Laser power stability control method based on active liquid crystal polarization grating

Abstract

A laser power stability control method based on an active liquid crystal polarization grating is characterized in that diffraction characteristics of the active liquid crystal polarization grating are combined with a precision temperature control system, a voltage-diffraction efficiency physical model of the active liquid crystal polarization grating is firstly established, and the model fully considers nonlinear characteristics and temperature dependence of a liquid crystal material; and then a nonlinear controller based on the model is designed, and accurate and stable control over the laser power is achieved. The polarizer is arranged at the light output end of the main path, so that the polarization stability of output light is ensured. According to the method, model parameter identification can be carried out by adopting an intelligent optimization algorithm, accurate model parameters are obtained through a global optimization method, the problems that a traditional liquid crystal device is low in response speed and high in temperature sensitivity are effectively solved, a high-stability laser light source is provided for the field of quantum precision measurement, and the method has important application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum precision measurement, in particular to a laser power stability control method based on an active liquid crystal polarization grating, which is used for detecting and controlling the power stability of laser in an atomic spin inertial measurement device, can effectively improve the measurement accuracy and system stability, and can also be applied to other precision measurement systems that require high stability laser sources, such as atomic clocks, quantum sensors and other high-precision measurement equipment. BACKGROUND

[0002] In an atomic spin inertial measurement device, the stability of laser power directly affects the measurement accuracy and reliability of the system. Atomic spin inertial measurement technology is based on atomic spin effect, which obtains inertial information by detecting the signal of laser-atom interaction. It has very high requirements for the power stability of laser source. Fluctuation of laser power will directly introduce measurement noise, reduce the signal-to-noise ratio of the system and measurement accuracy.

[0003] As a new type of optical control device, liquid crystal polarization grating adjusts the diffraction efficiency by controlling the orientation of liquid crystal molecules through voltage, providing a new solution for laser power stability. Compared with traditional light intensity modulator, liquid crystal polarization grating has the advantages of low driving voltage, low power consumption and easy integration. However, the existing liquid crystal polarization grating power stability system still has the following technical problems: the response speed of liquid crystal material is significantly affected by temperature. The viscosity of liquid crystal material is closely related to temperature. Temperature change will change the rotational viscosity of liquid crystal molecules, thereby affecting the response time constant of the system; the voltage-diffraction efficiency relationship of liquid crystal polarization grating has obvious nonlinear characteristics. This nonlinear characteristic makes it difficult for traditional PID controller to achieve precise control, and it is easy to have overshoot, oscillation and other problems. The existing system lacks a special physical model for the characteristics of liquid crystal polarization grating, and the control system design needs to establish an accurate physical model and design a special nonlinear controller.

[0004] In addition, the existing laser power stability system often ignores the influence of polarization stability on system performance. In atomic spin inertial measurement, not only the laser power stability is required, but also the polarization state of laser is strictly required. During the operation of active liquid crystal polarization grating, the adjustment of diffraction efficiency will be accompanied by the change of output light polarization state. This polarization fluctuation will affect the interaction efficiency of atoms and light, and then introduce measurement error. This limits its application in high-end measurement systems. SUMMARY

[0005] The technical problems to be solved by the present application are: in view of the demand for detecting and stabilizing the laser power in the atomic spin inertial measurement device, a laser power stabilizing control method based on an active liquid crystal polarization grating is provided, the stability of the laser power and the response speed of the system are improved through the integration of the temperature control system and the nonlinear feedback control, and the polarization stability of the output light is ensured through the post-polarizer.

[0006] The technical solution of the present application is as follows:

[0007] A laser power stabilizing control method based on an active liquid crystal polarization grating, characterized in that it comprises the following steps:

[0008] Step 1: For the active liquid crystal polarization grating located between the laser and the polarizer, a voltage-diffraction efficiency physical model is established according to the diffraction characteristics of the active liquid crystal polarization grating;

[0009] Step 2: A flexible non-magnetic electric heating film is attached to the surface of the active liquid crystal polarization grating, and a heating temperature control system of the active liquid crystal polarization grating is designed to control the time constant of the active liquid crystal polarization grating by controlling the temperature-dependent rotational viscosity of the liquid crystal material;

[0010] Step 3: A nonlinear controller is designed based on the voltage-diffraction efficiency physical model to convert the nonlinear system into an equivalent linear system by compensation;

[0011] Step 4: The output light of the active liquid crystal polarization grating is split into main path light and secondary path light, the secondary path light is used for laser power monitoring and feedback control, and the main path light is polarized filtered through the polarizer to obtain light path output light with polarization stability.

