Multi-parameter testing device and method of multi-branch optical fiber sensitive ring

Abstract

This invention provides a multi-parameter testing device and method for multiple fiber optic sensing rings, including the implemented device structure and testing procedure. Its key feature is the injection of swept-frequency light into the device under test (DUT) to generate a reflected signal carrying temperature and strain information. This reflected signal is then injected into an optical frequency domain reflectometer (OFDR) for testing. By controlling the testing sequence of the temperature chamber, a 1×N optical switch, the swept-frequency laser, and the OFDR, the multi-parameter performance of multiple fiber optic rings under temperature variations can be tested simultaneously. This device uses the same light source, testing structure, and temperature chamber to test multiple fiber optic rings simultaneously, ensuring testing accuracy and significantly improving testing efficiency. This invention has advantages such as high integration, comprehensive testing parameters, simple control method, and resistance to environmental interference. It can be widely used for high-precision measurement and analysis of the multi-parameter performance of optical devices such as polarization-maintaining fibers, fiber optic rings, and hydrophones.

Description

Technical fields:

[0001] This invention relates to the fields of optical measurement technology and fiber optic gyroscopes, specifically to a multi-parameter testing device and method for multiple fiber optic sensing loops. Background technology:

[0002] Fiber optic gyroscopes, invented in the 1970s, are non-mechanical angular velocity measuring instruments based on the Sagnac effect, and they play an important role in aerospace, military, and sensing fields. As the core component of a fiber optic gyroscope system, the geometric and optical symmetries of the fiber optic sensing loop have a decisive influence on the thermally induced drift performance of the gyroscope. Therefore, the measurement and analysis of the physical properties of the fiber itself are essential.

[0003] The accurate measurement of fiber refractive index is closely related to the accuracy of distributed fiber optic sensing. In 2020, Yuan Libo et al. from Guilin University of Electronic Technology (CN 110967048 A) invented a parallel integrated Mach Zehnder interferometer with orthogonal tilted three-core fiber gratings. By detecting the output intensity after the interference of three beams, the effective refractive index of the transmission modes within N fiber cores can be calculated. In 2022, Liang Huijuan et al. from the 38th Research Institute of China Electronics Technology Group Corporation (CN 114665957A) invented a fiber refractive index measurement system and method. A vector network analyzer provides a sweep signal including different frequencies to an optoelectronic modulator. The signal is modulated into an optical signal by the optoelectronic modulator and transmitted through the fiber under test. After demodulation by a detector, the signal is returned to the vector network analyzer to analyze the phase of the different frequency signals. Further measurement is performed by changing the length of the fiber under test, thus achieving high-precision calculation of the refractive index of the fiber under test.

[0004] On the other hand, under the influence of temperature fields, thermal strain exacerbates the deterioration of optical symmetry, leading to the Mohr and Shupe effects, which significantly aggravate thermal drift in fiber optic gyroscope systems. Therefore, accurate testing and analysis of the thermal strain of the fiber optic sensing ring is particularly important. In 2022, Liu Qingwen et al. from Shanghai Jiao Tong University (CN 117451203 A) invented a large-range quasi-distributed fiber optic sensing method and system. Based on the beat frequency signal, the frequency value of the difference frequency term is obtained to calculate the optical path between two points. The temperature change and strain of the fiber are obtained by detecting the change in optical path. In the same year, Wen Kunhua et al. from Guangdong University of Technology (CN 115452213 A) invented a distributed high-precision strain measurement method for fiber optic sensing rings under temperature change conditions. Combining DTS and BOTDA systems, temperature compensation for distributed stress testing of the fiber optic sensing ring is achieved through calculation, the temperature stability of its internal stress distribution is determined, and thus the high-precision internal stress distribution of the fiber optic sensing ring is calculated. In 2023, Rao Yunjiang et al. from Zhejiang Laboratory (CN 116576897 A) invented a multi-parameter fiber optic distributed sensing system and method. This system obtains the temperature or strain changes sensed by each fiber Bragg grating by measuring the wavelength changes corresponding to wavelength defects in the reflection spectrum of each fiber Bragg grating. In 2024, Dong Yongkang et al. from Harbin Institute of Technology (CN118623781 A) invented a temperature-strain decoupling method and device for OPGW optical cables based on a zero-strain reference point and an ANN algorithm. This method uses a zero-strain reference point-based temperature-strain decoupling method to demodulate multiple Brillouin gain spectra, obtaining the corresponding temperature value for each fiber and solving the problem of accurate data demodulation. Zhang Zhuo from Harbin Engineering University (Research on Physical Field Analysis and Coupling Characteristics of Marine Fiber Optic Gyroscopes) analyzed the error mechanism of the physical field of fiber optic gyroscopes under the coupling effect of temperature field and stress field, proposed the concepts of fiber optic ring temperature matrix, stress matrix, and weight matrix, and derived the error model in the traditional integral accumulation form into the form of multiple matrix inner products, providing guidance for the design of fiber optic ring parameters and the selection of fiber and adhesive materials, thereby improving the accuracy of gyroscopes.

