Interferometric fiber-optic gyroscope based on special mirror ring structure

Abstract

The application provides a special mirror ring structure-based interferometric fiber-optic gyroscope, which comprises a light source, a polarizer, a coupler, two loopers, two Y waveguides, a signal generator, a 2-in-2-out mirror fiber ring, two photoelectric detectors and a signal joint demodulation module; wherein the two equal-length polarization maintaining optical fibers of the 2-in-2-out mirror fiber ring are both fused at the middle point with the fast axis at 90 degrees, and when each polarization maintaining optical fiber is fused with the Y waveguide tail fiber, one end is fused with the fast axis at 0 degrees and the other end is fused with the fast axis at 90 degrees. In the fiber-optic gyroscope, the light is no longer sent into two polarization channels of the same fiber ring through a polarization beam splitter and combiner, but is fused with two spatial mirror fiber rings at 0 degrees and 90 degrees through two Y waveguides, so that the radial magnetic field phase error caused by the Faraday effect is suppressed, and the temperature phase error caused by the Shupe effect can be compensated by joint demodulation of the electric signals of the two photoelectric detectors.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gyroscopes, in particular to an interferometric fiber-optic gyroscope based on a special mirror ring structure. BACKGROUND

[0002] A fiber-optic gyroscope is an optical fiber sensor that can sense angular velocity. According to the working principle, it can be divided into interferometric and resonant types. The interferometric fiber-optic gyroscope is a more mature representative in the field of fiber-optic gyroscopes and has a very wide range of applications in navigation and guidance, attitude control, etc. The fiber-optic gyroscope described below refers to the interferometric fiber-optic gyroscope.

[0003] An interferometric fiber-optic gyroscope is a fiber-optic ring interferometer based on the Sagnac effect, which describes the phase difference between two coherent light beams propagating in opposite directions in a fiber-optic ring that is proportional to the rotation angle. The performance parameters of the fiber-optic gyroscope include bias instability (BI) and angle random walk (ARW). Bias instability is defined as the deviation of the output angular velocity from the actual rotation angular velocity, which is usually caused by environmental changes and polarization non-reciprocal errors. Angle random walk describes the size of short-time white noise in the output of the gyroscope, which is mainly caused by thermal noise, photon shot noise, and light source relative intensity noise. Temperature and magnetic field have a great influence on the performance parameters of the fiber-optic gyroscope.

[0004] During the operation of the fiber-optic gyroscope, the refractive index of the corresponding points on the fiber-optic ring changes with temperature, causing the time difference between the two light waves propagating in opposite directions through the point (except for the midpoint of the fiber-optic ring). Therefore, the phase change caused by temperature after the two light waves pass through the fiber-optic ring will also be different, which is equivalent to introducing an additional phase difference based on the Sagnac phase shift. This effect is known as the Shupe effect. In order to ensure the temperature stability of the fiber-optic gyroscope, the temperature change rates of the symmetric points relative to the midpoint of the fiber-optic ring must be the same. The four-pole symmetric winding method is the most commonly used fiber-optic ring winding method, which can effectively reduce the influence of temperature changes on the non-reciprocity of the fiber-optic ring. However, the four-pole symmetric winding method cannot completely eliminate the influence of temperature gradients in the fiber-optic ring, and the longer the fiber-optic length, the more obvious the influence of this residual effect.

[0005] When the fiber optic gyroscope works in a magnetic field environment, the fiber optic gyroscope will produce a magnetic field phase error in the magnetic field environment due to the magneto-optic effect in the fiber. The magnetic field phase error is one of the main error sources of the fiber optic gyroscope. The magnetic field phase error of the fiber optic gyroscope is mainly caused by the radial magnetic field phase error perpendicular to the sensitive axis of the fiber ring, which is caused by the Faraday effect. When a linearly polarized light passes through the fiber, if there is a magnetic field component in the direction of light propagation, the polarization plane of the light will turn an angle after the light passes through the material. This effect introduces an additional phase difference. The magnetic field phase error will be an inevitable factor affecting the accuracy of the fiber optic gyroscope.

