1. A method for testing the symmetry and the internal defect of a fiber-optic gyroscope sensitive ring is characterized by comprising the following steps:

step 101: data preprocessing including measuring and recording parameters of the fiber optic sensor ring (211) calculatedTo different layers, each turn corresponding to a length l of the optical fiber_p＝π·d_p,(d_min≤d_p≤d_maxP is 1,2, L M), wherein d_pCalculating the total length L of the optical fiber corresponding to the p-th layer of the optical fiber sensing ring (211) for the diameter corresponding to the p-th layer_p＝l_pN, frequency of turn change k_p＝1/l_pAnd a layer change frequency K_p＝1/L_pMeasuring to obtain a first distributed polarization crosstalk (301) with a spatial sampling interval delta L;

step 102: dividing the first distributed polarization crosstalk (301) into n segments of distributed polarization crosstalk (701), and initializing the cycle number i, namely i is 1;

step 103: multiplying the ith section of distributed polarization crosstalk (701) by a window function (702), then filling zero at the end of data, and finally performing Fourier transform on the data after zero filling to record the data as the ith section of frequency domain polarization crosstalk (801);

step 104: intercepting an ith frequency domain turn-changing area polarization crosstalk (901) from an ith frequency domain polarization crosstalk (801), and increasing the cycle number i, namely i is i + 1;

step 105: judging whether i is larger than n, if not, repeating the steps 103 to 105, and if so, performing the step 106;

step 106: synthesizing all n sections of frequency domain turn-changing area polarization crosstalk (901) to form a space frequency domain turn-changing area polarization crosstalk (1001), and then extracting space frequency domain turn-changing characteristics (1101) in the space frequency domain turn-changing area polarization crosstalk;

step 107: calculating a ridge line (1201) of the space-frequency domain turn-changing feature (1101), fitting the ridge line, and extracting the position of the midpoint of the optical fiber sensing ring (211);

step 108: and extracting characteristic parameters corresponding to the stress concentration part (1501) in the optical fiber sensitive ring (211) to finish the test.

2. The method for testing the symmetry and internal defect of the fiber-optic gyroscope sensing ring according to claim 1, wherein the parameters of the fiber-optic gyroscope sensing ring (211) in step 101 include the length L of the optical fiber and the diameter d of the optical fiber_fiberInner diameter d_minOuter diameter d_maxEach layer is changed into the number of turns N of turns (214) and changed into the layer(215) The number of layers M.

3. The method for testing symmetry and internal defect of fiber-optic gyroscope sensing ring according to claim 2, wherein the measuring in step 101 obtains a first distributed polarization crosstalk (301), specifically:

respectively measuring spatial domain polarization crosstalk, namely a first distributed polarization crosstalk (301), transmitted from a first end (212) to a second end (213) of a fiber-optic sensitive ring (211) and spatial domain polarization crosstalk, namely a second distributed polarization crosstalk (501), transmitted from the second end (213) to the first end (212) of the fiber-optic sensitive ring (211);

the first distributed polarization crosstalk (301) and the second distributed polarization crosstalk (501) are greater than a distributed polarization crosstalk threshold I_GRespectively labeled as I_1,qAnd I_2,qWherein, I_1,qRepresents the polarization crosstalk at the fiber length q meters in a first distributed polarization crosstalk (301), I_2,qRepresents the polarization crosstalk at the fiber length q meters in the second distributed polarization crosstalk (501), I_1,q、I_2,qIs to satisfy max_x∈(0,L)|I_1,q-I_2,q| ≦ ε, if not satisfied, re-measuring and updating the first distributed polarization crosstalk (301) and the second distributed polarization crosstalk (501), if satisfied, recording the first distributed polarization crosstalk (301).

4. The method for testing symmetry and internal defect of fiber-optic gyroscope sensor ring according to claim 3, wherein the step 102 is to divide the first distributed polarization crosstalk (301) into n segments of distributed polarization crosstalk (701), specifically:

the i-th segment of distributed polarization crosstalk (701) is data corresponding to a fiber length interval [ (1- α) (i-1) Δ L, (1- α) (i-1) Δ L + Δ L ] in the first distributed polarization crosstalk (301), wherein the segment length Δ L is the fiber length of each segment, and the redundancy length coefficient α satisfies α ∈ [0,1 ].

5. The method for testing the symmetry and internal defect of the fiber-optic gyroscope sensing ring according to claim 4, wherein the number of data points of the window function (702) in step 103 is P, and the type of the window function (702) is selected from a Hamming window or a Hanning window.

