1 times the light field, and the output is SPbOut. A proportional module named Gain2 with a variable value of g2 is used to generate a beam splitting of g2 times the light field, and the output is SPsOut. The above model is encapsulated to form a beam splitter module, namely the Beam Splitter module, and the beam splitting ratios g1 and g2 are set as cover parameters.

[0110] Step 3, according to the mathematical model of the acousto-optic modulator, based on the Simulink module, construct the acousto-optic modulator model and encapsulate it into an acousto-optic modulator module;

[0111] The light field E(t) output by the laser is modulated by the acousto-optic modulator and becomes a pulse signal with a width of w, that is, in is a rectangular function, that is, when t≤w, is 1, when t>w, is 0;

[0112] According to the above relationship, the output modulated by the acousto-optic modulator is generated by using a step module named Step, a parameter Step time value of nsc*ts, an Initial value value of 1, a Final value value of 0, and a Sample time value of ts and a multiplication module named Product. The output is EAOMOut. The above model is encapsulated to form an acousto-optic modulator module, namely, an AOM module, and the number of fiber units nsc and the time interval ts covered by each pulse are set as cover parameters.

[0113] Step 4, according to the mathematical model of the erbium-doped fiber amplifier and the mathematical model of the attenuator, based on the Simulink module, construct the erbium-doped fiber amplifier and attenuator models, and encapsulate them into an erbium-doped fiber amplifier module;

[0114] Assume that the erbium-doped fiber amplifier operates in the linear amplification region and its gain is G. Then the output signal P of the erbium-doped fiber amplifier is o (t) and input signal P i The relationship between (t) is: o (t) = P i (t)10 G / 10 , assuming the adjustment multiple of the attenuator is At, then the output optical signal after adjustment by the attenuator is A t P o (t);

[0115] According to the above relationship, a constant module named Constant with parameter G, an amplification module named Gain1 with parameter 1 / 10, and a function module named Math Function with function 10u are used to generate 10 G / 10 ; Then multiply the input signal EAOMIn by the multiplication module named Product to generate P i (t)10 G / 10 ; Then, the attenuator adjustment is generated by the amplifier module named Gain2 and the parameter At. The output signal is EDFAOut;

[0116] The above model is encapsulated to form a pulsed erbium-doped fiber amplifier module, namely, an EDFA module, and the erbium-doped fiber amplifier gain G and the adjustment multiple At of the attenuator are used as cover parameters.

[0117] Step 5, constructing a sensing optical fiber model based on the sensing optical fiber mathematical model and the Simulink module, and encapsulating it into a sensing optical fiber module;

[0118] The calculation formula of the electric field of the sensing optical fiber is given as E cobs (t) The mathematical model is:

[0119]

[0120] In the formula, is the backscattered light power capture factor, n f is the refractive index of the optical fiber core, λ is the wavelength of the backscattered light, λ = c / f 0, c is the speed of light in a vacuum, f 0 is the center frequency of the laser, r is the mode field radius of the optical fiber, α is the attenuation coefficient of light in the optical fiber, and v g =c / n f , N is the number of scatterers in the entire sensing fiber, τ i is the time delay, l i is the distance from the incident surface to the i-th scattering point, and τ i =2l i / v g , r i is the reflectivity of the ith scattering point, φ i is the phase delay of the ith scattering point, r i Satisfies the Rayleigh distribution, φ i It follows a uniform distribution in (-π,π), is a rectangular function, when hour, Otherwise, the rectangular function is 0, β is the propagation constant of light in the optical fiber,

[0121] Since the entire optical fiber is divided into N scatterers, let the pulse width w just cover n sc scatterers, the length of each scatterer is △l, then when the rising edge of the pulse reaches the i-th scatterer, the above formula is modified to the sensing fiber electric field calculation formula E cobs (t i ):

[0122]

[0123] In the formula, m = i-n + 1,

[0124] From this, the power P of the backscattered Rayleigh light can be obtained cobs (t) is:

