1. The optical performance testing method of the optical fiber sensitive ring based on the distributed polarization crosstalk is characterized by comprising the following steps:

data preprocessing link S1: processing the parameter data, and measuring the distributed polarization crosstalk;

frequency domain analysis segment S2: carrying out frequency domain analysis on the distributed polarization crosstalk, and extracting the frequency domain characteristics of the optical fiber sensitive ring (211);

spatial domain analysis link S3: and performing spatial domain analysis on the distributed polarization crosstalk to extract spatial domain characteristics of the optical fiber sensitive ring (211).

2. The method for testing optical performance of a fiber-optic sensitive ring based on distributed polarization crosstalk according to claim 1, wherein the data preprocessing step S1 includes: a geometry measuring step (101); a parameter setting step (102); a forward and reverse polarization crosstalk measurement step (103); a measurement result determination step (104); the steps are as follows:

the geometric measurement step (101) is to select a fiber-optic sensing ring (211) to be measured, measure and record the inner diameter d thereof_minOuter diameter d_maxAnd a fiber length L of the fiber sensing loop (211);

the parameter setting step (102) is to inquire the winding mode of the optical fiber sensitive ring (211) to be measured, obtain the number N of turns (214) of the turn change (214) and the number M of layers of the layer change (215) of the optical fiber sensitive ring (211), and calculate the length l of the optical fiber corresponding to each turn of the ith layer_i＝π·d_i,(d_min≤d_i≤d_maxI-1, 2, L M), wherein d_iCalculating the length L of the optical fiber corresponding to the ith layer for the diameter of the optical fiber sensitive ring (211) corresponding to the ith layer_i＝l_iN, calculating the turn-changing frequency k_i＝1/l_iAnd a layer change frequency K_i＝1/L_iRecording the test temperature, setting q to be 1 for carrying out the temperature variation test, and setting q to be 0 for not carrying out the temperature variation test;

the forward and reverse polarization crosstalk measurement step (103) is to measure and obtain a first distributed polarization crosstalk (301) of light transmitted from the first end (212) of the optical fiber sensing ring to the second end (213) of the optical fiber sensing ring and a second distributed polarization crosstalk (501) of light transmitted from the second end (213) of the optical fiber sensing ring (211) to the first end (212), respectively;

the step (104) of determining the measurement result is to select the peak of the polarization crosstalk greater than the polarization crosstalk threshold I in the first distributed polarization crosstalk (301) and the second distributed polarization crosstalk (501), and the light intensities are marked as I_1,xAnd I_2,x，I_1,xRepresents the polarization crosstalk of the first distributed polarization crosstalk (301) peak at the fiber length x, I_2,xA polarization crosstalk representing a peak of a second distributed polarization crosstalk (501) at a fiber length x requires I_1,x、I_2,xMaking a difference, wherein the difference is in the range of x epsilon (0, L)The absolute value of the value satisfies max_x∈(0,L)|I_1,x-I_2,xIf | ≦ ε, returning to the forward and reverse polarization crosstalk measurement step (103) for re-measurement if | ≦ ε, and recording the first distributed polarization crosstalk if | ≦ ε.

3. The method for testing optical performance of the fiber-optic sensitive ring based on distributed polarization crosstalk of claim 2, wherein the frequency-domain analysis step S2 comprises the steps of: a Fourier transform step (105); a frequency domain feature extraction step (106); the steps are as follows:

the Fourier transform step (105) is to perform Fourier transform on the first distributed polarization crosstalk (301) and convert the first distributed polarization crosstalk into frequency domain polarization crosstalk (701);

the frequency domain feature extraction step (106) intercepts the interval [ k ] in the frequency domain polarization crosstalk (701)_lb,k_rb]As a frequency domain turn-changing feature (705), intercept the interval [ K ] in the frequency domain polarization crosstalk (701)_lb，K_rb]As a frequency domain transposition feature (704), wherein the frequency domain transposition feature (705) extracts the left boundary k of the region_lbRight boundary k_rbAnd the left boundary K of the frequency domain layer change feature (704) extraction region_lbRight boundary K_rbSatisfy k respectively_lb≤1/l_max、k_rb≥1/l_min、K_lb≤1/L_maxAnd K_rb≥1/L_min。

