A Phase Noise Accurately Corrected Optical Frequency Domain Reflectometer with Dual-Scale Reference Interferometry

Abstract

The present invention belongs to the field of distributed fiber optic sensing, and specifically relates to a dual-scale reference interferometer with phase noise precision correction optical frequency domain reflectometer. The device includes a tunable laser source, a dual-scale auxiliary interferometer module, a main interferometer module, a device under test module, and a signal processing module. Its characteristics are: dual-scale delay arms are simultaneously introduced into the auxiliary interferometer, one using a short extension optical fiber of ten meters and the other using a long extension optical fiber of one hundred meters. This will generate two beat signals with different frequencies. By processing the two beat signals, the light source frequency sweep nonlinearity and phase noise can be accurately corrected respectively, thereby improving the spatial resolution of the optical frequency domain reflectometer. The present invention solves the problem that when measuring long-distance devices under test, it is impossible to accurately correct the light source frequency sweep nonlinearity and phase noise simultaneously by using a fixed delay value, and obtains more accurate reflection information of the long-distance device under test.

Description

Technical Field

[0001] The invention belongs to the field of distributed optical fiber sensing and relates to an optical frequency domain reflectometer. Background Art

[0002] Optical Frequency Domain Reflectometry (OFDR) is a fiber optic sensing technology based on optical heterodyne detection and frequency domain analysis. It accurately measures splices, bends, and breakpoints along the link by detecting Rayleigh scattering signals generated at different locations in the optical fiber. Currently, OFDR has a wide range of applications in fault location and length measurement. Furthermore, OFDR technology can be applied to high-precision measurements across a wide range of applications. Compared with other sensing technologies, it has the advantages of high spatial resolution and a large dynamic range.

[0003] In OFDR technology, the near-end scattering data is mainly affected by the nonlinearity of the frequency sweep, while the far-end scattering data is mainly limited by phase noise. A single-delay auxiliary interferometer is difficult to take into account the correction of the scattering spectrum of optical fibers of different lengths.

[0004] In OFDR technology, there is a phenomenon in which the tunable light source produces a nonlinear tuning effect during linear tuning. This causes the beat frequency interference signals in the interferometer to have unequal optical frequency intervals at the same time interval. Therefore, directly performing Fourier transform on the signals collected in the interferometer will produce errors.

[0005] The traditional method to eliminate the nonlinearity of light source frequency sweep is to build an auxiliary interferometer with a short delay loop. The auxiliary interferometer can detect the change in the intensity of the interference signal light, and obtain the change of the light source phase information over time. The nonlinearity of the light source frequency sweep can be eliminated through data processing.

[0006] Phase noise refers to the instability of the sinusoidal oscillation of light, resulting in random phase jumps at certain locations. Phase noise can cause the light source's linewidth to widen. Conventional OFDR distributed fiber sensing equipment can experience frequency offsets due to phase noise interference, making the location of reflection or scattering points less accurate.

[0007] In 2019, Zhao Can and others from Xinhuachuang (Wuhan) Optoelectronics Technology Co., Ltd. proposed an OFDR detection method (An OFDR Detection Method, 201910862111.6). By setting the delay value of the adjustable delay interferometer arm on the adjustable delay auxiliary interferometer, accurate phase noise compensation can be performed for specific abnormal frequency points on the optical fiber.

[0008] In 2019, Zhao Can and others from Xinhuachuang (Wuhan) Optoelectronics Technology Co., Ltd. proposed an OFDR detection device (an OFDR detection device, 201910862124.3), which uses an adjustable delay-assisted interferometer. Through multiple measurements, the phase noise of different frequencies can be measured at different time delays, thereby compensating for the phase noise of different abnormal frequencies.

[0009] In 2022, Zhang Lixun and others from the University of Electronic Science and Technology of China proposed a method to reduce the nonlinear phase influence of OFDR light source (A system and method to reduce the nonlinear phase influence of OFDR light source, 202011249634.2). It uses test optical fiber as the reference optical fiber of the auxiliary interferometer, which can achieve long-distance and high spatial resolution signal detection in the OFDR system.