[0012] In step 1, the output feedback end of the active liquid crystal polarization grating is connected to the negative input end of the second adder through a photodiode, the positive input end of the second adder is connected to the set input power, and the output end of the second adder is connected to the input end of the active liquid crystal polarization grating through a nonlinear controller.

[0013] In step 2, the flexible non-magnetic electric heating film is connected to the negative input end of the first adder through a platinum resistance, the positive input end of the first adder inputs the set temperature, and the output end of the first adder is connected to the flexible non-magnetic electric heating film through a PID controller and a heating film driver in sequence.

[0014] The expression of the voltage-diffraction efficiency physical model in step 1 is as follows:

[0015]

[0016] wherein P is laser power, t is time, tau is a time constant of the active liquid crystal polarization grating, the liquid crystal material rotation viscosity is related to temperature, g is a gain coefficient, u is a control voltage, s is a saturation coefficient, c is a damping coefficient, and cP is a damping term reflecting the inherent energy dissipation mechanism of the system.

[0017] The expression of the nonlinear controller in step 3 is as follows:

[0018]

[0019] wherein u is the nonlinear controller to be designed, k is a saturation characteristic coefficient, x is a state variable related to the laser power P, a is an intermediate quantity, a = c / tau, K is a controller parameter, e is a laser power error signal, b is an intermediate quantity, and b = g / tau.

[0020] The main path light in step 4 is +1 order diffracted light generated by the active liquid crystal polarization grating, and the main path light enters the atomic cell after passing through the polarizer, and the secondary path light is -1 order diffracted light generated by the active liquid crystal polarization grating.

[0021] The polarizer uses a high extinction ratio polarizing prism or a thin film polarizer, and the extinction ratio is better than 30dB, and the insertion loss is less than 0.2dB.

[0022] The technical effects of the present application are as follows: the laser power stabilization control method based on the active liquid crystal polarization grating is a kind of active liquid crystal polarization grating power stabilization scheme integrating temperature control and nonlinear feedback, which takes the detection laser of the atomic spin inertial measurement device as the control object and aims at the laser power stabilization control demand. The present application combines the diffraction characteristics of the active liquid crystal polarization grating with the precise temperature control system, first establishes a voltage-diffraction efficiency physical model of the active liquid crystal polarization grating, which fully considers the nonlinear characteristics and temperature dependence of the liquid crystal material; then designs a nonlinear controller based on the model, realizing accurate and stable control of the laser power. The present application sets a polarizer at the output end of the main path light to ensure the polarization stability of the output light. The present application is conducive to model parameter identification using intelligent optimization algorithm, and accurate model parameters are obtained through global optimization method, effectively solving the problems of slow response speed and high temperature sensitivity of traditional liquid crystal devices, providing a high-stability laser light source for the field of quantum precision measurement, and having important application value.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) The present application first applies the active liquid crystal polarization grating to the laser power stabilization system, and uses the voltage control diffraction efficiency characteristics to realize power regulation, which has the advantages of low driving voltage, low power consumption and high integration compared with traditional schemes.

[0025] (2) This invention establishes a physical model specifically for active liquid crystal polarization gratings, accurately describing their dynamic characteristics and laying a theoretical foundation for the design of high-performance controllers. The model considers multiple physical factors such as temperature effects, nonlinear characteristics, and energy dissipation, and has high prediction accuracy.

[0026] (3) This invention integrates a precision temperature control system, which effectively overcomes the influence of temperature on the performance of liquid crystal materials. The temperature control system adopts a multi-sensor fusion and zone control strategy to ensure the stability of the system under various environmental conditions.

