Fiber-optic gyroscope interference light path device for improving reciprocity

Abstract

The invention discloses a fiber-optic gyroscope interference light path device for improving reciprocity. The fiber-optic gyroscope interference light path device comprises a light path part and a circuit part, wherein the light path part is connected with the circuit part; the light path part comprises a light source, an optical fiber coupler and an interference light path; wherein the interference light path comprises a Y waveguide, an optical fiber ring and a detector; the light source is connected with the optical fiber coupler through an optical fiber; the optical fiber coupler is connected with the Y waveguide through an optical fiber; the Y waveguide is connected with the optical fiber ring through an optical fiber; the optical fiber coupler is connected with the detector through an optical fiber; the light source and the detector are both connected with the circuit part. According to the invention, the reciprocity is improved, and the full-temperature zero-bias stability qualification rate after compensation of the fiber-optic gyroscope product is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic gyroscopes, and in particular relates to a fiber optic gyroscope interference optical path device with improved reciprocity. Background Art

[0002] The reciprocity of the fiber optic gyroscope's optical path is fundamental to its high-precision angular measurement. The interferometer optical path consists of a fiber ring, a Y-waveguide, a double-ended pigtail, a double-ended Y-waveguide pigtail, and two polarization-maintaining splices. The interferometer optical path is the core sensitive component of the fiber optic gyroscope, performing the splitting, polarization, interference, and beam combining of the optical signal. It is the most direct location for optical signal sensing of angular velocity. Its reciprocity directly impacts the performance of the fiber optic gyroscope.

[0003] A common problem is that the reciprocity of the device itself is very good, but after the interference optical path is formed, the reciprocity is poor. Research has found that the reciprocity of the interference optical path is not only affected by the fiber ring and Y-waveguide devices themselves, but also by the processing of the double-ended fiber pigtails of the fiber ring and the double-ended fiber pigtails of the Y-waveguide during assembly, the quality of the polarization-maintaining fusion splices, and the interaction between the curing glue and the optical fiber. This assembly process involves winding, fusion, and gluing. Improper operation at any step will cause the tail polarization-maintaining fiber to be affected by external asymmetric effects such as bending, torsion, and tension (stress), causing additional birefringence within the tail and affecting the performance of the high-precision fiber optic gyroscope. Therefore, the back-end assembly process is extremely important for ensuring the reciprocity of the fiber optic gyroscope's interference optical path.

[0004] Existing technologies rely on fiber ring temperature testing and evaluation systems to assess the temperature performance of fiber rings. High-precision full-temperature screening testing methods for optical waveguides have also been developed to assess the temperature performance of Y-waveguide integrated optical devices. These testing methods only screen individual components, ignoring the processing of the fiber ring's double-ended pigtails, the Y-waveguide's double-ended pigtails, and the quality of the two polarization-maintaining splices. These methods are insufficiently representative of the temperature characteristics of the entire interferometric optical path. Summary of the Invention

[0005] The technical problem solved by the present invention is to overcome the deficiencies in the prior art and provide a fiber optic gyroscope interference optical path device with improved reciprocity, thereby improving the reciprocity and achieving an improvement in the full-temperature zero-bias stability pass rate of fiber optic gyroscope products after compensation.

[0006] The object of the present invention is achieved through the following technical solution: A fiber optic gyroscope interferometer optical path device with improved reciprocity includes: an optical path portion and a circuit portion; wherein the optical path portion and the circuit portion are connected; the optical path portion includes a light source, a fiber coupler and an interferometer optical path; wherein the interferometer optical path includes a Y-waveguide, a fiber ring and a detector; the light source and the fiber coupler are connected through an optical fiber; the fiber coupler and the Y-waveguide are connected through an optical fiber; the Y-waveguide and the fiber ring are connected through an optical fiber; the fiber coupler and the detector are connected through an optical fiber; and the light source and the detector are both connected to the circuit portion.

[0007] In the above-mentioned fiber optic gyroscope interferometric optical path device for improving reciprocity, the steps of connecting the Y-waveguide and the fiber ring through optical fibers include: cutting off excess polarization-maintaining optical fibers at both ends of the fiber ring according to a preset optical fiber length; performing multiple stress releases on the remaining polarization-maintaining optical fibers before coiling to prevent twisting and torsion; and then coiling the remaining polarization-maintaining optical fibers; wherein, during the coiling process, squeezing and stretching of the optical fibers are avoided to ensure that the paths of the two bundles of polarization-maintaining optical fibers are consistent and there are no asymmetric obstacles; cutting off excess polarization-maintaining optical fibers at both ends of the Y-waveguide according to a preset optical fiber length; and Some polarization-maintaining optical fibers undergo multiple stress releases before coiling to eliminate twisting and torsion. The remaining polarization-maintaining optical fibers are then coiled. During the coiling process, the optical fibers are squeezed and stretched to avoid aligning the paths of the two polarization-maintaining optical fibers without asymmetric obstacles. The polarization-maintaining pigtails at both ends of the optical fiber ring are fused with the polarization-maintaining pigtails at both ends of the Y-waveguide using a polarization-maintaining fusion splicer to form a closed loop. The fusion splicing process ensures that the cut surface is neat. The polarization-maintaining pigtails at both ends of the optical fiber ring are fused with the polarization-maintaining pigtails at both ends of the Y-waveguide and then fixed to the metal structure with glue. The glue should be applied along the fibers and evenly.

