A phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses

Abstract

The present invention belongs to the field of fiber optic sensing technology, specifically to a phase-sensitive optical time-domain reflectometer based on injection-locked chirped pulses. The instrument comprises a narrow-linewidth laser source, a signal modulation and injection-locking module, a sensing module, and a signal demodulation module. The instrument is characterized by utilizing a slave laser to select high-order modulation sweep sidebands to achieve widening of the system's sweep bandwidth. The slave laser can also lock the modulation sweep bandwidth, suppressing excess sidebands and eliminating interference peaks caused by harmonics during the correlation demodulation process. The present invention utilizes an injection-locking method to achieve flexible selection of the modulation sweep bandwidth, expand the system's sweep range, and improve the system's response sensitivity and strain demodulation range. Furthermore, the system suppresses excess modulation sidebands and improves the system's demodulation accuracy.

Description

Technical field:

[0001] The present invention belongs to the field of optical fiber sensing technology, and specifically relates to a phase-sensitive optical time domain reflectometer with injection-locked chirped pulses. Background technology:

[0002] An optical time-domain reflectometer (OTDR) is a distributed fiber optic sensing system that can perform non-destructive measurements along the entire length of an optical fiber and analyze defects and losses along the entire length. Its principle is to inject a modulated light pulse into the optical fiber. During propagation, the probe pulse interacts with the optical fiber medium, generating a backscattered Rayleigh light signal. The echo of the probe pulse and the scattered pulse is received at the injection end of the optical fiber, forming an attenuation curve of the backscattered light signal power. The location of defects and damaged points on the optical fiber is determined based on the power attenuation curve of the optical signal.

[0003] First proposed by Barnoski and Jensen in 1976, the OTDR system's transmission distance and spatial resolution are mutually constrained due to its device characteristics. In addition, the laser light source used has a wide linewidth and poor coherence, resulting in the echo signal being insensitive to external disturbances applied to the optical fiber, and therefore unable to achieve quantitative demodulation of the disturbance information.

[0004] Phase-Sensitive Optical Time Domain Reflectometer It is a distributed fiber optic sensing technology that can quantitatively measure the external disturbance at any position of the optical fiber. It has the advantages of simple structure and high sensitivity. When the output light of the narrow linewidth laser light source is modulated into a detection pulse light by the modulator and injected into the sensing fiber, a backscattered Rayleigh light signal is generated during the transmission process, and the backscattered Rayleigh light is detected by the detector. Using a narrow-linewidth laser source, the detector receives the result of the interference and superposition of Rayleigh-scattered backscatter signals within the pulse width. This echo signal is extremely sensitive to changes in temperature or strain. When a disturbance occurs at a fiber location, the fiber's length and refractive index change, causing a phase shift at that location, ultimately manifesting as a dramatic fluctuation in the scattered light intensity at that location.

[0005] In traditional direct detection systems In the system, what is detected is the light intensity signal, and the intensity variation shows a nonlinear relationship with the external disturbance. Therefore, it can only qualitatively analyze the external disturbance and cannot achieve quantitative measurement. In 2011, Pan Zhengqing and others from the Shanghai Institute of Optics and Fine Mechanics used coherent detection to obtain the beat frequency electrical signal of the backscattered Rayleigh light signal and the local light signal, and obtained the phase information of the beat frequency signal through the IQ demodulation method, and established a quantitative relationship between phase and strain, which made the coherent detection structure It can quantitatively solve external disturbance information. However, this IQ demodulation method is affected by interference fading and polarization fading, and the system measurement accuracy is limited.

[0006] In 2016, a Spanish research group proposed a direct detection method based on chirped pulse modulation. The system (WO2017093588A1) modulates a linear swept-frequency detection pulse with time-frequency correspondence characteristics, converting phase changes into time-shifted changes in the backward Rayleigh scattering pattern. Therefore, there is a linear relationship between the size of the external disturbance and the time delay. The size of the external disturbance is demodulated using a cross-correlation algorithm for time delay estimation. This correlation demodulation method can eliminate problems such as interference fading and improve the system demodulation accuracy. However, in the process of linear swept-frequency optical modulation, in addition to the required modulation sweep sidebands, there are also interferences such as carrier and redundant modulation sidebands. These redundant modulation harmonics will cause interference peaks in the correlation spectrum, which will also cause errors in the demodulation results and reduce the system measurement accuracy.