6. The method for testing the symmetry and internal defect of the fiber-optic gyroscope sensing ring as claimed in claim 5, wherein the number of the data points after zero padding in step 103 is P, which satisfies the requirement of

7. The method for testing the symmetry and internal defect of the fiber-optic gyroscope sensor ring according to claim 6, wherein in step 104, the i-th section of frequency domain turn-changing area polarization crosstalk (901) is intercepted from the i-th section of frequency domain polarization crosstalk (801), specifically:

calculating the minimum turn-changing frequency k_min＝1/(π·d_max) Maximum turn change frequency k_max＝1/(π·d_min) And a maximum layer change frequency K_max＝1/(π·N·d_min) Intercepting the characteristic interval (802) k of turn change in the i-th section of frequency domain polarization crosstalk_lb,k_rb]Inner change of turns feature data, where left boundary k of the region is truncated_lbRight boundary k_rbRespectively satisfy K_max≤k_lb≤k_min、k_max≤k_rb≤2k_min。

8. The method for testing the symmetry and the internal defect of the fiber-optic gyroscope sensing ring according to claim 7, wherein in step 106, the polarization crosstalk (901) of the frequency domain turn-changing region of all n segments is synthesized to form the polarization crosstalk (1001) of the space-frequency domain turn-changing region, and then the space-frequency domain turn-changing feature (1101) is extracted, specifically:

storing the i-th section of frequency domain turn-changing area polarization crosstalk (901) into an array A as the i-th row in the array A, obtaining the array A with n rows as the space frequency domain turn-changing area polarization crosstalk (1001), and extracting the polarization crosstalk which is larger than a turn-changing characteristic threshold value Z as the space frequency domain turn-changing characteristic (1101).

9. The method for testing the symmetry and the internal defect of the fiber-optic gyroscope sensing ring according to claim 8, wherein the step 107 is to calculate a ridge line (1201) of the space-frequency domain turn-changing feature (1101), fit the ridge line and extract the position of the midpoint of the fiber-optic gyroscope sensing ring (211), specifically:

searching the maximum value of each column in the space-frequency domain turn-changing characteristics (1101), recording the length position of the corresponding optical fiber and the diameter of the corresponding optical fiber sensitive ring (211), connecting the maximum value and the diameter of the corresponding optical fiber sensitive ring to form a ridge line (1201), fitting the ridge line according to an absolute value function d ═ a | L-b | + c, and satisfying a in the fitting process>0,c∈(c_min,c_max) Wherein c is_min≤d_min，c_max≥d_maxExtracting the parameter b in the fitting result as a coarse value of the position of the middle point of the surrounding ring of the optical fiber sensitive ring (211), and locating the optical fiber length in the interval [0, b ]]According to a first linear function (1401) d ═ a₁L+b₁，a₁<0 is fitted and is in the interval b, L for the length of the fiber]According to a second linear function (1402) d ═ a₂L+b₂，a₂>0, extracting the optical fiber length b ' corresponding to the intersection point (1403) of the first linear function (1401) and the second linear function (1402) as the precise value of the position of the middle point of the winding ring of the optical fiber sensitive ring (211), using the relative difference S between the precise value b ' of the position of the middle point of the winding ring and the half of the length L of the optical fiber ring as | (2b ' -L)/L | as the symmetry evaluation parameter of the optical fiber sensitive ring (211), and using the slope a of the first linear function₁And the second linear function slope a₂The ratio of the smaller absolute value to the larger absolute value of the absolute values of the optical fiber sensing ring (211) is used as a winding symmetry evaluation parameter of the optical fiber sensing ring.

10. The method for testing the symmetry and the internal defect of the fiber-optic gyroscope sensing ring according to claim 9, wherein the step 108 of extracting the characteristic parameters corresponding to the stress concentration (1501) in the fiber-optic gyroscope sensing ring (211) specifically comprises:

extracting data with amplitude larger than a stress characteristic extraction threshold value F in the space-frequency domain turn-changing characteristic (1101) to serve as a stress concentration part (1501), and recording characteristic parameters including corresponding optical fiber length L ', optical fiber ring diameter parameter d' and polarization crosstalk intensity E.

Background

The optical coherence domain polarization measurement (OCDP) is a technical solution for measuring the distributed polarization crosstalk of polarization-maintaining devices based on the white light interference principle. OCDP generally uses a wide-spectrum light source such as a superluminescent light emitting diode (SLD), and in order to avoid interference peaks having intrinsic side lobes, a wide-spectrum light source of a gaussian spectrum is generally used; the wide-spectrum light output by the wide-spectrum light source is injected into a device to be tested after passing through a polarizer, different polarizer axial angles are selected according to different devices to be tested, for the detection of an optical fiber ring, the wide-spectrum light is generally injected from a slow axis by using a 0-degree polarizer, the light output from a fast axis and a slow axis of the device to be tested is coupled to a single-mode output tail fiber of the device to be tested by a 45-degree polarization analyzer, and then enters a Mach-Zehnder Interferometer (Mach-Zehnder Interferometer, abbreviated as MZI) or Michelson Interferometer (Michelson Interferometer, abbreviated as MI) through a 2x2 coupler; and finally, detecting the signal output by the interferometer through a differential detection circuit. (Chinese patent application No.: CN 103900680A).

