A composite modulation pulse coding-based phi-otdr sensing method and system

Abstract

The application discloses a kind of Φ-OTDR sensing method and system based on composite modulation pulse coding, comprising: obtaining high coherence continuous laser and being divided into probe light and local light;DDS control word of sequence is generated using FPGA to drive DDS to generate two-phase coding sequence and generate linear sawtooth wave voltage to control voltage-controlled oscillator to form linear frequency modulation signal of specified slope;High coherence continuous laser is modulated into two-phase coding light, modulated into composite modulation pulse string twice and signal power amplification is carried out, and is injected into the optical fiber to be measured;Probe pulse is injected into the optical fiber to be measured, backscattering Rayleigh echo is received, and light beat frequency is carried out with local light, and intermediate frequency optical signal is generated and converted into real-time high-speed sampling intermediate frequency electrical signal, signal demodulation, noise reduction and positioning signal processing are carried out.The application breaks through the restriction problem between sensing distance and spatial resolution in traditional distributed optical fiber sensing system, and greatly improves system performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of real-time vibration sensing, and in particular to a Φ-OTDR sensing method and system based on composite modulation pulse coding. BACKGROUND

[0002] The Φ-OTDR system has the advantages of distributed sensing, long-range sensing, and anti-electromagnetic interference, and has broad application prospects in many fields such as rail transit safety monitoring, smart grid state 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. Therefore, breaking through the limitation of the mutual restriction between spatial resolution and sensing distance in traditional Φ-OTDR technology has important scientific significance and application value.

[0003] With the unremitting research of domestic and foreign scholars, the pulse compression technology commonly used in the field of radar can be used in the Φ-OTDR sensing system to effectively break through the bottleneck of mutual restriction between spatial resolution and sensing distance. The mainstream technical means includes phase coding modulation technology and linear frequency modulation technology. The phase coding technology can increase the coding gain by increasing the number of coding bits, thereby obtaining a higher signal-to-noise ratio, but the spatial resolution is limited by the single code pulse width, and the spatial resolution improvement capability is limited; the linear frequency modulation technology can increase the frequency modulation range to improve the bandwidth, thereby obtaining a higher spatial resolution, but the signal-to-noise ratio improvement capability is limited.

[0004] Therefore, how to simultaneously improve the signal-to-noise ratio and spatial resolution of the coded Φ-OTDR system is a problem that needs to be solved by those skilled in the art. SUMMARY

[0005] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0006] In view of the above existing problems, the present application is proposed.

[0007] Therefore, the purpose of the present application is to provide a Φ-OTDR sensing method and system based on composite modulation pulse coding, which solves the problem of how to simultaneously improve the signal-to-noise ratio and spatial resolution of the coded Φ-OTDR system.

[0008] To solve the above technical problems, the present application provides the following technical solutions:

[0009] In a first aspect, the embodiment of the present application provides a Φ-OTDR sensing method based on composite modulation pulse coding, comprising: obtaining high coherence continuous laser and dividing into probe light and local light;

[0010] The DDS control word sequence is generated by the FPGA to drive the DDS module to generate a binary phase coding sequence and to generate a linear sawtooth wave voltage to control the voltage-controlled oscillator to form a linear frequency modulation signal with a specified slope;

[0011] The high coherence continuous laser is modulated into a binary phase coding light and then into a composite modulation pulse train in combination with the linear frequency modulation signal;

[0012] The composite modulation pulse train is amplified in signal power and injected into a to-be-measured optical fiber to realize full-distributed sensing on the optical fiber link;

[0013] A probe pulse is injected into the to-be-measured optical fiber, and a backscattered Rayleigh scattering echo containing event point information on the optical fiber link is received;

[0014] The backscattered Rayleigh scattering echo and the local light are subjected to optical beat to generate an intermediate frequency optical signal and convert it into an intermediate frequency electrical signal;

[0015] The intermediate frequency electrical signal is sampled in real time at a high speed, and signal processing of signal demodulation, noise reduction and positioning is performed.

[0016] As the Φ-OTDR sensing method based on composite modulation pulse coding, the composite modulation pulse train comprises composite modulation probe pulse light with inter-code phase modulation and intra-code linear frequency modulation.