[0005] In fiber optic loop testing technology, B-OTDA and optical frequency domain reflection (OFDR) are two commonly used methods. B-OTDA provides absolute measurements, but its resolution needs improvement. Conversely, OFDR has better resolution, but it is only a relative measurement relative to a reference state. Since internal stress has a significant impact on winding quality, existing research has used B-OTDA to monitor the symmetrical stress of fiber optic sensitive loops. Han Zhengying of the 41st Research Institute of China Electronics Technology Group Corporation (Application of BOTDA Fiber Optic Sensing Technology in Fiber Optic Loop Quality Assessment) used B-OTDA technology to measure the strain distribution of fiber optic sensitive loops under different temperature conditions. By screening winding bodies with more symmetrical strain changes at various temperatures, the performance of the gyroscope optical path was improved. Yang Jigang et al. of the Beijing Institute of Automation Control Equipment published a study on methods to improve the quality of fiber optic winding bodies. Addressing the problem of asymmetrical fiber tension during inertial navigation winding, they fed back the strain data measured by B-OTDA to the tension control system in real time, thereby improving the stability and symmetry of tension control and significantly enhancing the symmetry of the sensitive loop. Meanwhile, OFDR technology based on Rayleigh scattering has developed rapidly in recent years. The OFDR system using the polarization-maintaining scheme can simultaneously test temperature and thermal strain. The University of Ottawa in Canada published a paper (Long-range high spatial resolution distributed temperature and strain sensing based on optical frequency-domain reflectionometry) which proposed a corresponding testing and demodulation scheme. Utilizing the characteristics that the temperature sensing coefficient is negative and the strain sensing coefficient is positive, a temperature resolution of ±0.8℃, a strain resolution of ±7.0με, and a spatial resolution of 1.3cm were achieved at a sensing distance of 170m

[74] . Yu Zhangjun et al. published a paper (Distributed Polarization Measurement for Fiber Sensing Coils: A Review) which proposed a high-performance method for obtaining a dynamic range >90dB, a measurement length >10km, a full-range spatial resolution <10cm, and time-domain, frequency-domain, and time-frequency-domain diagnostics in the distributed polarization measurement of fiber sensing coils based on OFDR, which provides important inspiration for our research.

[0006] However, based on extensive research, the parameters affecting the thermally induced drift of fiber optic loops and their relationships under environmental conditions remain unclear. Furthermore, the lack of suitable long-distance, high-precision, and high spatial resolution methods for temperature and thermal strain testing severely impacts measurement accuracy. Therefore, establishing a new transfer function from temperature to thermally induced drift and researching multi-parameter testing methods for temperature and thermal strain are of paramount importance for parameter detection in fiber optic gyroscopes and for distributed fiber optic sensing applications. Summary of the Invention:

[0007] The purpose of this invention is to provide an OFDR beat frequency interferometry testing device that is highly accurate, stable, reliable, capable of measuring multiple parameters, and able to simultaneously measure multiple fiber optic rings. A further purpose of this invention is to provide a testing method for the OFDR beat frequency interferometry testing device.

[0008] This invention discloses a multi-parameter testing device for multiple fiber optic sensing loops, characterized by comprising a TLS light source module 1, an auxiliary interferometer module 2, a main interferometer module 3, a device under test (DUT) 4, a temperature control sensing module 5, and a control and data processing module 6. The control and data processing module 6 controls the TLS light source 101, a data acquisition card 603, a temperature chamber 501, a temperature sensor 502, and an optical switch 410. The TLS light source module 1 injects a light beam into a first coupler 204, with a portion of the light injected into the auxiliary interferometer module 2 and the remaining portion injected into the main interferometer module 3. The DUT 4 is connected to the main interferometer module 3 and placed within the temperature control sensing module 5. The auxiliary and main interference signals are fed into the data acquisition card 603, ultimately obtaining the scattering and reflection characteristics of the DUT.

[0009] A multi-parameter testing device for multiple fiber optic sensing loops, the testing method of which includes the following steps:

[0010] (1) To ensure the stability of the fiber optic ring, a full-temperature environment test of the fiber optic ring was conducted.

[0011] (2) Connect the first fiber ring 429, the second fiber ring 430...the Nth fiber ring 431 to the test system to complete the optical path connection.

[0012] (3) The controller 601 controls the TLS light source 101, data acquisition card 603, temperature chamber 501, temperature sensor 502 and light switch 410 to start synchronously for system self-test.

[0013] (4) Place the fiber optic ring inside the temperature chamber 501, set the temperature chamber working curve in the control unit 601, set the temperature range to T1~T2, and keep the temperature change rate at T3 / min.

[0014] (5) The temperature chamber 501 is started. The timing is set to 0 at this time. The controller 601 starts timing and increments the timing by 1 every 1 minute.

[0015] (6) Define the initial timing of the first fiber ring 429, the second fiber ring 430, ... the Nth fiber ring 431 as 2, 3 ... N+1, and then determine the current timing.

[0016] (7) When the timing is 2, the optical switch 410 switches to the first output port, and the controller 601 triggers the TLS light source 101 and the data acquisition card 603 to test the first fiber optic ring 429.

[0017] (8) When the timing is 3, the optical switch 410 switches to the second output port, and the controller 601 triggers the TLS light source 101 and the data acquisition card 603 to test the second fiber optic ring 430.

[0018] (9) When the time sequence is N+1, the optical switch 410 switches to output port N, and the controller 601 triggers the TLS light source 101 and the data acquisition card 603 to test the Nth fiber optic ring 431.

[0019] (10) Collect test data and upload it to the data processing machine 602.

[0020] (11) Compensate for phase noise and determine whether the intensity of the end reflection peak after compensation is consistent with that at room temperature.

[0021] (12) If the strength is consistent, complete the test of the first fiber ring 429, the second fiber ring 430... the Nth fiber ring 431, and record the temperature sensor data of the corresponding time sequence.

[0022] (13) If the intensity is inconsistent, phase noise compensation should be performed again to ensure that the intensity of the end reflection peak after compensation is consistent with that at room temperature.

[0023] (14) For each fiber optic ring, the initial timing is tested once every N increments.

[0024] (15) Record the test data of P and S channels, and obtain the scattering spectrum signal after Fourier transformation.

[0025] (16) OFDR system strain demodulation.