[0010] In 2021, Qin Yuwen and others from Guangdong University of Technology proposed a distributed bidirectional polarization measurement device based on a dual-beat single-auxiliary interferometer (A Distributed Bidirectional Polarization Measurement Device Based on a Dual-beat Single-auxiliary Interferometer, 202110941018.1). This device uses a half-mirror and a full-reflector through an auxiliary interferometer to generate dual-beat signals using different optical path differences to match the transmission module and the reflection module respectively, thereby correcting the swept-frequency nonlinearity of the light source and quickly obtaining the transmission and reflection information of the fiber optic device. Qin Yuwen and others also proposed a distributed bidirectional polarization measurement device based on matched-corrected optical frequency domain interferometry (A Distributed Bidirectional Polarization Measurement Device Based on Matched-corrected Optical Frequency Domain Interferometry, 202110817517.X). This device uses multiple auxiliary interferometers with different optical path differences to match the transmission module and the reflection module respectively, thereby correcting the swept-frequency nonlinearity of the light source, improving the spatial resolution of the system, and quickly obtaining the transmission and reflection information of the fiber optic device. These two devices can only correct the swept-frequency nonlinearity of the light source, but cannot correct the phase noise during long-distance fiber testing.

[0011] The OFDR detection device currently used uses a fixed-delay auxiliary interferometer to compensate for phase noise and light source frequency sweep nonlinearity when testing long-distance devices. Because the auxiliary interferometer requires a long delay fiber when measuring long distances and has large phase noise, it is impossible to accurately correct the light source frequency sweep nonlinearity and phase noise at the same time by using a fixed delay value.

[0012] Based on improvements to existing technologies, the present invention discloses a dual-scale reference interferometer with precise phase noise correction for optical frequency domain reflectometry. When using long-distance optical fiber for testing and sensing, a beat signal containing information about the device under test is generated in the main interferometer. Simultaneously, by providing two scaled extended optical fibers in the auxiliary interferometer, two beat signals containing different phase noise information are obtained: one shorter segment is used to correct the light source's frequency-sweep nonlinearity, and the other segment matches the length of the fiber under test and is used to correct phase noise. This allows precise correction of both the light source's frequency-sweep nonlinearity and phase noise during long-distance testing and sensing, yielding higher-precision reflection information from the long-distance device under test. Summary of the Invention

[0013] The purpose of the present invention is to provide a dual-scale reference interferometer with accurate phase noise correction for optical frequency domain reflectometry, which solves the problem in the background art that it is difficult to accurately correct the light source frequency sweep nonlinearity and phase noise at one time during long-distance testing.

[0014] A dual-scale reference interferometer with phase noise precision correction optical frequency domain reflectometer, comprising five modules: a tunable laser source 1, a dual-scale auxiliary interferometer module 2, a main interferometer module 3, a device under test module 4, and a signal processing module 5, characterized by:

[0015] The signal light is emitted from the tunable laser source 1 and injected into the dual-scale auxiliary interferometer module 2 and the main interferometer module 3 through the first coupler 101. After being injected into the dual-scale auxiliary interferometer module 2, the optical signal is split into two beams by the second coupler 201. One beam is injected from the first output end 201a of the second coupler and then injected into the sixth coupler 206 from the first input end 206a of the sixth coupler; the other beam is injected from the second output end 201b of the second coupler into the fourth coupler 202. The fourth coupler 202 injects the optical signals into the first auxiliary interferometer delay fiber 203. and the second auxiliary interferometer delay fiber 204, and then injected into the fifth coupler 205; the signal light in the fifth coupler 205 is injected into the sixth coupler from the second input end 206b of the sixth coupler; after the optical signal is injected into the main interferometer module 3, it is injected into the device under test module 4 through the circulator 302, and the reflected signal light is injected back into the main interferometer module 3 through the circulator 302 again; the signals collected from the main interferometer module 3 and the dual-scale auxiliary interferometer module 2 are transmitted to the signal processing module 5, and the accurate measurement value of the device under test is obtained after data processing.