[0125]

[0126] When the light source is an incoherent light source, the mathematical model of the sensing fiber and the mathematical model of the backscattered Rayleigh light power are considered. The incoherent light source power P can be obtained obs (t) is:

[0127]

[0128] Where n sc is the number of scatterers covered by the pulse light,

[0129] Compare the optical power P of the time domain reflectometer mobs (t):

[0130] Pmobs (t)=0.5P 0 exp(-αv g t)Sα s v g w

[0131] It can be seen that

[0132]

[0133] In the formula, α s is the Rayleigh scattering coefficient, w represents the optical pulse width;

[0134] The calculation formula E of the electric field of the sensing optical fiber proposed in this scheme cobs (t) The mathematical model overcomes the problems in the commonly used one-dimensional pulse response model of Rayleigh backscattering that the backscattered light power capture factor S and the light propagation phase β are not considered, and when the light source is incoherent light, the light power cannot be degenerated into the general formula P of the time domain reflectometer. mobs (t) deficiencies;

[0135] The random number generation function rand based on Matlab can realize Rayleigh distribution and uniform distribution, among which Rayleigh distribution is r is is the Rayleigh distribution coefficient,

[0136] The Rayleigh distribution coefficient r is determined by is :

[0137]

[0138] In the formula, mean{-2r is log[1-rand(1,N)]} represents the logarithm of -2r is log[1-rand(1,N)] performs average calculation. rand(1,N) is the random number generation function of Matlab, which means that N random numbers in the range of (0,1) are generated.

[0139] Consider the coordinate l i There is an external disturbance ε(l i ), the refractive index is,

[0140]

[0141] The standard p in the formula 12 The photoelastic constant is p 12 =0.270, t i =2l i / v g ;

[0142] n fc (li ) into the electric field calculation formula E of the sensing optical fiber cobs (t i ) can realize the perception of external disturbance signals;

[0143] According to the electric field calculation formula E of the sensing optical fiber cobs (t i ), the power of the backscattered Rayleigh light P cobs (t), incoherent light source power P obs (t), optical power P of the time domain reflectometer mobs (t), write the Sensingfiber.m file function based on the S-function module to implement the calculation of the above formula. The input quantities in the Sensingfiber.m module are the system parameter vector fParam, the array length N1, the fiber incident electric field signal EAOM and the disturbance signal Epsilon, and the output quantities are the power P of the back Rayleigh scattered light. cobs (t), optical power P of the time domain reflectometer mobs (t), incoherent light source power P obs (t), the discrete value of optical fiber length l and the calculation formula of the electric field of the sensing optical fiber E cobs (t i ), since historical data cannot be used in simulink calculations, a persistent variable (i.e., persistent variable) counter is introduced to construct a complex array EAOMa to record historical data. At the same time, the random reflectivity ri and phase delay phii of the scattering points are also defined as persistent variables. In the first calculation, the random reflectivity and phase delay of all scattering points are calculated.

[0144] Outside the S-function module, 11 fiber parameter constant modules are converted into system parameter vector fParam through VectorConcatenate, and the input of array length N is generated through the constant module named N and the value is zeros(1,N). Among them, the 11 fiber parameter modules are: laser intensity named P0 and the value is P0, fiber length named L0 and the value is L0, laser wavelength named lambda and the value is lambda, light speed named c and the value is c, and nf and the value is nf. The core refractive index, the pulse cover with the name nsc and the value nsc is the number of units, the attenuation coefficient of the light in the optical fiber with the name alpha and the value alphas, the Rayleigh scattering coefficient with the name alphas and the value alphas, the light pulse width with the name w and the value w, the Rayleigh distribution coefficient with the name ris and the value ris and the mode field radius of the optical fiber with the name rfiber and the value rfiber, the above model is encapsulated to form a fiber optic sensing module, namely the Fiber module, and 11 fiber parameters and the array length N are set as cover parameters;

