Optimization method for performance of phi-otdr and interferometer fusion system based on arithmetic cascade pseudo-random mapping coding

Abstract

This invention discloses a performance optimization method for a Φ-OTDR and interferometer fusion system based on arithmetic concatenated pseudo-random mapping coding. By constructing a multi-level arithmetic concatenated pseudo-random coding sequence to modulate the transmitted pulses of the Φ-OTDR system, pulse compression is achieved at the receiving end through matched correlation decoding. This compresses the equivalent pulse width to the chip width while maintaining the transmitted power, improving the system's spatial resolution and reducing autocorrelation sidelobes. The cross-phase modulation phase disturbances generated when the coded pulses and continuous light propagate in the same optical fiber exhibit pseudo-random incoherent superposition characteristics during correlation decoding, suppressing nonlinear phase noise in the demodulated output and reducing its impact on the interferometer's continuous light measurement channel. Furthermore, the arithmetic concatenated pseudo-random coding modulation broadens the transmitted spectrum, reduces the optical power spectral density, and increases the stimulated Brillouin scattering threshold, enhancing the system's long-distance transmission capability. This method is suitable for performance optimization of Φ-OTDR and interferometer fusion measurement systems.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a performance optimization method for a Φ-OTDR and interferometer fusion system based on arithmetic concatenated pseudo-random mapping coding. Background Technology

[0002] A time-domain reflectometer (Φ-OTDR) system is fused with a fiber optic interferometer (such as a Michelson interferometer) using wavelength division multiplexing (WDM) technology. This allows pulsed light and continuous light to propagate in the same sensing fiber, thus achieving a fused system with both distributed measurement capabilities and high-sensitivity phase detection capabilities. This fused system not only inherits the long-distance, fully distributed measurement capabilities of the Φ-OTDR but also possesses the high phase sensitivity and wideband response characteristics of the interferometer. It can achieve simultaneous multi-parameter measurement in complex environments and has advantages such as strong anti-electromagnetic interference capabilities, flexible deployment, suitability for long-distance monitoring, and compatibility with existing fiber optic communication networks. Therefore, it has significant application value in fields such as oil and gas pipeline safety monitoring, perimeter security, underwater acoustic detection, and structural health monitoring.

[0003] However, existing fusion systems still suffer from several key drawbacks in practical operation. First, due to the high pulsed light power in Φ-OTDR systems, cross-phase modulation (XPM) occurs between continuous and pulsed light in the fiber. This nonlinear effect introduces additional phase noise, reducing the interferometer's phase demodulation accuracy and causing low-frequency drift. Second, narrow-pulse lasers are typically used to improve spatial resolution, but narrow pulses reduce single-pulse energy, leading to a decrease in signal-to-noise ratio and limiting the system's measurement distance. Third, when increasing the transmit power to compensate for insufficient signal-to-noise ratio, stimulated Brillouin scattering (SBS) is easily excited in the fiber, causing energy backflow, signal distortion, and even system instability. These drawbacks negatively impact the interferometer's phase measurement error, make it difficult to balance spatial resolution and measurement distance, and limit the system's maximum input power, thus hindering further improvements in the fusion system's performance.

[0004] To address the aforementioned issues, existing technologies have undertaken various improvement attempts. For example, to suppress the XPM effect, some studies have employed methods such as reducing pulse peak power or increasing wavelength spacing. However, the former reduces the system signal-to-noise ratio (SNR), while the latter is limited by the bandwidth of wavelength division multiplexing (WDM) devices and increases system complexity. Regarding the conflict between spatial resolution and SNR, existing technologies employ pulse coding methods such as pseudo-random sequence coding and Golay complementary coding to achieve pulse compression through correlation demodulation. However, these coded sequences have high autocorrelation sidelobes, easily leading to distance ambiguity and crosstalk, causing weak signals to be overwhelmed by nearby strong scattering points, thereby reducing the system's dynamic range and resulting in decreased distributed measurement accuracy. To address the SBS limitation problem, some studies have broadened the spectrum through phase modulation or frequency dithering. However, these methods introduce additional modulation devices and may reduce coherent detection efficiency.

