Implementation method and system of spectral domain reflectometer

Abstract

The present invention provides a spectral domain reflectometer system and an implementation method, comprising: a light source module generates a local optical signal and a detection optical signal with a comb spectrum, the local optical signal is directly connected to a coherent detection module, a portion of the detection optical signal enters an optical fiber to be tested after passing through a passive optical path module, a backscattered signal returned from the optical fiber to be tested enters the coherent detection module through the passive optical path module, beats with the local light and outputs a sensing electrical signal; the other portion directly enters the coherent detection module, beats with the local light and outputs a reference electrical signal; both the sensing electrical signal and the reference electrical signal are input into a signal processing module for data demodulation, and an intensity and phase distribution signal of the backscattered signal on the optical fiber link is obtained.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a method and system for implementing a spectral domain reflectometer, and more particularly to a method and system for detecting backscattering in an optical fiber and determining its intensity and phase. Background Art

[0002] Optical reflectometry is a technology that can detect and locate backscattered light (such as Rayleigh scattering) in optical fibers. By analyzing the intensity or phase of backscattered light signals at different locations along the fiber, it can detect fiber link loss and measure physical quantities such as environmental strain and temperature.

[0003] Based on the positioning principle of backscattered light signals, existing optical reflectometers mainly include three types: optical time domain reflectometer, optical frequency domain reflectometer and optical coherence domain reflectometer.

[0004] The optical time-domain reflectometer emits a detection pulse, receives the backscattered light generated by the detection pulse, and determines the location of the scattering based on the time it takes for the backscattered light to return. The shorter the duration of the detection pulse, the higher the spatial resolution, but the worse the signal-to-noise ratio of the backscattered light. The contradiction between spatial resolution and detection signal-to-noise ratio makes the spatial resolution of this type of reflectometer low, generally greater than 1 meter.

[0005] Optical frequency domain reflectometry uses a linearly tuned light source and coherent reception to beat the scattered light signal with the local light, mapping the time delay of the scattered light signal to the frequency of the beat signal. The spatial resolution of this scheme depends on the frequency tuning range of the light source and is no longer limited by the duration of the detection light. However, this scheme requires a highly linear, low-phase-noise swept-frequency light source, which is very expensive.

[0006] Optical coherence domain reflectometry uses low-coherence light as the light source. Interference signals can only be observed when the optical path of the scattered light is the same as that of the local light. This can achieve very high spatial resolution, but the measurement distance is generally very short.

[0007] Patent document CN113014313A (application number: 201911328434.3) discloses an optical time domain reflectometer, which includes: a laser for emitting a detection light source; a modulator for converting the detection light source into a first pulse signal and a second pulse signal and for sending the first pulse signal to the optical fiber to be tested, so that the optical fiber to be tested generates a reflected signal; a coupler for coupling the second pulse signal and the reflected signal of the optical fiber to be tested into an optical signal; a photoelectric conversion module for converting the optical signal into an electrical signal; and a programmable module for adjusting the detection light source emitted by the laser according to the electrical signal.

[0008] Patent document CN114964329A (application number: 202210559130.3) discloses a double-sideband optical frequency domain reflectometer, including: a modulation signal generating unit, a sensor signal receiving unit and a signal processing unit. The modulation signal generating unit generates a double-sideband detection light wave through external modulation and divides the detection light wave into two paths, one path is used as the detection light input to the optical fiber to be tested, and the other path is used as the local light input to the sensor signal receiving unit. The optical fiber to be tested couples the changes in external physical quantities to the detection light wave and transmits the generated backward Rayleigh scattering signal as signal light back to the sensor signal receiving unit. The sensor signal receiving unit uses the frequency shift method or the IQ reception method to separate the two different beat frequency signals generated by the two sideband sweeps from the double-sideband signal light. The signal processing unit aligns the two different beat frequency signals in the time domain according to the sweep range and performs Fourier transform to obtain the intensity and phase information of Rayleigh scattering on the optical fiber.