4. The method for testing optical performance of the fiber-optic sensitive ring based on distributed polarization crosstalk of claim 3, wherein the spatial analysis unit S3 comprises the following steps: a filter design step (107); a spatial domain feature extraction step (108); the steps are as follows:

a filter design step (107) calculates the turn-changing frequency k according to the geometric measurement step (101) and the parameter setting step (102)_minAnd a layer change frequency K_maxDesigning the low-pass filter (702) and the high-pass filter (703) in such a way that the passband cut-off frequency k of the low-pass filter (702) is required_LPFAnd a high-pass filter (703) passband cut-off frequency k_HPFSatisfies the following conditions:

in the spatial domain feature extraction step (108), a low-pass filter (702) and a high-pass filter (703) are used for filtering the first distributed polarization crosstalk (301), after the filtering is carried out by the low-pass filter (702), a spatial domain crosstalk background and layer change comprehensive feature (801) is extracted, and after the filtering is carried out by the high-pass filter (703), a spatial domain turn change feature (802) is extracted.

5. The method for testing the optical performance of the optical fiber sensitive ring based on the distributed polarization crosstalk according to claim 1, further comprising a temperature variation testing step after the spatial domain analysis step S3, wherein the temperature variation testing step comprises the steps of: a Fourier transform step (105); a frequency domain feature extraction step (106); a filter design step (107); a spatial domain feature extraction step (108); a temperature variation test step (109); a feature extraction step (110); a temperature determination step (111); a polarization crosstalk measurement step (112); a temperature change feature extraction step (113); the specific execution flow is as follows:

firstly, executing a temperature change test step (109), acquiring a user instruction and judging whether to perform a temperature change test;

if the judgment result in the step (109) is negative, executing a characteristic extraction step (110) to extract frequency domain characteristics and space domain characteristics, and finishing measurement;

if the judgment result in the step (109) is yes, setting the initial temperature of the test environment to be T₀End temperature of T_uThe rate of change in temperature is v_TThe variation of temperature sampling is delta T, and the test temperature T is T₀+v_TT, judging whether the test temperature is greater than T at the moment_uIf greater than T_uIf so, executing a temperature variation characteristic extraction step (113) and then ending the measurement; if less than T_uSequentially executing a polarization crosstalk measurement step (112), a Fourier transform step (105), a frequency domain feature extraction step (106), a filter design step (107), a spatial domain feature extraction step (108), a temperature variation test step (109), and a special test stepAnd the characterization extraction step (110) and the temperature judgment step (111) carry out measurement until the measurement is finished.

6. The method for testing optical performance of an optical fiber sensitive ring based on distributed polarization crosstalk according to claim 5, wherein the temperature-dependent characteristic extraction step (113) is specifically as follows: the temperature change characteristic of the optical fiber sensing ring is extracted, the distributed polarization crosstalk at normal temperature is selected as a reference value, and the distributed polarization crosstalk is considered as abnormal crosstalk when the relative change of the amplitude of the distributed polarization crosstalk and the reference value measured at different temperatures exceeds a set threshold value rho.

7. The method for testing optical performance of a fiber-optic sensitive ring based on distributed polarization crosstalk according to claim 5, wherein the polarization crosstalk measuring step (112) is specifically as follows:

a first distributed polarization crosstalk (301) is measured in which light is transmitted from a first end (212) of the fiber optic sensor ring to a second end (213) of the fiber optic sensor ring.