[0005] In summary, existing methods cannot simultaneously achieve multiple performance optimizations such as spatial resolution improvement, sidelobe suppression, XPM suppression, and SBS threshold enhancement. Therefore, a new encoding and demodulation method is still needed to comprehensively improve the overall performance of the distributed fiber optic sensing and interferometer fusion system at the system level. Summary of the Invention

[0006] To address the challenges in existing Φ-OTDR and fiber interferometer fusion systems, such as the difficulty in balancing spatial resolution and signal-to-noise ratio, severe crosstalk due to high coding sidelobes, XPM caused by co-fiber transmission of coded pulses and continuous light, and the limitation of SBS threshold under high-power operating conditions, this invention proposes a performance optimization method for Φ-OTDR and interferometer fusion systems based on Arithmetic Cascade Pseudo-Random Mapping (AC-PRM) coding. The aim is to achieve multiple performance optimizations, including improved spatial resolution, increased sidelobe suppression ratio, XPM suppression, and improved SBS threshold, without increasing system hardware complexity, through optimization of the coding structure and demodulation algorithm.

[0007] This invention adopts the following technical solution: a performance optimization method for a Φ-OTDR and interferometer fusion system based on AC-PRM encoding, comprising the following steps:

[0008] S1. Initialize the Φ-OTDR light source, use a narrow linewidth laser to generate a continuous optical carrier, load the AC-PRM encoding sequence through a modulator, encode and modulate the emitted pulse to form encoded pulse light;

[0009] S2. Generate a multi-level pseudo-random binary sequence using a linear feedback shift register or primitive polynomial, perform arithmetic weighted concatenation operation on each sequence and introduce nonlinear mapping to generate the AC-PRM encoded sequence.

[0010] S3. Inject the encoded pulse light into the sensing fiber to generate a backscattered Rayleigh signal, and simultaneously inject continuous light into the sensing fiber to form the interferometer measurement optical path, so as to realize the co-fiber propagation of the two optical signals.

[0011] S4. At the receiving end, the Rayleigh backscattered signal and the continuous light interference signal separated and returned by the wavelength division multiplexer are received by a photodetector, and the distributed information is recovered by correlation decoding based on the encoded sequence.

[0012] S5. Utilize the low sidelobe autocorrelation characteristics of the AC-PRM encoded sequence to achieve pulse compression, so that the spatial resolution is determined by the chip width, thereby improving the spatial resolution.

[0013] S6. The AC-PRM encoding sequence enables the XPM terms to be incoherently superimposed and canceled out during the correlation decoding process, thereby reducing nonlinear phase disturbances in continuous light.

[0014] S7. The coding modulation simultaneously broadens the optical signal spectrum bandwidth, reduces the power density per unit frequency, increases the SBS threshold, and improves the stability of the fusion system.

[0015] The Φ-OTDR and interferometer fusion system of the present invention includes: a first laser, a first optical coupler, an arbitrary waveform generator, an acousto-optic modulator, an optical amplifier, a circulator, a second optical coupler, a second laser, an optical isolator, a third optical coupler, a wavelength division multiplexer, a sensing fiber, a wavelength division multiplexer, a first Faraday rotator, a delay fiber, a second Faraday rotator, a first photodetector, a second photodetector, a data acquisition card (DAQ), and a computer (PC).

[0016] In this system, the optical signal output from the first laser is split into two paths by a first optical coupler. One path is output as intrinsic light to a second optical coupler, and the other path is output to an acousto-optic modulator. Driven by an arbitrary waveform generator, the modulator generates an AC-PRM coded pulse signal, which is then amplified by an optical amplifier and output to a circulator. The circulator is connected to a sensing fiber via a wavelength division multiplexer, with the end of the sensing fiber connected to the wavelength division multiplexer. The circulator is also connected to a second optical coupler, which couples the two beams and outputs them to a first photodetector. The output of the first photodetector is connected to a DAQ (Distributed Aqueous Queuing) synchronized with the arbitrary waveform generator. The DAQ transmits the acquired data to a PC.