[0008] In the above-mentioned fiber optic gyroscope interference optical path device for improving reciprocity, the circuit part includes an analog circuit and a digital circuit; wherein the analog circuit is connected to the light source; and the digital circuit is connected to the detector.

[0009] In the above-mentioned fiber optic gyroscope interferometric optical path device for improving reciprocity, the light source generates a light source signal i1, which is formed into a light signal i2 through a fiber optic coupler. After passing through a Y-waveguide, the light signal i2 is divided into two light signals, a light signal i3 and a light signal i4. After propagating in the fiber optic ring, the light signals i3 and i4 return to the Y-waveguide and interfere at the Y-waveguide to form an interference light signal i5. The interference light signal i5 is formed into a light signal i6 through a fiber optic coupler, and the light signal i6 enters a detector; the detector receives the light signal i6 and processes it to obtain an electrical signal.

[0010] In the above-mentioned fiber optic gyroscope interferometer optical path device for improving reciprocity, the analog circuit sends a driving signal to the light source, and the light source generates a light source signal i under the control of the driving signal; the analog circuit collects temperature information inside the light source tube core, and then controls the temperature of the light source tube core so that the light source emits a stable light signal.

[0011] In the above-mentioned fiber optic gyroscope interference optical path device for improving reciprocity, the digital circuit receives an electrical signal and processes the electrical signal to obtain an angular velocity.

[0012] The above-mentioned fiber optic gyroscope interference optical path device for improving reciprocity also includes: a test device; wherein the test device includes a test tool, a test cable, a power supply box, a computer and a temperature box; the circuit part also includes a temperature sensor; wherein the interference optical path is arranged in the test tool, the temperature sensor is arranged at the center of the optical fiber loop coil, and the test tool is placed in a temperature box with a vibration isolation foundation; the light source driving circuit, the digital circuit and the computer are all electrically connected to the power supply box through the test cable; the light source driving circuit and the digital circuit are all electrically connected to the computer through the test cable; the temperature sensor is connected to the computer.

[0013] In the above-mentioned fiber optic gyroscope interferometer optical path device for improving reciprocity, the power box supplies power to the light source driving circuit, the digital circuit and the computer, and the light source driving circuit, the digital circuit and the temperature sensor start working. The angular velocity output by the digital circuit and the temperature information measured by the temperature sensor are packaged and uploaded to the computer together.

[0014] In the above-mentioned fiber optic gyroscope interference optical path device for improving reciprocity, the computer processes the angular velocity and temperature information to obtain the temperature extreme difference and the compensated standard deviation.

[0015] In the fiber optic gyro interference optical path device for improving reciprocity, the temperature extreme difference is used to determine the temperature sensitivity of the interference optical path, and the compensated standard deviation is used to determine the accuracy level of the interference optical path after compensation.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention focuses on the processing of double-ended pigtails of optical fiber rings and double-ended pigtails of Y-waveguides, and fully improves the reciprocity of the optical path by treating the optical fiber ring, Y-waveguide, respective pigtails and fusion splice points as an integral component;

[0018] (2) The present invention performs temperature screening on the interference optical path, covering the entire path of the light wave from splitting to combining, and can cover more information than measuring a single device;

[0019] (3) The present invention provides the temperature performance index of the interference light path, the temperature extreme difference and the standard deviation after compensation, and provides a criterion for screening the interference light path. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0021] Figure 1 is a schematic diagram of a fiber optic gyroscope interferometric optical path device for improving reciprocity provided by an embodiment of the present invention;

[0022] Figure 2 is a schematic diagram of an analog circuit provided by an embodiment of the present invention;

[0023] Figure 3 is a schematic diagram of a digital circuit provided by an embodiment of the present invention;

[0024] FIG4( a ) is a schematic diagram of a comparative test curve of the fiber coiling process of the interference optical path assembly of the present invention;

[0025] FIG4( b ) is another schematic diagram of a comparative test curve of the fiber coiling process of the interference optical path assembly of the present invention;

[0026] FIG5( a ) is a schematic diagram of a comparative test curve of the welding process of the interference optical path component of the present invention;

[0027] FIG5( b ) is another schematic diagram of a comparative test curve of the welding process of the interference optical path component of the present invention;

[0028] FIG6( a ) is a schematic diagram of a comparative test curve of the gluing process of the interference optical path component of the present invention;

[0029] FIG6( b ) is a schematic diagram of a comparative test curve of the gluing process of the interference optical path component of the present invention;

[0030] Figure 7 This is a flow chart for evaluating the reciprocity of the fiber optic gyroscope interference optical path in the present invention. DETAILED DESCRIPTION

[0031] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0032] The interference optical path is composed of a fiber ring, a Y waveguide, respective pigtails, and two polarization-maintaining fusion splices. The interference optical path provides a propagation path for two beams of light traveling in opposite directions, and the sensitive angular velocity is obtained based on the phase shift of the interference light. The counter-propagating light can only interfere after traveling along a fiber of more than hundreds of meters. The phase shift caused by the optical path propagation reaches 10 8 ~10 10 rad, the detection accuracy of the phase difference needs to reach 10 -6 ~10 -8 rad, the relative phase detection accuracy reaches 10 -14 ~10 -18 Therefore, to achieve the precision of a fiber optic gyroscope (FOG), the optical path must exhibit reciprocity. Reciprocity means that, in the absence of angular velocity input, the phase shifts of the two beams from splitting to combining should be the same. FOG designs employ reciprocal optical path structures. However, in engineering implementation, some non-reciprocal errors may still be introduced.

