Digital simulation and demodulation system based on distributed optical fiber sensing

Abstract

The invention discloses a digital simulation and demodulation system based on distributed optical fiber sensing. The digital simulation and demodulation system comprises a laser simulation module, a beam splitter module, an AOM modulation module, an amplification module, a backward Rayleigh scattering light simulation module, a beam coupler module and a photoelectric conversion module. The laser simulation module is used for performing laser simulation to obtain a laser digital model; the beam splitter module is used for simulating laser beam splitting to generate a detection light field model and an intrinsic light field model; the AOM modulation module is used for modulating the detection light field into pulsed light and loading carrier frequency; the amplification module is used for amplifying the pulsed light; the backward Rayleigh scattering light simulation module is used for generating a backward Rayleigh scattering light model through convolution of the light field mathematical model and the one-dimensional optical fiber discretization scattering model; the light beam coupler module is used for simulating a beat frequency effect to generate two paths of output light signals; and the photoelectric conversion module is used for converting to obtain two paths of conversion voltage signals and outputting a difference value. The system can simulate the physical process of the distributed optical fiber sensing system in a full-link mode.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing, and in particular to a digital simulation and demodulation system based on distributed fiber optic sensing. Background Technology

[0002] With the widespread application of distributed fiber optic acoustic sensing technology in fields such as security, oil and gas exploration, and structural health monitoring, this system has encountered several key technical challenges in its actual development and deployment: the fiber optic acoustic sensing system relies on high-precision, high-cost optical and electronic devices, resulting in high system hardware costs; the system construction process is complex, involving the matching and debugging of multiple precision components such as lasers, modulators, and amplifiers, and any improper configuration of key parameters will lead to unsatisfactory demodulation results and degraded signal quality; frequent physical experimental verification not only significantly increases trial and error costs but also greatly prolongs the research and development cycle.

[0003] Furthermore, simulation in related technologies has obvious limitations. It either fails to systematically evaluate the impact of device parameters and link design on overall performance, or fails to establish a full-link simulation model that includes phase information, making it difficult to meet the engineering requirements of rapid system design and parameter optimization. Summary of the Invention

[0004] This application provides a digital simulation and demodulation system based on distributed optical fiber sensing, which can simulate the physical processes of a distributed optical fiber sensing system across the entire chain.

[0005] This application provides a digital simulation and demodulation system based on distributed optical fiber sensing. The system includes: a laser simulation module, a beam splitter module, an AOM modulation module, an amplification module, a backscattered Rayleigh light simulation module, a beam coupler module, and a photoelectric conversion module.

[0006] The laser simulation module is equipped with a laser parameter input port, which is used to perform laser simulation based on the parameters input into the laser parameter input port to obtain a digital model of the laser.

[0007] The beam splitter module is used to simulate laser beam splitting. Based on the laser digital model, the beam splitter module combines the beam splitting ratio to generate the probe light field model and the intrinsic light field model.

[0008] The AOM modulation module is equipped with an AOM modulation parameter input port, which is used to receive AOM modulation parameters. Based on the AOM modulation parameters, it simulates modulating the probe light field into pulse light of a fixed frequency and loads the carrier frequency into the optical frequency to generate a probe light AOM modulation model.

[0009] The amplification module is equipped with an amplification parameter input port, which is used to simulate the amplification of pulse light according to the amplification parameters, and generate a mathematical model of the amplified light field by combining the probe light AOM modulation model.

[0010] The back Rayleigh scattering light simulation module is used to convolve the optical field mathematical model with the one-dimensional fiber discretized scattering model to generate a back Rayleigh scattering light model.

[0011] The beam coupler module is used to simulate the beat frequency interaction between back Rayleigh scattered light and intrinsic light in the beam coupler, and generates two output optical signals based on the back Rayleigh scattered light model and the intrinsic light field model.

[0012] The photoelectric conversion module is used to convert two output optical signals to obtain two converted voltage signals and output the difference between the two converted voltage signals.

[0013] In one embodiment, the parameters input to the laser parameter input port include at least: the laser's output power, center angular frequency, linewidth, and laser wavelength;

[0014] In the digital model of the laser, the effect of phase noise is introduced, and the phase noise is configured to have an increment that follows a Gaussian normal distribution with a mean of 0.

[0015] In one embodiment, the AOM modulation parameters include at least: carrier frequency and target pulse width for modulation;

[0016] The probe light AOM modulation model is expressed by the following formula:

[0017]

[0018] In the formula, Represented as a rectangular function of length w, when t <w, Otherwise, it equals 0, E 0.9 (t) represents the probe light field model, w represents the modulated target pulse width, ω s For carrier frequency.

