CN115452015A - Double-scale reference interference phase noise accurate correction optical frequency domain reflectometer - Google Patents
Double-scale reference interference phase noise accurate correction optical frequency domain reflectometer Download PDFInfo
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Abstract
The invention belongs to the field of distributed optical fiber sensing, and particularly relates to a double-scale reference interference optical frequency domain reflectometer with accurate phase noise correction. The device comprises a tunable laser source, a double-scale auxiliary interferometer module, a main interferometer module, a device module to be tested and a signal processing module, and is characterized in that: the double-scale delay arm is introduced into the auxiliary interferometer at the same time, one short extension optical fiber with a ten-meter level and the other long extension optical fiber with a hundred-meter level are adopted, so that two beat frequency signals with different frequencies can be generated, the two beat frequency signals are processed, the non-linearity of the light source frequency sweep and the phase noise can be accurately corrected, and the spatial resolution of the optical frequency domain reflectometer is improved. The method solves the problem that the nonlinear frequency sweeping and phase noise of the light source cannot be simultaneously and accurately corrected by a fixed time delay value under the condition of measuring the long-distance device to be measured, and obtains the reflection information of the long-distance device to be measured with higher precision.
Description
Technical Field
The invention belongs to the field of distributed optical fiber sensing, and relates to an optical frequency domain reflectometer.
Background
An Optical Frequency Domain Reflectometer (OFDR) is an Optical fiber sensing technology based on Optical heterodyne detection and Frequency Domain analysis, which realizes accurate measurement of fusion points, bends, breakpoints and the like along a link line by detecting rayleigh scattering signals generated at different positions in an Optical fiber.
In the OFDR technique, the scattering data at the near end is mainly affected by the nonlinear frequency sweep, while the scattering data at the far end is mainly limited by phase noise, and the single-delay auxiliary interferometer is difficult to consider the fiber scattering spectrum correction of different lengths.
In the OFDR technique, a phenomenon that a tunable light source generates a nonlinear tuning effect during linear tuning exists, which causes beat frequency interference signals in an interferometer not to be at equal optical frequency intervals at the same time interval, so that an error is generated by directly performing fourier transform on signals collected in the interferometer.
According to the traditional method for eliminating the nonlinearity of the light source frequency sweep, an auxiliary interferometer is built, the length of a delay ring of the auxiliary interferometer is short, the auxiliary interferometer can detect the change of the light intensity of an interference signal, the change of the phase information of the light source along with the time can be obtained, and the nonlinearity of the light source frequency sweep can be eliminated through data processing.
Phase noise refers to the fact that the sinusoidal oscillation of light is unstable and random jump of phase occurs somewhere in time. The phase noise may cause the line width of the light source to be widened. The traditional OFDR distributed optical fiber sensing equipment has frequency offset due to problems of phase noise interference and the like, so that the positioning of a reflection point or a scattering point is not accurate enough.
In 2019, zhao Can et al of watson (wuhan) opto-electronic technology limited proposed an OFDR detection method (an OFDR detection method, 201910862111.6), which can perform accurate phase noise compensation for specific abnormal frequency points on optical fibers by setting a delay value of an adjustable delay interferometer arm on an adjustable delay auxiliary interferometer.
In 2019, zhao Can et al of the core hua chuang (wuhan) opto-electronic technology limited company proposed an OFDR detection device (201910862124.3), which adopts an adjustable delay auxiliary interferometer, and through multiple measurements, phase noises at different frequency points can be measured under different delays, so as to compensate phase noises at different abnormal frequency points.
In 2022, zhang Lixun et al, university of electronic technology, proposed a method for reducing the nonlinear phase effect of OFDR light source (a system and method for reducing the nonlinear phase effect of OFDR light source, 202011249634.2), which uses a test fiber as a reference fiber of an auxiliary interferometer to enable long-distance and high-spatial-resolution signal detection in an OFDR system.