[0027] (4) This invention designs a nonlinear controller based on a physical model, which overcomes the nonlinear characteristics of the system and improves the control accuracy. The controller adopts feedback linearization technology to globally compensate for the nonlinearity of the system, and realizes a fast and overshoot-free dynamic response.

[0028] (5) The present invention adopts a diffraction spectral dispersion scheme to achieve non-invasive power monitoring without affecting the main measurement optical path. The monitoring system has the characteristics of high precision and high stability, providing a reliable feedback signal for closed-loop control.

[0029] (6) The present invention sets a polarizer at the output end of the main path light, which effectively solves the problem of polarization state change during the operation of the active liquid crystal polarization grating, ensuring that the output light has stable polarization characteristics and meeting the strict requirements of atomic spin inertial measurement and other applications for the polarization stability of the light source.

[0030] (7) This invention uses the differential evolution algorithm for model parameter identification, which has better global search capability and convergence performance. The algorithm adopts an adaptive parameter adjustment strategy, which improves computational efficiency while ensuring optimization accuracy.

[0031] (8) This invention adopts a modular design, which has good scalability and maintainability. It is easy to deploy and maintain in practical applications. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the laser optical path system structure involved in the laser power stabilization control method based on an active liquid crystal polarization grating of the present invention. Figure 1 1 is the laser, 2 is the optical power stabilization controller, 3 is the liquid crystal heating controller, 4 is the platinum resistance thermometer, 5 is the flexible non-magnetic electric heating film, and 6 is the optical path output light.

[0033] Figure 2 yes Figure 1 A schematic diagram of the structure and principle of the optical power stabilization controller. Figure 2 China P setHere, + represents the positive input of the adder, - represents the negative input, e represents the output of the adder or the power error (transmitted to the nonlinear controller), u represents the output voltage of the nonlinear controller, u is transmitted as the control voltage to the active liquid crystal polarization grating (LCPG), and P represents the actual output power of the active liquid crystal polarization grating. set The input is given to the + terminal of the adder, and P is fed back to the - terminal of the adder.

[0034] Figure 3 This is a schematic diagram illustrating the structural principle of the dual-loop control of temperature and laser power involved in implementing the laser power stabilization control method based on an active liquid crystal polarization grating of the present invention. Figure 3 The system includes two parallel closed-loop feedback control loops: an upper temperature stabilization control loop and a lower laser power stabilization control loop. The temperature stabilization control loop comprises a PID (proportional-integral-derivative) controller, a heating film driver, and a non-magnetic heating film connected in sequence. The input of the PID controller is connected to the output of the first adder (outputting the temperature error signal e). The non-magnetic heating film acts as the actuator. The platinum resistance thermometer is connected to the negative input (-) of the first adder, and the positive input (+) of the first adder receives the set temperature Tset. The laser power stabilization control loop comprises a nonlinear controller, a driver circuit, and an active LCPG connected in sequence. The active LCPG is connected to the negative input (-) of the second adder via a photodiode, and the positive input (+) of the second adder receives the set power P. set The main output of the active LCPG is connected to the atomic gas cell via a polarizer. The temperature stabilization control loop provides a constant thermal environment for the laser power stabilization control loop, ensuring that the physical model parameters of the active LCPG (LCPG is a liquid crystal polarization grating) remain constant, thereby ensuring that the nonlinear controller can work stably for a long time. The two work together to achieve high-precision and high-stability laser output. Detailed Implementation

[0035] The following is in conjunction with the attached diagram ( Figures 1-3 The present invention will be described in conjunction with the embodiments.

