Pumping optical power control device of high-performance atom sensor for inertial measurement

Abstract

The invention provides a pumping optical power control device of a high-performance atom sensor for inertial measurement. The pumping optical power control device comprises a laser, a polarizer, a liquid crystal rotator, a polarization analyzer, a polarization beam splitter, a wave plate, a gas chamber and a first photoelectric detector which are sequentially arranged from left to right and share the same central axis, the device further comprises a controller and a second photoelectric detector. The second photoelectric detector is located right below the polarization beam splitter; compared with a traditional liquid crystal stable power system control scheme, nonlinear errors of the system are reduced, the influence of liquid crystal long-time working parameter drifting is restrained, and the long-term stability of pumping optical power under the liquid crystal stable power system is improved; the inconsistency of power stability of pumping light and monitoring laser in a liquid crystal stable power system is improved, and the control effect is improved.

Description

Technical Field

[0001] The invention belongs to the technical field, in particular to a pumping light power control device of a high-performance atomic sensor used for inertial measurement. Background Art

[0002] High-performance atomic sensors for inertial measurement combine the high precision of quantum technology with the miniaturization advantages of microelectromechanical (MEMS) technology, and are 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 use the magneto-optical effect to use linearly polarized light to detect the nuclear precession signal that carries the carrier's angular velocity. High-performance atomic sensors need to use lasers when performing atomic polarization and atomic spin detection. The stability of the laser will directly affect the performance of high-performance atomic sensors for inertial measurement. The instability of the laser light source is an important error term in current high-performance atomic sensors for inertial measurement.

[0004] In order to improve the accuracy of high-performance atomic sensors for inertial measurement, it is necessary to take reasonable measures to suppress the fluctuation interference of laser power. The existing technology usually adopts the following measures, including:

[0005] ①Use a laser power stabilization system based on liquid crystal variable phase retarder;

[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 bypass beam stability. Incremental PID control is used in the control method. In view of the inconsistency of the stability of the two laser beams after splitting caused by the coupling of the splitting ratio of the polarization beam splitter and the phase delay of the liquid crystal in the system, the splitting ratio of the laser at the PBS is adjusted to be about 1:1, so that the impact of the splitting ratio error on the system is minimized.

[0007] However, this control method will cause waste of laser power, high energy consumption, and is not conducive to energy conservation and environmental protection.

[0008] ② A pumping light power stabilization system based on high-performance atomic sensors;

[0009] The light splitting element is used, and the control method also adopts incremental PID control to achieve stable detection laser during closed-loop control;

[0010] However, this method does not adequately suppress the system errors caused by optical components, and the long-term effect of stabilizing power is not ideal. In the control loop, due to the coupling between the extinction ratio of the splitter element and the phase delay of the liquid crystal, a splitting ratio error occurs between the main laser and the monitoring laser, making it impossible for the monitoring laser stability achieved by the closed-loop control to represent the pumping light entering the gas chamber of the high-performance atomic sensor. At the same time, nonlinear errors are introduced, and the drift of the liquid crystal parameters with the laser power during continuous operation cannot be effectively suppressed, resulting in long-term drift. Summary of the invention

[0011] In order to solve the above technical problems, the present invention provides a pumping light power control device for a high-performance atomic sensor for inertial measurement. In view of the defects of the prior art, the stability of the pumping light power in the gas chamber is ensured, and the pumping light after passing through the gas chamber is used as a reference for compensation. Based on the model-free adaptive control method (MFAC), the controller parameters are designed based on the error characteristics to suppress the influence of the liquid crystal parameter changes, the splitting ratio error of the polarization beam splitter and the nonlinear problem of the system, so as to improve the long-term stability of the pumping light power.

[0012] A pumping light power control device for a high-performance atomic sensor for inertial measurement, comprising: from left to right, a laser, a polarizer, a liquid crystal rotator, an analyzer, a polarization beam splitter, a wave plate, an air chamber and a first photodetector arranged in sequence on a central axis; further comprising a controller and a second photodetector; the second photodetector is located directly below the polarization beam splitter;

[0013] The liquid crystal optical 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 optical rotator comprises: a liquid crystal variable phase retarder and an optical rotator wave plate, wherein the fast axes of the liquid crystal variable phase retarder and the optical rotator wave plate form an angle of 45°;

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

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

[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 optical rotator.