[0019] In one embodiment, the amplification parameters include the attenuator factor and the amplifier gain;

[0020] The mathematical model of the light field is expressed by the following formula:

[0021]

[0022] In the formula, At represents the attenuator coefficient, and G represents the amplifier gain.

[0023] In one embodiment, the backscattered Rayleigh light simulation module is also configured with an excitation source mode selection port for selecting an excitation source. The backscattered Rayleigh light simulation module simulates the fiber sensing strain caused by the excitation transmission acting on the fiber according to the selected excitation source.

[0024] A one-dimensional discretized scattering model of an optical fiber is generated based on the fiber's strain sensing and the reflection amplitude of scattering points at different locations of the fiber that follow a Rayleigh distribution.

[0025] In one embodiment, the backscattering Rayleigh light simulation module converts the one-dimensional fiber discretized scattering model into a function of propagation time before convolving it with the optical field mathematical model.

[0026] In one embodiment, the backscattered Rayleigh light simulation module is also equipped with a selection port for two fiber optic stress sensing models: straight fiber and spiral fiber. Based on the selected fiber type and the corresponding fiber optic stress sensing model, the fiber optic strain caused by the excitation transmission acting on the fiber is simulated.

[0027] In one embodiment, the system further includes a demodulation module configured to:

[0028] Establish a pair of orthogonal reference signals, with the reference signal mode being the AOM carrier frequency.

[0029] The two converted voltage signals output from the photoelectric conversion module are multiplied separately to form a mixed signal.

[0030] The sum-frequency term of the mixing signal is filtered out by a low-pass filter while the phase component is retained.

[0031] The phase value is obtained by arctangent, and the obtained phase value is used to obtain the phase change on the sensing fiber through differential operation.

[0032] In one embodiment, the demodulation module is provided with a demodulation configuration parameter input port for inputting demodulation configuration parameters, which include at least the low-pass cutoff frequency, gauge length, and spatial resolution.

[0033] The differential operation includes: performing spatial domain differential based on demodulation configuration parameters to obtain the phase change rate.

[0034] In one embodiment, the demodulation module performs time-domain differential based on the phase change rate to obtain strain rate information.

[0035] The aforementioned digital simulation and demodulation system based on distributed fiber optic sensing generates a digital laser model containing phase noise through a laser simulation module. This model is then split into two signals—a probe light field model and an intrinsic light field model—by a beam splitter module. The probe light field model is modulated into an AOM modulation model carrying the carrier frequency by an AOM modulation module. After power enhancement by an amplification module, an amplified optical field mathematical model is generated. A backscattering Rayleigh light simulation module combines the discretized fiber optic scattering model with the amplified optical field mathematical model through convolution operations to generate a backscattering Rayleigh light model carrying vibration information. This model, along with the intrinsic light field model, generates two optical signals through beat frequency interaction in a beam coupler module. These signals are then converted into differential voltage signals by a photoelectric conversion module for output. This system can provide key parameter verification for the laser, modulation module, and other components by simulating different design schemes, guiding parameter configuration optimization, effectively reducing hardware trial-and-error costs, and providing a full-link design basis for the construction of distributed fiber optic sensing systems. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the main interface of a digital simulation and demodulation system in one embodiment.

[0037] Figure 2 This is a schematic diagram of the configuration page of a digital simulation and demodulation system in one embodiment;

[0038] Figure 3 This is a schematic diagram of the fiber optic and disturbance parameter configuration interface in one embodiment;

[0039] Figure 4 This is a schematic diagram of the simulated excitation source parameter setting interface in one embodiment;

[0040] Figure 5 Here is a simulated time-domain waterfall plot in one embodiment;

[0041] Figure 6 Here is a simulated frequency domain waterfall plot in one embodiment;

[0042] Figure 7 This is a simulated single-channel spectrum diagram in one embodiment;

[0043] Figure 8 This is a schematic diagram of a digital simulation and demodulation system based on distributed optical fiber sensing in one embodiment;

[0044] Figure 9 This is a single-channel spectrum of the simulated excitation results of the laser at a linewidth of 3kHz in one embodiment;

[0045] Figure 10 This is a single-channel spectrum of the simulated excitation results of the laser at a linewidth of 1kHz in one embodiment;

[0046] Figure 11 This is a single-channel spectrum of the simulated excitation results of the laser at a linewidth of 500Hz in one embodiment.

[0047] Figure 12 This is a single-channel spectrum diagram of the simulated excitation results of the laser at a linewidth of 100Hz in one embodiment.

[0048] Figure 13 This is a time-domain waterfall plot of the spatial resolution of a 500ns pulse width, 10m gauge length system in one embodiment.

[0049] Figure 14 This is a time-domain waterfall plot of the spatial resolution of a 100ns pulse width, 30m gauge length system in one embodiment;

[0050] Figure 15 This is a time-domain waterfall plot of the spatial resolution of a 100ns pulse width, 10m gauge length system in one embodiment. Detailed Implementation

[0051] The present application will be described in detail below with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present application. Any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the protection scope of the present application.

