An optical time domain reflection device and method based on pulse self-coherence

Abstract

An optical time domain reflectometry device and method based on pulse autocoherence belongs to the field of optical fiber sensing technology. The device includes five parts: a laser light source, a self-coherent chirped pulse modulation module, an optical pulse adjustment module, a signal transmission module, and an optical detection and demodulation module. Continuous light emitted by a laser passes through the self-coherent chirped pulse modulation module to obtain self-coherent chirped light pulses containing both an optical carrier frequency and a first-order swept sideband. The mutual beat frequency of these light pulses during the photoelectric conversion process can generate a Rayleigh scattering signal with a linear chirp characteristic, and the interference signal is processed using a non-matching filter to improve the spatial resolution. This solution breaks the contradiction between pulse width and spatial resolution, and achieves both high sensitivity and high spatial resolution measurement performance while maintaining a simple structure and immunity to interference fading.

Description

Technical field:

[0001] The present invention belongs to the technical field of optical fiber sensing, and in particular relates to an optical time domain reflection device and method based on pulse self-coherence. Background technology:

[0002] Optical Time Domain Reflectometry (OTDR) is a distributed fiber optic sensing system that performs non-destructive measurements on optical fibers and analyzes the loss of an entire section of fiber. Its principle is to utilize the interaction of light pulses with the fiber medium during their propagation to generate backscattered Rayleigh light. The light pulse and the echo of the scattered pulse are received at the transmitting end to form an attenuation curve of the backscattered light power. The location of defects on the fiber is determined based on the optical power attenuation curve.

[0003] In 1976, Bamoski and Jensen first proposed that due to its device characteristics, OTDR has the phenomenon of mutual constraints between transmission distance and spatial resolution. In addition, the laser light source has a wide linewidth and very poor coherence, and is insensitive to external disturbances applied to the optical fiber. Therefore, the disturbance information cannot be quantitatively demodulated.

[0004] Phase-Sensitive Optical Time Domain Reflectometry It is a distributed fiber optic sensing technology that can realize vibration measurement. When the output light of the laser light source is modulated into pulse light by the modulator and injected into the sensing fiber, the backscattered light is detected by the detector, and the information of the corresponding fiber position is obtained according to the time delay of receiving the scattered light. Because a narrow-linewidth light source is used, the detector receives the interference superposition of backward Rayleigh scattered light within the pulse width. When external disturbances act on the fiber, the refractive index at that location changes, causing the optical phase at that location to shift, ultimately manifesting as dramatic fluctuations in the scattered light intensity at that location.

[0005] In 1988, Dakin, Lamb and others first proposed a dual-pulse method in their patent (GB2222247A). They used optical switches and frequency shifters to modulate the detection pulse into a dual-pulse signal with different frequencies and separated in time. Due to the time difference between the front and back pulses, the phase information at different positions in the optical fiber can be modulated into the interference signal, realizing the measurement of the disturbance phase by direct detection OTDR.

[0006] In 2010, Roger Ian Crickmore and David John Hill first disclosed a dual-pulse distributed fiber optic sensing system in their patent (US07652245B2). Based on the OTDR, the continuous light emitted by the laser is divided into two paths, and two acousto-optic modulators are used to modulate two pulses of different frequencies. A time-delayed optical fiber is connected to one of the paths to form a dual-pulse signal with different frequencies and separated in time. Since this device is a direct detection OTDR, the pulse energy directly depends on the pulse width, so the detection distance is constrained by the spatial resolution. In addition, this dual-pulse The spatial resolution of the system depends on the pulse width and the interval between two pulses, which further degrades the spatial resolution of the system;

[0007] In 2016, a Spanish research group proposed a method based on chirped pulses and direct detection. The system (WO2017093588A1) modulates the pulsed light input into the sensing fiber into a linear chirped pulse. When there is an external disturbance, the phase change caused by the disturbance is equivalent to a frequency change. Due to the time-frequency mapping relationship of the linear chirped pulse, the frequency change is equivalent to a time shift of the Rayleigh scattering curve, which ultimately manifests as a time delay in the backscattered Rayleigh scattering spectrum at the disturbance. By cross-correlating the Rayleigh scattering curves before and after the disturbance, the delay and, therefore, the disturbance can be calculated, achieving quantitative measurement of the external disturbance signal. However, optical time-domain reflectometry suffers from a contradiction between spatial resolution and sensing distance. On the one hand, increasing the pulse width can increase the sensing distance; on the other hand, because the signal collected at any time during the signal acquisition process is the superposition of all scattered signals within half the pulse width, increasing the pulse width also leads to a decrease in spatial resolution.