[0007] In 2018, Dong Yongkang's research group at Harbin Institute of Technology proposed a phase-sensitive OTDR measurement method based on frequency-space domain matching and injection locking technology (CN109443590A). This invention uses a single-frequency pulse to quickly step over the laser center frequency instead of the swept pulse, eliminating the nonlinear problem of the tuned laser sweep frequency, and uses injection locking technology to achieve rapid tuning of the laser frequency during pulse modulation. In the injection locking technology, the slave laser has the function of locking the center wavelength of the master laser, avoiding the nonlinear problem in the frequency scanning process and improving the measurement accuracy of the system.

[0008] In 2019, the Spanish research team proposed The strain response sensitivity of the system can be characterized by the Cramer-Rao lower bound, which is expressed as It is directly related to the sweep range. The larger the sweep range, the smaller the Cramer-Rao lower limit. The higher the sensitivity (HFMartins, et al, Fully Distributed Optical Fiber Strain Sensor With 10 -12 ε / √Hz Sensitivity. Journal of Lightwave Technology. 2019, 37(18), 4487-4495.).

[0009] In 2022, the Spanish research team proposed The strain measurement range of the system also depends on the sweep frequency range of the system. When the strain magnitude of the sensing fiber is 4% of the sweep frequency range, the correlation demodulation result has the highest accuracy and the best effect. However, when the strain magnitude is greater than 5% of the sweep frequency range, a large interference peak will appear in the correlation demodulation process, resulting in an error in the demodulation result (HFMartins, et al., Reaching Long-Term Stability in Journal of Lightwave Technology. 2022, 40(12), 3916-3922.). Thus, the The system's frequency sweep range can effectively improve the system's strain measurement range and response sensitivity. However, expanding the system's frequency sweep range often requires replacing expensive signal generators with large frequency sweep ranges, increasing system costs.

[0010] In 2018, Dong Yongkang's research group at Harbin Institute of Technology proposed a phase-sensitive OTDR measurement method based on frequency-space domain matching and injection locking technology (CN109443590A). This invention uses injection locking technology to achieve rapid tuning of the laser frequency during pulse modulation. In the injection locking technology, the slave laser has the function of locking the central wavelength of the master laser, avoiding nonlinear problems in the frequency scanning process and improving the measurement accuracy of the system.

[0011] In 2020, Yang Jun's research group at Guangdong University of Technology proposed an optical time domain reflectometer based on chirped pulses (CN112713929A). Based on the system, the Sipmlex encoding method is used to improve the system's signal-to-noise ratio. In order to avoid coherence between adjacent pulses and ensure the linearity of the system, this method has special requirements for the laser source linewidth. The demodulation process requires inverse combination decoding processing, which is achieved by circulating the inverse matrix of the Sipmlex matrix. The amount of data that needs to be processed is relatively large.

[0012] The present invention is an improvement based on the existing technology and provides a phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses. The injection locking technology is introduced on the basis of single-sideband pulse modulation. It can not only suppress the redundant sweep sidebands generated in the modulation process, eliminate the amplitude error caused by the harmonic interference peak in the correlation demodulation process, and improve the system demodulation measurement accuracy; it can also flexibly select the modulation sweep bandwidth by adjusting the output optical frequency of the slave laser, and expand the sweep range without increasing the system cost. On the other hand, the slave laser can lock the modulated sweep bandwidth for a long time, eliminating the problem of laser wavelength drift and increasing system stability. Summary of the invention:

[0013] The object of the present invention is to provide a phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses with high demodulation accuracy, large strain measurement range, high response sensitivity and high stability.