[0026] (17) The strain data of the fiber optic ring is obtained by correcting the influence of the thermo-optic coefficient based on the temperature sensor data.

[0027] 1. A multi-parameter testing device with multiple fiber optic sensing loops, characterized in that the auxiliary interferometer module 2 includes: a 45° polarizer 202, a first coupler 204, a first circulator 207, a second coupler 209, a first Faraday rotator mirror 212, a second Faraday rotator mirror 213, and a first balanced photodetector 214. Light undergoes beat frequency interference at the second coupler 209.

[0028] (1) The 45° polarizer 202 is connected to the TLS light source 101 via the first flange 201.

[0029] (2) The left arm 218 of the first coupler is connected to the 45° polarizer 202 via the second flange 203.

[0030] (3) The first circulator A port 221 is connected to the lower right arm 220 of the first coupler through the fourth flange 206.

[0031] (4) The upper right arm 224 of the second coupler is connected to the port B 222 of the first circulator via the fifth flange 208.

[0032] (5) The lower right arm 215 of the second coupler and the port C 223 of the first circulator are respectively connected to the first balanced photodetector 214.

[0033] (6) The first Faraday rotating mirror 212 is connected to the sixth flange 210 and the upper left arm 225 of the second coupler.

[0034] (7) The second Faraday rotating mirror 213 is connected to the seventh flange 211 and the lower left arm 226 of the second coupler.

[0035] (8) The first optical fiber 216, the second optical fiber 217, the third optical fiber 218, and the fourth optical fiber 219 are all polarization-maintaining optical fibers.

[0036] (9) The first circulator A port 221, the first circulator B port 222, the first circulator C port 223, the upper right arm 224, the lower right arm 215, the upper left arm 225, and the lower left arm 226 of the second coupler are all single-mode optical fibers.

[0037] 2. A multi-parameter testing device for multiple fiber optic sensing loops, characterized in that the main interferometer module 3 includes: a third coupler 302, a fourth coupler 306, a first polarization-maintaining beam splitter 315, a second polarization-maintaining beam splitter 319, a second balanced photodetector 321, a third balanced photodetector 325, and a fifth coupler 308. Light undergoes beat frequency interference at the fourth coupler 306.

[0038] (1) The right arm 301 of the third coupler is connected to the upper right arm 219 of the first coupler via the third flange 205.

[0039] (2) The upper right arm 305 of the fourth coupler is connected to the upper left arm 303 of the third optical coupler via the eighth flange 304.

[0040] (3) The lower right arm 311 of the fourth coupler is connected to the upper arm 309 of the fifth optical coupler via the ninth flange 310.

[0041] (4) The right arm 314 of the first polarization-maintaining beam splitter is connected to the upper left arm 312 of the fourth coupler through the tenth flange 313.

[0042] (5) The right arm 318 of the second polarization-maintaining beam splitter is connected to the lower left arm 316 of the fourth coupler via the eleventh flange 317.

[0043] (6) The second balanced photodetector 321 is connected to the upper left arm 320 of the first polarization-maintaining beam splitter and the upper left arm 323 of the second polarization-maintaining beam splitter, respectively.

[0044] (7) The third balanced photodetector 325 is connected to the lower left arm 322 of the first polarization-maintaining beam splitter and the lower left arm 324 of the second polarization-maintaining beam splitter, respectively.

[0045] (8) The right arm 301 of the third coupler, the upper left arm 303 of the third coupler, the lower left arm 307 of the third coupler, the upper right arm 305 of the fourth coupler, the lower right arm 311 of the fourth coupler, the upper left arm 312 of the fourth coupler, the lower left arm 316 of the fourth coupler, the right arm 314 of the first polarization-maintaining beam splitter, the right arm 318 of the second polarization-maintaining beam splitter, the upper left arm 320 of the first polarization-maintaining beam splitter, the lower left arm 322 of the first polarization-maintaining beam splitter, the upper left arm 323 of the second polarization-maintaining beam splitter, the lower left arm 324 of the second polarization-maintaining beam splitter, the Nth lower arm 326 of the fifth coupler, the first lower arm 327 of the fifth coupler, the second lower arm 328 of the fifth coupler, and the upper arm 309 of the fifth coupler are all polarization-maintaining fibers.

[0046] 3. A multi-parameter testing device for multiple fiber optic sensitive rings, characterized in that the module under test 4 includes: an optical switch 410, a second circulator 416, a third circulator 418... an Nth circulator 424, a first fiber optic ring 429, a first right-side pigtail 432, a first left-side pigtail 435, a second fiber optic ring 430, a second right-side pigtail 433, a second left-side pigtail 436... an Nth fiber optic ring 431, an Nth right-side pigtail 434, an Nth left-side pigtail 437, a first reflection device 438, a second reflection device 439... an Nth reflection device 440. Light is controlled by the optical switch 410 to flow through a certain fiber optic ring to obtain its scattering spectrum.

[0047] (1) The optical switch 410 is a 1×N switch, including an optical switch input arm 402, an optical switch output first port 404, an optical switch output second port 411... an optical switch output Nth port 421 and an optical path converter 403. The use of an optical switch in one arm of the interferometer effectively reduces the influence of optical switch reflection.

[0048] (2) The optical switch input arm 402 is connected to the lower left arm 307 of the third coupler via the twelfth flange 401.

[0049] (3) The second circulator A port 406 is connected to the first output port 404 of the optical switch via the thirteenth flange 405.

[0050] (4) The second circulator B port 408 is connected to the first right-side tail fiber 432 through the fourteenth flange 409.

[0051] (5) The second circulator C port 415 is connected to the first lower arm 328 of the fifth coupler through the fifteenth flange 407.

[0052] (6) The third circulator A port 413 is connected to the second output port 411 of the optical switch via the sixteenth flange 412.