In 2021, qin Yuwen et al, the university of guangdong industry, proposed a distributed bidirectional polarization measurement device based on a dual-beat-frequency single-auxiliary interferometer (a distributed bidirectional polarization measurement device based on a dual-beat-frequency single-auxiliary interferometer, 202110941018.1), which uses a half-mirror and a total reflector through an auxiliary interferometer, and generates dual-beat-frequency signals by using different optical path differences to respectively match a transmission module and a reflection module, thereby correcting the sweep nonlinearity of a light source and rapidly obtaining the transflective information of an optical fiber device. Qin Yuwen et al further provides a distributed bidirectional polarization measurement device based on matching correction optical frequency domain interference (a distributed bidirectional polarization measurement device based on matching correction optical frequency domain interference, 202110817517. X), which uses a plurality of auxiliary interferometers with different optical path differences to respectively match a transmission module and a reflection module, thereby realizing correction of the non-linearity of the optical source sweep frequency, improving the spatial resolution of the system, and rapidly obtaining the transflective information of the optical fiber device. The two devices can only correct the non-linearity of the frequency sweep of the light source, but can not correct the phase noise when testing the long-distance optical fiber.
The OFDR detection device used at present uses a fixed delay auxiliary interferometer to compensate phase noise and light source frequency sweep nonlinearity when testing a long-distance device to be tested, and the auxiliary interferometer needs a longer delay optical fiber when measuring a long distance and has larger phase noise, so that the light source frequency sweep nonlinearity and the phase noise cannot be accurately corrected through a fixed delay value.
The invention discloses a double-scale reference interference phase noise accurate correction optical frequency domain reflectometer based on the prior art improvement, wherein when a long-distance optical fiber is used for testing and sensing, a beat frequency signal containing information of a device to be tested is generated in a main interferometer; meanwhile, two sections of beat frequency signals containing different phase noise information are obtained by arranging two scaled extension optical fibers in the auxiliary interferometer, one section is shorter and used for correcting the sweep frequency nonlinearity of a light source, and the other section is matched with the length of the optical fiber to be detected and used for correcting phase noise. Therefore, the nonlinear frequency sweeping and phase noise of the light source can be accurately corrected in long-distance test and sensing simultaneously, and the reflection information of the long-distance device to be tested with higher precision can be obtained.
Disclosure of Invention
The invention aims to provide a double-scale reference interference phase noise accurate correction optical frequency domain reflectometer, which solves the problem that in the background technology, the accurate correction of the optical source frequency sweep nonlinearity and the phase noise is difficult to be carried out at one time during long-distance testing.
A dual scale reference interferometric phase noise precision corrected optical frequency domain reflectometer comprising five modules: tunable laser source 1, two scale auxiliary interferometer module 2, main interferometer module 3, device module 4, the signal processing module 5 that awaits measuring, characterized by:
signal light is emitted from a tunable laser source 1 and injected into a double-scale auxiliary interferometer module 2 and a main interferometer module 3 through a first coupler 101, after being injected into the double-scale auxiliary interferometer module 2, an optical signal is divided into two beams by a second coupler 201, wherein 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 the sixth coupler; the other beam is injected into the fourth coupler 202 from the second output end 201b of the second coupler, 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 into the fifth coupler 205; the signal light in the fifth coupler 205 is injected into the sixth coupler from the sixth coupler second input terminal 206 b; after the optical signal is injected into the main interferometer module 3, the optical signal is injected into the device module 4 to be tested through the circulator 302, and the reflected signal light is injected into the main interferometer module 3 through the circulator 302 again; the signals collected from the main interferometer module 3 and the double-scale auxiliary interferometer module 2 are transmitted to the signal processing module 5, and the accurate measurement value of the device to be measured is obtained after data processing.
The tunable laser source 1 is characterized in that: the linearly tunable continuous light emitted by the tunable laser source 1 is divided into two beams by the first coupler 101, and the two beams are 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.
The double-scale auxiliary interferometer module 2 is characterized in that: after being injected into the dual-scale auxiliary interferometer module 2, the optical signal is divided into two beams by the second coupler 201, wherein 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 to be used as reference light; the other beam is injected into the fourth coupler 202 from the second output end 201b of the second coupler, 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 into the fifth coupler 205; the signal light in the fifth coupler 205 is injected into the sixth coupler from the sixth coupler second input terminal 206b, and then the signal detected by the first balanced detector 207 is collected by the first collecting unit 501.
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.
The main interferometer module 3 is characterized in that: the 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, the light is injected into the device module 4 to be tested through the second port of the circulator, the reflected light is injected into the main interferometer module 3 again through the third port 302c of the circulator, and then the reflected light is injected into the seventh coupler 304; the other beam passes through a main interferometer delay fiber 303 and then is injected into a seventh coupler 304; interference occurs in the seventh coupler 304, and an interference signal thereof is detected by the second balanced detector 305 and then acquired by the second acquisition unit 501.
