Method for acquiring optimal modulation depth of fiber-optic gyroscope nested with Michelson interferometer

Abstract

The invention relates to an optical fiber gyroscope, in particular to a method for acquiring the optimal modulation depth of an optical fiber gyroscope nested with a Michelson interferometer, and aims to overcome the defects that in the prior art, when the optimal modulation depth of the optical fiber gyroscope nested with the Michelson interferometer is determined, a large number of debugging tests and data analysis need to be carried out, the operation process is complex, and time is wasted. The method for obtaining the optimal modulation depth of the fiber-optic gyroscope nested with the Michelson interferometer comprises the following steps: measuring the optical power P1 and the superposed optical power P2 of an interference optical signal, controlling the amplitude of a square wave electric signal output by a signal generator arranged at an electrical modulation port of a Y waveguide integrated modulator, taking the superposed optical power P2i corresponding to CT2i = 0dB, calculating to obtain the optimal modulation voltage, and obtaining the optimal modulation depth of the fiber-optic gyroscope nested with the Michelson interferometer. The method disclosed by the invention is convenient and efficient, and is beneficial to batch production and debugging of the fiber-optic gyroscope.

Description

Technical Field

[0001] The invention relates to a fiber optic gyroscope, and in particular to a method for acquiring an optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer. Background Art

[0002] Fiber optic gyroscope is an angular velocity sensor based on the optical Sagnac effect. It is one of the core components of the inertial navigation system and 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 usually use overmodulation technology to suppress the relative intensity noise of a part of the light source and obtain the signal error before and after reset, so as to obtain a higher gyro output signal-to-noise ratio and better suppression of reset error, while reducing the gyro random walk coefficient. However, the modulation depth cannot be infinitely close to π, otherwise the linearity of the random walk coefficient and scale factor will deteriorate.

[0003] In recent years, the relative intensity noise suppression technology of fiber optic gyroscopes with nested Michelson interferometers has become a hot research direction. This technology is one of the effective ways to improve the accuracy of fiber optic gyroscopes. The above-mentioned relative intensity noise suppression technology is specifically 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 light intensity and perpendicular polarization states, and delay the transit time of a fiber ring in time. In order to ensure that the modulated signal light and the reference light maintain equal light intensity, it is necessary to determine the optimal modulation depth of the fiber optic gyroscope. At present, the method of determining the optimal modulation depth of the fiber optic gyroscope usually requires changing the modulation depth multiple times in the closed-loop software of the fiber optic gyroscope. At each modulation depth, the steady-state output data of the fiber optic gyroscope is measured, and the steady-state output data of the fiber optic gyroscope is compared multiple times to obtain the optimal modulation depth. The optimal modulation depth is determined through this process, which requires a lot of debugging tests and data analysis. The operation process is complicated and wastes a lot of time. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art that when determining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer, a large amount of debugging tests and data analysis are required, the operation process is complicated, and a long time is wasted, and a method for obtaining the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer is provided.

[0005] To achieve the above objectives, the technical solutions provided by the present invention are as follows:

[0006] The invention discloses a method for acquiring the optimal modulation depth of an optical fiber gyroscope with a nested Michelson interferometer. The method is special in that: the optical fiber gyroscope with a nested Michelson interferometer comprises an ASE light source, a polarization-maintaining polarization beam splitter connected to the ASE light source, a Y-waveguide integrated modulator connected to a first output end of the polarization-maintaining polarization beam splitter, a polarization-maintaining optical fiber ring connected to two output ends of the Y-waveguide integrated modulator, a reflector connected to a second output end of the polarization-maintaining polarization beam splitter, and a photodetector connected to a third output end of the polarization-maintaining polarization beam splitter; light emitted by the ASE light source is divided into a reference light and a signal light of orthogonal linear polarization by the polarization-maintaining polarization beam splitter; the signal light is returned to form a modulated interference light signal by the Y-waveguide integrated modulator and the polarization-maintaining optical fiber ring; the reference light is attenuated and reflected by the reflector, and then the light intensity is superimposed with the returned interference light signal in the photodetector and output; the method for acquiring the optimal modulation depth comprises the following steps:

[0007] Step 1, build a fiber optic gyroscope with a nested Michelson interferometer, replace its photodetector with a detection device, set 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: Adjust the signal generator to the 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 an amplitude is adjusted, the detection device measures the corresponding superimposed optical power P 2i and polarization crosstalk CT 2i ; Take CT 2i =0dB corresponding superimposed optical power P 2i , the corresponding optimal modulation voltage V is calculated by the following formula i ;

[0009] P 2i =P1×(1+cos(V i / V 2π ))

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

[0011] Step 3: Calculate the optimal modulation voltage V obtained in step 2 i Calculate the optimal modulation depth.