[0008] In 2019, Liu Tiegen et al. from Tianjin University disclosed in patent (CN110864797A) a differential COTDR distributed acoustic sensing device and method for heterogeneous double-sideband chirped pulses. This system is based on a coherent detection OTDR and uses an IQ modulator to load two different electrical signals, making the detection signal a single pulse containing two chirped swept-frequency lights with opposite slopes. Reference light is used to enhance the sensitivity of the signal to be measured and improve the signal-to-noise ratio. However, due to the use of a coherent detection structure, the system introduces additional phase noise and is more complex in structure.

[0009] Matched filtering technology is a common way to solve the contradiction between spatial resolution and pulse width in radar systems, and this method is also applicable to some specific optical time domain reflection devices. For example, in 2016, He Zuyuan, Liu Qingwen and others from Shanghai Jiaotong University proposed a distributed fiber optic sensing system and its vibration detection and positioning method (CN 201610719172.3). It uses matched filtering technology to process the received scattered signals, breaking the constraint relationship between spatial resolution and pulse width, and greatly improving the spatial resolution of the system. However, since the system uses a coherent detection structure, its optical path structure is complex and will bring additional system noise; on the other hand, the demodulation method of this system uses phase demodulation, and its demodulation process is affected by interference fading, which affects the reliability of the system. Additional signal processing methods must be used to suppress it, so its system demodulation complexity is relatively large. On the other hand, the direct detection type proposed by the Spanish research team in 2016 The system also uses chirped pulses and employs a correlation demodulation method, which not only simplifies the structure but also ignores interference fading, significantly improving system reliability. However, because the sensor signal obtained by this system does not meet the conditions for pulse compression, its spatial resolution is still limited by the pulse width.

[0010] The present invention improves upon the existing technology and provides an optical time domain reflectometry device and method based on pulse autocoherence, implementing matched filtering on a direct detection optical time domain reflectometry device. Its optical path is of direct detection type, with a simple structure and no need to introduce local light, resulting in lower system noise and alleviating the conflict between spatial resolution and pulse width. Furthermore, the device uses a correlation demodulation method, which has a greater suppressive effect on interference fading, resulting in higher overall system sensitivity and stability. Summary of the invention:

[0011] The object of the present invention is to provide an optical time domain reflectometry device and method based on pulse self-coherence with high spatial resolution, high sensitivity, reliability and simple structure.

[0012] The purpose of the present invention is to be achieved through the following measures:

[0013] An optical time domain reflectometer based on pulse autocoherence includes five parts: a laser light source 1, a self-coherent chirped pulse modulation module 2, an optical pulse adjustment module 3, a signal transmission module 4, and an optical detection and demodulation module 5; its characteristics are:

[0014] The single-frequency continuous light output by the laser light source 1 is frequency modulated by the optical modulator 201 in the self-coherent chirped pulse modulation module 2, and then input to the first coupler 202 to be split into two beams.

[0015] The first output end 202a of the first coupler is connected to the first optical filter 204, and the output end of the first optical filter 204 after filtering is connected to the second coupler 206;

[0016] The second output end 202b of the first coupler is connected to the second optical filter 205, and the output end of the second optical filter 205 is connected to the second coupler 206 after filtering;

[0017] The output end of the second coupler 206 is connected to the pulse modulator 207. After optical pulse modulation, the output end of the pulse modulator 207 is connected to the erbium-doped fiber amplifier 301 in the optical pulse adjustment module 3. The output optical signal is noise-reduced by the filter 302 and then power-adjusted by the tunable attenuator 303.