[0017] The optical signal output from the second laser is transmitted to the third optical coupler after passing through an optical isolator, splitting the light into two paths. One path passes through a wavelength division multiplexer and is output to the sensing fiber, which is then transmitted to a wavelength division demultiplexer connected to a first Faraday rotator. The other path passes through a delay fiber and is output to a second Faraday rotator. The two paths are coupled at the third optical coupler to form interference light, which is received by the second photodetector and transmitted to the DAQ. The DAQ then transmits the acquired data to the PC.

[0018] As a preferred embodiment, the AC-PRM encoding sequence is expressed as follows:

[0019] ;

[0020] in, For the first The first level of the AC-PRM coding sequence Each code element For the first Weight coefficients of level coding, For the concatenation series of arithmetic concatenation encoding, This is a pseudo-random perturbation term used to control the instantaneous power distribution in order to suppress XPM.

[0021] As a preferred embodiment, the pseudo-random sequences at each level Generated by a linear feedback shift register or a pseudo-random map, and satisfying:

[0022] ;

[0023] To ensure that the encoded sequence is a bipolar modulated signal;

[0024] The pseudo-random perturbation term satisfies:

[0025] ;

[0026] in, For perturbation weighting coefficients, It is a zero-mean pseudo-random sequence used to adjust the statistical distribution of the encoded sequence and reduce the instantaneous power peak.

[0027] As a preferred option, the encoded pulse optical power Represented as:

[0028] ;

[0029] in, For chip width, It is a single-chip pulse envelope. It is an AC-PRM encoded sequence. It is a continuous-time variable;

[0030] The autocorrelation characteristic expression of the encoded sequence is:

[0031] ;

[0032] in, For encoding the autocorrelation function of the sequence, For relevant delayed indexes, ensure the main peak satisfies The side lobes satisfy To achieve low sidelobe pulse compression characteristics.

[0033] As a preferred embodiment, the equivalent spatial resolution of the encoded pulse after correlation decoding is... for:

[0034] ;

[0035] in, For fiber group speed, For chip width, The original pulse width, The spatial resolution of uncoded pulses is such that the equivalent spatial resolution is improved compared to that of uncoded pulses. times.

[0036] As a preferred embodiment, the XPM phase change generated by continuous light in the optical fiber is: :

[0037] ;

[0038] in, For fiber nonlinearity coefficients, The length of the optical fiber. This represents the position to which light propagates within the optical fiber;

[0039] After encoding and decoding, the XPM term satisfies the following in the related output:

[0040] ;

[0041] when hour The value approaches 0, thereby achieving nonlinear noise suppression and reducing continuous light phase noise.

[0042] As a preferred option, the coding sequence sidelobe suppression ratio ( )satisfy:

[0043] ;

[0044] in, To be the main peak, For the side lobes; in In the case of side lobe terms With cascaded stages Increase and decrease, thus With cascaded stages Increase and improve.

[0045] As a preferred embodiment, the coding sequence broadens the optical signal spectrum. for:

[0046] ;

[0047] Thus, the SBS threshold is reached. Improved to:

[0048] ;

[0049] in, The effective mode area of ​​the optical fiber. The Brillouin gain coefficient is... For effective fiber length, This represents the Brillouin gain bandwidth.

[0050] As a preferred option, the AC-PRM encoding length Determined by effective fiber length Highest vibration frequency and fiber group speed Jointly determined; the AC-PRM encoding length satisfies This ensures that the encoding covers the maximum round-trip time and meets the requirements for high-frequency vibration sampling.

[0051] As a preferred embodiment, the AC-PRM encoding simultaneously achieves the following effects: 1) pulse compression improves spatial resolution; 2) low autocorrelation improves sidelobe suppression ratio; 3) encoding-correlation-decoding suppresses XPM; 4) spectral broadening improves SBS threshold.

