A super-resolution white light interference signal recognition method

Abstract

The present invention addresses the problem in the prior art of degrading the resolution of the measurement system due to the superposition of white-light interference signals. A super-resolution white-light interference signal recognition method is provided to improve the resolution of the white-light interference system. The method finds the relationship between the change in area when two interference signals are superimposed and the optical path difference between the two coupling points. By measuring the extinction ratio of the two coupling points, the actual area of the two interference signals is calculated. Even if the interference signals have overlapped and cannot be identified, the optical path difference between the two interference signals can still be inferred. This method can increase the spatial resolution of the white-light interference signal from approximately 10 cm to approximately 1 cm. This method can improve the resolution of the white-light interference system and is conducive to further development in aspects such as beat length measurement of polarization-maintaining devices and stress sensing.

Description

Technical Field

[0001] The present invention relates to the technical field of white light interference signals, and in particular to a method for identifying super-resolution white light interference signals. Background Art

[0002] White-light interferometry, with its advantages of wide dynamic range, high resolution, non-destructive measurement, and absolute measurement, has gradually developed into the optimal method for measuring the beat length of polarization-maintaining fibers. The existing implementation involves measuring the interference signal corresponding to two coupling points in a polarization-maintaining fiber through white-light interferometry to obtain the optical path difference between the two coupling points. A frequency-stabilized interferometer is then used to precisely measure the spatial distance between the two coupling points. The birefringence difference of the polarization-maintaining fiber is calculated using the formula dividing the optical path difference by the spatial distance. An optical wavelength meter is then used to measure the central wavelength of the light source output in the interferometer system. The beat length is calculated using the formula: beat length equals wavelength divided by birefringence difference. This approach offers the advantage of traceability to a length standard, significantly improving the accuracy of beat length measurements.

[0003] The invention patent with the patent number "CN107976300A" uses white light interferometry to measure the optical path difference and uses a frequency-stabilized interferometer to accurately measure the spatial distance. The measurement results can be traced back to the length standard, which greatly improves the accuracy of the beat length measurement. However, in actual application, we found that because the white light interference signal has a certain width, when using a white light interferometer to measure the beat length of a short optical fiber less than 10 cm, the interference signal will be superimposed, and it will not be possible to measure it using conventional methods. With the continuous development of polarization-maintaining optical fiber, the beat length is getting smaller and smaller. Currently, a 2mm beat length measurement requirement has been proposed. If conventional methods are used, short optical fibers with small beat lengths will be more difficult to measure using white light interferometry. Therefore, the existing technology has defects and needs to be improved. Summary of the Invention

[0004] The purpose of the present invention is to address the shortcomings of existing test methods in identifying white light interference signals and propose a super-resolution white light interference signal identification method. When the distance between two coupling points is less than 10 cm, the interference signals overlap. The test system is limited by the measurement principle and can only obtain interference signal information at low resolution. The present invention calculates the area change of the low-resolution interference signal and extracts high-resolution data parameters from the low-resolution signal.

[0005] The key point of the present invention is to find the relationship between the change in signal area caused by the overlap of white-light interference signals and the distance between the coupling points; a measurement process for the signal area change is proposed; and a resolution higher than the coherence length of the light source is obtained based on the area change, thereby achieving super-resolution recognition of white-light interference signals. This method can realize beat length measurement of short optical fibers.

[0006] To achieve the above objectives, an embodiment of the present invention provides a method for identifying a super-resolution white light interference signal, which includes the following steps:

[0007] Step 1: Start the measurement and prepare the optical fiber to be tested;

[0008] Step 2: Splice the optical fiber to be tested with the light source output pigtail, and use an extinction ratio tester to measure the first coupling point to obtain the extinction ratio PER1 of the first coupling point;

[0009] Step 3: Splice the optical fiber to be tested with the polarization beam splitter pigtail, and use an extinction ratio tester to measure the second coupling point to obtain the extinction ratio PER2 of the second coupling point.

[0010] Step 4: Connect the polarization beam splitter to the white-light interferometry test system. The principle of the white-light interferometry system is as follows: a beam of polarized broadband light is coupled into one polarization axis of the polarization-maintaining fiber. When the polarized light is transmitted to a disturbance point, part of the polarized light will be coupled into the polarization axis in the orthogonal direction. At the output end of the fiber, the light in the two polarization directions is separated by the polarization beam splitter. The light in one polarization direction enters the reference arm, and the light in the other polarization direction enters the moving arm with a delay line after a 90° polarization rotation. As the optical path of the delay line is compensated, the transmitted light in the two polarization directions will interfere, and a low-resolution white-light interference signal V(x) can be measured. The amplitude of the interference signal V(x) can be used to determine the magnitude of the crosstalk at the disturbance point, and the location of the crosstalk point in the fiber can be determined based on the position of the interference signal V(x).