[0006] With the increasing application demand for improving the accuracy of the fiber optic gyroscope in complex environments in recent years, how to overcome the limitations of temperature and magnetic field on the performance of the fiber optic gyroscope has become a great challenge in the research process of the fiber optic gyroscope. SUMMARY

[0007] The purpose of the present application is to provide an interferometric fiber optic gyroscope based on a special mirror ring structure to at least solve one of the above-mentioned defects of the existing interferometric fiber optic gyroscope.

[0008] The embodiment of the present application provides an interferometric fiber optic gyroscope based on a special mirror ring structure, comprising:

[0009] a light source, a polarizer, a coupler, two loopers, two Y waveguides, a signal generator, a 2-in-2-out mirror fiber ring, two photodetectors and a signal joint demodulation module;

[0010] Wherein, the two equal-length polarization maintaining fibers around the 2-in-2-out mirror fiber ring are both fused at the midpoint with the fast axis at 90 degrees, and when each polarization maintaining fiber is fused with the Y waveguide tail fiber, one end is fused with the fast axis at 0 degrees and the other end is fused with the fast axis at 90 degrees.

[0011] The light source outputs light of any polarization state to the polarizer;

[0012] The polarizer converts the light of any polarization state output by the light source into linearly polarized light;

[0013] The coupler divides the linearly polarized light output by the polarizer into two light beams, and couples the two light beams into the first looper and the second looper respectively;

[0014] The first looper outputs the first light beam output by the coupler to the first Y waveguide; the second looper outputs the second light beam output by the coupler to the second Y waveguide;

[0015] The signal generator provides a modulation signal to the two Y waveguides;

[0016] The first Y waveguide outputs the light beam output by the first circulator after polarization, coupling and modulation to the corresponding port of the 2-in-2-out mirror fiber ring.

[0017] The light beams output by the two Y waveguides independently interfere in the 2-in-2-out mirror fiber ring to obtain first and second interference signals.

[0018] The first Y waveguide outputs the first interference signal to the first circulator, and the second Y waveguide outputs the second interference signal to the second circulator.

[0019] The two circulators output the interference signals returned by the two Y waveguides to the two photodetectors, respectively.

[0020] The two photodetectors convert the interference signals output by the two circulators into electrical signals and output the electrical signals to the signal joint demodulation module.

[0021] The signal joint demodulation module jointly demodulates the two electrical signals output by the two photodetectors.

[0022] In a possible implementation, the signal generator provides the two Y waveguides with modulation signals of equal amplitude and opposite phase.

[0023] In a possible implementation, the signal generator provides the two Y waveguides with modulation signals of equal amplitude and the same phase.

[0024] In a possible implementation, the circulator is a single-mode circulator.

[0025] In a possible implementation, the circulator is a polarization-maintaining circulator.

[0026] In a possible implementation, the two Y waveguides have similar performance and high extinction ratio.

[0027] In a possible implementation, the 2-in-2-out mirror fiber ring is made by cross-winding two equal-length polarization-maintaining optical fibers in opposite directions and in reverse order on the same skeleton or on the left and right two partitions of the skeleton, so that the two equivalent fiber rings are in mirror relationship.

[0028] In a possible implementation, the signal joint demodulation module adopts an open-loop fiber optic gyroscope multi-harmonic demodulation method.

[0029] In a possible implementation, the light source is a laser light source or an ASE light source.

[0030] The application has the advantages compared with the prior art:

[0031] The application provides an interferometric fiber-optic gyroscope based on a special mirror ring structure, which uses a 2-in-2-out mirror fiber ring to replace the fiber ring in the prior art double-polarization fiber-optic gyroscope. The 2-in-2-out mirror fiber ring can be equivalent to two independent but spatially mirrored fiber rings, and the fast axes at the midpoints of the two fiber rings are fused at 90 degrees. Two polarization beam splitters and combiners are cancelled, and the light is no longer sent into two polarization channels of the same fiber ring through the polarization beam splitters and combiners, but is fused with the two spatially mirrored fiber rings at 0 degrees and 90 degrees through two Y waveguides, thereby suppressing the radial magnetic field phase error caused by the Faraday effect. The electrical signals of the two photoelectric detectors are jointly demodulated, and the temperature phase error compensation caused by the Shupe effect can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0032] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the present application. Moreover, the same reference numerals are used throughout the same figures. In the drawings:

