A multi-phase coded φ-OTDR sensing system and modulation and demodulation method

Abstract

The present invention relates to the field of distributed optical fiber sensing technology, and in particular to a multi-phase coded φ-OTDR sensing system and a modulation and demodulation method. It includes a narrow linewidth laser, which is connected to the A port of a 1*2 optical fiber coupler, and the B port of the 1*2 optical fiber coupler is sequentially connected to an electro-optic phase modulator, an acousto-optic modulator and an erbium-doped optical fiber amplifier, and the output end of the erbium-doped optical fiber amplifier is connected to the A port of a circulator; the C port of the circulator is connected to the A port of a 2*2 optical fiber coupler, and the B port of the 2*2 optical fiber coupler is connected to the C port of a 1*2 optical fiber coupler. The output port of the 2*2 optical fiber coupler is connected to the input port of a balanced photodetector, and the output port of the balanced photodetector is connected to the input end of a data acquisition card, and the output end of the data acquisition card is connected to a computer. The present invention has a higher sidelobe suppression ratio, and can effectively improve the signal-to-noise ratio and sensitivity of the optical fiber sensing system.

Description

Technical Field

[0001] The invention relates to the technical field of distributed optical fiber sensing, and in particular to a multi-phase coded φ-OTDR sensing system and a modulation and demodulation method. Background Art

[0002] The φ-OTDR system has the characteristics of distributed sensing, long-distance sensing, and anti-electromagnetic interference. It has broad application prospects in many fields such as rail transit safety monitoring, oil and gas resource exploration and development, smart grid status monitoring, and infrastructure perimeter security. In the process of moving from theoretical research to various engineering applications, the sensing distance and spatial resolution of the φ-OTDR system always play a crucial role. For example, φ-OTDR can be used to monitor the safety status of long-distance railway transportation, and can perform distributed monitoring of vibration signals generated by fault behaviors such as axle noise, train shaking, and foundation vibration. However, the safety monitoring of vehicle-road faults needs to take into account the working conditions of long track distances and small wheel spacing. If the vibration characteristics of long sensing distances and high spatial resolution cannot be accurately identified, the risk of safety accidents caused by vehicle-road faults will continue to exist, seriously endangering the safety of railway transportation. Therefore, breaking through the bottleneck of the mutual constraints between spatial resolution and sensing distance in traditional φ-OTDR technology has important scientific significance and application value.

[0003] Prior art 1: Pulse coding is to modulate the continuous light output by the laser into a pulse sequence according to a specific coding rule through an intensity modulation device. The coded pulse modulation scheme can effectively increase the detection pulse energy, and with the help of decoding processing, it has the advantage of enhancing the signal-to-noise ratio of the equivalent single pulse response, thereby ensuring the extension of the sensing distance under the premise of high spatial resolution, but it still does not meet the needs of long-distance detection.

[0004] The second existing technology, linear frequency modulated pulse, uses frequency modulation equipment to modulate the optical frequency of the detection light into a frequency modulated signal that changes linearly with time. The long-duration single detection pulse used by the linear frequency modulated pulse modulation type φ-OTDR has higher detection power and can obtain high spatial resolution through time domain pulse compression. Therefore, it can further break through the limitations of sensing distance and spatial resolution, but its pulse modulation method is complex and is greatly restricted by device performance. In addition, the complex frequency easily causes frequency mixing and compensation difficulties during the transmission process.

[0005] In summary, the existing technology still faces the problem of how to further achieve simultaneous improvement of spatial resolution and sensing distance. Summary of the invention

[0006] In order to solve the problem of mutual restriction between spatial resolution and sensing distance in the prior art, the present invention provides a multi-phase coded φ-OTDR sensing system and a modulation and demodulation method.

[0007] The present invention adopts the following technical scheme: a multi-phase coded φ-OTDR sensing system, comprising a narrow linewidth laser, the narrow linewidth laser is connected to the A port of a 1*2 optical fiber coupler, the B port of the 1*2 optical fiber coupler is sequentially connected to an electro-optic phase modulator, an acousto-optic modulator and an erbium-doped fiber amplifier, and the output end of the erbium-doped fiber amplifier is connected to the A port of a circulator.

[0008] The C port of the circulator is connected to the A port of the 2*2 fiber coupler, the B port of the 2*2 fiber coupler is connected to the C port of the 1*2 fiber coupler, the output port of the 2*2 fiber coupler is connected to the input port of the balanced photodetector, the output port of the balanced photodetector is connected to the input end of the data acquisition card, and the output end of the data acquisition card is connected to the computer.