[0036] Figure 1 This is a schematic diagram of the laser optical path system structure involved in the laser power stabilization control method based on an active liquid crystal polarization grating of the present invention. Figure 2 yes Figure 1 A schematic diagram of the structure and principle of the optical power stabilization controller. Figure 3 This is a schematic diagram illustrating the structural principle of the dual-loop control of temperature and laser power involved in implementing the laser power stabilization control method based on an active liquid crystal polarization grating according to the present invention. (Reference) Figures 1 to 3As shown, a laser power stabilization control method based on an active liquid crystal polarization grating includes the following steps: Step 1, for the active liquid crystal polarization grating located between the laser and the polarizer, a voltage-diffraction efficiency physical model is established based on the diffraction characteristics of the active liquid crystal polarization grating; Step 2, a flexible non-magnetic electric heating film is attached to the surface of the active liquid crystal polarization grating, and a heating temperature control system for the active liquid crystal polarization grating is designed to control the time constant of the active liquid crystal polarization grating by controlling the rotational viscosity of the liquid crystal material related to temperature; Step 3, a nonlinear controller is designed based on the voltage-diffraction efficiency physical model to transform the nonlinear system into an equivalent linear system through compensation; Step 4, the output light of the active liquid crystal polarization grating is split into a main path light and a secondary path light. The secondary path light is used for laser power monitoring and feedback control, and the main path light is polarized filtered by the polarizer to obtain a polarization-stable output light.

[0037] In step 1, the output feedback terminal of the active liquid crystal polarization grating is connected to the negative input terminal of the second adder via a photodiode. The positive input terminal of the second adder is connected to a set input power, and the output terminal of the second adder is connected to the input terminal of the active liquid crystal polarization grating via a nonlinear controller. In step 2, the flexible non-magnetic electric heating film is connected to the negative input terminal of the first adder via a platinum resistance thermometer. The positive input terminal of the first adder is connected to a set temperature, and the output terminal of the first adder is connected to the flexible non-magnetic electric heating film via a PID controller and a heating film drive.

[0038] The expression for the voltage-diffraction efficiency physical model in step 1 is as follows:

[0039]

[0040] Where P is the laser power, t is the time, τ is the time constant of the active liquid crystal polarization grating, τ is related to the rotational viscosity of the liquid crystal material, the rotational viscosity of the liquid crystal material is related to the temperature, g is the gain coefficient, u is the control voltage, s is the saturation coefficient, c is the damping coefficient, and cP is the damping term reflecting the inherent energy dissipation mechanism of the system.

[0041] The expression for the nonlinear controller in step 3 is as follows:

[0042]

[0043] Where u is the nonlinear controller to be designed, k is the saturation characteristic coefficient, x is the state variable related to the laser power P, a is an intermediate quantity, a=c / τ, K is the controller parameter, e is the laser power error signal, and b is an intermediate quantity, b=g / τ.

[0044] In step 4, the main path light is the +1st order diffracted light generated by an active liquid crystal polarization grating. This main path light enters the atomic gas cell after passing through a polarizer. The secondary path light is the -1st order diffracted light generated by an active liquid crystal polarization grating. The polarizer employs a high extinction ratio polarizing prism or a thin-film polarizer, with an extinction ratio better than 30dB and an insertion loss less than 0.2dB.

[0045] A laser power stabilization control method based on an active liquid crystal polarization grating includes the following steps:

[0046] (1) Establish a voltage-diffraction efficiency physical model based on the diffraction characteristics of an active liquid crystal polarization grating;

[0047] (2) Design a heating temperature control system for an active liquid crystal polarization grating;

[0048] (3) Design a nonlinear controller based on the constructed physical model;

[0049] (4) The main path light is polarized and filtered by a polarizer to ensure the polarization stability of the output light.

[0050] The physical model established in step (1) is as follows:

[0051]

[0052] Where P is the laser power, τ is the time constant of the liquid crystal polarization grating, g is the gain coefficient, u is the control voltage, s is the saturation coefficient, and c is the damping coefficient.

[0053] The model fully considers the physical characteristics of active liquid crystal polarization gratings: the reorientation process of liquid crystal molecules under the action of an electric field has saturated nonlinear characteristics, and the molecular orientation change gradually saturates as the electric field strength increases; the damping term cP reflects the inherent energy dissipation mechanism of the system; the time constant τ characterizes the response speed of the system and is closely related to the viscosity of the liquid crystal material.