[0011] Step 5: Obtain the highest point V in the low-resolution white light interference signal V(x) max (x), extracted from V(x) data to V max (x) is the interference signal V1(x) with 4001 data points, 2000 data points to the left and right of the center. The V1(x) signal will include the first low-resolution white-light interference signal and the second low-resolution white-light interference signal corresponding to the first coupling point and the second coupling point mentioned above. Calculate the area S1 of the white-light interference signal V1(x). The area calculation formula is as follows:

[0012]

[0013] The theoretical area S2 of the two interference signals is calculated using PER1 and PER2. The calculation formula is as follows:

[0014]

[0015] L in the above formula c is the coherence length of the light source of the interferometer system;

[0016] Step 6: Calculate the difference between the actual measured area and the theoretical area. The calculation formula is as follows;

[0017] Error=S1-S2

[0018] Step 7: Use the area difference Error obtained by subtracting the theoretical area S2 from the actual area S1 to calculate the distance Δl between the two coupling points. The relationship between Δl and Error is as follows:

[0019]

[0020] In the above formula, k0 = 2π / λ, where λ is the central wavelength of the light source, Δn is the birefringence of the fiber to be tested,

[0021] The above parameters are provided by the light source and optical fiber manufacturers;

[0022] Step 8: The distance Δl can be solved using the above formula, but there will be multiple solutions Δl1,

[0023] Δl2, Δl3....., so it is necessary to use the effective area integral width W to find the unique solution for the distance Δl between the two coupling points; set the highest point of the interference signal V1 (x_) to the zero point Z zero , the effective width of the V1(x) interference signal is set to W, and the area S3 within the effective width is calculated as follows:

[0024]

[0025] When S3 / S1=99%, W is the effective width

[0026] Step 9: The true distance Δl and the effective area integral width W have the following corresponding relationship:

[0027]

[0028] The above formula can be used to obtain a unique solution for the distance Δl, where Δl is the actual distance between the two coupling points.

[0029] The present invention provides a method for identifying super-resolution white light interference signals, and the beneficial effects of the measurement method involved are as follows:

[0030] (1) The relationship between the area change of the two interference signals and the distance between the two coupling points was found, and the resolution was improved from about 10 cm in space to about 1 cm.

[0031] (2) The change in the effective area integral width after the superposition of white light interference signals can further accurately confirm the true optical path difference between the coupling points.

[0032] (3) A new test procedure is proposed to measure the true extinction ratio of two coupling points with a distance less than 10 cm. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a flow chart of a method for recognizing super-resolution white light interference signals according to the present invention. DETAILED DESCRIPTION

[0034] For ease of understanding of the present invention, the present invention will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those generally understood by those skilled in the art of the technical field of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more related listed items.

[0035] One embodiment of the present invention is as follows: Step 1: measurement starts, preparing the optical fiber to be tested;

[0036] Step 2: Splice the optical fiber to be tested with the light source output pigtail, and use an extinction ratio tester to measure the first coupling point to obtain the extinction ratio PER1 of the first coupling point;

[0037] Step 3: Splice the optical fiber to be tested with the polarization beam splitter pigtail, and use an extinction ratio tester to measure the second coupling point to obtain the extinction ratio PER2 of the second coupling point.

[0038] Step 4: Connect the polarization beam splitter to the white-light interferometry test system. The principle of the white-light interferometry system is as follows: a beam of polarized broadband light is coupled into one polarization axis of the polarization-maintaining fiber. When the polarized light is transmitted to a disturbance point, part of the polarized light will be coupled into the polarization axis in the orthogonal direction. At the output end of the fiber, the light in the two polarization directions is separated by the polarization beam splitter. The light in one polarization direction enters the reference arm, and the light in the other polarization direction enters the moving arm with a delay line after a 90° polarization rotation. As the optical path of the delay line is compensated, the transmitted light in the two polarization directions will interfere, and a low-resolution white-light interference signal V(x) can be measured. The amplitude of the interference signal V(x) can be used to determine the magnitude of the crosstalk at the disturbance point, and the location of the crosstalk point in the fiber can be determined based on the position of the interference signal V(x).

[0039] Step 5: Obtain the highest point V in the low-resolution white light interference signal V(x) max (x), extracted from V(x) data to V max(x) is the interference signal V1(x) with 4001 data points, 2000 data points to the left and right of the center. The V1(x) signal will include the first low-resolution white-light interference signal and the second low-resolution white-light interference signal corresponding to the first coupling point and the second coupling point mentioned above. Calculate the area S1 of the white-light interference signal V1(x). The area calculation formula is as follows:

[0040]

[0041] The theoretical area S2 of the two interference signals is calculated using PER1 and PER2. The calculation formula is as follows:

[0042]

[0043] L in the above formula c is the coherence length of the light source of the interferometer system;

[0044] Step 6: Calculate the difference between the actual measured area and the theoretical area. The calculation formula is as follows;

