SERF gyroscope probe light polarization multidimensional compensation system

Abstract

The invention relates to an SERF gyroscope probe light polarization multidimensional compensation system. Comprising a detection laser, an optical isolator, a first laser beam splitter, a first photoelectric detector, a liquid crystal phase retarder, a lambda / 4 wave plate, a second laser beam splitter, a Sole-Babinet compensator, a third laser beam splitter, an atomic gas chamber, a first lambda / 2 wave plate, a first polarization beam splitter prism, a second photoelectric detector, a third photoelectric detector, a second lambda / 2 wave plate and a second polarization beam splitter prism. A fourth photoelectric detector, a fifth photoelectric detector, a polarization analyzer and a sixth photoelectric detector. According to the invention, a polarization rotation angle compensation loop based on the combination of the liquid crystal phase delayer and the lambda / 4 wave plate and a delay phase compensation loop based on the Sole-Babinet compensator are adopted, comprehensive feedback compensation is carried out on the polarization change of the SERF gyroscope detection light from two dimensions of light polarization, and the polarization instability of the detection light can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of SERF gyroscope detection, and in particular relates to a SERF gyroscope detection light polarization multi-dimensional compensation system. Background Art

[0002] In the SERF gyroscope, there are two main parts of laser, namely the detection light and the pump light. The pump light is a circularly polarized laser, which is used to interact with the atoms of the working material to achieve the pump polarization of the alkali metal atoms. The detection light is a linearly polarized laser. After the detection light passes through the atomic gas chamber, the polarization direction will change. The gyroscope signal can be detected by detecting the rotation of the polarization angle of the linearly polarized light. Therefore, the polarization stability of the detection laser is directly related to the stability of the gyroscope output.

[0003] Ideally, the polarization of the laser remains unchanged, but in actual experiments, the polarization of the laser will be unstable due to the influence of various environmental factors and the non-ideal factors of the laser light source itself. For linearly polarized light, the instability is mainly divided into two aspects: on the one hand, the instability of the polarization direction; on the other hand, the instability of the polarization phase delay. The jitter or drift of the polarization direction will directly affect the zero-bias stability performance of the gyro output, and the elliptically polarized light generated by the unstable phase delay will interact with the atoms, causing the detection light power to be lost, thereby affecting the amplitude of the output signal. Therefore, feedback compensation for the polarization of the detection laser can effectively improve the performance of the SERF gyroscope in many aspects.

[0004] At present, common laser polarization stabilization methods mainly focus on the polarization stabilization of laser transmission in optical fiber, such as CN201910952356.8, CN201910242731.X, CN202110824822.1, CN202311448545.4, and CN201410584081.4. Free-space light polarization stabilization methods include random gradient algorithms based on polarization analyzers and polarization controllers, such as CN202011294682.3, which are large in size and not convenient for integration into gyro prototypes. There are also compensation methods for polarization rotation angles based on electrically controlled 1 / 2 wave plates, such as CN202111634239.0, but they require mechanical rotation, so the response time is relatively slow. There are also open-loop compensation methods for laser phase based on liquid crystal phase retarders, but their compensation efficiency is low, and the real-time compensation is poor during the actual use of the gyro. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention proposes a SERF gyro detection light polarization multi-dimensional compensation system which can realize real-time high-precision compensation, thereby realizing comprehensive maintenance of the polarization stability of the detection light.

[0006] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0007] A SERF gyro detection light polarization multi-dimensional compensation system, comprising a detection laser, an optical isolator, a first laser beam splitter, a first photodetector, a liquid crystal phase retarder, a λ / 4 wave plate, a second laser beam splitter, a Soleil-Babinet compensator, a third laser beam splitter, an atomic gas chamber, a first λ / 2 wave plate, a first polarization beam splitter prism, a second photodetector, a third photodetector, a second λ / 2 wave plate, a second polarization beam splitter prism, a fourth photodetector, a fifth photodetector, an analyzer and a sixth photodetector;