[0014] The object of the present invention is achieved by the following measures:

[0015] A phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses includes a narrow linewidth laser 1, a signal modulation and injection locking module 2, a sensing module 3, and a signal demodulation module 4, and is characterized by:

[0016] The signal modulation and injection locking module 2 comprises an optical modulator 201, a signal generator 202, an attenuator 203, a slave laser 204, a first circulator 205, a pulse modulator 206, and a driver 207. The narrow linewidth laser output terminal 101a is connected to the optical modulator input terminal 201a. The optical modulator driver port 201c is connected to the first output terminal 202a of the signal generator. The optical modulator output terminal 201b is connected to the first terminal 205a of the first circulator via the attenuator 203, and the second terminal 205b of the first circulator is connected to the slave laser 204. The third terminal 205c of the first circulator is connected to the pulse modulator input terminal 206a. The pulse modulator driver port 206c is connected to the driver output terminal 207b. The driver input terminal 207a is connected to the second output port 202b of the signal generator. The pulse modulator output terminal 206b is connected to the first optical amplifier input terminal 301a.

[0017] The first output terminal 202a of the signal generator outputs a swept frequency electrical signal 22 with a starting frequency of υ0 and a sweep frequency range of δυ to drive the optical modulator 201, modulating the single-frequency continuous light 11 with a frequency of υ into a multi-order sideband chirped continuous light 21. The second output terminal 202b of the signal generator outputs a pulse electrical signal 23 with a pulse width of τ to drive the pulse modulator 206 to modulate the continuous light into pulsed light.

[0018] The optical modulator 201 is an intensity modulator or a frequency modulator, and is used to generate multi-order sideband chirped continuous light 21;

[0019] The attenuator 203 is used to attenuate the multi-sideband chirped contact light 21 injected into the slave laser 204, thereby reducing its peak optical power;

[0020] The multi-order sideband chirped continuous light 21 includes a first-order frequency sweep sideband 51 with a center frequency of υ1 and a frequency sweep range of δυ and a second-order frequency sweep sideband 51 with a center frequency of υ n (n≥2), high-order swept sidebands with a sweep range of n·δυ(n≥2)55;

[0021] The pulse modulator is an acousto-optic modulator or a semiconductor optical amplifier, which is used to generate high extinction ratio light pulses, with an extinction ratio ER ≥ 30dB;

[0022] The slave laser 204 adjusts the frequency of the slave laser output light 24 and the center frequency υ of the n-order swept sideband 55 by changing the driving voltage. n The sideband locked swept continuous light 25 after injection locking only contains the center frequency υ n , the n-order swept sideband with a sweep range of n.δυ is 55, and the other modulation sidebands are suppressed;

[0023] The injection ratio k of the slave laser 204 needs to satisfy the condition k≥10, and the slave laser 204 is in an ideal working state.

[0024] The pulse modulation method of injection-locked high-order swept sideband is as follows:

[0025] S1: The first output terminal 202a of the signal generator sends out a frequency sweeping electrical signal 22 with a starting frequency of υ0 and a frequency sweeping range of δυ, driving the optical modulator 201 to modulate the single-frequency continuous light 11 with a frequency of υ output by the narrow linewidth laser 1 into a multi-order sideband chirped continuous light 21. The multi-order sideband chirped continuous light 21 includes a first-order frequency sweeping sideband 51 with a center frequency of υ0 and a frequency sweeping range of δυ and a first-order frequency sweeping sideband 51 with a center frequency of υ0 and a frequency sweeping range of δυ. n (n≥2), the sweep range is n.δυ(n≥2) with the nth order swept sideband 55;

[0026] S2: Adjust the driving voltage of the optical modulator 201 to change the energy of each modulation sideband and keep the center frequency at υ n The energy of the n-order modulation sweep sideband 55 (n≥2) is the largest; the energy of the carrier and the first-order sweep sideband 51 is suppressed to a certain extent;

[0027] S3: adjusting the attenuator 203 to control the injection ratio of the slave laser so that the slave laser 204 is in an ideal working state;

