Auxiliary interferometer delay fiber length coding device

Abstract

The invention provides an auxiliary interferometer delay optical fiber self-adaptive matching optical path coding device for an optical frequency domain reflection technology, which belongs to the technical field of optical fiber device testing, comprises a programmable optical switch, an optical fiber delay ring and an upper computer, and is characterized in that according to different lengths of optical fibers to be measured, the optical fiber delay ring is matched with the programmable optical switch; the optimal auxiliary interferometer delay optical fiber length is matched, and the upper computer is used for freely coding and combining a plurality of delay optical fiber rings according to a self-adaptive matching result by controlling a programmable electric dimming switch, so that the optimal strain precision demodulation under different lengths of the optical fiber to be measured is realized. According to the device, adaptive dynamic matching is carried out on to-be-tested optical fibers with different lengths to assist an interferometer in delaying the length of the optical fibers, so that the test strain precision reaches the optimal value, a device light path is simplified, and the influence of frequent equipment disassembly and assembly on instrument stability and performance precision is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of optical testing, and in particular relates to an auxiliary interferometer delayed optical fiber length coding device used in optical frequency domain reflection technology. Background Art

[0002] Strain parameters are important parameters in the development and manufacture of optical devices, optical systems and photonic integrated circuits. Testing the strain parameters of optical fiber devices is essential during their preparation, production and application. Optical fiber sensing strain testing technology based on optical frequency domain reflectometry (OFDR) is widely used in the fields of large-scale building structure health monitoring, three-dimensional shape sensing, and optical fiber device detection.

[0003] Due to the influence of the nonlinearity of the tunable light source frequency sweep, the auxiliary interferometer has become an essential component of the current optical frequency domain reflection system for high-precision testing, and there is a matching correspondence between the auxiliary interferometer delay fiber length and the optimal test distance of the optical fiber to be tested.

[0004] In 2004, the American company LUNA proposed the use of an auxiliary interferometer to correct the errors generated by a laser with non-ideal tuning characteristics in the optical frequency domain reflection system (Apparatus and method for correcting errors generated by a laser with non-ideal tuning characteristics, US6900897B2), which greatly improved the test accuracy of the OFDR system. However, it did not find the matching correspondence between the arm length difference of the auxiliary interferometer and the arm length difference of the main interferometer.

[0005] Wang Feng and others from Nanjing University published a method for compensating the nonlinear tuning effect of lasers for optical frequency domain reflectometry (CN111397644B). An acousto-optic frequency shifter (AOM) was connected to one of the interferometer arms of the OFDR auxiliary interferometer to shift the frequency of the light wave and increase the beat signal frequency of the auxiliary interferometer. The zero crossing point of the signal was used as a reference point to correct the measurement signal of the main interferometer. However, the acousto-optic frequency shifting scheme used in the method has noise interference from the AOM itself, and does not consider the matching problem between the auxiliary interferometer delay and the main interferometer delay, which results in the final strain demodulation result failing to reach the ideal optimal value.

[0006] Zhang Lixun and others from the University of Electronic Science and Technology of China published a system and method for reducing the nonlinear phase effect of OFDR light sources (CN112461276B), which uses the test fiber as the reference fiber of the auxiliary interferometer to achieve long-distance and high spatial resolution signal detection. Since there is an optimal value matching relationship between the delay of the auxiliary interferometer and the delay of the main interferometer, directly using the device under test as the delay fiber of the main interferometer cannot achieve the best strain test accuracy.

[0007] Wuhan Haoheng Technology Co., Ltd. has disclosed an OFDR segmented acquisition device and method (CN111578971B) that uses an auxiliary interferometer to generate a beat signal as the external clock of the data acquisition card to achieve equal frequency interval sampling of the beat signal of the main interferometer. At the same time, the optical fiber to be tested is divided into N segments for segmented testing. Although dividing the optical fiber to be tested into shorter sections for measurement can effectively suppress the accumulation of residual phase noise, this method does not consider the matching relationship between the arm length difference of the auxiliary interferometer and the arm length difference of the main interferometer, resulting in the final test result failing to meet expectations.