[0017] As the Φ-OTDR sensing method based on composite modulation pulse coding, the signal processing of signal demodulation, noise reduction and positioning comprises,

[0018] The intermediate frequency electrical signal of the backscattered Rayleigh scattering is obtained by a data acquisition card;

[0019] The intermediate frequency electrical signal is subjected to Hilbert transform and digital down-conversion to shift the signal to a baseband.

[0020] As the Φ-OTDR sensing method based on composite modulation pulse coding, the method further comprises,

[0021] The baseband signal is subjected to matched filtering processing to realize pulse compression and restore the signal to a single pulse response;

[0022] The single pulse signal is subjected to intensity demodulation or phase demodulation to obtain positioning information.

[0023] In a second aspect, the embodiment of the present application provides a Φ-OTDR sensing system based on composite modulation pulse coding, comprising,

[0024] A narrow line width laser for generating high coherence continuous wave laser;

[0025] An electrical modulation signal generation module for forming a two-phase encoding and a linear frequency modulation signal;

[0026] An optical pulse signal modulation module for modulating the high coherence continuous wave laser into a two-phase encoding light by an electro-optical phase modulator and into a composite modulation pulse train by an electro-optical intensity modulator;

[0027] A probe optical fiber module, the composite modulation pulse train is signal power amplified by an erbium-doped fiber amplifier and injected into a to-be-measured optical fiber by a circulator to realize full-distributed sensing on the optical fiber link;

[0028] A signal processing module, which collects Rayleigh backscattering echoes containing event point information on the optical fiber link by the circulator, outputs to a 2*2 optical fiber coupler, performs optical beat frequency of the Rayleigh backscattering echoes and the local oscillator light obtained from the 1*2 optical fiber coupler, generates an intermediate frequency optical signal, and performs photoelectric conversion by a balanced detector to obtain an intermediate frequency electrical signal, and a data acquisition card acquires the intermediate frequency electrical signal in real time at a high speed, and a computer demodulates the signal to obtain sensing information.

[0029] As the Φ-OTDR sensing system based on the composite modulation pulse encoding, the electrical modulation signal generation module comprises,

[0030] An FPGA module for generating a sequence of DDS control word driving and a linear sawtooth wave voltage signal;

[0031] A DDS module for generating a two-phase encoding sequence;

[0032] A voltage-controlled oscillator for linear frequency modulation to form a linear frequency modulation signal with a specified slope;

[0033] As the Φ-OTDR sensing system based on the composite modulation pulse encoding, the FPGA module generates a sequence of DDS control word driving, the DDS module generates a two-phase encoding sequence, and the linear sawtooth wave voltage signal controls the voltage-controlled oscillator to form a linear frequency modulation signal with a specified slope.

[0034] As the Φ-OTDR sensing system based on the composite modulation pulse encoding, the 1*2 optical fiber coupler comprises a signal branching for coherent detection, and the high coherence continuous wave laser is branched into probe light and local oscillator light.

[0035] In a third aspect, an embodiment of the present application provides a computing device, comprising:

[0036] A memory and a processor;

[0037] The memory is configured to store computer-executable instructions, and the processor is configured to execute the computer-executable instructions, and when the one or more programs are executed by the one or more processors, the one or more processors implement the Φ-OTDR sensing method based on composite modulation pulse coding according to any one of the embodiments of the present application.

[0038] In a fourth aspect, the embodiments of the present application provide a computer-readable storage medium storing computer-executable instructions, and the computer-executable instructions are executed by a processor to implement the Φ-OTDR sensing method based on composite modulation pulse coding.

[0039] The present application has the following beneficial effects: The present application can break through the restriction between sensing distance and spatial resolution in a traditional distributed optical fiber sensing system, and through composite modulation and matched filtering processing, the spatial resolution and signal-to-noise ratio of the optical fiber sensing system are respectively associated with the composite modulation signal of frequency modulation and phase modulation, so that the system performance is greatly improved. The Φ-OTDR sensing method and system based on composite modulation pulse coding can effectively improve the signal-to-noise ratio and sensitivity of the optical fiber sensing system, and realize synchronous improvement of spatial resolution and sensing distance. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings. Among them:

[0041] Figure 1 The modulation flowchart of the Φ-OTDR sensing method based on composite modulation pulse coding according to the present application.

[0042] Figure 2 The demodulation flowchart of the Φ-OTDR sensing method based on composite modulation pulse coding according to the present application.

[0043] Figure 3 The device diagram of the Φ-OTDR sensing system based on composite modulation pulse coding according to the present application. DETAILED DESCRIPTION

[0044] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings of the specification.