[0033] The interference optical path of the fiber optic gyroscope is fixed at a preset device position and coiled on a metal structural part of a certain size. In order to improve the mechanical properties of the product, the loose optical fiber (or pigtail) in the interference optical path is usually fixed to the structural part with glue. In this way, the pigtail, glue, and metal structure form a whole. The reciprocity of the optical fiber ring and Y-waveguide itself is guaranteed by the device supplier. Each end of the optical fiber ring and Y-waveguide pigtail is up to 1 meter long and is the farthest from the midpoint of the interference optical path. The non-reciprocity has the greatest impact on the interference optical path. The pigtail operation process involves fiber coiling methods, fixing methods, and gluing methods. Any improper operation will destroy the reciprocity of the entire fiber optic gyroscope interference optical path and affect the performance of the product. Therefore, it is very important to study the process methods of the interference optical path in order to handle the pigtail.

[0034] A method for evaluating the reciprocity of a fiber optic gyroscope (FOG) interferometer optical path is proposed. Evaluation indicators for this interferometer optical path are proposed to accurately reflect the quality of reciprocity and provide guidance for improving reciprocity process methods. The interferometer optical path and its test fixture are placed in a temperature chamber with a vibration-isolating foundation. Other optical components (light source, fiber coupler, detector) and gyro circuits (analog and digital) are placed outside the temperature chamber. Test cables are used to electrically connect the power supply box, FOG, and data acquisition equipment. Based on the full-temperature output data, the extreme values ​​before temperature compensation and the standard deviation after compensation are calculated, which together form the evaluation indicators for the interferometer optical path.

[0035] Figure 1 FIG. 1 is a schematic diagram of a fiber optic gyroscope interference optical path device for improving reciprocity provided by an embodiment of the present invention. Figure 1As shown, the fiber optic gyroscope interferometric optical path device for improving reciprocity includes: an optical path portion and a circuit portion; wherein the optical path portion and the circuit portion are connected; the optical path portion includes a light source 1, a fiber coupler 2 and an interferometric optical path; wherein the interferometric optical path includes a Y-waveguide 3, a fiber ring 4 and a detector 5; the light source 1 and the fiber coupler 2 are connected via an optical fiber; the fiber coupler 2 and the Y-waveguide 3 are connected via an optical fiber; the Y-waveguide 3 and the fiber ring 4 are connected via an optical fiber; the fiber coupler 2 and the detector 5 are connected via an optical fiber; and both the light source 1 and the detector 5 are connected to the circuit portion. Light source 1 generates light source signal i1, which is converted into light signal i2 through optical fiber coupler 2. Light signal i2 is divided into two light signals, light signal i3 and light signal i4, after passing through Y waveguide 3. After propagating through optical fiber ring 3, light signals i3 and i4 return to enter Y waveguide 3, interfere with each other at the Y waveguide to form interference light signal i5, and interfere with light signal i5 to form light signal i6 through optical fiber coupler 2. Light signal i6 enters detector 5; detector 5 receives light signal i6 and processes it to obtain an electrical signal.

[0036] The steps of connecting the Y-waveguide 3 and the optical fiber ring 4 through optical fibers include: cutting off excess polarization-maintaining optical fibers at both ends of the optical fiber ring according to a preset optical fiber length; performing multiple stress releases on the remaining polarization-maintaining optical fibers before coiling to prevent twisting and torsion; and then coiling the remaining polarization-maintaining optical fibers; wherein, during the coiling process, squeezing and stretching of the optical fibers are avoided to ensure that the paths of the two polarization-maintaining optical fibers are consistent and there are no asymmetric obstacles; cutting off excess polarization-maintaining optical fibers at both ends of the Y-waveguide according to a preset optical fiber length; and coiling the remaining polarization-maintaining optical fibers. Perform multiple stress releases before winding to eliminate twisting and torsion; then coil the remaining polarization-maintaining optical fiber; during the winding process, avoid squeezing and stretching the optical fiber to ensure that the paths of the two polarization-maintaining optical fibers are consistent and there are no asymmetric obstacles; weld the polarization-maintaining pigtails at both ends of the optical fiber ring and the polarization-maintaining pigtails at both ends of the Y-waveguide through a polarization-maintaining fusion splicer to form a closed loop; the welding process makes the cutting surface neat; weld the polarization-maintaining pigtails at both ends of the optical fiber ring and the polarization-maintaining pigtails at both ends of the Y-waveguide and then fix them on the metal structure with glue; the gluing method should be to apply glue along the fibers and apply the glue evenly.

[0037] Figure 2 is a schematic diagram of an analog circuit provided by an embodiment of the present invention; Figure 3 Schematic diagram of a digital circuit provided by an embodiment of the present invention. Figure 2 and Figure 3 As shown, the circuit part includes an analog circuit 8 and a digital circuit 9 ; wherein, the analog circuit 8 is connected to the light source 1 ; and the digital circuit 9 is connected to the detector 5 .

[0038] Analog circuit 8 sends a drive signal to light source 1, which generates light source signal i1 under the control of the drive signal. Analog circuit 8 collects temperature information within the light source die and controls the temperature of the light source die to ensure that the light source emits a stable light signal. Digital circuit 9 receives the electrical signal and processes it to obtain the angular velocity.