[0012] Furthermore, step 1 is specifically as follows:

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

[0014] Step 1.2. Connect the polarization-maintaining polarization 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 end of the polarization-maintaining polarization beam splitter.

[0015] Furthermore, in step 2, the adjustment step of the amplitude is 20 mV; the intrinsic frequency f of the polarization-maintaining fiber ring is calculated by the following formula:

[0016] f=c / (2nL)

[0017] L=π·N·H / D·(R+N·D)

[0018] Wherein, 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 optical fiber.

[0019] Furthermore, the output end of the ASE light source and the input end of the polarization-maintaining polarization beam splitter adopt a "single mode-polarization-maintaining" welding mode; the first output end of the polarization-maintaining polarization beam splitter and the reflector adopt a "polarization-maintaining" welding mode; the second output end of the polarization-maintaining polarization 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 optical fiber ring all adopt a "polarization-maintaining" welding mode.

[0020] Furthermore, the reflector is a polarization-maintaining Faraday rotation reflector, and the reflection ratio is 1%-5%;

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

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

[0023] The reflection ratio of the reflector is 5%;

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

[0025] Beneficial effects of the present invention:

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

[0027] 2. The present invention applies a modulation signal through a signal generator to avoid the polarization crosstalk of the reference light being higher than the polarization crosstalk of the interference light signal, which is conducive to finding the specific position of the modulation depth.

[0028] 3. A reflector is arranged in the fiber optic gyroscope of the nested Michelson interferometer used in the present invention, so that the reference light carrying the intensity noise information is attenuated by 95% to 99% and then enters the photodetector, where it is superimposed with the intensity of the interference light signal carrying the intensity noise information, 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 remains consistent, thereby achieving relative intensity noise suppression.

[0029] 4. The fiber optic gyroscope with nested Michelson interferometer used in the present invention divides the incident light into reference light and signal light of orthogonal linear polarization through a polarization-maintaining polarization beam splitter, wherein the reference light is attenuated by a reflector, and the signal light passes through a Y-waveguide integrated modulator and a polarization-maintaining fiber ring, and then is combined with the attenuated reference light. No interference occurs in the photodetector, and only light intensity superposition is performed.

[0030] 5. In the fiber optic gyroscope with a nested Michelson interferometer used in the present invention, a "single mode-polarization maintaining" splicing mode and a "polarization maintaining-polarization maintaining" 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 splitting ratio of the polarization maintaining polarization beam splitter, a reflection ratio of the reflector, and a modulation depth of the Y-waveguide integrated modulator, the three are combined to ensure that the output interference light signal and the attenuated reference light have the same energy. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0032] Figure 2 It is a schematic diagram of the structure of an optimal modulation depth acquisition device of a fiber optic gyroscope embedded with a Michelson interferometer in an embodiment of the present invention;

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

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

[0035] Figure 5Graph showing how polarization crosstalk and superimposed optical power vary with modulation depth in an embodiment of the present invention.

[0036] Description of reference numerals:

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

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

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

[0040] The method for acquiring the optimal modulation depth of a fiber optic gyroscope with a nested Michelson interferometer of the present invention is based on a fiber optic gyroscope with a nested Michelson interferometer, a signal generator 7 is added, and its photodetector 6 is set 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, and the third output end of the polarization-maintaining polarization beam splitter 2 is connected to the polarization extinction ratio meter and the optical power meter through an optical adapter, respectively, for testing the degree of polarization and the optical power, respectively.