[0008] The detection laser is used to emit a light beam, and the optical isolator at the rear is used to isolate the reflected light of the rear optical path to avoid damage to the laser; the first laser beam splitter is used to perform the first beam splitting output on the light beam emitted by the optical isolator, and the reflected light outputted by the first beam splitting is detected by the first photodetector and converted into an electrical signal, which is used as the input of the laser power stabilization circuit, and the control current of the laser is fed back after the PID algorithm operation; the transmitted light outputted by the first beam splitting passes through the liquid crystal phase retarder 5 and the λ / 4 wave plate, and then is secondarily split by the second laser beam splitter, and the reflected light after the second beam splitting output is input into the polarization rotation angle compensation loop; the transmitted light after the second beam splitting output passes through the Soleil-Babinet compensator and is thirdly split by the third laser beam splitter; the reflected light after the third beam splitting output enters the laser phase delay compensation loop; the transmitted light after the third beam splitting output passes through the atomic gas chamber and enters the differential polarization method signal detection optical path composed of the first λ / 2 wave plate, the first polarization beam splitting prism, the second photodetector and the third photodetector;

[0009] In the polarization rotation angle compensation loop, a differential detection optical path composed of a second λ / 2 wave plate, a second polarization beam splitter prism, a fourth photodetector and a fifth photodetector is used as a detection optical path, and an optical path composed of a liquid crystal retarder and a λ / 4 wave plate is used as an execution optical path; a PID algorithm of a polarization rotation angle feedback compensation current is used to control the peak value of a square wave applied to a liquid crystal phase retarder to control the phase delay of the liquid crystal phase retarder, and the polarization rotation angle is adjusted in combination with the effect of the λ / 4 wave plate, so as to control the differential output to remain near a target value;

[0010] In the laser phase delay compensation loop, a detection optical path is composed of a polarizer and a sixth photodetector, and a Soleil-Babinet compensator is used as an actuator; the Soleil-Babinet compensator is a continuously adjustable zero-order delay device, and the phase delay amount of the laser is adjusted by feedback controlling the moving distance of the long optical wedge on the Soleil-Babinet compensator through a PID algorithm, so that the output of the sixth photodetector is kept at zero, thereby realizing compensation for the phase delay amount.

[0011] Moreover, the detection laser output light beam is transmitted along the y-axis direction; the polarization direction of the output light of the detection laser is along the x-axis direction, the fast axis direction of the liquid crystal phase retarder is at an angle of 45° to the x-axis direction, and the fast axis direction of the λ / 4 wave plate is along the z-axis direction; the fast axis direction of the second λ / 2 wave plate is at an angle of 22.5° to the horizontal x-axis direction; the Soleil-Babinet compensator is at an angle of 135° to the horizontal x-axis direction, and the polarization direction of the analyzer is along the z-axis direction.

[0012] Moreover, the Soleil-Babinet compensator is coated with an anti-reflection film, and the central wavelength of the anti-reflection film is 780nm.

[0013] The advantages and positive effects of the present invention are:

[0014] 1. The detection light system and device of the present invention performs feedback compensation on the detection light from two dimensions: the rotation angle of light polarization and the delayed phase, and can more comprehensively maintain the polarization stability of the detection light.

[0015] 2. The present invention adopts a combination of a liquid crystal phase retarder and a λ / 4 wave plate to realize compensation of the polarization rotation angle, which is convenient to control, has a fast response time, and can ensure a high execution accuracy.

[0016] 3. The present invention adopts the Soleil compensation method based on the Soleil-Babinet compensator combined with a precise electric control promotion component to realize the feedback compensation of the phase delay amount, which has a very high compensation accuracy.

[0017] 4. The polarization rotation angle compensation loop and the phase delay compensation loop of the present invention both use PID algorithm to perform real-time closed-loop feedback to ensure real-time compensation of the polarization rotation angle and phase delay of the detection light. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is an overall schematic diagram of the SERF gyro detection light polarization multi-dimensional compensation system of the present invention. DETAILED DESCRIPTION

[0019] The structure of the present invention is further described below with reference to the accompanying drawings and by way of examples. It should be noted that the present examples are descriptive rather than restrictive.

[0020] A SERF gyro detection light polarization multi-dimensional compensation system, see Figure 1The invention point is that it includes: a detection laser 1, an optical isolator 2, a first laser beam splitter 3, a first photodetector 4, a liquid crystal phase retarder 5, a λ / 4 wave plate 6, a second laser beam splitter 7, a Soleil-Babinet compensator 8, a third laser beam splitter 9, an atomic gas chamber 10, a first λ / 2 wave plate 11, a first polarization beam splitter prism 12, a second photodetector 13, a third photodetector 14, a second λ / 2 wave plate 15, a second polarization beam splitter prism 16, a fourth photodetector 17, a fifth photodetector 18, an analyzer 19 and a sixth photodetector 20. The working substance in the atomic gas chamber is an alkali metal. 87 Rb, 129 Xe gas and N2 buffer gas.

