High-precision lossless calibration device and method for length of optical fiber sensitive ring

Abstract

The invention provides a high-precision lossless calibration device and method for the length of an optical fiber sensitive ring. The high-precision lossless calibration device comprises an implemented device structure and a calibration method flow. The device is characterized in that two weak reflection gratings are connected with tail fibers on the left side and the right side of the optical fiber sensitive ring; an optical frequency domain reflectometer is adopted to test the scattering spectrum of the optical fiber sensitive ring; by identifying the position of a reflection peak of a weak reflection grating in a scattering spectrum, high-precision lossless calibration of the length of the optical fiber sensitive ring is realized, and testing and calibration are performed synchronously. According to the optical fiber sensitive ring calibration device and method, the length calibration precision can reach the micron level, the requirement for high-precision calibration is met, and the calibration device can be repeatedly used, is high in reliability and can be widely applied to high-precision length calibration of optical devices such as polarization maintaining optical fibers, optical fiber sensitive rings and optical fiber hydrophones.

Description

Technical Field

[0001] The invention relates to the field of optical measurement technology and fiber optic gyroscope, and in particular to a high-precision lossless calibration device and method for the length of a fiber optic sensitive ring. Background Art

[0002] Fiber optic gyroscope is a non-mechanical angular velocity measuring instrument based on Sagnac effect invented in the 1970s. It plays an important role in the fields of aerospace, military, and sensing. As the core component of the fiber optic gyroscope system, the geometric symmetry and optical symmetry of the fiber optic sensitive ring have a decisive influence on the thermal drift performance of the fiber optic gyroscope. Therefore, it is imperative to measure and analyze the physical properties of the optical fiber itself.

[0003] The precise measurement of the refractive index of optical fiber is closely related to the accuracy of distributed optical fiber sensing. In 2020, Yuan Libo and others from Guilin University of Electronic Technology (CN 110967048 A) invented an orthogonal tilted three-core fiber Bragg grating parallel integrated MachZehnder interferometer. By detecting the output intensity after the interference of three beams, the effective refractive index of the transmission mode in N fiber cores can be calculated. In 2022, Liang Huijuan and others from the 38th Institute of China Electronics Technology Group Corporation (CN 114665957 A) invented a system and method for measuring the refractive index of optical fiber. A vector network analyzer is used to provide a sweeping signal including signals of different frequencies to the optoelectronic modulator, which is modulated into an optical signal by the optoelectronic modulator and transmitted through the optical fiber to be tested. After that, it is demodulated by the detector and returned to the vector network analyzer to analyze the phase of signals of different frequencies. The length of the optical fiber to be tested is further changed and measured again, thereby achieving high-precision calculation of the refractive index of the optical fiber to be tested.

[0004] On the other hand, under the action of temperature field, thermal strain will aggravate the deterioration of optical symmetry, thereby inducing Mohr effect and Shupe effect, significantly aggravating the thermal drift in the fiber optic gyroscope system. Therefore, it is particularly important to accurately test and analyze the thermal strain of the fiber optic sensitive ring. In 2022, Liu Qingwen et al. (CN 117451203 A) from Shanghai Jiaotong University invented a large-scale quasi-distributed fiber optic sensing method and system. The frequency value of the difference frequency term is obtained based on the beat frequency signal to calculate the optical path between two points, and the temperature change and strain of the optical fiber are obtained by detecting the change in the optical path. In the same year, Wen Kunhua et al. (CN 115452213 A) from Guangdong University of Technology invented a distributed high-precision strain measurement method for fiber optic sensitive rings under temperature variation conditions. It combines DTS and BOTDA systems, realizes temperature compensation of distributed stress test of fiber optic sensitive rings by inference, determines the temperature stability of its internal stress distribution, and thus infers the high-precision internal stress distribution of fiber optic sensitive rings. In 2023, Rao Yunjiang et al. (CN 116576897 A) from Zhijiang Laboratory invented a multi-parameter fiber-optic distributed sensing system and method thereof, which obtains the temperature or strain changes felt by each fiber Bragg grating in the sensing fiber by sensing the wavelength changes corresponding to the wavelength defects in the reflection spectrum of each fiber Bragg grating. In 2024, Dong Yongkang et al. (CN118623781 A) from Harbin Institute of Technology invented a method and device for decoupling temperature and strain of OPGW optical cables based on zero strain reference point and ANN algorithm, and used the temperature-strain decoupling method based on zero strain reference point to demodulate multiple Brillouin gain spectra, obtain the corresponding temperature value of each optical fiber, and realize accurate data demodulation. Zhang Zhuo from Harbin Engineering University (Physical Field Analysis and Coupling Characteristics of Marine Fiber Optic Gyroscopes) analyzed the physical field error mechanism of fiber optic gyroscopes under the coupling of temperature field and stress field, proposed the concepts of fiber optic ring temperature matrix, stress matrix, and weight matrix, and derived the traditional integral accumulation error model into the form of inner products of multiple matrices, providing guidance for the design of fiber optic ring parameters and the selection of optical fiber and solid adhesive materials, thereby improving the accuracy of gyroscopes.