[0008] Japan's Anritsu Corp publicly used an auxiliary interferometer to calibrate the nonlinear effects of the OFDR system light source frequency sweep, and found that its correction effect depends on the reference arm length difference between the main interferometer and the auxiliary interferometer, namely the auxiliary interferometer reference arm delay fiber length (Optical frequency domain reflection measurement device and optical frequency domain reflection measurement method, JP2017181115A). However, it did not accurately calculate the optimal matching relationship between the auxiliary interferometer arm length difference and the main interferometer arm length difference, and was unable to implement the adaptive dynamic matching technology of the auxiliary interferometer delay fiber.

[0009] The present invention provides an auxiliary interferometer delayed fiber adaptive matching optical path encoding device, and its design idea is: based on the optimal strain demodulation accuracy matching relationship between the auxiliary interferometer and the main interferometer arm length difference in the optical frequency domain reflectometer, the host computer calculates the optimal matching auxiliary interferometer delayed fiber length of the current optical fiber to be tested, and replaces the original auxiliary interferometer delayed fiber with an adaptive optical path encoding device that can be controlled by the host computer. According to the strain accuracy test requirements of different optical fiber lengths to be tested, after the computer calculates the optimal auxiliary interferometer optical path difference, the host computer controls the optical switch to adaptively and dynamically match the optimal auxiliary interferometer delayed fiber length, so that the strain demodulation accuracy of the device to be tested approaches the theoretical limit. Based on the optimal matching method of the auxiliary interferometer reference arm delayed fiber length, the present invention controls the optical switch to select the optical path through the host computer coding form to realize the adaptive dynamic matching of the auxiliary interferometer arm length difference, thereby greatly improving the strain test accuracy of the optical fiber to be tested. It has the advantages of high measurement accuracy, good stability, simple optical path structure, etc., which not only reduces the system cost, but also improves the test efficiency and saves the test cost. It can be widely used in the quantitative test of optical device performance with high requirements for strain test accuracy. Summary of the invention

[0010] An auxiliary interferometer delayed optical fiber length coding device comprises a light source module 1, an auxiliary interferometer and adaptive matching optical path coding module 2, a main interferometer module 3, and a host computer signal processing and control module 4, and is characterized in that:

[0011] The tunable laser source 101 generates a linear frequency-sweeping continuous light whose frequency changes with time at a rate γ. After passing through the first coupler 102, the continuous frequency-sweeping optical signal is divided into two paths. One path enters the main interferometer module 3 for obtaining information of the device to be tested, and the other path enters the auxiliary interferometer and the adaptive optical path encoding module 2 for obtaining the frequency-sweeping nonlinear information of the tunable laser source 101, thereby improving the strain demodulation accuracy of the device test.

[0012] The auxiliary interferometer and adaptive optical path encoding module according to claim 1 are characterized in that:

[0013] The optical path encoding module is mainly composed of n optical switches and n-1 groups of delay optical fibers. According to the different paths of the optical switches controlled by the host computer, the encoding module can realize arbitrary encoding methods and thus arbitrarily configure the delay optical fibers. At the beginning of the test, after the host computer calculates the optimal auxiliary interferometer two-arm optical path difference corresponding to the optical fiber to be tested according to the length of the different optical fibers to be tested, the output optical path of the optical path encoding module is automatically adjusted to achieve adaptive matching, thereby optimizing the test accuracy to the greatest extent.

[0014] Assuming that the optical switch type selected in the device is an m-way optical switch, the delay optical fiber length of the delay optical fiber length coding module is an m-ary coding mode. If it is calculated that the maximum length of the auxiliary interferometer delay optical fiber required in this test is L.

[0015] The calculation formula for the delayed optical fiber length of the m paths of optical switch No. 1 204 is:

[0016]

[0017] That is, the delay fiber length between each path of optical switch 204 No. 1 is The interval is divided into m intervals, and the lengths of the m delay optical fibers of the first delay optical fiber group 209 are respectively set to: 0, , , …, Optical switch No. 1 204 preliminarily divides the auxiliary interferometer delay fiber into m-1 intervals, and optical switch No. 2 (205) further refines the delay fiber length intervals. The calculation formula for the delay fiber length of the m paths of optical switch No. 2 (205) is:

[0018]

[0019] That is, the delay fiber length between each path of optical switch 205 No. 2 is The interval is divided into m intervals, and the lengths of the m delay optical fibers of the second delay optical fiber group 210 are respectively set to: 0, , , …, The configuration of the intermediate optical switch 207 and the intermediate delay fiber group 211 is the same as that of the No. 1 optical switch 204 and the No. 2 optical switch 205. The channels and quantity of the optical switches can be selected according to the estimated longest auxiliary interferometer delay fiber length required in the actual test process.