[0033] Figure 1 A schematic diagram of an existing interferometric fiber-optic gyroscope is shown;

[0034] Figure 2 A schematic diagram of an interferometric fiber-optic gyroscope based on a special mirror ring structure is shown;

[0035] Figure 3 A schematic diagram of a polarization-maintaining fiber fusion is shown;

[0036] Figure 4 A flowchart for joint demodulation to compensate for temperature noise is shown;

[0037] Figure 5 A comparison chart of output angular velocity data analysis of a fiber-optic gyroscope using the application is shown;

[0038] Figure 6 A comparison chart of output angular velocity data analysis of a fiber-optic gyroscope using the application is shown. DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present application. In addition, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessary confusion of the concepts of the present application.

[0040] Various structural diagrams according to embodiments of the present application are shown in the drawings. These diagrams are not drawn to scale, in which certain details are exaggerated for clarity and others omitted. The shapes of various regions, layers, and the relative sizes and positional relationships among them shown in the drawings are merely exemplary, and may deviate in actuality due to manufacturing tolerances or technical limitations, and regions / layers with different shapes, sizes, and relative positions can be additionally designed according to actual needs by those skilled in the art.

[0041] Figure 1 A schematic diagram of an existing dual-polarization interferometric fiber-optic gyroscope is shown. As shown in Figure 1 The existing dual-polarization interferometric fiber-optic gyroscope generally includes a light source, a polarizer, a coupler, two loopers (looper 1 and looper 2), two Y waveguides (Y waveguide 1 and Y waveguide 2), a signal generator, two polarization beam splitters and combiners (polarization beam splitter and combiner 1 and polarization beam splitter and combiner 2), two photodetectors (photodetector 1 and photodetector 2), and a fiber loop.

[0042] Figure 1 The dual-polarization interferometric fiber-optic gyroscope structure shown cannot simultaneously overcome the limitations of temperature and magnetic field on the performance of the fiber-optic gyroscope, thereby restricting the improvement of the precision of the fiber-optic gyroscope in complex environments. In order to solve this situation, the embodiments of the present application provide an interferometric fiber-optic gyroscope based on a special mirror loop structure. The open-loop fiber-optic gyroscope after adopting the scheme can simultaneously suppress the magnetic field phase error, and jointly process the output data of the 2-in-2-out mirror fiber loop to realize compensation for the temperature phase error caused by the Shupe effect.

[0043] Figure 2 A schematic diagram of an interferometric fiber-optic gyroscope based on a special mirror loop structure provided by the present application is shown. As shown in Figure 2 The interferometric fiber-optic gyroscope based on a special mirror loop structure provided by the present application includes a light source 10, a polarizer 20, a coupler 30, two loopers (looper 41 and looper 42), two Y waveguides (Y waveguide 51 and Y waveguide 52), a signal generator 60, a 2-in-2-out mirror fiber loop 70, two photodetectors (photodetector 81 and photodetector 82), and a signal joint demodulation module 90. The Y waveguide refers to an integrated optical multifunctional optical waveguide modulator.

[0044] In this embodiment, the coupler 30 is a polarization-maintaining coupler. The loopers 41 and 42 can be three-port loopers.

[0045] In this embodiment, the 2-in, 2-out mirrored fiber ring 70 is made by using a four-stage symmetrical winding method to cross-wind two equal-length polarization-maintaining fibers in opposite directions and arrangements onto the same frame or the left and right sections of the frame, so that the two equivalent fiber rings are mirror images of each other. This winding method also ensures the mirror image relationship between the two equivalent fiber rings. The fast axis of both equal-length polarization-maintaining fibers is fused at 90 degrees at the midpoint.

[0046] One Y-waveguide corresponds to one fiber ring in a 2-in, 2-out mirrored fiber ring 70. When each polarization-maintaining fiber is fused to the Y-waveguide pigtail, one end is fused at 0 degrees to the fast axis, and the other end is fused at 90 degrees to the fast axis. For example... Figure 2 As shown, the first Y-waveguide 51 is connected to one of the fiber rings in the 2-input 2-output mirrored fiber ring 70, and the second Y-waveguide 52 is connected to the other fiber ring in the 2-input 2-output mirrored fiber ring 70. Figure 3 The diagram shown is a schematic of a polarization-maintaining fiber axial fusion splice.