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

[0019] Also included is a control method for a pumping light power control device of a high-performance atomic sensor for inertial measurement, which is specifically designed as follows:

[0020] Step 1, the laser emits laser light, and after passing through the polarizer, the linear polarization direction of the laser light is 45° with the fast axis of the liquid crystal rotator;

[0021] Step 2: adjusting the driving voltage of the liquid crystal optical rotator so that the linear polarization direction of the laser emitted after passing through the liquid crystal optical rotator rotates by a corresponding angle;

[0022] Step 3: The laser passes through the analyzer and enters the polarization beam splitter, so that the laser is divided into two paths, a main path laser and a bypass monitoring laser;

[0023] The bypassed monitoring laser is received by a second photodetector as an input to a controller;

[0024] After the main path laser passes through the wave plate, the main path laser is converted from linearly polarized light to circularly polarized light, enters the gas chamber as pumping 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 optical rotator according to the calculation, so as to achieve stable control of the laser power after the laser passes through the analyzer.

[0026] Beneficial effects of the present invention:

[0027] 1) The present invention improves the control scheme of the liquid crystal power stabilization system to avoid the problem of nonlinear errors 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 errors, so that the improved pump light power fluctuation is reduced to 0.0105%.

[0028] 2) The present invention introduces the pumping light emitted from the gas chamber as a new observation quantity, improves the inconsistency between the pumping light and the monitoring laser power stability in the liquid crystal power stabilization system, and improves the control effect.

[0029] 3) The present invention utilizes the sum of the monitoring laser power and the post-pumping optical power of the gas chamber to compensate for the drift error of the liquid crystal power stabilization system parameters caused by the thermal disturbance of the laser power on the liquid crystal parameters.

[0030] 4) The present invention utilizes the difference in the driving voltage amplitude of the liquid crystal to compensate for the splitting ratio error of the beam splitter. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the overall structural design diagram of the pumping light power control device of the high-performance atomic sensor used for inertial measurement of the present invention.

[0032] Figure 2 The figure is a schematic diagram of the working principle of the controller of the pumping light power control device of the high-performance atomic sensor for inertial measurement of the present invention.

[0033] Figure 3 The figure is a schematic diagram of the calculation flow of the controller of the pumping light power control device of the high-performance atomic sensor for inertial measurement of the present invention. DETAILED DESCRIPTION

[0034] Below, reference Figures 1 to 3 As shown, the pumping light power control device of the high-performance atomic sensor for inertial measurement includes: from left to right, a laser 1, a polarizer 2, a liquid crystal rotator 3, an analyzer 4, a polarization beam splitter 5, a wave plate 6, a gas chamber 7 and a first photodetector 8 arranged in sequence with the central axis; and 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 optical 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 optical rotator 3 comprises: a liquid crystal variable phase retarder and an optical rotator wave plate, wherein the fast axes of the liquid crystal variable phase retarder and the optical rotator wave plate form an angle of 45°;

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

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

[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 polarizer 4, the polarization beam splitter 5, the first photodetector 8 and the second photodetector 9 are all measurement links, and together constitute a nonlinear controlled system.

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

[0041] Also included is a control method for a pumping light power control device of a high-performance atomic sensor for inertial measurement, which is specifically designed as follows:

[0042] Step 1: The laser 1 emits laser light, and after passing through the polarizer 2, the linear polarization direction of the laser light is 45° with the fast axis of the liquid crystal rotator 3;

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

[0044] Step 3: The laser passes through the analyzer 4 and enters the polarization beam splitter 5, so that the laser is divided into two paths, a main path laser and a bypass monitoring laser;

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

[0046] After the main path laser passes through the wave plate 6, the main path laser is transformed from linearly polarized light to circularly polarized light, enters the gas chamber 7 as pumping light, and is received by the first photodetector 8 to calculate the adaptive parameters of the controller 10;

[0047] Step 4: The controller 10 outputs a driving voltage to the liquid crystal optical rotator 3 according to the calculation, so as to realize 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 derivative of the controlled system φ(k)=[φ1(k),φ2(k),φ3(k),φ4(k)] T , using the pseudo partial derivative φ(k), to estimate the parameters of the controlled system;

[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, |y(k+1)-y(k)|≤b|u(k)-u(k-1|;

[0053] in:

[0054] The input of the controlled system is: the current driving voltage amplitude of the liquid crystal optical rotator, recorded as u(k); that is, the driving voltage of the liquid crystal optical 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, recorded as y(k);

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

[0057] The pumping light power after passing through the gas chamber received by the second photodetector is denoted as y1(k),

[0058] The expected 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 flow chart Figure 3 As shown, the specific calculation steps are as follows:

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

[0061]

[0062] in:

[0063] μ: parameter estimation weight factor, a constant;

[0064] η i : is the step size coefficient of parameter estimation added to control more flexibility, η i ∈(0,2), compensate for the drift error of liquid crystal parameters;

[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, and is taken as:

[0066]

[0067] Compensating for the splitting ratio error, the difference in the amplitude of the driving voltage u(k) can characterize the change in the phase delay of the liquid crystal, taking:

[0068]

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

[0070]

[0071] in:

[0072] λ: is the control input weight factor, which affects the stability of the controlled system;

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

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

[0075] In order to better illustrate the design principle of the present invention, the principle idea is briefly introduced again as follows:

[0076] High-performance atomic sensors used for inertial measurement achieve quantum state preparation by polarizing atoms with lasers. The laser power stability directly affects the quantum state preparation effect 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 retarder is the first choice for stabilizing laser power with external optical modulation devices due to its mature technology and small size and low cost.