[0016] The tunable laser source 1 is characterized in that the linear tunable continuous light emitted by the tunable laser source 1 is divided into two beams by the first coupler 101, output from the first output end 101a of the first coupler and the second output end 101b of the first coupler, and enter the second coupler 201 and the third coupler 301 respectively.

[0017] The dual-scale auxiliary interferometer module 2 is characterized in that: after the optical signal is injected into the dual-scale auxiliary interferometer module 2, it is divided into two beams by the second coupler 201, one beam is injected from the first output end 201a of the second coupler and then injected into the sixth coupler 206 from the first input end 206a of the sixth coupler, serving as reference light; the other beam is injected from the second output end 201b of the second coupler into the fourth coupler 202, and the fourth coupler 202 injects the optical signal into the first auxiliary interferometer delay fiber 203 and the second auxiliary interferometer delay fiber 204 respectively, and then injects it into the fifth coupler 205; the signal light in the fifth coupler 205 is injected into the sixth coupler from the second input end 206b of the sixth coupler, and then the signal is detected by the first balanced detector 207 and then collected by the first acquisition unit 501.

[0018] The first auxiliary interferometer delay fiber 203 and the second auxiliary interferometer delay fiber 204 are characterized in that the length of the first auxiliary interferometer delay fiber 203 is shorter than the length of the second auxiliary interferometer delay fiber 204 .

[0019] The main interferometer module 3 is characterized in that: an optical signal is injected into the main interferometer module 3 through the second output port 101b of the first coupler 101, and is divided into two beams after entering the third coupler 301. One beam enters the first port 302a of the circulator, and the light is injected into the device under test module 4 through the second port of the circulator. The reflected light is then injected into the main interferometer module 3 again through the third port 302c of the circulator, and then injected into the seventh coupler 304; the other beam passes through the main interferometer delay fiber 303 and is then injected into the seventh coupler 304; interference occurs in the seventh coupler 304, and its interference signal is detected by the second balanced detector 305 and then collected by the second acquisition unit 501.

[0020] The signal processing module 5 is characterized in that: according to the signal processing module 5, it is characterized in that: the signal detected by the first balanced detector 207 is collected by the first acquisition unit 501, the dual-scale auxiliary interferometer signal is filtered, the low-pass filter 503 filters out the first beat signal 503a in the dual-scale auxiliary interferometer signal, and the band-pass filter 504 filters out the second beat signal 504a in the dual-scale auxiliary interferometer signal; the signal detected by the second balanced detector 305 is collected by the second acquisition unit 502, and the collected main interferometer beat signal 502a; the main interferometer beat signal 502a first enters the light source nonlinearity correction unit 505, and the light source sweep nonlinearity is corrected by obtaining the information in the first beat signal 503a. Then, the main interferometer beat signal 505a after the light source nonlinearity is corrected enters the phase noise correction unit 506 for phase noise correction, and the phase noise is corrected by obtaining the information in the second beat signal 504a. After the data is corrected, the scattering position amplitude is obtained, and finally it enters the spectrum analysis unit 507 for analysis to obtain accurate reflection information of the device under test.

[0021] The light source nonlinearity correction unit 505 is characterized by using a resampling method to correct the light source frequency sweep nonlinearity, using the beat frequency signal 511 output by the auxiliary interferometer 514 to obtain the optical frequency information of the tunable light source, and obtaining equal optical frequency positions, and then using the interpolation method to resample the signal of the main interferometer 515 to finally obtain the main interferometer signal with equal optical frequency intervals.

[0022] The phase noise correction 506 is characterized in that the phase noise term carried by the second beat signal 504a generated by the second delay fiber 204 and the reference arm in the dual-scale auxiliary interferometer module 2 is Φ2(t)-Φ2(t-τ2), and the phase noise term carried by the main interferometer beat signal 502a generated by the device under test module 4 and the main interferometer reference arm 301b is Φ0(t)-Φ0(t-τ z ), let Φ2(t)-Φ2(t-τ2) and Φ0(t)-Φ0(t-τ z ) matching to eliminate the phase noise in the main interferometer beat signal.