[0045] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods have not been described in detail in order not to unnecessarily obscure aspects of the present application.

[0046] Secondly, the "one embodiment" or "an embodiment" referred to herein means a specific feature, structure, or characteristic under discussion. Each of the various aspects presented in this description can be implemented in many different embodiments and each of the described aspects can be implemented alone or in combination with other aspects. It should be understood that the various embodiments described herein are not necessarily mutually exclusive, and that features or components of one embodiment can be combined with features or components of another embodiment.

[0047] Thirdly, the present application is described in detail in conjunction with the schematic diagram. In the detailed description of the embodiments of the present application, the cross-sectional view of the device structure is locally enlarged without the general proportion for the convenience of description, and the schematic diagram is only an example which should not limit the scope of protection of the present application. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in the actual manufacture.

[0048] Embodiment 1

[0049] Reference Figure 1 For one embodiment of the present application, a Φ-OTDR sensing method and system based on composite modulation pulse coding are provided, which comprises:

[0050] As shown in the method provided by the present application, the specific steps are as follows: Figures 1-2 The phase coding of the present application is determined by the coding length N and the symbol width τ, so the time width T of the probe light pulse is N*τ. Each symbol has the same frequency modulation coefficient, thereby forming a composite modulation coding sequence. The probe light pulse signal with a large time width has sufficient energy to transmit a longer distance, and the frequency modulation within the code enables the Φ-OTDR system to have higher spatial resolution, thereby solving the problem of mutual restriction between spatial resolution and sensing distance in the prior art.

[0051] In the present embodiment, the optical fiber to be measured can be laid in a scene that needs to be monitored. Taking a laboratory scene as an example, a PZT (piezoelectric ceramic oscillator) is used to simulate the disturbance signal. The composite modulated probe light pulse signal is input to the optical fiber to be measured, a PZT is wound around a certain place of the optical fiber to be measured, and a sinusoidal signal is applied to the PZT to simulate the disturbance. The disturbed optical fiber returns the back Rayleigh scattering light signal carrying the disturbance information to the circulator, which is frequency-mixed with the local oscillator light, acquired by the balanced detector, and collected and processed.

[0052] As shown in the modulation process steps of the present application:

[0053] Figure 1 As shown in the modulation process steps of the present application:

[0054] ​According to a sidelobe suppression ratio of a matched filter and a sensing distance, the code length N and the code width tau are selected to construct a two-phase code sequence by DDS; according to a spatial resolution requirement, the frequency modulation coefficient K and the frequency modulation period Tc are adjusted to construct a driving signal of a voltage-controlled oscillator.

[0055] The two modulation signals are used to adjust the radio frequency input voltage signal, and the electro-optical phase modulator 3 and the electro-optical intensity modulator are controlled respectively, the modulated phase and frequency signals are modulated to the probe pulse, the composite modulation process is realized, and the expected probe pulse light is finally generated.

[0056] In the process of generating the probe light pulse under the coherent detection system, synchronization needs to be ensured. Firstly, the two driving signals of the FPGA need to keep clock synchronization through the internal clock. Secondly, the phase modulation process of the electro-optical phase modulator, the intensity modulation process of the electro-optical intensity modulator and the trigger acquisition process of the data acquisition card need to be synchronized to ensure that the modulation and acquisition are performed simultaneously.

[0057] The probe light pulse signal obtained through the composite modulation is injected into the optical fiber to be measured through the circulator, the backscattered Rayleigh scattering light signal in the optical fiber to be measured is collected, and the demodulation processing is realized through the matched filtering means.

[0058] As shown in Figure 2 , the demodulation process steps of the present application are as follows:

[0059] The balanced detector converts the beat frequency light of the backscattered Rayleigh scattering light and the local oscillator light into a beat frequency electrical signal, and considering the backscattered Rayleigh scattering signal at each position on the optical fiber and the interference process thereof, the beat frequency electrical signal E beat (t) can be obtained:

[0060]

[0061] Wherein, h(t) is the basic inherent characteristic of the optical fiber channel in the Φ-OTDR system, which is called the impulse response of the system, t z is the time delay of receiving the Rayleigh scattering light at the position z of the sensing optical fiber, and p(t) is the probe pulse signal after the secondary modulation.