The signal processing module 5 is characterized in that: the signal processing module 5 of claim 1, wherein: the signal detected by the first balanced detector 207 is acquired by the first acquisition unit 501, the dual-scale auxiliary interferometer signal is filtered, the low-pass filter 503 filters out a first beat frequency signal 503a in the dual-scale auxiliary interferometer signal, and the band-pass filter 504 filters out a second beat frequency signal 504a in the dual-scale auxiliary interferometer signal; the signal detected by the second balanced detector 305 is collected by the second collecting unit 502, and the collected beat signal 502a of the main interferometer is obtained; the beat signal 502a of the main interferometer firstly enters a light source nonlinearity correction unit 505, the light source sweep nonlinearity is corrected by acquiring the information in the first beat signal 503a, then the beat signal 505a of the main interferometer after the light source nonlinearity is corrected enters a phase noise correction unit 506 for correcting the phase noise, and the phase noise is corrected by acquiring the information in the second beat signal 504 a; after the data is corrected, the position amplitude of the scattering is obtained, and finally the position amplitude enters a spectrum analysis unit 507 for analysis, so that accurate reflection information of the device to be measured is obtained.
The light source nonlinearity correction unit 505 is characterized in that: the light source frequency sweep nonlinearity is corrected by using a resampling method, the optical frequency information of the tunable light source is obtained by using the frequency sweep signal 511 output by the auxiliary interferometer 514, the equal optical frequency position can be obtained, the signal of the main interferometer 515 is resampled by using an interpolation method, and finally the main interferometer signal with the equal optical frequency interval is obtained.
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 Φ 2 (t)-Φ 2 (t-τ 2 ) The device under test module 4 and the master interferometer reference arm 301b generateThe phase noise term carried by the master interferometer beat signal 502a is Φ 0 (t)-Φ 0 (t-τ z ) Let phi 2 (t)-Φ 2 (t-τ 2 ) And phi 0 (t)-Φ 0 (t-τ z ) And matching to eliminate the phase noise in the beat signal of the main interferometer.
A master interferometer beat signal 502aI generated by the reflected light in the DUT module 4 and the reference light in the master interferometer reference arm 301b 0 The specific formula of (t) is:
wherein E is 0 Is the amplitude of the beat optical signal of the master interferometer; r (tau) z ) Is the reflection coefficient of the fiber; f. of 0 Is the initial frequency of the light source; γ is the tunable rate of the light source; tau is z Is the time delay of the test fiber and the reference arm of the main interferometer; wherein τ is z =2nz/c; where c is the propagation speed of light in vacuum; n is the effective refractive index of the fiber; z is the length of the test fiber; phi (phi) of 0 (t)-Φ 0 (t-τ z ) Is the phase noise term induced at the main interferometer.
The first auxiliary interferometer delay fiber 203 and the first beat signal 503aI generated by the auxiliary interferometer reference arm 201a 1 The specific formula of (t) is:
I 1 (t)＝2E 1 2 cos(2πf 0 τ 1 +2πγτ 1 t+πγτ 1 2 +Φ 1 (t)-Φ 1 (t-τ 1 )) (2)
wherein E is 1 Is the amplitude of the beat light signal of the auxiliary interferometer; f. of 0 Is the initial frequency of the light source; tau. 1 Is the time delay of the first delay fiber and the reference arm fiber; wherein τ is 1 ＝nL 1 C; where c is the propagation speed of light in vacuum; n is the effective refractive index of the fiber; l is a radical of an alcohol 1 Is the length of the first delay fiber; phi 1 (t)-Φ 1 (t-τ 1 ) Is in the first extension of the auxiliary interferometerPhase noise terms induced on the fiber.
The second auxiliary interferometer delay fiber 204 and the second beat signal 504aI generated by the auxiliary interferometer reference arm 201a 2 The specific formula of (t) is:
I 2 (t)＝2E 1 2 cos(2πf 0 τ 2 +2πγτ 2 t+πγτ 2 2 +Φ 2 (t)-Φ 2 (t-τ 2 ))
wherein E is 1 Is the amplitude of the beat light signal of the auxiliary interferometer; f. of 0 Is the initial frequency of the light source; tau is 2 Is the time delay of the first delay fiber and the reference arm fiber; wherein tau is 2 ＝nL 2 C; where c is the propagation speed of light in vacuum; n is the effective refractive index of the fiber; l is a radical of an alcohol 2 Is the length of the second delay fiber; phi 2 (t)-Φ 2 (t-τ 2 ) Is the phase noise term induced on the second elongated fiber of the secondary interferometer.