[0041] The working principle is as follows: the low polarization ASE light source 1 emits incident light, and the polarization-maintaining polarization beam splitter 2 divides the incident light into a reference light and a signal light with an optical power ratio of 1:1, and the reference light and the signal light are orthogonal linear polarized lights. The Y branch of the Y waveguide integrated modulator 4 divides the signal light into two beams of linear polarized light with a ratio of 1:1, which are respectively transmitted to the polarization-maintaining fiber ring 5, transmitted in opposite directions along the polarization-maintaining fiber ring 5, and returned to the Y branch along the original path, and the beams are combined to form an interference light signal carrying angular velocity information. The reference light enters the reflector 3, where the light intensity attenuation and light reflection are completed. The interference light signal and the attenuated reference light maintain polarization states perpendicular to each other, and enter the detection device 8 in turn through the polarization-maintaining polarization beam splitter 2. The interference light signal and the attenuated reference light are superimposed in intensity in the detection device 8, so that the superimposed optical power can be obtained. The signal generator 7 is used to apply a modulation signal to the Y waveguide integrated modulator 4. In the present invention, the modulation signal is a square wave electrical signal with a 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 modulation signal and the attenuated reference light remain perpendicular. After entering the polarization extinction ratio meter, the polarization crosstalk of the detected reference light is still relatively high. Therefore, in order to make the light intensity amplitude of the interference light signal and the reference light the same, it is necessary to add a modulation signal to the interference light signal to find the specific position of the modulation depth.

[0042] In this embodiment, the polarization-maintaining polarization beam splitter 2 is a 2x2 polarization-maintaining polarization beam splitter, and the reflector 3 is a polarization-maintaining Faraday rotator reflector with a reflection ratio of 1%-5%, thereby ensuring that the interference light signal modulated by the Y-waveguide integrated modulator 4 and the reference light intensity after attenuation by the reflector 3 are equal, and can adapt to different polarization-maintaining fiber rings 5, so that the accuracy of the gyroscope is wider, wherein 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, respectively 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; specifically:

[0045] Step 1.1, follow Figure 3Perform signal optical path welding and record optical parameters. Specifically, connect the ASE light source 1, polarization-maintaining polarization beam splitter 2, Y-waveguide integrated modulator 4, polarization-maintaining fiber ring 5 and detection device 8, set the signal generator 7 at the electrical modulation port of the Y-waveguide integrated modulator 4, wherein the ASE light source 1 and the input end of the polarization-maintaining polarization beam splitter 2 adopt the "single mode-polarization-maintaining" welding mode, and the second output end of the polarization-maintaining polarization 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 the "polarization-maintaining" welding mode. Control the ASE light source 1 to emit incident light, and record the interference light signal optical power P1 and polarization crosstalk CT1 output by the third output end of the polarization-maintaining polarization beam splitter 2.

[0046] Step 1.2, follow Figure 4 Perform reference optical path welding and record optical parameters. Specifically, connect the polarization-maintaining polarization beam splitter 2 and the reflector 3, and use the "polarization-maintaining" welding mode between the first output end of the polarization-maintaining polarization beam splitter 2 and the reflector 3. Control the ASE light source 1 to emit incident light, and record the superimposed optical power P2 and polarization crosstalk CT2 of the interference light signal and the reference light.

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

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

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

[0050] However, in the actual measurement process, there is a certain error in directly measuring the optical power. When the superimposed optical power meets the requirements, the corresponding polarization crosstalk cannot be guaranteed to meet the requirements. Therefore, in the actual measurement, the amplitude of the square wave electrical signal is adjusted. Each time an amplitude gear is adjusted, the polarization degree CT of the optical field superimposed by the interference optical signal and the attenuated reference light is recorded. 2i And the superimposed optical power P 2i , take the superimposed optical power P corresponding to the polarization crosstalk of 0dB measured by the polarization extinction ratio instrument 2i , and then calculate the corresponding optimal modulation voltage V by the following formula i ;

[0051] P 2i=P1×(1+cos(V i / V2π))

[0052] At this time, it is ensured that 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 shown.

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

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

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

[0056] L=π·N·H / D·(R+N·D),

[0057] Wherein, 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 optical fiber.

[0058] Step 3, calculate the corresponding modulation depth value in the gyro closed-loop software according to the optimal modulation voltage obtained in step 5, which is the optimal modulation depth.

