Pumping light power control device for high-performance atomic sensors used in inertial measurement

Abstract

This invention provides a pump power control device for a high-performance atomic sensor used in inertial measurement. From left to right, arranged coaxially along the central axis, it comprises a laser, a polarizer, a liquid crystal rotator, an analyzer, a polarization beam splitter, a waveplate, a gas cell, and a first photodetector. It also includes a controller and a second photodetector, located directly below the polarization beam splitter. Compared to traditional liquid crystal power stabilization systems, this invention reduces system nonlinearity errors, suppresses the influence of long-term liquid crystal operating parameter drift, and improves the long-term stability of pump power in liquid crystal power stabilization systems. It also improves the inconsistency between the pump power and the monitored laser power stability in liquid crystal power stabilization systems, thus enhancing control performance.

Description

Technical Field

[0001] This invention belongs to the technical field, specifically a pump optical power control device for high-performance atomic sensors used in inertial measurement. Background Technology

[0002] High-performance atomic sensors for inertial measurement combine the high precision of quantum technology with the miniaturization advantages of microelectromechanical systems (MEMS) technology, and represent one of the important development directions for future miniaturized, high-performance inertial navigation systems.

[0003] High-performance atomic sensors for inertial measurement use lasers to polarize the spins of alkali metal atoms and utilize the magneto-optical effect to detect the nucleon precession signal carrying the angular velocity of the carrier using linearly polarized light. Both atomic polarization and atomic spin detection in high-performance atomic sensors require the use of lasers. The stability of the laser directly affects the performance of high-performance atomic sensors used for inertial measurement. The instability of the laser source is currently an important error term in high-performance atomic sensors for inertial measurement.

[0004] To improve the accuracy of high-performance atomic sensors used for inertial measurement, it is necessary to take appropriate measures to suppress interference from laser power fluctuations. Existing technologies typically employ the following measures, including:

[0005] ① A laser power stabilization system based on a liquid crystal variable phase delayer is adopted;

[0006] In the control loop, a polarization beam splitter is used to split the laser into two beams, and the main laser is stabilized by controlling the stabilization of the bypass beam. Incremental PID control is used in the control method. In view of the problem of inconsistent stability of the two laser beams after splitting caused by the coupling between the splitting ratio of the polarization beam splitter and the phase delay of the liquid crystal, the splitting ratio of the laser at the PBS is adjusted by adjusting the 1 / 2 wave plate to make the splitting ratio of the laser at the PBS about 1:1, so as to minimize the impact of the splitting ratio error on the system.

[0007] However, this control method results in wasted laser power, high energy consumption, and is not conducive to energy conservation and environmental protection.

[0008] ② A pump optical power stabilization system based on a high-performance atomic sensor;

[0009] It employs a beam splitter and uses incremental PID control to stabilize the detection laser during closed-loop control.

[0010] However, this method is insufficient in suppressing system errors caused by optical components, and the long-term effect of power stabilization is not ideal. In the control loop, due to the coupling between the extinction ratio of the beam splitter and the phase delay of the liquid crystal, there is a beam splitting ratio error between the main laser and the monitoring laser. This means that the stability of the monitoring laser achieved by the closed-loop control cannot represent the stability of the pump light entering the gas chamber of the high-performance atomic sensor. In addition to introducing nonlinear errors, it cannot effectively suppress the drift of liquid crystal parameters with laser power during continuous operation, resulting in long-term drift. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a pump optical power control device for a high-performance atomic sensor used in inertial measurement. Addressing the shortcomings of existing technologies, it ensures the stability of the pump optical power within the gas chamber by using the pump light after passing through the gas chamber as a reference for compensation. Based on a model-free adaptive control method (MFAC), it designs controller parameters based on error characteristics to suppress the impact of liquid crystal parameter variations, polarization beam splitter splitting ratio errors, and system nonlinearity issues, thereby improving the long-term stability of the pump optical power.

[0012] A pump optical power control device for a high-performance atomic sensor used in inertial measurement includes: a laser, a polarizer, a liquid crystal rotator, an analyzer, a polarization beam splitter, a waveplate, a gas cell, and a first photodetector, arranged sequentially from left to right along the central axis; it also includes a controller and a second photodetector; the second photodetector is located directly below the polarization beam splitter.

[0013] The liquid crystal rotator is used to change the linear polarization direction of the incident light without changing the power of the incident light.

[0014] The liquid crystal rotator includes: a liquid crystal variable phase retarder and a rotator waveplate, wherein the fast axes of the liquid crystal variable phase retarder and the rotator waveplate are at a 45° angle.