[0052] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0053] In one embodiment, the main interface of a digital simulation and demodulation system based on distributed fiber optic sensing is as follows: Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 as well as Figure 7 As shown.

[0054] Specifically, Figure 1The main interface of the digital simulation and demodulation system includes four basic parameters on the left: fiber length, spatial sampling interval, repetition frequency, and sampling time, as well as two specialized settings: equipment parameters and vibration information. The central display area provides BPD output, time-domain waterfall plot, frequency-domain waterfall plot, single-channel waveform plot, and single-channel display. Figure 5 It offers several visualization modes, supporting strain / strain rate switching and dual-coordinate display; the right-hand data area is equipped with data storage control, BPD output, and demodulation result item storage functions.

[0055] Figure 2 The configuration page for the digital simulation and demodulation system has an instrument parameter selection area on the left, providing parameter configuration entries for the laser simulation module, beam splitter module, AOM modulation module, amplification module, backscattered Rayleigh light simulation module, beam coupler module, and photoelectric conversion module, with a unified save button. The right side is the detailed parameter setting area for the currently selected module (taking the laser simulation module as an example), including parameter input boxes for output power (mW), center frequency (THz), frequency shift rate (Hz), linewidth (Hz), and laser wavelength (nm).

[0056] Figure 3 The layout of the fiber optic and disturbance parameter configuration interface includes a selection port on the left for both straight fiber and spiral fiber fiber sensing stress models. The wet-end parameter setting group contains four input items: fiber Poisson's ratio, fiber elastic modulus, acoustic sensitivity elastic modulus, and fiber winding ratio, as well as a save button. The excitation mode area on the right provides a custom mode selection function, along with settings for spatial channel number, time point number parameters, and a file browsing button.

[0057] It should be noted that this application not only establishes a digital simulation and demodulation system based on distributed optical fiber sensing, but also establishes an evolution model of the wet-end sensor's response to external stimuli. This model, by introducing key strain parameters such as the fiber's Poisson's ratio and elastic modulus, can effectively invert the complete physical process after an external signal acts on the sensing optical cable.

[0058] When the excitation signal is transmitted to the acoustically sensitive core rod, the core rod deforms, which in turn transmits strain to the sensing optical fiber uniformly wound on it. This causes the optical fiber to deform periodically with the core rod, generating a corresponding optical path difference within the fiber. This mechanical strain is converted into a phase change in the backscattered Rayleigh light. The wet-end sensor model accurately loads this phase change into the backscattered Rayleigh light in the optical path simulation model, ensuring that the strain information from the external excitation is completely transmitted to the distributed sensing system. To be compatible with different wet-end sensor types, such as straight optical fibers and spiral optical cables, the model also adds two key parameters: the elastic modulus of the acoustically sensitive core rod and the fiber winding ratio (corresponding to...). Figure 3(Relevant settings in the interface) to improve the system's compatibility with different sensor structures and simulation accuracy.

[0059] Figure 4 This is a specific configuration example of the interface for setting parameters of the simulated excitation source. The interface uses a modular layout and is available in both straight fiber and sinusoidal function excitation modes. Figure 5 This is a time-domain waterfall plot based on configuration parameters. The horizontal axis represents fiber distance (in meters), the vertical axis displays the time series (in milliseconds), and the color depth corresponds to the signal strength (in dB). Figure 6 This is a simulated frequency domain waterfall plot based on configuration parameters. The vertical axis represents frequency (unit: kHz), the horizontal axis represents fiber distance (unit: m), and the color brightness represents power spectral density. Figure 7 This is a frequency domain plot of a single-point simulation based on configuration parameters. The horizontal axis represents frequency (in kHz), and the vertical axis represents power spectral density (in dB).

[0060] like Figure 4 As shown, a single-point excitation source was set at 30m of the optical cable, with configuration parameters including: influence range ±10m, amplitude 5nm, frequency 50Hz, and initial phase 0rad. Using a wet-end sensor model and signal demodulation algorithm, not only can the excitation location be accurately located, but the amplitude, frequency, and phase information of the external excitation can also be completely reconstructed. Simulation results are as follows. Figure 6 The results show that the excitation center point is 35m, and the influence range covers the interval of 25-45m, which is consistent with the preset ±10m influence range. The 5m positional error is within the allowable range of the system's spatial resolution (10m resolution corresponding to a pulse width of 100ns). Frequency domain analysis results (such as...) Figure 7 As shown in the figure, the main frequency components of the restored signal are strictly concentrated at 50Hz, and the signal-to-noise ratio reaches 53dB, which verifies the system's high-fidelity restoration capability of the frequency characteristics of external excitation.