[0009] Patent document CN203617996U (application number: 201320800522.0) discloses a coherent optical time-domain reflectometer device, characterized by comprising a laser, an optical beam splitter, a pair of pulse generators, an optical circulator, and a photodetector. A coherent optical time-domain reflectometry method is described, characterized by using test pulse light to obtain scattering / reflection information of the device under test, using local pulse light to interfere with the scattered / reflected light signal, and adjusting the repetition frequency of the test pulse light and the local pulse light to completely construct the reflected / scattered light signal. Then, through photoelectric conversion and analog-to-digital conversion, the scattered / reflected light position information is obtained. The pulse widths of the test pulse light and the local pulse light are adapted to the required spatial resolution, and the distance between adjacent pulses is much greater than the pulse width. Summary of the Invention

[0010] In view of the defects in the prior art, the present invention aims to provide a spectral domain reflectometer system and implementation method.

[0011] According to the present invention, a spectral domain reflectometer system includes: a light source module generates a local optical signal and a detection optical signal with a comb spectrum, the local optical signal is directly connected to a coherent detection module, a portion of the detection optical signal enters the optical fiber to be tested after passing through a passive optical path module, a backscattered signal returned from the optical fiber to be tested enters the coherent detection module through the passive optical path module, beats with the local light and outputs a sensing electrical signal; the other portion directly enters the coherent detection module, beats with the local light and outputs a reference electrical signal; both the sensing electrical signal and the reference electrical signal are input into a signal processing module for data demodulation to obtain an intensity and phase distribution signal of the backscattered signal on the optical fiber link.

[0012] Preferably, the light source module is a single optical comb light source module, which includes: a narrow linewidth laser light source or an optical frequency comb light source, a signal generator, a phase or intensity modulator, an acousto-optic modulator, a first coupler and an optical filter;

[0013] The narrow-linewidth laser light source is divided into a local optical path and a detection optical path through the first coupler; the local optical path is input into the acousto-optic modulator to cause the narrow-band laser to produce a frequency shift, thereby obtaining a local optical signal; the narrow-band laser corresponding to the detection optical path is modulated by the periodic signal generated by the signal generator in the phase or modulator to produce a detection optical signal with a comb spectrum.

[0014] The optical frequency comb light source is divided into a local optical path and a detection optical path by the first coupler; the local optical path is input into the optical filter for filtration to obtain a single-frequency comb tooth and a local optical signal; the detection optical path is the optical signal with a comb spectrum generated by the optical frequency comb light source.

[0015] Preferably, the light source module is a dual-comb light source module, which simultaneously generates two optical frequency combs with slightly different repetition frequencies, which serve as local light and detection light respectively.

[0016] Preferably, the passive optical path module includes a first coupler, a third coupler and an optical circulator;

[0017] The detection optical signal with a comb spectrum enters the first coupler and is divided into two paths. The optical signal with larger energy enters the optical circulator and is connected to the optical fiber to be tested, and the optical signal with smaller energy enters the fourth coupler; the backscattered signal returned from the optical fiber to be tested enters the second coupler; the local optical signal enters the third coupler, the optical signal with relatively high splitting enters the second coupler, and the optical signal with relatively small splitting enters the fourth coupler.

[0018] Preferably, the coherent detection module comprises: a second coupler, a fourth coupler, a first balanced photodetector and a second balanced photodetector;

[0019] The local light output by the passive optical path module and the detection light signal beat at the second coupler and the fourth coupler respectively, and the generated beat light signals are input into the first balanced photodetector and the second balanced photodetector respectively; the first balanced photodetector and the second balanced photodetector convert the beat light signals into electrical signals and output a sensing electrical signal and a reference electrical signal respectively.

[0020] Preferably, the signal processing module includes: a data acquisition card and a digital signal processor;

[0021] The input sensing electric signal and reference electric signal are collected and stored by the data acquisition card, and the collected sensing electric signal and reference electric signal are input into the digital signal processor for signal demodulation.

