Wavelength division multiplexing phi-OTDR and BOTDR fusion demodulation method, system and device and storage medium

Abstract

The invention discloses a wavelength division multiplexing phi-OTDR and BOTDR fusion demodulation method, system and device and a storage medium, and relates to the technical field of distributed optical fiber sensing, and the method comprises the steps: employing a double independent narrow linewidth laser to output continuous laser, enabling each path to be divided into two beams through a coupler, enabling one beam to be subjected to pulse modulation, and enabling the other beam to be used as local oscillation light; pulse light is modulated into frequency-shift pulse light through an acousto-optic modulator, and the frequency-shift pulse light is injected into a sensing optical fiber after being combined by an optical combiner. And the backscattered light is separated by the optical wave separator according to the wavelength. Rayleigh signals are subjected to coherent receiving and orthogonal demodulation to obtain light intensity; brillouin signal amplification, frequency mixing and the like are performed to extract frequency shift. In combination with light intensity and frequency shift, temperature strain is decoupled, and vibration information is demodulated; according to the invention, the measurement precision is improved, and the line potential risk can be found in time; efficient signal isolation and transmission and temperature strain decoupling measurement are achieved, and pipeline safety is guaranteed; the structure is simple and easy to expand, and long-distance, low-cost and high-precision monitoring and timely disaster early warning can be realized.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber sensing technology, and in particular to a method, system, device, and storage medium for the fusion demodulation of wavelength division multiplexing Φ-OTDR and BOTDR. Background Technology

[0002] With the increasing demand for distributed, multi-parameter, and high-precision sensing systems in fields such as smart grids, oil pipeline safety, and slope monitoring, distributed fiber optic sensing technology has attracted widespread attention due to its advantages such as resistance to electromagnetic interference, suitability for long-distance deployment, and high spatial resolution. Currently, Φ-OTDR (phase-sensitive optical time-domain reflectometry) is mainly used for vibration detection, while BOTDR (Brillouin scattering-based optical time-domain reflectometry) is used for temperature and strain measurement. Since these two sensing mechanisms are based on different scattering principles, integrating them can achieve complementarity and is an effective means of realizing multi-parameter monitoring. Brillouin scattering and Rayleigh scattering signals are close in the frequency domain, and achieving efficient separation and joint demodulation has been a long-standing technical challenge. At the same time, in BOTDR systems, due to the extremely weak intensity of the Brillouin scattering signal, the accuracy of optical power information extraction is easily affected by noise and loss. In recent years, the development of microwave heterodyne detection and wavelength division multiplexing (WDM) technologies based on LPR has provided new solutions to problems such as difficulty in signal separation and insufficient accuracy in frequency shift measurement.

[0003] Currently, mainstream BOTDR systems employ narrow-linewidth lasers and frequency modulation schemes combined with microwave heterodyne detection to extract Brillouin frequency shifts for acquiring temperature and strain information. However, these systems typically use a single Brillouin channel, failing to effectively utilize Rayleigh scattering information. Consequently, they struggle to correct measurement errors caused by losses and resolve cross-interference issues between temperature and strain. Other systems physically integrate Φ-OTDR with BOTDR, but these generally suffer from signal interference, high system complexity, and poor multiplexing capabilities. Some solutions introduce wavelength division multiplexing (WDM) technology to multiplex multiplexed signals, but fail to incorporate LPR ratio optimization for scattering demodulation, thus failing to improve overall measurement accuracy and stability. In BOTDR systems, the Brillouin scattering signal is extremely weak and highly susceptible to losses, bending, and connector reflections, resulting in limited measurement accuracy. Existing systems do not utilize the inherent proportional relationship between Rayleigh and Brillouin signals and fail to introduce LPR ratios to correct Brillouin scattering measurement errors. Most systems lack WDM mechanisms, leading to significant waste of channel resources and poor scalability. Furthermore, BOTDR systems exhibit cross-sensitivity to temperature and strain, making decoupling analysis difficult. Summary of the Invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problems solved by this invention are: how to improve the measurement accuracy of Brillouin scattering power in the BOTDR system and solve the intensity error problem caused by fiber loss; to achieve efficient multiplexing and separation of Φ-OTDR and BOTDR signals in the same fiber and simplify the system structure; to solve the problem of temperature and strain cross-sensitivity in the BOTDR system and achieve accurate decoupling; and to construct a multi-parameter fusion distributed sensing system based on DWDM to achieve simultaneous measurement of physical quantities such as temperature, strain, and vibration over long distances, at low cost and with high precision.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for fusion demodulation of wavelength division multiplexing Φ-OTDR and BOTDR, comprising:

[0008] Two independent narrow-linewidth lasers are used to output continuous laser light. Each laser is split into two beams by a coupler. One beam is used for pulse modulation and the other is used as the local oscillator light.

[0009] The beam used for pulse modulation is modulated into pulsed light using an acousto-optic modulator, and the optical frequency is shifted.

[0010] Two pulsed lights are combined into one beam by an optical combiner in a wavelength division multiplexer and injected into the sensing fiber through an optical circulator.