[0018] The signal generator 203 in the self-coherent chirped pulse modulation module 2 generates a swept frequency electrical signal and a pulse electrical signal for driving the optical modulator 201 to perform swept frequency optical modulation and the synchronous pulse modulator 207 to perform optical pulse modulation;

[0019] The output end of the tunable attenuator 303 is connected to the circulator 401 in the signal transmission module 4, wherein the first output end 401a of the circulator is connected to the sensing optical fiber 402, and the second output end 401b of the circulator is connected to the photodetector 501 in the optical detection and demodulation module 5;

[0020] The output end of the photodetector 501 is connected to the acquisition card 502. After completing signal acquisition, the acquisition card 502 transmits the data to the demodulation device 503 for demodulation processing. First, only the beat frequency components of the single-frequency Rayleigh scattered light and the first-order swept-frequency Rayleigh scattered light are retained through the digital bandpass filter 504, and the beat frequency signal is compressed by the unmatched filter 505 to improve the spatial resolution. Then, the compressed beat frequency signal and the reference signal are correlated and demodulated 506. Since the time domain pattern of the beat frequency signal at the vibration position will be offset, the offset of the correlation peak in the cross-correlation result indicates that the position belongs to the disturbance area. The size of the disturbance Δε is determined by the offset of the cross-correlation peak, that is, Where K is the sweep rate, V0 is the center frequency, and Δt is the cross-correlation peak offset;

[0021] The signal generator 203 generates an electrical signal with a starting frequency v0 and a sweep frequency range of δv, which drives the optical modulator 201 to modulate the single-frequency continuous light v1 into a swept-frequency continuous light with multi-order sidebands. The signal generator 203 also outputs a pulsed electrical signal with a pulse width of T to drive the pulse modulator 207 to generate self-coherent chirped optical pulses. The frequency domain characteristics of each self-coherent chirped optical pulse are as follows: the spectrum of each self-coherent chirped optical pulse consists of two parts: one part is the chirped light with a starting frequency v0 and a sweep frequency range of δv, and the other part is the single-frequency light that only retains the optical carrier frequency v1. The minimum interval between these two parts must satisfy v0-v1≥δv to prevent the mutual beat frequency components of the two parts from aliasing with the self-beat frequency components. Figure 2 As shown;

[0022] The filtering bandwidth range of the first optical filter 204 is [v1-v0, v1+v0], the filtering lower limit range of the second optical filter 205 is [v1, v1+v0], and the filtering upper limit range is [v1+v0+δv, 2v1+2v0];

[0023] The pulse modulator 207 is an acousto-optic modulator or a semiconductor optical amplifier, used to generate a pulsed optical signal with a high extinction ratio;

[0024] The electric field expression of the light pulse e(t) output by the pulse modulator 207 is:

[0025]

[0026] Among them, E0 and E1 are amplitudes, v1 is the optical carrier frequency, and v0 is the starting frequency of the chirp part. is the sweep rate, δv is the sweep range, T is the pulse width, and rect(·) is the rectangular function.

[0027] The optical modulator 201 is a frequency modulator or a phase modulator, which is used to generate multi-order sideband optical signals;

[0028] The erbium-doped fiber amplifier 301 is used to amplify the optical pulse signal and increase its peak power;

[0029] The filter 302 is used to filter out the spontaneous emission noise generated during the amplification process of the erbium-doped fiber amplifier 302;

[0030] The tunable attenuator 303 is used to attenuate the peak power of the optical pulse to prevent excessive peak power from breaking down the connected devices;

[0031] The sensing optical fiber 402 is a single-mode optical fiber, a polarization-maintaining optical fiber, or a multi-mode optical fiber;

[0032] The photodetector 501 is a single-ended photodetector used to convert the received Rayleigh scattered light signal into a beat frequency electrical signal. The beat frequency electrical signal I(t) is expressed as:

[0033] I(t)=ILL (t)+I LS (t)+I SS (t) (2)

[0034] Among them, I LL (t) is the signal component formed by the beat frequency of the single-frequency light itself, I SS (t) is the signal component formed by the beat frequency of the chirped light itself, I LS (t) is the signal component formed by the beat frequency between the single-frequency light and the chirped light.