[0039] like Figure 1 As shown, the fiber optic gyroscope interference optical path device for improving reciprocity also includes: a test device; wherein the test device includes a test fixture 11, a test cable 12, a power box 13, a computer 14 and a temperature box 15; the circuit part also includes a temperature sensor 10; wherein, the interference optical path is arranged in the test fixture 11, the temperature sensor 10 is arranged at the center of the coil of the optical fiber ring 4, and the test fixture 11 is placed in the temperature box 15 with a vibration isolation foundation; the light source driving circuit 8, the digital circuit 9 and the computer 14 are all electrically connected to the power box 13 through the test cable 12; the light source driving circuit 8 and the digital circuit 9 are all electrically connected to the computer 14 through the test cable 12; the temperature sensor 10 and the computer 14 are connected.

[0040] Power supply box 13 supplies power to light source driver circuit 8, digital circuit 9, and computer 14, which begin operating. The angular velocity output by digital circuit 9 and the temperature information measured by temperature sensor 10 are packaged and uploaded to computer 14. Computer 14 processes the angular velocity and temperature information to obtain the temperature range and compensated standard deviation. The temperature range is used to determine the temperature sensitivity of the interferometer optical path, while the compensated standard deviation is used to determine the accuracy of the compensated interferometer optical path.

[0041] The reciprocity of the fiber optic gyroscope optical path is the basis for the fiber optic gyroscope to achieve high-precision angle measurement. In the fiber optic gyroscope optical path based on Sagnac interferometer, the light waves propagating in opposite directions can only produce interference after propagating along the optical fiber for more than hundreds of meters. The phase shift caused by the optical path propagation can reach 10 8 ~10 10 rad, and the detection accuracy of the phase difference needs to reach 10 -6 ~10 -8 rad, the relative phase detection accuracy reaches 10 -14 ~10 -18 Therefore, any inconsistent effect of any factor anywhere in the entire optical path on the two counter-propagating light waves may cause gyro errors.

[0042] Optical path reciprocity in fiber optic gyroscopes (FOGs) primarily refers to the reciprocity of the phase shifts between two counter-propagating light waves. Single-mode reciprocity and polarization reciprocity are essential for achieving phase shift reciprocity. Y-waveguide integrated optical devices (Y-waveguides) and fiber rings are crucial to FOG reciprocity. The Y-waveguide ensures both reciprocity between input and output ports and polarization reciprocity, while the fiber ring ensures single-mode reciprocity. Currently, the polarization-maintaining fiber used in fiber rings is stress-induced polarization-maintaining fiber, manufactured based on the stress-photoelastic effect. This PM fiber maintains a single polarization state, ensuring that the forward and reverse optical signals in the fiber ring have identical and fully coherent characteristics, thus guaranteeing optical path reciprocity. However, in actual engineering applications, stresses on the PM fiber, including its own bending and twisting, the effects of cured adhesive on the fiber, and external fields (such as stress, electromagnetic, and acoustic fields), can cause changes in the refractive index or polarization characteristics of the optical path, resulting in non-reciprocity errors. Currently, in the interferometric optical path of a fiber optic gyroscope, a loose, 1-meter-long polarization-maintaining fiber pigtail is left at each end of the fiber ring and Y-waveguide. Operators use a fusion splicer to perform polarization-maintaining fusion splicing to form a closed optical path. This assembly process involves coiling, splicing, and gluing. Improper operation at any step can subject the tail polarization-maintaining fiber to external asymmetric effects such as bending, torsion, and tension (stress), causing additional birefringence within the pigtail and compromising the performance of the high-precision fiber optic gyroscope. Therefore, the back-end assembly process is crucial for ensuring reciprocity in the interferometric optical path of the fiber optic gyroscope.

[0043] In a fiber optic gyroscope, the optical path consists of a light source 1, a fiber coupler 2, a Y-waveguide 3, a fiber ring 4, and a detector 5. The optical signal propagation path in this optical path is as follows: The light source receives a drive signal from the light source driver circuit. Under the control of the drive signal, it generates a light source signal i1. This signal passes through the fiber coupler 2 to form a light signal i2, which then enters the Y-waveguide 3 and splits into two light signals i3 and i4. After propagating through the fiber ring 3, light signals i3 and i4 return to the Y-waveguide 3, where they interfere with each other to form an interference light signal i5. This interference light signal i6 passes through the fiber coupler 2 and enters the detector 5.

[0044] The circuitry in a fiber optic gyroscope includes analog circuitry 8 and digital circuitry 9. The analog circuitry refers to the light source driver circuitry. This circuitry sends a drive signal to the pump laser, causing it to emit a light signal. It also collects temperature information within the light source die, controlling the temperature of the die to ensure a stable light signal. The digital circuitry includes a front-end signal processing circuitry, a digital signal processing logic chip (FPGA), and a back-end signal processing circuitry. The front-end signal processing circuitry consists of a filter, an amplifier circuitry, and an analog-to-digital converter. The back-end signal processing circuitry consists of a digital-to-analog converter, an amplifier circuitry, and a switch.

[0045] Fiber optic gyroscope reciprocity includes the reciprocity of the optical path structure, optoelectronic components, signal modulation, and the impact of external factors on optical path reciprocity. Although the design considers the reciprocity of the optical path structure, components, and signal modulation, there are still some operational steps in engineering implementation that can destroy optical path reciprocity.