[0061] It should be noted that, as Figure 5 The time-domain waterfall plot clearly shows the dynamic process of signal phase change within the 25m to 45m section of the optical cable. This system overcomes the limitations of traditional distributed fiber optic sensing that relies solely on amplitude detection, by using multi-parameter demodulation technology to fully capture the amplitude, frequency, and phase temporal changes of external excitations. This comprehensive signal acquisition capability enables the system to accurately record common signal abrupt changes in practical applications, improving the consistency between simulation results and real-world operating conditions.

[0062] In one embodiment, such as Figure 8As shown, a digital simulation and demodulation system based on distributed optical fiber sensing is provided. The system includes: a laser simulation module 801, a beam splitter module 802, an AOM modulation module 803, an amplification module 804, a backscattered Rayleigh light simulation module 805, a beam coupler module 806, and a broadcast conversion module 807.

[0063] The laser simulation module 801 is equipped with a laser parameter input port, which is used to perform laser simulation based on the parameters input into the laser parameter input port to obtain a digital model of the laser.

[0064] Beam splitter module 802 is used to simulate laser beam splitting. Based on the laser digital model, the beam splitter module combines the beam splitting ratio to generate the probe light field model and the intrinsic light field model.

[0065] The AOM modulation module 803 is equipped with an AOM modulation parameter input port, which is used to receive AOM modulation parameters. Based on the AOM modulation parameters, it simulates modulating the probe light field into pulse light of a fixed frequency and loads the carrier frequency into the optical frequency to generate a probe light AOM modulation model.

[0066] The amplification module 804 is equipped with an amplification parameter input port, which is used to simulate amplify the pulse light according to the amplification parameters and generate a mathematical model of the amplified light field by combining the probe light AOM modulation model.

[0067] The back Rayleigh scattering light simulation module 805 is used to convolve the optical field mathematical model with the one-dimensional fiber discretized scattering model to generate a back Rayleigh scattering light model.

[0068] The beam coupler module 806 is used to simulate the beat frequency interaction between back Rayleigh scattered light and intrinsic light in the beam coupler, and to generate two output optical signals based on the back Rayleigh scattered light model and the intrinsic light field model.

[0069] The photoelectric conversion module 807 is used to convert two output optical signals to obtain two converted voltage signals and output the difference between the two converted voltage signals.

[0070] Specifically, the laser simulation module 801, as the optical source of the entire digital simulation and demodulation system, can perform laser simulation based on the laser parameters configured by the user through the laser parameter input port, and obtain a digital model of the laser. The laser parameters can include laser output power, center angular frequency, laser wavelength, and linewidth. The expression for this digital model of the laser is:

[0071]

[0072] Where E0 is the electric field intensity of the laser, ω0 is the center angular frequency of the emitted laser, and γ is the frequency shift rate. Here, represents phase noise, and j is the imaginary unit. P0 is the laser output frequency. Phase noise is introduced into the laser digital model. and It is caused by spontaneous emission and can be considered a Wiener process. Its random increment follows a zero-mean Gaussian distribution with variance proportional to the laser linewidth Δf, and its expression is:

[0073]

[0074] Where τ is the sampling interval and Δf is the linewidth of the laser. The linewidth Δf controls the severity of phase noise fluctuations, thus simulating the coherent characteristics of the laser. Therefore, the digital model of the laser output by the laser simulation module is not an ideal monochromatic light, but a coherent light field containing specific power, frequency, wavelength, and phase noise characteristics determined by the linewidth.

[0075] like Figure 9 , Figure 10 , Figure 11 as well as Figure 12 The figures show the single-channel spectra of the simulated excitation results of the laser at linewidths of 3kHz, 1kHz, 500Hz, and 800Hz, respectively. As can be seen from the single-channel spectra corresponding to each linewidth, the narrower the linewidth of the laser, the lower the phase noise and frequency noise in the laser. Therefore, ultra-narrow linewidth lasers should be selected as the system light source during equipment development and device selection, which can effectively reduce the system noise floor of acoustic wave detection and improve the signal-to-noise ratio.

[0076] The beam splitter module 802 can simulate the laser beam splitting process. Based on the laser digital model output by the laser simulation module, the module uses a built-in unbalanced fiber beam splitter structure to asymmetrically distribute the incident laser energy according to a preset splitting ratio, generating two different energy levels of output light fields: one is a high-energy detection light field model that undertakes the main detection task, and the other is a weak-energy intrinsic light field model that serves as a phase reference.

