Optimal modulation depth acquisition method for fiber-optic gyroscope with nested michelson interferometer

Abstract

This invention relates to fiber optic gyroscopes, specifically to a method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer. This method addresses the shortcomings of existing technologies where determining the optimal modulation depth for a fiber optic gyroscope with a nested Michelson interferometer requires extensive debugging, testing, and data analysis, resulting in a complex and time-consuming process. The method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer includes the following steps: measuring the optical power P1 and superimposed optical power P2 of the interference optical signal; controlling the amplitude of the square wave electrical signal output by the signal generator at the electrical modulation port of the Y-waveguide integrated modulator; and taking the CT... 2i =0dB corresponds to the superimposed optical power P 2i The optimal modulation voltage is calculated, and then the optimal modulation depth is calculated based on the optimal modulation voltage. This method is convenient and efficient, and helps in the mass production and debugging of fiber optic gyroscopes.

Description

Technical Field

[0001] This invention relates to fiber optic gyroscopes, and more specifically to a method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer. Background Technology

[0002] A fiber optic gyroscope is an angular velocity sensor based on the optical Sagnac effect and is one of the core components of inertial navigation systems. It is widely used in military and civilian fields such as aviation, aerospace, navigation, weapon systems, and unmanned equipment. Closed-loop interferometric high-precision fiber optic gyroscopes typically employ overmodulation techniques to suppress some of the relative intensity noise from the light source and to obtain the signal error before and after reset, resulting in a higher gyroscope output signal-to-noise ratio and better suppression of reset errors, while also reducing the gyroscope's random walk coefficient. However, the modulation depth cannot approach π infinitely; otherwise, the linearity of the random walk coefficient and scaling factor will deteriorate.

[0003] In recent years, relative intensity noise suppression technology for fiber optic gyroscopes with nested Michelson interferometers has become a hot research topic, as it is one of the effective ways to improve the accuracy of fiber optic gyroscopes. Specifically, this relative intensity noise suppression technology involves optical path noise reduction. During the noise reduction process, it is necessary to ensure that the modulated signal light and the reference light maintain equal intensity and perpendicular polarization, with a time delay of one fiber loop transit time. To ensure that the modulated signal light and the reference light maintain equal intensity, the optimal modulation depth of the fiber optic gyroscope needs to be determined. Currently, determining the optimal modulation depth typically requires multiple changes to the modulation depth in the fiber optic gyroscope's closed-loop software. At each modulation depth, the steady-state output data of the fiber optic gyroscope is measured, and the results are compared to obtain the optimal modulation depth. This process of determining the optimal modulation depth requires extensive debugging, testing, and data analysis, making it complex and time-consuming. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies where determining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer requires extensive debugging, testing, and data analysis, resulting in a complex and time-consuming process. This invention provides a method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] A method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer is characterized in that: the fiber optic gyroscope with a nested Michelson interferometer includes an ASE light source, a polarization-maintaining beam splitter connected to the ASE light source, a Y-waveguide integrated modulator connected to the first output end of the polarization-maintaining beam splitter, a polarization-maintaining fiber ring connected to the two output ends of the Y-waveguide integrated modulator, a reflector connected to the second output end of the polarization-maintaining beam splitter, and a photodetector connected to the third output end of the polarization-maintaining beam splitter; the light emitted from the ASE light source is split into orthogonally linearly polarized reference light and signal light by the polarization-maintaining beam splitter; the signal light passes through the Y-waveguide integrated modulator and the polarization-maintaining fiber ring to form a modulated interference signal that returns; the reference light is attenuated and reflected by the reflector, and then superimposed with the returned interference signal at the photodetector for light intensity and output; the method for obtaining the optimal modulation depth includes the following steps:

[0007] Step 1: Construct a fiber optic gyroscope with a nested Michelson interferometer, replace its photodetector with a detection device, set up a signal generator at the electrical modulation port of the Y-waveguide integrated modulator, and record the optical power P1 of the interference light signal and the superimposed optical power P2 of the interference light signal and the reference light during the construction process.

[0008] Step 2: Set the signal generator to square wave electrical signal output mode, set the square wave electrical signal frequency to the intrinsic frequency f of the polarization-maintaining fiber loop, and continuously adjust the amplitude of the square wave electrical signal from 0 to V. 2π Each time the amplitude is adjusted, the detection device measures the corresponding superimposed optical power P. 2i and polarization crosstalk CT 2i Take a CT scan 2i =0dB corresponds to the superimposed optical power P 2i The optimal modulation voltage V can be calculated using the following formula. i ;

[0009] P 2i =P1×(1+cos(V) i / V 2π ))

[0010] Among them, V 2π This represents the 2π voltage value of the Y-waveguide integrated optical modulator;

[0011] Step 3, based on the optimal modulation voltage V obtained in Step 2 i The optimal modulation depth was calculated.