[0005] In terms of fiber optic ring testing technology, B-OTDA and optical frequency domain reflectometry (OFDR) are two commonly used methods. B-OTDA provides absolute measurements, but its resolution needs to be improved. On the contrary, OFDR has better resolution, but it is only a relative measurement relative to the reference state. Since internal stress has a significant impact on winding quality, some studies have used B-OTDA to monitor the symmetrical stress of fiber optic sensitive rings. Han Zhengying of China Electronics 41 Research Institute (Application of BOTDA fiber optic sensing technology in fiber optic ring quality assessment) used B-OTDA technology to measure the strain distribution of fiber optic sensitive rings under different temperature conditions, and improved the performance of the gyro optical path by screening winding bodies with more symmetrical strain changes at each temperature. Yang Jigang et al. of Beijing Institute of Automation and Control Equipment (Study on methods to improve the quality of winding bodies of fiber optic winding bodies) aimed at the problem of asymmetric fiber tension during inertial navigation ring winding, and fed back the strain data measured by B-OTDA to the tension control system in real time, thereby improving the stability and symmetry of tension control and significantly improving the symmetry of sensitive rings. At the same time, OFDR technology based on Rayleigh scattering has developed rapidly in recent years. The OFDR system using the polarization-maintaining scheme can simultaneously test temperature and thermal strain. The University of Ottawa in Canada published a paper (Long-range high spatial resolution distributed temperature and strain sensing based on optical frequency-domain reflectometry) proposing a corresponding test and demodulation scheme. By using the characteristics of negative temperature sensing coefficient and positive strain sensing coefficient, it achieved a temperature resolution of ±0.8°C and a thermal strain resolution of ±7.0°C at a sensing distance of 170m. strain resolution and 1.3 cm spatial resolution

[74] . Yu Zhangjun et al. (Distributed Polarization Measurement for FiberSensing Coils: A Review) proposed a high-performance method to obtain a dynamic range of >90 dB, a measurement length of >10 km, a full-range spatial resolution of <10 cm, and time domain, frequency domain, and time-frequency domain diagnosis in the distributed polarization measurement of fiber sensing coils based on OFDR. W Hong et al. (Accurate measurement and enhancement of fiber coil symmetry) proposed an equivalent midpoint compensation technology based on OFDR, which can accurately test the symmetry of the fiber ring and ensure accurate adjustment of the length of the two ends of the fiber ring, providing important inspiration for our research. Yu Ting et al. (CN 106706001 A) improved the measurement accuracy of the fiber gyroscope by engraving the fiber grating near the center point of the polarization-maintaining fiber ring and relying on OFDR technology to accurately detect the position of the fiber grating and accurately locate the center point of the polarization-maintaining fiber ring optical path.

[0006] However, based on a large number of studies, the parameters that affect the thermal drift of the optical fiber ring and the relationship between the changes of these parameters in the environment are still unclear. At the same time, there is a lack of suitable long-distance, high-precision, and high-spatial resolution temperature and thermal strain test methods, which seriously affects its measurement accuracy. Therefore, the establishment of a new high-precision optical fiber sensitive ring length calibration device and method is of great significance for the parameter detection of optical fiber gyroscopes and distributed optical fiber sensing applications. Summary of the invention

[0007] The purpose of the present invention is to provide a highly accurate, stable and reliable OFDR sensitive loop length calibration device. The purpose of the present invention is also to provide a calibration method for the sensitive loop length calibration device based on OFDR beat frequency interferometry.

[0008] The invention discloses a high-precision non-destructive calibration device for the length of a fiber sensitive loop, which is characterized by comprising a TLS light source module 1, an auxiliary interferometer module 2, a main interferometer module 3, a module to be calibrated 4 and a data processing module 5. The TLS light source module 1 injects a light beam into the first coupler 204, a part of the light is injected into the auxiliary interferometer module 2, and the other part of the light is injected into the main interferometer module 3. The module to be calibrated 4 is connected to the main interferometer module 3, and the auxiliary interference signal and the main interference signal are integrated into the data acquisition card 502, and finally the scattering characteristics of the device to be calibrated are obtained.