[0062] The Hilbert transform of the beat frequency signal is performed on the computer, and a low-pass filter is used to realize digital down-conversion, so as to convert the beat frequency electrical signal into a complex sequence at the baseband, and then the beat frequency electrical signal E beat (t) is demodulated.

[0063] A digital domain matched filter p*(-t) is constructed on the computer, and the matched filter is used to realize matched filtering processing on the complex sequence of the beat frequency electrical signal, so as to obtain the matched filtering result R(t) containing the disturbance signal information:

[0064]

[0065] Wherein, p*(-t) is the conjugate of p(t), and p'(t) is a single-frequency narrow pulse signal obtained after the matched filtering processing.

[0066] Intensity demodulation is performed on the matched filtering result R(t) to obtain the intensity information of the back Rayleigh scattering, and then the accumulation average algorithm is performed to obtain the positioning information of the vibration signal on the sensing optical fiber.

[0067] The application further provides a Φ-OTDR sensing system based on composite modulation pulse coding, comprising:

[0068] A narrow linewidth laser 100 is used to generate high coherence continuous laser;

[0069] An electric modulation signal generation module 200 is used to form a two-phase coded and linear frequency modulation signal;

[0070] An optical pulse signal modulation module 300 is used to modulate the high coherence continuous laser into two-phase coded light by using an electro-optic phase modulator 301 and then into a composite modulation pulse string by using an electro-optic intensity modulator 302;

[0071] A probe optical fiber module 400 is used to amplify the signal power of the composite modulation pulse string by using an erbium-doped optical fiber amplifier 401, and inject the composite modulation pulse string into a to-be-measured optical fiber 403 by using a circulator 402, so that full-distributed sensing on the optical fiber link is realized.

[0072] A signal processing module 500 is used to collect the back Rayleigh scattering echo containing event point information on the optical fiber link by using the circulator 402, output the back Rayleigh scattering echo to a 2*2 coupler 502, and perform optical beat frequency on the back Rayleigh scattering echo and the local oscillator light obtained from a 1*2 optical fiber coupler 501, so that intermediate frequency light signals are generated, photoelectric conversion is performed on the intermediate frequency light signals by using a balanced detector 503, intermediate frequency electric signals are obtained, a data acquisition card 504 is used to collect the intermediate frequency electric signals in real time at a high speed, signal demodulation is performed on the intermediate frequency electric signals by using a computer, and sensing information is acquired.

[0073] The 1*2 optical fiber coupler 501 is used for signal branching of coherent detection, and the high coherence continuous laser is branched into probe light and local oscillator light.

[0074] Specifically, the electric modulation signal generation module 200 comprises,

[0075] An FPGA module 201 is used to generate a sequence of DDS control words and a linear sawtooth wave voltage signal;

[0076] A DDS module 202 is used to generate a two-phase coded sequence;

[0077] A voltage-controlled oscillator 203 is used for linear frequency modulation to form a linear frequency modulation signal with a specified slope.

[0078] The FPGA module 201 generates a sequence of DDS control words to drive the DDS module 202 to generate a bi-phase encoded sequence and a linear sawtooth voltage signal to control the voltage-controlled oscillator 203 to form a linear frequency modulation signal with a specified slope.

[0079] Preferably, the narrow linewidth laser has a working wavelength of 1550.12 nm, a laser emission power of 10 mW, and a linewidth less than 50 kHz to ensure sufficient coherence length; the 1*2 optical fiber coupler 501 is a 90:10 coupler, 90% of the laser serving as probe light (corresponding to the B port of the 1*2 optical fiber coupler 501) and 10% of the laser serving as reference light (corresponding to the C port of the 1*2 optical fiber coupler 501); the FPGA module 201 has an internal source clock of 50 MHz, and a 400M virtual clock generated by frequency multiplication through a phase-locked loop is used as the system clock; the electro-optical phase modulator 301 has a modulation bandwidth of 10 GHz, and its half-wave voltage needs to be less than 5V; the electro-optical intensity modulator 302 has a modulation bandwidth of 10 GHz, and its half-wave voltage needs to be less than 5V; the 2*2 optical fiber coupler 502 is a 50:50 coupler, used for beat frequency between scattered echo and intrinsic light, reference phase acquisition, and power increase of weak scattered signals; the balanced detector 503 has double-ended differential input, suppresses common-mode signals and DC bias, and has a detection bandwidth greater than 400 MHz; the data acquisition card 504 has a sampling rate of 1GSa / s, which needs to be more than twice the bandwidth of the output signal of the balanced detector 503.