Claims

1. A method for acquiring 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 comprises an ASE light source (1), a polarization-maintaining polarization beam splitter (2) connected to the ASE light source (1), a Y-waveguide integrated modulator (4) connected to a first output end of the polarization-maintaining polarization beam splitter (2), a polarization-maintaining optical fiber ring (5) connected to two output ends of the Y-waveguide integrated modulator (4), a reflector (3) connected to a second output end of the polarization-maintaining polarization beam splitter (2), and a photodetector (6) connected to a third output end of the polarization-maintaining polarization beam splitter (2); light emitted by the ASE light source (1) is divided into a reference light and a signal light of orthogonal linear polarization via the polarization-maintaining polarization beam splitter (2); the signal light is returned as a modulated interference light signal via the Y-waveguide integrated modulator (4) and the polarization-maintaining optical fiber ring (5); the reference light is attenuated and reflected via the reflector (3), and then the light intensity of the reference light and the returned interference light signal are superimposed on the photodetector (6) and output; The optimal modulation depth acquisition method comprises 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 superimposed optical power P2 of the interference light signal and the reference light during the construction process; Step 2: adjust the signal generator (7) to the square wave electrical signal output mode, set the frequency of the square wave electrical signal to the intrinsic frequency f of the polarization-maintaining optical fiber ring (5), and continuously adjust the amplitude of the square wave electrical signal from 0 to V 2π Each time an amplitude is adjusted, the detection device (8) measures the corresponding superimposed optical power P 2i and polarization crosstalk CT 2i ; Take CT 2i =0dB corresponding superimposed optical power P 2i , the corresponding optimal modulation voltage V is calculated by the following formula i ; P 2i =P1×(1+cos(V i / V2π)) Among them, V 2π is the 2π voltage value of the Y-waveguide integrated optical modulator; Step 3: Calculate the optimal modulation voltage V obtained in step 2 i Calculate the optimal modulation depth.

2. The method for acquiring 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. Build a fiber gyroscope with a nested Michelson interferometer. Without connecting the polarization-maintaining polarization beam splitter (2) and the reflector (3), replace the photodetector (6) with a detection device (8). Set a signal generator (7) at the electrical modulation port of the Y-waveguide integrated modulator (4), control the ASE light source (1) to emit incident light, and record the optical power P1 and polarization crosstalk CT1 output from the third output end of the polarization-maintaining polarization beam splitter (2); Step 1.

2. Connect the polarization-maintaining polarization beam splitter (2) and the reflector (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 end of the polarization-maintaining polarization beam splitter (2).

3. The method for acquiring 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 adjustment step of the amplitude is 20 mV; the eigenfrequency f of the polarization-maintaining optical fiber ring (5) is calculated by the following formula: f=c / (2nL) L=π·N·H / D·(R+N·D) Wherein, L is the length of the polarization-maintaining optical fiber ring (5), R is the inner diameter of the polarization-maintaining optical fiber ring (5), H is the ring height of the polarization-maintaining optical fiber ring (5), N is the number of layers of the polarization-maintaining optical fiber ring (5), D is the outer diameter of the polarization-maintaining optical fiber ring (5), c is the speed of light in vacuum, and n is the refractive index of the optical fiber.

4. The 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 polarization beam splitter (2) adopt a "single mode-polarization-maintaining" fusion splicing mode; the first output end of the polarization-maintaining polarization beam splitter (2) and the reflector (3) adopt a "polarization-maintaining" fusion splicing mode; the second output end of the polarization-maintaining polarization 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 optical fiber ring (5) all adopt a "polarization-maintaining" fusion splicing mode.

5. The fiber optic gyroscope with embedded Michelson interferometer according to claim 4, characterized in that: The reflector (3) is a polarization-maintaining Faraday rotation reflector, and the reflection ratio is 1%-5%; The polarization-maintaining polarization beam splitter (2) is a 2x2 polarization-maintaining polarization beam splitter.

6. The fiber optic gyroscope with nested Michelson interferometer according to claim 5, characterized in that: The splitting ratio of the polarization-maintaining polarization beam splitter (2) is 1:1; The reflection ratio of the reflector (3) is 5%; The beam splitting ratio of the Y-waveguide integrated modulator (4) is 1:1.

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