[0009] 1. The high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1, characterized in that the auxiliary interferometer module 2 comprises: a 45° polarizer 202, a first coupler 204, a first circulator 207, a second coupler 209, a first Faraday rotator 212, a second Faraday rotator 213, and a first balanced photodetector 214. Light undergoes beat frequency interference in the second coupler 209.

[0010] (1) The 45° polarizer 202 is connected to the TLS light source 101 through the first flange 201.

[0011] (2) The left arm 218 of the first coupler is connected to the 45° polarizer 202 through the second flange 203.

[0012] (3) The first circulator A port 221 is connected to the first coupler right lower arm 220 through the fourth flange 206.

[0013] (4) The second coupler right upper arm 224 is connected to the first circulator B port 222 through the fifth flange 208.

[0014] (5) The second coupler right lower arm 215 and the first circulator C port 223 are respectively connected to the first balanced photodetector 214.

[0015] (6) The first Faraday rotation mirror 212 is connected to the second coupler left upper arm 225 via the sixth flange 210 .

[0016] (7) The second Faraday rotation mirror 213 is connected to the second coupler left lower arm 226 via the seventh flange 211 .

[0017] (8) The first optical fiber 216, the second optical fiber 217, the third optical fiber 218, and the fourth optical fiber 219 are all polarization-maintaining optical fibers.

[0018] (9) The sixth optical fiber 221 , the seventh optical fiber 222 , the eighth optical fiber 223 , the ninth optical fiber 224 , the tenth optical fiber 215 , the eleventh optical fiber 225 , and the delay optical fiber 226 are all single-mode optical fibers.

[0019] 2. The high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1 is characterized in that the main interferometer module 3 comprises: a third coupler 302, a fourth coupler 306, a second circulator 309, a first polarization-maintaining beam splitter 318, a second polarization-maintaining beam splitter 326, a second balanced photodetector 320, and a third balanced photodetector 322. Light undergoes beat frequency interference in the fourth coupler 306.

[0020] (1) The third coupler right arm 301 is connected to the first coupler right upper arm 219 through the third flange 205 .

[0021] (2) The fourth coupler right upper arm 305 is connected to the third coupler left upper arm 303 through the eighth flange 304 .

[0022] (3) The second circulator A port 310 is connected to the third coupler left lower arm 307 through the ninth flange 308.

[0023] (4) The second circulator C port 312 is connected to the fourth coupler right lower arm 314 through the tenth flange 313.

[0024] (5) The first polarization-maintaining beam splitter right arm 317 is connected to the fourth coupler left upper arm 315 through the eleventh flange 316 .

[0025] (6) The right arm 325 of the second polarization-maintaining beam splitter is connected to the left lower arm 323 of the fourth coupler through the twelfth flange 324.

[0026] (7) The second balanced photodetector 320 is connected to the first polarization-maintaining beam splitter left upper arm 319 and the second polarization-maintaining beam splitter left upper arm 327 respectively.

[0027] (8) The third balanced photodetector 322 is connected to the left lower arm 321 of the first polarization-maintaining beam splitter and the left lower arm 328 of the second polarization-maintaining beam splitter respectively.

[0028] (9) The twelfth optical fiber 301, the thirteenth optical fiber 303, the fourteenth optical fiber 307, the fifteenth optical fiber 305, the sixteenth optical fiber 310, the seventeenth optical fiber 311, the eighteenth optical fiber 312, the nineteenth optical fiber 314, the twentieth optical fiber 315, the twenty-first optical fiber 323, the twenty-second optical fiber 317, the twenty-third optical fiber 325, the twenty-fourth optical fiber 319, the twenty-fifth optical fiber 327, the twenty-sixth optical fiber 321, and the twenty-seventh optical fiber 328 are all polarization-maintaining optical fibers.

[0029] 3. According to the high-precision non-destructive calibration device for the length of an optical fiber sensitive ring as described in claim 1, it is characterized in that the module to be calibrated 4 includes: an optical fiber ring 403, a first calibration grating 402, a second calibration grating 407, and an alcohol solution 405.

[0030] (1) The alcohol solution 405 has a reflectivity of 0.2%.

[0031] (2) The optical fiber 407 on the right side of the optical fiber ring is fused with the first calibration grating 402.

[0032] (3) The optical fiber 408 on the left side of the optical fiber ring is fused with the second calibration grating 404.

[0033] (4) The right pigtail 406 is connected to the second circulator B port 311 through the thirteenth flange 401.

[0034] (5) Cut the end of the left pigtail 409 flat and place it in the alcohol solution 405.