[0011] The backscattered light returning from the sensing fiber is led out by the optical circulator to the optical demultiplexer in the wavelength division multiplexer, and separated into two signals according to wavelength: one corresponds to the dominant wavelength of Rayleigh scattering and the other corresponds to the dominant wavelength of Brillouin scattering.

[0012] The signal corresponding to the dominant wavelength of Rayleigh scattering interferes with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, the beat frequency signal is output. Then, the signal is obtained by an orthogonal demodulator for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering intensity is further obtained by orthogonal demodulation.

[0013] The signal corresponding to the dominant wavelength of Brillouin scattering is amplified by an erbium-doped fiber amplifier and mixed with the local oscillator light of the corresponding wavelength. The mixture is then converted into an electrical signal by a photodetector, mixed with a sweep frequency source, filtered, and envelope detected to extract the Brillouin frequency shift.

[0014] The intensity of Brillouin scattered light is calculated based on Rayleigh scattered light intensity and Landau-Platzczek ratio. Combined with Brillouin frequency shift, temperature and strain are decoupled through calibration model, and vibration information is demodulated using Rayleigh phase signal.

[0015] As a preferred solution for the fusion demodulation method of wavelength division multiplexing Φ-OTDR and BOTDR, wherein:

[0016] The method uses two independent narrow-linewidth lasers to output continuous laser light. Each laser beam is split into two beams by a coupler. One beam is used for pulse modulation, and the other beam serves as the local oscillator light.

[0017] Two independent narrow-linewidth lasers are used to output continuous lasers with a fixed wavelength interval. Each continuous laser is split into two beams after entering the coupler. One beam with a larger power is used for subsequent pulse modulation, and the other beam with a smaller power is used as the local oscillator.

[0018] The beneficial effects of this preferred technical solution are as follows: using continuous lasers with fixed wavelength intervals provides a stable and distinguishable wavelength basis for subsequent wavelength division multiplexing operations, ensuring that different signals are independent during transmission and processing, and reducing interference. Allocating each laser beam according to its optical power, with higher power beams used for pulse modulation to ensure sufficient energy for generating effective pulse signals, and lower power beams used as local oscillators, satisfies the requirements of coherent detection without interfering with other signals due to excessive power, thus improving system stability and signal processing accuracy.

[0019] As a preferred solution for the fusion demodulation method of wavelength division multiplexing Φ-OTDR and BOTDR, wherein:

[0020] The process of combining two pulsed light streams into a single beam via an optical combiner in a wavelength division multiplexer and injecting it into the sensing fiber via an optical circulator includes:

[0021] The two pulsed light beams modulated by the acousto-optic modulator are combined into one beam by the optical combiner in the wavelength division multiplexer; the combined beam is then injected into the sensing fiber by the help of an optical circulator.

[0022] As a preferred solution for the fusion demodulation method of wavelength division multiplexing Φ-OTDR and BOTDR, wherein:

[0023] The backscattered light returning from the sensing fiber is guided by an optical circulator to an optical demultiplexer in the wavelength division multiplexer, where it is separated into two signals according to wavelength: one corresponding to the dominant Rayleigh scattering wavelength, and the other corresponding to the dominant Brillouin scattering wavelength, including:

[0024] The backscattered light carrying Brillouin and Rayleigh scattering light returned by the sensing fiber is transmitted to the optical demultiplexer via the optical circulator in the wavelength division multiplexer. The optical demultiplexer separates the backscattered light according to wavelength to obtain two signal lights of different wavelengths, corresponding to the Rayleigh scattering dominant wavelength and the Brillouin scattering dominant wavelength, respectively.

[0025] The beneficial effects of this preferred technical solution are: it ensures the accurate separation of Rayleigh scattering and Brillouin scattering light carrying different information. This method of separating signals by wavelength can effectively distinguish different types of scattered light, providing a basis for subsequent processing and demodulation of Rayleigh scattering and Brillouin scattering signals, thereby improving the targeting and accuracy of signal processing.

[0026] As a preferred solution for the fusion demodulation method of wavelength division multiplexing Φ-OTDR and BOTDR, wherein:

[0027] The signal corresponding to the dominant wavelength of Rayleigh scattering interferes with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, a beat frequency signal is output, which is then passed through an orthogonal demodulator to obtain an electrical signal for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering intensity is further obtained by using an orthogonal demodulation method, including:

[0028] The signal corresponding to the dominant wavelength of Rayleigh scattering is filtered by a narrowband filter to extract the effective frequency components, and then interferes with the local oscillator light of the corresponding wavelength in a coherent receiver to form a beat frequency signal. The beat frequency signal is then processed by photoelectric detection and subsequent processing to output an electrical signal, thereby realizing the demodulation and extraction of the Rayleigh scattering signal. The output electrical signal is processed by an orthogonal demodulation method to separate two signals related to the amplitude and phase of the Rayleigh scattering light, and thus the intensity of the Rayleigh scattering light is obtained.