[0021] The detection laser emits a beam along the y-axis, first passing through the optical isolator 2, and then splitting through the first laser beam splitter 3. The reflected light after splitting is directly detected by the first photodetector 4 and converted into an electrical signal, which is used as the input of the laser power stabilization circuit. After the PID algorithm is calculated, the control current of the laser is fed back to control the laser, thereby achieving the purpose of stabilizing the laser output power. The detection laser needs to have a feedback port for controlling the current.

[0022] The transmitted light split by the first laser beam splitter 3 passes through the liquid crystal phase retarder 5 and the λ / 4 wave plate 6, and is then split by the second laser beam splitter 7. The reflected light after the splitting enters the polarization rotation angle compensation loop, and the transmitted light after the splitting continues to be transmitted forward.

[0023] The polarization direction of the laser output beam is along the x-axis, the fast axis direction of the liquid crystal phase retarder 5 is at an angle of 45° to the x-axis, and the fast axis direction of the λ / 4 wave plate 6 is along the z-axis. At this time, the fast axis direction of the liquid crystal phase retarder 5 is at an angle of 45° to the fast axis direction of the λ / 4 wave plate 6, and the polarization direction of the linear polarized light can be rotated by changing the phase delay of the liquid crystal phase retarder 5. The specific principle is as follows:

[0024] The Stokes matrix of linearly polarized light with intensity I and angle θ with the x-axis is:

[0025]

[0026] The Mueller matrix of the liquid crystal retarder is:

[0027]

[0028] The Mueller matrix of the λ / 4 wave plate is:

[0029]

[0030] Where θ is the angle between the fast axis of the LCVR and the λ / 4 wave plate and the horizontal x-axis, and δ represents the phase delay caused by the LCVR.

[0031] In the present invention, the polarization direction of the incident light is along the x-axis, the angle between the fast axis of the liquid crystal phase retarder (LCVR) and the x-direction is 45°, the angle between the fast axis of the λ / 4 wave plate and the x-direction is 90°, and the phase delay δ generated by the LCVR is related to the peak-to-peak value of the applied square wave signal. Therefore, at this time, their Mueller matrices are:

[0032] The Stokes matrix of incident linearly polarized light is:

[0033]

[0034] The Mueller matrix of the liquid crystal retarder is

[0035]

[0036] The Mueller matrix of the λ / 4 wave plate is:

[0037]

[0038] Therefore, the Stokes matrix of the outgoing light is:

[0039]

[0040] Combining equation 7 with equation (1), it can be seen that the outgoing light is linearly polarized light, and the polarization direction of the outgoing light is related to the phase delay amount added by the liquid crystal phase retarder, and δ = -2θ. Therefore, the polarization direction of the linearly polarized light can be adjusted by adjusting the phase delay amount of the liquid crystal phase retarder.

[0041] In the polarization rotation angle compensation loop, a differential detection optical path is formed by the second λ / 2 wave plate 15, the second polarization beam splitter prism 16, the fourth photodetector 17 and the fifth photodetector 18, which is used as a test optical path for light polarization. The angle between the fast axis direction of the second λ / 2 wave plate 15 and the horizontal y-axis direction is 22.5°. If the liquid crystal phase retarder 5 and the λ / 4 wave plate 6 are not considered at this time, the voltage signal of the differential output should be zero in theory under ideal conditions. The principle is:

[0042] The Mueller matrix of the λ / 2 wave plate is:

[0043]

[0044] Because the angle between the fast axis direction of the λ / 2 wave plate 15 and the horizontal axis direction is 22.5°, the Mueller matrix can be written as:

[0045]

[0046] After the horizontally polarized incident light passes through, the Stokes matrix of the outgoing light is:

[0047]

[0048] Combining equation 10 and equation (1), it can be seen that the angle between the polarization direction of the outgoing light and the horizontal x-axis is 45°. Therefore, the p-light and s-light components after passing through the polarization beam splitter in the differential optical path are equal, and the output after differentiation is zero. If the polarization rotation angle deviates from the x-axis direction, the angle between the polarization direction of the incident light beam in the above-mentioned light polarization test optical path and the horizontal x-axis is not 45°, and the p-light and s-light components of the light beam are not equal, so the differential output is not zero. Therefore, the rotation change of the polarization direction of the light beam can be detected by the differential output.