[0052] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0053] 1. The proposed performance optimization method for the Φ-OTDR and interferometer fusion system based on AC-PRM coding achieves equivalent compression of the coded pulse through multi-level arithmetic concatenation coding, significantly improving the system's spatial resolution while maintaining a high signal-to-noise ratio, enabling fine positioning capabilities even under long-distance measurement conditions. Secondly, the constructed coded sequence has excellent autocorrelation characteristics, effectively reducing sidelobe amplitude and improving the sidelobe suppression ratio, thereby reducing crosstalk between adjacent scattering points and improving the system's dynamic range. Thirdly, the coded pulse exhibits a pseudo-random power distribution in the time domain, disrupting the coherent accumulation process between pulsed light and continuous light, significantly weakening the influence of XPM on continuous light signals, and improving the stability of the fusion system. Furthermore, the spectral broadening introduced by coding modulation reduces the concentration of optical power within the Brillouin gain bandwidth, thereby increasing the SBS threshold and enhancing the system's ability to operate under high power and long-distance conditions.

[0054] 2. The method of the present invention can achieve a comprehensive improvement in spatial resolution, anti-crosstalk capability, anti-nonlinear capability and system stability without increasing system complexity. It can significantly improve the measurement accuracy, dynamic range and stability of the Φ-OTDR and fiber interferometer fusion system, and meet the application requirements of long distance, high sensitivity and multi-parameter synchronous detection. Attached Figure Description

[0055] Figure 1 This is a structural diagram of the Φ-OTDR and interferometer fusion system of the present invention.

[0056] Figure 2 This is a flowchart of the performance optimization method for the Φ-OTDR and interferometer fusion system of the present invention.

[0057] Figure 3 This is a time-domain comparison diagram of the demodulation result and the signal under test in an embodiment of the present invention.

[0058] Figure 4 This is a spatiotemporal waterfall diagram of one Φ-OTDR channel under the AC-PRM encoded pulse condition in an embodiment of the present invention.

[0059] Figure 5 It is the autocorrelation function of the signal sampled under the AC-PRM encoded pulse condition in the embodiment of the present invention.

[0060] Figure 6 This is a comparison chart of the forward optical-to-fiber optical power curves of a traditional uncoded fusion system and the fusion system of this invention. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the application will be further described in detail below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments involved in this invention. All non-innovative embodiments based on these embodiments by other researchers in the art are within the protection scope of this invention. Furthermore, the step numbers in the embodiments of this invention are only set for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0062] In one embodiment of the present invention, a performance optimization method for a Φ-OTDR and interferometer fusion system based on AC-PRM encoding is provided. The AC-PRM encoding method is used to perform pseudo-random cascade modulation on pulse light to achieve the purpose of improving spatial resolution, suppressing XPM, and increasing SBS threshold.

[0063] In this embodiment, the structural diagram of the Φ-OTDR and interferometer fusion system is as follows: Figure 1 As shown, it includes: a first laser, a first optical coupler, an arbitrary waveform generator, an acousto-optic modulator, an optical amplifier, a circulator, a second optical coupler, a second laser, an optical isolator, a third optical coupler, a wavelength division multiplexer, a sensing fiber, a wavelength division multiplexer, a first Faraday rotator, a delay fiber, a second Faraday rotator, a first photodetector, a second photodetector, a DAQ, and a PC.

[0064] As a preferred embodiment, the first laser is selected as a narrow linewidth laser with a center wavelength of 1550nm and a linewidth of 1kHz. The optical signal output by the first laser is split into two paths by a first optical coupler (1×2 coupler). One path is output as intrinsic light to a second optical coupler (2×1 coupler), and the other path is output to an acousto-optic modulator. The modulator is driven by an arbitrary waveform generator to generate an AC-PRM encoded pulse signal, which is then amplified by an optical amplifier and output to circulator port 1.

[0065] Circulator port 2 is connected to a wavelength division multiplexer (WDM), which is connected to a 20km sensing fiber. The end of the sensing fiber is connected to the WDM. Circulator port 3 is connected to a second optical coupler. The second optical coupler couples the two beams of light and outputs them to a first photodetector. The output of the first photodetector is connected to a DAQ (Distributed Aqueous Array Controller) that is time-synchronized with an arbitrary waveform generator. The DAQ transmits the acquired data to a computer.