[0145] Step 6, according to the mathematical model of the photodetector, based on the Simulink module, construct a photodetector model and encapsulate it into a photodetector module;

[0146] The function of the photodetector is to convert the optical power signal P(t) into an electrical signal VP(t) that can be collected by the data acquisition card. Without relying on filtering characteristics, the mathematical model of the photodetector is:

[0147]

[0148] Where P min is the minimum detection power, k p is the conversion gain, a p is the adjustment factor, P s is the saturated input power, b p is the nonlinear coefficient, c p is the attenuation coefficient, when P(t)=2P s When So we can get c p =0.0465, b p From P = a p P s The continuity at b is determined, that is, p =k p / c p ,

[0149] When the overall output noise voltage is considered, the above equation is expressed as:

[0150] VP(t)=VP'(t)+u n (t)

[0151] In the formula, u n (t) = 2u 0 ·rand-u 0 , used to simulate the generation of ±u 0 The noise voltage, rand is a standard uniform distribution random function in the interval (0,1);

[0152] The minimum measurable power P can be obtained by multiplying the noise equivalent power in the photodetector manual by the square root of the bandwidth. min The conversion gain k is obtained by multiplying the detector responsivity and the quartz resistance gain. p , and assume a p =1.34, and then according to the saturated input power in the manual, the calculation of the mathematical model of the photodetector can be realized;

[0153] When the detector is a double-balanced detector, there is a positive power input P p (t) and negative power input P n (t), combined with the mathematical model of the photodetector and the noise voltage, the mathematical model of the double-balanced detector output is:

[0154] VP(t)=VP p (t)-VP n (t)

[0155] Among them, VP p (t) = VP′ p (t)+u np (t), VP n (t) = VP' n (t)+u nn (t), it should be noted that when the negative power input P n When (t) is 0, u nn (t) is also zero;

[0156] According to the mathematical model of the photodetector, the Photoelectricdetector.m file function is written based on the S-function module to realize the calculation of the above formula. The inputs of the S-function module are the photodetector parameter vector DParam, the positive power input Pp and the negative power input Pn, and the output is the difference power Vpcobs. Outside the S-function module, the four photodetector parameter constant modules are converted into the photodetector parameter vector DParam through Vector Concatenate. These four constant modules are the minimum detection power named Pmin and the value Pmin, the saturation power named Ps and the value Ps, the adjustment coefficient named ap and the value ap, and the conversion gain named kp and the value kp;

[0157] The above model is encapsulated to form a photoelectric detector module, namely, a Photoelectric detector module, and the four photoelectric detector parameters are set as cover parameters.

[0158] Step 7, according to the mathematical model of the external disturbance, based on the Simulink module, construct an external disturbance model and encapsulate it into an external disturbance module;

[0159] When only pulse disturbance is considered, ε(t) = ε 0 δ(tt 0 ), when t = t 0 When δ(tt 0 )=1,

[0160] According to the above relationship, a step module named Step1, a parameter Steptime value of llong*ts, an Initialvalue value of eps0, a Finalvalue value of 0, and a Sampletime value of ts, a step module named Step2, a parameter Steptime value of (llong-1)*ts, an Initialvalue value of 0, a Finalvalue value of eps0, and a Sampletime value of ts, and a multiplication module are used to generate a pulse disturbance ε(t), and the output is EpsilonOut, where t0=llong*ts,

[0161] The above model is encapsulated to form an external disturbance module, namely the Epsilonp module, and the number of disturbance position points llong and the time interval ts are set as cover parameters;

[0162] Step 8, according to the mathematical model of the optical fiber coupler, based on the Simulink module, construct the optical fiber coupler model and encapsulate it into an optical fiber coupler module;

[0163] For input light E In1 (t) and input light E In2 (t) After passing through the fiber coupler, two paths of light are generated:

[0164]

[0165] After the above four-way light is mixed, two beat frequency signals are formed:

[0166]

[0167] When received by the photodetector, it is converted into an optical power signal:

[0168]