[0028] S4: Adjust the driving voltage of the slave laser 204 to change the frequency of the output light 24 of the slave laser 204 so that it is consistent with the center frequency υ of the n-order swept sideband 55 n (n≥2) is consistent, so that the slave laser output light 24 is exactly at the center of the n-order swept sideband 55, realizing injection locking of the n-order swept bandwidth. The sideband locked swept continuous light 25 after injection locking only contains the center frequency υ n (n≥2), the sweep range is n·δυ(n≥2) of the nth-order swept sideband, and the rest of the modulation sidebands are suppressed;

[0029] S5: The second output terminal 202b of the signal generator provides a pulse electrical signal 23 with a pulse width of τ to the pulse modulator 206. The pulse modulator 206 modulates the injection-locked sideband-locked swept continuous light 25 into a sideband-locked swept pulse 26 with a pulse width of τ and a sweep range of n.δυ (n≥2).

[0030] The sideband-locked swept pulse 26 is connected to the first optical amplifier input terminal 301a, the first optical amplifier output terminal is connected to the first filter input terminal 302a, the first filter output terminal 302b is connected to the second circulator first terminal 303a, and the second circulator second terminal 303b is connected to the sensing fiber 304. The sideband-locked swept pulse 26 is transmitted in the sensing fiber 304 and generates a backscattered Rayleigh signal 41. The backscattered Rayleigh signal 41 is injected into the second optical amplifier 401 through the second circulator third terminal 303c.

[0031] The first optical amplifier 301 is used to amplify the sideband locked pulse 26 injected into the sensing optical fiber 304 to increase its peak power;

[0032] The first filter 302 is used to filter out the spontaneous amplification radiation generated during the amplification process of the first optical amplifier 301;

[0033] The sensing optical fiber 304 is a single-mode optical fiber, a polarization-maintaining optical fiber or a multi-mode optical fiber.

[0034] The backscattered Rayleigh signal 41 outputted by the third terminal 303c of the second circulator is connected to the second optical amplifier input terminal 401a, the second optical amplifier output terminal 401b is connected to the second filter input terminal 402a, the second filter output terminal 402b is connected to the detector input terminal 403a, the detector output terminal 403b is connected to the acquisition card input terminal 404a, and the acquisition card output terminal 404b is connected to the processor 405;

[0035] The second optical amplifier 401 is used to amplify the Rayleigh scattered signal 41 injected into the detector 403 to increase its peak power;

[0036] The detector 403 is a single-ended photodetector, which is used to convert the received Rayleigh scattered light signal into a beat frequency electrical signal;

[0037] The processor 405 is a high-performance computer used to analyze and process the collected signals and perform related demodulation.

[0038] The specific principle of injection locking to improve system measurement accuracy is as follows:

[0039] When a certain amount of stress is applied to the optical fiber, the backward Rayleigh scattering signal in the disturbance area will produce a time shift of Γ0, which will affect the Rayleigh scattering signal i before and after the disturbance. a (t) and ib After cross-correlating (t), we get formula (1):

[0040] in R ab (Γ) is further expanded to obtain formula (2):

[0041] N(t) represents the noise in the system, which can be regarded as Gaussian white noise, R N It represents the cross-correlation result between the scattering curve and the noise. Since there is no correlation between the signal and the noise, this term can be ignored.

[0042] The first term in formula (2) This represents the cross-correlation result of the scattered signal generated by the m-th-order modulation swept frequency sideband. When only the first-order swept frequency signal exists in the swept frequency signal, only R1 exists in this term, and the delay value corresponding to its correlation peak corresponds to the magnitude of the external disturbance. However, when higher-order harmonics exist in the swept frequency signal, the cross-correlation result in this term will have redundant interference peaks, affecting the accuracy of strain demodulation.

[0043] The second term in formula (2) It represents the cross-correlation result between the scattered signals generated by the m-th order swept frequency sideband. It is the response of different frequency bands, and there is no correlation between the scattered signals.