[0077] The AOM modulation module 803 can modulate the probe optical field model. It modulates the probe optical field model into pulsed light of a fixed frequency and loads the carrier frequency into the optical frequency. This process can be achieved through mathematical modeling. After receiving the probe optical field model from the beam splitter, the AOM modulation module 803 establishes the probe optical AOM modulation model based on the pulse width and carrier frequency parameters set through the AOM modulation parameter input port. The pulse width parameter modulates the continuous probe optical field model into a pulse sequence with a fixed repetition frequency, achieving pulsed processing in the time domain. The carrier frequency parameter is used to frequency-shift the probe optical field model, loading the carrier frequency into the optical frequency. The generated probe optical AOM modulation model is as follows:

[0078]

[0079] in, Represented as a rectangular function of length w, when t <w, Otherwise, it equals 0. E 0.9 (t) represents the beam splitter output probe light field model, w represents the modulated target pulse width, ω s The carrier frequency is ω. In practical applications, the carrier frequency ω that AOM can achieve is... s The range is mostly concentrated in the hundreds of MHz. Therefore, ω s <<ω0.

[0080] To achieve a longer sensing distance and better suit real-world applications, an amplification module 804 is needed to amplify the pulsed light. A commonly used amplification module 804 is an erbium-doped fiber amplifier (EDFA). The EDFA primarily amplifies the intensity of the input light. After receiving the AOM modulation model of the probe light from the AOM modulation module 803, the EDFA establishes a mathematical model of the optical field after intensity amplification based on the attenuator coefficient At and amplifier gain G set through the amplification parameter input port, as follows:

[0081]

[0082] Among them, E AOM (t) represents the input probe light AOM modulation model, At is the set attenuator coefficient, and G is the set amplifier gain. In this mathematical model, the amplifier gain G is expressed in decibels (dB) and is calculated exponentially. The decibel value is converted into a power amplification factor in the linear domain, which is responsible for the AOM modulation model E of the input probe light. AOM(t) realizes the main amplification function, and its value directly determines the degree of signal power enhancement; the attenuator coefficient At can be used as a linear adjustment factor (the value range is usually 0 to 1), located at the output end of the amplification link, to precisely fine-tune the power of the amplified signal, and prevent optical nonlinear effects or device saturation caused by excessive power.

[0083] The backscattering Rayleigh light simulation module 805 can receive the amplified optical field mathematical model from the amplification module 804, and generate the backscattering Rayleigh light model by convolving the amplified optical field mathematical model with the one-dimensional fiber discretized scattering model. The backscattering Rayleigh light model takes into account the Rayleigh distribution characteristics of the reflection amplitude at the fiber scattering point, the modulation effect of strain caused by external vibration on the scattering point position, and the cumulative effect of strain on the scattering phase.

[0084] It should be noted that convolving the magnified optical field mathematical model with the one-dimensional fiber discretized scattering model can simulate the interaction between the probe light pulse and each scattering point along the fiber as the light pulse propagates: when the light pulse propagates forward in the fiber, each scattering point generates a weak backscattered wave, and these backscattered waves superimpose in time to form the total backscattered Rayleigh signal. Through the convolution operation, the strain information caused by external vibrations is effectively encoded into the phase of the backscattered Rayleigh light, thereby generating a backscattered Rayleigh light model containing complete vibration information.

[0085] The backscattered Rayleigh light to be detected serves as one input to the beam coupler module 806, while the other input is the 10% intrinsic light field separated from the laser's light field. The two inputs undergo beat frequency interaction in the beam coupler module 806 to obtain two output optical signals, as shown in the following model:

[0086]

[0087] Among them, the backscattered Rayleigh light E s (t), E 0.1 (t) represents the intrinsic light, the superscript * indicates conjugate, and real{x} represents taking the real part of x. The two signals I output from the optical coupler module 806 are... out1 (t) and I out2 (t) Remove the optical frequency ω0, and retain only the AOM carrier frequency ω s Composition. By backscattering Rayleigh light (containing optical frequency ω0 and carrier frequency ω) s The carrier frequency (ω0 component) is subjected to interference mixing with the intrinsic light (containing only the optical frequency ω0 component). This eliminates the high-frequency optical frequency ω0 component in the output signal, retaining only the lower-frequency carrier frequency ω0. s Element.

[0088] The photoelectric conversion module 807 can convert two output optical signals into two converted voltage signals, which are then identified and acquired by the data acquisition card. The photoelectric conversion module model is as follows:

[0089]

[0090] In the formula, P min For minimum detection power, P s For saturated detection power, k p For conversion gain, a p To adjust the coefficient, b p c is a nonlinear coefficient. p This is the attenuation coefficient.

[0091] set up The two signals I output from the optocoupler out1 (t) and I out2 Substituting I(t) into the above equation, we obtain the conversion voltage I. pout1 (t) and I pout2 (t), the final output voltage is the difference between the two:

[0092] V p (t)=I pout1 (t)-I pout2 (t).