[0020] The minimum delay fiber group 212 of the nth optical switch 208 is the most accurate adjustment switch of the delay fiber length encoding device of the auxiliary interferometer. The calculation formula of the delay fiber length of the m paths of the nth optical switch 208 is:

[0021]

[0022] That is, the delay fiber length between each path of the n-number optical switch 208 is In order to divide the interval into m intervals, the lengths of the m delayed optical fibers of the minimum delay optical fiber group 212 are respectively set to: , , …, When the n optical switches finally all select the maximum length of each group of delayed optical fibers, the maximum auxiliary interferometer delay optical fiber length in the estimated calculation is reached, thereby realizing high-precision auxiliary interferometer length encoding.

[0023] By connecting the optical path encoding module to one of the arms of the auxiliary interferometer module, the optical frequency domain reflectometer auxiliary interferometer can extract the nonlinear information of the light source frequency sweep, and convert the light source frequency sweep information into interference fringes of the auxiliary interferometer, which are extracted by the first balanced detector 211 and converted into electrical signals and input into the host computer signal processing and control module 4.

[0024] The main interferometer module 4 and the host computer signal processing and control module 5 described in claim 1 are characterized in that:

[0025] The test optical signal input to the main interferometer is divided into two paths through the second coupler 301. One path is input to the reference arm of the main interferometer and is ensured to be equal in intensity in the P and S directions of the optical signal in the interferometer through the polarization controller 302, thereby achieving the best test accuracy. The other path enters the test arm and is input from the No. 1 port of the circulator 303 and then output from the No. 2 port. The optical information of the device under test is output from the No. 3 port of the circulator 303 in the form of reflection. After passing through the fourth coupler 304 with the reference interference signal, the second balanced detector 305 collects the two-path interference and converts it into an electrical signal, thereby extracting the optical information of the device under test.

[0026] The upper computer signal processing and control module 4 includes a data acquisition card 401, a computer 402, and the first balanced detector 211 and the second balanced detector 305 convert the collected interference fringe signals into electrical signals and input them into the signal acquisition card 401 for recording and then input them into the computer 402 for data processing. The computer 402 is also responsible for controlling each optical switch in the auxiliary interferometer adaptive matching optical path encoding device, so as to realize the switching of auxiliary interferometer delayed optical fibers of different lengths.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] The device can make the OFDR system have lower residual phase noise when measuring strain, thereby improving the strain demodulation accuracy. The host computer performs adaptive dynamic matching according to the length of the optical fiber to be measured, and the optical path encoding device always keeps the current optical frequency domain reflectometer auxiliary interferometer arm length difference and the main interferometer arm length difference in the best matching state, so that the strain test accuracy is close to the theoretical limit.

[0029] The device controls the optical path coding device to perform adaptive delayed fiber matching based on the arm length difference matching calculation results through the host computer, thereby improving the feasibility and stability of the system. According to the needs of different scenarios, the optical path coding effects of different bases can be achieved by adjusting the number of channels of the optical switch, thereby enhancing the adaptability of the system. This design simplifies the overall testing process and avoids problems such as system disassembly, which not only improves the convenience of operation, but also saves time and cost. With the continuous optimization of technology, the device will show great potential in a wider range of application fields in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of an auxiliary interferometer delay fiber adaptive matching optical path coding device used in an OFDR system;

[0031] Figure 2 It is a schematic diagram of an optical frequency domain reflection system-assisted interferometer delay fiber adaptive matching optical path coding device based on the Mach-Zehnder (MZ) interferometer structure;

[0032] Figure 3 It is a schematic diagram of an optical frequency domain reflection system-assisted interferometer delay fiber adaptive matching optical path encoding device based on the Ma Michelson (MI) interferometer structure;

[0033] Figure 4 It is a schematic diagram of the structure of a quaternary auxiliary interferometer delayed fiber adaptive matching optical path encoding device based on a Michelson interferometer structure. DETAILED DESCRIPTION