Fiber Optic Gyroscopes (FOG) are based on the Sagnac effect principle, i.e. when a ring interferometer rotates, a phase difference proportional to the rotation rate is produced. Therefore, when one light beam enters the closed optical path of the optical fiber ring, the light beam is divided into two light beams which are transmitted along the closed optical path in the same optical path. Provided that the optical path is not rotated at this time, the two beams of light will simultaneously return to the point of initial injection of light, in which case the characteristics of the optical path are said to be reciprocal (i.e., the same for the effect when light is incident from both directions). If the optical path is rotated, the light traveling in the same direction as the rotation direction will travel a longer path than the light traveling in the opposite direction (in this case, the optical path is said to have nonreciprocity), thereby generating an optical path difference proportional to the rotational angular velocity.

The optical fiber sensitive ring is one of core components in the optical fiber gyroscope. The optical fiber sensing gyro ring generally comprises an annular supporting framework, an optical fiber wound outside and glue for curing, wherein the supporting framework of the optical fiber ring, the size parameters of the optical fiber ring, the optical fiber parameters, the glue fixing parameters, the ring winding method and the like all have certain influence on the performance test of the optical fiber ring, and the winding quality of the optical fiber sensing ring determines the measurement precision of the optical fiber gyro. The traditional optical fiber ring detection method evaluates the performance of a polarization maintaining optical fiber ring by means of an extinction ratio or an optical time domain reflection technology, cannot completely and accurately reflect the surrounding quality of the optical fiber ring, cannot provide accurate process modification data for improving the quality of the optical fiber ring, and has limitations. (Chinese patent application No.: CN 200910243964.8).

In the winding method of the optical fiber sensitive ring, a quadrupole symmetry method is generally adopted for winding the optical fiber ring, and the method greatly inhibits the nonreciprocal phase error caused by temperature in the ring, but cannot completely eliminate the Shupe effect error caused by spatial temperature gradient. In order to further suppress the temperature effect, a cross-type quadrupole symmetry method is proposed (U.S. patent: 5465150), in which the whole loop is divided into a plurality of winding sub-regions satisfying the quadrupole symmetry requirement, and the winding sequence of the optical fiber at the left and right sides of the midpoint between the adjacent sub-regions is reversed, so as to overcome the spatial temperature gradient influence in the loop, however, due to the winding level limitation, the winding method still cannot effectively suppress the temperature shupe effect error.

In 2018, Chen Wen Xin et al disclose an octupole symmetric winding device (Chinese patent application No. CN201821762556.4) based on a fiber-optic gyroscope, which solves the problem that the conventional quadrupole symmetric winding machine cannot effectively adjust the winding tension when the control system fails due to the tension of the optical fiber, protects the optical fiber when the tension is too high, prevents the optical fiber from being broken, avoids the waste of the optical fiber, and reduces the production cost.

In 2020, plum, et al disclose a cross sixteen-pole symmetric winding method (chinese patent application No. CN202010096977.3) for an ultra-high precision fiber optic gyroscope, in which each of two side coils symmetric with respect to the thickness center position of the fiber optic ring contains forward and backward fibers with equal length, and each of the two side coils in each sixteen layers are arranged symmetrically with sixteen opposite poles.

Disclosure of Invention

The invention provides a method for testing the symmetry and internal defects of a fiber-optic gyroscope sensitive ring, which realizes effective analysis of the symmetry performance of the fiber-optic gyroscope sensitive ring and distribution of internal stress defects based on distributed polarization crosstalk.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a method for testing the symmetry and internal defects of a fiber-optic gyroscope sensing ring comprises the following steps:

step 101: data preprocessing, including measuring and recording parameters of the fiber-optic sensing ring 211, and calculating to obtain the length l of the optical fiber corresponding to each turn of different layers_p＝π·d_p,(d_min≤d_p≤d_maxP is 1,2, L M), wherein d_pCalculating the total length L of the optical fiber corresponding to the p-th layer for the diameter corresponding to the p-th layer of the optical fiber sensing ring 211_p＝l_pN, frequency of turn change k_p＝1/l_pAnd a layer change frequency K_p＝1/L_pMeasuring to obtain a first distributed polarization crosstalk 301, wherein the spatial sampling interval is delta L;

step 102: dividing the first distributed polarization crosstalk 301 into n segments of distributed polarization crosstalk 701, initializing a cycle number i, i being 1;