[0046] The process methods for reciprocity of interference optical paths include fiber coiling, fusion splicing, and gluing. The fiber coiling process involves fiber coiling length, fiber coiling path, and fiber coiling sequence. The fusion splicing process involves splicing quality, splicing position, and splicing fixation. The gluing process involves the amount of glue applied, the method of gluing, and the uniformity of gluing. As a general rule, the fiber coiling process requires smooth fiber coiling, no fiber crossing, no fiber twisting, and no small fiber bending radius. The fusion splicing process requires low splice point loss, few foreign fibers at the splice point, and symmetrical splicing fixation. The gluing process requires an appropriate amount of glue, a method of gluing that allows the fibers to be impregnated along the fiber, and good gluing uniformity. Developing a specific assembly process based on the structural characteristics of each fiber optic gyroscope can improve the reciprocity of the interference optical path.

[0047] During the fiber coiling process in the interferometric optical path reciprocity test, after coiling according to the requirements, the fiber arrangement is inspected using a microscope. If any abnormalities are found, re-coiling is required.

[0048] During the reciprocity process of interference optical paths, after welding as required, the welding machine's display parameters are used to check the welding condition. If any abnormal points are found, re-welding is required.

[0049] During the interferometric optical reciprocity process, after applying the glue as required, use a microscope to inspect the curing of the glue and the optical fiber. If any abnormalities are found, re-apply glue.

[0050] By utilizing the reciprocity of optical paths, which is affected by external factors, a full-temperature test system was built to stimulate reciprocity errors in the interferometric optical paths using the temperature environment to evaluate the reciprocity of the interferometric optical paths.

[0051] The reciprocity test method for an interference optical path includes an optical path, a circuit, and test equipment. The optical path comprises a light source 1, a fiber coupler 2, an interference optical path including a Y-waveguide 3, a fiber ring 4, a polarization-maintaining fusion splice 6, a polarization-maintaining fiber pigtail 7, and a detector 5. The circuit comprises a light source driver circuit 8, a digital circuit 9, and a temperature sensor 10. The test equipment comprises a test fixture 11, a test cable 12, a power supply box 13, a computer 14, and a temperature chamber 15. The interference optical path is placed within the test fixture 11, the temperature sensor 10 is placed at the center of the fiber ring 4 coil, and the test fixture 11 is placed within the temperature chamber 15 with a vibration-isolating foundation. The light source driver circuit 8, the digital circuit 9, the power supply box 13, and the computer 14 are electrically connected via a three-port test cable 12. The power supply box 13 supplies power to the gyroscope, which activates the light source driver circuit 8, the digital circuit 9, and the temperature sensor 10, causing the gyroscope to output angular velocity information. The temperature information measured by the temperature sensor 10 is sent to the data transmission interface in the circuit part. The temperature information is packaged together with the output angular velocity information of the gyroscope and uploaded to the computer 14; the computer 14 is equipped with an evaluation system.

[0052] The reciprocity evaluation method of the interference optical path includes the range and the standard deviation after compensation under the temperature test of the interference optical path. The range is used to judge the temperature sensitivity of the interference optical path, and the standard deviation after compensation is used to judge the accuracy level of the interference optical path after compensation.

[0053] The temperature range calculation method of the reciprocity of the interference optical path is as follows: first, the original data is smoothed for 100 seconds, then the smoothed data is subjected to 10-second sliding smoothing, and finally, the maximum and minimum values ​​of the sliding smoothed data are found and subtracted to obtain the range.

[0054] The specific implementation process is as follows: set the temperature range of the incubator 15 to -40°C to +60°C, the temperature change rate to 1°C / min, and the high and low temperature holding time to 3 hours. Save and process the output angular velocity and temperature data of the gyroscope. Specifically, let the original data, i.e. the output angular velocity of the gyroscope, be B, and the sampling time be t. Then, the data after 100s smoothing is:

[0055]

[0056] Among them, i represents the number of data, Represents the total number of data collected within 100 seconds. mean() represents the average value of all the data in the brackets.

[0057] Smooth the B_100 data curve for 10 seconds to obtain a smoother curve. Subtract the maximum and minimum values ​​in the curve to obtain the temperature range.

[0058]

[0059] in, Represents the total number of data collected within 10s. Find the maximum value and the minimum value and subtract them to get the range.

[0060] The standard deviation of the reciprocity of the interference optical path is calculated as:

[0061] Setting temperature range: -40℃~+60℃, temperature change rate: 1℃ / min, high and low temperature holding time: 3 hours.

[0062] Collect and save the output signal and temperature signal of the fiber optic gyroscope, and pre-process the output signal and temperature signal of the fiber optic gyroscope, including data smoothing and temperature-related data calculation. Use the ratio of the temperature difference before and after to the time. As the temperature change rate, where T is the temperature, t is the sampling time, and Δt is the time interval.

[0063] Assume that the derived signal T is based on the temperature signal T, T 2 、 T 3 、 x1, x2, ..., x m , x1=T,

[0064] Suppose x1,x2,…,x m variables, the multiple linear regression model is expressed as

[0065] B=β0+β1x1+β2x2+…+β m x m +ε;

[0066] Where B is the output angular velocity of the gyroscope, β m is the parameter to be determined, and ε is the residual of the fitting.

[0067] β0,β1,…β m There are m+1 unknowns. If we have n sets of observations, the linear regression model is

[0068]

[0069] Written in matrix form as

[0070]

[0071] in

[0072]

[0073] The unknowns of the multivariate linear regression equation are usually estimated using the least squares method. The estimated value using the least squares method is:

[0074]

[0075] Then the sample regression model under ordinary least squares method is:

[0076]

[0077] The data after compensation is Seek Standard deviation To compensate for the gyro bias stability.