[0009] It also includes a first arbitrary wave generator and a second arbitrary wave generator, the clock end of the first arbitrary wave generator is connected to the clock end of the second arbitrary wave generator to maintain clock synchronization, the output end of the first arbitrary wave generator is connected to the input end of the first radio frequency amplifier and the modulation end of the data acquisition card, the output end of the first radio frequency amplifier is connected to the radio frequency signal input end of the electro-optic phase modulator, the output end of the second arbitrary wave generator is connected to the input end of the second radio frequency amplifier, and the output end of the second radio frequency amplifier is connected to the modulation end of the acousto-optic modulator.

[0010] Further, the B port of the circulator is connected to the A port of the second dense wavelength division multiplexer, the C port of the second dense wavelength division multiplexer is connected to the input end of the sensing optical fiber, the output end of the sensing optical fiber is connected to the C port of the first dense wavelength division multiplexer, the A port of the first dense wavelength division multiplexer is suspended, and the B ports of the first dense wavelength division multiplexer and the second dense wavelength division multiplexer are respectively connected to two pump ports of the Raman optical fiber amplifier; the Raman optical fiber amplifier emits two beams of 1460nm high-power pump light, which are transmitted in the optical fiber simultaneously with the backward Rayleigh scattered light of wavelength 1550.12nm, the backward Raman pump light enters the sensing optical fiber through the second dense wavelength division multiplexer, and the pump light and the backward Rayleigh scattered light to be amplified are transmitted in the sensing optical fiber in opposite directions; the forward Raman pump light enters the sensing optical fiber through the first dense wavelength division multiplexer, and the pump light wave and the backward Rayleigh scattered light are transmitted in the same direction in the sensing optical fiber.

[0011] Furthermore, the 1*2 optical fiber coupler is a 90:10 coupler; the first arbitrary wave generator and the second arbitrary wave generator have a 2.5G sampling rate and a modulation bandwidth greater than 1GHz; the electro-optical phase modulator has a 10GHz modulation bandwidth; and the balanced photodetector has a detection bandwidth greater than or equal to 1GHz.

[0012] A modulation and demodulation method for a multi-phase coded φ-OTDR sensing system, wherein the modulation process comprises the following steps:

[0013] S11~Constructing multi-phase coding sequences f i ,

[0014]

[0015] in i Represents the first phase of the multi-phase coded sequence i phases, not exceeding the code length N ; Select the phase adjustment factor according to the signal bandwidth x 0, select the code length based on the sidelobe suppression effect N ;Choose the appropriate phase adjustment factor x 0 and the encoding length N Determine the multi-phase coding sequence f i .

[0016] S12: Adjust the multi-phase coding sequence according to the modulation half-wave voltage of the electro-optic phase modulator and the gain of the first radio frequency amplifier f i RF output power; Multi-phase coded sequence f i The first arbitrary wave generator outputs the signal to the first radio frequency amplifier, and then modulates the signal to the electro-optic phase modulator to implement the phase modulation process, and performs pre-distortion processing on the modulation result.

[0017] S13~The second arbitrary wave generator generates an AOM driving signal according to a specific window type, and the AOM is controlled by the second RF amplifier so that the optical power of the multi-phase coded signal is modulated according to the same window type, thereby improving the sidelobe suppression ratio of the matched filter stage, and finally obtaining a multi-phase coded detection optical pulse.

[0018] The demodulation process includes the following steps:

[0019] S21~ The balanced photodetector converts the beat frequency light of the back Rayleigh scattered light and the local oscillator light into a beat frequency electrical signal, and converts the beat frequency electrical signal into a complex sequence through Hilbert transform;

[0020] S22~Build a digital domain matched filter on the computer, perform matched filtering on the complex sequence of the beat frequency signal, realize pulse compression of the beat frequency signal, and improve the spatial resolution of the sensor system;

[0021] S23: performing intensity demodulation on the result after matched filtering to obtain the intensity information of backward Rayleigh scattering, and then performing a moving differential average algorithm to obtain the positioning information of the vibration signal on the sensing optical fiber;

[0022] S24~Perform phase demodulation on the result after matched filtering to obtain a vibration waveform.