[0169] In the formula, the real() function represents taking the real part of a complex number;

[0170] According to the above relationship, a constant module named Constant1 with a value of 0 is used as the real part, a constant module named Constant2 with a value of 1 is used as the imaginary part, and the complex number generation function Real-Imag to Complex1 is used to generate a complex number. Then, through the multiplication module Product1 and the input light E In1 (t) multiplied to produce E In11 (t); Generate a complex number using a constant module named Constant2 with a value of 0 as the real part, a constant module named Constant3 with a value of 1 as the imaginary part, and the complex number generation function Real-Imag to Complex2 Then, through the multiplication module Product2 and the input light E In2 (t) multiplied to produce E In21 (t); Input light E In1 (t) and input light E In21 (t) is added by the addition module Add1 to generate E 1 (t), and then it is divided into two paths. One path passes through the complex number conversion module Comlex to Real-Imag1 to generate real and imaginary signals. The imaginary signal passes through the proportional module Gain1 with a value of -1, and then passes through the real and imaginary part conversion module Real-Imag to Comlex3 to generate the input light E 1 The complex conjugate of (t) Then through the multiplication module Product3 and E 1 (t) directly multiply to form Then the real part is taken through the complex number conversion module Comlex to Real-Imag3 to generate the output optical power signal POut1 (t); Input light E In11 (t) and input light E In2 (t) is added by the addition module Add2 to produce E 2 (t), and then divided into two paths, one of which is converted to real and imaginary parts by the complex number conversion module Comlex to Real-Imag2 to generate real and imaginary signals, of which the imaginary signal is passed through the proportional module Gain2 with a value of -1, and then input into the optical E through the real and imaginary part conversion module Real-Imag to Comlex4 2 The complex conjugate of (t) Then through the multiplication module Product4 and E 2 (t) directly multiply to form Then the real part is taken through the complex number conversion module Comlex to Real-Imag4 to generate the output optical power signal P Out2 (t).

[0171] The above model is encapsulated to form a fiber optic coupler module, namely, a Coupler module.

[0172] Step 9, according to the optical path diagram of the distributed optical fiber acoustic sensing system, add the corresponding functional module to the Simulink workspace, use the signal line to connect the input signal of the module with the output signal of other modules with the same name, and connect the output signal of the module to To Workspace to complete the Simulink modeling of the distributed optical fiber acoustic sensing system;

[0173] Step 10, according to the parameters of the distributed optical fiber acoustic sensing system, calculate the simulation time and sampling interval of the Simulink system, set the parameters of each functional module of the distributed optical fiber acoustic sensing system, use a fixed step size and ode1 solution method to simulate the system, obtain the calculation data from the To Workspace of the output signal of each module, and analyze it;

[0174] The simulation time and sampling interval are calculated as follows:

[0175] The simulation time is:

[0176] T=2L 0 / v g

[0177] The number of scatterer units is:

[0178] N = fix (T / 2w), fix() means taking an integer for the calculation result

[0179] The sampling interval is:

[0180] tx =T / (N-1).

[0181] Example 1

[0182] like Figure 10-13 As shown in the figure, the model and simulation method of direct detection distributed fiber optic acoustic sensing system:

[0183] 1. Build a direct detection distributed fiber optic acoustic sensing system model

[0184] Drag the required functional modules from the model library into the Simulink model workspace, connect the modules with signal lines, and build a direct detection distributed fiber optic acoustic sensor system model, such as Fig.10 As shown;

[0185] 2. Parameter calculation

[0186] The system parameters are: L0 = 10000; lambda = 1550*1e-9; c = 299792458; nf = 1.4685; ndu = 20; then vg = c / nf;

[0187] The calculation can be obtained:

[0188] T=9.7968e-05, N=8163, ts=1.2003e-08;

[0189] The fixed step size and ode1 solution method are used, where the simulation time is T and the fixed step size is ts;

[0190] 3. Module parameter settings

[0191] Other parameters are: P0 = 20 / 1000; alpha = 0.0495 / 1000; alphas = 1.020 / 1000; ris = 6.1465e-04;

[0192] rfiber=10.5*10^-6 / 2;G=13;At=0.2;eps0=1*10^-6;Ps=150;ap=1.34;kp=28.5。 In the laser module: t0=0;phi0=0。

[0193] For the manual switch module, select the Epsilon0 module and set the value to 0, indicating that there is no external disturbance input.