step 103: multiplying the ith section of distributed polarization crosstalk 701 by a window function 702, then filling zero at the end of data, and finally performing Fourier transform on the data after zero filling to record the data as the ith section of frequency domain polarization crosstalk 801;

step 104: intercepting the i-th section of frequency domain turn-changing area polarization crosstalk 901 from the i-th section of frequency domain polarization crosstalk 801, and increasing the cycle number i by itself, namely i is i + 1;

step 105: judging whether i is larger than n, if not, repeating the steps 103 to 105, and if so, performing the step 106;

step 106: synthesizing all n sections of frequency domain turn-changing area polarization crosstalk 901 to form a space frequency domain turn-changing area polarization crosstalk 1001, and then extracting space frequency domain turn-changing characteristics 1101;

step 107: calculating a ridge line 1201 of the air-frequency domain turn-changing characteristics 1101, fitting the ridge line, and extracting the position of the midpoint of the optical fiber sensing ring 211;

step 108: and extracting characteristic parameters corresponding to stress concentration 1501 in the optical fiber sensing ring 211 to finish the test.

Preferably, the parameters of the optical fiber sensing ring 211 in step 101 include an optical fiber length L and an optical fiber diameter d_fiberInner diameter d_minOuter diameter d_maxEach layer is changed by turns 214, the number of turns N and the number of layers M of the layer change 215.

Preferably, the measuring in step 101 obtains a first distributed polarization crosstalk 301, specifically:

measuring spatial polarization crosstalk, namely a first distributed polarization crosstalk 301, transmitted from a first end 212 to a second end 213 of a fiber sensor ring 211 and spatial polarization crosstalk, namely a second distributed polarization crosstalk 501, transmitted from the second end 213 to the first end 212 of the fiber sensor ring 211 respectively;

the first distributed polarization crosstalk 301 and the second distributed polarization crosstalk 501 are greater than the distributed polarization crosstalk threshold I_GRespectively labeled as I_1,qAnd I_2,qWherein, I_1,qRepresents the polarization crosstalk at the fiber length q meters, I, in the first distributed polarization crosstalk 301_2,qRepresents the polarization crosstalk at the fiber length q meters, I, in the second distributed polarization crosstalk 501_1,q、I_2,qIs required to be full ofFoot max_x∈(0,L)|I_1,q-I_2,q| ≦ ε, if not satisfied, re-measuring and updating the first distributed polarization crosstalk 301 and the second distributed polarization crosstalk 501, if satisfied, recording the first distributed polarization crosstalk 301.

Preferably, the dividing step 102 of the first distributed polarization crosstalk 301 into n segments of distributed polarization crosstalk 701 includes:

the ith segment of distributed polarization crosstalk 701 is data corresponding to the fiber length interval [ (1- α) (i-1) Δ L, (1- α) (i-1) Δ L + Δ L ] in the first distributed polarization crosstalk 301, where the segment length Δ L is the fiber length of each segment, and the redundancy length coefficient α satisfies α e [0,1 ].

Preferably, the number of data points of the window function 702 in step 103 is P, and the type of the window function 702 is a hamming window or a hanning window.

Preferably, the number of data points after zero padding in step 103 is P, which satisfies

Preferably, in step 104, the step of cutting the i-th section of frequency domain turn-changing area polarization crosstalk 901 from the i-th section of frequency domain polarization crosstalk 801 specifically includes:

calculating the minimum turn-changing frequency k_min＝1/(π·d_max) Maximum turn change frequency k_max＝1/(π·d_min) And a maximum layer change frequency K_max＝1/(π·N·d_min) Intercepting the i-th section of the turn-changing characteristic interval 802 k in the frequency domain polarization crosstalk_lb,k_rb]Inner change of turns feature data, where left boundary k of the region is truncated_lbRight boundary k_rbRespectively satisfy K_max≤k_lb≤k_min、k_max≤k_rb≤2k_min。

Preferably, in step 106, the frequency domain turn-changing region polarization crosstalk 901 of all n segments is synthesized to form a space frequency domain turn-changing region polarization crosstalk 1001, and then the space frequency domain turn-changing feature 1101 in the space frequency domain turn-changing region polarization crosstalk is extracted, specifically:

storing the i-th section of frequency domain turn-changing area polarization crosstalk 901 into an array A as the i-th row in the array A, obtaining an array A with n rows as the space frequency domain turn-changing area polarization crosstalk 1001, and extracting the polarization crosstalk larger than a turn-changing characteristic threshold value Z as the space frequency domain turn-changing characteristic 1101.