[0035] (6) The twenty-eighth optical fiber 406, the twenty-ninth optical fiber 407 and the optical fiber ring 403 are all polarization-maintaining optical fibers.

[0036] 4 . The high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1 , wherein the data processing module 5 comprises: a data processor 501 and a data acquisition card 502 .

[0037] (1) The first balanced photodetector 214 is connected to the data acquisition card 502 via the first electrical conductor 503 .

[0038] (2) The second balanced photodetector 320 is connected to the data acquisition card 502 via the second electrical conductor 504 .

[0039] (3) The third balanced photodetector 322 is connected to the data acquisition card 502 via a third electrical conductor 505 .

[0040] (4) The data acquisition card 502 is connected to the data processing machine 501 via a fourth electrical conductor 506 .

[0041] The present invention provides a calibration method for a high-precision non-destructive calibration device for the length of an optical fiber sensitive loop, which is characterized by:

[0042] (1) Two weak reflection gratings are used to connect the left and right pigtails of the fiber sensitive ring. The right fiber 407 of the fiber ring is connected to the first calibration grating 402, the left fiber 408 of the fiber ring is connected to the second calibration grating 404, and the end of the left pigtail 409 of the fiber ring is cut flat and placed in the alcohol solution 405.

[0043] (2) Measure the reflection peak length S1 at the end of the fiber ring, and measure the first calibration grating position S2 and the second calibration grating position S3.

[0044] (3) Connect the optical frequency domain reflectometer optical path and start the TLS light source 101.

[0045] (4) Use an optical frequency domain reflectometer to test the scattering spectrum of the optical fiber sensitive ring.

[0046] (5) Identify the reflection peak position of the weak reflection grating in the scattering spectrum. Find the end reflection peak according to the intensities S1, S2 and S3, and calibrate the grating tail fiber lengths S2 and S3.

[0047] (6) Observe whether the reflection peak intensity at the end of the fiber ring reaches U1~U2 and whether the fiber Bragg grating reflection intensity reaches U3.

[0048] (7) If the reflection peak intensity at the end of the fiber ring reaches U1~U2, and the reflection intensity of the fiber Bragg grating reaches U3, then record the reflection intensity of the end peak and the fiber Bragg grating.

[0049] (8) If the reflection peak intensity at the end of the fiber ring does not reach U1~U2, or the reflection intensity of the fiber Bragg grating does not reach U3, change the alcohol concentration and replace the corresponding fiber Bragg grating until the reflection peak intensity at the end of the fiber ring reaches U1~U2 and the reflection intensity of the fiber Bragg grating reaches U3, and record the reflection intensity of the end peak and the fiber Bragg grating to complete the calibration.

[0050] The purpose of the present invention is to provide a device and method for accurately calibrating the length of a fiber sensitive ring by accurately detecting the positions of fiber gratings on both sides of the fiber sensitive ring, and to solve the problem that the scattered information in the fiber ring in gyroscope technology cannot be accurately located by constructing an optical frequency domain test system. The present invention is a device and method for calibrating the length of an optical fiber under rapid environmental changes in multi-parameter testing and performance evaluation of an optical fiber ring and a distributed optical fiber sensing system.

[0051] The principle diagram of the OFDR-based calibration device proposed in the present invention is shown in the attached figure. Figure 1 As shown, its characteristics are:

[0052] 1. It consists of a TLS light source 101, a 45° polarizer 202, a first coupler 204, a first circulator 207, a second coupler 209, a first Faraday rotator 212, a second Faraday rotator 213, a first balanced photodetector 214, a third coupler 302, a second circulator 309, a fourth coupler 306, a first polarization-maintaining beam splitter 318, a second polarization-maintaining beam splitter 326, a second balanced photodetector 320, a third balanced photodetector 322, and a device to be calibrated 801.

[0053] 2. The TLS light source 101 provides input light through the 45° polarizer 202 and the first coupler 204. 1% of the output light enters the first circulator 207 through the first connecting optical fiber 802, and enters the second coupler 209 through the B port of the first circulator and the second connecting optical fiber 803. The remaining 99% of the output light enters the third coupler 302 through the third connecting optical fiber 804.

[0054] 3. 50% of the light entering the second coupler 209 passes through the fourth connecting optical fiber 805 and is reflected by the first Faraday rotator 212 to form the first reflected light 806, and the other 50% passes through the delay optical fiber 807 and is reflected by the second Faraday rotator 213 to form the second reflected light 808. The first reflected light 806 and the second reflected light 808 generate beat frequency interference at the second coupler 209. A part of the beat frequency interference signal is sequentially input into the first balanced photodetector 214 through the second connecting optical fiber 803, the first circulator B port, the first circulator C port, and the fifth connecting optical fiber 809, and another part of the beat frequency interference signal is also input into the first balanced photodetector 214 through the sixth connecting optical fiber 810, and the two parts of the beat frequency interference signal are differentially detected.