8. The method for testing optical performance of a fiber-optic sensitive loop based on distributed polarization crosstalk according to claim 2, wherein the measuring method of the first distributed polarization crosstalk (301) and the second distributed polarization crosstalk (501) in the forward-backward polarization crosstalk measuring step (103) comprises: injecting a beam of wide-spectrum polarized light along the polarization axis direction of the polarization-maintaining fiber, forming an excitation mode (231) in the polarization axis direction, and transmitting the excitation mode forwards along the fiber; if a perturbation point (230) exists in the transmission polarization maintaining optical fiber, the excitation mode is coupled at the perturbation point, and a coupling mode (232) is generated; because the effective mode refractive indexes of two polarization axes of the polarization maintaining fiber are different, a certain optical path difference can be generated after an excitation mode (231) and a coupling mode (232) transmitted along the fiber pass through a distance, two wave packets with different powers and a certain optical path difference can be generated by coupling the two modes into a common single mode fiber by using a 45-degree polarization analyzer, the two wave packets are respectively coupled into two arms of an interferometer, the arm length of a scanning arm is changed to adjust the arm length difference of the two arms of the interferometer, so that wave trains in the two arms are interfered, and a polarization crosstalk measurement result is finally obtained.

9. The method according to claim 8, wherein the polarization-maintaining fiber polarization axis into which the broad-spectrum polarized light is injected is a slow axis.

10. The method according to claim 8, wherein the polarization-maintaining fiber polarization axis into which the broad-spectrum polarized light is injected is a fast axis.

Background

The optical fiber gyroscope sensitive ring is one of core components in a high-precision optical fiber gyroscope, and generally comprises three parts, namely an annular supporting framework, an optical fiber wound outside and glue for curing, wherein the supporting framework of the optical fiber gyroscope sensitive ring, the size parameter of the optical fiber ring, the optical fiber parameter, the glue fixing parameter, the ring winding method, the temperature and the like all have certain influence on the performance of the optical fiber gyroscope sensitive ring. And the difference of winding schemes can cause the difference of the overall performance of the fiber-optic gyroscope sensitive ring. The winding scheme of the current fiber optic gyroscope sensing ring mainly comprises the following steps: four-pole winding, improved four-pole winding, eight-pole winding, sixteen-pole winding, etc. Of these, the symmetrical four-pole winding method is the most commonly used winding scheme at present. Publication No. CN104251698A, publication date: 2014-12-31, the method for preparing the sensing ring capable of reducing the temperature drift of the fiber optic gyroscope comprises the steps of installing a winding tool on two layers of stepped ring frameworks, and winding the optical fiber according to a quadrupole symmetric winding method, so that the defects of the prior art are overcome, and the performance of the sensing ring is improved.

In order to obtain the winding quality and defects of the fiber-optic gyroscope sensitive ring, the fiber-optic gyroscope sensitive ring needs to be detected. The traditional method for detecting the fiber optic gyroscope sensitive ring evaluates the performance of the fiber optic gyroscope sensitive ring by means of extinction ratio or optical time domain reflection technology, but the method cannot completely and accurately reflect the winding quality and defects of the fiber optic gyroscope sensitive ring, so that accurate suggestions for improving the quality of the fiber optic ring cannot be provided, and the method has limitation.

The distributed polarization crosstalk of the fiber-optic gyroscope sensitive ring is analyzed, and the method can be used for measuring the winding quality of the fiber-optic gyroscope sensitive ring and searching for the defects of the fiber-optic gyroscope sensitive ring. The current distributed polarization crosstalk analysis method mainly comprises the following steps: a threshold method, an integration method, etc. The threshold method is to divide the distributed polarization crosstalk into two parts for analysis by setting a threshold; the integration method is to integrate the distributed polarization crosstalk and then perform corresponding calculation analysis.

Publication No. CN102494877A, publication date: 2012-06-13, the method for demodulating the extinction ratio test data of the white light interferometry polarization device can be used for measuring the polarization device, i.e. the fiber optic gyroscope sensitive ring. The method utilizes distributed polarization crosstalk to obtain the extinction ratio, the threshold value is designed, the distributed polarization crosstalk is divided into two parts, the extinction ratio is calculated, and therefore the extinction ratio is more accurate to measure.