[0066] As a preferred embodiment, the second laser is a narrow-linewidth laser with a center wavelength of 1563 nm. The optical signal output from the second laser is transmitted to a third optical coupler (2×2 coupler) after passing through an optical isolator. The third optical coupler splits the light into two paths. One path passes through a wavelength division multiplexer and is output to the aforementioned 20 km sensing fiber, from where it is transmitted to a wavelength division demultiplexer connected to a first Faraday rotator. The other path passes through a delay fiber and is output to a second Faraday rotator. The two paths couple at the third optical coupler to form interference light, which is received by a second photodetector and transmitted to a DAQ (Distributed Amplifier). The DAQ then transmits the acquired data to a PC.

[0067] In this embodiment, the AC-PRM encoding uses a three-layer cascaded structure. The first layer is a pseudo-random kernel generated by a linear feedback shift register, the second layer is a second-order nonlinear recursive model, and the third layer is a jump scrambling term. The AC-PRM encoding sequence... The expression can be simplified to:

[0068] ;

[0069] in, It is a pseudo-random kernel. This is a second-order nonlinear recursive perturbation term. For time-domain jump scrambling code terms, These are the weighting coefficients of the pseudo-random kernel and the weighting coefficients of the nonlinear recursive perturbation, respectively.

[0070] Specifically, the performance optimization method steps in this embodiment are as follows: Figure 2 As shown, it includes:

[0071] S1. Initialize the Φ-OTDR light source to generate a narrow linewidth continuous laser. After modulation, it forms periodic light pulses, which serve as the detection pulse optical path. At the same time, turn on the interferometer continuous light source to output another wavelength of frequency-stabilized continuous light, which is sent into the interferometer (Michelson structure) to form a reference arm and a sensing arm, thus forming a continuous light interferometric measurement optical path.

[0072] S2. Generate multi-level pseudo-random binary sequences using linear feedback shift registers or primitive polynomials, and perform arithmetic weighted concatenation operations on each sequence to obtain a set of AC-PRM encoded sequences with good autocorrelation and orthogonality.

[0073] S3. The above AC-PRM encoded sequence is converted into an electrical drive signal through an arbitrary waveform generator and applied to the acousto-optic modulator to modulate the pulsed optical carrier generated in S1.

[0074] Each modulated optical pulse carries complete coded sequence information, forming a coded pulse light whose time-domain waveform is consistent with the coded sequence, its frequency domain is broadened, and the periodic characteristics of the original pulse are preserved.

[0075] S4: The coded pulse light is injected into the sensing fiber via a circulator, continuously generating Rayleigh backscattered signals as it propagates within the fiber. Simultaneously, the continuous interference light in S1 also propagates forward through the same fiber, wavelength-division multiplexing and sharing the fiber with the pulse light. Both optical signals propagate independently within the same fiber, but are both modulated by external environmental disturbances.

[0076] S5. Because the encoded pulse light has a high peak power, it generates XPM on the co-propagating continuous light through the fiber Kerr effect, so that the instantaneous phase of the continuous light is modulated by the intensity of the encoded pulse light.

[0077] The photodetector receives the Rayleigh backscattered signal separated and returned by the wavelength division multiplexer and the continuous optical interference signal output by the interferometer, and converts them into electrical signals.

[0078] S6. Using the original encoded sequence generated in S2 as a matching template, correlation decoding is performed on the received encoded Rayleigh signal to achieve encoded pulse compression. The equivalent spatial resolution after compression is determined by the width of the encoded chip, which is significantly improved compared to the original spatial resolution. At the same time, the autocorrelation impulse characteristics of the encoding are used to suppress sidelobes and greatly improve the signal-to-noise ratio.

[0079] S7. Utilizing the orthogonality of the encoded sequence, perform the same correlation decoding on the interference signal, and subtract the decoded result from the Rayleigh decoded signal by difference or ratio to cancel the phase noise caused by XPM and extract pure interference phase information.

[0080] In addition, the spectrum of the encoded pulse is broadened to the code rate level, which effectively reduces the optical power density per unit frequency, significantly improves the threshold of SBS, and avoids nonlinear loss;

[0081] Finally, by combining the backscattered Rayleigh scattering signal from one Φ-OTDR channel with the phase demodulation results of the interference signal from one interferometer channel, distributed measurement data with high spatial resolution, high signal-to-noise ratio, and large dynamic range is output.