[0053] (7) The third circulator B port 419 is connected to the second right tail fiber 433 through the seventeenth flange 420.

[0054] (8) The third circulator C port 417 is connected to the second lower arm 328 of the fifth coupler through the eighteenth flange 414.

[0055] (9) The Nth circulator A port 423 is connected to the optical switch output N port 421 through the nineteenth flange 422.

[0056] (10) The Nth circulator B port 427 is connected to the Nth right tail fiber 434 through the twentieth flange 428.

[0057] (11) The Nth circulator C port 426 is connected to the Nth lower arm 326 of the fifth coupler via the twenty-first flange 425.

[0058] (12) The end of the first left tail fiber 435 is cut flat to form the first reflective device 438.

[0059] (13) The end of the second left tail fiber 436 is cut flat to form the second reflective device 439.

[0060] (14) The end of the Nth left tail fiber 437 is cut flat to form the Nth reflective device 440.

[0061] (15) Optical switch input arm 402, optical switch output first port 404, optical switch output second port 411, optical switch output Nth port 421, second circulator A port 406, third circulator A port 413, Nth circulator A port 423, second circulator B port 408, third circulator B port 419, Nth circulator B port 427, second circulator C port 415, third circulator C port 417, Nth circulator C port 426, and the fiber optic ring and its two side pigtails are all polarization-maintaining fibers.

[0062] 4. A multi-parameter testing device with multiple fiber optic sensing rings, characterized in that the temperature control sensing module 5 includes: a temperature chamber 501 and a temperature sensor 502. The temperature sensor 502 is placed inside the temperature chamber 501. The first fiber optic ring 429, the second fiber optic ring 430...the Nth fiber optic ring 431 are all placed inside the temperature chamber 501.

[0063] 5. A multi-parameter testing device for multiple fiber optic sensing loops, characterized in that the control and data processing module 6 includes: a controller 601, a data processor 602, and a data acquisition card 603.

[0064] (1) The first balanced photodetector 214 is connected to the data acquisition card 603 through the first electrical wire 604.

[0065] (2) The second balanced photodetector 321 is connected to the data acquisition card 603 through the second electrical wire 605.

[0066] (3) The third balanced photodetector 325 is connected to the data acquisition card 603 through the third electrical wire 606.

[0067] (4) The data acquisition card 603 is connected to the data processor 602 via the fourth electrical wire 607.

[0068] (5) The controller 601 is connected to the data acquisition card 603 via the fifth electrical wire 608.

[0069] (6) The controller 601 is connected to the temperature sensor 502 via the sixth wire 609.

[0070] (7) The controller 601 is connected to the temperature chamber 501 via the seventh electrical wire 610.

[0071] (8) The controller 601 is connected to the optical switch 410 via the eighth electrical wire 611.

[0072] (9) The controller 601 is connected to the TLS light source 101 via the ninth electrical wire 612.

[0073] The purpose of this invention is to provide an apparatus and method that can improve testing efficiency, measure multiple parameters within multiple fiber optic rings in a single rapid temperature cycle, construct an optical frequency domain testing system, and be used for multi-parameter testing and performance evaluation of fiber optic rings and measurement of the influence of rapid temperature changes on relative thermal strain in distributed fiber optic sensing systems.

[0074] The OFDR-based measurement device proposed in this invention is shown in the appendix. Figure 1 As shown, its characteristics are:

[0075] 1. It consists of a TLS light source 101, a 45° polarizer 202, a first coupler 204, a first circulator 207, a second coupler 209, a first Faraday rotator 212, a second Faraday rotator 213, a first balanced photodetector 214, a third coupler 302, a fifth circulator 801, a fourth coupler 306, a first polarization-maintaining beam splitter 315, a second polarization-maintaining beam splitter 319, a second balanced photodetector 321, a third balanced photodetector 325, and a device under test 802.

[0076] 2. The TLS light source 101 provides input light through a 45° polarizer 202 and a first coupler 204. 1% of the output light enters the first circulator 207 through the first connecting fiber 803, then enters the second coupler 209 through the B port of the first circulator and the second connecting fiber 804. The remaining 99% of the output light enters the third coupler 302 through the third connecting fiber 805.

[0077] 3. Of the light entering the second coupler 209, 50% is reflected by the first Faraday rotator mirror 212 after passing through the fourth connecting fiber 806 to form the first reflected light 807, and the other 50% is reflected by the second Faraday rotator mirror 213 after passing through the delay fiber 808 to form the second reflected light 809. The first reflected light 807 and the second reflected light 809 undergo beat frequency interference at the second coupler 209. A portion of the beat frequency interference signal passes sequentially through the second connecting fiber 804, the B port of the first circulator, the C port of the first circulator, and the fifth connecting fiber 810 and is input into the first balanced photodetector 214. The other portion of the beat frequency interference signal passes through the sixth connecting fiber 811 and is also input into the first balanced photodetector 214. The two portions of the beat frequency interference signal are differentially detected.

[0078] 4. Of the light entering the third coupler 302, 1% passes through the seventh connecting fiber 812 to enter the fourth coupler 306, and the remaining 99% passes through the eighth connecting fiber 813 and the fifth circulator 801, sequentially entering the device under test 802 through the ninth connecting fiber 814 from the fifth circulator's A port and B port. The third reflected signal 815, formed after reflection, also enters the fourth coupler 306 through the ninth connecting fiber 814, the fifth circulator's B port, the fifth circulator's C port, and the tenth connecting fiber 816, generating a beat frequency interference signal.

[0079] 5. 50% of the beat frequency interference signal generated at the fourth coupler 306 enters the first polarization-maintaining beam splitter 315 through the eleventh connecting fiber 817, and the other 50% enters the second polarization-maintaining beam splitter 319 through the twelfth connecting fiber 818.