Publication No. CN111964873A, publication date: 2020-11-20, the proposed high-precision distributed extinction ratio measurement method for the polarization maintaining fiber can be used for measuring a fiber optic gyroscope sensitive ring obtained by winding the polarization maintaining fiber. The method utilizes an integral mode to calculate and obtain the distributed extinction ratio, the measurement principle can be well understood, but the algorithm is complex, and the calculation time is too long. The method can only simply analyze the distributed polarization crosstalk to obtain an integral result, cannot obtain complete information of the sensitive defect of the fiber-optic gyroscope, and cannot search the sensitive local defect of the fiber-optic gyroscope.

Disclosure of Invention

The invention aims to accurately analyze the distributed polarization crosstalk of the optical fiber sensitive ring, and the analysis result can obtain the optical performance and the temperature change characteristic of the optical fiber sensitive ring, thereby providing help for the improvement of the ring winding process and improving the performance of the optical fiber sensitive ring.

The optical performance testing method of the optical fiber sensitive ring based on the distributed polarization crosstalk comprises the following steps:

data preprocessing link S1: processing the parameter data, and measuring the distributed polarization crosstalk;

frequency domain analysis segment S2: performing frequency domain analysis on the distributed polarization crosstalk, and extracting frequency domain characteristics of the optical fiber sensitive ring 211;

spatial domain analysis link S3: performing spatial domain analysis on the distributed polarization crosstalk, and extracting spatial domain characteristics of the optical fiber sensitive ring 211;

the technical scheme is based on the white light interference principle, on the basis of obtaining the distributed polarization crosstalk of the fiber-optic gyroscope sensitive ring, the spatial domain characteristic and the frequency domain characteristic of the fiber-optic gyroscope sensitive ring are respectively obtained through spatial domain analysis and frequency domain analysis, and then the temperature change characteristic of the fiber-optic gyroscope sensitive ring is obtained through applying the method to a temperature change test. The method can extract the characteristic parameters of various optical properties of the optical fiber sensing ring, and can be widely used for evaluating the performance of the optical fiber gyroscope sensing ring and evaluating the winding process.

Further, the data preprocessing step S1 includes the following steps:

the geometry measuring step 101 is to select a fiber-optic sensing ring 211 to be measured, measure and record the inner diameter d thereof_minOuter diameter d_maxAnd the fiber length L of the fiber sensing ring 211;

the parameter setting step 102 is to inquire the winding mode of the fiber-optic sensing ring 211 to be measured, obtain the number of turns N of the turn-changing 214 and the number M of layers of the layer-changing 215 of the fiber-optic sensing ring 211, and calculate the length l of the fiber corresponding to each turn of the ith layer_i＝π·d_i,(d_min≤d_i≤d_maxI-1, 2, L M), wherein d_iCalculating the length L of the optical fiber corresponding to the ith layer for the diameter of the optical fiber sensing ring 211 corresponding to the ith layer_i＝l_iN, calculating the turn-changing frequency k_i＝1/l_iAnd a layer change frequency K_i＝1/L_iRecording the test temperature, setting q to be 1 for carrying out the temperature variation test, setting q to be 0 for not carrying out the temperature variation test, and setting q as a judgment parameter for judging whether the temperature variation test is carried out or not;

the forward and reverse polarization crosstalk measuring step 103 is to measure and obtain a first distributed polarization crosstalk 301 in which light is transmitted from the first end 212 of the optical fiber sensing ring to the second end 213 of the optical fiber sensing ring and a second distributed polarization crosstalk 501 in which light is transmitted from the second end 213 of the optical fiber sensing ring 211 to the first end 212;

the measurement result determining step 104 is to select the firstThe peak of the polarization crosstalk greater than the polarization crosstalk threshold I in the distributed polarization crosstalk 301 and the second distributed polarization crosstalk 501, the light intensity thereof is denoted as I_1,xAnd I_2,x，I_1,xThe polarization crosstalk, I, representing the peak of the first distributed polarization crosstalk 301 at the fiber length x_2,xThe polarization crosstalk representing the peak of the second distributed polarization crosstalk 501 at the fiber length x requires I_1,x、I_2,xMaking a difference, and enabling the absolute value of the difference value to satisfy max in the range of x epsilon (0, L)_x∈(0,L)|I_1,x-I_2,xIf | < epsilon, returning to the forward and reverse polarization crosstalk measurement step 103 for re-measurement if | < epsilon > is not greater than |, and recording a first distributed polarization crosstalk 301 if |;

in the technical scheme, the value of the parameter q is obtained by acquiring a user instruction.