[0078] The interferometric optical path of a fiber optic gyroscope includes a fiber ring, a Y-waveguide, a double-ended pigtail, and two fusion splices, all of which affect the reciprocity of the interferometric optical path. The reciprocity of the fiber ring and Y-waveguide itself is guaranteed by the component supplier and is not considered within the scope of this patent. This embodiment primarily considers the reciprocity of pigtail processing. Pigtail processing operations include fiber coiling, fiber fusion splicing, and fiber gluing. Therefore, the assembly process includes fiber coiling, fusion splicing, and gluing.

[0079] A 1-meter-long polarization-maintaining fiber is coiled at each end of the fiber ring and the Y-waveguide. These fibers are then fused and glued to the metal structure. The fiber length is determined based on the structure's dimensions. Excess polarization-maintaining fiber is cut, and the remaining polarization-maintaining fiber is coiled. Similar to fiber ring winding, coiling stress will occur. In theory, the polarization-maintaining fiber at the end of the fiber ring and Y-waveguide plays the same role as the fiber inside the ring, participating in the propagation of both beams. To reduce coiling stress, fiber rings are typically wound using a multi-stage symmetrical, low-stress fiber winding machine. However, multi-stage symmetrical coiling is not possible at the end of the fiber, and since the end fiber is farthest from the midpoint of the interference loop, low-stress treatment of the end fiber is even more important. Before coiling, the polarization-maintaining fiber undergoes multiple stress relief procedures to eliminate twisting and torsion. Low-stress coiling is then performed. During the coiling process, compression and stretching of the fiber are minimized to ensure that the paths of the two polarization-maintaining fibers are aligned and free of asymmetry. In order to verify the effect of the fiber coiling process on the reciprocity of the interference optical path, two fiber coiling conditions were set: one was to add multiple stress points on a single bundle of polarization-maintaining fibers, and the other was to have the same stress points on both bundles of polarization-maintaining fibers. The test curves are shown in Figures 4(a) and 4(b).

[0080] The polarization-maintaining pigtails at both ends of the fiber ring and the polarization-maintaining pigtails at both ends of the Y-waveguide are fused together using a polarization-maintaining fusion splicer to form a closed loop. As the optical signal propagates through the loop, clockwise light passes through two polarization-maintaining fusion splices, A and B, and counterclockwise light passes through two polarization-maintaining fusion splices, B and A. Because the fusion splice is located far from the midpoint of the closed loop, the resulting error is relatively large. The introduction of the fusion splice destroys the polarization reciprocity and single-mode reciprocity of the light, thereby affecting the phase shift reciprocity of the light. The fusion splicing process requires a neat cut surface, low axial error, and low fusion splice loss. To verify the impact of the fusion splicing process on the reciprocity of the interference optical path, two fusion splicing states were set: one with large fusion splice axial error and large fusion splice loss, and the other with small fusion splice axial error and low fusion splice loss. The test curves are shown in Figures 5(a) and 5(b).

[0081] The polarization-maintaining pigtails at both ends of the fiber ring and the polarization-maintaining pigtails at both ends of the Y-waveguide need to be fixed with glue after fusion splicing to improve the mechanical properties of the interference optical path. The glue, optical fiber, and structure form a whole under the action of the glue. The expansion coefficients of the glue, optical fiber, and metal materials change due to the influence of temperature, which will cause the optical fiber to be squeezed and stretched, resulting in changes in the refractive index of the optical fiber, affecting the reciprocity of the interference optical path. Therefore, a strict glue application process is required to guide the operation. The glue application process involves the amount of glue applied, the glue application method, and the glue application uniformity. The amount of glue applied should be appropriate. Too much glue will easily squeeze the optical fiber, and too little glue will easily loosen the optical fiber. The glue application method should apply glue along the fiber to prevent the glue from affecting the original position of the optical fiber. The glue application uniformity should be good to avoid some optical fibers having too much glue and others having too little glue. After the glue application is completed, a microscopic inspection should be performed to check the glue application effect. In order to verify the effect of the sizing process on the reciprocity of the interference optical path, two sizing conditions are set: one is a large amount of sizing with poor uniformity, and the other is an appropriate amount of sizing with good uniformity. The test curves are shown in Figure 6(a) and Figure 6(b).

[0082] The reciprocity evaluation method for fiber optic gyroscope interferometer optical paths utilizes the fact that optical path reciprocity is affected by external factors. A full-temperature test system is built, and the reciprocity error of the interferometer optical path is stimulated by the temperature environment to evaluate the reciprocity of the interferometer optical path.

[0083] The optical circuit comprises a light source 1, a fiber coupler 2, an interference optical path including a Y-waveguide 3, a fiber ring 4, a polarization-maintaining fusion splice 6, a polarization-maintaining fiber pigtail 7, and a detector 5. The circuit comprises a light source driver circuit 8, a digital circuit 9, and a temperature sensor 10. The test equipment includes a test fixture 11, a test cable 12, a power supply box 13, a computer 14, and a temperature chamber 15. The interference optical path is placed within the test fixture 11, the temperature sensor 10 is placed at the center of the fiber ring 4 coil, and the test fixture 11 is placed within the temperature chamber 15 with a vibration-isolating foundation. The light source driver circuit 8, the digital circuit 9, the power supply box 13, and the computer 14 are electrically connected via a three-port test cable 12. The power supply box 13 supplies power to the gyroscope, which activates the light source driver circuit 8, the digital circuit 9, and the temperature sensor 10, causing the gyroscope to output angular velocity information. The temperature information measured by the temperature sensor 10 is transmitted to a data transmission interface within the circuit. This temperature information is then packaged with the gyroscope's output angular velocity information and uploaded to the computer 14, which is equipped with an evaluation system.