[0080] 6. The light entering the first polarization-maintaining beam splitter 315 is partly input to the second balanced photodetector 321 through the thirteenth connecting fiber 819, and partly input to the third balanced photodetector 325 through the fourteenth connecting fiber 820.

[0081] 7. Part of the light entering the second polarization-maintaining beam splitter 319 is input to the second balanced photodetector 321 through the fifteenth connecting fiber 821, and the other part is input to the third balanced photodetector 325 through the sixteenth connecting fiber 822.

[0082] The flowchart of the fiber optic ring temperature and strain testing method proposed in this invention is attached. Figure 2 As shown, its characteristics are:

[0083] Step 701 is the full-temperature environment test of the fiber optic ring. The fiber optic ring is tested for its full-temperature performance by setting the temperature environment typically used by the fiber optic ring system.

[0084] Step 702 involves connecting the first fiber optic ring, the second fiber optic ring, ... the Nth fiber optic ring to the test system to complete the optical path connection.

[0085] Step 703 involves using a controller to synchronously start the light source, data acquisition card, temperature chamber, temperature sensor, and light switch to perform a system self-test.

[0086] Step 704 involves placing the fiber optic ring inside the temperature chamber, setting the temperature chamber's operating curve to a temperature range of T1 to T2, and maintaining the temperature rate at T3 / min.

[0087] Step 705 is to start the temperature chamber, set the timing to 0 at this time, and start the controller to start timing, incrementing the timing by 1 every 1 minute.

[0088] Step 706 is to define the initial timing of the first fiber ring, the second fiber ring, ... the Nth fiber ring as 2, 3, ... N+1 respectively, and start judging the timing.

[0089] If the timing reaches 2 in step 706, step 707 is executed: the optical switch is switched to the first port, the controller triggers the light source and the acquisition card, thereby testing the first fiber optic ring.

[0090] If the timing reaches 3 in step 706, step 708 is executed: the optical switch is switched to the second port, the controller triggers the light source and the acquisition card, thereby testing the second fiber optic ring.

[0091] If the timing reaches N+1 as per step 706, then step 709 is executed: the optical switch is switched to port N, the controller triggers the light source and the acquisition card, thereby testing the Nth fiber optic ring.

[0092] Step 710 involves uploading the test data collected by the data acquisition card to the data processing machine.

[0093] Step 711 is to compensate for phase noise and determine whether the intensity of the end reflection peak after compensation is consistent with that at room temperature.

[0094] If the intensity of the end reflection peak after compensation is consistent with the normal temperature, proceed to step 712: complete the testing of the first fiber ring, the second fiber ring, ... the Nth fiber ring, and record the temperature sensor data of the corresponding time sequence.

[0095] If the intensity of the end reflection peak after compensation is inconsistent with that at room temperature, proceed to step 713: perform phase noise compensation again.

[0096] Step 714 involves performing a test every N increments to the initial timing of each fiber optic ring.

[0097] Step 715 involves recording the test results of P and S at different temperatures, and obtaining the scattering spectrum signal after Fourier transform.

[0098] Step 716 is the OFDR system strain demodulation. The reference signal and the test signal are cross-correlated using a demodulation algorithm to obtain the Rayleigh divergence frequency shift of the fiber loop under temperature changes.

[0099] Step 717 involves correcting the influence of the thermo-optic coefficient based on temperature sensor data to obtain fiber optic ring strain data.

[0100] The present invention proposes a multi-parameter testing device and method for a multi-branch fiber optic sensitive ring. Its basic principle is the working principle of an optical frequency domain reflectometer. By using an OFDR system formed by an interferometer to demodulate the reflected signal inside the fiber optic ring, the influence of temperature and strain on the frequency shift of the fiber optic ring can be obtained.

[0101] Device testing principle:

[0102] The constructed OFDR system can perform separate strain and temperature measurements. Based on two signals, P and S, the frequency shift and the relationship between temperature and strain obtained from the measurements are as follows:

[0103]

[0104] Where: ε c It is the strain coefficient of cross-correlation frequency shift, T c It is the temperature coefficient of the cross-correlation frequency shift.

[0105] As can be seen, the test results of OFDR include both strain and temperature. The frequency shift obtained by OFDR testing includes the effects of both temperature and strain. The obtained spectral shift is converted into the corresponding temperature and strain values ​​using temperature and strain coefficients.

[0106] Compared with the prior art, the advantages of the present invention are as follows:

[0107] 1. This invention effectively reduces the impact of optical switch reflection by using an optical switch on one arm of the interferometer.

[0108] 2. The testing device proposed in this invention can realize distributed high-precision measurement of multiple parameters (temperature and strain) of long-distance fiber optic sensing rings under rapid temperature changes.

[0109] 3. This invention, through the design of a system timing control method, can simultaneously test the multi-parameter performance of multiple fiber optic rings under temperature variations.

[0110] 4. This invention has a simple structure, high testing accuracy, and resistance to environmental interference, effectively improving testing efficiency. It can be widely used for high-precision measurement and analysis of multiple parameters of optical devices such as polarization-maintaining optical fibers, optical fiber rings, and hydrophones. Attached image description:

[0111] Figure 1 This is a schematic diagram of the optical frequency domain reflectance (OFDR) testing principle.