[0023] During the modulation process of S12 and S13, synchronization needs to be ensured in the generation process of the multi-phase coded detection light pulse. First, the first arbitrary wave generator and the second arbitrary wave generator maintain clock synchronization through the external clock port. Secondly, the phase modulation process of the electro-optic phase modulator, the intensity modulation process of the acousto-optic modulator, and the trigger acquisition process of the data acquisition card are synchronized to ensure that modulation and acquisition are carried out simultaneously.

[0024] In step S12, according to the multi-phase coding sequence f i Adjustment over time t The RF input voltage signal is continuously changed, and the first arbitrary wave generator outputs the RF input voltage signal to the first RF amplifier. u rf ( t )for:

[0025]

[0026] The code element width t Usually determined by the spatial resolution, V rf is the RF output voltage of the multi-phase coded modulation, rect (∙) is a rectangular function; i Represents the first phase of the multi-phase coded sequence i phases, not exceeding the code length N The above RF input voltage signal u rf ( t ) After power amplification, the electro-optic phase modulator is controlled so that the phase information of the multi-phase encoding is modulated onto the detection light to realize the phase modulation process; the detection light with the multi-phase encoding phase information p' ( t ) is expressed as:

[0027]

[0028] in V π is the modulation half-wave voltage of the electro-optic phase modulator (3), N is the code length of the polyphase encoding, j Is an imaginary unit.

[0029] In step S13, the optical pulse signal is detected p ( t ):

[0030]

[0031] in w (∙) is the window signal, which is used to suppress the side lobes after matched filtering.∆f is the frequency shift introduced by the AOM.

[0032] Compared with the existing φ-OTDR technology, in terms of structure, the present invention uses an electro-optic phase modulator and an acousto-optic modulator to jointly modulate the detection light pulse signal containing multi-phase coded information; in terms of modulation method, the present invention uses multi-phase coded modulation means, and utilizes its excellent time domain pulse compression performance to compress the wide detection light pulse signal in the time domain into a single-frequency narrow pulse signal through matched filtering processing. Accordingly, the large time width signal has enough energy to transmit a longer distance, and the narrower code width enables the φ-OTDR system to have a higher spatial resolution capability. This multi-phase coded modulation and demodulation method has a higher sidelobe suppression ratio, which can effectively improve the signal-to-noise ratio and sensitivity of the optical fiber sensing system; in addition, this method links the spatial resolution of the optical fiber sensing system with the code element width, breaking through the restriction problem between the sensing distance and the spatial resolution in the traditional distributed optical fiber sensing system, and realizing the simultaneous improvement of the spatial resolution and the sensing distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a block diagram of a sensing system of a multi-phase coded φ-OTDR of the present invention;

[0034] Figure 2 is a flow chart of the multi-phase coded modulation process of the present invention;

[0035] Figure 3 is a flow chart of the multi-phase coding demodulation process of the present invention;

[0036] Figure 4 It is a schematic diagram of the multi-phase coding demodulation process in an example of the present invention;

[0037] Among them, 1- narrow linewidth laser, 2- 1*2 fiber coupler, 3- electro-optic phase modulator, 4- acousto-optic modulator, 5- erbium-doped fiber amplifier, 6- circulator, 7- 2*2 fiber coupler, 8- balanced photodetector, 9- data acquisition card, 10- computer, 11- first arbitrary wave generator, 12- second arbitrary wave generator, 13- first dense wavelength division multiplexer, 14- sensing fiber, 15- second dense wavelength division multiplexer, 16- Raman fiber amplifier, 17- first radio frequency amplifier, 18- second radio frequency amplifier. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0039] like Figure 1As shown, the present invention proposes a multi-phase coded φ-OTDR sensing system device, including a narrow linewidth laser 1, a 1*2 fiber coupler 2, an electro-optic phase modulator 3, an acousto-optic modulator 4, an erbium-doped fiber amplifier 5, a circulator 6, a 2*2 fiber coupler 7, a balanced photodetector 8, a data acquisition card 9, a computer 10, a first arbitrary wave generator 11, a second arbitrary wave generator 12, a first dense wavelength division multiplexer 13, a sensing fiber 14, a second dense wavelength division multiplexer 15, a Raman fiber amplifier 16, a first radio frequency amplifier 17 and a second radio frequency amplifier 18.