[0080] As shown in Figure 3 The application also provides a device of a Φ-OTDR sensing system based on composite modulation pulse coding, which comprises:

[0081] The output end of the narrow line width laser 100 is connected to the A port of the 1*2 optical fiber coupler 501, the B port of the 1*2 optical fiber coupler 501 is connected to the input end of the electro-optic phase modulator 301, the output end of the electro-optic phase modulator 301 is connected to the input end of the electro-optic intensity modulator 302, the output end of the electro-optic intensity modulator 302 is connected to the input end of the erbium-doped fiber amplifier 401, the output end of the erbium-doped fiber amplifier 401 is connected to the A port of the circulator 402, the B port of the circulator 402 is connected to the to-be-measured optical fiber 403; the C port of the circulator 402 is connected to the B port of the 2*2 optical fiber coupler 502, the C port of the 1*2 optical fiber coupler 501 is connected to the A port of the 2*2 optical fiber coupler 502, the C port and the D port of the 2*2 optical fiber coupler 502 are connected to the A input port and the B input port of the balanced detector 503 respectively, the output end of the balanced detector 503 is connected to the input end of the data acquisition card 504, and the output end of the data acquisition card 504 is connected to a computer; the FPGA module 201 provides two signal paths, one of which is connected to the input end of the DDS module 202, and the other of which is connected to the input end of the voltage-controlled oscillator 203, the output end of the DDS module 202 is connected to the modulation end of the electro-optic phase modulator 301, and the output end of the voltage-controlled oscillator 203 is connected to the modulation end of the electro-optic intensity modulator 302.

[0082] In the formula, the FPGA module 201 simultaneously provides driving signals for the DDS module 202 and the voltage-controlled oscillator 203, realizes the generation of a modulated electrical signal, and the modulated signals generated by the DDS module 202 and the voltage-controlled oscillator 203 perform radio frequency modulation on continuous laser through the electro-optic phase modulator 301 and the electro-optic intensity modulator 302 respectively; the two driving paths of the FPGA module 201 need to keep clock synchronization; the electro-optic phase modulator 301 realizes two-phase encoding modulation, and the electro-optic intensity modulator 302 realizes linear frequency modulation in the two-phase encoding pulse; the modulation process is processed synchronously with the data acquisition card 504, so that the modulation and acquisition are performed simultaneously.

[0083] Embodiment 2

[0084] As another embodiment of the application, which is different from the first embodiment, a verification test of a Φ-OTDR sensing method and system based on composite modulation pulse coding is provided, and the technical effects used in the method are verified and explained.

[0085] In order to verify the superiority of the present application, the pulse compression signal processing method of the present application is compared with the conventional Φ-OTDR system in a simulation test. In the simulation test, it is assumed that the probe pulse light of the conventional Φ-OTDR system is a repetitive square wave pulse generated by a 1550 nm wavelength laser, the modulation signal is a 1 kHz frequency, 100 ns pulse width single square wave pulse; while the probe pulse train of the system of the present application is generated by the same specification laser, the modulation signal is set to a phase encoding length of 255 bit Golay code sequence, the single code element width is also set to 100 ns, and the linear frequency modulation range is 0.5 GHz. The test assumes that the fiber to be tested is 100 km, the loss is 0.2 dB / km, a 20 Hz low frequency weak vibration signal is applied at the same position of 5 km, and the same system channel noise is set, and finally correlation processing and demodulation are performed. The test results are shown in Table 1.

[0086] Table 1: Test results

[0087] System Conventional OTDR system The system of the invention Signal to noise ratio (dB @ 5km) 10 22 Spatial resolution (m) 10 0.2 Sensing distance (km) 20 80

[0088] As can be seen from Table 1, compared with the conventional Φ-OTDR system, the system of the present application can significantly improve the sensing distance and spatial resolution while keeping the same probe pulse light parameters, and the signal-to-noise ratio is also improved, so that the positioning of the low frequency weak vibration signal is more sensitive and accurate. (This test is only a simulation under ideal conditions, and the actual effective sensing distance will be accelerated by the interference fading problem as the distance increases, but the superiority of the system of the present application is still obvious compared with the conventional Φ-OTDR system).