Further, in the method for testing optical performance of the optical fiber sensitive ring based on distributed polarization crosstalk, the frequency domain analysis step S2 includes the following steps:

the fourier transform step 105 is to perform fourier transform on the first distributed polarization crosstalk 301 to convert it into a frequency domain polarization crosstalk 701;

frequency domain feature extraction step 106 intercepts interval [ k ] in frequency domain polarization crosstalk 701_lb,k_rb]The data of (1) is used as a frequency domain turn-changing characteristic 705, and an interval [ K ] in the frequency domain polarization crosstalk 701 is intercepted_lb，K_rb]As a frequency domain transposition feature 704, wherein the frequency domain transposition feature 705 extracts the left boundary k of the region_lbRight boundary k_rbAnd the left boundary K of the sum frequency domain layer change feature 704 extraction region_lbRight boundary K_rbSatisfy k respectively_lb≤1/l_max、k_rb≥1/l_min、K_lb≤1/L_maxAnd K_rb≥1/L_min；

Further, in the method for testing optical performance of a fiber optic sensing ring based on distributed polarization crosstalk, the spatial analysis link S3 includes the following steps:

the filter design step 107 calculates the turn-changing frequency k according to the geometric measurement step 101 and the parameter setting step 102_minAnd a layer change frequency K_maxThe low-pass filter 702 and the high-pass filter 703 are designed in such a manner that the passband cut-off frequency k of the low-pass filter 702 is required_LPFAnd a high pass filter 703 passband cutoff frequency k_HPFSatisfy the requirement of

The spatial domain feature extraction step 108 is to filter the first distributed polarization crosstalk 301 by using a low-pass filter 702 and a high-pass filter 703, extract a spatial domain crosstalk background and layer change comprehensive feature 801 after filtering by the low-pass filter 702, and extract a spatial domain turn change feature 802 after filtering by the high-pass filter 703;

further, the optical performance testing method of the optical fiber sensitive ring based on the distributed polarization crosstalk is used for measuring temperature variation characteristics, and the temperature variation testing link S4 includes the following steps:

a temperature change testing link: judging whether to perform temperature change test according to the value of q, otherwise, extracting frequency domain characteristics and space domain characteristics in a characteristic extraction step 110, finishing the measurement, and if so, setting the initial temperature of the test environment to be T₀End temperature of T_uThe rate of change in temperature is v_TThe variation of temperature sampling is delta T, and the test temperature T is T₀+v_TT, judging whether the test temperature is greater than T at the moment_uIf so, ending the measurement, otherwise, repeating the steps 112, 105, 106, 107, 108, 109, 110 and 111 to perform the measurement until the measurement is completed, extracting the temperature change characteristic of the optical fiber sensitive ring by the temperature change characteristic extraction step 113, selecting the distributed polarization crosstalk at the normal temperature as a reference value, and considering the distributed polarization crosstalk as abnormal crosstalk when the relative change between the amplitude of the distributed polarization crosstalk measured at different temperatures and the reference value exceeds a set threshold value rho.

Further, the polarization crosstalk measuring step 112:

the polarization crosstalk measurement step 112 is to measure a first distributed polarization crosstalk 301 transmitted from the first end 212 of the fiber sensing ring to the second end 213 of the fiber sensing ring.

The test principle of the method for testing the optical performance of the fiber sensing ring based on the distributed polarization crosstalk is as shown in fig. 2(b), wherein a beam of wide-spectrum polarized light is injected along a certain polarization axis (fast axis or slow axis) direction of the polarization maintaining fiber, an excitation mode 231 is formed in the polarization axis direction, and the beam is transmitted along the fiber. If the polarization maintaining fiber in transmission has a perturbation point 230, the excited modes will couple there, creating a coupled mode 232. Because the effective mode refractive indexes of the two polarization axes of the polarization maintaining fiber are different, a certain optical path difference can be generated after the excitation mode 231 and the coupling mode 232 transmitted along the fiber pass through a certain distance, two wave packets with different powers and a certain optical path difference can be generated by coupling the two modes into the common single-mode fiber by using a 45-degree polarization analyzer, the two wave packets are respectively coupled into two arms of an interferometer, the arm length of a scanning arm is changed to adjust the arm length difference of the two arms of the interferometer, so that wave trains in the two arms are interfered, and finally measurement data are obtained.