[0012] Furthermore, step 1 specifically includes:

[0013] Step 1.1. Construct a fiber optic gyroscope with a nested Michelson interferometer. Without connecting the polarization-maintaining beam splitter and the mirror, replace the photodetector with a detection device. Set up a signal generator at the electrical modulation port of the Y-waveguide integrated modulator to control the ASE light source to emit incident light. Record the optical power P1 and polarization crosstalk CT1 output from the third output terminal of the polarization-maintaining beam splitter.

[0014] Step 1.2. Connect the polarization-maintaining beam splitter and the reflector, control the ASE light source to emit incident light, and record the optical power P2 and polarization crosstalk CT2 output from the third output terminal of the polarization-maintaining beam splitter.

[0015] Further, in step 2, the amplitude adjustment step size is 20mV; the intrinsic frequency f of the polarization-maintaining fiber loop is calculated using the following formula:

[0016] f = c / (2nL)

[0017] L=π·N·H / D·(R+N·D)

[0018] Where L is the length of the polarization-maintaining fiber ring, R is the inner diameter of the polarization-maintaining fiber ring, H is the ring height of the polarization-maintaining fiber ring, N is the number of layers of the polarization-maintaining fiber ring, D is the outer diameter of the polarization-maintaining fiber ring, c is the speed of light in vacuum, and n is the refractive index of the fiber.

[0019] Furthermore, the output end of the ASE light source and the input end of the polarization-maintaining beam splitter adopt a "single-mode-polarization-maintaining" fusion splicing mode; the first output end of the polarization-maintaining beam splitter and the reflector adopt a "polarization-maintaining" fusion splicing mode; the second output end of the polarization-maintaining beam splitter and the input end of the Y-waveguide integrated modulator, and the two output ends of the Y-waveguide integrated modulator and the two input ends of the polarization-maintaining fiber ring all adopt a "polarization-maintaining" fusion splicing mode.

[0020] Furthermore, the reflector is a polarization-maintaining Faraday rotating reflector with a reflection ratio of 1%-5%;

[0021] The polarization-maintaining beam splitter is a 2x2 polarization-maintaining beam splitter.

[0022] Furthermore, the beam splitting ratio of the polarization-maintaining beam splitter is 1:1;

[0023] The reflectivity of the mirror is 5%;

[0024] The beam splitting ratio of the Y-waveguide integrated modulator is 1:1.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention directly and accurately calculates the optimal modulation depth by monitoring the interference light signal and the reference light, providing data support for fiber optic gyroscope debugging. It is convenient and efficient, and helps with mass production and debugging.

[0027] 2. This invention applies a modulation signal through a signal generator, avoiding the polarization crosstalk of the reference light being higher than that of the interference light signal, which is beneficial for accurately determining the specific location of the modulation depth.

[0028] 3. The fiber optic gyroscope of the nested Michelson interferometer used in this invention is equipped with a reflector, so that the intensity of the reference light carrying intensity noise information is attenuated by 95% to 99% before entering the photodetector. The reference light then enters the photodetector and is superimposed with the intensity of the interference light signal carrying intensity noise information, thus providing conditions for achieving relative intensity noise subtraction. After reflection, the attenuation ratio of the reference light is 95% to 99%, so that the intensity of the reference light and the interference light signal are kept consistent, thereby achieving relative intensity noise suppression.

[0029] 4. The fiber optic gyroscope of the nested Michelson interferometer used in this invention splits the incident light into orthogonally linearly polarized reference light and signal light through a polarization-maintaining beam splitter. The reference light is attenuated by a mirror, and the signal light is combined with the attenuated reference light after passing through a Y-waveguide integrated modulator and a polarization-maintaining fiber loop. No interference occurs in the photodetector; only the light intensity is superimposed.