[0034] In order to clearly illustrate the auxiliary interferometer delayed fiber adaptive matching optical path encoding device of the present invention, the present invention is further described in conjunction with the embodiments and drawings, but this should not limit the protection scope of the present invention. Specific implementation method one:

[0036] In the optical frequency domain reflection system based on Mach-Zehnder (MZ) interferometer, as shown in the attached Figure 3 As shown in the optical path structure, the optical signal entering the auxiliary interferometer passes through the delay optical fiber configured by the adaptive matching optical path encoding device and is directly output by the path selected by the optical switch n 26 as the reference arm of the auxiliary interferometer. The delayed optical signal and the local oscillator optical signal undergo beat frequency interference in the balanced detector 35, thereby correcting the accuracy degradation problem of the OFDR system caused by the nonlinearity of the light source scanning frequency. Specific implementation method 2:

[0038] In an optical frequency domain reflectometry system using a Michelson (MI) interferometer as an auxiliary interferometer, as shown in the attached Figure 2 As shown in the optical path structure in FIG. 1 , a Faraday rotator needs to be connected after each path of the n-number optical switch 49 at the end of the adaptive matching optical path encoding device, as shown in the attached Figure 2 As shown, in the example, there are two paths after the optical switch No. n, and the first path and the second path are connected to a Faraday rotator 44 respectively. Similarly, when there are n paths after the optical switch No. n 49, n Faraday rotators need to be connected. The reference light signal passes through the specific length delay fiber selected in the fiber length encoding device, is reflected by the Faraday rotator, and after experiencing twice the fiber delay loop length, returns to the first photodetector 43 to interfere with the local oscillator reference light, thereby correcting the accuracy degradation problem caused by the nonlinearity of the light source frequency sweep in the OFDR system. Specific implementation method three:

[0040] The fiber delay ring encoding method of different bases can be realized according to the number of optical switch paths selected, as shown in the attached Figure 4 As shown in the figure, taking the Michelson interferometer auxiliary interferometer as an example, a four-channel optical switch can be used to configure the auxiliary interferometer fiber delay loop in a quaternary encoding manner to achieve higher precision fiber length interval control.

[0041] Taking the case where the device under test requires an auxiliary interferometer with a maximum length of 128 meters, a total of three sets of optical switches and optical fiber delay rings are used, that is, the middle optical switch 68 and all the middle delay optical fiber rings 78, 79, 80, 81 are not configured. The first group of optical fiber delay rings can first determine the required length range within 0-32 meters, 33-64 meters, 65-96 meters or 97-128 meters, that is, the lengths of the first group of optical fiber delay rings are respectively configured as follows: the first delay ring 70 is set to 0 meters, the second delay ring 71 is set to 32 meters, the third delay ring 72 is set to 64 meters, and the fourth delay ring 73 is set to 96 meters; the second group of optical fiber delay rings can be further subdivided into the required length range, and the lengths of the second group of optical fiber delay rings are configured as follows: the fifth delay ring 74 is set to 0 meters, the sixth delay ring 75 is set to 8 meters, the seventh delay ring 76 is set to 16 meters, and the eighth delay ring 77 is set to 24 meters; the lengths of the third group of optical fiber delay rings are configured as follows: the ninth delay ring 82 is set to 0 meters, the tenth delay ring 83 is set to 2 meters, the eleventh delay ring 84 is set to 4 meters, and the twelfth delay ring 85 is set to 6 meters, so as to realize the dynamic encoding of the quaternary delay optical fiber length within the 128-meter range and quickly match the auxiliary interferometer delay optical fiber length required for the test.

Claims

1. An auxiliary interferometer delayed optical fiber length coding device, comprising a light source module (1), an auxiliary interferometer and adaptive matching optical path coding module (2), a main interferometer module (3), and a host computer signal processing and control module (4), wherein: The tunable laser source (101) generates linear frequency-sweeping continuous light whose frequency changes with time at a rate γ. After passing through the first coupler (102), the continuous frequency-sweeping light signal is divided into two paths, one path entering the main interferometer module (3) for obtaining information of the device to be tested, and the other path entering the auxiliary interferometer and the adaptive optical path encoding module (2) for obtaining frequency-sweeping nonlinear information of the tunable laser source (101), thereby improving the strain demodulation accuracy of the device test.