[0078] However, the liquid crystal power stabilization system is a complex nonlinear system. Using linear approximation to approximate nonlinearity will introduce nonlinear errors. In addition, under continuous operation, the liquid crystal parameters will drift due to laser power. At the same time, the splitting ratio of the polarization beam splitter is coupled with the phase delay of the liquid crystal, so the stability of the two laser beams after splitting may not be consistent.

[0079] Therefore, the power stabilization effect achieved by the control system composed of general feedback control optical path and traditional PID control is not ideal in the long run. It is necessary to develop a laser power stabilization control scheme that can improve the observation quantity and realize adaptive adjustment based on the error characteristics of the pumping light power stabilization system of high-performance atomic sensors.

[0080] The above are only preferred embodiments of the present invention. It should be understood that the description of the above embodiments is only used to help understand the method and core ideas of the present invention, and is not used to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, etc. made within the ideas and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A pumping light power control device for a high-performance atomic sensor for inertial measurement, characterized in that: include: From left to right, a laser, a polarizer, a liquid crystal rotator, an analyzer, a polarization beam splitter, a wave plate, an air chamber and a first photodetector are arranged on the same central axis in sequence; a controller and a second photodetector are also included; the second photodetector is located directly below the polarization beam splitter; The liquid crystal optical rotator is used to change the linear polarization direction of the incident light without changing the power of the incident light; The liquid crystal optical rotator comprises: a liquid crystal variable phase retarder and an optical rotator wave plate, wherein the fast axes of the liquid crystal variable phase retarder and the optical rotator wave plate form an angle of 45°; The wave plate coincides with the fast axis of the analyzer; The polarization beam splitter is tilted to the left at an angle of 45°; 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 optical rotator.

2. The pumping light power control device of the 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 of the pumping light power control device of the high-performance atomic sensor for inertial measurement according to claim 1 is specifically designed as follows: Step 1, the laser emits laser light, and after passing through the polarizer, the linear polarization direction of the laser light is 45° with the fast axis of the liquid crystal rotator; Step 2: adjusting the driving voltage of the liquid crystal optical rotator so that the linear polarization direction of the laser emitted after passing through the liquid crystal optical rotator rotates by a corresponding angle; Step 3: The laser passes through the analyzer and enters the polarization beam splitter, so that the laser is divided into two paths, a main path laser and a bypass monitoring laser; The bypassed monitoring laser is received by a second photodetector as an input to a controller; After the main path laser passes through the wave plate, the main path laser is converted from linearly polarized light to circularly polarized light, enters the gas chamber as pumping light, and is received by the first photodetector for calculating the adaptive parameters of the controller; Step 4: The controller outputs a driving voltage to the liquid crystal optical rotator according to the calculation, so as to achieve stable control of the laser power after the laser passes through the analyzer.

4. The pumping light power control device of the 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 derivative of the controlled system φ(k)=[φ1(k),φ2(k),φ3(k),φ4(k)] T , using pseudo partial derivative φ(k) to estimate the parameters of the controlled system; English: 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)|≤bu(k)-u(k-1|; in: The input of the controlled system is: the current driving voltage amplitude of the liquid crystal optical rotator, denoted as u(k); that is, the driving voltage of the liquid crystal optical 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, recorded as y(k); The output signal of the controlled system at the next moment is denoted as y(k+1); The pumping light power after passing through the gas chamber received by the second photodetector is denoted as y1(k), The expected monitoring laser power is set as y d (k+1); ② The calculation steps of the controller output signal u(k) are as follows: a. Solve the pseudo partial derivative φ(k); in: μ: parameter estimation weight factor, a constant; η i : It is to control the step size coefficient of the additional parameter estimation for more flexibility. η i ∈(0,2), compensate for the drift error of liquid crystal parameters; 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, and is taken as: Compensating for the splitting ratio error, the difference in the amplitude of the driving voltage u(k) can characterize the change in the phase delay of the liquid crystal, taking: b. Calculate u(k) using pseudo partial derivative φ(k); in: λ: is the control input weight factor, which affects the stability of the controlled system; ρ∈(0,1], is the step coefficient of the additional control input, λ and ρ are constants; to ensure the stability of the system, λ, ρ, and b satisfy

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