[0023] The specific formula of the main interferometer beat signal 502aI0(t) generated by the reflected light in the device under test module 4 and the reference light in the main interferometer reference arm 301b is:

[0024]

[0025] Where E0 is the amplitude of the beat frequency optical signal of the main interferometer; R(τ z ) is the reflection coefficient of the optical fiber; f0 is the initial frequency of the light source; γ is the tunable rate of the light source; τ zis the time delay between the test fiber and the reference arm of the main interferometer; where τ z = 2nz / c; where c is the speed of light in a vacuum; n is the effective refractive index of the optical fiber; z is the length of the test optical fiber; Φ0(t)-Φ0(t-τ z ) is the phase noise term induced in the main interferometer.

[0026] The specific formula of the first beat signal 503aI1(t) generated by the first auxiliary interferometer delay fiber 203 and the auxiliary interferometer reference arm 201a is:

[0027] I1(t)=2E1 2 cos(2πf0τ1+2πγτ1t+πγτ1 2 +Φ1(t)-Φ1(t-τ1)) (2)

[0028] Wherein, E1 is the amplitude of the auxiliary interferometer beat frequency optical signal; f0 is the initial frequency of the light source; τ1 is the time delay between the first delay fiber and the reference arm fiber; τ1 = nL1 / c; c is the propagation speed of light in vacuum; n is the effective refractive index of the fiber; L1 is the length of the first delay fiber; Φ1(t)-Φ1(t-τ1) is the phase noise term caused on the first extended fiber of the auxiliary interferometer.

[0029] The specific formula of the second beat signal 504aI2(t) generated by the second auxiliary interferometer delay fiber 204 and the auxiliary interferometer reference arm 201a is:

[0030] I2(t)=2E1 2 cos(2πf0τ2+2πγτ2t+πγτ2 2 +Φ2(t)-Φ2(t-τ2))

[0031] Wherein, E1 is the amplitude of the auxiliary interferometer beat frequency light signal; f0 is the initial frequency of the light source; τ2 is the time delay between the first delay fiber and the reference arm fiber; τ2 = nL2 / c; c is the propagation speed of light in a vacuum; n is the effective refractive index of the fiber; L2 is the length of the second delay fiber; Φ2(t)-Φ2(t-τ2) is the phase noise term caused by the second extended fiber of the auxiliary interferometer.

[0032] The light source nonlinear correction unit 505 is characterized in that the first delay fiber is of shorter length and contains less phase noise, so the beat signal generated by the first delay fiber and the reference arm is used to first correct the light source sweep nonlinearity.

[0033] The phase noise correction unit 506 is characterized in that: after the main interferometer signal 502a passes through the light source nonlinearity correction unit 505, the light source sweep nonlinearity is corrected, and then it enters the phase noise correction unit, and the phase noise of the main interferometer beat signal is corrected by the information in the beat signal generated by the second delay fiber and the reference arm.

[0034] The phase noise correction unit 506 is characterized in that the phase noise term carried by the main interferometer beat signal 502a is Φ0(t)-Φ0(t-τ z ), z is the length of the device under test, so that the delay of the second delay fiber of the auxiliary interferometer is τ2=τ z / 10, the main interferometer phase noise term Φ0(t)-Φ0(t-τ) can be eliminated by the auxiliary interferometer phase noise term Φ2(t)-Φ2(t-τ) z ).