[0055] 4. 1% of the light entering the third coupler 302 enters the fourth coupler 306 through the seventh connecting optical fiber 811, and the other 99% passes through the eighth connecting optical fiber 812 and the second circulator 309, and enters the device to be calibrated 801 from the second circulator A port, the second circulator B port, and the ninth connecting optical fiber 813 in sequence. The third reflected signal 814 formed by reflection is also input into the fourth coupler 306 through the ninth connecting optical fiber 813, the second circulator B port, the second circulator C port, and the tenth connecting optical fiber 815 to generate a beat frequency interference signal.

[0056] 5. 50% of the beat frequency interference signal generated at the fourth coupler 306 enters the first polarization-maintaining beam splitter 318 through the eleventh connecting optical fiber 816 , and the other 50% enters the second polarization-maintaining beam splitter 326 through the twelfth connecting optical fiber 817 .

[0057] 6. A portion of the light entering the first polarization-maintaining beam splitter 318 is input to the second balanced photodetector 320 via the thirteenth connecting optical fiber 818 , and another portion is input to the third balanced photodetector 322 via the fourteenth connecting optical fiber 819 .

[0058] 7. A portion of the light entering the second polarization-maintaining beam splitter 326 is input into the second balanced photodetector 320 via the fifteenth connecting optical fiber 820 , and another portion is input into the third balanced photodetector 322 via the sixteenth connecting optical fiber 821 .

[0059] The flowchart of the calibration method of the high-precision non-destructive calibration device for the length of the optical fiber sensitive loop proposed by the present invention is shown in the attached figure. Figure 2 As shown, its characteristics are:

[0060] Step 701 is to use two weak reflection gratings to connect the left and right pigtails of the optical fiber sensitive ring. Connect the right optical fiber 407 of the optical fiber ring to the first calibration grating 402, connect the left optical fiber 408 of the optical fiber ring to the second calibration grating 404, and cut the end of the left pigtail 409 of the optical fiber ring flat and place it in the alcohol solution 405.

[0061] Step 702 is to measure the reflection peak length S1 at the end of the optical fiber ring, and to measure the first calibration grating position S2 and the second calibration grating position S3.

[0062] Step 703 is to connect the optical frequency domain reflectometer optical path and start the TLS light source 101.

[0063] Step 704 is to test the scattering spectrum of the optical fiber sensitive ring using an optical frequency domain reflectometer. The scattering signal test is performed at normal temperature and normal conditions, and a scattering spectrum signal is obtained by Fourier transformation.

[0064] Step 705 is to identify the reflection peak position of the weak reflection grating in the scattering spectrum, find the end reflection peak according to the intensities S1, S2 and S3, and calibrate the grating pigtail lengths S2 and S3.

[0065] Step 706 is to observe and determine whether the reflection peak intensity at the end of the fiber ring reaches U1~U2, and whether the fiber Bragg grating reflection intensity reaches U3.

[0066] From step 706, if the reflection peak intensity at the end of the fiber ring reaches U1-U2, and the reflection intensity of the fiber grating reaches U3, then step 707 is executed: recording the reflection intensity of the end peak and the fiber grating.

[0067] According to step 706, if the reflection peak intensity of the fiber ring end does not reach U1~U2, or the fiber grating reflection intensity does not reach U3, then execute step 708: change the alcohol concentration and replace the corresponding fiber grating, return to step 701, etc., until the reflection peak intensity of the fiber ring end reaches U1~U2 and the fiber grating reflection intensity reaches U3, and execute step 707: record the reflection intensity of the end peak and the fiber grating. Complete the calibration.

[0068] The present invention proposes a high-precision lossless calibration device and method for the length of an optical fiber sensitive loop. The basic principle of the device and method is the working principle of an optical frequency domain reflectometer. The OFDR system formed by an interferometer is used to accurately position the fiber gratings at both ends of the optical fiber loop to accurately calibrate the length of the optical fiber sensitive loop.