[0084] Fiber optics are used to connect the optical path components, and detectors and wires are used to connect the optical path and the circuit components. Test cables connect the circuit components, power supply box, and computer to complete the electrical connection of the test system.

[0085] Before the improvement, the fiber ring was placed in the incubator alone. After the improvement, the entire interference optical path, consisting of the fiber ring, Y-waveguide, polarization-maintaining fiber pigtail, and polarization-maintaining fusion splice, was placed in the incubator. From an optical path perspective, the fiber ring is merely a component for the propagation of two counter-rotating light waves, while the interference optical path includes light polarization, modulation, and interference, and is the component for light splitting, two-way light wave propagation, and beam combining, more fully demonstrating the reciprocity of the interference optical path.

[0086] The interference optical path is placed in the test fixture, and the temperature sensor is placed in the center of the fiber optic ring. Both are placed together in a temperature chamber with a vibration-isolating foundation. The single-ended pigtail of the interference optical path passes through a specific outlet of the temperature chamber and is connected to an external fiber optic coupler via a fusion splicer. The temperature sensor wire passes through a specific outlet of the temperature chamber and is connected to the circuit board via a connector. The light source drive line and Y-waveguide modulation line are connected to the circuit board via a connector. The power box, computer, and circuit board are connected via the connector of the test cable. Use a multimeter to check the correctness of the electrical connections. Once confirmed, set up the acquisition software, turn on the power box, and monitor and save the data from the fiber optic ring and temperature sensor.

[0087] The temperature conditions for the interference optical path test are consistent with the test conditions after the gyro is assembled.

[0088] The full-temperature test was conducted with a temperature range of -40°C to +60°C, a temperature gradient of 1°C / min, and a hold time of 3 hours. The curves of the interferometric optical path are shown in Figures 4(a), 4(b), 5(a), 5(b), 6(a), and 6(b).

[0089] The evaluation method for the reciprocity of the fiber optic gyroscope interference optical path includes the temperature range and the standard deviation after compensation under the temperature test of the interference optical path. The temperature range represents the temperature sensitivity of the interference optical path. The larger the value, the poorer the symmetry of the temperature range. The standard deviation after compensation represents the accuracy level of the interference optical path after compensation. The larger the value, the poorer the accuracy of the fiber optic gyroscope after compensation. The smaller the requirements for the two indicators, the better. The quality of the interference optical path can be judged by these two indicators. The specific calculation process is as follows: Figure 7 .

[0090] Figure 4(a): Temperature range of 0.1° / h and bias stability after compensation of 0.006° / h (100s, 1σ). Figure 4(b): Temperature range of 0.08° / h and bias stability after compensation of 0.005° / h (100s, 1σ). It can be seen that by changing the fiber coiling process, the full temperature range of the interference optical path is reduced from 0.1° / h to 0.08° / h, a 1.25-fold reduction. Furthermore, the bias stability after compensation is increased from 0.006° / h (100s, 1σ) to 0.005° / h (100s, 1σ), improving accuracy by 1.2-fold.

[0091] Figure 5(a): Temperature range of 0.11° / h and bias stability after compensation of 0.01° / h (100s, 1σ). Figure 5(b): Temperature range of 0.1° / h and bias stability after compensation of 0.009° / h (100s, 1σ). It can be seen that by changing the welding process, the full temperature range of the interference optical path is reduced from 0.11° / h to 0.1° / h, a 1.1-fold reduction. Furthermore, the bias stability after compensation is increased from 0.01° / h (100s, 1σ) to 0.009° / h (100s, 1σ), a 1.1-fold improvement in accuracy.

[0092] Figure 6(a): Temperature range of 0.15° / h and bias stability after compensation of 0.013° / h (100s, 1σ). Figure 6(b): Temperature range of 0.06° / h and bias stability after compensation of 0.008° / h (100s, 1σ). It can be seen that by changing the sizing process, the full temperature range of the interference optical path is reduced from 0.15° / h to 0.06° / h, a 2.5-fold reduction. Furthermore, the bias stability after compensation is increased from 0.013° / h (100s, 1σ) to 0.008° / h (100s, 1σ), a 1.6-fold improvement in accuracy.

[0093] Figures 4(a), 4(b), 5(a), 5(b), 6(a), and 6(b) show that only by testing the entire interference optical path can the effects of the fiber coiling, splicing, and gluing processes on the reciprocity of the interference optical path be determined. The magnitude of the temperature extremes reflects the symmetry of the interference optical path. The size of the compensated standard deviation reflects the accuracy of the compensated interference optical path.

[0094] This embodiment involves a coiling process, a fusion splicing process, and a gluing process, focusing on the processing of double-ended fiber pigtails in optical fiber rings and double-ended fiber pigtails in Y-waveguides. The optical fiber ring, Y-waveguide, respective pigtails, and fusion splicing points are treated as an integral component, fully considering the reciprocity of the optical path. The testing portion performs temperature screening on the interference optical path, covering the entire path of the light wave from splitting to combining, and can include more information than testing a single device. The evaluation portion provides temperature performance indicators for the interference optical path, temperature extremes, and standard deviations after compensation, providing criteria for screening the interference optical path. The testing and evaluation portions provide positive feedback to the process part, allowing accurate adjustment of the direction of process improvement.