[0029] As a preferred solution for the fusion demodulation method of wavelength division multiplexing Φ-OTDR and BOTDR, wherein:

[0030] The signal corresponding to the dominant Brillouin scattering wavelength is amplified by an erbium-doped fiber amplifier and mixed with the local oscillator light of the corresponding wavelength. This mixture is then converted into an electrical signal by a photodetector, mixed with a swept frequency source, filtered, and subjected to envelope detection. The extraction of the Brillouin frequency shift includes:

[0031] The signal corresponding to the dominant wavelength of Brillouin scattering is mixed with the continuous light from the local oscillator branch in the optical coupler after passing through the erbium-doped fiber amplifier to form a second beat frequency signal. The second beat frequency signal is converted into an electrical signal by a photodetector and then sent to a mixer for down-conversion with a sweep frequency signal source. The amplitude envelope curve is extracted by a filter and an envelope detector, and the sweep frequency corresponding to the peak value of the curve is the Brillouin scattering frequency.

[0032] As a preferred solution for the fusion demodulation method of wavelength division multiplexing Φ-OTDR and BOTDR, wherein:

[0033] The calculation of Brillouin scattered light intensity based on Rayleigh scattered light intensity and Landau-Placchek ratio, combined with Brillouin frequency shift, decoupling temperature and strain through a calibration model, and demodulating vibration information using Rayleigh phase signal include:

[0034] The intensity of Rayleigh scattering and Brillouin scattering are measured from the reflected light spectrum of an optical fiber to determine the Landau-Praček ratio in a specific fiber. The intensity of Rayleigh scattering signal is obtained through coherent reception and IQ demodulation, and then the intensity of Brillouin scattering is calculated by combining the Landau-Praček ratio, thus achieving decoupling of temperature and strain and demodulation of vibration information.

[0035] The beneficial effects of this preferred technical solution are as follows: The Landau-Placchek ratio is determined by measuring the correlated light intensity from the optical fiber reflected light spectrum. The Brillouin scattered light intensity is calculated by combining the Rayleigh scattering signal intensity obtained from coherent reception and IQ demodulation. This method fully utilizes the characteristics of different scattered light, improving the accuracy of Brillouin scattered light intensity calculation. Furthermore, by incorporating the Brillouin frequency shift and calibrating the model, temperature and strain can be accurately decoupled. Simultaneously, vibration information is demodulated using the Rayleigh phase signal, enabling the simultaneous measurement and demodulation of multiple physical quantities, thus enhancing the system's multifunctionality and practicality.

[0036] Secondly, the present invention provides a wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation system, comprising:

[0037] The laser beam splitting and local oscillator configuration module is used to output continuous laser light using two independent narrow linewidth lasers. Each laser is split into two beams by a coupler, one beam is used for pulse modulation, and the other beam is used as the local oscillator light.

[0038] The pulse modulation and frequency shifting module is used to modulate the light beam used for pulse modulation into pulsed light through an acousto-optic modulator and to shift the light frequency.

[0039] The pulse beam combining and injection module is used to combine two pulse beams into one beam through the optical combiner in the wavelength division multiplexer, and then inject it into the sensing fiber through the optical circulator.

[0040] The backscattered light separation module is used to guide the backscattered light returning from the sensing fiber through the optical circulator to the optical demultiplexer in the wavelength division multiplexer, and separate it into two signals according to wavelength: one corresponding to the dominant wavelength of Rayleigh scattering and the other corresponding to the dominant wavelength of Brillouin scattering.

[0041] The Rayleigh scattering signal demodulation module is used to interfere the signal corresponding to the dominant wavelength of Rayleigh scattering with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, the beat frequency signal is output, and then the signal is obtained by an orthogonal demodulator for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering light intensity is further obtained by orthogonal demodulation.

[0042] The Brillouin frequency shift extraction module is used to amplify the signal corresponding to the dominant wavelength of Brillouin scattering by an erbium-doped fiber amplifier and mix it with the local oscillator light of the corresponding wavelength. The signal is then converted into an electrical signal by a photodetector, mixed with a sweep frequency source, filtered, and envelope detected to extract the Brillouin frequency shift.

[0043] The parametric decoupling and information demodulation module is used to calculate the Brillouin scattered light intensity based on the Rayleigh scattered light intensity and the Landau-Placchek ratio. Combined with the Brillouin frequency shift, it decouples temperature and strain through the calibration model and demodulates vibration information using the Rayleigh phase signal.

[0044] Thirdly, the present invention provides an electronic device, comprising:

[0045] Memory and processor;

[0046] The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the one or more programs are executed by the one or more processors, the one or more processors implement the wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method as described in this invention.

[0047] Fourthly, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method.