[0093] For the conversion voltage I pout1 (t) and I pout2 (t) Differential operation can achieve balanced detection, effectively suppress common-mode interference such as laser intensity noise, and improve the signal-to-noise ratio.

[0094] In this embodiment, the system generates a digital laser model containing phase noise through a laser simulation module. This model is then split into two signals: a probe light field model and an intrinsic light field model, by a beam splitter module. The probe light field model is modulated into a probe light AOM modulation model carrying the carrier frequency by an AOM modulation module. After power enhancement by an amplification module, an amplified optical field mathematical model is generated. A backscattering Rayleigh light simulation module combines the discretized fiber scattering model with the amplified optical field mathematical model through convolution operations to generate a backscattering Rayleigh light model carrying vibration information. This model and the intrinsic light field model generate two optical signals through beat frequency interaction in a beam coupler module, which are then converted into differential voltage signals for output by a photoelectric conversion module. This system can provide key parameter verification for lasers, modulation modules, etc., by simulating different design schemes, guiding parameter configuration optimization, effectively reducing hardware trial and error costs, and providing a full-link design basis for the construction of distributed fiber optic sensing systems.

[0095] In one embodiment, the backscattered Rayleigh light simulation module is also configured with an excitation source mode selection port for selecting an excitation source. The backscattered Rayleigh light simulation module simulates the fiber sensing strain caused by the excitation transmission acting on the fiber according to the selected excitation source.

[0096] A one-dimensional discretized scattering model of an optical fiber is generated based on the fiber's strain sensing and the reflection amplitude of scattering points at different locations of the fiber that follow a Rayleigh distribution.

[0097] Specifically, the backscattered Rayleigh light simulation module is equipped with an excitation source mode selection port for receiving the selected excitation source mode. This module has multiple built-in excitation modes, allowing the simulated excitation source to be set to a sine function mode, square wave function mode, pulse function mode, and a custom function mode. In the custom function mode, actual vibration data can be uploaded. In the other modes, based on configurable parameter inputs, the vibration signal and optical cable response parameters can be simulated to simulate the response effect of the excitation source.

[0098] The essence of the detection model for distributed sensing fiber optics can be understood as the interaction between forward-propagating light and numerous light scattering points on the fiber, producing backscattered Rayleigh light. The position and amplitude of the scattering points on the fiber are random. A one-dimensional discretized fiber optic scattering model E f The expression for (x) is as follows:

[0099]

[0100] Where α is the attenuation coefficient of the optical fiber, representing the degree of optical signal loss per kilometer transmitted through the optical fiber; l ′ (x i ) is the position function of the discretized fiber scattering unit under the influence of disturbance, and r(x) is the reflection amplitude of the scattering point at different positions in the fiber, which follows a Rayleigh distribution, i.e.,

[0101]

[0102] Where, r is =6.1465*10 -4 is the Rayleigh distribution coefficient, and rand(0,1) is a random number between [0,1].

[0103] Furthermore, l ′ (x i )satisfy:

[0104]

[0105] In the formula, Δl is the fiber discrete sampling interval, N is the number of spatial samples, and ε(x) i) represents the strain caused by vibration at different locations. The term rand(0,1)·Δl can represent the randomness of the distribution of scattering points within a unit spatial interval of the optical fiber.

[0106] Furthermore, For phase terms, Specifically, it is expressed as follows:

[0107]

[0108] In the formula, β is the propagation coefficient of light in the optical fiber, and λ is the laser wavelength. eff n is the equivalent fiber refractive index. eff The equivalent refractive index of the optical fiber is expressed as:

[0109]

[0110] Where, n f It is the refractive index of the optical fiber, v is Poisson's ratio, and p is the refractive index of the optical fiber. 11 With p 12 This is the photoelastic constant, determined based on the actual characteristics of the optical fiber. Before convolving the one-dimensional discretized scattering model of the optical fiber with the forward propagating light, it is necessary to transform the one-dimensional discretized scattering model of the optical fiber into a function of propagation time based on the time-distance relationship, that is:

[0111]

[0112] Where c is the speed of light.

[0113] In one embodiment, the backscattering Rayleigh light simulation module converts the one-dimensional fiber discretized scattering model into a function of propagation time before convolving it with the optical field mathematical model.

[0114] Specifically, by convolving the optical field mathematical model with the one-dimensional fiber discretized scattering model, the formula for the backscattered Rayleigh light model is as follows:

[0115]

[0116] in, This represents the convolution operation.

[0117] In one embodiment, the backscattered Rayleigh light simulation module is also equipped with a selection port for two fiber optic stress sensing models: straight fiber and spiral fiber. Based on the selected fiber type and the corresponding fiber optic stress sensing model, the fiber optic strain caused by the excitation transmission acting on the fiber is simulated.