[0022] Preferably, in the signal processing module, an analog-to-digital converter is used to digitize the sensing electrical signal and the reference electrical signal, and then a Fourier transform is used to obtain the frequency spectra of the sensing electrical signal and the reference electrical signal respectively. The frequency spectrum of the reference electrical signal is conjugated in phase, the modulus value is taken as the inverse, and then multiplied with the frequency spectrum of the sensing electrical signal. The result is inverse Fourier transformed to obtain the intensity and phase information of the backscattered signal on the optical fiber to be tested.

[0023] According to the present invention, a method for implementing a spectral domain reflectometer includes: a light source module generates a local optical signal and a detection optical signal with a comb spectrum, the local optical signal is directly connected to a coherent detection module, a portion of the detection optical signal enters the optical fiber to be tested after passing through a passive optical path module, a backscattered signal returned from the optical fiber to be tested enters the coherent detection module through the passive optical path module, beats with the local light, and outputs a sensing electrical signal; the other portion directly enters the coherent detection module, beats with the local light, and outputs a reference electrical signal; both the sensing electrical signal and the reference electrical signal are input into a signal processing module for data demodulation to obtain an intensity and phase distribution signal of the backscattered signal on the optical fiber link.

[0024] Preferably, when the light source module is a single-comb light source module, the light source module includes: a narrow-linewidth laser light source, a pulse generator, a phase modulator, an acousto-optic modulator and a first coupler;

[0025] The narrow-linewidth laser light source is divided into a local optical path and a detection optical path via the first coupler; the local optical path is input into the acousto-optic modulator to cause the narrow-band laser to undergo frequency shift, thereby obtaining a local optical signal; the narrow-band laser corresponding to the detection optical path is pulse-modulated by the pulse generator in the phase modulator to generate a detection optical signal having a comb-shaped spectrum;

[0026] When the light source module is a dual-comb light source module, the light source module includes: a narrow linewidth laser light source, a pulse generator, a first phase modulator, a second phase modulator, a first coupler, a first optical filter, and a second optical filter;

[0027] The narrow-linewidth laser light source is evenly divided into a local optical path and a detection optical path through the first coupler; the local optical path and the detection optical path are respectively input into the first phase modulator and the second phase modulator, and the first phase modulator and the second phase modulator are respectively modulated by the pulse generator to generate different sequences; the output optical signal of the first phase modulator enters the first optical filter for filtering processing to obtain an optical comb signal within the required frequency range, and is output as a detection optical signal; the output light of the second phase modulator enters the second optical filter for filtering processing to obtain an optical comb signal within the required frequency range, and is output as a local optical signal.

[0028] Preferably, the passive optical path module includes a second coupler, a fourth coupler and an optical circulator;

[0029] The detection optical signal with a comb spectrum enters the second coupler to obtain an optical signal with 90% energy and an optical signal with 10% energy respectively; the optical signal with 90% energy enters the optical circulator to connect to the optical fiber to be tested, and the optical signal with 10% energy enters the fifth coupler; the backscattered signal returned from the optical fiber to be tested enters the third coupler; the local optical signal with a comb spectrum enters the fourth coupler to obtain an optical signal with 90% energy and an optical signal with 10% energy respectively; the optical signal with 90% energy enters the third coupler, and the optical signal with 10% energy enters the fifth coupler;

[0030] The coherent detection module includes: a third coupler, a fifth coupler, a first balanced photodetector, and a second balanced photodetector;

[0031] The local light output by the passive optical path module and the detection light signal beat at the third coupler and the fifth coupler, respectively, and the generated beat frequency light signals are input into the first balanced photodetector and the second balanced photodetector, respectively; the first balanced photodetector and the second balanced photodetector convert the beat frequency light signals into electrical signals, and output a sensing electrical signal and a reference electrical signal, respectively;

[0032] The signal processing module includes: a data acquisition card and a digital signal processor;

[0033] The input sensor electrical signal and reference electrical signal are collected and stored by the data acquisition card, and the collected sensor electrical signal and reference electrical signal are input into the digital signal processor for signal demodulation;