The light source nonlinearity correction unit 505 is characterized in that: the first delay optical fiber is short in length and low in phase noise, so that the beat frequency signal generated by the first delay optical fiber and the reference arm is used for correcting the nonlinearity of the light source frequency sweep.
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 the main interferometer signal enters the phase noise correction unit, and the main interferometer beat signal is subjected to phase noise correction through information in the beat signal generated by the second delay fiber and the reference arm.
The phase noise correction unit 506 is characterized in that: the phase noise term carried by the master interferometer beat signal 502a is Φ 0 (t)-Φ 0 (t-τ z ) Z is the length of the device to be measured, and the time delay tau brought by the second delay optical fiber of the auxiliary interferometer is enabled 2 ＝τ z 10, the phase noise term phi of the auxiliary interferometer can be passed 2 (t)-Φ 2 (t-tau) to eliminate the phase noise term phi of the main interferometer 0 (t)-Φ 0 (t-τ z )。
The principle of Optical Frequency Domain Reflection (OFDR) measurement is shown in fig. 3: the chirped continuous light emitted by the tunable laser source 1 is divided into two beams after passing through the coupler 210, one beam is injected into a first output end 211 of the coupler and is injected into a device to be measured 215 through a three-port circulator 213, and because Rayleigh scattering and Fresnel reflection exist in an optical fiber to be measured, a part of light is reflected back and enters the coupler 216 as the light to be measured through the three-port circulator 213; the other beam is injected into the second input end 212 of the coupler as reference light, an optical path difference is generated in the coupler 216 after passing through the delay fiber 214 and the light to be measured, after a time delay tau, a frequency difference is generated between the light to be measured and the reference light, namely a beat frequency signal, the beat frequency signal is received by the balance detector 217 for differential detection, the acquisition card 218 performs data synchronous acquisition and storage on the optical signal, after correcting sweep frequency nonlinearity, the FFT is performed to convert optical frequency domain information into a distance domain, and finally Rayleigh scattering peak amplitude and position information corresponding to a single defect point on the device to be measured are obtained.
Compared with the prior art, the invention has the advantages that:
(1) The invention relates to a double-scale reference interference phase noise accurate correction optical frequency domain reflectometer, which is based on the optical frequency domain interference principle, improves the test rate and the measurement accuracy at one time through the quick linear frequency scanning of a tunable laser source, and quickly obtains the reflection information of a device;
(2) The invention utilizes a plurality of auxiliary interferometers with different arm length differences, and can accurately correct the phase noise and nonlinearity of the device to be tested under long-distance test, so that the spectrum does not widen, the spatial resolution of the system is improved, and the measurement precision of the system is improved;
(3) The invention utilizes a plurality of auxiliary interferometers with different arm length differences, can accurately correct the sweep frequency nonlinearity of the light source, realizes equal optical frequency interval sampling, and improves the measurement precision of the system.
Description of the drawings:
FIG. 1 is a simplified schematic of a double-scale reference interferometric phase noise accurate correction optical frequency domain reflectometer;
FIG. 2 is an illustration of a swept frequency nonlinear correction resampling method;
FIG. 3 is a schematic diagram of an Optical Frequency Domain Reflectometry (OFDR) measurement technique for single defect point measurement;
FIG. 4 is a double scale reference interferometric phase noise accurate correction optical frequency domain reflectometer for fiber optic measurements.
The specific implementation mode is as follows:
in order to make the objects, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are merely illustrative of the present application and are not intended to be limiting of the present application.
An optical frequency domain reflectometer was accurately calibrated for phase noise using a double scale reference interference for measurements on a 5km fiber.
The main photoelectric devices of the device are selected and the parameters are as follows:
the light source is a narrow-linewidth tunable laser source, the relative intensity noise RIN-145dB/Hz, the linewidth of the light source is 60kHz (coherent control switch), the frequency sweep range is 10nm, the wavelength tuning range is 1545 nm-1555 nm, the frequency sweep rate is 10nm/s, and the frequency sweep time is 1s;
the photosensitive materials of the first differential detector 206 and the second differential detector 304 are InGaAs, the light detection range is 900-1700 nm, the responsivity is larger than 1A/W, and the typical value of the common mode rejection ratio is 25dB. If a 1817-FC type balanced optical fiber receiver of Newport company is adopted, the maximum detection bandwidth of the detector is 80MHz, the saturation differential detection power is 55uW, and the common mode rejection ratio is 25dB;
the maximum sampling rate of the acquisition card 501 is 400MHz/s, and the acquisition card can simultaneously acquire four channels and has 2 independent full-function ports, for example, an M4i.4471-x8 acquisition card of SPECTRUM company is adopted; the number of sampling points is 400M, the sampling time is 1s, and the triggering mode is triggered by the external part of a laser;
the splitting ratio of the first coupler 101 is 1: 99, the working center wavelength is 1550nm, the bandwidth is +/-40nm, the 99% end insertion loss is less than or equal to 0.2dB, and the 1% end insertion loss is less than or equal to 24.1dB.