[0044] A specific analysis is conducted on the case where only the first-order swept frequency sideband and the second-order swept frequency sideband exist, where the second-order swept frequency sideband is regarded as an unnecessary modulation sideband. According to the definition of the frequency domain cross-correlation operation, equation (3) is obtained:

[0045]

[0046] In formula (3), I1(ω) and I2(ω) are the frequency spectra of i1(t) and i2(t), respectively. Expanding them into amplitude spectrum and phase spectrum, we can get: At this time R ab It can be expressed as:

[0047]

[0048] It can be seen from the above formula (4) that since there is no correlation between the first-order swept frequency sideband and the second-order swept frequency sideband scattered signals, the cross-correlation term R 12 and R 21 The influence of can be ignored, so the main influence on the demodulation result is the cross-correlation peak between the second-order swept frequency sideband scattering curves. Therefore, the measurement accuracy of the system can be improved by filtering out the redundant swept frequency modulation sidebands.

[0049] Compared with the prior art, the advantages of the present invention are:

[0050] 1. The present invention is a phase-sensitive optical time-domain reflectometer based on injection-locked chirped pulses. By adjusting the center frequency of a slave laser so that the output wavelength of the slave laser falls at the center of different-order modulation sweep sidebands, sweep signals of different bandwidths can be obtained. In particular, when the center wavelength of the slave laser falls at the center of a high-order sweep sideband, the system sweep range can be expanded. When the output wavelength of the slave laser falls at the center of a second-order sweep sideband, the injection-locked sideband is a second-order sideband, and the optical sweep range is twice the electrical sweep range of the signal generator output. When the output wavelength of the slave laser falls at the center of a third-order sweep sideband, the injection-locked sideband is a third-order sideband, and the optical sweep range is three times the electrical sweep range. This can extend the system sweep range without increasing the cost of system components, thereby improving the system's strain measurement magnitude and response sensitivity.

[0051] 2. Injection locking not only allows for flexible selection of the system sweep bandwidth, but also suppresses unwanted sweep sidebands during signal modulation, eliminating the amplitude error caused by unwanted sideband harmonic interference peaks during the correlation demodulation process, thereby improving the system's measurement accuracy.

[0052] 3. The present invention uses a slave laser to lock the modulation sideband. When the narrow-linewidth laser has wavelength drift, the output wavelength of the slave laser can follow the narrow-linewidth laser within a certain range, solving the problem of laser wavelength drift. Compared with the passive narrowband grating filtering solution, the measurement stability of the system is improved. Description of the drawings:

[0053] Figure 1 Schematic diagram of the structure of a phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses

[0054] Figure 2 Flowchart of the pulse modulation method for injection-locked high-order swept sidebands

[0055] Figure 3 Schematic diagram of how high-order harmonic interference peaks affect cross-correlation results

[0056] Figure 4 Schematic diagram of the backscattered Rayleigh signal generated by the scattering point in the detection pulse

[0057] Figure 5 Schematic diagram of injection locking for different order sidebands Specific implementation methods:

[0058] In order to more clearly illustrate the phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses 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.

[0059] Figure 1 The schematic diagram of the structure of a phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses is shown, which includes four parts: a narrow linewidth laser 1, a signal modulation and injection locking module 2, a sensing module 3, and a signal demodulation module 4.

[0060] The optical modulator 201 is a single-sideband intensity modulator;

[0061] The pulse modulator 207 is a semiconductor optical amplifier with an extinction ratio of 32 dB;

[0062] The first optical amplifier 301 and the second optical amplifier 401 are both erbium-doped fiber amplifiers;

[0063] The first filter 302 and the second filter 402 are both 100 GHz dense wavelength division multiplexing filters;

[0064] Sensing fiber 304 single-mode fiber;

[0065] Detector 403 is an InGaAs single-ended detector with a bandwidth of 4 GHz;

[0066] The sampling rate of the acquisition card 404 is 10Gsa / s;

[0067] Figure 2 This is a flow chart of the pulse modulation method for injection-locked high-order swept sidebands. The specific steps are as follows:

[0068] S1: One channel of the signal generator 203 outputs a linear sweep signal 22 with a pulse width of 200ns and a sweep frequency range of 1GHz to drive the optical modulator 201, and another channel generates a synchronous pulse signal 23 with a pulse width of 100ns to drive the pulse modulator 207 for synchronous output.