[0034] In the signal processing module, an analog-to-digital converter is used to digitize the sensing electrical signal and the reference electrical signal, and then a Fourier transform is used to obtain the frequency spectra of the sensing electrical signal and the reference electrical signal respectively. The frequency spectrum of the reference electrical signal is conjugated in phase, the modulus value is taken as the inverse, and then multiplied with the frequency spectrum of the sensing electrical signal. The result is subjected to an inverse Fourier transform to obtain the intensity and phase information of the backscattered signal on the optical fiber to be tested.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. This invention utilizes the technical features of continuous light and spectrum sampling to overcome the contradiction between spatial resolution and detection signal-to-noise ratio, achieving the technical effect of higher spatial resolution and dynamic range;

[0037] 2. The present invention, through the technical features of a non-swept frequency light source (i.e., an optical comb), avoids frequency sweep nonlinearity, greatly simplifies system complexity, and ensures stable and accurate system performance.

[0038] 3. The present invention uses the technical features of a coherent light source to achieve the technical effect that the signal can be observed without adjusting the coherence length as long as the optical path difference between the detection path and the reference path does not exceed the coherence length of the light source without performing phase noise compensation.

[0039] 4. The present invention avoids a series of problems caused by the frequency-sweep nonlinearity of the swept-frequency light source, reduces the cost and system complexity of optical frequency domain reflectometry; compared with optical time domain reflectometry and optical coherence domain reflectometry, it has high positioning accuracy and signal-to-noise ratio and a longer measurable distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0041] Figure 1 This is the system block diagram of the spectral domain reflectometer solution.

[0042] Figure 2 This is a diagram of the module of a single-frequency laser source as a single-comb light source.

[0043] Figure 3 Module diagram of an optical frequency comb as a single optical comb light source.

[0044] Figure 4 It is a dual-comb light source module.

[0045] Figure 1Middle: 1-light source module, 2-optical coupler, 3-optical circulator, 4-second coupler, 5-third coupler, 6-fourth coupler, 7-first balanced detector, 8-second balanced detector, 9-data acquisition card, 10-signal processing unit.

[0046] Figure 2 Middle: 1- narrow linewidth laser source, 2- optical coupler, 3- signal generator, 4- modulator, 5- modulator.

[0047] Figure 3 Middle: 1- optical frequency comb laser source, 2- optical coupler, 3- optical filter.

[0048] Figure 4 Middle: 1-Dual-comb laser source. DETAILED DESCRIPTION

[0049] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0050] Example 1

[0051] In response to the shortcomings of existing reflectometers in terms of performance indicators and device costs, the present invention proposes a spectral domain reflectometer method and system. By utilizing a detection light signal with a comb spectrum, distributed measurement of the sensor elements to be measured can be achieved without frequency scanning. High spatial resolution can be achieved, the adverse effects caused by frequency scanning nonlinearity can be avoided, and the system structure can be simplified.

[0052] like Figure 1As shown, the present invention discloses a spectral domain reflectometer system using a single optical comb, comprising: a light source module, a passive optical path module, a coherent detection module, and a signal processing module. The output of the light source module is divided into a detection optical path and a local optical path, which are respectively input into a first coupler 2 and a third coupler 5. The first coupler 2 splits the incident detection optical path into two parts. The part with higher energy enters port 1 of an optical circulator 3 and is output to the optical fiber under test through port 2. The Rayleigh backscattered light generated by the optical fiber under test enters the optical circulator 3 through port 2 and enters the second coupler 4 through port 3. The part with lower energy enters the fourth coupler 6. The local light is divided into two parts with equal energy by the third coupler 5, and is respectively input into the second coupler 4 and the fourth coupler 6. The local light and the detection light signal beat at the second coupler 4 and the fourth coupler 6, and the generated beat frequency light signals are input into the first balanced photodetector 7 and the second balanced photodetector 8 respectively; the balanced photodetectors convert the beat frequency light signals into electrical signals and input them into the data acquisition card 9 for subsequent signal processing and data demodulation to obtain the intensity and phase of the backward scattered light.

[0053] The passive optical path module includes: a first coupler 2, a third coupler 5 and an optical circulator 3, wherein the first coupler 2 is a 90:10 fiber coupler, 90% of the output ports are port 1 and 10% of the output ports are port 2, and the third coupler 5 is a 50:50 coupler.