[0040] Wherein, the output end of the narrow linewidth laser 1 is connected to the A port of the 1*2 fiber coupler 2, the B port of the 1*2 fiber coupler 2 is connected to the input end of the electro-optic phase modulator 3, the output end of the electro-optic phase modulator 3 is connected to the input end of the acousto-optic modulator 4, the output end of the acousto-optic modulator 4 is connected to the input end of the erbium-doped fiber amplifier 5, the output end of the erbium-doped fiber amplifier 5 is connected to the A port of the circulator 6, the B port of the circulator 6 is connected to the A port of the second dense wavelength division multiplexer 15, the C port of the second dense wavelength division multiplexer 15 is connected to the input end of the sensing fiber 14, the output end of the sensing fiber 14 is connected to the C port of the first dense wavelength division multiplexer 13, the B port of the first dense wavelength division multiplexer 13 and the B port of the second dense wavelength division multiplexer 15 are respectively connected to the two pump ports of the Raman fiber amplifier 16, and the A port of the first dense wavelength division multiplexer 13 is suspended; The C port is connected to the A port of the 2*2 optical fiber coupler 7, the C port of the 1*2 optical fiber coupler 2 is connected to the B port of the 2*2 optical fiber coupler 7, the output port of the 2*2 optical fiber coupler 7 is connected to the input port of the balanced photodetector 8, the output port of the balanced photodetector 8 is connected to the input end of the data acquisition card 9, and the output end of the data acquisition card 9 is connected to the computer 10; the clock end of the first arbitrary wave generator 11 is connected to the clock end of the second arbitrary wave generator 12 to keep clock synchronization, the output end of the first arbitrary wave generator 11 is connected to the input end of the first radio frequency amplifier 17 and the modulation end of the data acquisition card 9, the output end of the first radio frequency amplifier 17 is connected to the radio frequency signal input end of the electro-optic phase modulator 3, the output end of the second arbitrary wave generator 12 is connected to the input end of the second radio frequency amplifier 18, and the output end of the second radio frequency amplifier 18 is connected to the modulation end of the acousto-optic modulator 4.

[0041] Among them, the electro-optic phase modulator 3 and the acousto-optic modulator 4 perform radio frequency modulation on the first radio frequency amplifier 17 and the second radio frequency amplifier 18 through the first arbitrary wave generator 11 and the second arbitrary wave generator 12 respectively; the first arbitrary wave generator 11 and the second arbitrary wave generator 12 maintain clock synchronization; the electro-optic phase modulator 3 realizes multi-phase coded modulation, and the acousto-optic modulator 4 realizes multi-phase coded optical pulse intensity modulation, and synchronizes with the data acquisition card 9 during the modulation process to ensure that modulation and acquisition are carried out simultaneously.

[0042] Optionally, the 1*2 fiber coupler 2 is a 90:10 coupler; the first arbitrary wave generator 11 and the second arbitrary wave generator 12 have a sampling rate of 2.5GSa / s, and a modulation bandwidth greater than 1GHz; the electro-optical phase modulator 3 has a modulation bandwidth of 10GHz; the detection bandwidth of the balanced photodetector 8 is greater than 1GHz; the Raman fiber amplifier 16 has two 1460nm Raman pump sources, and simultaneously amplifies the 1550.12nm backward Rayleigh scattered light in the sensing fiber 14, and the backward Raman pump light enters the sensing fiber 14 through the second dense wavelength division multiplexer 15, and the pump light wave and the backward Rayleigh scattered light to be amplified are transmitted in the sensing fiber 14 in opposite directions; the forward Raman pump light enters the sensing fiber 14 through the first dense wavelength division multiplexer 13, and the pump light and the backward Rayleigh scattered light are transmitted in the same direction in the sensing fiber 14.

[0043] The present invention provides a multi-phase coded modulation and demodulation method, which includes a multi-phase coded signal modulation and demodulation process.

[0044] A modulation and demodulation method for a multi-phase coded φ-OTDR sensing system, wherein the multi-phase coding is composed of a coding length N、 Symbol width t Determines the detection light pulse width T = Nt Different code elements have different phase values, thus forming a multi-phase coding sequence. The detection optical pulse signal with a large time width has enough energy to transmit over a longer distance. The narrower code width enables the φ-OTDR system to have a higher spatial resolution, thereby solving the problem of the mutual restriction between spatial resolution and sensing distance in the existing technology.