[0069] The narrow-linewidth laser 1 outputs a single-frequency continuous light 11 with a wavelength of 1550.12 nm. After passing through the single-sideband modulator 201, it is modulated into a multi-order swept-sideband chirped continuous light 21, which mainly includes a carrier with a central wavelength of 1550.12 nm, a first-order swept sideband 51 with a central wavelength of 1550.1 nm and a sweep range of 1 GHz, a second-order swept sideband 53 with a central wavelength of 1550.07 nm and a sweep range of 2 GHz, and the remaining n-order swept sidebands 55.

[0070] S2: adjusting the driving voltage of the single optical modulator 201 to ensure that the energy of the second-order swept sideband 53 in the modulated multi-order sideband chirped continuous light 21 is the largest, and the multi-order sideband chirped continuous light 21 is injected into the slave laser 204 through the first circulator 205 .

[0071] S3: Adjust the attenuator 203 to attenuate the optical power of the multi-order sideband chirped continuous light 21 injected into the slave laser 204 to 10uW. At this time, the injection ratio of the slave laser 204 is 27dB, which is in an ideal working state.

[0072] S4: Adjust the slave laser drive voltage to control the wavelength of the laser output light to be 1550.07 nm at the center of the second-order swept sideband 53, thereby achieving injection locking of the second-order modulation bandwidth;

[0073] After injection locking, the multi-order sideband chirped continuous light 21 contains only the second-order swept sideband 53 with a center frequency of 1550.07 nm and a sweep range of 2 GHz. The carrier, the first-order swept sideband 51, and other n-order swept sidebands 55 are all suppressed, with a suppression ratio of 35 dB.

[0074] S5: The injection-locked multi-order sideband swept continuous light 21 is injected into the pulse modulator 206 through the third end 205c of the first circulator, and is intercepted into a second-order sideband swept pulse 54 with a pulse width of 100ns, a sweep frequency range of 2GHz, and a repetition rate of 20kHz; its sweep frequency range is widened to twice the output electrical pulse signal of the signal generator, which is 2GHz.

[0075] The modulated second-order sideband swept-frequency pulse 54 is injected into the sensing module 3, amplified to 200 mW by the first optical amplifier 301, and then filtered out by the first filter 302 to remove the spontaneous amplification radiation noise of the first optical amplifier 301. The pulse is then injected into the sensing optical fiber 304 through the second end 303b of the second circulator. During the transmission of the second-order sideband swept-frequency pulse 54 in the sensing optical fiber 304, the internal scattering points of the pulse interfere with each other to form a backward Rayleigh scattered signal 41, which is injected into the signal demodulation module 4 through the third end 303c of the second circulator.

[0076] The backscattered Rayleigh signal 41 is amplified to an optical power of 2 mW by the second optical amplifier 401, and then passes through the second filter 402 to filter out the spontaneous amplification radiation noise of the second optical amplifier 401. It enters the detector 403 and is converted into a beat frequency electrical signal. Its spectrum mainly contains the second-order sideband self-beat frequency signal, and the beat frequency interference signals of the redundant modulation sidebands are all suppressed. Its spectrum distribution is [0, 2 GHz].

[0077] The acquisition card 404 performs analog-to-digital conversion on the beat frequency electrical signal output by the detector 403 and transmits it to the processor 405 for processing. The measured Rayleigh scattering pattern is cross-correlated with the reference pattern according to a certain window length. The Rayleigh scattering pattern at the vibration position will be offset. The disturbance area and strain magnitude are determined by the location and size of the cross-correlation peak. The strain magnitude is determined by the offset of the cross-correlation peak, that is, Where K is the frequency sweep rate and Δt is the cross-correlation peak offset.

[0078] According to formula (4), the main factors that affect the demodulation results in the correlation demodulation process are the cross-correlation peak R1(Γ) between the first-order swept-frequency sideband scattering curves and the cross-correlation peak R2(Γ) between the second-order swept-frequency sideband scattering curves. and the cross-correlation peaks between the n-order swept sideband scattering curves When the beat signal contains only the second-order swept sideband 53, the cross-correlation result is given by Dominant, unwanted sideband cross-correlation interference peak R1(Γ) and The influence on the cross-correlation result is negligible, and the measurement accuracy of the system is improved.