[0030] 5. In the fiber optic gyroscope of the nested Michelson interferometer used in this invention, a "single-mode-polarization-maintaining" fusion splicing mode and a "polarization-maintaining" fusion splicing mode are used at specific positions to ensure that the reference light and the interference light signal are always in a vertical polarization state. At the same time, by setting a fixed beam splitting ratio of the polarization-maintaining beam splitter, a reflection ratio of the mirror, and a modulation depth of the Y-waveguide integrated modulator, the three factors are combined to ensure that the output interference light signal and the attenuated reference light have the same energy. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a fiber optic gyroscope structure with a nested Michelson interferometer in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the optimal modulation depth acquisition device for a fiber optic gyroscope with a nested Michelson interferometer in an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of the signal optical path in an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the signal optical path and the reference optical path in an embodiment of the present invention;

[0035] Figure 5This is a graph showing the variation of polarization crosstalk and superimposed optical power with modulation depth in an embodiment of the present invention.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1-ASE light source, 2-polarization-maintaining beam splitter, 3-reflector, 4-Y-waveguide integrated modulator, 5-polarization-maintaining fiber ring, 6-photodetector, 7-signal generator, 8-detection device. Detailed Implementation

[0038] The fiber optic gyroscope of the nested Michelson interferometer used in this invention includes an ASE light source 1, a polarization-maintaining beam splitter 2, a reflector 3, a Y-waveguide integrated modulator 4, a polarization-maintaining fiber loop 5, and a photodetector 6, as shown. Figure 1 As shown.

[0039] The output of ASE light source 1 is optically connected to the input of polarization-maintaining beam splitter 2; the first output of polarization-maintaining beam splitter 2 is optically connected to the input of mirror 3; the second output of polarization-maintaining beam splitter 2 is optically connected to the input of Y-waveguide integrated modulator 4; the third output of polarization-maintaining beam splitter 2 is connected to the input of photodetector 6, which detects the optical signal and converts it into a corresponding electrical signal. The two outputs of Y-waveguide integrated modulator 4 are optically connected to the two inputs of polarization-maintaining fiber ring 5, respectively.

[0040] The optimal modulation depth acquisition method for a fiber optic gyroscope with a nested Michelson interferometer in this invention adds a signal generator 7 to the fiber optic gyroscope with a nested Michelson interferometer, and sets its photodetector 6 as a detection device 8, such as... Figure 2 As shown, the two electrodes of the electrical modulation port of the Y-waveguide integrated modulator 4 are electrically connected to the signal generator 7. The detection device 8 includes a polarization extinction ratio meter and an optical power meter. The third output terminal of the polarization-maintaining beam splitter 2 is connected to the polarization extinction ratio meter and the optical power meter respectively through an optical adapter, and is used to test the degree of polarization and optical power respectively.

[0041] The working principle is as follows: An ASE light source 1 with low polarization degree emits incident light. A polarization-maintaining beam splitter 2 splits the incident light into a reference beam and a signal beam with a power ratio of 1:1, and the reference beam and signal beam are orthogonally linearly polarized. The Y branch of the Y-waveguide integrated modulator 4 splits the signal beam into two linearly polarized beams with a 1:1 ratio, which are then sent to the polarization-maintaining fiber ring 5. These beams propagate towards each other along the polarization-maintaining fiber ring 5 and return to the Y branch along the original path, combining to form an interference light signal carrying angular rate information. The reference light enters the reflector 3, where light intensity attenuation and reflection are completed. The interference light signal and the attenuated reference light maintain their polarization states perpendicular to each other and sequentially enter the detection device 8 via the polarization-maintaining beam splitter 2. The interference light signal and the attenuated reference light are superimposed in the detection device 8 to obtain the superimposed optical power. The signal generator 7 applies a modulation signal to the Y-waveguide integrated modulator 4. In this invention, the modulation signal is a square wave electrical signal with continuously variable amplitude, and the frequency of the square wave electrical signal is consistent with the intrinsic frequency of the polarization-maintaining fiber ring 5. The polarization states of the interference light signal without a modulation signal and the attenuated reference light remain perpendicular. After entering the polarization extinction meter, the polarization crosstalk of the detected reference light is still relatively high. Therefore, in order to make the intensity amplitudes of the interference light signal and the reference light the same, a modulation signal needs to be added to the interference light signal to accurately locate the specific position of the modulation depth.

[0042] In this embodiment, the polarization-maintaining beam splitter 2 is a 2x2 polarization-maintaining beam splitter, and the reflector 3 is a polarization-maintaining Faraday rotating reflector with a reflection ratio of 1%-5%. This ensures that the intensity of the interference light signal modulated by the Y-waveguide integrated modulator 4 is equal to that of the reference light signal attenuated by the reflector 3, and can adapt to different polarization-maintaining fiber rings 5, thus making the gyroscope more accurate. The reflection ratio of the reflector 3 is preferably 5%.