[0035] The acquisition card 502 is a high-speed acquisition card with a sampling rate of f s Need to meet f s ≥2·(v0-v1+δv);

[0036] The demodulation device 503 is a high-performance computer used to analyze and process the collected signals, including digital bandpass filtering 504, non-matched filtering 505 and correlation demodulation 506;

[0037] The digital bandpass filter 504 is used to retain the signal component I formed by the beat frequency of the single-frequency light and the chirped light. LS (t), the lower limit of the filtering bandwidth is v0-v1, the upper limit of the filtering bandwidth is v0-v1+δv, the bandwidth of the filtered signal is δv, the spatial resolution is W, and the frequency component I formed by the mutual beating of single-frequency light and chirped light is filtered out. LL (t) and I SS (t), its frequency component distribution is shown in the attached Figure 4 As shown. Among them, the signal component I formed by the beat frequency of the single-frequency light and the chirped light LS The complex signal expression of (t) is:

[0038]

[0039] Among them, τ i and τ j is the time delay required for receiving the scattered light from the i-th and j-th scattering points, R(τ i ) and R(τ j ) is the time delay τ i and τ j is the Rayleigh scattering reflectivity at , and N is the number of scattering units in the sensing fiber.

[0040] The non-matched filter 505 is used to implement pulse compression on the signal, that is, to compress the mutual beat frequency component with a spatial resolution of W, and increase the spatial resolution W to W′, and satisfy W′<W; wherein, the pulse width of the non-matched filter is T1, and satisfies T1>T, the starting frequency is v0-v1, the ending frequency is v0-v1+δv,, and the frequency sweep range is δv, wherein the expression of the non-matched filter h(t) is:

[0041]

[0042] in, is the sweep rate, v0-v1 is the starting frequency, δv is the sweep range, T1 is the unmatched filter width, and rect(·) is the rectangular function;

[0043] Spatial resolution of the system after unmatched filtering Where T is the sensing length, n is the refractive index, and c is the speed of light in a vacuum;

[0044] After non-matched filtering, the mutual beat signal component I LS After convolution of (t) and the non-matched filter h(t), the spatial resolution of the system is Where c is the speed of light, n is the fiber refractive index, T is the pulse width, δv is the frequency sweep range, and T1 is the unmatched filter width.

[0045] The correlation demodulation 506 identifies the location of the disturbance region by cross-correlation. That is, the location where the peak value in the cross-correlation result is not 0 is the disturbance region. The magnitude of the disturbance Δε is determined by the offset of the cross-correlation peak, that is, Where K is the sweep rate, V0 is the center frequency, and Δt is the cross-correlation peak offset;

[0046] Compared with the existing technology, the advantages of the present invention are:

[0047] 1. This invention is an optical time-domain reflectometry device and method based on pulse autocoherence. By generating self-coherent chirped pulses containing both an optical carrier frequency and a linearly swept frequency, the device generates a cross-beat frequency signal with a linear chirp characteristic during the photoelectric conversion process. This improves spatial resolution through matched filtering technology, alleviating the conflict between pulse width, sensing distance, and spatial resolution.

[0048] 2. This invention uses a direct detection structure, significantly simplifying system complexity while eliminating the additional noise introduced by local light in coherent detection. This device utilizes correlation demodulation during demodulation, avoiding misinterpretations caused by interference fading during phase demodulation. This device achieves both high sensitivity and high spatial resolution in signal measurement. Description of the drawings:

[0049] Figure 1 This is a schematic diagram of the structure of an optical time domain reflectometry device based on pulse self-coherence;

[0050] Figure 2 This is a schematic diagram of the time-frequency domain output of the self-coherent chirped pulse modulation module;

[0051] Figure 3This is the output timing diagram of the self-coherent chirped pulse modulation module;

[0052] Figure 4 Schematic diagram of the frequency domain of the Rayleigh backscattered light generated by pulse self-coherence. Specific implementation method:

[0053] In order to more clearly illustrate the optical time domain reflectometry device and method based on pulse autocoherence proposed by the present invention, the present invention is described in more detail below with reference to embodiments and drawings, but this should not limit the scope of protection of the present invention.