Preferably, in step 107, the ridge 1201 of the space-frequency domain turn-changing feature 1101 is calculated and fitted, and the position of the midpoint of the fiber-optic sensing ring 211 is extracted, specifically:

searching the maximum value of each column in the space-frequency domain turn-changing characteristic 1101, recording the length position of the corresponding optical fiber and the diameter of the corresponding optical fiber sensitive ring 211, connecting the maximum value and the diameter of the corresponding optical fiber sensitive ring into a ridge line 1201, and fitting the ridge line according to an absolute value function d ═ a | L-b | + c, wherein a is satisfied during fitting>0,c∈(c_min,c_max) Wherein c is_min≤d_min，c_max≥d_maxExtracting the parameter b in the fitting result as the coarse value of the position of the middle point of the surrounding ring of the optical fiber sensitive ring 211, and locating the optical fiber length in the interval [0, b ]]According to a first linear function 1401d ═ a₁L+b₁，a₁<0 is fitted and is in the interval b, L for the length of the fiber]According to a second linear function 1402d ═ a₂L+b₂，a₂>0, extracting the fiber length b ' corresponding to the intersection (1403) of the first linear function 1401 and the second linear function 1402 as the precise value of the position of the middle point of the surrounding ring of the optical fiber sensitive ring 211, using the relative difference S | (2b ' -L)/L | between the precise value b ' of the position of the middle point of the surrounding ring and the half of the length L of the optical fiber ring as the symmetry evaluation parameter of the optical fiber sensitive ring 211, and using the slope a of the first linear function₁And the second linear function slope a₂The ratio of the smaller absolute value to the larger absolute value of the absolute values of (a) is used as the winding symmetry evaluation parameter of the optical fiber sensitive ring 211.

Preferably, the extracting of the characteristic parameters corresponding to the stress concentration 1501 in the fiber sensing ring 211 in step 108 specifically includes:

data with amplitude larger than the stress feature extraction threshold value F in the air-frequency domain turn changing feature 1101 is extracted as a stress concentration part 1501, and characteristic parameters including the corresponding optical fiber length L ', the optical fiber loop diameter parameter d' and the polarization crosstalk intensity E are recorded.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that:

1, carrying out short-time Fourier transform on first distributed polarization crosstalk measurement data of the optical fiber sensitive ring, and intercepting the data according to geometric parameters of the optical fiber sensitive ring, so that the polarization crosstalk of a frequency domain turn-changing area of the optical fiber sensitive ring can be obtained;

compared with the traditional method for testing the performance of the optical fiber sensitive ring by means of the extinction ratio or the optical time domain reflection technology, the analysis method can simultaneously obtain the air-frequency domain turn changing characteristics of the same optical fiber sensitive ring, and further realize effective analysis on the symmetrical performance of the optical fiber sensitive ring;

3, by applying the measurement and analysis method to the detection and analysis of the optical fiber sensitive ring manufacturing process in the optical fiber gyroscope, the intra-ring stress concentration distribution area of the optical fiber sensitive ring can be obtained, the positioning of a stress concentration point in the ring winding process is realized, the analysis result is favorable for improving the winding process of the optical fiber sensitive ring, and the method can be widely applied to the field of performance test of the optical fiber sensitive ring.

Drawings

FIG. 1 is a schematic flow diagram of the process of the present invention;

FIG. 2 is a schematic diagram of a fiber optic sensor ring;

FIG. 3 is a schematic diagram of distributed polarization crosstalk measurement;

FIG. 4 is a first distributed polarization cross-talk diagram;

FIG. 5 is a detailed view of a first distributed polarization crosstalk

FIG. 6 is a second distributed polarization cross-talk diagram;

FIG. 7 is a detailed view of a second distributed polarization crosstalk;

FIG. 8 is a truncated distributed polarization cross-talk chart;

FIG. 9 is a frequency domain plot of truncated distributed polarization crosstalk;

FIG. 10 is a truncated frequency domain polarization cross-talk plot;

FIG. 11 is a diagram of space-frequency domain polarization crosstalk commutation region;

FIG. 12 is a space-frequency domain polarization crosstalk commutation diagram;

FIG. 13 is a spatial-frequency domain polarization crosstalk ridge diagram;

FIG. 14 is a ridge line fit graph;

FIG. 15 is a ridge line fit detail view;

fig. 16 is a stress concentration profile.

Detailed Description

The drawings are for illustrative purposes only and are not to be construed as limiting the patent;

for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;

it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.