[0048] The beneficial effects of this invention are as follows: This invention can effectively solve technical problems in practical scenarios. In smart grid monitoring, the measurement accuracy of previous BOTDR systems is limited by factors such as weak Brillouin scattering signals and losses, making it difficult to accurately obtain line temperature and strain information, which may lead to safety hazards. This invention uses microwave heterodyne detection and spectrum scanning to accurately obtain Brillouin frequency shift, introduces a broadband light source and orthogonal demodulation to extract Rayleigh scattering signals, and uses the LPR ratio to correct the Brillouin scattering intensity, effectively improving measurement accuracy and enabling timely detection of potential line risks. In terms of oil pipeline safety monitoring, traditional systems struggle to solve the problems of signal interference and the cross-sensitivity of temperature and strain, and cannot simultaneously monitor pipeline vibration, temperature, and strain. This invention uses wavelength division multiplexing (DWDM) technology to achieve efficient isolation and transmission of Rayleigh and Brillouin signal channels, improving system reusability, and also achieves decoupled measurement of temperature and strain signals, enabling real-time and comprehensive monitoring of pipeline status and ensuring safe pipeline operation. In slope monitoring scenarios, existing systems suffer from high complexity and poor scalability, making it difficult to adapt to complex terrain and large-scale monitoring needs. This invention has good scalability and engineering adaptability, and can flexibly expand sensing capabilities to meet the monitoring needs of large capacity and multiple parameters. It can perform long-distance, low-cost, and high-precision monitoring of slope temperature, strain, and vibration, and provide timely early warning of disasters such as landslides. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is an overall flowchart of the wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method provided by the present invention.

[0051] Figure 2 This is a schematic diagram of the wavelength division multiplexer structure of the wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method provided by the present invention.

[0052] Figure 3 This is a schematic diagram illustrating the orthogonal demodulation principle of the wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method provided by the present invention. Detailed Implementation

[0053] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0054] Example 1, referring to Figure 1 This is the first embodiment of the present invention, which provides a method for fusion demodulation of wavelength division multiplexing Φ-OTDR and BOTDR, including:

[0055] S1: Two independent narrow linewidth lasers are used to output continuous laser light. Each laser is split into two beams by a coupler. One beam is used for pulse modulation and the other beam is used as the local oscillator.

[0056] S2: The light beam used for pulse modulation is modulated into pulsed light by an acousto-optic modulator, and the light frequency is shifted;

[0057] S3: The two pulse beams are combined into one beam by the optical combiner in the wavelength division multiplexer and injected into the sensing fiber through the optical circulator.

[0058] S4: The backscattered light returning from the sensing fiber is led out by the optical circulator to the optical demultiplexer in the wavelength division multiplexer, and separated into two signals according to wavelength: one corresponds to the dominant wavelength of Rayleigh scattering and the other corresponds to the dominant wavelength of Brillouin scattering.

[0059] S5: The signal corresponding to the dominant wavelength of Rayleigh scattering interferes with the local oscillator light of the corresponding wavelength in the coherent receiver. After photoelectric conversion, the beat frequency signal is output. Then, the signal is obtained by the quadrature demodulator for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering intensity is further obtained by the quadrature demodulation method.

[0060] S6: The signal corresponding to the dominant wavelength of Brillouin scattering is amplified by an erbium-doped fiber amplifier and mixed with the local oscillator light of the corresponding wavelength. The signal is then converted into an electrical signal by a photodetector, mixed with a sweep frequency source, filtered, and envelope detected to extract the Brillouin frequency shift.

[0061] S7: Calculate the Brillouin scattered light intensity based on Rayleigh scattered light intensity and Landau-Placchek ratio, combine with Brillouin frequency shift, decouple temperature and strain through calibration model, and demodulate vibration information using Rayleigh phase signal.

[0062] It should be noted that, through steps S1-S7, in the Φ-OTDR and BOTDR integrated distributed fiber optic sensing system, the Rayleigh scattered light demodulated by IQ (in-phase and quadrature) is measured using the Landau-Placchek ratio method, that is, the ratio of Rayleigh scattered light intensity to Brillouin scattered light intensity to accurately measure the Brillouin scattered light power; the frequency shift and intensity of the Brillouin signal are extracted by microwave heterodyne demodulation, and combined with the LPR compensation method, the problem of temperature and strain cross-sensitivity in the BOTDR system is effectively solved, realizing the decoupled measurement of the two; a distributed integrated fiber optic sensing system based on wavelength division multiplexing is designed and implemented, which can simultaneously measure multiple physical quantities such as temperature, strain, and vibration, and is particularly suitable for environmental monitoring along long-distance, high-reliability transmission lines.

[0063] Example 2, refer to Figures 1-3 As an embodiment of the present invention, based on the previous embodiment, a method for fusion demodulation of wavelength division multiplexing Φ-OTDR and BOTDR is provided, including:

[0064] In this embodiment, step S1 above uses two independent narrow-linewidth lasers to output continuous laser light. Each laser beam is split into two beams by a coupler. One beam is used for pulse modulation, and the other beam serves as the local oscillator light.

[0065] Two narrow-linewidth laser sources are used to output laser light sources with a fixed wavelength interval. In this embodiment, the wavelength interval is preferably 0.8nm. The two continuous light outputs are split into upper and lower paths by a 90:10 coupler. 90% of the optical power is used to generate pulsed light, and 10% of the optical power is used as local oscillator light.

[0066] In another possible implementation, a polarization beam splitter can be used for beam splitting. A polarization beam splitter can split a beam of light into two beams with mutually perpendicular polarization directions based on the polarization characteristics of the light. By adjusting the polarization state of the laser output light, the two split beams can respectively meet the requirements of pulse modulation and local oscillator light. For example, one beam can be used for pulse modulation after polarization rotation and power adjustment, while the other beam can be used directly as the local oscillator light.