[0054] The coherent detection module includes a second coupler 4, a fourth coupler 6, a first balanced detector 7, and a second balanced detector 8. The second coupler 4 and the fourth coupler 6 are both 50:50 couplers.

[0055] The bandwidth of the first balanced detector 7 and the second balanced detector 8 are both 1.6 GHz.

[0056] The signal processing module includes a data acquisition card 9 and a signal processing unit 10 .

[0057] The data acquisition card 9 samples the input electrical signal and inputs the raw data into the signal processing unit 10 for data demodulation.

[0058] The sampling rate f of the data acquisition card 9 is c =1GHz, resolution is 8bit.

[0059] The specific steps of this embodiment are as follows:

[0060] Step 1: Turn on the laser and put the light source module into working state. Record the optical power signals detected by the two balanced detectors. The output electrical signal of the first balanced detector can be used to obtain the detection light receiving signal I1(t). Perform Fourier transform on it to obtain the frequency domain information I1(f) of the detection path electrical signal.

[0061] Step 2: After obtaining the signals received by the first and second balanced detectors, perform Fourier transform on the output signal I2(t) of the second balanced detector to obtain the frequency domain information I2(f), and multiply I1(f) by Then divide it by the product of the amplitudes of I1(f) and I2(f), that is Where * indicates conjugation.

[0062] Step 3: Perform inverse Fourier transform on R(f) to obtain the Rayleigh reflectivity curve, that is, {R(t) = IFFT(R(f))}. The position of a point on the optical fiber to be tested is Where: c is the speed of light in vacuum, n is the effective refractive index of the optical fiber, f c is the system sampling rate in Hertz (Hz), and k is the index value corresponding to the point.

[0063] Step 4: Zoom in at the reflection peak position to obtain spatial resolution. The spatial resolution of this embodiment is determined by the frequency coverage of the detection optical frequency comb, i.e. Where B is the frequency coverage bandwidth of the optical comb, and the actual spatial resolution is defined by the full width at half maximum of the reflection peak.

[0064] Example 2

[0065] Example 2 is a method for implementing a single light comb system light source module. Figure 2 As shown, this embodiment includes: a narrow linewidth laser source 1, a first coupler 2, a signal generator 3, a modulator 4, and an acousto-optic modulator 5.

[0066] Preferably, the narrow linewidth laser source has a linewidth of less than 1 kHz;

[0067] The coupler is a 50:50 fiber coupler;

[0068] The modulator is a phase or intensity modulator,

[0069] The specific steps of this embodiment are as follows:

[0070] Step 1: First, load pre-programmed data into the signal generator 3. Connect the output signal to the phase or intensity modulator 4. Turn on the laser 1. The output optical signal is split into two equal energy components by the first coupler 2. One component enters the phase or intensity modulator 4, and the other enters the acousto-optic modulator 5. The outputs of the phase or intensity modulator 4 and the acousto-optic modulator 5 serve as the detection path and local path optical signals, respectively, and are connected to the subsequent optical system.

[0071] Example 3

[0072] Example 3 is a method for implementing a single light comb system light source module. Figure 3 As shown, this embodiment includes: an optical frequency comb laser source 1 , a first coupler 2 , and an optical filter 3 .

[0073] The optical filter is a tunable optical filter.

[0074] The specific steps of this embodiment are as follows:

[0075] Laser 1 is turned on, and the output optical signal is divided into two parts with equal energy through the first coupler 2. One part is directly output as the detection path signal and connected to the subsequent optical path, while the other part enters the optical filter 3. The center frequency of the optical filter 3 is adjusted, and a comb tooth at a frequency is selected as the local path optical signal to be connected to the subsequent optical system.

[0076] Example 4

[0077] Example 4 is a method for implementing a dual-comb system light source module. Figure 4 As shown, this embodiment includes: a dual-comb light source 1.