[0194] After the system simulation is completed, the optical power curve is obtained with l.data as the horizontal axis and Pcobs.data, Pmobs.data and Pobs.data as the vertical axis. Fig.11 As shown;

[0195] With l.data as the horizontal axis and VPcobs.data as the vertical axis, the output voltage curve of the photodetector is obtained as follows: Fig.12 As shown. At the same time, let VPcobs1 = VPcobs;

[0196] 4. Change parameters to do differential simulation

[0197] In the laser module: t0 = 9.7968e-05; phi0 = 0.7225.

[0198] The manual switch module selects the Epsilon1 module, indicating that there is external disturbance. The parameters of the disturbance module, namely Epsilonp, are llong=820, ts=9.7968e-05; lshort=810.

[0199] After the simulation is completed, set VPcobs2 = VPcobs. With l.data as the horizontal coordinate and VPcobs2.data-VPcobs1.data as the vertical coordinate, the output difference voltage curve of the photodetector after the disturbance is obtained as follows: Fig.13 As shown, it can be seen that there is an obvious disturbance at 820*ts*vg=1000m.

[0200] Example 2

[0201] like Figure 14-16 As shown in FIG. 1 , the heterodyne detection distributed optical fiber acoustic sensor (DAS) system model and simulation method are shown in FIG. 1 . The heterodyne detection distributed optical fiber acoustic sensor (DAS) system model is shown in FIG. Fig.14 As shown;

[0202] The beam splitter module, i.e., Beam Splider, has parameters g1 = 0.9, g2 = 0.1. With l.data as the horizontal coordinate and VPcobs.data as the vertical coordinate, the output voltage curve of the photodetector is obtained as follows: Fig.15 As shown;

[0203] The parameters of the perturbation module (i.e., Epsilonp) are llong=504, ts=9.7968e-05; lshort=500. With l.data as the horizontal coordinate and VPcobs2.data-VPcobs1.data as the vertical coordinate, the output difference voltage curve of the photodetector after the perturbation is obtained as follows: Fig.16 As shown, it can be seen that there is an obvious disturbance at 504*ts*vg=610m.

[0204] The invention discloses a simulation modeling method for a distributed optical fiber acoustic sensor system. Based on a mathematical model and a user manual of an optoelectronic device of the distributed optical fiber acoustic sensor system, a device model is constructed, and a Simulink device module is formed after packaging, and a device module library is formed. A user selects a suitable device module from the device module library, and can freely construct a distributed optical fiber acoustic sensor system structure required by the user. The device module constructed according to the device module can simulate the influence of device parameters on system operation, and can verify and optimize the user's design scheme. In the output signal part of the device module, it is easy to connect to To Workspace, and obtain the optical phenomenon of the optical signal after passing through different optical devices after the system is running, so as to provide an intuitive basis for the debugging, installation, fault diagnosis and system optimization of the distributed optical fiber acoustic sensor system, and solve the problem of no Simulink modeling method and system for the distributed optical fiber acoustic sensor system.

[0205] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0206] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0207] Those skilled in the art will also appreciate that the various illustrative logic blocks, modules, circuits, and algorithmic steps described in conjunction with the embodiments herein can all be implemented as electronic hardware, computer software, or a combination thereof. In order to clearly illustrate the interchangeability between hardware and software, various illustrative components, blocks, modules, circuits, and steps are generally described above around their functions. Whether such functions are implemented as hardware or software depends on specific applications and the design constraints imposed on the entire system. A skilled person can implement the described functions in an alternative manner for each specific application, but such implementation decisions should not be interpreted as departing from the scope of protection of the present disclosure.