[0069] Device calibration principle:

[0070] Assume that the light fields of the reference signal and the measurement signal are

[0071]

[0072] The splitting ratio of the third coupler 302 is 1:99, so , then the interference intensity of the two signals is

[0073]

[0074] When the interference signal is split by the fourth coupler (306) with a splitting ratio of 50:50, the output light of the two arms will have a phase difference of π / 2, so the interference signal is divided into two beams with equal intensity and detected by balanced photodetectors. The photocurrent generated by the two balanced detectors can be expressed as

[0075]

[0076] in are the transmitted light intensities in the reference arm and the measurement arm, respectively, is the optical path delay of the measurement arm compared to the reference arm. From the above formula, we can see that the photocurrent generated by the balanced photodetector contains DC and AC components, and the DC component can be eliminated by differential operation. By solving the spectrum of the Rayleigh scattering signal and comparing the calibrated positions of the optical fibers on both sides, the length of the optical fiber ring can be deduced from the spectrum.

[0077] It can be seen that the Rayleigh scattering spectrum results based on OFDR contain the position information of the calibration gratings on both sides, based on which the length of the fiber ring can be accurately inferred and the calibration of the fiber ring length can be completed.

[0078] Compared with the prior art, the advantages of the present invention are:

[0079] 1. The present invention utilizes a weak grating fusion method to non-destructively calibrate the length of the optical fiber sensitive loop without destroying the optical and mechanical properties of the optical fiber sensitive loop.

[0080] 2. The present invention utilizes the reflection peak of the scattering spectrum of the weak grating in the optical frequency domain reflectometer to achieve accurate calibration of the optical fiber ring length. The calibration accuracy meets the requirements of high-precision calibration, and the length calibration accuracy can reach the micron level.

[0081] 3. This device is anti-interference and has good repeatability, ensuring the accuracy and reliability of the calibration results. It can be widely used in high-precision length calibration of optical devices such as polarization-maintaining optical fibers, optical fiber sensitive rings, and optical fiber hydrophones. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 This is the principle diagram of optical frequency domain reflectometry (OFDR) calibration;

[0083] Figure 2 It is a flow chart of the optical fiber sensitive ring calibration method;

[0084] Figure 3 is the structural diagram of the optical fiber ring to be calibrated;

[0085] Figure 4 The diagram is a high-precision non-destructive calibration device for the length of an optical fiber sensitive loop.

[0086] Figure 5 It is the scattering spectrum of the fiber sensitive ring.

[0087] Figure 6 This is the second calibration grating and end reflection peak diagram of the fiber sensitive ring.

[0088] Figure 7 It is the reflection peak diagram of the first calibration grating of the fiber sensitive ring. DETAILED DESCRIPTION

[0089] In order to clearly illustrate the high-precision non-destructive calibration device and method for the length of an optical fiber sensitive ring of the present invention, the present invention is further described in conjunction with the accompanying drawings, but this should not limit the protection scope of the present invention.

[0090] Figure 3 This is the structure of the optical fiber ring to be calibrated of the present invention. Its characteristics are:

[0091] The optical fiber ring structure to be calibrated is composed of an optical fiber ring 403, a first calibration grating 402, a second calibration grating 407, and an alcohol solution 405;

[0092] The reflectivity of the grating and the alcohol solution is as small as possible, for example, less than 2‰.

[0093] When the device to be calibrated 4 is connected to the optical path of the OFDR test system, the swept light first passes through the second calibration grating 407, and the reflected light carries the position information of the second calibration grating and returns to the optical path of the OFDR test system through the right pigtail 406. The transmitted light passes through the fiber ring to be calibrated 403 and then undergoes a slight reflection and transmission at the first calibration grating 404. The reflected light carries the position information of the first calibration grating and returns to the optical path of the OFDR test system; the transmitted light also undergoes a slight reflection and transmission at the second calibration grating 407 through the fiber ring 403, and is reflected by the left pigtail and the alcohol solution 405. The reflected light passes through the second calibration grating 407, the fiber ring to be calibrated 403, and the first calibration grating 402 in sequence, and returns to the optical path of the OFDR test system through the right pigtail 406, thereby obtaining the position information of the calibration gratings on both sides of the fiber ring, and then accurately obtaining the fiber ring length information.

[0094] Figure 4 The invention is a high-precision non-destructive calibration device for the length of a fiber sensitive loop, comprising a TLS light source module 1, an auxiliary interferometer module 2, a main interferometer module 3, a module to be calibrated 4, and a data processing module 5. The structure of the module to be calibrated 4 is similar to Figure 3 The structure of the optical fiber ring to be calibrated is the same.

[0095] Combination Figure 4One implementation of the present invention is: setting the sweep range of the TLS light source 101 to 10nm~160nm and the sweep speed to 10nm / s, and 1% of the swept light emitted by the first coupler 204 enters the auxiliary interferometer module 2 and 99% enters the main interferometer module 3.