[0118] Specifically, after the excitation is transmitted to the optical fiber, the vibration location and the characteristics of the optical cable itself will lead to different influence ranges. The backscattered Rayleigh light simulation module is equipped with an optical fiber type selection port for switching between two stress sensing models: straight fiber and spiral fiber. For both the optical fiber model and the excitation source model, the position, influence range, amplitude, frequency, phase, pulse width, and rise / fall edge width are used as configurable input parameters. Based on the strain response capabilities of two different sensors, straight fiber and spiral fiber, an optical fiber stress sensing model is established as follows:

[0119]

[0120] Where, ε HWC With ε ST These represent the axial strain generated by the stress τ in the spiral optical cable and the straight optical fiber, respectively. Ne>1 is the spiral fiber winding ratio, and E1 is the Young's modulus of the wound fiber acoustic sensing core rod; E2 is the Young's modulus of the straight optical fiber, and v2 is the fiber Poisson's ratio, approximately 0.2. E1 is much smaller than E2, therefore, compared to the straight fiber, the spiral optical cable produces a larger strain under the same stress, achieving a sensitization effect. The backscattered Rayleigh light simulation module calls the corresponding strain model according to the selected fiber type, using the strain term ε... HWC or ε ST Influence the position and phase of the scattering point to generate backscattered Rayleigh light models with different strain response characteristics.

[0121] In one embodiment, such as Figure 8 As shown, the digital simulation and demodulation system based on distributed optical fiber sensing also includes a demodulation module 808, which is configured as follows:

[0122] Establish a pair of orthogonal reference signals, with the reference signal mode being the AOM carrier frequency.

[0123] The two converted voltage signals output from the photoelectric conversion module 807 are multiplied respectively to form a mixed signal.

[0124] The sum-frequency term of the mixing signal is filtered out by a low-pass filter while the phase component is retained.

[0125] The phase value is obtained by arctangent, and the obtained phase value is used to obtain the phase change on the sensing fiber through differential operation.

[0126] Specifically, the demodulation module 808 generates a pair of orthogonal reference signals based on the carrier frequency set in the AOM modulation module 803, and multiplies the voltage signal output by the photoelectric conversion module 807 with the orthogonal reference signals to generate a mixed signal containing sum and difference frequency components. The demodulation module 808 further filters out the high-frequency sum frequency components in the mixed signal using a low-pass filter, retaining the low-frequency difference frequency signal containing vibration phase information. The demodulation module 808 performs an arctangent operation on the filtered orthogonal signal to extract the instantaneous phase value carrying vibration information, and performs spatial domain differential operation on the demodulated phase along the sensing fiber to obtain the phase change characterizing the axial strain of the fiber.

[0127] In one embodiment, the demodulation module is provided with a demodulation configuration parameter input port for inputting demodulation configuration parameters, which include at least the low-pass cutoff frequency, gauge length, and spatial resolution.

[0128] The differential operation includes: performing spatial domain differential based on demodulation configuration parameters to obtain the phase change rate.

[0129] Specifically, the demodulation module is equipped with a demodulation configuration parameter input port to receive key parameters including the low-pass cutoff frequency, gauge length, and spatial resolution. The low-pass cutoff frequency sets the passband boundary of the filter, ensuring that while filtering out high-frequency and frequency-term components generated by mixing, the low-frequency phase components characterizing vibration information are fully preserved. The gauge length parameter defines the core interval for spatial domain differential operations. Based on this parameter value, discretized spatial domain differential operations are performed to obtain the phase change rate reflecting the axial strain of the fiber. The spatial resolution parameter works in conjunction with the gauge length to jointly determine the minimum localization capability for vibration events and the signal-to-noise ratio.

[0130] In one embodiment, such as Figure 13 , Figure 14 as well as Figure 15 The figures show time-domain waterfall plots for the spatial resolution of a 500ns pulse width, 10m gauge length system, a 100ns pulse width, 30m gauge length system, and a 100ns pulse width, 10m gauge length system, respectively. To design a digital simulation and demodulation system with a spatial resolution better than 10m, since the spatial resolution is affected by the pulse width and gauge length of the emitted pulses, the emitted pulse width should be ≤100ns and the gauge length should be ≤10m during system parameter configuration and design. This example demonstrates the ability to assist researchers in rapid system parameter design and verification.

[0131] In one embodiment, the demodulation module performs time-domain differential based on the phase change rate to obtain strain rate information.

[0132] Specifically,

[0133] In the formula, To demodulate the phase, distinguish it from the pulse propagation time t in the above formula, t s This represents the signal sampling time. The pulse propagation time t is based on the formula: This is converted into a spatial position x on the optical fiber. The phase change rate is obtained from the demodulated phase difference. This represents the strain information of the vibration signal. By taking the time derivative of the phase change rate, strain rate information can be obtained. The choice of gauge length is crucial for the signal-to-noise ratio and spatial resolution of the demodulation results.