[0208] The steps of the method or algorithm described in conjunction with the embodiments herein may be directly embodied as hardware, a software module executed by a processor, or a combination thereof. The software module may be located in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a mobile disk, a CD-ROM, or any other form of storage medium well known in the art. An exemplary storage medium is connected to the processor so that the processor can read information from the storage medium and can write information to the storage medium. Of course, the storage medium may also be an integral part of the processor. The processor and the storage medium may be located in an ASIC. The ASIC may be located in a user terminal. Of course, the processor and the storage medium may also be present in a user terminal as discrete components.

[0209] For software implementation, the techniques described in this application can be implemented with modules (e.g., procedures, functions, etc.) that perform the functions described in this application. These software codes can be stored in a memory unit and executed by a processor. The memory unit can be implemented within the processor or outside the processor. In the latter case, it is coupled to the processor in a communication manner via various means, which are well known in the art.

[0210] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," is explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A simulation modeling method for a distributed optical fiber acoustic sensing system, characterized in that: The following steps are involved: Step 1: According to the laser mathematical model, based on the Simulink module, a laser model is constructed and packaged into a laser module; In step 1, when the phase noise and frequency shift characteristics of the laser are considered, the light field of the amplitude-stabilized single-mode laser is: Where E0 is the electric field strength of the laser, P0 is the power of the laser, ω=2πf0, f0 is the center frequency of the laser, is the phase noise of the laser, γ is the frequency shift rate of the laser, where, It is caused by spontaneous radiation and can be considered as a Wiener process. Its increment obeys a Gaussian normal distribution with a mean of 0, that is: In the formula, It is a Gaussian distribution with a mean of 0 and a variance of 2πτ△f, where τ is the sampling interval and △f is the line width of the laser; Step 2, according to the beam splitter mathematical model, based on the Simulink module, construct the beam splitter model and encapsulate it into a beam splitter module; In step 2, the laser light field E(t) is divided into two parts after passing through the beam splitter. Assuming that the beam splitting ratio of the beam splitter is g1:g2, one part is g1 times the laser light field E(t), that is, g1E(t), and the other part is g2 times the laser light field E(t), that is, g2E(t); Step 3, according to the mathematical model of the acousto-optic modulator, based on the Simulink module, construct the acousto-optic modulator model and encapsulate it into an acousto-optic modulator module; In step 3, the light field E(t) output by the laser is modulated by the acousto-optic modulator and becomes a pulse signal with a width of w, that is, in is a rectangular function, that is, when t≤w, is 1, when t>w, is 0; Step 4, according to the mathematical model of the erbium-doped fiber amplifier and the mathematical model of the attenuator, based on the Simulink module, construct the erbium-doped fiber amplifier and attenuator models, and encapsulate them into an erbium-doped fiber amplifier module; In step 4, assuming that the erbium-doped fiber amplifier operates in the linear amplification region and its gain is G, the output signal P of the erbium-doped fiber amplifier is o (t) and input signal P i The relationship between (t) is: o (t) = P i (t)10 G / 10 , assuming the adjustment multiple of the attenuator is At, then the output optical signal after adjustment by the attenuator is A t P o (t); Step 5, constructing a sensing optical fiber model based on the sensing optical fiber mathematical model and the Simulink module, and encapsulating it into a sensing optical fiber module; The calculation formula E of the sensing optical fiber electric field given in step 5 is cobs (t) The mathematical model is: In the formula, is the backscattered light power capture factor, n f is the refractive index of the fiber core, λ is the wavelength of the backscattered light, λ = c / f0, c is the speed of light in a vacuum, f0 is the center frequency of the laser, r is the mode field radius of the fiber, α is the attenuation coefficient of light in the fiber, v g =c / n f , N is the number of scatterers in the entire sensing fiber, τ i is the