[0047] In the aforementioned interferometric fiber optic gyroscope based on a special mirror ring structure, the light emitted from the light source is filtered by a polarizer and output as linearly polarized light. It is then split into two power-equalized paths by a polarization-maintaining coupler and input into the fiber optic ring via a circulator and a Y-waveguide, respectively, to interfere and output interference signals. The interference signals are then connected to photodetectors, and the two signals detected by the photodetectors are jointly demodulated.

[0048] The following is combined Figure 2 The above-mentioned interferometric fiber optic gyroscope based on a special mirror ring structure is described in detail.

[0049] like Figure 2 As shown, the light source 10 outputs light with arbitrary polarization to the polarizer 20. Specifically, the light source 10 can be a laser light source or an ASE light source. An ASE light source (Amplified Spontaneous Emission) is a broadband light source based on erbium-doped fiber amplification of spontaneous emission.

[0050] Polarizer 20 converts light of arbitrary polarization state output from light source 10 into linearly polarized light. Coupler 30 splits the linearly polarized light output from polarizer 20 into two beams, and couples the two beams to the first circulator 41 and the second circulator 42, respectively. Specifically, the two circulators here can be single-mode circulators or polarization-maintaining circulators. Polarization-maintaining circulators are more effective at suppressing polarization non-reciprocity errors.

[0051] The first circulator 41 outputs the first light beam outputted by the coupler 30 to the first Y waveguide 51; the second circulator 42 outputs the second light beam outputted by the coupler 30 to the second Y waveguide 52. Specifically, the two Y waveguides should have similar performance and have high extinction ratio. For example, the two Y waveguides have the same or similar main performance parameters such as insertion loss and polarization crosstalk.

[0052] The signal generator 60 provides modulation signals to the two Y waveguides (51, 52), and the signal generator provides the modulation signals with the same amplitude to the two Y waveguides, and the phase can be the same or opposite.

[0053] Specifically, when the signal generator provides the modulation signals with the same phase to the two Y waveguides, the signals are subjected to differential operation to obtain the output signal after noise compensation; when the signal generator provides the modulation signals with opposite phases to the two Y waveguides, the signals are subjected to summation operation to obtain the output signal after noise compensation.

[0054] The first Y waveguide 51 outputs the light beam outputted by the first circulator 41 after polarization, coupling and modulation to the corresponding port of the 2-in-2-out mirror fiber ring 70, and the second Y waveguide 52 outputs the light beam outputted by the second circulator 42 after polarization, coupling and modulation to the corresponding port of the 2-in-2-out mirror fiber ring 70.

[0055] The light beams outputted by the two Y waveguides independently interfere in the 2-in-2-out mirror fiber ring 70 to obtain first and second interference signals. The first Y waveguide 51 outputs the first interference signal to the first circulator 41; the second Y waveguide 52 outputs the second interference signal to the second circulator 42.

[0056] The specific process that the two polarized lights successively pass through the two orthogonal axes of the fiber ring and interfere and output is as follows:

[0057] The linearly polarized lights outputted by the two Y waveguides are respectively inputted into the two fast axes of the 2-in-2-out mirror fiber ring, the clockwise linearly polarized light starts from one end of the Y waveguide, passes through the fast axis with an angle of 0 degree, and does not change the polarization direction, propagates to the midpoint of the fiber ring with a distance of L1, passes through the fast axis with an angle of 90 degrees, the linearly polarized light changes the polarization direction to propagate along the slow axis, returns to the other end of the Y waveguide with a distance of L2, passes through the fast axis with an angle of 90 degrees, and changes the polarization direction to propagate along the fast axis. The counterclockwise linearly polarized light starts from the other end of the Y waveguide, passes through the fast axis with an angle of 90 degrees, changes the polarization direction to the slow axis, propagates to the midpoint of the fiber ring with a distance of L2, passes through the fast axis with an angle of 90 degrees, the linearly polarized light changes the polarization direction to propagate along the fast axis, returns to the other end of the Y waveguide with a distance of L2, and passes through the fast axis with an angle of 0 degree without changing the polarization direction. The two counter-propagating lights work in the same polarization direction at any position in the fiber ring and interfere.