The light splitting ratio of the rest couplers is 50: 50, the working center wavelength is 1550nm, the bandwidth is +/-40 nm, and the insertion loss is less than or equal to 3.6dB;
the working wavelength of the circulator 302 is 1550nm, the insertion loss is 0.8dB, and the isolation is more than 50dB;
the main interferometer module 3 adopts Mach-Zehnder type interferometer with optical path difference S FUT ＝L FUT n =7280m, refractive index n =1.456 of the single-mode fiber;
device under test module 4: the device to be tested is a single-mode optical fiber with the diameter of 250 mu m and the length of L FUT ＝5km。
At this time L FUT The time delay brought is:
n is the effective refractive index of the fiber, n =1.456; c is the propagation speed of light in vacuum.
The double-scale auxiliary interferometer module 2 adopts a Mach-Zehnder type interferometer, is provided with a double-scale auxiliary interferometer, and has an arm length difference of L 1 And L 2 ，L 1 ＜10m，L 2 ＞100m。
The length difference of the first extension optical fiber of the auxiliary interferometer is L 1 For correcting source sweep nonlinearity, in this case, L 1 ＝5m。
At L 1 And acquiring optical frequency information of the tunable light source from the beat frequency signal output by the auxiliary interferometer reference arm to obtain an equal optical frequency position, resampling the signal of the main interferometer by using an interpolation method, and finally obtaining the signal of the main interferometer at an equal optical frequency interval.
The time delay generated by the second delay optical fiber of the auxiliary interferometer and the reference arm is as follows: tau is 2 ＝2nL 2 In this case, take
So take L 2 ＝500m。
The phase noise term caused by the nonlinearity of the swept-frequency light source in the main interferometer is
L FUT Maximum test distance for the device under test is L FUT =5km, second delay fiber of auxiliary interferometerIncoming time delay L 2 =500m, phase noise term Φ (t) - Φ (t- τ) by means of an auxiliary interferometer 2 ) To the phase noise term of the main interferometer
And carrying out accurate correction.
After being corrected by the light source nonlinearity correction unit 505 and the phase noise correction unit 506, the optical fiber enters the spectrum analysis unit 507 for analysis, and reflection information of the 5km long-distance optical fiber is obtained.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (8)
1. A dual scale reference interferometric phase noise precision corrected optical frequency domain reflectometer comprising five modules: tunable laser source (1), two scale auxiliary interferometer module (2), main interferometer module (3), device module to be measured (4), signal processing module (5), characterized by:
signal light is emitted from a tunable laser source (1) and injected into a double-scale auxiliary interferometer module (2) and a main interferometer module (3) through a first coupler (101), the optical signal is divided into two beams by a second coupler (201) after being injected into the double-scale auxiliary interferometer module (2), and one beam is injected from a first output end (201 a) of the second coupler and then injected into a sixth coupler (206) from a first input end (206 a) of the sixth coupler; the other beam is injected into a fourth coupler (202) from a second output end (201 b) of the second coupler, and the fourth coupler (202) injects the optical signals into a first auxiliary interferometer delay fiber (203) and a second auxiliary interferometer delay fiber (204) respectively and then into a fifth coupler (205); the signal light in the fifth coupler (205) is injected into the sixth coupler from the sixth coupler second input terminal (206 b); after an optical signal is injected into the main interferometer module (3), the optical signal is injected into the device module to be tested (4) through the circulator (302), and the reflected signal light is injected back into the main interferometer module (3) through the circulator (302); signals collected from the main interferometer module (3) and the double-scale auxiliary interferometer module (2) are transmitted to the signal processing module (5), and an accurate measurement value of the device to be measured is obtained after data processing.
2. The tunable laser source (1) according to claim 1, characterized in that: linear tunable continuous light emitted by a tunable laser source (1) is divided into two beams by a first coupler (101), and the two beams are output from a first output end (101 a) of the first coupler and a second output end (101 b) of the first coupler and respectively enter a second coupler (201) and a third coupler (301).