[0078] The dual-comb light source can be generated by electro-optical modulation or mode-locked laser;

[0079] The specific steps of this embodiment are as follows:

[0080] Put the dual-comb light source into working state and connect it to the subsequent optical system.

[0081] Those skilled in the art will appreciate that, in addition to implementing the system, device, and various modules provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, embedded microcontrollers, and the like by logically programming the method steps. Therefore, the system, device, and various modules provided by the present invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; the modules for implementing various functions can also be considered both software programs for implementing the method and structures within the hardware component.

[0082] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A spectral domain reflectometer system, characterized in that: include: The light source module generates a local optical signal and a detection optical signal with a comb spectrum. The local optical signal is directly connected to the coherent detection module. After passing through the passive optical path module, a portion of the detection optical signal enters the optical fiber to be tested. The backscattered signal returned from the optical fiber to be tested enters the coherent detection module through the passive optical path module, beats with the local light, and outputs a sensing electrical signal; the other portion directly enters the coherent detection module, beats with the local light, and outputs a reference electrical signal. Both the sensing electrical signal and the reference electrical signal are input into the signal processing module for data demodulation to obtain the intensity and phase distribution signal of the backscattered signal on the optical fiber link. The passive optical path module includes a first coupler, a third coupler and an optical circulator; The detection light signal with a comb spectrum enters the first coupler and is divided into two paths. The light signal with a larger energy enters the optical circulator and is connected to the optical fiber to be tested, and the light signal with a smaller energy enters the fourth coupler; the backscattered signal returned from the optical fiber to be tested enters the second coupler; The local optical signal enters the third coupler, the optical signal with a relatively high beam splitting rate enters the second coupler, and the optical signal with a relatively low beam splitting rate enters the fourth coupler; The coherent detection module includes: a second coupler, a fourth coupler, a first balanced photodetector and a second balanced photodetector; The local light output by the passive optical path module and the detection light signal beat at the second coupler and the fourth coupler respectively, and the generated beat frequency light signals are input into the first balanced photodetector and the second balanced photodetector respectively; the first balanced photodetector and the second balanced photodetector convert the beat frequency light signals into electrical signals, and output a sensing electrical signal and a reference electrical signal respectively; The signal processing module includes: a data acquisition card and a digital signal processor; The input sensing electric signal and reference electric signal are collected and stored by the data acquisition card, and the collected sensing electric signal and reference electric signal are input into the digital signal processor for signal demodulation.

2. The spectral domain reflectometer system according to claim 1, wherein: The light source module is a single optical comb light source module, which includes: a narrow linewidth laser light source or an optical frequency comb light source, a signal generator, a phase or intensity modulator, an acousto-optic modulator, a first coupler and an optical filter; The narrow-linewidth laser light source is divided into a local optical path and a detection optical path via the first coupler; the local optical path is input into the acousto-optic modulator to cause the narrow-band laser light to undergo frequency shift, thereby obtaining a local optical signal; the narrow-band laser light corresponding to the detection optical path is modulated by the periodic signal generated by the signal generator in the phase or intensity modulator to generate a detection optical signal having a comb-shaped spectrum; The optical frequency comb light source is divided into a local optical path and a detection optical path by the first coupler; the local optical path is input into the optical filter for filtration to obtain a single-frequency comb tooth and a local optical signal; the detection optical path is the optical signal with a comb spectrum generated by the optical frequency comb light source.

3. The spectral domain reflectometer system according to claim 1, wherein: The light source module is a dual-comb light source module, which simultaneously generates two optical frequency combs with slightly different repetition frequencies, which serve as local light and detection light respectively.

4. The spectral domain reflectometer system according to claim 1, wherein: In the signal processing module, an analog-to-digital converter is used to digitize the sensing electrical signal and the reference electrical signal, and then a Fourier transform is used to obtain the frequency spectra of the sensing electrical signal and the reference electrical signal respectively. The frequency spectrum of the reference electrical signal is conjugated in phase, the modulus value is taken as the inverse, and then multiplied with the frequency spectrum of the sensing electrical signal. The result is subjected to an inverse Fourier transform to obtain the intensity and phase information of the backscattered signal on the optical fiber to be tested.