[0054] Figure 1 This is a schematic diagram of the structure of an optical time domain reflectometer based on pulse self-coherence. Figure 1 As shown, it includes five parts: a laser light source 1, a self-coherent chirped pulse modulation module 2, an optical pulse adjustment module 3, a signal transmission module 4 and an optical detection and demodulation module 5.

[0055] Laser light source 1 is a narrow linewidth laser;

[0056] The optical modulator 201 is a single sideband modulator;

[0057] The pulse modulator 207 is a semiconductor optical amplifier;

[0058] The sensing optical fiber 402 is a single-mode optical fiber;

[0059] The photodetector 501 is an InGaAs single-ended detector with a bandwidth of 4 GHz;

[0060] The acquisition card 502 is a high-speed acquisition card with a sampling rate of 10GSa / s;

[0061] The first optical filter 204 and the second optical filter 205 are both narrowband optical filters, both with a bandwidth of 5 GHz and center frequencies of 1550.12 nm and 1550.14 nm respectively;

[0062] One channel of the signal generator 203 outputs a linear frequency modulation signal with a pulse width of 1us, a starting frequency of 2GHz, and a sweep frequency range of 1GHz to drive the optical modulator 201, and the other channel generates a synchronous pulse signal with a pulse width of 1us to drive the pulse modulator 207 for synchronous output;

[0063] The laser light source 1 outputs a single-frequency continuous light of 1550.12 nm. After passing through the optical modulator 201 in the self-coherent chirped pulse modulation module 2, a continuous optical signal containing a carrier and a single-sided high-order sideband is generated. The optical carrier frequency and the positive first-order swept sideband are obtained by passing through the first optical filter 204 and the second optical filter 205 respectively. Finally, the optical carrier frequency and the positive first-order swept sideband are combined by the coupler 206 and then enter the pulse modulator 207 for modulation into a self-coherent chirped optical pulse signal. The output timing is as follows: Figure 3 As shown;

[0064] The self-coherent chirped optical pulse signal is power-adjusted by the optical pulse adjustment module 3 and then input to the circulator 401 in the signal transmission module 4 and transmitted to the sensing optical fiber 402;

[0065] The backscattered Rayleigh light generated by the sensing fiber 402 is transmitted to the photodetector 501 in the optical detection and demodulation module 5 via the circulator 401 and converted into a beat frequency electrical signal. The spectrum of the signal is divided into two parts. One part is the I signal generated by the beat frequency of the optical carrier frequency and the positive first-order swept sideband. LL (t)+I SS (t), whose spectrum distribution is [0, 1GHz]; the other part is the I generated by the beat frequency between the optical carrier frequency and the positive first-order swept frequency sideband. LS (t), its spectrum distribution is [2GHz, 3GHz], and these two spectrum components are completely separated and do not overlap;

[0066] The acquisition card 502 performs analog-to-digital conversion on the electrical signal output by the photodetector 501 and transmits it to the demodulation device 503 for processing. The steps are as follows:

[0067] 1) A digital bandpass filter 504 with a lower bandwidth of 2 GHz and an upper bandwidth of 3 GHz is implemented by a demodulator 503, and the beat frequency component I in the collected Rayleigh scattering interference signal is LS (t) is retained, and the component I of the single beat frequency in the collected Rayleigh scattering interference signal is LL (t)+I SS (t) Filter out, such as Figure 4 As shown;

[0068] 2) The demodulator 503 generates an interference signal I LS (t) The digital filter with non-matched filter characteristics is used for non-matched filtering. The pulse width of the non-matched filter is 1.01us, and the sweep frequency range is 1GHz. The spatial resolution of the system before compression is W = 100m. After the non-matched filter compression, the spatial resolution of the system is W′≈0.85m.

[0069] 3) The measured Rayleigh scattering pattern is cross-correlated with the Rayleigh scattering reference pattern according to a window of a certain length. The Rayleigh scattering pattern at the vibration position will shift. The disturbance area and strain magnitude are determined by the shift position of the correlation peak. The magnitude of the strain is determined by the shift amount of the cross-correlation peak, that is, Where K is the frequency sweep rate and Δt is the cross-correlation peak offset.