[0095] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. A fiber optic gyroscope interferometer optical path device for improving reciprocity, characterized in that include: Optical path part and circuit part; among them, The optical path portion is connected to the circuit portion; The optical path portion includes a light source (1), an optical fiber coupler (2) and an interference optical path; wherein, The interference optical path includes a Y waveguide (3), an optical fiber ring (4) and a detector (5); The light source (1) and the optical fiber coupler (2) are connected via an optical fiber; The optical fiber coupler (2) and the Y-waveguide (3) are connected via an optical fiber; The Y-waveguide (3) and the optical fiber ring (4) are connected via optical fibers; The optical fiber coupler (2) and the detector (5) are connected via an optical fiber; The light source (1) and the detector (5) are both connected to the circuit part.

2. The fiber optic gyro interference optical path device with improved reciprocity according to claim 1, characterized in that: The step of connecting the Y-waveguide (3) and the optical fiber ring (4) via optical fiber comprises: The excess polarization-maintaining fibers at both ends of the fiber ring are cut according to the preset fiber length; the remaining polarization-maintaining fibers are subjected to multiple stress releases before coiling to eliminate twisting and torsion; and the remaining polarization-maintaining fibers are then coiled. During the coiling process, compression and stretching of the fibers are avoided to ensure that the paths of the two polarization-maintaining fibers are consistent and free of asymmetric obstacles. The excess polarization-maintaining fibers at both ends of the Y-waveguide are cut according to the preset fiber length. The remaining polarization-maintaining fibers are subjected to multiple stress releases before coiling to eliminate twisting and torsion. The remaining polarization-maintaining fibers are then coiled. During the coiling process, compression and stretching of the fibers are avoided to ensure that the paths of the two polarization-maintaining fibers are consistent and free of asymmetric obstacles. The polarization-maintaining pigtails at both ends of the optical fiber ring and the polarization-maintaining pigtails at both ends of the Y waveguide are fused together using a polarization-maintaining fusion splicer to form a closed loop. The fusion process ensures that the cut surface is neat. After fusing the polarization-maintaining pigtails at both ends of the optical fiber ring and the polarization-maintaining pigtails at both ends of the Y waveguide, they are fixed on the metal structure with glue. The glue should be applied along the fibers and evenly.

3. The fiber optic gyro interference optical path device with improved reciprocity according to claim 1, characterized in that: The circuit part includes an analog circuit (8) and a digital circuit (9); wherein, The analog circuit (8) is connected to the light source (1); The digital circuit (9) is connected to the detector (5).

4. The fiber optic gyroscope interferometer optical path device with improved reciprocity according to claim 1, characterized in that: The light source (1) generates a light source signal i1, which is converted into a light signal i2 via an optical fiber coupler (2). The light signal i2 is divided into two light signals, a light signal i3 and a light signal i4, after passing through a Y waveguide (3). After propagating through the optical fiber ring (3), the light signals i3 and i4 return to the Y waveguide (3) and interfere with each other at the Y waveguide to form an interference light signal i5. The interference light signal i5 is converted into a light signal i6 via the optical fiber coupler (2). The light signal i6 enters a detector (5); the detector (5) receives the light signal i6 and processes it to obtain an electrical signal.

5. The fiber optic gyro interference optical path device with improved reciprocity according to claim 3, characterized in that: The analog circuit (8) sends a driving signal to the light source (1), and the light source (1) generates a light source signal i1 under the control of the driving signal; the analog circuit (8) collects temperature information inside the light source tube core, and then controls the temperature of the light source tube core, so that the light source emits a stable light signal.

6. The fiber optic gyro interference optical path device with improved reciprocity according to claim 3, characterized in that: The digital circuit (9) receives the electrical signal and processes the electrical signal to obtain the angular velocity.

7. The fiber optic gyro interference optical path device with improved reciprocity according to claim 1, characterized in that It also includes: a test device; wherein the test device includes a test tool (11), a test cable (12), a power supply box (13), a computer (14) and a temperature box (15); the circuit part also includes a temperature sensor (10); wherein, The interference optical path is set in the test fixture (11), the temperature sensor (10) is set at the center of the coil of the optical fiber ring (4), and the test fixture (11) is placed in a temperature box (15) with a vibration isolation foundation; The light source driving circuit (8), the digital circuit (9) and the computer (14) are all electrically connected to the power supply box (13) via a test cable (12); the light source driving circuit (8) and the digital circuit (9) are all electrically connected to the computer (14) via a test cable (12); The temperature sensor (10) is connected to the computer (14).

8. The fiber optic gyro interference optical path device with improved reciprocity according to claim 7, characterized in that: The power box (13) supplies power to the light source driving circuit (8), the digital circuit (9) and the computer (14), and the light source driving circuit (8), the digital circuit (9) and the temperature sensor (10) start to work. The angular velocity output by the digital circuit (9) and the temperature information measured by the temperature sensor (10) are packaged and uploaded to the computer (14).

9. The fiber optic gyro interference optical path device with improved reciprocity according to claim 8, characterized in that: The computer (14) processes the angular velocity and temperature information to obtain the temperature extreme difference and the compensated standard deviation.

10. The fiber optic gyro interference optical path device with improved reciprocity according to claim 9, characterized in that: The temperature extreme difference is used to judge the temperature sensitivity of the interference light path, and the standard deviation after compensation is used to judge the accuracy level of the interference light path after compensation.

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