[0058] The radial magnetic field errors corresponding to the fast axis and the slow axis can be respectively expressed as

[0059]

[0060]

[0061] Other parameters are consistent, ignore the fiber tail length, L1 = L2, according to the above formula (1), (2) can be seen that the radial magnetic field error corresponding to the fast axis and the slow axis after superposition is compensated.

[0062] The photoelectric detector 81 is connected to the first circulator 41, and the photoelectric detector 82 is connected to the second circulator 42. The two circulators output the interference signals returned by the two Y waveguides to the two photoelectric detectors respectively; the two photoelectric detectors convert the interference signals output by the two circulators into electrical signals and output to the signal joint demodulation module 90.

[0063] The signal joint demodulation module 90 jointly demodulates the two electrical signals output by the two photoelectric detectors. Specifically, the signal joint demodulation module 90 uses an open-loop fiber optic gyroscope multi-harmonic demodulation method to jointly demodulate the two electrical signals output by the two photoelectric detectors. Figure 4 The joint demodulation compensation temperature noise flow chart in the 2-in-2-out mirror fiber ring fiber optic gyroscope is shown, and the specific process will not be repeated here.

[0064] The temperature phase errors caused by the Shupe effect when the two fiber rings are implemented with the same phase modulation are respectively:

[0065] Δφ1 = φ S + φ s upe Equation (3);

[0066] Δφ2 = -φ S + φ s upe Equation (4);

[0067] After differential compensation:

[0068] Δφ sub = Δφ1-Δφ2 = 2φ S Equation (5);

[0069] Wherein, φ S represents the Sagnac phase on one of the two-in-two-out mirror fiber ring,

[0070] φ s upe represents the temperature phase error caused by the Shupe effect.

[0071] Similarly, the temperature phase errors caused by the Shupe effect when the two fiber rings are implemented with opposite phase modulation are respectively:

[0072] Δφ1=φ S +φ supe Equation (6);

[0073] Δφ2=φ S -φ supe Equation (7);

[0074] After summation compensation:

[0075] Δφ sum =Δφ1+Δφ2=2φ S Equation (8);

[0076] It can be seen that the temperature phase error caused by Shupe effect is compensated.

[0077] Taking an open-loop fiber optic gyroscope built with the following device as an example: an ASE light source with a wavelength of 1550 nm and a spectral width of 40 nm is used, the 2-in-2-out fiber ring length of the fiber optic gyroscope used is 2 km, the diameter is 148 mm, the modulation frequency is 50 kHz, and the modulation depth is 1.84.

[0078] Read the output angular velocity data of the above open-loop fiber optic gyroscope for one hour for Allan variance method analysis and comparison with the results after relative intensity noise suppression (as shown in Figure 5 , wherein SUM represents the relative intensity noise suppression result) and comparison with self-noise (as shown in Figure 6 ).

[0079] From the error analysis and comparison results of the output angular velocity data of the above open-loop fiber optic gyroscope before and after using the noise suppression method provided in the present application (Figures Figure 5 , Figure 6 ) can be seen that the two photodetectors PD1 and PD2 are almost coincident, indicating that the dual-port output has strong correlation, and the short-time and long-time performance of the fiber optic gyroscope are obviously improved after applying the present solution.

[0080] The interferometric fiber optic gyroscope based on the special mirror ring structure provided in the present application uses a 2-in-2-out mirror fiber ring to replace the fiber ring in the existing dual-polarization fiber optic gyroscope, the 2-in-2-out mirror fiber ring can be equivalent to two independent but spatially mirrored fiber rings, and the fast axes at the midpoints of the two fiber rings are fused at 90 degrees. And cancel two polarization beam splitters, the light is no longer sent into two polarization channels of the same fiber ring through the polarization beam splitter, but is fused with two spatially mirrored fiber rings at 0 degrees and 90 degrees through two Y waveguides, respectively, thereby suppressing the radial magnetic field phase error caused by the Faraday effect, and jointly demodulating the electrical signals of the two photodetectors, which can realize compensation for the temperature phase error caused by Shupe effect.