Example 1

The embodiment provides a method for testing symmetry and internal defects of a fiber-optic gyroscope sensing ring, as shown in fig. 1, comprising the following steps:

step 101: data preprocessing, including measuring and recording parameters of the fiber-optic sensing ring 211, and calculating to obtain the length l of the optical fiber corresponding to each turn of different layers_p＝π·d_p,(d_min≤d_p≤d_maxP is 1,2, L M), wherein d_pCalculating the total length L of the optical fiber corresponding to the p-th layer for the diameter corresponding to the p-th layer of the optical fiber sensing ring 211_p＝l_pN, frequency of turn change k_p＝1/l_pAnd a layer change frequency K_p＝1/L_pMeasuring to obtain a first distributed polarization crosstalk 301, wherein the spatial sampling interval is delta L;

step 102: dividing the first distributed polarization crosstalk 301 into n segments of distributed polarization crosstalk 701, initializing a cycle number i, i being 1;

step 103: multiplying the ith section of distributed polarization crosstalk 701 by a window function 702, then filling zero at the end of data, and finally performing Fourier transform on the data after zero filling to record the data as the ith section of frequency domain polarization crosstalk 801;

step 104: intercepting the i-th section of frequency domain turn-changing area polarization crosstalk 901 from the i-th section of frequency domain polarization crosstalk 801, and increasing the cycle number i by itself, namely i is i + 1;

step 105: judging whether i is larger than n, if not, repeating the steps 103 to 105, and if so, performing the step 106;

step 106: synthesizing all n sections of frequency domain turn-changing area polarization crosstalk 901 to form a space frequency domain turn-changing area polarization crosstalk 1001, and then extracting space frequency domain turn-changing characteristics 1101;

step 107: calculating a ridge line 1201 of the air-frequency domain turn-changing characteristics 1101, fitting the ridge line, and extracting the position of the midpoint of the optical fiber sensing ring 211;

step 108: and extracting characteristic parameters corresponding to stress concentration 1501 in the optical fiber sensing ring 211 to finish the test.

The embodiment provides a method for testing the symmetry performance and the stress defect of an optical fiber sensitive ring based on distributed polarization crosstalk. Dividing the obtained distributed polarization crosstalk of the optical fiber sensing ring into an infinite section, performing Fourier transform on the infinite section, performing data interception according to geometric parameters of the optical fiber sensing ring, further obtaining the polarization crosstalk of a frequency domain turn-changing area of the optical fiber sensing ring, and performing space-frequency domain joint analysis on the polarization crosstalk to obtain the symmetric performance and the stress concentration of the optical fiber sensing ring. The method can simultaneously obtain the air-frequency domain turn-changing characteristics of the same optical fiber sensing ring, further realize effective analysis on the symmetrical performance of the optical fiber sensing ring and the distribution situation of internal stress defects, and the analysis result is favorable for improving the ring winding process and can be widely applied to the field of performance test of the optical fiber sensing ring.

The parameters of the optical fiber sensing ring 211 in step 101 include the length L of the optical fiber, and the diameter d of the optical fiber_fiberInner diameter d_minOuter diameter d_maxEach layer is changed by turns 214, the number of turns N and the number of layers M of the layer change 215.

In step 101, the measurement obtains a first distributed polarization crosstalk 301, specifically:

measuring spatial polarization crosstalk, namely a first distributed polarization crosstalk 301, transmitted from a first end 212 to a second end 213 of a fiber sensor ring 211 and spatial polarization crosstalk, namely a second distributed polarization crosstalk 501, transmitted from the second end 213 to the first end 212 of the fiber sensor ring 211 respectively;

the first distributed polarization crosstalk 301 and the second distributed polarization crosstalk 501 are greater than the distributed polarization crosstalk threshold I_GRespectively labeled as I_1,qAnd I_2,qWherein, I_1,qRepresents the polarization crosstalk at the fiber length q meters, I, in the first distributed polarization crosstalk 301_2,qRepresents the polarization crosstalk at the fiber length q meters, I, in the second distributed polarization crosstalk 501_1,q、I_2,qIs to satisfy max_x∈(0,L)|I_1,q-I_2,q| ≦ ε, if not satisfied, re-measuring and updating the first distributed polarization crosstalk 301 and the second distributed polarization crosstalk 501, if satisfied, recording the first distributed polarization crosstalk 301.

In step 102, the dividing the first distributed polarization crosstalk 301 into n segments of distributed polarization crosstalk 701 specifically includes:

the ith segment of distributed polarization crosstalk 701 is data corresponding to the fiber length interval [ (1- α) (i-1) Δ L, (1- α) (i-1) Δ L + Δ L ] in the first distributed polarization crosstalk 301, where the segment length Δ L is the fiber length of each segment, and the redundancy length coefficient α satisfies α e [0,1 ].

In step 103, the number of data points of the window function 702 is P, and a hamming window or a hanning window is selected as the type of the window function 702.