[0045] In one embodiment, the sensing optical fiber 14 can be laid in a scene that needs to be monitored. In a laboratory scene, the disturbance simulation unit can be a piezoelectric ceramic oscillator, and the modulated detection light pulse signal is input into the sensing optical fiber 14. The piezoelectric ceramic oscillator is used to apply a signal at a certain point of the sensing optical fiber 14 to simulate the disturbance. After the disturbance, the sensing optical fiber 14 returns the backward Rayleigh scattered light signal carrying the disturbance information to the circulator 6, which is obtained by the photodetector 8 after beating with the local oscillator light and collected and processed.

[0046] Attached Figure 2 The flowchart of the multi-phase coded modulation process is shown, and the modulation process may include the following steps:

[0047] S11, code length N and code element width t It is a necessary characteristic quantity to determine multi-phase encoding. The symbol width is selected according to the spatial resolution requirement. t; Select the code length based on the sidelobe suppression ratio of the matched filter and the sensing distance N , and then construct a multi-phase coding sequence.

[0048] In this example, the multi-phase coded sequence f i It is expressed as:

[0049]

[0050] in i Represents the first phase of the multi-phase coded sequence i phases, not exceeding the code length N . Select the phase adjustment factor according to the signal bandwidth x 0, select the code length based on the sidelobe suppression effect N . Choose the appropriate phase adjustment factor x 0 and the encoding length N The multi-phase coded sequence can be determined f i .

[0051] S12, according to the multi-phase coding sequence f i The RF input voltage signal is adjusted, and the RF input voltage signal output by the first arbitrary wave generator 11 to the first RF amplifier 17 is u rf ( t )for:

[0052]

[0053] The code element width t Usually determined by the spatial resolution, V rf is the RF output voltage of the multi-phase coded modulation, rect (∙) is a rectangular function. The above RF input voltage signal u rf ( t ) After power amplification, the electro-optic phase modulator 3 is controlled so that the phase information of the multi-phase encoding is modulated onto the detection light to realize the phase modulation process. p' ( t ) is expressed as:

[0054]

[0055] in V π is the modulation half-wave voltage of the electro-optical phase modulator 3.

[0056] S13, the second arbitrary wave generator generates an AOM drive signal according to a specific window type, and the AOM is controlled by the second RF amplifier, so that the optical power of the multi-phase coded signal is modulated according to the same window type, thereby improving the sidelobe suppression ratio of the matched filter stage. Finally, the detection optical pulse signal p ( t ):

[0057]

[0058] in w (∙) is the window signal, which is used to suppress the side lobes after matched filtering. ∆f is the frequency shift introduced by the acousto-optic modulator 4. In this example, the window signal adopts a Hanning window, which can effectively improve the sidelobe suppression performance of the detection optical pulse signal, thereby improving the signal-to-noise ratio of the sensing system.

[0059] S14. Synchronization needs to be ensured during the generation of multi-phase coded detection light pulses. First, the first arbitrary wave generator and the second arbitrary wave generator need to maintain clock synchronization through the external clock port. Secondly, the phase modulation process of the electro-optic phase modulator, the intensity modulation process of the acousto-optic modulator, and the trigger acquisition process of the data acquisition card need to be synchronized to ensure that modulation and acquisition are carried out simultaneously.

[0060] The detection optical pulse signal obtained by multi-phase coding modulation is input into the sensing optical fiber 14 through the circulator 6, and the backward Rayleigh scattered light signal in the sensing optical fiber 14 is collected and demodulated by means of matched filtering.

[0061] Attached Figure 3 The flowchart of the multi-phase coded demodulation process is shown, and the demodulation process may include the following steps:

[0062] S21, the balanced photodetector 8 converts the beat frequency light of the backward Rayleigh scattered light and the local oscillator light into a beat frequency electrical signal. Considering the backward Rayleigh scattered signal at each position on the optical fiber and its interference process, the beat frequency electrical signal can be obtained. E beat ( t ):

[0063]

[0064] in h ( t ) contains the basic inherent characteristics of the multi-phase coded modulation φ-OTDR system, which is called the impulse response of the system. t z To receive the sensing fiber z The time delay of the Rayleigh scattered light.

[0065] The beat frequency electrical signal is processed by Hilbert transform on the computer 10, the beat frequency electrical signal is converted into a complex sequence, and then the beat frequency electrical signal is processed. E beat ( t ) for demodulation.

[0066] S22. Constructing digital domain matched filter on computer p * (- t ), using the matched filter to process the complex sequence of the beat frequency electrical signal, and obtain the matched filtering result containing the disturbance signal information R ( t ):

[0067]

[0068] in p * ( t )for p ( t ), p' ( t ) is a single-frequency narrow pulse signal obtained after matched filtering.