[0081] The person skilled in the art can also design methods which are not exactly the same as the methods described above in order to form the same structure. Furthermore, although the individual embodiments are described separately above, this does not mean that measures from the individual embodiments cannot be used advantageously in combination.

[0082] The embodiments of the application described above are intended to be illustrative only. The application is not limited in its scope to the embodiments of the application described herein. Alternatives and modifications of the embodiments of the application described herein will be apparent to persons skilled in the art upon reading this description and can be made without departing from the scope of the application.

Claims

1. An interferometric fiber-optic gyroscope based on a special mirror ring structure, characterized in that, The application relates to a polarization-maintaining fiber ring interferometer, which comprises the following components: a light source, a polarizer, a coupler, two loopers, two Y waveguides, a signal generator, a 2-in-2-out mirror fiber ring, two photodetectors and a signal joint demodulation module. The 2-in-2-out mirror fiber ring is made by cross-winding two equal-length polarization-maintaining fibers in opposite directions and in reverse order on the same skeleton or on the left and right two partitions of the skeleton, so that the two equivalent fiber rings are in mirror relationship. The two equal-length polarization-maintaining fibers for winding the 2-in-2-out mirror fiber ring are both fused at the midpoint of the fast axis at an angle of 90 degrees, and when each polarization-maintaining fiber is fused with the Y waveguide tail fiber, one end of the fast axis is fused at an angle of 0 degrees and the other end of the fast axis is fused at an angle of 90 degrees. The light source outputs light of any polarization state to the polarizer. The polarizer converts the light of any polarization state output by the light source into linearly polarized light. The coupler divides the linearly polarized light output by the polarizer into two light beams and couples the two light beams into the first looper and the second looper respectively. The first looper outputs the first light beam output by the coupler to the first Y waveguide, and the second looper outputs the second light beam output by the coupler to the second Y waveguide. The signal generator provides modulation signals to the two Y waveguides. The first Y waveguide outputs the light beam output by the first looper after polarization, coupling and modulation to the corresponding port of the 2-in-2-out mirror fiber ring, and the second Y waveguide outputs the light beam output by the second looper after polarization, coupling and modulation to the corresponding port of the 2-in-2-out mirror fiber ring. The light beams output by the two Y waveguides independently interfere in the 2-in-2-out mirror fiber ring to obtain first and second interference signals. The first Y waveguide outputs the first interference signal to the first looper, and the second Y waveguide outputs the second interference signal to the second looper. The two loopers output the interference signals returned by the two Y waveguides to the two photodetectors respectively. The two photodetectors convert the interference signals output by the two loopers into electrical signals and output the electrical signals to the signal joint demodulation module. The signal joint demodulation module jointly demodulates the two electrical signals output by the two photodetectors. The signal generator provides the two Y waveguides with modulation signals of equal amplitude and opposite phase.

2. The interferometric fiber optic gyroscope based on a special mirror ring structure according to claim 1, wherein, The signal generator provides the two Y waveguides with modulation signals of equal amplitude and the same phase.

3. The interferometric fiber optic gyroscope based on a special mirror ring structure of claim 1, wherein, The loopers are single-mode loopers.

4. The interferometric fiber optic gyroscope based on a special mirror ring structure of claim 1, wherein, The loopers are polarization-maintaining loopers.

5. The interferometric fiber optic gyroscope based on a special mirror ring structure of claim 1, wherein, The two Y waveguides have similar performance and high extinction ratio.

6. The interferometric fiber optic gyroscope based on a special mirror ring structure of claim 1, wherein, The signal joint demodulation module adopts an open-loop fiber-optic gyroscope multi-harmonic demodulation method.

7. The special mirror ring structure based interferometric fiber-optic gyroscope according to claim 1, wherein, The light source is a laser light source or an ASE light source.

8. The special mirror ring structure based interferometric fiber-optic gyroscope according to claim 1, wherein, ​

Images