[0070] The spatial resolution of this embodiment is affected by pulse width. A pulse width of 1µs corresponds to a spatial resolution of 100m, and larger pulse widths degrade the spatial resolution. When processed with an unmatched filter, the spatial resolution is determined by the length of the unmatched filter and the linear chirp range, reaching the centimeter level, an improvement of nearly two orders of magnitude.

[0071] As can be seen from the specific examples, the present invention proposes an optical time domain reflection device and method based on pulse autocoherence, which solves the contradiction between spatial resolution and pulse width in traditional devices. With the advantages of simple structure and immunity to interference fading, it simultaneously achieves high-sensitivity and high-spatial resolution signal measurement, expanding the application scenarios of the system.

[0072] In addition, all components in the above embodiments may be commercially available products. The present invention is intended to protect their connection relationships and implementation principles, and therefore does not limit the model of each product itself. The terms used in the drawings to describe the positional relationships are for illustrative purposes only and should not be construed as limiting this patent.

[0073] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. An optical time domain reflectometer based on pulse self-coherence, comprising a laser light source (1), a self-coherent chirped pulse modulation module (2), an optical pulse adjustment module (3), a signal transmission module (4), and an optical detection and demodulation module (5), characterized in that: The laser light source (1) outputs single-frequency continuous light, which is frequency modulated by an optical modulator (201) in a self-coherent chirped pulse modulation module (2) and then input into a first coupler (202) to be divided into two beams of light; a first output end (202a) of the first coupler is connected to a first optical filter (204), and after filtering, the output end of the first optical filter (204) is connected to a second coupler (206); a second output end (202b) of the first coupler is connected to a second optical filter (205), and after filtering, the output end of the second optical filter (205) is connected to a second coupler (206); The output end of the second coupler (206) is connected to the pulse modulator (207). After optical pulse modulation, the output end of the pulse modulator (207) is connected to the erbium-doped fiber amplifier (301) in the optical pulse modulation module (3). The output optical signal is subjected to noise reduction by the filter A (302) and then power-regulated by the tunable attenuator (303). The signal generator (203) in the self-coherent chirped pulse modulation module (2) generates a swept frequency electrical signal and a pulse electrical signal, respectively, for driving the optical modulator (201) to perform swept frequency optical modulation and the synchronous pulse modulator (207) to perform optical pulse modulation. The output end of the tunable attenuator (303) is connected to the circulator (401) in the signal transmission module (4), wherein the first output end of the circulator is connected to the sensing optical fiber (402), and the second output end (401b) of the circulator is connected to the photodetector (501) in the light detection and demodulation module (5); the output end of the photodetector (501) is connected to the acquisition card (502), and after the acquisition card (502) completes signal acquisition, it transmits the data to the demodulation device (503) for demodulation processing, firstly, only retains the beat frequency signal I of the single-frequency Rayleigh scattered light and the first-order swept-frequency Rayleigh scattered light through the digital bandpass filter (504). LS (t), and the beat frequency signal I is filtered by non-matched filtering (505). LS (t) is compressed to improve the spatial resolution, and then the compressed beat signal and the reference signal are correlated and demodulated (506). Since the beat signal time domain pattern at the vibration position will be offset, the offset of the correlation peak in the cross-correlation result indicates that the position belongs to the disturbance area, and the size of the disturbance Δε is determined by the offset of the cross-correlation peak, that is, Wherein, K is the frequency sweep rate, V0 is the center frequency, and Δt is the cross-correlation peak offset; in the self-coherent chirped pulse modulation module (2), the signal generator (203) generates an electrical signal with a starting frequency of v0 and a frequency sweep range of δν to drive the optical modulator (201) to modulate the single-frequency continuous light ν1 into a frequency sweep continuous light containing multiple-order sidebands, and outputs a pulse electrical signal with a pulse width of T to drive the pulse modulator (207) to generate a self-coherent chirped optical pulse, the frequency domain characteristics of which are as follows: the spectrum of each self-coherent chirped optical pulse consists of two parts, one part is the chirped light with a starting frequency of v0 and a frequency sweep range of δν, and the other part is the chirped light with only the optical carrier frequency ν1 retained. The single-frequency light of the two parts must satisfy ν0-ν1≥δv, so that the mutual beat frequency components of the two parts of light will not be mixed with the self-beat frequency components; the filtering bandwidth range of the first optical filter (204) is [v1-v0, v1+v0], the filtering lower limit range of the second optical filter (205) is [v1, v1+v0], and the filtering upper limit range is [v1+v0+δv, 2v1+2v0]; the pulse modulator (207) is an acousto-optic modulator or a semiconductor optical amplifier, which is used to generate high extinction ratio optical pulses; the optical modulator (201) is a frequency modulator or a phase modulator, which is used to generate multi-order swept frequency sideband optical signals.