[0043] The specific method for obtaining the optimal modulation depth includes the following steps:

[0044] Step 1: During the optical path connection process of the optimal modulation depth acquisition device, record the optical power P1 of the interference light signal and the superimposed optical power P2 of the interference light signal and the reference light respectively; specifically:

[0045] Step 1.1, according to Figure 3The signal optical path is fused and the optical parameters are recorded. Specifically, the ASE light source 1, polarization-maintaining beam splitter 2, Y-waveguide integrated modulator 4, polarization-maintaining fiber ring 5, and detection device 8 are connected. A signal generator 7 is set at the electrical modulation port of the Y-waveguide integrated modulator 4. The input ends of the ASE light source 1 and the polarization-maintaining beam splitter 2 adopt a "single-mode-polarization-maintaining" fusion mode. The second output end of the polarization-maintaining beam splitter 2 and the input end of the Y-waveguide integrated modulator 4, and the two output ends of the Y-waveguide integrated modulator 4 and the two input ends of the polarization-maintaining fiber ring 5, all adopt a "polarization-maintaining-polarization-maintaining" fusion mode. The ASE light source 1 is controlled to emit incident light, and the interference light signal power P1 and polarization crosstalk CT1 output from the third output end of the polarization-maintaining beam splitter 2 are recorded.

[0046] Step 1.2, according to Figure 4 The reference optical path is fused together and the optical parameters are recorded. Specifically, the polarization-maintaining beam splitter 2 and the reflector 3 are connected, and the first output end of the polarization-maintaining beam splitter 2 and the reflector 3 are fused together in a "polarization-maintaining" mode. The ASE light source 1 is controlled to emit incident light, and the superimposed optical power P2 of the interference light signal and the reference light and the polarization crosstalk CT2 are recorded.

[0047] Step 2: Apply a square wave electrical signal to the Y-waveguide integrated optical modulator via signal generator 7, adjust the amplitude of the square wave electrical signal, and control the polarization extinction ratio meter and optical power meter to measure the optical field polarization degree CT respectively. 2i and superimposed optical power P 2i .

[0048] Theoretically, the superimposed optical power P 2i When condition 2(P2-P1) is met, the polarization crosstalk is 0dB. The corresponding optimal modulation voltage V can be directly calculated using the following formula. i ;

[0049] 1 / 2×P1×(1+cos(V i / V2π))=P2-P1

[0050] In actual measurement, directly measuring optical power introduces a certain error. While the superimposed optical power meets the requirements, the corresponding polarization crosstalk cannot be guaranteed to meet the requirements. Therefore, in actual measurement, the amplitude of the square wave electrical signal is adjusted, and the polarization degree CT of the superimposed optical field of the interference optical signal and the attenuated reference light is recorded for each amplitude adjustment. 2i and superimposed optical power P 2i The superimposed optical power P corresponding to a polarization crosstalk of 0 dB as measured by the polarization extinction ratio meter is taken. 2i The optimal modulation voltage V is then calculated using the following formula. i ;

[0051] P 2i=P1×(1+cos(V) i / V2π))

[0052] At this point, the relative intensity noise of the ASE light source 1 is well suppressed at the eigenfrequency of the polarization-maintaining fiber ring 5, such as... Figure 5 As shown.

[0053] In this embodiment, the amplitude V of the square wave electrical signal is adjusted. i Specifically, the amplitude is adjusted from 0 to V. 2π , where V 2π The 2π voltage value of the Y-waveguide integrated optical modulator was obtained by consulting the device datasheet of the Y-waveguide integrated optical modulator. The amplitude adjustment step is 20mV.

[0054] The frequency of the square wave electrical signal is the intrinsic frequency f of the fiber optic loop. The intrinsic frequency f of the polarization-maintaining fiber optic loop 5 is calculated using the following formula:

[0055] f = c / (2nL),

[0056] L=π·N·H / D·(R+N·D),

[0057] Where L is the length of polarization-maintaining fiber ring 5, R is the inner diameter of polarization-maintaining fiber ring 5, H is the ring height of polarization-maintaining fiber ring 5, N is the number of layers of polarization-maintaining fiber ring 5, D is the outer diameter of polarization-maintaining fiber ring 5, c is the speed of light in vacuum, and n is the refractive index of the fiber.

[0058] Step 3: Calculate the corresponding modulation depth value in the gyroscope closed-loop software based on the optimal modulation voltage obtained in Step 5, which is the optimal modulation depth.