[0079] Each component in the above embodiments may be a commercial product on the market. The present invention is intended to protect their connection relationship and implementation principle, and therefore does not limit the model of each product itself. The positional relationship described in the drawings is for illustrative purposes only and should not be understood as a limitation of this patent.

[0080] As can be seen from the specific examples, the present invention proposes a phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses, which eliminates the influence of redundant harmonic interference peaks on the cross-correlation results during the correlation demodulation process, improves the measurement accuracy of the system, and by locking the high-order sweep sidebands, widens the system sweep range, improves the strain measurement range and response sensitivity, and expands the application scenarios of the system.

[0081] 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. A person skilled in the art would be able to make other variations or modifications 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. A phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses, comprising a narrow linewidth laser (1), a signal modulation and injection locking module (2), a sensing module (3) and a signal demodulation module (4), characterized in that: In the signal modulation and injection locking module (2), the signal modulation and injection locking module (2) is composed of an optical modulator (201), a signal generator (202), an attenuator (203), a slave laser (204), a first circulator (205), a pulse modulator (206) and a driver (207); the narrow linewidth laser output end (101a) is connected to the optical modulator input end (201a); the optical modulator drive end (201c) is connected to the first output end ( 202a); the optical modulator output end (201b) is connected to the first end (205a) of the first circulator through the attenuator (203), and the second end (205b) of the first circulator is connected to the slave laser (204); the third end (205c) of the first circulator is connected to the pulse modulator input end (206a); the pulse modulator driving end (206c) is connected to the driver output end (207b), and the driver input end (207a) is connected to the second output end (202 b), the pulse modulator output end (206b) is connected to the first optical amplifier input end (301a); the first output end (202a) of the signal generator outputs a sweeping frequency electrical signal (22) with a starting frequency of υ0 and a sweeping frequency range of δυ to drive the optical modulator (201), modulating the single-frequency continuous light (11) with a frequency of υ into a multi-order sideband chirped continuous light (21); the second output end (202b) of the signal generator outputs a pulse electrical signal (23) with a pulse width of τ to drive the pulse The modulator (206) modulates the continuous light into pulses; the optical modulator (201) is an intensity modulator or a frequency modulator, and is used to generate multi-order sideband chirped continuous light (21); the attenuator (203) is used to attenuate the multi-order sideband chirped continuous light (21) injected into the slave laser (204) to reduce its peak optical power; the multi-order sideband chirped continuous light (21) comprises a carrier, a first-order swept sideband (51) with a center frequency of υ1 and a sweep range of δυ, and a second-order swept sideband (51) with a center frequency of υ n , n≥2, the sweep range is n·δυ, n≥2, the nth order sweep sideband (55); the pulse modulator (206) is an acousto-optic modulator or a semiconductor optical amplifier, which is used to generate high extinction ratio optical pulses, and the extinction ratio ER is ≥30dB.