[0015] The waveplate coincides with the fast axis of the analyzer;

[0016] The polarization beam splitter is tilted to the left at a 45° angle;

[0017] The controller is used to receive signals from the first photodetector and the second photodetector, and output a driving voltage to control the working state of the liquid crystal rotator.

[0018] As an example, the gas chamber is a high-performance atomic sensor gas chamber.

[0019] It also includes a control method for a pump optical power control device of a high-performance atomic sensor for inertial measurement, specifically designed as follows:

[0020] Step 1: The laser emits laser light, which, after passing through the polarizer, forms a 45° angle with the fast axis of the liquid crystal rotator.

[0021] Step 2: Adjust the driving voltage of the liquid crystal rotator so that the linear polarization direction of the laser emitted after passing through the liquid crystal rotator is rotated by a corresponding angle.

[0022] Step 3: The laser then passes through the analyzer and enters the polarization beam splitter, which splits the laser into two paths: the main laser and the bypass monitoring laser.

[0023] The bypass monitoring laser is received by a second photodetector and used as input to the controller;

[0024] After passing through the waveplate, the main laser beam is transformed from linearly polarized light to circularly polarized light, which then enters the gas chamber as pump light and is received by the first photodetector to calculate the adaptive parameters of the controller.

[0025] Step 4: The controller outputs a driving voltage to the liquid crystal rotator based on the calculation, thereby achieving stable control of the laser power after the laser passes through the analyzer.

[0026] The beneficial effects of this invention are:

[0027] 1) This invention improves the control scheme of the liquid crystal power stabilization system, avoiding the problem of nonlinear error introduced in the traditional liquid crystal power stabilization system control scheme; the adaptive parameters of the controller are designed based on the model-free adaptive control method (MFAC) to suppress system error, so that the pump power fluctuation is reduced to 0.0105% after the improvement.

[0028] 2) This invention introduces the pump light emitted from the gas chamber as a new observation, which improves the inconsistency between the pump light and the stability of the monitored laser power in the liquid crystal power stabilization system and enhances the control effect.

[0029] 3) This invention utilizes the sum of the monitoring laser power and the pump light power after the gas chamber to compensate for the drift error of the liquid crystal power stabilization system parameters caused by the thermal disturbance effect of the laser power on the liquid crystal parameters.

[0030] 4) This invention utilizes the difference in the amplitude of the driving voltage of the liquid crystal to compensate for the beam splitter's splitting ratio error. Attached Figure Description

[0031] Figure 1 This is an overall structural design diagram of the pump optical power control device for the high-performance atomic sensor used in inertial measurement according to the present invention.

[0032] Figure 2 This is a schematic diagram illustrating the working principle of the controller of the pump optical power control device for the high-performance atomic sensor used in inertial measurement according to the present invention.

[0033] Figure 3 This is a schematic diagram of the controller calculation process for the pump optical power control device of the high-performance atomic sensor used for inertial measurement according to the present invention. Detailed Implementation

[0034] Below, for reference Figures 1 to 3 As shown, the pump optical power control device for a high-performance atomic sensor used for inertial measurement includes: a laser 1, a polarizer 2, a liquid crystal rotator 3, an analyzer 4, a polarization beam splitter 5, a waveplate 6, a gas cell 7, and a first photodetector 8, arranged sequentially from left to right along the central axis; it also includes a controller 10 and a second photodetector 9; the second photodetector 9 is located directly below the polarization beam splitter 8.

[0035] The liquid crystal rotator 3 is used to change the linear polarization direction of the incident light without changing the power of the incident light.

[0036] The liquid crystal rotator 3 includes: a liquid crystal variable phase retarder and a rotator waveplate, wherein the fast axis of the liquid crystal variable phase retarder and the rotator waveplate is at a 45° angle.

[0037] The waveplate 6 coincides with the fast axis of the analyzer 4;

[0038] The polarization beam splitter 5 is tilted to the left at a 45° angle;

[0039] The controller 10 is used to receive signals from the first photodetector 8 and the second photodetector 9, and output a driving voltage to control the working state of the liquid crystal rotator 3; the liquid crystal rotator 3, the analyzer 4, the polarization beam splitter 5, the first photodetector 8 and the second photodetector 9 are all measurement links, which together constitute a nonlinear controlled system.

[0040] As an example, the gas chamber 7 is a high-performance atomic sensor gas chamber.

[0041] It also includes a control method for a pump optical power control device of a high-performance atomic sensor for inertial measurement, specifically designed as follows:

[0042] Step 1: The laser 1 emits laser light, which, after passing through the polarizer 2, forms a 45° angle with the fast axis of the liquid crystal rotator 3.