[0035] The principle of optical frequency domain reflectometry (OFDR) measurement technology is shown in the attached figure. Figure 3 As shown, a tunable laser source 1 emits linear frequency modulated continuous light, which is then split into two beams after passing through a coupler 210. One beam is injected into the first output port 211 of the coupler and injected into the device under test 215 through a three-port circulator 213. Due to Rayleigh scattering and Fresnel reflection in the optical fiber under test, a portion of the light is reflected back as the test light and enters the coupler 216 through the three-port circulator 213. The other beam is injected into the second input port 212 of the coupler as reference light. After passing through a delay fiber 214, an optical path difference is generated between the test light and the reference light in the coupler 216. After a time delay τ, a frequency difference, i.e., a beat signal, is generated between the test light and the reference light. The beat signal is received by a balanced detector 217 for differential detection. An acquisition card 218 synchronously acquires and stores the optical signal data. After correcting for the nonlinearity of the frequency sweep, an FFT is performed to convert the optical frequency domain information into the distance domain. Finally, the Rayleigh scattering peak amplitude and position information corresponding to a single defect point on the device under test are obtained.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] (1) The present invention is a dual-scale reference interferometer with phase noise precision correction. Based on the principle of optical frequency domain interferometry, the invention improves the test rate and measurement accuracy at one time through the rapid linear frequency scanning of a tunable laser source, and quickly obtains the reflection information of the device.

[0038] (2) The present invention utilizes multiple auxiliary interferometers with different arm length differences to accurately correct the phase noise and nonlinearity of the device under test during long-distance testing, eliminating spectrum broadening and improving the spatial resolution of the system, thereby improving the accuracy of system measurements.

[0039] (3) The present invention utilizes multiple auxiliary interferometers with different arm length differences to accurately correct the frequency sweeping nonlinearity of the light source and achieve equal optical frequency interval sampling, thereby improving the measurement accuracy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a phase noise accurate correction optical frequency domain reflectometer with dual scale reference interferometry.

[0041] Figure 2 Illustration of the swept frequency nonlinear correction resampling method;

[0042] Figure 3 Schematic diagram of optical frequency domain reflectometry (OFDR) measurement technology for measuring a single defect point;

[0043] Figure 4 A phase noise accurate correction optical frequency domain reflectometer with dual-scale reference interferometry for measuring optical fibers. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. The specific embodiments described here are only used to explain this application and are not intended to limit this application.

[0045] A phase noise accurate correction optical frequency domain reflectometer with dual-scale reference interferometry was implemented for measurements over a pair of 5 km optical fibers.

[0046] The selection and parameters of the main optoelectronic devices of this device are as follows:

[0047] The light source is a narrow-linewidth tunable laser source with a relative intensity noise RIN of -145dB / Hz, a light source linewidth of 60kHz (coherence control off), a sweep range of 10nm, a wavelength tuning range of 1545nm to 1555nm, a sweep rate of 10nm / s, and a sweep time of 1s.

[0048] The first differential detector 206 and the second differential detector 304 are both made of InGaAs photosensitive materials, with a light detection range of 900 to 1700 nm, a responsivity greater than 1 A / W, and a typical common-mode rejection ratio of 25 dB. If a Newport 1817-FC balanced fiber optic receiver is used, the detector has a maximum detection bandwidth of 80 MHz, a saturated differential detection power of 55 uW, and a common-mode rejection ratio of 25 dB.

[0049] The maximum sampling rate of the acquisition card 501 is 400MHz / s, which can acquire data on four channels simultaneously and has two independent full-function ports. For example, the M4i.4471-x8 acquisition card from SPECTRUM is used. The sampling points are 400M, the sampling time is 1s, and the triggering mode is external laser triggering.

[0050] The first coupler 101 has a splitting ratio of 1:99, an operating center wavelength of 1550 nm, a bandwidth of ±40 nm, a 99% end insertion loss of ≤0.2 dB, and a 1% end insertion loss of ≤24.1 dB.

[0051] The remaining couplers all have a splitting ratio of 50:50, an operating center wavelength of 1550nm, a bandwidth of ±40nm, and an insertion loss of ≤3.6dB;

[0052] The operating wavelength of the circulator 302 is 1550 nm, the insertion loss is 0.8 dB, and the isolation is greater than 50 dB;

[0053] The main interferometer module 3 adopts Mach-Zehnder interferometer with an optical path difference S FUT =L FUT n = 7280m, the refractive index of single-mode optical fiber is n = 1.456;

[0054] DUT module 4: The DUT is a single-mode optical fiber with a diameter of 250 μm and a length of L. FUT =5km.