time delay, l i is the distance from the incident surface to the i-th scattering point, and τ i =2l i / v g , r i is the reflectivity of the ith scattering point, φ i is the phase delay of the ith scattering point, r i Satisfies the Rayleigh distribution, φ i It follows a uniform distribution in (-π,π), is a rectangular function, when hour, Otherwise, the rectangular function is 0, β is the propagation constant of light in the optical fiber, Since the entire optical fiber is divided into N scatterers, let the pulse width w just cover n sc scatterers, the length of each scatterer is △l, then when the rising edge of the pulse reaches the i-th scatterer, the above formula is modified to the sensing fiber electric field calculation formula E cobs (t i ): Where m = i-n+1, From this, the power P of the backscattered Rayleigh light can be obtained cobs (t) is: When the light source is an incoherent light source, the mathematical model of the sensing fiber and the mathematical model of the backscattered Rayleigh light power are considered. The incoherent light source power P can be obtained obs (t) is: Where n sc is the number of scatterers covered by the pulse light, Comparison of optical power P of time domain reflectometer mobs (t): P mobs (t)=0.5P0exp(-αv g t)Sα s v g w It can be seen that In the formula, α s is the Rayleigh scattering coefficient, w represents the optical pulse width; The random number generation function rand based on Matlab can realize Rayleigh distribution and uniform distribution, among which Rayleigh distribution is r is is the Rayleigh distribution coefficient, The Rayleigh distribution coefficient r is determined by is : In the formula, mean{-2r is log[1-rand(1,N)]} represents the logarithm of -2r is log[1-rand(1,N)] performs average calculation. rand(1,N) is the random number generation function of Matlab, which means that N random numbers in the range of (0,1) are generated. Consider the coordinate l i There is an external disturbance ε(l i ), the refractive index is, The standard p in the formula 12 The photoelastic constant is p 12 =0.270, t i =2l i / v g ; n fc (l i ) into the electric field calculation formula E of the sensing optical fiber cobs (t i ) can realize the perception of external disturbance signals; According to the electric field calculation formula E of the sensing optical fiber cobs (t i ), the power of the backscattered Rayleigh light P cobs (t), incoherent light source power P obs (t), optical power P of the time domain reflectometer mobs (t), write the Sensingfiber.m file function based on the S-function module to implement the calculation of the above formula. The input quantities in the Sensingfiber.m module are the system parameter vector fParam, the array length N1, the fiber incident electric field signal EAOM and the disturbance signal Epsilon, and the output quantities are the power P of the back Rayleigh scattered light. cobs (t), optical power P of the time domain reflectometer mobs (t), incoherent light source power P obs (t), the discrete value of optical fiber length l and the calculation formula of the electric field of the sensing optical fiber E cobs (t i ), since historical data cannot be used in simulink calculations, a persistent variable counter is introduced to construct a complex array EAOMa to record historical data. At the same time, the random reflectivity ri and phase delay phii of the scattering points are also defined as persistent variables. In the first calculation, the random reflectivity and phase delay of all scattering points are calculated. Outside the S-function module, 11 fiber parameter constant modules are converted into system parameter vector fParam through VectorConcatenate, and the input of array length N is generated through the constant module named N and the value is zeros(1,N). Among them, the 11 fiber parameter modules are: laser intensity named P0 and the value is P0, fiber length named L0 and the value is L0, laser wavelength named lambda and the value is lambda, light speed named c and the value is c, and nf and the value is nf. The core refractive index, the pulse cover with the name nsc and the value nsc is the number of units, the attenuation coefficient of the light in the optical fiber with the name alpha and the value alphas, the Rayleigh scattering coefficient with the name alphas and the value alphas, the light pulse width with the name w and the value w, the Rayleigh distribution coefficient with the name ris and the value ris and the mode field radius of the optical fiber with the name rfiber and the value rfiber, the above model is encapsulated to form a fiber optic sensing module, namely the Fiber module, and 11 fiber parameters and the array length N are set as cover parameters; Step 6, according to the mathematical model