5. A method for implementing a spectral domain reflectometer, characterized in that: include: The light source module generates a local optical signal and a detection optical signal with a comb spectrum. The local optical signal is directly connected to the coherent detection module. After passing through the passive optical path module, a portion of the detection optical signal enters the optical fiber to be tested. The backscattered signal returned from the optical fiber to be tested enters the coherent detection module through the passive optical path module, beats with the local light, and outputs a sensing electrical signal; the other portion directly enters the coherent detection module, beats with the local light, and outputs a reference electrical signal. Both the sensing electrical signal and the reference electrical signal are input into the signal processing module for data demodulation to obtain the intensity and phase distribution signal of the backscattered signal on the optical fiber link. The passive optical path module includes a second coupler, a fourth coupler and an optical circulator; The detection optical signal with a comb spectrum enters the second coupler to obtain an optical signal with 90% energy and an optical signal with 10% energy respectively; the optical signal with 90% energy enters the optical circulator and is connected to the optical fiber to be tested, and the optical signal with 10% energy enters the fifth coupler; the backscattered signal returned from the optical fiber to be tested enters the third coupler; the local optical signal with a comb spectrum enters the fourth coupler to obtain an optical signal with 90% energy and an optical signal with 10% energy respectively; The optical signal with 90% energy enters the third coupler, and the optical signal with 10% energy enters the fifth coupler; The coherent detection module includes: a third coupler, a fifth coupler, a first balanced photodetector, and a second balanced photodetector; The local light output by the passive optical path module and the detection light signal beat at the third coupler and the fifth coupler, respectively, and the generated beat frequency light signals are input into the first balanced photodetector and the second balanced photodetector, respectively; the first balanced photodetector and the second balanced photodetector convert the beat frequency light signals into electrical signals, and output a sensing electrical signal and a reference electrical signal, respectively; The signal processing module includes: a data acquisition card and a digital signal processor; The input sensor electrical signal and reference electrical signal are collected and stored by the data acquisition card, and the collected sensor electrical signal and reference electrical signal are input into the digital signal processor for signal demodulation; In the signal processing module, an analog-to-digital converter is used to digitize the sensing electrical signal and the reference electrical signal, and then a Fourier transform is used to obtain the frequency spectra of the sensing electrical signal and the reference electrical signal respectively. The frequency spectrum of the reference electrical signal is conjugated in phase, the modulus value is taken as the inverse, and then multiplied with the frequency spectrum of the sensing electrical signal. The result is subjected to an inverse Fourier transform to obtain the intensity and phase information of the backscattered signal on the optical fiber to be tested.

6. The method for implementing the spectral domain reflectometer according to claim 5, wherein: When the light source module is a single-comb light source module, the light source module includes: a narrow-linewidth laser light source, a pulse generator, a phase or intensity modulator, an acousto-optic modulator and a first coupler; The narrow-linewidth laser light source is divided into a local optical path and a detection optical path via the first coupler; the local optical path is input into the acousto-optic modulator to cause the narrow-band laser to undergo frequency shift, thereby obtaining a local optical signal; the narrow-band laser corresponding to the detection optical path is pulse-modulated by the pulse generator in the phase or intensity modulator to generate a detection optical signal having a comb-shaped spectrum; When the light source module is a dual-comb light source module, the light source module includes: a narrow linewidth laser light source, a pulse generator, a first phase modulator, a second phase modulator, a first coupler, a first optical filter, and a second optical filter; The narrow-linewidth laser light source is evenly divided into a local optical path and a detection optical path through the first coupler; the local optical path and the detection optical path are respectively input into the first phase modulator and the second phase modulator, and the first phase modulator and the second phase modulator are respectively modulated by the pulse generator to generate different sequences; the output optical signal of the first phase modulator enters the first optical filter for filtering processing to obtain an optical comb signal within the required frequency range, and is output as a detection optical signal; the output light of the second phase modulator enters the second optical filter for filtering processing to obtain an optical comb signal within the required frequency range, and is output as a local optical signal.

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