3. The dual-scale auxiliary interferometer module (2) of claim 1, wherein: after being injected into the double-scale auxiliary interferometer module (2), the optical signal is divided into two beams by the second coupler (201), wherein one beam is injected from the first output end (201 a) of the second coupler and then injected into the sixth coupler (206) from the first input end (206 a) of the sixth coupler to be used as reference light; the other beam is injected into a fourth coupler (202) from a second output end (201 b) of the second coupler, and the fourth coupler (202) injects the optical signals into a first auxiliary interferometer delay fiber (203) and a second auxiliary interferometer delay fiber (204) respectively and then into a fifth coupler (205); the signal light in the fifth coupler (205) is injected into the sixth coupler from the second input end (206 b) of the sixth coupler, and then the signal detected by the first balanced detector (207) is collected by the first collecting unit (501).
4. The first auxiliary interferometer delay fiber (203) and the second auxiliary interferometer delay fiber (204) of claim 3, wherein: the first auxiliary interferometer delay fiber (203) has a length L 1 The second auxiliary interferometer delay fiber (204) has a length L 2 ，L 1 ＜10m，L 2 ＞100m。
5. A main interferometer module (3) as claimed in claim 1, wherein: an optical signal is injected into a main interferometer module (3) through a second output end (101 b) of a first coupler (101), and is divided into two beams after entering a third coupler (301), one beam enters a first port (302 a) of a circulator, light is injected into a device module to be tested (4) through the second port of the circulator, and then reflected light is injected into the main interferometer module (3) again through a third port (302 c) of the circulator and then injected into a seventh coupler (304); the other beam passes through a delay optical fiber (303) of the main interferometer and then is injected into a seventh coupler (304); interference occurs in the seventh coupler (304), and an interference signal thereof is detected by the second balanced detector (305) and then acquired by the second acquisition unit (501).
6. The signal processing module (5) according to claim 1, characterized by: the signal detected by the first balanced detector (207) is acquired by a first acquisition unit (501), the double-scale auxiliary interferometer signal is subjected to filtering processing, a first beat frequency signal (503 a) in the double-scale auxiliary interferometer signal is filtered out by a low-pass filter (503), and a second beat frequency signal (504 a) in the double-scale auxiliary interferometer signal is filtered out by a band-pass filter (504); the signal detected by the second balanced detector (305) is collected by a second collecting unit (502), and a main interferometer beat frequency signal (502 a) is collected; the method comprises the following steps that a main interferometer beat frequency signal (502 a) enters a light source nonlinearity correction unit (505) firstly, the light source sweep frequency nonlinearity is corrected by acquiring information in a first beat frequency signal (503 a), then the main interferometer beat frequency signal (505 a) after the light source nonlinearity is corrected enters a phase noise correction unit (506) to be corrected for phase noise, and the phase noise is corrected by acquiring information in a second beat frequency signal (504 a); after the data are corrected, the position amplitude of scattering is obtained, and finally the data enter a spectrum analysis unit (507) for analysis to obtain accurate reflection information of the device to be detected.
7. The light source non-linearity correction unit (505) of claim 6, characterized by: the light source frequency sweep nonlinearity is corrected by using a resampling method, the optical frequency information of the tunable light source is obtained by using a frequency sweep signal (511) output by the auxiliary interferometer (514), the equal optical frequency position can be obtained, the signal of the main interferometer (515) is resampled by using an interpolation method, and finally the main interferometer signal reaching the equal optical frequency interval is obtained.
8. The phase noise correction (506) of claim 6, characterized by: the phase noise term carried by the second beat signal (504 a) generated by the second delay fiber (204) and the reference arm in the double-scale auxiliary interferometer module (2) is phi 2 (t)-Φ 2 (t-τ 2 ) The phase noise term carried by the beat frequency signal (502 a) of the main interferometer generated by the device module (4) to be tested and the reference arm (301 b) of the main interferometer is phi 0 (t)-Φ 0 (t-τ z ) Let phi 2 (t)-Φ 2 (t-τ 2 ) And phi 0 (t)-Φ 0 (t-τ z ) And matching to eliminate the phase noise in the beat signal of the main interferometer.
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| CN117007170A (en) * | 2023-07-04 | 2023-11-07 | 哈尔滨工业大学 | OFDR vibration measurement device, method and system |
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