The principle that the optical fiber sensing ring has the periodic characteristic is taken as an example of a quadrupole symmetric winding method, the number of optical fiber layers of the quadrupole symmetric winding method is a multiple of 4, and therefore, each four layers is a unit. As shown in fig. 2(a), the winding method of the optical fiber sensing ring is bounded by the middle point 221 of the optical fiber, and half of the optical fiber 222 is selected to start winding a layer of optical fiber on the framework from right to left; then using the other half of the optical fiber 223 to wind 1 layer of optical fiber from left to right, and then using the small changing layer 224 to wind 1 layer of optical fiber from right to left; and next, winding 1 layer of optical fiber by using the optical fiber 222 through the large exchange layer 225, then winding 1 layer of optical fiber by using the small exchange layer 224, sequentially winding the optical fiber according to the sequence of alternately separating two layers, and so on to form a complete optical fiber sensing ring. The winding process shows that when winding each layer of optical fiber, stress is introduced every time one turn is changed, and further polarization crosstalk is generated; each time the small switching layer 224 and the large switching layer 225 are implemented, a corresponding stress is also introduced, resulting in a corresponding polarization crosstalk. These occur periodically. The periodic characteristics of the optical fiber sensitive ring can be obtained by analyzing the polarization crosstalk obtained by measuring the optical fiber sensitive ring.

Compared with the prior art, the invention has the advantages that:

the method can obtain the frequency domain layer changing characteristic and the frequency domain turn changing characteristic of the optical fiber sensitive ring by carrying out frequency domain analysis on the distributed polarization crosstalk of the optical fiber sensitive ring;

the method can obtain the airspace characteristics of the optical fiber sensitive ring by performing airspace analysis on the distributed polarization crosstalk of the optical fiber sensitive ring, namely the airspace characteristics of the optical fiber sensitive ring, namely the airspace crosstalk background and layer changing comprehensive characteristics and airspace turn changing characteristics.

The method can obtain the frequency domain and the periodic temperature variation characteristic of the space domain of the optical fiber sensing ring by carrying out temperature variation test on the optical fiber sensing ring and carrying out space domain analysis and frequency domain analysis on the optical fiber sensing ring.

The method can accurately analyze the distributed polarization crosstalk of any optical fiber sensing ring, extract the multi-parameter characteristics of the optical fiber sensing ring, and can be widely used for evaluating the optical fiber sensing ring manufacturing process.

Drawings

FIG. 1 is a flow chart of a method for measuring optical performance and temperature change characteristics of an optical fiber sensing ring;

FIG. 2(a) is a diagram of a fiber optic sensor ring device;

FIG. 2(b) is a schematic diagram of distributed polarization crosstalk measurement

FIG. 3 is a first distributed polarization cross-talk diagram;

FIG. 4 is a detailed diagram of a first distributed polarization crosstalk;

FIG. 5 is a second distributed polarization cross talk diagram;

FIG. 6 is a detailed view of a second distributed polarization crosstalk;

FIG. 7 is a frequency domain diagram of distributed polarization crosstalk for a fiber optic sensor ring;

FIG. 8 is a spatial domain diagram of distributed polarization crosstalk for a fiber optic sensor ring;

FIG. 9 is a bottom view of optical fiber sensor ring crosstalk at different temperatures;

FIG. 10 is a detailed diagram of the background of the crosstalk of the fiber-optic sensor ring at different temperatures;

FIG. 11 is a frequency domain plot of the fiber optic sensor ring at different temperatures.