[0067] In another possible implementation, an acousto-optic beamsplitter can be used for beam splitting. An acousto-optic beamsplitter utilizes the acousto-optic effect; by changing the radio frequency signal applied to the acousto-optic medium, it can split the input light into two beams in different directions. The parameters of the radio frequency signal can be adjusted as needed to ensure that the two split beams have a suitable power ratio, which can be used for pulse modulation and as local oscillator light, respectively.

[0068] In this embodiment, step S2 above, which modulates the light beam used for pulse modulation into pulsed light using an acousto-optic modulator and shifts the light frequency, includes:

[0069] Two beams of the same optical power are modulated by acousto-optic modulation to form a pulsed optical signal, and the optical frequency is shifted.

[0070] It should be noted that the acousto-optic modulator in the heterodyne coherent detection system plays two roles: firstly, it modulates the intensity of continuous light into pulsed light; secondly, it shifts the frequency of the light source, which is crucial for the output of the subsequent intermediate frequency signal.

[0071] Pulse modulation is achieved by modulating a light beam into pulsed light using an acousto-optic modulator and shifting the light frequency. Alternatively, an electro-optic modulator can be used. Electro-optic modulators are based on the electro-optic effect, where certain crystals change their optical properties (such as refractive index) under the influence of an electric field. By rapidly changing the voltage applied to the electro-optic crystal, parameters such as the phase and amplitude of the light can be quickly modulated to generate pulsed light. This can be combined with mode-locking techniques, such as active or passive mode-locking, to achieve more precise and stable pulse output within the laser cavity, and frequency shifting can be achieved by adjusting the mode-locking parameters.

[0072] In another possible implementation, pulse modulation can also be performed using a semiconductor optical amplifier (SOA). A semiconductor optical amplifier has gain characteristics, and its gain can be changed by rapidly controlling the injection current, thereby pulse modulating the input continuous light. Simultaneously, nonlinear effects of semiconductor materials, such as four-wave mixing, can be utilized to achieve frequency shifting, converting the frequency of the input light to the desired frequency.

[0073] In this embodiment, step S3 above, which combines two pulsed lights into one beam using an optical combiner in a wavelength division multiplexer and injects it into the sensing fiber via an optical circulator, includes:

[0074] Two pulsed light beams modulated by an acousto-optic modulator are combined into a single beam by an optical combiner in a wavelength division multiplexer, and then sent into the sensing fiber by an optical circulator. The structure of the wavelength division multiplexer is as follows: Figure 2 As shown, it includes devices such as optical multiplexer (OMU), optical demultiplexer (ODU) and optical circulator, which enable the excitation and backscattered signals of multiple sensors to be transmitted and demodulated without interference in the same optical fiber, greatly improving the utilization of optical fiber bandwidth.

[0075] In this embodiment, the backscattered light returned from the sensing fiber in step S4 is led out by an optical circulator to the optical demultiplexer in the wavelength division multiplexer, where it is separated into two signals according to wavelength: one corresponding to the dominant Rayleigh scattering wavelength and the other corresponding to the dominant Brillouin scattering wavelength, including:

[0076] Simultaneously, the signal light carrying both Brillouin and Rayleigh scattering light passes through the optical circulator in the wavelength division multiplexer and enters the optical demultiplexer, where it is separated into signal lights carrying different wavelengths of scattered light. One path corresponds to the dominant Rayleigh scattering wavelength, and the other corresponds to the dominant Brillouin scattering wavelength.

[0077] In another possible implementation, wavelength separation can be achieved using interference filters. Interference filters utilize the principle of light interference to allow only light within a specific wavelength range to pass through. Two interference filters with different center wavelengths can be selected, corresponding to the dominant wavelengths of Rayleigh scattering and Brillouin scattering, respectively. By passing the backscattered light through these two filters sequentially, two signal lights of different wavelengths can be separated.

[0078] In another possible implementation, a diffraction grating can be used for wavelength separation. A diffraction grating is an optical element with a periodic structure. When light shines on the grating, diffraction occurs, and light of different wavelengths diffracts at different angles. By setting appropriate receiving positions, light corresponding to the dominant Rayleigh scattering wavelength and the dominant Brillouin scattering wavelength can be received separately, thus achieving signal separation.

[0079] Backscattered light returning from the sensing fiber is guided by an optical circulator to an optical demultiplexer in a wavelength division multiplexer, where it is separated into two signals based on wavelength: one corresponding to the dominant Rayleigh scattering wavelength and the other to the dominant Brillouin scattering wavelength. This is for backscattered light signal separation. In another possible implementation, a fiber Bragg grating (FBG) array can also be used for signal separation. A fiber Bragg grating is a periodic refractive index modulation structure formed inside an optical fiber, which reflects light of a specific wavelength. The reflected wavelength depends on the grating period and the effective refractive index of the fiber. By designing fiber Bragg grating arrays with different periods, they can reflect light of the dominant Rayleigh scattering wavelength and the dominant Brillouin scattering wavelength, respectively, thus achieving signal separation.