2. The auxiliary interferometer and adaptive optical path length coding module according to claim 1, characterized in that: The optical path coding module is mainly composed of n optical switches and n-1 groups of delay optical fibers. According to the different optical switch paths controlled by the host computer, the encoding module can realize arbitrary encoding methods to arbitrarily configure the delay fiber. At the beginning of the test, the host computer calculates the optimal auxiliary interferometer two-arm optical path difference corresponding to the tested fiber according to the length of the different tested fibers, and automatically adjusts the output optical path of the optical path encoding module to achieve adaptive matching, thereby optimizing the test accuracy to the greatest extent. Assuming that the optical switch type selected in the device is an m-way optical switch, the delay optical fiber length of the delay optical fiber length coding module is an m-ary coding mode. If it is calculated that the maximum length of the auxiliary interferometer delay optical fiber required in this test is L. The calculation formula for the delayed optical fiber length of the m paths of optical switch No. 1 (204) is: That is, the delay fiber length between each path of optical switch No. 1 (204) is In order to divide the interval into m intervals, the lengths of the m delay optical fibers of the first delay optical fiber group (209) are respectively set to: 0, , , …, Optical switch No. 1 (204) preliminarily divides the auxiliary interferometer delay fiber into m-1 intervals, and optical switch No. 2 (205) further refines the delay fiber length intervals. The calculation formula for the delay fiber lengths of the m paths of optical switch No. 2 (205) is: That is, the delay fiber length between each path of optical switch No. 2 (205) is In order to divide the interval into m intervals, the lengths of the m delay optical fibers of the second delay optical fiber group (210) are respectively set to: 0, , , …, The configuration of the intermediate optical switch (207) and the intermediate delay fiber group (211) is the same as that of the No. 1 optical switch (204) and the No. 2 optical switch (205). The path and quantity of the optical switch can be selected according to the estimated longest auxiliary interferometer delay fiber length required in the actual test process. The minimum delay fiber group (212) of the nth optical switch (208) is the most accurate adjustment switch of the delay fiber length encoding device of the auxiliary interferometer. The calculation formula of the delay fiber length of the m paths of the nth optical switch (208) is: That is, the delay fiber length between each path of the n-number optical switch (208) is To divide the interval into m intervals, the lengths of the m delayed optical fibers of the minimum delay optical fiber group (212) are respectively set as: , , …, When the n optical switches finally all select the maximum length of each group of delayed optical fibers, the maximum auxiliary interferometer delay optical fiber length in the estimated calculation is reached, thereby realizing high-precision auxiliary interferometer length encoding. By connecting the optical path encoding module to one arm of the auxiliary interferometer module, the optical frequency domain reflectometer auxiliary interferometer can extract the nonlinear information of the light source frequency sweep, and convert the light source frequency sweep information into interference fringes of the auxiliary interferometer, which are extracted by the first balanced detector (211) and converted into electrical signals and input into the upper computer signal processing and control module (4).

3. The main interferometer module (4) and the host computer signal processing and control module (5) according to claim 1 are characterized in that: The test optical signal input into the main interferometer is divided into two paths through the second coupler (301), one path is input into the reference arm of the main interferometer and passes through the polarization controller (302) to ensure that the intensity of the optical signal in the P and S directions in the interferometer is equal, thereby achieving the best test accuracy; the other path enters the test arm and is input from the first port of the circulator (303) and then output from the second port, and the optical information of the device under test is output from the third port of the circulator (303) in the form of reflection, and after passing through the fourth coupler (304) with the reference interference signal, the second balanced detector (305) collects the two-path interference and converts it into an electrical signal, thereby extracting the optical information of the device under test. The upper computer signal processing and control module (4) includes a data acquisition card (401), a computer (402), a first balanced detector (211) and a second balanced detector (305). The collected interference fringe signals are converted into electrical signals and then input into the signal acquisition card (401) for recording and then input into the computer (402) for data processing. The computer (402) is also responsible for controlling each optical switch in the auxiliary interferometer adaptive matching optical path encoding device, thereby realizing the switching of auxiliary interferometer delayed optical fibers of different lengths.

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