[0112] Figure 2 This is a flowchart of the fiber optic loop temperature and strain testing method;

[0113] Figure 3 This is a diagram of the fiber optic ring structure under test;

[0114] Figure 4 This is a flowchart of the full-temperature testing method;

[0115] Figure 5 This is a diagram of a multi-parameter testing device with multiple fiber optic sensing loops;

[0116] Figure 6 This is a schematic diagram of the fiber optic ring strain test results. Detailed implementation method:

[0117] To clearly illustrate the testing apparatus and method for multiple parameters within an optical fiber ring of the present invention, the present invention will be further described in conjunction with embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0118] Figure 3 This is the structure of the fiber optic ring to be tested according to the present invention. Its characteristics are:

[0119] The fiber optic ring structure under test consists of a first fiber optic ring 429, a first reflector 438, a second fiber optic ring 430, a second reflector 439, ..., an Nth fiber optic ring 431, and an Nth reflector 440. The first fiber optic ring 429 includes a first right-side pigtail 432 and a first left-side pigtail 435; the second fiber optic ring 430 includes a second right-side pigtail 433 and a second left-side pigtail 436; and the Nth fiber optic ring 431 includes an Nth right-side pigtail 434 and an Nth left-side pigtail 437.

[0120] When any of the fiber optic loops is connected to the OFDR test system's optical path, the light undergoes strong reflection after passing through the right pigtail, the fiber optic loop under test, and the left pigtail. The strongly reflected light then passes sequentially through the left pigtail, the fiber optic loop under test, and the right pigtail before returning to the OFDR test system's optical path.

[0121] Combination Figure 4 The full-temperature test method is as follows:

[0122] Step 718 is to set the temperature range of the high and low temperature chamber to T1~T2 and the temperature change rate to 1℃ / min.

[0123] Step 719 involves placing the fiber optic ring inside the temperature chamber to ensure that the sensitive ring is heated on all four sides.

[0124] Step 720 involves holding the fiber optic ring at temperature T3 for 30 minutes.

[0125] Step 721 is to cool the chamber from T3 to T1 at a rate of 1℃ / min.

[0126] Step 722 involves holding the fiber optic ring at temperature T1 for 60 minutes.

[0127] Step 723 is to heat the chamber from T1 to T2 at a rate of 1℃ / min.

[0128] Step 724 involves holding the fiber optic ring at temperature T2 for 60 minutes.

[0129] Step 725 involves the OFDR system performing a test every 5 minutes.

[0130] Figure 5 This diagram illustrates a multi-parameter testing device with multiple fiber optic sensing loops, comprising a TLS light source module 1, an auxiliary interferometer module 2, a main interferometer module 3, a module under test 4, a temperature control sensing module 5, and a control and data processing module 6. The structure of the module under test 4 is similar to... Figure 3 The N fiber optic rings to be tested have the same structure.

[0131] Combination Figure 5 One embodiment of the present invention is as follows: the frequency sweep range of the TLS light source 101 is set to 10nm~160nm and the frequency sweep speed is 10nm / s. The emitted frequency sweep light enters the auxiliary interferometer module 2 by 1% and the main interferometer module 3 by 99% respectively through the first coupler 204.

[0132] 1% of the light entering the main interferometer module 3 passes through the upper left arm 303 of the third coupler and the upper right arm 305 of the fourth coupler to enter the fourth coupler 306, while the other 99% passes through the lower left arm 307 of the third coupler and enters the optical switch 410.

[0133] The 1% of light passing through the upper left arm 303 of the third coupler and the upper right arm 305 of the fourth coupler is used as a reference signal, and the 99% of light passing through the lower left arm 307 of the third coupler, input to the optical switch 410, and the light in a certain gyroscope optical path is used as a test signal. The two signals undergo beat frequency interference at the fourth coupler 306 and are then received by a data acquisition card 603 with a sampling frequency of 180MHz.

[0134] The controller 601 controls the opening and closing of the 1×N optical switches 410N output ports.

[0135] If the current timing sequence is a value in an arithmetic sequence with a first term of 2 and a common difference of N, then the optical switch switches to the first port 404, and the controller 601 triggers the TLS light source 101 and the data acquisition card 603 to test the first fiber optic ring 429.

[0136] If the current timing sequence is a value in an arithmetic sequence with the first term being 3 and the common difference being N, then the optical switch switches to the second port 411, and the controller 601 triggers the TLS light source 101 and the data acquisition card 603 to test the second fiber optic ring 430.

[0137] If the current timing sequence is a value in an arithmetic sequence with the first term being N+1 and the common difference being N, then the optical switch switches to the Nth port 421, and the controller 601 triggers the TLS light source 101 and the data acquisition card 603 to test the Nth fiber optic ring 431.

[0138] When any of the fiber optic loops is connected to the OFDR test system's optical path, the light undergoes strong reflection after passing through the right pigtail, the fiber optic loop under test, and the left pigtail, and is then reflected by the reflector. The strongly reflected light then passes sequentially through the left pigtail, the fiber optic loop under test, and the right pigtail, carrying the fiber optic loop's scattering information back to the OFDR test system's optical path.

[0139] Collect test data. Perform phase noise compensation on the data uploaded to the data processor and determine whether the intensity of the reflected peak at the end after compensation is consistent with that at room temperature. If consistent, complete the fiber optic loop test and record the temperature sensor data at the corresponding time sequence. If inconsistent, repeat phase noise compensation until the intensity of the reflected peak at the end after compensation is consistent with that at room temperature.

[0140] Record the test data from both P and S channels, and obtain the scattering spectrum signal after Fourier transform.

[0141] OFDR system strain demodulation. The Rayleigh divergence frequency shift of the fiber optic loop under temperature changes is obtained by cross-correlation calculation of the reference signal and the test signal through demodulation algorithm.

[0142] The strain data of the fiber optic ring was obtained by correcting for the influence of the thermo-optic coefficient based on temperature sensor data. The fiber optic ring strain test results are as follows: Figure 6 As shown, the spatial resolution of this OFDR-based fiber optic ring multi-parameter testing device is 5 cm, and the strain resolution is ±1 με.