[0096] 1% of the light entering the main interferometer module 3 passes through the third coupler left upper arm 303 and the fourth coupler right upper arm 305 and enters the fourth coupler 306 , and the other 99% passes through the third coupler left lower arm 307 and the second circulator 309 .

[0097] The 1% light passing through the third coupler left upper arm 303 and the fourth coupler right upper arm 305 is used as a reference signal, and the 99% light passing through the third coupler left lower arm 307 and the second circulator 309 then passes through the first calibration grating 402, the fiber ring 403, the second calibration grating 407 and returns to the original path as a test signal carrying the position information of the two calibration gratings. The two signals are received by the data acquisition card 502 with a sampling frequency of 180MHz after the beat frequency interference occurs at the fourth coupler 306.

[0098] The TLS light source 101 and the data acquisition card 502 are triggered to calibrate the calibration gratings on both sides of the optical fiber ring to be calibrated.

[0099] Collect test data. Observe and determine whether the reflection peak intensity at the end of the fiber ring reaches U1~U2, and the fiber Bragg grating reflection intensity reaches U3. If the judgment conditions are met, complete the calibration of the fiber ring and record the temperature sensor data of the corresponding time series. If the judgment conditions are not met, change the alcohol concentration, replace the corresponding fiber Bragg grating, and restart the fiber ring calibration step until the judgment conditions are met. Record the reflection intensity of the end peak and the fiber Bragg grating to complete the calibration.

[0100] According to the calibration method of the high-precision non-destructive calibration device of the optical fiber sensitive loop length of the present invention, the Figure 5 Fiber sensitive ring scattering spectrum, Figure 6 The second calibration grating and end reflection peak diagram of the fiber sensitive ring Figure 7 It is the reflection peak diagram of the first calibration grating of the fiber sensitive ring.

[0101] This calibration device and method meet the requirements of high-precision calibration, and the position accuracy can reach the millimeter level.

Claims

1. A high-precision non-destructive calibration device for the length of an optical fiber sensitive loop, characterized by: The invention comprises a TLS light source module (1), an auxiliary interferometer module (2), a main interferometer module (3), a module to be calibrated (4) and a data processing module (5). The TLS light source module (1) injects a light beam into a first coupler (204), a part of the light is injected into the auxiliary interferometer module (2), and another part of the light is injected into the main interferometer module (3). The module to be calibrated (4) is connected to the main interferometer module (3), and the auxiliary interference signal and the main interference signal are fed into a data acquisition card (502), and finally the scattering characteristics of the device to be calibrated are obtained.

2. A high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1, characterized in that The auxiliary interferometer module (2) comprises: a 45° polarizer (202), a first coupler (204), a first circulator (207), a second coupler (209), a first Faraday rotation mirror (212), a second Faraday rotation mirror (213), and a first balanced photodetector (214). Light undergoes beat frequency interference in the second coupler (209). (1) A 45° polarizer (202) is connected to a TLS light source (101) via a first flange (201). (2) The left arm (218) of the first coupler is connected to the 45° polarizer (202) via the second flange (203). (3) The A port (221) of the first circulator is connected to the right lower arm (220) of the first coupler via the fourth flange (206). (4) The right upper arm (224) of the second coupler is connected to the B port (222) of the first circulator via the fifth flange (208). (5) The second coupler right lower arm (215) and the first circulator C port (223) are respectively connected to the first balanced photodetector (214). (6) The first Faraday rotation mirror (212) is connected to the left upper arm (225) of the second coupler via the sixth flange (210). (7) The second Faraday rotation mirror (213) is connected to the left lower arm (226) of the second coupler via the seventh flange (211). (8) The first optical fiber (216), the second optical fiber (217), the third optical fiber (218), the fourth optical fiber (219), and the fifth optical fiber (220) are all polarization-maintaining optical fibers. (9) The sixth optical fiber (221), the seventh optical fiber (222), the eighth optical fiber (223), the ninth optical fiber (224), the tenth optical fiber (215), the eleventh optical fiber (225), and the delay optical fiber (226) are all single-mode optical fibers.