The number of the data points after zero padding in the step 103 is P, which satisfies

In step 104, the step of intercepting the i-th section of frequency domain turn-changing area polarization crosstalk 901 from the i-th section of frequency domain polarization crosstalk 801 specifically includes:

calculating the minimum turn-changing frequency k_min＝1/(π·d_max) Maximum turn change frequency k_max＝1/(π·d_min) And a maximum layer change frequency K_max＝1/(π·N·d_min) Intercepting the i-th section of the turn-changing characteristic interval 802 k in the frequency domain polarization crosstalk_lb,k_rb]Inner change of turns characteristic data, in which truncation is carried outLeft boundary k of the region_lbRight boundary k_rbRespectively satisfy K_max≤k_lb≤k_min、k_max≤k_rb≤2k_min。

In step 106, the frequency domain turn-changing region polarization crosstalk 901 of all n segments is synthesized to form a space-frequency domain turn-changing region polarization crosstalk 1001, and then a space-frequency domain turn-changing feature 1101 is extracted, specifically:

storing the i-th section of frequency domain turn-changing area polarization crosstalk 901 into an array A as the i-th row in the array A, obtaining an array A with n rows as the space frequency domain turn-changing area polarization crosstalk 1001, and extracting the polarization crosstalk larger than a turn-changing characteristic threshold value Z as the space frequency domain turn-changing characteristic 1101.

In step 107, the ridge 1201 of the space-frequency domain turn-changing feature 1101 is calculated and fitted, and the position of the midpoint of the optical fiber sensing ring 211 is extracted, specifically:

searching the maximum value of each column in the space-frequency domain turn-changing characteristic 1101, recording the length position of the corresponding optical fiber and the diameter of the corresponding optical fiber sensitive ring 211, connecting the maximum value and the diameter of the corresponding optical fiber sensitive ring into a ridge line 1201, and fitting the ridge line according to an absolute value function d ═ a | L-b | + c, wherein a is satisfied during fitting>0,c∈(c_min,c_max) Wherein c is_min≤d_min，c_max≥d_maxExtracting the parameter b in the fitting result as the coarse value of the position of the middle point of the surrounding ring of the optical fiber sensitive ring 211, and locating the optical fiber length in the interval [0, b ]]According to a first linear function 1401d ═ a₁L+b₁，a₁<0 is fitted and is in the interval b, L for the length of the fiber]According to a second linear function 1402d ═ a₂L+b₂，a₂>0, extracting the fiber length b ' corresponding to the intersection (1403) of the first linear function 1401 and the second linear function 1402 as the precise value of the position of the middle point of the surrounding ring of the optical fiber sensitive ring 211, using the relative difference S | (2b ' -L)/L | between the precise value b ' of the position of the middle point of the surrounding ring and the half of the length L of the optical fiber ring as the symmetry evaluation parameter of the optical fiber sensitive ring 211, and using the slope a of the first linear function₁And the second linear function slope a₂The smaller of the absolute values of (A) and (B)The larger ratio is used as the winding symmetry evaluation parameter of the fiber-optic sensing ring 211.

In step 108, the extracting of the characteristic parameters corresponding to the stress concentration 1501 in the optical fiber sensing ring 211 specifically includes:

data with amplitude larger than the stress feature extraction threshold value F in the air-frequency domain turn changing feature 1101 is extracted as a stress concentration part 1501, and characteristic parameters including the corresponding optical fiber length L ', the optical fiber loop diameter parameter d' and the polarization crosstalk intensity E are recorded.

The distributed polarization crosstalk of the polarization maintaining optical fiber means that the polarization maintaining optical fiber in a light path to be tested generates stress inside the polarization maintaining optical fiber due to a production process, or is influenced by external temperature, bending and the like, so that polarization crosstalk is generated at a defect point by originally transmitting polarized light on a slow axis or a fast axis, and part of energy of the transmitted light is coupled to the fast axis or the slow axis, so that the energy is mutually coupled; as shown in fig. 3, a beam of polarized light with a broad spectrum is injected along the fast axis or the slow axis of a polarization-maintaining fiber, forms an excitation mode 231 in the polarization axis direction, and 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.

FIG. 2 is a diagram of quadrupole symmetric winding principle of the fiber sensing ring, which only shows 5 layers of fiber rings in the quadrupole symmetric winding method, and distinguishes the winding directions thereof by colors, wherein the first layer of fiber and the fourth layer of fiber are white, which represents clockwise winding, and the second layer of fiber and the third layer of fiber are black, which represents counterclockwise winding; the winding method of the optical fiber sensitive ring takes the optical fiber midpoint 221 as a boundary, and a half of the optical fibers 222 are selected to start to wind a layer of optical fibers 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.