Claims

1. A multi-parameter testing device for multiple fiber optic sensing loops, characterized in that: The system includes a TLS light source module (1), an auxiliary interferometer module (2), a main interferometer module (3), a device under test (4), a temperature control and sensing module (5), and a control and data processing module (6). The control and data processing module (6) controls the TLS light source (101), the data acquisition card (603), the temperature chamber (501), the temperature sensor (502), and the optical switch (410). The TLS light source module (1) injects the light beam into the first coupler (204), a portion of the light is injected into the auxiliary interferometer module (2), and the other portion of the light is injected into the main interferometer module (3). The device under test (4) is connected to the main interferometer module (3) and placed in the temperature control and sensing module (5). The auxiliary interference signal and the main interference signal are fed into the data acquisition card (603), and finally the scattering and reflection characteristics of the device under test are obtained. The multi-parameter testing device for multi-fiber sensing rings described above is used for testing, and the testing method steps are as follows: (1) To ensure the stability of the fiber optic ring, a full-temperature environment test of the fiber optic ring was conducted; (2) Connect the first fiber ring (429), the second fiber ring (430) ... the Nth fiber ring (431) to the test system to complete the optical path connection; (3) The controller (601) controls the TLS light source (101), data acquisition card (603), temperature chamber (501), temperature sensor (502) and light switch (410) to start synchronously for system self-test; (4) Place the fiber optic ring in the temperature chamber (501), and set the temperature chamber working curve in the control unit (601). Set the temperature range to T1~T2 and keep the temperature change rate at T3 / min. (5) The temperature chamber (501) is started. The timing is set to 0 at this time. The controller (601) starts timing and increments the timing by 1 every 1 minute. (6) Define the initial timing of the first fiber ring (429), the second fiber ring (430) ... the Nth fiber ring (431) as 2, 3 ... N+1 and then determine the current timing; (7) When the timing is 2, the optical switch (410) switches to the first output port, and the controller (601) triggers the TLS light source (101) and the data acquisition card (603) to test the first fiber optic ring (429); (8) When the timing is 3, the optical switch (410) switches to the second output port, and the controller (601) triggers the TLS light source (101) and the data acquisition card (603) to test the second fiber optic ring (430); (9) When the time sequence is N+1, the optical switch (410) switches to output port N, and the controller (601) triggers the TLS light source (101) and data acquisition card (603) to test the Nth fiber optic ring (431); (10) Collect test data and upload it to the data processing machine (602); (11) Compensate for phase noise and determine whether the intensity of the end reflection peak after compensation is consistent with that at room temperature; (12) If the strength is consistent, the test of the first fiber ring (429), the second fiber ring (430) ... the Nth fiber ring (431) is completed, and the temperature sensor data of the corresponding time sequence is recorded. (13) If the intensity is inconsistent, phase noise compensation shall be performed again to ensure that the intensity of the end reflection peak after compensation is consistent with that at room temperature. (14) The initial timing of each fiber optic ring is tested once every N increments; (15) Record the test data of polarized P-beam and S-beam, and obtain the scattering spectrum signal after Fourier transform; (16) Strain demodulation of optical frequency domain reflection system; (17) The strain data of the fiber optic ring is obtained by correcting the influence of the thermo-optic coefficient based on the temperature sensor data.

2. The multi-parameter testing device for multiple fiber optic sensing loops according to claim 1, characterized in that: The auxiliary interferometer module (2) includes: a 45° polarizer (202), a first coupler (204), a first circulator (207), a second coupler (209), a first Faraday rotator (212), a second Faraday rotator (213), and a first balanced photodetector (214); light undergoes beat frequency interference at the second coupler (209); (1) A 45° polarizer (202) is connected to a TLS light source (101) via a first flange (201); (2) The left arm (218) of the first coupler is connected to the 45° polarizer (202) via the second flange (203); (3) The first circulator A port (221) is connected to the lower right arm (220) of the first coupler through the fourth flange (206); (4) The upper right arm (224) of the second coupler is connected to the B port (222) of the first circulator via the fifth flange (208); (5) The lower right arm (215) of the second coupler and the C port (223) of the first circulator are respectively connected to the first balanced photodetector (214); (6) The first Faraday rotating mirror (212) is connected to the second coupler via the sixth flange (210) and the upper left arm (225); (7) The second Faraday rotating mirror (213) is connected to the lower left arm (226) of the second coupler via the seventh flange (211); (8) The first optical fiber (216), the second optical fiber (217), the left arm (218) of the first coupler, the upper right arm (219) of the first coupler, and the lower right arm (220) of the first coupler are all polarization-maintaining optical fibers; (9) The first circulator A port (221), the first circulator B port (222), the first circulator C port (223), the upper right arm (224) of the second coupler, the lower right arm (215) of the second coupler, the upper left arm (225) of the second coupler, and the lower left arm (226) of the second coupler are all single-mode optical fibers.