[0082] As a preferred embodiment, in one Φ-OTDR channel, the pulse width is 50 ns, the pulse repetition frequency is 10 kHz, and the coded sequence length is 1024. A sinusoidal vibration signal with a frequency of 500 Hz and an amplitude of 5 rad is applied at a sensing distance of 15 km. This signal is acquired and demodulated using the AC-PRM-coded fusion system mentioned in this invention.

[0083] The time-domain comparison diagram of the demodulation result obtained from one interferometer path and the signal under test is shown below. Figure 3 As shown, the waterfall plot drawn from the results obtained through Φ-OTDR is as follows. Figure 4 As shown. Among them, Figure 3 (a) in the figure is the time-domain diagram of the signal restored by the fusion system mentioned in this invention. Figure 3 (b) in the diagram is the time-domain plot of the signal under test. A comparison shows that the signal acquired by the AC-PRM-based fusion system mentioned in this invention, after demodulation, eliminates the influence of XPM, and the obtained result is consistent with the signal under test, accurately reconstructing the original signal. Furthermore, according to... Figure 4 It can be seen that the coding method proposed in this invention greatly improves spatial resolution, which can be improved to the millimeter level, and successfully breaks through the constraints between spatial resolution, pulse width and sensing distance.

[0084] Furthermore, after processing the signal obtained from one Φ-OTDR path through matched filtering and other operations, its autocorrelation function is plotted, such as... Figure 5 As shown, the coding method proposed in this invention can present a clear main peak, thereby achieving low sidelobe and high-resolution pulse compression, with its sidelobe suppression ratio improved to -21.9297dB.

[0085] Furthermore, a comparison of the forward and input optical power curves of the AC-PRM-coded fusion system mentioned in this invention with those of a traditional uncoded fusion system is provided. Figure 6 As shown, compared to traditional uncoded fusion systems, the SBS threshold in the AC-PRM-coded fusion system mentioned in this invention is significantly improved, making the system capable of withstanding greater input fiber power.

[0086] In summary, this invention constructs a multi-level pseudo-random sequence and generates an coded sequence through arithmetic weighted concatenation and nonlinear mapping to modulate the transmitted pulse. Matched correlation decoding is then performed at the receiving end. The impulse autocorrelation characteristics of the coded sequence are utilized to achieve correlation compression of long pulses, thereby improving spatial resolution. Simultaneously, the low sidelobe autocorrelation characteristics of AC-PRM coding cause the XPM terms to incoherently superimpose and tend towards zero during correlation operations, thus suppressing XPM noise. Furthermore, the pseudo-random mapping coding can alter the temporal statistical distribution of pulse power and broaden the spectral bandwidth, thereby increasing the SBS threshold and significantly enhancing the system's nonlinear resistance.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for performance optimization of a Φ-OTDR and interferometer fusion system based on arithmetic cascade pseudo-random mapping coding, characterized in that, Includes the following steps: S1. Initialize the Φ-OTDR light source, use a narrow linewidth laser to generate a continuous optical carrier, load an arithmetic concatenated pseudo-random mapping coding sequence through a modulator, and encode and modulate the emitted pulse to form coded pulse light; S2. Generate a multi-level pseudo-random binary sequence using a linear feedback shift register or primitive polynomial, perform arithmetic weighted concatenation operation on each sequence and introduce nonlinear mapping to generate the arithmetic concatenation pseudo-random mapping encoding sequence. S3. Inject the encoded pulse light into the sensing fiber to generate a backscattered Rayleigh signal, and simultaneously inject continuous light into the sensing fiber to form the interferometer measurement optical path, so as to realize the co-fiber propagation of the two optical signals. S4. At the receiving end, the Rayleigh backscattered signal and the continuous light interference signal separated and returned by the wavelength division multiplexer are received by a photodetector, and the distributed information is recovered by correlation decoding based on the encoded sequence. S5. Utilize the low sidelobe autocorrelation characteristics of the arithmetic concatenated pseudo-random mapping coding sequence to achieve pulse compression, so that the spatial resolution is determined by the chip width, thereby improving the spatial resolution; S6. The arithmetic concatenated pseudo-random mapping coding sequence enables the cross-phase modulation terms to be incoherently superimposed and canceled out during the correlation decoding process, thereby reducing nonlinear phase disturbances in continuous light. S7. The coding modulation simultaneously broadens the optical signal spectral bandwidth, reduces the power density per unit frequency, increases the stimulated Brillouin scattering threshold, and improves the stability of the fusion system.