[0043] Step 2: Adjust the driving voltage of the liquid crystal rotator 3 so that the linear polarization direction of the laser emitted after passing through the liquid crystal rotator 3 is rotated by a corresponding angle.

[0044] Step 3: The laser then passes through the analyzer 4 and enters the polarization beam splitter 5, which splits the laser into two paths: the main laser and the bypass monitoring laser.

[0045] The bypass monitoring laser is received by the second photodetector 9 and used as the input to the controller 10;

[0046] After passing through the waveplate 6, the main laser beam is transformed from linearly polarized light to circularly polarized light, which then enters the gas chamber 7 as pump light and is received by the first photodetector 8 for calculating the adaptive parameters of the controller 10.

[0047] Step 4: The controller 10 outputs a driving voltage to the liquid crystal rotator 3 according to the calculation, so as to realize the stable control of the laser power after the laser passes through the analyzer 4.

[0048] As an example, the algorithm architecture of the controller 10 is designed as follows:

[0049] ① The pseudo-partial derivatives of the controlled system are φ(k) = [φ1(k), φ2(k), φ3(k), φ4(k)] T The parameters of the controlled system are estimated using the pseudo-partial derivative φ(k);

[0050] State quantity: H(k)=[y(k),y(k-1),u(k),u(k-1)] T ;

[0051] Establish the input-output model of the controlled system: Δy(k+1)=φ T (k)ΔH(k);

[0052] The controlled system satisfies the generalized Lipschitz, that is, for any k and Δu(k)≠0, we have: |y(k+1)-y(k)|≤b|u(k)-u(k-1)|;

[0053] in:

[0054] The input to the controlled system is the current driving voltage amplitude of the liquid crystal rotator, denoted as u(k); that is, the driving voltage of the liquid crystal rotator output by the controller.

[0055] The output of the controlled system is: the power of the bypass monitoring laser measured by the second photodetector at the current moment, denoted as y(k);

[0056] The output signal of the controlled system at the next moment is denoted as y(k+1);

[0057] The pump light power received by the second photodetector after passing through the gas cell is denoted as y1(k).

[0058] The desired monitoring laser power is set as y. d (k+1);

[0059] ② The calculation process of the controller output signal u(k) is shown in the flowchart. Figure 3 As shown, the specific calculation steps are as follows:

[0060] a. Solve for the pseudo-partial derivative φ(k);

[0061]

[0062] in:

[0063] μ: Parameter estimation weighting factor, which is a constant;

[0064] η i η is an additional step size coefficient for parameter estimation, added to provide more flexible control. i ∈(0,2), to compensate for liquid crystal parameter drift error;

[0065] The thermal disturbance effect of laser power on liquid crystal parameters is proportional to the laser power y(k) + y1(k) acting on the liquid crystal at the current moment, where:

[0066]

[0067] To compensate for the splitting ratio error, the difference in the amplitude of the driving voltage u(k) can characterize the change in the phase retardation of the liquid crystal. Let:

[0068]

[0069] b. Calculate u(k) using the pseudo-partial derivative φ(k);

[0070]

[0071] in:

[0072] λ: The input weighting factor that controls the stability of the controlled system;

[0073] ρ∈(0,1] is the step size coefficient of the additional control input, where λ and ρ are constants;

[0074] To ensure system stability, λ, ρ, and b satisfy...

[0075] To better illustrate the design principles of this invention, the underlying concept is briefly described again below:

[0076] High-performance atomic sensors for inertial measurement use laser-polarized atoms to prepare quantum states. The stability of the laser power directly affects the preparation effect of the quantum states and the long-term performance of the sensor.

[0077] Therefore, a laser power stabilization control scheme suitable for high-performance atomic sensors is needed. Liquid crystal variable phase delay devices (LCDs) are the preferred choice for stabilizing laser power due to their mature technology, miniaturization, and low cost, especially when combined with external optical modulation devices.

[0078] However, liquid crystal power stabilization systems are complex nonlinear systems. Using linear approximation of nonlinearity will introduce nonlinear errors. Furthermore, under continuous operation, the liquid crystal parameters are subject to drift caused by laser power. At the same time, the splitting ratio of the polarization beam splitter is coupled with the phase delay of the liquid crystal, which means that the stability of the two laser beams after splitting is not necessarily the same.

[0079] Therefore, the power stabilization effect achieved by a control system consisting of a general feedback control optical path and traditional PID control is not ideal in the long run. A laser power stabilization control scheme is needed that improves the observation of the system error characteristics of the pump optical power stabilization system of high-performance atomic sensors and achieves adaptive adjustment.