3. The high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1 is characterized in that The main interferometer module (3) comprises: a third coupler (302), a fourth coupler (306), a second circulator (309), a first polarization-maintaining beam splitter (318), a second polarization-maintaining beam splitter (326), a second balanced photodetector (320), and a third balanced photodetector (322). Light undergoes beat frequency interference in the fourth coupler (306). (1) The third coupler right arm (301) is connected to the first coupler right upper arm (219) via the third flange (205). (2) The fourth coupler right upper arm (305) is connected to the third coupler left upper arm (303) via the eighth flange (304). (3) The A port (310) of the second circulator is connected to the left lower arm (307) of the third coupler through the ninth flange (308). (4) The C port (312) of the second circulator is connected to the right lower arm (314) of the fourth coupler through the tenth flange (313). (5) The right arm (317) of the first polarization-maintaining beam splitter is connected to the left upper arm (315) of the fourth coupler through the eleventh flange (316). (6) The right arm (325) of the second polarization-maintaining beam splitter is connected to the left lower arm (323) of the fourth coupler through the twelfth flange (324). (7) The second balanced photodetector (320) is respectively connected to the left upper arm (319) of the first polarization-maintaining beam splitter and the left upper arm (327) of the second polarization-maintaining beam splitter. (8) The third balanced photodetector (322) is respectively connected to the left lower arm (321) of the first polarization-maintaining beam splitter and the left lower arm (328) of the second polarization-maintaining beam splitter. (9) The twelfth optical fiber (301), the thirteenth optical fiber (303), the fourteenth optical fiber (307), the fifteenth optical fiber (305), the sixteenth optical fiber (310), the seventeenth optical fiber (311), the eighteenth optical fiber (312), the nineteenth optical fiber (314), the twentieth optical fiber (315), the twenty-first optical fiber (323), the twenty-second optical fiber (317), the twenty-third optical fiber (325), the twenty-fourth optical fiber (319), the twenty-fifth optical fiber (327), the twenty-sixth optical fiber (321), and the twenty-seventh optical fiber (328) are all polarization-maintaining optical fibers.

4. The high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1 is characterized in that The module to be calibrated (4) comprises: an optical fiber ring (403), a first calibration grating (402), a second calibration grating (407), and an alcohol solution (405). (1) The alcohol solution (405) has a reflectivity of 0.2%. (2) The optical fiber (407) on the right side of the optical fiber ring is fused with the first calibration grating (402). (3) The optical fiber (408) on the left side of the optical fiber ring is fused with the second calibration grating (404). (4) The right pigtail (406) is connected to the B port (311) of the second circulator through the thirteenth flange (401). (5) The end of the left pigtail (409) is cut flat and placed in the alcohol solution (405). (6) The fiber ring and its left and right sides, the calibration grating and its pigtails (402-404, 406-409) are all polarization-maintaining fibers.

5. The high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1, characterized in that The data processing module (5) comprises: a data processing machine (501) and a data acquisition card (502). (1) The first balanced photodetector (214) is connected to the data acquisition card (502) via a first electrical conductor (503). (2) The second balanced photodetector (320) is connected to the data acquisition card (502) via a second electrical conductor (504). (3) The third balanced photodetector (322) is connected to the data acquisition card (502) via a third electrical conductor (505). (4) The data acquisition card (502) is connected to the data processing machine (501) via a fourth electrical conductor (506).

6. The calibration method of a high-precision non-destructive calibration device for the length of an optical fiber sensitive loop according to claim 1 is characterized by: (1) Two weak reflection gratings are used to connect the left and right pigtails of the optical fiber sensitive ring. The right optical fiber (407) of the optical fiber ring is connected to the first calibration grating (402), the left optical fiber (408) of the optical fiber ring is connected to the second calibration grating (404), and the end of the left pigtail (409) of the optical fiber ring is cut flat and placed in an alcohol solution (405). (2) Measure the reflection peak length S1 at the end of the fiber ring, and measure the first calibration grating position S2 and the second calibration grating position S3. (3) Connect the optical frequency domain reflectometer optical path and start the TLS light source (101). (4) Use an optical frequency domain reflectometer to test the scattering spectrum of the optical fiber sensitive ring. (5) Identify the reflection peak position of the weak reflection grating in the scattering spectrum. Find the end reflection peak according to the intensities S1, S2 and S3, and calibrate the grating tail fiber lengths S2 and S3. (6) Observe whether the reflection peak intensity at the end of the fiber ring reaches U1~U2 and whether the fiber Bragg grating reflection intensity reaches U3. (7) If the reflection peak intensity at the end of the fiber ring reaches U1~U2, and the reflection intensity of the fiber Bragg grating reaches U3, then record the reflection intensity of the end peak and the fiber Bragg grating. (8) If the reflection peak intensity at the end of the fiber ring does not reach U1~U2, or the reflection intensity of the fiber Bragg grating does not reach U3, change the alcohol concentration and replace the corresponding fiber Bragg grating until the reflection peak intensity at the end of the fiber ring reaches U1~U2 and the reflection intensity of the fiber Bragg grating reaches U3, and record the reflection intensity of the end peak and the fiber Bragg grating to complete the calibration.

Images