Claims

1. A method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer, characterized in that: The fiber optic gyroscope with nested Michelson interferometer includes an ASE light source (1), a polarization-maintaining beam splitter (2) connected to the ASE light source (1), a Y-waveguide integrated modulator (4) connected to the first output end of the polarization-maintaining beam splitter (2), a polarization-maintaining fiber ring (5) connected to the two output ends of the Y-waveguide integrated modulator (4), a reflector (3) connected to the second output end of the polarization-maintaining beam splitter (2), and a photodetector (6) connected to the third output end of the polarization-maintaining beam splitter (2). The light emitted from the ASE light source (1) is split into orthogonally linearly polarized reference light and signal light by the polarization-maintaining beam splitter (2). The signal light is modulated into an interference light signal by the Y-waveguide integrated modulator (4) and the polarization-maintaining fiber ring (5) and returns. The reference light is attenuated and reflected by the reflector (3) and then superimposed with the returned interference light signal in the photodetector (6) and output. The method for obtaining the optimal modulation depth includes the following steps: Step 1: Build a fiber optic gyroscope with a nested Michelson interferometer, replace its photodetector (6) with a detection device (8), set a signal generator (7) at the electrical modulation port of the Y-waveguide integrated modulator (4), and record the optical power P1 of the interference light signal and the superposition optical power P2 of the interference light signal and the reference light during the construction process. Step 2: Set the signal generator (7) to square wave electrical signal output mode, set the frequency of the square wave electrical signal to the intrinsic frequency f of the polarization-maintaining fiber loop (5), and continuously adjust the amplitude of the square wave electrical signal from 0 to V. 2π For each adjustment of amplitude, the detection device (8) measures the corresponding superimposed optical power P. 2i and polarization crosstalk CT 2i Take a CT scan 2i =0dB corresponds to the superimposed optical power P 2i The optimal modulation voltage V can be calculated using the following formula. i ; P 2i =P1×(1+cos(V i / V 2π )) Among them, V 2π This represents the 2π voltage value of the Y-waveguide integrated optical modulator; Step 3, based on the optimal modulation voltage V obtained in Step 2 i The optimal modulation depth was calculated.

2. The method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer according to claim 1, characterized in that, Step 1 is as follows: Step 1.

1. Construct a fiber optic gyroscope with a nested Michelson interferometer. Without connecting the polarization-maintaining beam splitter (2) and the mirror (3), replace the photodetector (6) with a detection device (8). Set up a signal generator (7) at the electrical modulation port of the Y-waveguide integrated modulator (4) to control the ASE light source (1) to emit incident light. Record the optical power P1 and polarization crosstalk CT1 output from the third output terminal of the polarization-maintaining beam splitter (2). Step 1.

2. Connect the polarization-maintaining beam splitter (2) and the mirror (3), control the ASE light source (1) to emit incident light, and record the optical power P2 and polarization crosstalk CT2 output from the third output terminal of the polarization-maintaining beam splitter (2).

3. The method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer according to claim 1 or 2, characterized in that: In step 2, the amplitude adjustment step size is 20mV; the intrinsic frequency f of the polarization-maintaining fiber loop (5) is calculated using the following formula: f = c / (2nL) L=π·N·H / D·(R+N·D) Where L is the length of the polarization-maintaining fiber ring (5), R is the inner diameter of the polarization-maintaining fiber ring (5), H is the ring height of the polarization-maintaining fiber ring (5), N is the number of layers of the polarization-maintaining fiber ring (5), D is the outer diameter of the polarization-maintaining fiber ring (5), c is the speed of light in vacuum, and n is the refractive index of the fiber.

4. The method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer according to claim 3, characterized in that: The output end of the ASE light source (1) and the input end of the polarization-maintaining beam splitter (2) adopt a "single-mode polarization-maintaining" fusion splicing mode; the first output end of the polarization-maintaining beam splitter (2) and the reflector (3) adopt a "polarization-maintaining" fusion splicing mode; the second output end of the polarization-maintaining beam splitter (2) and the input end of the Y-waveguide integrated modulator (4), and the two output ends of the Y-waveguide integrated modulator (4) and the two input ends of the polarization-maintaining fiber ring (5) all adopt a "polarization-maintaining" fusion splicing mode.

5. The method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer according to claim 4, characterized in that: The reflector (3) is a polarization-maintaining Faraday rotating reflector with a reflection ratio of 1%-5%; The polarization-maintaining beam splitter (2) is a 2x2 polarization-maintaining beam splitter.

6. The method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer according to claim 5, characterized in that: The polarization-maintaining beam splitter (2) has a beam splitting ratio of 1:1; The reflectance of the mirror (3) is 5%; The beam splitting ratio of the Y-waveguide integrated modulator (4) is 1:1.

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