In the specific implementation process:

(1) taking a fiber sensitive ring 211 to be measured, measuring and recording the length L of the fiber as 3051m and the diameter d of the fiber_fiberIs 250, inner diameter d_min0.130m, outer diameter d_maxIs 0.143m, the number of turns N is 100 and the number of layers is 64, l is calculated_min＝0.408m，l_max＝0.449m,L_max44.92m, minimum commutation frequency k_min＝2.227m^-1Maximum turn change frequency K_max＝0.025m^-1And a maximum layer change frequency K_max＝0.025m^-1The spatial sampling interval delta L is 1.638 multiplied by 10^-4；

(2) Measuring a first distributed polarization crosstalk 301 transmitted from the first end 212 to the second end 213 of the optical fiber sensing ring 211 and a second distributed polarization crosstalk 501 transmitted from the second end 213 to the first end 212 of the optical fiber sensing ring 211, as shown in fig. 4 and 6, which are respectively shown in fig. 5 and 7 in detail;

(3) the polarization crosstalk greater than the distributed polarization crosstalk threshold value by-40 dB in the first distributed polarization crosstalk 301 and the second distributed polarization crosstalk 501 is respectively marked as I_1,qAnd I_2,qNumbered 302 to 323 and 502 to 523, respectively, by a difference satisfying max_x∈(0,L)|I_1,q-I_2,qRecording a first distributed polarization crosstalk 301 with | ≦ 1 dB;

(4) dividing the first distributed polarization crosstalk 301 into 88 segments, setting Δ L to 40m and α to 0.125, that is, extracting data corresponding to the fiber length positions [35(i-1),35(i-1) +40] as an i-th segment of distributed polarization crosstalk 701, as shown in fig. 8;

(5) selecting a Hamming window as a window function 702, wherein the data point number of the window function 702 is the same as the data length of the i-th section of distributed polarization crosstalk 701, multiplying the i-th section of distributed polarization crosstalk 701 by the window function, and then filling zero at the end of data, wherein the data point number after zero filling meets the condition that P is more than or equal to 9.057 multiplied by 10⁵Selecting P10¹⁰Finally, Fourier transform is carried out on the polarization cross talk signal, and the polarization cross talk signal is recorded as the i-th section of frequency domain polarization cross talk 801, as shown in figure 9;

(6) the left boundary of the i-th section frequency domain polarization crosstalk change characteristic interval 802 meets 0.025m^-1≤k_lb≤2.227m^-1And the right boundary satisfies 2.449m^-1≤k_rb<4.454m^-1Take k_lb＝2.195m^-1、k_rb＝2.546m^-1Intercepting the ith frequency domain polarization crosstalk middle interval [2.195,2.546 ]]Inner change turn characterization data, as shown in fig. 10;

(7) storing the i-th section of frequency domain turn-changing area polarization crosstalk 901 into an array A as the i-th row in the array A to obtain an array A of 88 rows, extracting to obtain a frequency domain turn-changing area polarization crosstalk 901, and extracting a polarization crosstalk which is 0.8dB greater than a turn-changing characteristic threshold value as an air-frequency domain turn-changing characteristic 1101, as shown in figures 11 and 12;

(8) the maximum value of each column is found in the space-frequency domain turn-changing characteristic 1101, the length position of the corresponding optical fiber and the diameter of the corresponding optical fiber sensitive ring 211 are recorded to be connected into a ridgeline 1201, as shown in fig. 13, and the ridgeline is fitted according to an absolute value function d which is a | L-b | + c, a ═ 8.384 × 10^-6C 0.1301, b 1495, degree of fit R²0.994, the parameter b 1495 in the fitting result is extracted as the coarse value of the position of the middle point of the ring-surrounding of the fiber-sensitive ring 211, and is located in the interval [0,1495 ] for the fiber length]According to a first linear function 1401d ═ a₁L+b₁，a₁<0 is fitted, a₁＝-8.045×10^-6,b₁0.1424 forThe length of the optical fiber being in the interval [1495,3051 ]]According to a second linear function 1402d ═ a₂L+b₂，a₂>0 is fitted, a₂＝8.689×10^-6,b₂0.1169, as shown in fig. 14 and 15, the fiber length b '1522 corresponding to the intersection 1403 of the first linear function 1401 and the second linear function 1402 is extracted as the precise value of the position of the fiber-sensitive loop 211 around the loop midpoint, the relative difference S between the position b' of the loop midpoint and half of the fiber loop length L is 0.0023, and the slope a of the first linear function is₁And the second linear function slope a₂The ratio of the smaller absolute value to the larger absolute value of the absolute values of the optical fiber sensor ring 211 is 0.92, so that the optical fiber sensor ring 211 has good symmetry performance;

(9) data with an amplitude greater than 4dB of the stress feature extraction threshold in the air-frequency domain turn change feature 1101 is extracted as a stress concentration site 1501, where the corresponding fiber length where the stress is most concentrated is 2615m, the fiber loop diameter parameter is 0.140m, and the polarization crosstalk intensity is 5.822dB, as shown in fig. 16.

The same or similar reference numerals correspond to the same or similar parts;

the terms describing positional relationships in the drawings are for illustrative purposes only and are not to be construed as limiting the patent;

it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.