2. According to the phase-sensitive optical time domain reflectometer based on injection-locked chirped pulses according to claim 1, the pulse modulation method performed by the signal modulation and injection locking module (2) comprises the following steps: S1: The first output terminal (202a) of the signal generator emits a frequency sweeping electrical signal (22) with a starting frequency of υ0 and a frequency sweeping range of δυ, driving the optical modulator (201) to modulate the single-frequency continuous light (11) with a frequency of υ output by the narrow linewidth laser (1) into a multi-order sideband chirped continuous light (21). The multi-order sideband chirped continuous light (21) includes a carrier, a first-order frequency sweeping sideband (51) with a center frequency of υ0 and a frequency sweeping range of δυ, and a first-order frequency sweeping sideband (51) with a center frequency of υ n , n≥2, the sweep range is n·δυ, n≥2, the nth-order swept sideband (55); S2: Adjust the driving voltage of the optical modulator (201), change the energy of each modulation sideband, and keep the center frequency at υ n , n≥2, the sweep range is n·δυ, and the energy of the nth-order modulation sweep sideband (55) is the largest when n≥2; and the energy of the carrier and the first-order sweep sideband (51) is suppressed to a certain extent; S3: adjusting the attenuator (203) to control the injection ratio of the slave laser (204) so that the slave laser 204 is in an ideal working state; S4: Adjust the driving voltage of the slave laser (204) to change the frequency of the output light (24) of the slave laser (204) to ensure that it is consistent with the center frequency υ of the n-order swept sideband (55). n , n≥2, so that the output light (24) of the slave laser is exactly at the center of the n-order sweep sideband (55), and the injection locking of the n-order sweep bandwidth is realized. The sideband-locked sweep continuous light (25) after injection locking only contains the center frequency υ n , n ≥ 2, the sweep range is n·δυ, n ≥ 2, the nth-order sweep sideband (55), and the rest of the modulation sidebands are suppressed; S5: The second output terminal (202b) of the signal generator provides a pulse electrical signal (23) with a pulse width of τ to the pulse modulator (206). The pulse modulator (206) modulates the injection-locked sideband-locked swept-frequency continuous light (25) into a sideband-locked swept-frequency pulse (26) with a pulse width of τ and a sweep frequency range of n·δυ, where n≥2.

3. The phase-sensitive optical time domain reflectometer based on injection-locked chirped pulse according to claim 2, characterized in that In the sensing module (3), a sideband-locked frequency sweep pulse (26) is connected to the input end (301a) of a first optical amplifier, an output end of the first optical amplifier is connected to the input end (302a) of a first filter, an output end (302b) of the first filter is connected to the first end (303a) of a second circulator, and a second end (303b) of the second circulator is connected to a sensing optical fiber (304). The sideband-locked frequency sweep pulse (26) is transmitted in the sensing optical fiber (304) and generates a backward Rayleigh scattered signal (41); the backward Rayleigh scattered signal (41) is injected into the signal demodulation module (4) through the third end (303c) of the second circulator; the first optical amplifier (301) is used to amplify the sideband-locked pulse (26) injected into the sensing optical fiber (304) to increase its peak power; The first filter (302) is used to filter out the spontaneous emission noise generated during the amplification process of the first optical amplifier (301); and the sensing optical fiber (304) is a single-mode optical fiber, a polarization-maintaining optical fiber, or a multi-mode optical fiber.

4. The phase-sensitive optical time domain reflectometer based on injection-locked chirped pulse according to claim 1, characterized in that: In the signal demodulation module (4), the backscattered Rayleigh scattering signal (41) outputted by the third end (303c) of the second circulator is connected to the input end (401a) of the second optical amplifier, the output end (401b) of the second optical amplifier is connected to the input end (402a) of the second filter, the output end (402b) of the second filter is connected to the input end (403a) of the detector, the output end (403b) of the detector is connected to the input end (404a) of the acquisition card, and the output end (404b) of the acquisition card is connected to the processor (405); the second optical amplifier (401) is used to amplify the backscattered Rayleigh scattering signal (41) injected into the detector (403) to increase its peak power; the detector (403) is a single-ended photodetector, used to convert the received backscattered Rayleigh scattering signal (41) into a beat frequency electrical signal; and the processor (405) is a high-performance computer, used to analyze and process the collected signal and perform correlation demodulation.

5. The phase-sensitive optical time domain reflectometer based on injection-locked chirped pulse according to claim 1, characterized in that: The slave laser (204) in the signal modulation and injection locking module (2) performs the following steps: 1) The slave laser (204) is configured to adjust the frequency of the slave laser output light (24) and the center frequency υ of the n-order sweep sideband (55) by changing the driving voltage. n , n≥1, the sideband locked swept continuous light (25) after injection locking only contains the center frequency υ n , n ≥ 1, the sweep range is n·δυ, n ≥ 1, the nth-order sweep sideband (55), and the rest of the modulation sidebands are suppressed; 2) The injection ratio k of the slave laser (204) needs to satisfy the condition k≥10, and the slave laser (204) is in an ideal working state.

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