[0080] In another possible implementation, an acousto-optic tunable filter (AOTF) can also be used for signal separation. The AOTF utilizes the principle of acousto-optic interaction; by changing the frequency of the radio frequency signal applied to the acousto-optic medium, it can selectively allow light of specific wavelengths to pass through, thereby achieving the separation of light of different wavelengths. By adjusting the radio frequency signal frequency, signals corresponding to the dominant Rayleigh scattering wavelength and the dominant Brillouin scattering wavelength can be separated respectively.

[0081] In this embodiment, in step S5 above, the signal corresponding to the dominant wavelength of Rayleigh scattering interferes with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, a beat frequency signal is output, which is then passed through an orthogonal demodulator to obtain an electrical signal for demodulating and extracting the Rayleigh scattering signal. Further, the Rayleigh scattering light intensity is obtained by using an orthogonal demodulation method, including:

[0082] One signal corresponding to the dominant wavelength of Rayleigh scattering is used for demodulation of the Rayleigh scattering light signal. After the effective frequency components are extracted by a 100G narrowband filter, it interferes with the reference light (the local oscillator light of the corresponding wavelength) in a coherent receiver to form the first beat frequency signal. After photoelectric detection and subsequent processing, the first beat frequency signal outputs an electrical signal, which can realize the demodulation and extraction of the Rayleigh scattering signal.

[0083] Furthermore, the Rayleigh scattering signal after heterodyne coherent detection is represented as:

[0084]

[0085] Where ΔI(t) is the Rayleigh scattering signal after heterodyne coherent detection, and A s (t) represents the intensity of the Rayleigh scattered light signal, and Δω represents the frequency of the Rayleigh scattered light signal. This refers to the perturbation signal doped into the Rayleigh scattering light signal.

[0086] Rayleigh scattering intensity is obtained using the orthogonal demodulation method. The principle of orthogonal demodulation is as follows: Figure 3 As shown, the signal after low-pass filtering is:

[0087]

[0088] Where I(t) and Q(t) are two signals after low-pass filtering, and the amplitude and phase signals of the Rayleigh scattered light can be obtained from these two signals, respectively, as follows:

[0089]

[0090] Where ∝ represents direct proportion.

[0091] In this embodiment, the signal corresponding to the dominant Brillouin scattering wavelength in step S6 is amplified by an erbium-doped fiber amplifier and mixed with the local oscillator light of the corresponding wavelength. This mixture is then converted into an electrical signal by a photodetector, mixed with a swept frequency source, filtered, and envelope detected. Extracting the Brillouin frequency shift includes:

[0092] The signal corresponding to the dominant Brillouin scattering wavelength is mixed with continuous light from the local oscillator branch in an optical coupler after passing through an erbium-doped fiber amplifier, forming a second beat frequency signal. This second beat frequency signal is converted into an electrical signal by a photodetector and then sent to a mixer for down-conversion with a swept frequency signal source. Subsequently, the amplitude envelope curve is extracted using a filter and an envelope detector; the swept frequency corresponding to the peak amplitude is the Brillouin scattering frequency, thus achieving accurate extraction of the Brillouin frequency shift.

[0093] In this embodiment, step S7 above involves calculating the Brillouin scattered light intensity based on the Rayleigh scattered light intensity and the Landau-Placchek ratio, combining this with the Brillouin frequency shift, decoupling temperature and strain through a calibration model, and demodulating vibration information using the Rayleigh phase signal, including:

[0094] It should be noted that the Landau-Placzek ratio (LPR) is an important physical quantity in Brillouin scattering spectroscopy, used to describe the ratio between the intensity of the Rayleigh scattering peak (central peak) and the intensity of the two Brillouin scattering peaks (Stokes and anti-Stokes peaks), defined as:

[0095]

[0096] Among them, R LP I represents the Landau-Placzek ratio (LPR). R It is the intensity of the Rayleigh scattering peak, I B For the intensity of the light scattered by one-sided Brillouin, 2I B It is the sum of the light intensities of both sides of the Brillouin peak. R LP Related to the thermodynamic properties of materials (such as compressibility, thermal conductivity, and heat capacity ratio), these properties are usually considered constant or approximately constant under specific materials and temperatures.

[0097] Specifically, the intensity of Rayleigh scattering and Brillouin-side scattering are precisely measured from the spectrum of the reflected light from the optical fiber. Multiple measurements are taken and the average value is calculated to obtain a specific Landau-Placchet ratio in this type of fiber. The intensity I of the Rayleigh scattering signal is then obtained through coherent reception and IQ demodulation. R Based on the known LPR value, the intensity of the unilateral Brillouin scattering light can be deduced as follows:

[0098]

[0099] Example 3: The above is a schematic scheme of the wavelength division multiplexing (WDM) Φ-OTDR and BOTDR fusion demodulation method of this embodiment. It should be noted that the technical solution of the WDM Φ-OTDR and BOTDR fusion demodulation system belongs to the same concept as the technical solution of the WDM Φ-OTDR and BOTDR fusion demodulation method described above. Details not described in detail in the technical solution of the WDM Φ-OTDR and BOTDR fusion demodulation system in this embodiment can be found in the description of the technical solution of the WDM Φ-OTDR and BOTDR fusion demodulation method described above.