[0080] The above description is only a preferred embodiment of the present invention. It should be understood that the above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention, and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, etc. made within the idea and principle of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pump optical power control device for a high-performance atomic sensor used in inertial measurement, characterized in that, include: From left to right, arranged along the central axis are a laser, a polarizer, a liquid crystal rotator, an analyzer, a polarization beam splitter, a waveplate, a gas cell, and a first photodetector; it also includes a controller and a second photodetector; the second photodetector is located directly below the polarization beam splitter; the polarization beam splitter splits the laser into two paths, a main laser and a bypass monitoring laser; the bypass monitoring laser is received by the second photodetector; the main laser, after passing through the waveplate, is converted from linearly polarized light to circularly polarized light, which enters the gas cell as pump light and is received by the first photodetector; The liquid crystal rotator is used to change the linear polarization direction of the incident light without changing the power of the incident light. The liquid crystal rotator includes: a liquid crystal variable phase retarder and a rotator waveplate, wherein the fast axes of the liquid crystal variable phase retarder and the rotator waveplate are at a 45° angle. The waveplate coincides with the fast axis of the analyzer; The polarization beam splitter is tilted to the left at a 45° angle; The controller is used to receive signals from the first photodetector and the second photodetector, and output a driving voltage to control the working state of the liquid crystal rotator.

2. The pump optical power control device for a high-performance atomic sensor for inertial measurement according to claim 1, characterized in that, The gas chamber is a high-performance atomic sensor gas chamber.

3. The control method for the pump optical power control device of the high-performance atomic sensor for inertial measurement as described in claim 1 is specifically designed as follows: Step 1: The laser emits laser light, which, after passing through the polarizer, forms a 45° angle with the fast axis of the liquid crystal rotator. Step 2: Adjust the driving voltage of the liquid crystal rotator so that the linear polarization direction of the laser emitted after passing through the liquid crystal rotator is rotated by a corresponding angle. Step 3: The laser then passes through the analyzer and enters the polarization beam splitter, which splits the laser into two paths: the main laser and the bypass monitoring laser. The bypass monitoring laser is received by a second photodetector and used as input to the controller; After passing through the waveplate, the main laser beam is transformed from linearly polarized light to circularly polarized light, which then enters the gas chamber as pump light and is received by the first photodetector to calculate the adaptive parameters of the controller. Step 4: The controller outputs a driving voltage to the liquid crystal rotator based on the calculation, thereby achieving stable control of the laser power after the laser passes through the analyzer.

4. The pump optical power control device for a high-performance atomic sensor for inertial measurement according to claim 3, characterized in that, The algorithm architecture of the controller is designed as follows: ① The pseudo-partial derivatives of the controlled system are φ(k) = [φ1(k), φ2(k), φ3(k), φ4(k)] T The parameters of the controlled system are estimated using the pseudo-partial derivative φ(k); State variable: H(k) = [y(k), y(k-1), u(k), u(k-1)] T ; Establish the input-output model of the controlled system: Δy(k+1)=φ T (k)ΔH(k); The controlled system satisfies the generalized Lipschitz, that is, for any k and Δu(k)≠0, we have: |y(k+1)-y(k)|≤b|u(k)-u(k-1)|; in: The input to the controlled system is: the amplitude of the driving voltage of the liquid crystal rotator at the current moment, denoted as u(k); that is, the driving voltage of the liquid crystal rotator output by the controller; The output of the controlled system is: the power of the bypass monitoring laser measured by the second photodetector at the current moment, denoted as y(k); The output signal of the controlled system at the next moment is denoted as y(k+1); The pump power received by the second photodetector after passing through the gas cell is denoted as y1(k). The desired monitoring laser power is set as y. d (k+1); ②The calculation steps for the controller output signal u(k) are as follows: a. Solve for the pseudo-partial derivative φ(k); in: μ: Parameter estimation weighting factor, which is a constant; η i η is an additional step size coefficient added to allow for more flexible parameter estimation. i ∈(0,2), to compensate for liquid crystal parameter drift error; The thermal disturbance effect of laser power on liquid crystal parameters is proportional to the laser power y(k) + y1(k) acting on the liquid crystal at the current moment, where: To compensate for the splitting ratio error, the difference in the amplitude of the driving voltage u(k) can characterize the change in the phase retardation of the liquid crystal. Let: b. Calculate u(k) using the pseudo-partial derivative φ(k); in: λ: The input weighting factor that controls the stability of the controlled system; ρ∈(0,1] is the step size coefficient of the additional control input, where λ and ρ are constants; To ensure system stability, λ, ρ, and b satisfy...

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