[0134] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a solid-state disk (SSD), etc.

[0135] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The above are merely preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A distributed fiber optic sensing based digital simulation and demodulation system, characterized in that, The system comprises: a laser simulation module configured with a laser parameter input port, for laser simulation according to the parameters input by the laser parameter input port, to obtain a laser digital model; a beam splitter module for simulating laser beam splitting, based on the laser digital model, the beam splitter module combines a light splitting ratio to generate a probe light field model and an intrinsic light field model; an AOM modulation module configured with an AOM modulation parameter input port, the AOM modulation parameter input port is used to receive AOM modulation parameters, according to the AOM modulation parameters, the probe light field is modulated into pulsed light of a fixed frequency, and a carrier frequency is loaded into the optical frequency to generate a probe light AOM modulation model; an amplification module configured with an amplification parameter input port, for simulating amplification of pulsed light according to amplification parameters, and combining the probe light AOM modulation model to generate a mathematical model of amplified light field; a back Rayleigh scattering light simulation module for convolving the mathematical model of light field with a one-dimensional optical fiber discretization scattering model to generate a back Rayleigh scattering light model; a beam coupler module for simulating the beat effect of back Rayleigh scattering light and intrinsic light in a beam coupler, and generating two output optical signals according to the back Rayleigh scattering light model and the intrinsic light field model; a photoelectric conversion module for converting the two output optical signals to obtain two converted voltage signals, and outputting the difference between the two converted voltage signals.

2. The digital simulation and demodulation system based on distributed optical fiber sensing according to claim 1, wherein the parameters input by the laser parameter input port at least include: output power, center angular frequency, line width and laser wavelength of the laser; in the laser digital model, the influence of phase noise is introduced, and the phase noise is configured to follow a Gaussian normal distribution with a mean of 0.

3. The digital simulation and demodulation system based on distributed optical fiber sensing according to claim 1, wherein the AOM modulation parameters at least include: carrier frequency and target pulse width of modulation; the probe light AOM modulation model is represented by the following formula: wherein is represented as a rectangular function of length w, when t < w, is equal to 0 otherwise, E 0.9 (t) represents the probe light field model, w represents the modulated target pulse width, ω s is the carrier frequency.

4. The digital simulation and demodulation system based on distributed optical fiber sensing according to claim 1, wherein the amplification parameters include attenuator coefficients and amplifier gains; the mathematical model of light field is represented by the following formula: wherein At represents the attenuator coefficient, and G represents the amplifier gain.

5. The digital simulation and demodulation system based on distributed optical fiber sensing according to claim 1, wherein the back Rayleigh scattering light simulation module is further configured with an excitation source mode selection port for selecting an excitation source, and the scattering back Rayleigh scattering light simulation module simulates the excitation transfer acting on the optical fiber to cause the optical fiber sensing strain according to the selected excitation source; based on the optical fiber sensing strain and the reflection amplitude of the scattering points at different positions of the optical fiber following the Rayleigh distribution, the one-dimensional optical fiber discretization scattering model is generated.

6. The digital simulation and demodulation system based on distributed optical fiber sensing according to claim 5, wherein The back Rayleigh scattering light simulation module converts the one-dimensional fiber discrete scattering model into a function about the propagation time and then convolves the function with the light field mathematical model.

7. The distributed fiber sensing based digital simulation and demodulation system according to claim 5, wherein, The back Rayleigh scattering light simulation module is further configured with a selection port of two fiber stress sensing models of straight fiber and spiral fiber, and according to the selected fiber type, simulates the fiber sensing strain caused by the excitation transmission acting on the fiber based on the corresponding type of fiber sensing stress model.

8. The distributed fiber-optic sensing based digital simulation and demodulation system of claim 1, wherein, The system further comprises a demodulation module configured to: establish a pair of orthogonal reference signals with a reference signal mode of AOM carrier frequency, respectively multiply two converted voltage signals output by the photoelectric conversion module to form mixed frequency signals, filter the sum frequency items of the mixed frequency signals and retain the phase components based on a low-pass filter, obtain the phase value through an inverse tangent, and obtain the phase change on the sensing fiber through a difference operation.

9. The distributed fiber sensing based digital simulation and demodulation system according to claim 8, wherein, The demodulation module is provided with a demodulation configuration parameter input port for inputting demodulation configuration parameters, and the demodulation configuration parameters at least include a low-pass cutoff frequency, a gauge length and a spatial resolution; The difference operation includes: based on the demodulation configuration parameters, performing spatial domain difference based on the demodulation configuration parameters to obtain the phase change rate.

10. The distributed fiber sensing based digital simulation and demodulation system according to claim 9, wherein, The demodulation module performs time domain difference based on the phase change rate to obtain strain rate information.

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