[0055] At this time L FUT The resulting delay is: n is the effective refractive index of the optical fiber, n = 1.456; c is the speed of light in a vacuum.

[0056] The dual-scale auxiliary interferometer module 2 adopts a Mach-Zehnder interferometer, and a dual-scale auxiliary interferometer is set, and the arm length difference thereof is L1 and L2, L1 < 10m, L2 > 100m.

[0057] The arm length difference of the first extended optical fiber of the auxiliary interferometer is L1, which is used to correct the nonlinearity of the light source frequency sweep. In this case, L1 = 5m.

[0058] By obtaining the optical frequency information of the tunable light source from the beat signal output by L1 and the reference arm of the auxiliary interferometer, the equal optical frequency position can be obtained, and then the signal of the main interferometer is resampled using the interpolation method to finally obtain the main interferometer signal with equal optical frequency intervals.

[0059] The delay between the second delay fiber of the auxiliary interferometer and the reference arm is: τ2=2nL2 / c. In this case, So take L2=500m.

[0060] The phase noise term caused by the nonlinearity of the swept-frequency light source itself in the main interferometer is: L FUT The maximum test distance for the device under test is L FUT=5km, so that the delay L2 of the second delay fiber of the auxiliary interferometer is 500m, and the phase noise term of the main interferometer is adjusted by the auxiliary interferometer phase noise term Φ(t)-Φ(t-τ2) Perform precise calibration.

[0061] After being corrected by the light source nonlinear correction unit 505 and the phase noise correction unit 506, the signal finally enters the spectrum analysis unit 507 for analysis to obtain the reflection information of the 5 km long-distance optical fiber.

[0062] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A dual-scale reference interferometer with phase noise precision correction optical frequency domain reflectometer, comprising five modules: a tunable laser source (1), a dual-scale auxiliary interferometer module (2), a main interferometer module (3), a device under test module (4), and a signal processing module (5), characterized in that: Signal light is emitted from a tunable laser source (1) and injected into a dual-scale auxiliary interferometer module (2) and a main interferometer module (3) through a first coupler (101). After being injected into the dual-scale auxiliary interferometer module (2), the optical signal is divided into two beams by a second coupler (201). One beam is injected from a first output end (201a) of the second coupler and then injected into a sixth coupler (206) from a first input end (206a) of a sixth coupler; the other beam is injected from a second output end (201b) of the second coupler into a fourth coupler (202). The fourth coupler (202) injects the optical signal into a first auxiliary interferometer delay fiber (203) and a second auxiliary interferometer delay fiber (204) respectively, and then injects the optical signal into a fifth coupler (205); the signal light in the fifth coupler (205) is injected into the sixth coupler from a second input end (206b) of the sixth coupler; after being injected into the main interferometer module (3), the optical signal is injected into the sixth coupler through a circulator ( 302) is injected into the device under test module (4), and the reflected signal light is injected back into the main interferometer module (3) again through the circulator (302); the signals collected from the main interferometer module (3) and the dual-scale auxiliary interferometer module (2) are transmitted to the signal processing module (5), and the accurate measurement value of the device under test is obtained after data processing. After the optical signal is injected into the dual-scale auxiliary interferometer module (2), it is divided into two beams by the second coupler (201), one beam is injected from the first output end (201a) of the second coupler and then injected into the sixth coupler (206) from the first input end (206a) of the sixth coupler as reference light; the other beam is injected from the second output end (201b) of the second coupler into the fourth coupler (202), and the fourth coupler (202) injects the optical signal into the first auxiliary interferometer delay fiber (203) and the second auxiliary interferometer delay fiber (204) respectively, and then injects it into the fifth coupler (205); The signal light in the fifth coupler (205) is injected into the sixth coupler from the second input end (206b) of the sixth coupler, and then the signal is detected by the first balanced detector (207) and then collected by the first collection unit (501).