[0100] This embodiment also provides a wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation system, including:

[0101] The laser beam splitting and local oscillator configuration module is used to output continuous laser light using two independent narrow linewidth lasers. Each laser is split into two beams by a coupler, one beam is used for pulse modulation, and the other beam is used as the local oscillator light.

[0102] The pulse modulation and frequency shifting module is used to modulate the light beam used for pulse modulation into pulsed light through an acousto-optic modulator and to shift the light frequency.

[0103] The pulse beam combining and injection module is used to combine two pulse beams into one beam through the optical combiner in the wavelength division multiplexer, and then inject it into the sensing fiber through the optical circulator.

[0104] The backscattered light separation module is used to guide the backscattered light returning from the sensing fiber through the optical circulator to the optical demultiplexer in the wavelength division multiplexer, and separate it into two signals according to wavelength: one corresponding to the dominant wavelength of Rayleigh scattering and the other corresponding to the dominant wavelength of Brillouin scattering.

[0105] The Rayleigh scattering signal demodulation module is used to interfere the signal corresponding to the dominant wavelength of Rayleigh scattering with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, the beat frequency signal is output, and then the signal is obtained by an orthogonal demodulator for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering light intensity is further obtained by orthogonal demodulation.

[0106] The Brillouin frequency shift extraction module is used to amplify the signal corresponding to the dominant wavelength of Brillouin scattering by an erbium-doped fiber amplifier and mix it with the local oscillator light of the corresponding wavelength. The signal is then converted into an electrical signal by a photodetector, mixed with a sweep frequency source, filtered, and envelope detected to extract the Brillouin frequency shift.

[0107] The parametric decoupling and information demodulation module is used to calculate the Brillouin scattered light intensity based on the Rayleigh scattered light intensity and the Landau-Placchek ratio. Combined with the Brillouin frequency shift, it decouples temperature and strain through the calibration model and demodulates vibration information using the Rayleigh phase signal.

[0108] This embodiment also provides an electronic device applicable to the fusion demodulation method of wavelength division multiplexing Φ-OTDR and BOTDR, including:

[0109] The system includes a memory and a processor. The memory stores computer-executable instructions, and the processor executes these instructions to implement the wavelength division multiplexing (WDM) Φ-OTDR and BOTDR fusion demodulation method proposed in the above embodiments.

[0110] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements the wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method proposed in the above embodiments.

[0111] The storage medium proposed in this embodiment belongs to the same inventive concept as the wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method proposed in the above embodiments. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for demodulating wavelength division multiplexing (WDM) Φ-OTDR and BOTDR, characterized in that, include: Two independent narrow-linewidth lasers are used to output continuous laser light. Each laser is split into two beams by a coupler. One beam is used for pulse modulation and the other is used as the local oscillator light. The beam used for pulse modulation is modulated into pulsed light using an acousto-optic modulator, and the optical frequency is shifted. Two pulsed lights are combined into one beam by an optical combiner in a wavelength division multiplexer and injected into the sensing fiber through an optical circulator. The backscattered light returning from the sensing fiber is led out by the optical circulator to the optical demultiplexer in the wavelength division multiplexer, and separated into two signals according to wavelength: one corresponds to the dominant wavelength of Rayleigh scattering and the other corresponds to the dominant wavelength of Brillouin scattering. The signal corresponding to the dominant wavelength of Rayleigh scattering interferes with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, the beat frequency signal is output. Then, the signal is obtained by an orthogonal demodulator for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering intensity is further obtained by orthogonal demodulation. The signal corresponding to the dominant wavelength of Brillouin scattering is amplified by an erbium-doped fiber amplifier and mixed with the local oscillator light of the corresponding wavelength. The mixture is then converted into an electrical signal by a photodetector, mixed with a sweep frequency source, filtered, and envelope detected to extract the Brillouin frequency shift. The intensity of Brillouin scattered light is calculated based on Rayleigh scattered light intensity and Landau-Platzczek ratio. Combined with Brillouin frequency shift, temperature and strain are decoupled through calibration model, and vibration information is demodulated using Rayleigh phase signal.

2. The wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method as described in claim 1, characterized in that, The method uses two independent narrow-linewidth lasers to output continuous laser light. Each laser beam is split into two beams by a coupler. One beam is used for pulse modulation, and the other beam serves as the local oscillator light. Two independent narrow-linewidth lasers are used to output continuous lasers with a fixed wavelength interval. Each continuous laser is split into two beams after entering the coupler. One beam with a larger power is used for subsequent pulse modulation, and the other beam with a smaller power is used as the local oscillator.

3. The wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method as described in claim 2, characterized in that, The process of combining two pulsed light streams into a single beam via an optical combiner in a wavelength division multiplexer and injecting it into the sensing fiber via an optical circulator includes: The two pulsed light beams modulated by the acousto-optic modulator are combined into one beam by the optical combiner in the wavelength division multiplexer; the combined beam is then injected into the sensing fiber by the help of an optical circulator.