Detailed Description

For clearly explaining the method for testing optical performance of the fiber-optic sensitive ring based on distributed polarization crosstalk, the present invention will be further described with reference to examples and drawings, but the scope of the present invention should not be limited thereby.

Examples

Selecting a fiber-optic sensing ring 201 to be measured, measuring and recording the inner diameter d thereof_min0.1365m, outer diameter d_max0.1435m and the fiber length L of the fiber sensing ring 211 is 3051 m;

the number of turns N of the optical fiber sensing ring 201 is 100, the number of layers M is 64, and l is calculated_min0.43m, l_maxIs 0.45m, L_min43.48m and L_maxIs 50.38 m;

measuring and obtaining a first distributed polarization crosstalk 301 transmitted from the first end 212 to the second end 213 of the fiber sensor ring 211 and a second distributed polarization crosstalk 501 transmitted from the second end 213 to the first end 212 of the fiber sensor ring 211, respectively, as shown in fig. 3 and 5;

as shown in FIGS. 3 and 5, the peaks of the first distributed polarization crosstalk 301 and the second distributed polarization crosstalk 501 greater than the polarization crosstalk threshold by-40 dB are selected, and the polarization crosstalk is denoted as I_1,xAnd I_2,xThe numbers are 302 to 323 and 502 to 523, and difference comparison is performed to satisfy max_x∈(0,3051)|I_1,x-I_2,xRecording a first distributed polarization crosstalk 301 according to the requirement that | ≦ 1 dB;

the first distributed polarization crosstalk 301 is fourier transformed into a distributed frequency domain polarization crosstalk 701, as shown in fig. 7;

the left boundary of the selected region of the frequency domain turn-changing characteristic 705 is k through calculation_lb≤2.22m^-1The right boundary is k_rb≥2.32m^-1The left boundary of the frequency domain layer change feature 704 frame region is K_lb≤0.019m^-1The right boundary is K_rb≥0.023m^-1The extracted frequency domain turn-changing peak and frequency domain layer-changing peak are shown in figure 7;

calculated turn change frequency k_minIs 2.32m-1 and a layer-changing frequency K_maxFor 0.0198m-1, a low-pass filter 702 and a high-pass filter 703 are designed, the pass-band frequency k of the low-pass filter 702_LPFAnd a high pass filter 703 passband frequency k_HPFSatisfy 0.0594<k_LPF,k_HPF<1.16；

After filtering through a low-pass filter 702, extracting a spatial domain crosstalk background and a layer change comprehensive characteristic 801, wherein the crosstalk background is about-80 dB, the strength of a layer change peak is-60-30 dB, two adjacent peak values are separated by about 50m, after filtering through a high-pass filter 703, extracting a spatial domain turn change characteristic 802, the strength of a turn change peak is-70-60 dB, and the distance between the two adjacent peak values is about 0.4m, as shown in figure 8;

setting the initial temperature T of the test environment₀At-45 ℃ and a finishing temperature T_uAt 60 ℃ and a temperature change rate v_TThe temperature sampling variation delta T is 1 ℃/min, the temperature sampling variation delta T is 5 ℃, the testing temperature T is-45 + T, the phenomenon at the low temperature of-45 ℃, the normal temperature of 20 ℃ and the high temperature of 60 ℃ is most obvious after the measurement, as shown in attached figures 9 and 10, the polarization crosstalk at the positions of 1a, 2a, 3a, 1b, 2b and 3b is analyzed, and the crosstalk background of the outer ring of the optical fiber sensitive ring and the change layer area is obviously reduced along with the temperature rise in an airspace. The polarization crosstalk at 1c, 2c and 3c is analyzed, and abnormal polarization crosstalk can be generated when the temperature is reduced; in fig. 11, cross talk of the change-over regions at 1104, 1106 and 1108 at different temperatures is analyzed, and the cross talk of the change-over regions is found to be obviously reduced along with the increase of the temperature, and cross talk of the change-over regions at 1105, 1107 and 1109 at different temperatures is analyzed, and the cross talk of the change-over regions is found to be slightly lower at lower temperature, but the cross talk at different diameters is more different.