of the photodetector, based on the Simulink module, construct a photodetector model and encapsulate it into a photodetector module; In step 6, the function of the photodetector is to convert the optical power signal P(t) into an electrical signal VP(t) that can be collected by the data acquisition card. Without relying on filtering characteristics, the mathematical model of the photodetector is: Where P min is the minimum detection power, k p is the conversion gain, a p is the adjustment factor, P s is the saturated input power, b p is the nonlinear coefficient, c p is the attenuation coefficient, when P(t)=2P s When So we can get c p =0.0465, b p From P = a p P s The continuity at b is determined, that is, p =k p / c p , When the overall output noise voltage is considered, the above equation is expressed as: VP(t)=VP'(t)+u n (t) In the formula, u n (t) = 2u0·rand-u0, used to simulate the noise voltage of ±u0, rand is a standard uniform distribution random function in the interval (0,1); The minimum measurable power P can be obtained by multiplying the noise equivalent power in the photodetector manual by the square root of the bandwidth. min The conversion gain k is obtained by multiplying the detector responsivity and the quartz resistance gain. p , and assume a p =1.34, and then according to the saturated input power in the manual, the calculation of the mathematical model of the photodetector can be realized; When the detector is a double-balanced detector, there is a positive power input P p (t) and negative power input P n (t), combined with the mathematical model of the photodetector and the noise voltage, the mathematical model of the double-balanced detector output is: VP(t)=VP p (t)-VP n (t) Among them, VP p (t) = VP′ p (t)+u np (t), VP n (t) = VP' n (t)+u nn (t), it should be noted that when the negative power input P n When (t) is 0, u nn (t) is also zero; Step 7, according to the mathematical model of the external disturbance, based on the Simulink module, construct an external disturbance model and encapsulate it into an external disturbance module; In step 7, when only the pulse disturbance is considered, ε(t)=ε0δ(t-t0), when t=t0, δ(t-t0)=1, According to the above relationship, a step module named Step1, a parameter Steptime value of llong*ts, an Initialvalue value of eps0, a Finalvalue value of 0, and a Sampletime value of ts, a step module named Step2, a parameter Steptime value of (llong-1)*ts, an Initialvalue value of 0, a Finalvalue value of eps0, and a Sampletime value of ts, and a multiplication module are used to generate a pulse disturbance ε(t), and the output is EpsilonOut, where t0=llong*ts, The above model is encapsulated to form an external disturbance module, namely the Epsilonp module, and the number of disturbance position points llong and the time interval ts are set as cover parameters; Step 8, according to the mathematical model of the optical fiber coupler, based on the Simulink module, construct the optical fiber coupler model and encapsulate it into an optical fiber coupler module; In step 8, for the input light E In1 (t) and input light E In2 (t) After passing through the fiber coupler, two paths of light are generated: After the above four-way light is mixed, two beat frequency signals are formed: When received by the photodetector, it is converted into an optical power signal: In the formula, the real() function represents taking the real part of a complex number; Step 9, according to the optical path diagram of the distributed optical fiber acoustic sensing system, add the corresponding functional module to the Simulink workspace, use the signal line to connect the input signal of the module with the output signal of other modules with the same name, and connect the output signal of the module to To Workspace to complete the Simulink modeling of the distributed optical fiber acoustic sensing system; Step 10, according to the parameters of the distributed fiber optic acoustic sensing system, calculate the simulation time and sampling interval of the Simulink system, set the parameters of each functional module of the distributed fiber optic acoustic sensing system, use a fixed step size and ode1 solution method to simulate the system, obtain the calculation data from the To Workspace of the output signal of each module, and analyze it.

2. A simulation modeling method for a distributed optical fiber acoustic sensing system according to claim 1, characterized in that: In step 10, the simulation time and sampling interval are calculated as follows: The simulation time is: T=2L0 / v g The number of scatterer units is: N = fix (T / 2w), fix() means taking an integer for the calculation result The sampling interval is: t x =T / (N-1)。

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