[0049] Through the PID algorithm of the polarization rotation angle feedback compensation current, the peak value of the square wave applied to the liquid crystal phase retarder is controlled to control the phase delay of the liquid crystal phase retarder, thereby combining the effect of the λ / 4 wave plate to adjust the polarization rotation angle so that the differential output remains at zero. In turn, feedback compensation of the polarization rotation angle is achieved. However, in practice, there may be phase delays, elliptical polarization parts appear, resulting in non-zero differential outputs. Therefore, manual feedback compensation is required to make the differential output as close to zero as possible. Then use this position as the zero position of the PID feedback control for automatic feedback compensation.

[0050] The transmitted light after being split by the second laser beam splitter 7 passes through the Soleil-Babinet compensator 8 and is then split by the third laser beam splitter 9. The reflected light after being split by the third laser beam splitter 9 enters the laser phase delay compensation circuit, and the transmitted light after being split passes through the atomic gas chamber 10 and enters the differential polarization signal detection optical path composed of the first λ / 2 wave plate 11, the first polarization beam splitting prism 12, the second photodetector 13 and the third photodetector 14. The reflected light after being split by the third laser beam splitter 9 enters the phase delay compensation circuit, passes through the analyzer 19 and then enters the sixth photodetector 20. The angle between the Soleil-Babinet compensator 8 and the horizontal x-axis direction is 135°, and the polarization direction of the analyzer 19 is along the z-axis direction.

[0051] Without considering the Soleil-Babinet compensator, ideally, since the polarization direction of the analyzer 19 is orthogonal to the polarization direction of the detection laser output light, the output of the sixth photodetector 20 should be zero. However, the elliptical polarization part caused by the phase delay will make the detector output non-zero. The phase delay of the laser is adjusted by electrically controlling the moving distance of the long optical wedge on the Soleil-Babinet compensator through PID algorithm feedback, so that the output of the sixth photodetector 20 remains zero, thereby achieving compensation for the phase delay.

[0052] The Soleil-Babinet compensator is a continuously adjustable zero-order retarder that can operate in a long wavelength range. The Soleil-Babinet compensator consists of a long birefringent wedge and a fixed wedge mounted on a compensating plate. The phase delay can be adjusted by using the accompanying electronically controlled precision promotion component to control the movement of the long wedge relative to the short wedge. It can not only continuously adjust the phase delay, but also maintain a uniform delay throughout the entire clear aperture under any setting. In the present invention, in order to reduce the loss of laser power, the Soleil-Babinet compensator is coated with an anti-reflection film (central wavelength 780nm).

[0053] The relationship between the phase delay δ of the Soleil-Babinet compensator and the distance D that the long birefringent wedge moves relative to the short wedge is:

[0054]

[0055] Where α is the inclination angle of the optical wedge; μ = n e -n o is the birefringence of the wedge; λ is the laser wavelength. Since these parameters are constants, the phase delay δ and the moving distance D are linearly related.

[0056] Assume that the phase delay of the laser beam due to external factors such as the environment is The phase delay provided by the Soleil-Babinet compensator is δ, so the outgoing light intensity at the rear end of the analyzer 19 is

[0057]

[0058] When When , the phase delay of the system is compensated, and the transmitted light intensity of the analyzer 19 is minimum, which is in the extinction state. Therefore, in the phase delay compensation loop, by adjusting the phase delay amount of the Soleil-Babinet compensator to make the detector signal as small as possible, the phase delay compensation is achieved.

[0059] The system of the present invention needs to perform multiple splitting operations. Therefore, in the experiment, the maximum output power of the laser should be large enough to ensure that the laser power incident on the atomic gas chamber and each control loop can meet the requirements.

[0060] For ease of description, the present invention makes the laser output light polarization along the x-axis direction. In practice, as long as the fast axis direction or polarization direction of the relevant device in the optical path corresponds to the placement angle described in the present invention, the output light in other directions can also achieve the compensation effect of the present invention.