[0089] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A Φ-OTDR sensing method based on composite modulation pulse coding, characterized in that: include, Highly coherent continuous laser light is obtained and divided into probe light and local oscillator light; The DDS control word generated by the FPGA drives the DDS module to generate a two-phase coded sequence and a linear sawtooth wave voltage-controlled oscillator to form a linear frequency modulation signal with a specified slope. The highly coherent continuous laser light is modulated into binary coded light and then modulated again into a composite modulation pulse train by combining the linear frequency modulated signal. The composite modulated pulse train is amplified in signal power and injected into the optical fiber under test to realize fully distributed sensing on the optical fiber link. Inject probe pulses into the fiber under test and receive back Rayleigh scattering echoes containing event point information on the fiber link. The backscattered Rayleigh echo and the local oscillator light are beat to generate an intermediate frequency optical signal and then converted into an intermediate frequency electrical signal. Signal processing that acquires intermediate frequency electrical signals in real time at high speed and performs signal demodulation, noise reduction, and positioning.

2. The Φ-OTDR sensing method based on composite modulation pulse coding as described in claim 1, characterized in that, The composite modulation pulse train includes composite modulation probe pulses consisting of inter-symbol phase modulation and intra-symbol linear frequency modulation.

3. The Φ-OTDR sensing method based on composite modulation pulse coding as described in claim 1, characterized in that: Signal processing for demodulation, noise reduction, and positioning includes, The intermediate frequency electrical signal backscattered by Rayleigh is obtained from the data acquisition card; The intermediate frequency electrical signal is subjected to Hilbert transform and digital downconversion to shift the signal to baseband.

4. The Φ-OTDR sensing method based on composite modulation pulse coding as described in claim 3, characterized in that: It also includes, Matched filtering is applied to the baseband signal to achieve pulse compression and restore the signal to a single-pulse response. Positioning information is obtained by demodulating the intensity or phase of a single pulse signal.

5. A Φ-OTDR sensing system based on composite modulation pulse code, characterized in that, include: Narrow linewidth laser (100) for generating highly coherent continuous laser; An electrical modulation signal generation module (200) is used to generate a two-phase coded and linear frequency modulated signal; The optical pulse signal modulation module (300) is used to modulate highly coherent continuous laser light into binary coded light using an electro-optic phase modulator (301) and then modulate it into a composite modulation pulse train by an electro-optic intensity modulator (302). The detection fiber module (400) amplifies the signal power of the composite modulation pulse train through an erbium-doped fiber amplifier (401) and injects it into the fiber under test (403) through a circulator (402) to realize fully distributed sensing on the fiber link; The signal processing module (500) uses a circulator (402) to collect back Rayleigh scattering echoes containing event point information on the optical fiber link, and outputs them to a 2*2 optical fiber coupler (502) to beat the back Rayleigh scattering echoes with the optical beat frequency of the local oscillator light obtained from the 1*2 optical fiber coupler (501) to generate an intermediate frequency optical signal. The signal is then converted into an intermediate frequency electrical signal by a balanced detector (503). The data acquisition card (504) acquires the intermediate frequency electrical signal in real time at high speed, and demodulates the signal through a computer to obtain sensing information.

6. The Φ-OTDR sensing system based on composite modulation pulse coding as described in claim 5, characterized in that: The electronically modulated signal generation module (200) includes, FPGA module (201) is used to generate sequential DDS control word drive and linear sawtooth voltage signals; The DDS module (202) generates a binary phase-coded sequence; A voltage-controlled oscillator (203) is used for linear frequency modulation to generate a linear frequency modulation signal with a specified slope.

7. The Φ-OTDR sensing system based on composite modulation pulse coding as described in claim 6, characterized in that: The FPGA module (201) generates a sequence of DDS control words to drive the DDS module (202) to generate a two-phase coded sequence and generate a linear sawtooth wave voltage signal to control the voltage-controlled oscillator (203) to form a linear frequency modulation signal with a specified slope.

8. The Φ-OTDR sensing system based on composite modulation pulse coding as described in claim 5, characterized in that: The 1*2 fiber coupler (501) includes a signal splitter for coherent detection, which splits a highly coherent continuous laser into a probe beam and a local oscillator beam.

9. A computing device, comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, they implement the steps of the Φ-OTDR sensing method based on composite modulation pulse code as described in any one of claims 1 to 4.

10. A computer-readable storage medium storing computer-executable instructions that, when executed by a processor, implement the steps of the Φ-OTDR sensing method based on composite modulation pulse code as described in any one of claims 1 to 4.

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