2. The optical frequency domain reflectometer with phase noise precision correction using dual-scale reference interferometry according to claim 1, characterized in that: The linear tunable continuous light emitted by the tunable laser source (1) is divided into two beams through a first coupler (101), output from a first output end (101a) of the first coupler and a second output end (101b) of the first coupler, and enter a second coupler (201) and a third coupler (301) respectively.

3. The optical frequency domain reflectometer with phase noise precision correction based on dual-scale reference interferometry according to claim 1, characterized in that: The length of the first auxiliary interferometer delay fiber (203) is L1, and the length of the second auxiliary interferometer delay fiber (204) is L2, where L1 is less than 10 m and L2 is greater than 100 m.

4. The optical frequency domain reflectometer with phase noise precision correction using dual-scale reference interferometry according to claim 1, characterized in that: An optical signal is injected into the main interferometer module (3) through the second output end (101b) of the first coupler (101), and is divided into two beams after entering the third coupler (301). One beam enters the first port (302a) of the circulator, and the light is injected into the device under test module (4) through the second port of the circulator. Subsequently, the reflected light is injected into the main interferometer module (3) again through the third port (302c) of the circulator, and then injected into the seventh coupler (304); the other beam passes through the main interferometer delay fiber (303) and is injected into the seventh coupler (304); interference occurs in the seventh coupler (304), and the interference signal is detected by the second balanced detector (305), and then collected by the second collection unit (502).

5. The optical frequency domain reflectometer with phase noise precision correction based on dual-scale reference interferometry according to claim 1, characterized in that: The signal detected by the first balanced detector (207) is collected by the first acquisition unit (501), and the dual-scale auxiliary interferometer signal is filtered. The low-pass filter (503) filters out the first beat signal (503a) in the dual-scale auxiliary interferometer signal, and the band-pass filter (504) filters out the second beat signal (504a) in the dual-scale auxiliary interferometer signal; the signal detected by the second balanced detector (305) is collected by the second acquisition unit (502), and the main interferometer beat signal (502a) is collected; the main interferometer beat signal (502 a) first enters the light source nonlinearity correction unit (505), and corrects the light source frequency sweep nonlinearity by acquiring information in the first beat frequency signal (503a), then the corrected main interferometer beat frequency signal (505a) after the light source frequency sweep nonlinearity is corrected enters the phase noise correction unit (506) for phase noise correction, and corrects the phase noise by acquiring information in the second beat frequency signal (504a); after the data is corrected, the position amplitude of the scattering is obtained, and finally enters the spectrum analysis unit (507) for analysis to obtain accurate reflection information of the device under test.

6. The optical frequency domain reflectometer with phase noise precision correction based on dual-scale reference interferometry according to claim 1, characterized in that: The nonlinearity of the light source frequency sweep is corrected by using a resampling method. The beat frequency signal (511) output by the auxiliary interferometer (514) is used to obtain the optical frequency information of the tunable light source, and the equal optical frequency position can be obtained. Then, the signal of the main interferometer (515) is resampled by an interpolation method, and finally the main interferometer signal with equal optical frequency interval is obtained.

7. The optical frequency domain reflectometer with phase noise precision correction based on dual-scale reference interferometry according to claim 1, characterized in that: The phase noise term carried by the second beat signal (504a) generated by the second auxiliary interferometer delay fiber (204) and the reference arm in the dual-scale auxiliary interferometer module (2) is Φ2(t)-Φ2(t-τ2), and the phase noise term carried by the main interferometer beat signal (502a) generated by the device under test module (4) and the main interferometer reference arm (301b) is Φ0(t)-Φ0(t-τ z ), let Φ2(t)-Φ2(t-τ2) and Φ0(t)-Φ0(t-τ z ) matching to eliminate the phase noise in the main interferometer beat signal.

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