[0061] In summary, the present invention adopts two feedback compensation loops, namely, a polarization rotation angle compensation loop based on a liquid crystal phase retarder and a delay phase compensation loop based on a Soleil-Babinet compensator, to provide comprehensive feedback compensation for the polarization change of the SERF gyro detection light from two dimensions of light polarization, which can effectively improve the polarization instability of the detection light, thereby improving the performance of the gyro. At the same time, the liquid crystal phase retarder and the Soleil-Babinet compensator are used as actuators to ensure high execution accuracy.

[0062] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A SERF gyro detection light polarization multi-dimensional compensation system, characterized in that: It includes a detection laser, an optical isolator, a first laser beam splitter, a first photodetector, a liquid crystal phase retarder, a λ / 4 wave plate, a second laser beam splitter, a Soleil-Babinet compensator, a third laser beam splitter, an atomic gas chamber, a first λ / 2 wave plate, a first polarization beam splitter prism, a second photodetector, a third photodetector, a second λ / 2 wave plate, a second polarization beam splitter prism, a fourth photodetector, a fifth photodetector, an analyzer, and a sixth photodetector; The detection laser is used to emit a light beam, and the optical isolator at the rear is used to isolate the reflected light beam of the rear optical path to avoid damage to the laser; The first laser beam splitter is used to perform a first beam splitting output on the light beam emitted by the optical isolator. The reflected light of the first beam splitting output is detected by the first photodetector and converted into an electrical signal, which is used as the input of the laser power stabilization circuit, and is fed back to control the control current of the laser after the PID algorithm operation; the transmitted light of the first beam splitting output passes through the liquid crystal phase retarder and the λ / 4 wave plate, and is then secondarily split by the second laser beam splitter, and the reflected light after the second beam splitting output is input into the polarization rotation angle compensation loop; the transmitted light after the second beam splitting output passes through the Soleil-Babinet compensator and is thirdly split by the third laser beam splitter; the reflected light after the third beam splitting output enters the laser phase delay compensation loop; the transmitted light after the third beam splitting output passes through the atomic gas chamber and enters the differential polarization method signal detection optical path composed of the first λ / 2 wave plate, the first polarization beam splitting prism, the second photodetector and the third photodetector; In the polarization rotation angle compensation loop, a differential detection optical path composed of a second λ / 2 wave plate, a second polarization beam splitter prism, a fourth photodetector and a fifth photodetector is used as a detection optical path, and an optical path composed of a liquid crystal retarder and a λ / 4 wave plate is used as an execution optical path; a PID algorithm of a polarization rotation angle feedback compensation current is used to control the peak value of a square wave applied to a liquid crystal phase retarder to control the phase delay of the liquid crystal phase retarder, and the polarization rotation angle is adjusted in combination with the effect of the λ / 4 wave plate, so as to control the differential output to remain near a target value; In the laser phase delay compensation loop, a detection optical path is composed of a polarizer and a sixth photodetector, and a Soleil-Babinet compensator is used as an actuator; the Soleil-Babinet compensator is a continuously adjustable zero-order delay device, and the phase delay amount of the laser is adjusted by feedback controlling the moving distance of the long optical wedge on the Soleil-Babinet compensator through a PID algorithm, so that the output of the sixth photodetector is kept at zero, thereby realizing compensation for the phase delay amount.

2. The SERF gyro detection light polarization multi-dimensional compensation system according to claim 1, characterized in that: The detection laser output light beam is transmitted along the y-axis direction; the polarization direction of the detection laser output laser is along the x-axis direction, the fast axis direction of the liquid crystal phase retarder is at an angle of 45° to the x-axis direction, and the fast axis direction of the λ / 4 wave plate 6 is along the z-axis direction; the fast axis direction of the second λ / 2 wave plate is at an angle of 22.5° to the horizontal y-axis direction; the Soleil-Babinet compensator is at an angle of 135° to the horizontal x-axis direction, and the polarization direction of the analyzer is along the z-axis direction.

3. The SERF gyro detection light polarization multi-dimensional compensation system according to claim 1, characterized in that: The Soleil-Babinet compensator is coated with an anti-reflection film, and the central wavelength of the anti-reflection film is 780nm.

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