3. The multi-parameter testing device for multiple fiber optic sensing loops according to claim 1, characterized in that: The main interferometer module (3) includes: a third coupler (302), a fourth coupler (306), a first polarization-maintaining beam splitter (315), a second polarization-maintaining beam splitter (319), a second balanced photodetector (321), a third balanced photodetector (325), and a fifth coupler (308); light undergoes beat frequency interference at the fourth coupler (306); (1) The right arm (301) of the third coupler is connected to the upper right arm (219) of the first coupler via the third flange (205); (2) The upper right arm (305) of the fourth coupler is connected to the upper left arm (303) of the third coupler via the eighth flange (304); (3) The lower right arm (311) of the fourth coupler is connected to the upper arm (309) of the fifth coupler via the ninth flange (310); (4) The right arm (314) of the first polarization-maintaining beam splitter is connected to the upper left arm (312) of the fourth coupler via the tenth flange (313); (5) The right arm (318) of the second polarization-maintaining beam splitter is connected to the lower left arm (316) of the fourth coupler via the eleventh flange (317); (6) The second balanced photodetector (321) is connected to the upper left arm (320) of the first polarization-maintaining beam splitter and the upper left arm (323) of the second polarization-maintaining beam splitter respectively; (7) The third balanced photodetector (325) is connected to the lower left arm (322) of the first polarization-maintaining beam splitter and the lower left arm (324) of the second polarization-maintaining beam splitter respectively; (8) The right arm (301) of the third coupler, the upper left arm (303) of the third coupler, the lower left arm (307) of the third coupler, the upper right arm (305) of the fourth coupler, the lower right arm (311) of the fourth coupler, the upper left arm (312) of the fourth coupler, the lower left arm (316) of the fourth coupler, the right arm (314) of the first polarization-maintaining beam splitter, the right arm (318) of the second polarization-maintaining beam splitter, the upper left arm (320) of the first polarization-maintaining beam splitter, the lower left arm (322) of the first polarization-maintaining beam splitter, the upper left arm (323) of the second polarization-maintaining beam splitter, the lower left arm (324) of the second polarization-maintaining beam splitter, the Nth lower arm (326) of the fifth coupler, the first lower arm (327) of the fifth coupler, the second lower arm (328) of the fifth coupler, and the upper arm (309) of the fifth coupler are all polarization-maintaining fibers.

4. The multi-parameter testing device for multiple fiber optic sensing loops according to claim 1, characterized in that: The module under test (4) includes: an optical switch (410), a second circulator (416), a third circulator (418) ... the N+1th circulator (424), a first fiber optic ring (429), a first right-side pigtail (432), a first left-side pigtail (435), a second fiber optic ring (430), a second right-side pigtail (433), a second left-side pigtail (436) ... the Nth fiber optic ring (431), the Nth right-side pigtail (434), the Nth left-side pigtail (437), a first reflection device (438), a second reflection device (439) ... the Nth reflection device (440); the light is controlled by the optical switch (410) to flow through a certain fiber optic ring to obtain its scattering spectrum; (1) The optical switch (410) is a 1×N switch, including an optical switch input arm (402), an optical switch output first port (404), an optical switch output second port (411)... an optical switch output Nth port (421) and an optical path converter (403). The use of an optical switch in one arm of the interferometer effectively reduces the influence of optical switch reflection. (2) The optical switch input arm (402) is connected to the lower left arm (307) of the third coupler via the twelfth flange (401); (3) The second circulator A port (406) is connected to the first output port (404) of the optical switch via the thirteenth flange (405); (4) The second circulator B port (408) is connected to the first right-side pigtail (432) through the fourteenth flange (409); (5) The second circulator C port (415) is connected to the first lower arm (327) of the fifth coupler through the fifteenth flange (407); (6) The third circulator A port (413) is connected to the second output port (411) of the optical switch via the sixteenth flange (412); (7) The third circulator B port (419) is connected to the second right-side tail fiber (433) through the seventeenth flange (420); (8) The third circulator C port (417) is connected to the second lower arm (328) of the fifth coupler through the eighteenth flange (414); (9) The Nth circulator A port (423) is connected to the optical switch output Nth port (421) through the nineteenth flange (422); (10) The Nth circulator B port (427) is connected to the Nth right tail fiber (434) through the twentieth flange (428); (11) The Nth circulator C port (426) is connected to the Nth lower arm (326) of the fifth coupler via the twenty-first flange (425); (12) The end of the first left-side tail fiber (435) is cut flat to form a first reflective device (438); (13) The end of the second left tail fiber (436) is cut flat to form a second reflective device (439); (14) The end of the Nth left tail fiber (437) is cut flat to form the Nth reflective device (440); (15) Optical switch input arm (402), optical switch output first port (404), optical switch output second port (411), optical switch output Nth port (421), second circulator A port (406), third circulator A port (413), Nth circulator A port (423), second circulator B port (408), third circulator B port (419), Nth circulator B port (427), second circulator C port (415), third circulator C port (417), Nth circulator C port (426), the fiber optic ring and the pigtails on both sides are all polarization-maintaining fibers.

5. A multi-parameter testing device for multiple fiber optic sensing loops according to claim 1, characterized in that: The temperature control sensing module (5) includes: a temperature chamber (501) and a temperature sensor (502); the temperature sensor (502) is placed inside the temperature chamber (501); the first fiber optic ring (429), the second fiber optic ring (430) ... the Nth fiber optic ring (431) are all placed inside the temperature chamber (501).

6. A multi-parameter testing device for multiple fiber optic sensing loops according to claim 1, characterized in that: The control and data processing module (6) includes: a controller (601), a data processor (602), and a data acquisition card (603); (1) The first balanced photodetector (214) is connected to the data acquisition card (603) through the first electrical wire (604); (2) The second balanced photodetector (321) is connected to the data acquisition card (603) via the second electrical wire (605); (3) The third balanced photodetector (325) is connected to the data acquisition card (603) via the third electrical wire (606); (4) The data acquisition card (603) is connected to the data processor (602) via the fourth electrical wire (607); (5) The control unit (601) is connected to the data acquisition card (603) via the fifth electrical wire (608); (6) The controller (601) is connected to the temperature sensor (502) via the sixth electrical wire (609); (7) The control unit (601) is connected to the temperature chamber (501) via the seventh electrical wire (610); (8) The controller (601) is connected to the optical switch (410) via the eighth electrical wire (611); (9) The controller (601) is connected to the TLS light source (101) via the ninth electrical wire (612).

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