2. The optical time domain reflectometry device based on pulse self-coherence according to claim 1, characterized in that: In the optical pulse adjustment module (3), the erbium-doped fiber amplifier (301) is used to amplify the optical pulse signal and increase its peak power; the filter A (302) is used to filter out the spontaneous emission noise generated during the amplification process of the erbium-doped fiber amplifier (301); and the tunable attenuator (303) is used to attenuate the peak power of the optical pulse to prevent excessive peak power from breaking down connected devices.

3. The optical time domain reflectometry device based on pulse self-coherence according to claim 1, characterized in that: In the signal transmission module (4), the sensing optical fiber (402) is a single-mode optical fiber, a polarization-maintaining optical fiber, or a multi-mode optical fiber.

4. The optical time domain reflectometry device based on pulse self-coherence according to claim 1, characterized in that: In the light detection and demodulation module (5), the photodetector (501) is a single-ended photodetector, which is used to convert the received Rayleigh scattered light signal into a beat frequency electrical signal; the acquisition card (502) is a high-speed acquisition card with a sampling rate of f s Need to meet f s ≥2·(v0-v1+δν); the demodulation device (503) is a high-performance computer for analyzing and processing the collected signals, including a digital bandpass filter (504), an unmatched filter (505) and a correlation demodulation (506).

5. The optical time domain reflectometry device based on pulse self-coherence according to claim 1, characterized in that: In the digital bandpass filter (504) of the optical detection and demodulation module (5), the digital bandpass filter (504) is used to retain the signal component I formed by the beat frequency of the single-frequency light and the chirped light. LS (t), the lower limit of the filtering bandwidth is v0-v1, the upper limit of the filtering bandwidth is v0-v1+δv, the spatial resolution is W, and the frequency component I formed by the mutual beating of single-frequency light and chirped light is filtered out. LL (t) and I SS (t).

6. The optical time domain reflectometry device based on pulse self-coherence according to claim 1, characterized in that: In the non-matched filter (505) of the optical detection and demodulation module (5), the non-matched filter (505) is used to realize pulse compression of the signal, that is, the mutual beat frequency component I with a bandwidth of δν and a spatial resolution of W is LS (t) compression, and its spatial resolution is increased to W′, and W′>W; wherein, the pulse width of the non-matched filter is T1, and T1<T, the starting frequency is v0-v1, and the ending frequency is v0-v1+δv.

7. The optical time domain reflectometry device based on pulse self-coherence according to claim 1, characterized in that: In the correlation demodulation (506) of the optical detection and demodulation module (5), the correlation demodulation (506) identifies the position of the disturbance area by means of cross-correlation. When there is external disturbance, the phase change caused by the disturbance is equivalent to the frequency change. Due to the time-frequency mapping relationship of the linear chirped pulse, the frequency change is equivalent to the Rayleigh scattering curve being offset in time, which is ultimately manifested as a time delay phenomenon in the time domain of the back Rayleigh scattering spectrum at the disturbance. By cross-correlating the Rayleigh scattering curves before and after the disturbance, the size of the time delay can be calculated, and then the size of the disturbance can be calculated, thereby achieving quantitative measurement of the external disturbance signal. The position where the peak value in the cross-correlation result is not 0 is the disturbance area, and the size of its disturbance amount Δε is determined by the offset of the cross-correlation peak, that is, Where K is the sweep rate, V0 is the center frequency, and Δt is the cross-correlation peak offset.

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