[0069] See attached Figure 4 , it can be seen that the code element width t The detection optical pulse signal is compressed into a narrow pulse signal with side lobes after matched filtering. Although the detection optical pulse signal is a wide pulse in the time domain, it is equivalent to a single-frequency narrow pulse signal after compression. t is the main lobe width of the compressed pulse. System spatial resolution Z SR With code width t The relationship can be expressed as: Z SR = c / 2 n ,in c is the speed of light, n is the refractive index of the optical fiber.

[0070] As attached Figure 3 As shown: S23, the results of matched filtering R ( t ) performs intensity demodulation to obtain the intensity information of backward Rayleigh scattering, and then performs moving differential average algorithm to obtain the positioning information of the vibration signal on the sensing optical fiber.

[0071] S24, then perform phase demodulation to obtain a vibration waveform.

[0072] The present invention can break through the constraint between sensing distance and spatial resolution in traditional distributed optical fiber sensing systems, and link the spatial resolution of the optical fiber sensing system with the symbol width through matched filtering processing, greatly improving system performance. This multi-phase coded φ-OTDR sensing system and modulation and demodulation method can effectively improve the signal-to-noise ratio and sensitivity of the optical fiber sensing system, and achieve synchronous improvement of spatial resolution and sensing distance.

[0073] Those skilled in the art will appreciate that all or part of the above steps need to be accomplished through hardware and computer software processing units.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A modulation and demodulation method for a multi-phase coded φ-OTDR sensing system, characterized in that: The multi-phase coded φ-OTDR sensing system comprises a narrow linewidth laser (1), the narrow linewidth laser (1) is connected to the A port of a 1*2 optical fiber coupler (2), the B port of the 1*2 optical fiber coupler (2) is connected in sequence to an electro-optic phase modulator (3), an acousto-optic modulator (4) and an erbium-doped optical fiber amplifier (5), and the output end of the erbium-doped optical fiber amplifier (5) is connected to the A port of a circulator (6); The C port of the circulator (6) is connected to the A port of the 2*2 optical fiber coupler (7), the B port of the 2*2 optical fiber coupler (7) is connected to the C port of the 1*2 optical fiber coupler (2), the output port of the 2*2 optical fiber coupler (7) is connected to the input port of the balanced photodetector (8), the output port of the balanced photodetector (8) is connected to the input end of the data acquisition card (9), and the output end of the data acquisition card (9) is connected to the computer (10); It also includes a first arbitrary wave generator (11) and a second arbitrary wave generator (12), wherein a clock end of the first arbitrary wave generator (11) is connected to a clock end of the second arbitrary wave generator (12) to maintain clock synchronization, an output end of the first arbitrary wave generator (11) is connected to an input end of a first radio frequency amplifier (17) and a modulation end of a data acquisition card (9), an output end of the first radio frequency amplifier (17) is connected to a radio frequency signal input end of an electro-optic phase modulator (3), an output end of the second arbitrary wave generator (12) is connected to an input end of a second radio frequency amplifier (18), and an output end of the second radio frequency amplifier (18) is connected to a modulation end of an acousto-optic modulator (4); The B port of the circulator (6) is connected to the A port of the second dense wavelength division multiplexer (15), the C port of the second dense wavelength division multiplexer (15) is connected to the input end of the sensing optical fiber (14), the output end of the sensing optical fiber (14) is connected to the C port of the first dense wavelength division multiplexer (13), the A port of the first dense wavelength division multiplexer (13) is suspended, and the B ports of the first dense wavelength division multiplexer (13) and the second dense wavelength division multiplexer (15) are respectively connected to two pump ports of a Raman optical fiber amplifier (16); the Raman optical fiber The amplifier (16) emits two beams of 1460nm high-power pump light, which are transmitted in the optical fiber simultaneously with the backward Rayleigh scattered light with a wavelength of 1550.12nm; the backward Raman pump light enters the sensing optical fiber (14) through the second dense wavelength division multiplexer (15); the pump light and the backward Rayleigh scattered light to be amplified are transmitted in the sensing optical fiber (14) in opposite directions; the forward Raman pump light enters the sensing optical fiber (14) through the first dense wavelength division multiplexer (13); the pump light wave and the backward Rayleigh scattered light are transmitted in the same direction in the sensing optical fiber (14); The modulation process includes the following steps: S11~Constructing multi-phase coding sequences φ i , in i Represents the first phase of the multi-phase coded sequence i phases, not exceeding the code length N ; Select the phase adjustment factor based on the signal bandwidth ξ 0, select the code length based on the sidelobe suppression effect N ;Choose the appropriate phase adjustment factor ξ 0 and the encoding length N Determine the multi-phase coding sequence φ i ; S12: adjusting the multi-phase coding sequence according to the modulation half-wave voltage of the electro-optical phase modulator (3) and the gain of the first radio frequency amplifier (17) φ i RF output power; Multi-phase coded sequence φ i The first arbitrary wave generator (11) outputs the signal to the first radio frequency amplifier (17), thereby modulating the signal to the electro-optical phase modulator (3) to implement a phase modulation process, and performing pre-distortion processing on the modulation result; S13: The second arbitrary wave generator (12) generates an acousto-optic modulator (4) driving signal, and the acousto-optic modulator (4) is controlled via the second radio frequency amplifier (18), so that the multi-phase coded signal optical power is modulated according to the same window type, thereby improving the sidelobe suppression ratio in the matched filter stage, and finally obtaining a multi-phase coded detection optical pulse; The demodulation process includes the following steps: S21~balanced photodetector (8) converts the beat frequency light of the back Rayleigh scattered light and the local oscillation light into a beat frequency electrical signal, and converts the beat frequency electrical signal into a complex sequence through Hilbert transform; S22~constructing a digital domain matched filter on the computer (10), performing matched filtering on the complex sequence of the beat frequency signal, realizing pulse compression of the beat frequency signal, and improving the spatial resolution of the sensor system; S23: performing intensity demodulation on the result after matched filtering to obtain the intensity information of backward Rayleigh scattering, and then performing a moving differential average algorithm to obtain the positioning information of the vibration signal on the sensing optical fiber (14); S24~Perform phase demodulation on the result after matched filtering to obtain a vibration waveform.