4. The wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method as described in claim 3, characterized in that, The backscattered light returning from the sensing fiber is guided by an optical circulator to an optical demultiplexer in the wavelength division multiplexer, where it is separated into two signals according to wavelength: one corresponding to the dominant Rayleigh scattering wavelength, and the other corresponding to the dominant Brillouin scattering wavelength, including: The backscattered light carrying Brillouin and Rayleigh scattering light returned by the sensing fiber is transmitted to the optical demultiplexer via the optical circulator in the wavelength division multiplexer. The optical demultiplexer separates the backscattered light according to wavelength to obtain two signal lights of different wavelengths, corresponding to the Rayleigh scattering dominant wavelength and the Brillouin scattering dominant wavelength, respectively.

5. The wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method as described in claim 4, characterized in that, The signal corresponding to the dominant wavelength of Rayleigh scattering interferes with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, a beat frequency signal is output, which is then passed through an orthogonal demodulator to obtain an electrical signal for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering intensity is further obtained by using an orthogonal demodulation method, including: The signal corresponding to the dominant wavelength of Rayleigh scattering is filtered by a narrowband filter to extract the effective frequency components, and then interferes with the local oscillator light of the corresponding wavelength in a coherent receiver to form a beat frequency signal. The beat frequency signal is then processed by photoelectric detection and subsequent processing to output an electrical signal, thereby realizing the demodulation and extraction of the Rayleigh scattering signal. The output electrical signal is processed by an orthogonal demodulation method to separate two signals related to the amplitude and phase of the Rayleigh scattering light, and thus the intensity of the Rayleigh scattering light is obtained.

6. The wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method as described in claim 5, characterized in that, The signal corresponding to the dominant Brillouin scattering wavelength is amplified by an erbium-doped fiber amplifier and mixed with the local oscillator light of the corresponding wavelength. This mixture is then converted into an electrical signal by a photodetector, mixed with a swept frequency source, filtered, and subjected to envelope detection. The extraction of the Brillouin frequency shift includes: The signal corresponding to the dominant wavelength of Brillouin scattering is mixed with the continuous light from the local oscillator branch in the optical coupler after passing through the erbium-doped fiber amplifier to form a second beat frequency signal. The second beat frequency signal is converted into an electrical signal by a photodetector and then sent to a mixer for down-conversion with a sweep frequency signal source. The amplitude envelope curve is extracted by a filter and an envelope detector, and the sweep frequency corresponding to the peak value of the curve is the Brillouin scattering frequency.

7. The wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation method as described in claim 6, characterized in that, The calculation of Brillouin scattered light intensity based on Rayleigh scattered light intensity and Landau-Placchek ratio, combined with Brillouin frequency shift, decoupling temperature and strain through a calibration model, and demodulating vibration information using Rayleigh phase signal include: The intensity of Rayleigh scattering and Brillouin scattering are measured from the reflected light spectrum of an optical fiber to determine the Landau-Praček ratio in a specific fiber. The intensity of Rayleigh scattering signal is obtained through coherent reception and IQ demodulation, and then the intensity of Brillouin scattering is calculated by combining the Landau-Praček ratio, thus achieving decoupling of temperature and strain and demodulation of vibration information.

8. A wavelength division multiplexing Φ-OTDR and BOTDR fusion demodulation system, using the method described in any one of claims 1 to 7, characterized in that, include: The laser beam splitting and local oscillator configuration module is used to output continuous laser light using two independent narrow linewidth lasers. Each laser is split into two beams by a coupler, one beam is used for pulse modulation, and the other beam is used as the local oscillator light. The pulse modulation and frequency shifting module is used to modulate the light beam used for pulse modulation into pulsed light through an acousto-optic modulator and to shift the light frequency. The pulse beam combining and injection module is used to combine two pulse beams into one beam through the optical combiner in the wavelength division multiplexer, and then inject it into the sensing fiber through the optical circulator. The backscattered light separation module is used to guide the backscattered light returning from the sensing fiber through the optical circulator to the optical demultiplexer in the wavelength division multiplexer, and separate it into two signals according to wavelength: one corresponding to the dominant wavelength of Rayleigh scattering and the other corresponding to the dominant wavelength of Brillouin scattering. The Rayleigh scattering signal demodulation module is used to interfere the signal corresponding to the dominant wavelength of Rayleigh scattering with the local oscillator light of the corresponding wavelength in a coherent receiver. After photoelectric conversion, the beat frequency signal is output, and then the signal is obtained by an orthogonal demodulator for demodulating and extracting the Rayleigh scattering signal. The Rayleigh scattering light intensity is further obtained by orthogonal demodulation. The Brillouin frequency shift extraction module is used to amplify the signal corresponding to the dominant wavelength of Brillouin scattering by an erbium-doped fiber amplifier and mix it with the local oscillator light of the corresponding wavelength. The signal is then converted into an electrical signal by a photodetector, mixed with a sweep frequency source, filtered, and envelope detected to extract the Brillouin frequency shift. The parametric decoupling and information demodulation module is used to calculate the Brillouin scattered light intensity based on the Rayleigh scattered light intensity and the Landau-Placchek ratio. Combined with the Brillouin frequency shift, it decouples temperature and strain through the calibration model and demodulates vibration information using the Rayleigh phase signal.

9. An electronic device, characterized in that, include: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions, which, when executed by the processor, implement the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, It stores computer-executable instructions that, when executed by a processor, implement the steps of the method according to any one of claims 1 to 7.

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