[0045] Error=S1-S2

[0046] Step 7: Use the area difference Error obtained by subtracting the theoretical area S2 from the actual area S1 to calculate the distance Δl between the two coupling points. The relationship between Δl and Error is as follows:

[0047]

[0048] In the above formula, k0 = 2π / λ, where λ is the central wavelength of the light source, Δn is the birefringence of the fiber to be tested,

[0049] The above parameters are provided by the light source and optical fiber manufacturers;

[0050] Step 8: The distance Δl can be solved using the above formula, but there will be multiple solutions Δl1,

[0051] Δl2, Δl3, etc. Therefore, it is necessary to use the effective area integration width W to find the unique solution for the distance Δl between the two coupling points; set the highest point of the interference signal V1(x) to the zero point Z zero , the effective width of the V1(x) interference signal is set to W, and the area S3 within the effective width is calculated as follows:

[0052]

[0053] When S3 / S1=99%, W is the effective width.

[0054] Step 9: The true distance Δl and the effective area integral width W have the following corresponding relationship:

[0055]

[0056] The above formula can be used to obtain a unique solution for the distance Δl, where Δl is the actual distance between the two coupling points.

[0057] The present invention provides a method for identifying super-resolution white light interference signals, and the beneficial effects of the measurement method involved are as follows:

[0058] (1) The relationship between the area change of the two interference signals and the distance between the two coupling points was found, and the resolution was improved from about 10 cm in space to about 1 cm.

[0059] (2) The change in the effective area integral width after the superposition of white light interference signals can further accurately confirm the true optical path difference between the coupling points.

[0060] (3) A new test procedure is proposed to measure the true extinction ratio of two coupling points with a distance less than 10 cm.

[0061] It should be noted that the above-mentioned technical features are further combined with each other to form various embodiments not listed above, which are all regarded as the scope of the present invention; and, for ordinary technicians in this field, they can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for identifying super-resolution white light interference signals, characterized in that: The following steps are involved: Step 1: Start the measurement and prepare the optical fiber to be tested; Step 2: Splice the optical fiber to be tested with the light source output pigtail, and use an extinction ratio tester to measure the first coupling point to obtain the extinction ratio PER1 of the first coupling point; Step 3: Splice the optical fiber to be tested with the polarization beam splitter pigtail, and use an extinction ratio tester to measure the second coupling point to obtain the extinction ratio PER2 of the second coupling point. Step 4: Measure and obtain the low-resolution white light interference signal V(x); Step 5: Obtain the highest point V in the low-resolution white light interference signal V(x) max (x), extracted from V(x) data to V max (x) is the interference signal V1(x) with 4001 data points, 2000 data points to the left and right of the center. The V1(x) signal will include the first low-resolution white-light interference signal and the second low-resolution white-light interference signal corresponding to the first coupling point and the second coupling point mentioned above. Calculate the measurement area S1 of the white-light interference signal V1(x). The measurement area calculation formula is as follows: Calculate the theoretical area S2 of the two interference signals using PER1 and PER2, The calculation formula is as follows: L in the above formula c is the coherence length of the light source of the interferometer system; Step 6: Calculate the difference between the actual measured area and the theoretical area. The calculation formula is as follows; Error=S1-S2 Step 7: Use the area difference Error obtained by subtracting the theoretical area S2 from the measured area S1 to calculate the distance Δl between the two coupling points. The relationship between Δl and Error is as follows: In the above formula, k0 = 2π / λ, where λ is the central wavelength of the light source and Δn is the birefringence of the fiber to be tested. Step 8: Use the above formula to solve the distance Δl. Since there may be multiple solutions Δl1, Δl2, Δl3, etc., use the effective area integration width W to find the unique solution for the distance Δl between the two coupling points; set the highest point of the interference signal V1(x) to zero point Z zero , the effective width of the V1(x) interference signal is set to W, and the area S3 within the effective width is calculated as follows: When S3 / S1=99%, W is the effective width Step 9: The true distance Δl and the effective area integral width W have the following corresponding relationship: The above formula is used to obtain a unique solution for the distance Δl, where Δl is the true distance between the two coupling points.

2. The method for recognizing a super-resolution white light interference signal according to claim 1, wherein: In step 4, the specific steps for measuring the low-resolution white light interference signal V(x) are as follows: connecting a polarization beam splitter to a white light interference test system. The principle of the white light interference system is as follows: a beam of polarized broadband light is coupled into one polarization axis of a polarization-maintaining optical fiber. When the polarized light is transmitted to a disturbance point, part of the polarized light will be coupled into the polarization axis in the orthogonal direction. At the output end of the optical fiber, the light in the two polarization directions is separated by a polarization beam splitter, and the light in one polarization direction enters the reference arm, and the light in the other polarization direction enters the moving arm with a delay line after being rotated 90° in the polarization direction. As the optical path of the delay line is compensated, the transmitted light in the two polarization directions will interfere, and the low-resolution white light interference signal V(x) is measured at this time.

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