2. The modulation and demodulation method of the multi-phase coded φ-OTDR sensing system according to claim 1, characterized in that: The 1*2 optical fiber coupler (2) is a 90:10 coupler; the first arbitrary wave generator (11) and the second arbitrary wave generator (12) have a 2.5G sampling rate and a modulation bandwidth greater than 1GHz; the electro-optic phase modulator (3) has a 10GHz modulation bandwidth; and the balanced photodetector (8) has a detection bandwidth greater than or equal to 1GHz.

3. The modulation and demodulation method of the multi-phase coded φ-OTDR sensing system according to claim 1, characterized in that: During the modulation process of S12 and S13, synchronization needs to be ensured during the generation of the multi-phase coded detection optical pulse. First, the first arbitrary wave generator (11) and the second arbitrary wave generator (12) maintain clock synchronization through an external clock port. Secondly, the phase modulation process of the electro-optic phase modulator (3), the intensity modulation process of the acousto-optic modulator (4), and the trigger acquisition process of the data acquisition card (9) are synchronized to ensure that modulation and acquisition are performed simultaneously.

4. The modulation and demodulation method of the multi-phase coded φ-OTDR sensing system according to claim 3 is characterized in that: In step S12, according to the multi-phase coding sequence φ i The first arbitrary wave generator (11) adjusts the radio frequency input voltage signal, and the radio frequency input voltage signal outputted by the first arbitrary wave generator (11) to the first radio frequency amplifier (17) u rf ( t )for: The code element width τ Usually determined by the spatial resolution, V rf is the RF output voltage of the multi-phase coded modulation, is a rectangular function, i Represents the first phase of the multi-phase coded sequence i phases, not exceeding the code length N ; The above RF input voltage signal u rf ( t ) after power amplification, controls the electro-optic phase modulator (3) so that the multi-phase coded phase information is modulated onto the detection light, thereby realizing the phase modulation process; the detection light with multi-phase coded phase information p' ( t ) is expressed as: in V π is the modulation half-wave voltage of the electro-optic phase modulator (3), N is the code length of the polyphase encoding, j Is an imaginary unit.

5. The modulation and demodulation method of the multi-phase coded φ-OTDR sensing system according to claim 3 is characterized in that: In step S13, the optical pulse signal is detected p ( t ): in is the window signal, which is used to suppress the side lobes after matched filtering. is the frequency shift introduced by the AOM (4), and T is the duration of the detection light pulse.

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