2. The method of claim 1, wherein the method further comprises: The expression for the arithmetic concatenated pseudo-random mapping encoding sequence is: ； in, For the first The first level of the arithmetic concatenated pseudo-random mapping coding sequence Each code element For the first Weight coefficients of level coding, For the concatenation series of arithmetic concatenation encoding, This is a pseudo-random perturbation term used to control the instantaneous power distribution to suppress cross-phase modulation.

3. The performance optimization method for the Φ-OTDR and interferometer fusion system according to claim 2, characterized in that, Pseudorandom sequences at various levels generated by a linear feedback shift register or a pseudorandom mapping, satisfying: ； To ensure that the encoded sequence is a bipolar modulated signal; The pseudo-random perturbation term satisfies: ； wherein is a perturbation weight coefficient, is a zero-mean pseudo-random sequence used to adjust the statistical distribution of the code sequence and to reduce the instantaneous power peaks.

4. The performance optimization method for the Φ-OTDR and interferometer fusion system according to claim 2, characterized in that, The power of the coded pulse light is represented as: ； wherein, is a chip width, is a single chip pulse envelope, is an arithmetic cascade pseudo-random mapping code sequence, is a continuous time variable; The autocorrelation characteristic expression of the encoded sequence is: ； wherein, is the autocorrelation function of the coded sequence, is the correlation delay index; is the main peak, satisfying , is the side lobe, satisfying , is the coded sequence length, to achieve low side lobe pulse compression characteristics.

5. The method of claim 4, wherein the method further comprises: The distributed signal is recovered through relevant decoding, and its relevant output is: ； wherein is the relevant demodulation output signal, is the received signal after photodetection, is the time delay.

6. The performance optimization method for the Φ-OTDR and interferometer fusion system according to claim 4, characterized in that, The equivalent spatial resolution of the encoded pulse after correlation decoding for: ； in, For fiber group speed, For chip width, The original pulse width, The spatial resolution of uncoded pulses is such that the equivalent spatial resolution is improved compared to that of uncoded pulses. times.

7. The performance optimization method for the Φ-OTDR and interferometer fusion system according to claim 6, characterized in that, The phase change caused by the cross-phase modulation of the continuous light in the sensing fiber is: : ； in, For fiber nonlinearity coefficients, The length of the optical fiber. This represents the position to which light propagates within the optical fiber; After encoding-correlation-decoding, the cross-phase modulation term satisfies the following in the correlation output: ； when hour The value approaches 0, thereby achieving nonlinear noise suppression and reducing continuous light phase noise.

8. The performance optimization method for the Φ-OTDR and interferometer fusion system according to claim 4, characterized in that, coding sequence sidelobe suppression ratio satisfy: ； Among them, In the case of side lobe terms With cascaded stages Increase and decrease, thus With cascaded stages Increase and improve.

9. The performance optimization method for the Φ-OTDR and interferometer fusion system according to claim 4, characterized in that, The coding sequence broadens the optical signal spectrum. for: ； This results in the stimulated Brillouin scattering threshold. Improved to: ； in, The effective mode area of ​​the optical fiber. The Brillouin gain coefficient is... For effective fiber length, This represents the Brillouin gain bandwidth.

10. The performance optimization method for the Φ-OTDR and interferometer fusion system according to claim 9, characterized in that, The length of the arithmetic concatenated pseudo-random mapping encoding sequence Determined by effective fiber length Highest vibration frequency and fiber group speed Jointly decided, to satisfy: ； To ensure that the coding covers the maximum round-trip propagation time and meets the requirements of high-frequency vibration sampling, pulse compression is used to improve spatial resolution, low autocorrelation is used to improve the sidelobe suppression ratio, coding-correlation-decoding is used to suppress cross-phase modulation, and spectral broadening is used to improve the stimulated Brillouin scattering threshold.

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