[0054] The model is based on in-depth analysis of the physical mechanism. First, through theoretical analysis of the orientation process of liquid crystal molecules in an electric field, we determined that saturation nonlinearity is the most important nonlinear characteristic of the system. This nonlinearity originates from the saturation of the order parameters of the liquid crystal molecules; that is, when the electric field strength reaches a certain value, the orientation degree of the liquid crystal molecules tends to saturate, and further increasing the electric field strength has a gradually decreasing effect on molecular orientation. Mathematically, this physical mechanism is represented by the (1+sP) term in the denominator, where the saturation coefficient s reflects the nonlinear intensity of the system.

[0055] Secondly, the introduction of the damping term cP is based on energy conservation considerations. During the reorientation of liquid crystal molecules, some electrical energy is converted into heat energy and dissipated. This dissipation effect is related to the instantaneous state of the system. Unlike traditional velocity damping, state damping can more accurately describe the energy dissipation mechanism in liquid crystal materials, especially under high-frequency operating conditions.

[0056] The time constant τ is one of the most critical parameters in the model. It is closely related to the rotational viscosity γ1 of the liquid crystal material, the elastic constant K, and the cell thickness d of the device structure, specifically, τ∝γ1d² / K. This relationship indicates that the system's time constant can be effectively adjusted by optimizing the liquid crystal material formulation and device structure. Particularly important is that the rotational viscosity γ1 satisfies γ1∝exp(E / T). a / RT), where E a Let R be the activation energy and R be the gas constant. This temperature dependence explains why temperature control is crucial to system performance.

[0057] For model parameter identification, we adopted a multi-experimental-condition combination strategy. We collected dynamic response data of the system at different temperatures and operating points, and obtained accurate model parameters through a global optimization algorithm.

[0058] Step (2) involves designing an active liquid crystal polarization grating heating temperature control scheme, which is based on a complete control logic of temperature-viscosity-response speed-system stability:

[0059] The rotational viscosity γ1 of the liquid crystal material and the temperature T satisfy the Arrhenius relation: γ1 = γ0 * exp(E a / RT), where γ0 is the initial viscosity, E a Let R be the activation energy and γ be the gas constant. The system's response time constant τ is directly proportional to the viscosity γ1: τ∝γ1. Changes in the response time τ directly affect the phase margin and bandwidth of the control system, thereby affecting the system's stability and dynamic performance.

[0060] Based on this physical mechanism, this invention employs a platinum resistance thermometer as a temperature sensor and a flexible, non-magnetic electric heating film as a heating actuator, achieving precise temperature stabilization through an improved PID control algorithm. By stabilizing the temperature, the viscosity of the liquid crystal material is stabilized, thereby ensuring consistent system response speed and providing a reliable hardware foundation for stable power control.

[0061] The flexible, non-magnetic electric heating film uses polyimide as its substrate and constantan alloy as its heating element. This material boasts a low temperature coefficient and excellent stability. With a thickness of only 0.2 mm, the heating film can be tightly bonded to the surface of a liquid crystal polarizing grating, ensuring efficient heat conduction. The heating film employs a zoned design, allowing independent control of the heating power in different areas, thus achieving precise temperature field regulation.

[0062] The nonlinear controller design process in step (3) includes:

[0063] Step 1) Convert the physical model into state-space form:

[0064]

[0065] Where x is the state variable, corresponding to the laser power P, u is the controller to be designed, a=c / τ is the damping coefficient of the system, b=g / τ is the gain coefficient, and k=s is the saturation characteristic coefficient.

[0066] Step 2) Accurately identify the model parameters a, b, and k through step response experiments and differential evolution algorithm;

[0067] Step 3) Design a nonlinear controller based on an accurate model:

[0068]

[0069] Where K represents the controller parameters and e represents the power error signal;

[0070] Step 4) Burn the controller program to the power control circuit board to achieve real-time stable power control.

[0071] The design of nonlinear controllers is based on feedback linearization theory. By introducing a nonlinear compensation term (1+kx), the original nonlinear system is transformed into an equivalent linear system, allowing the application of mature linear control theory in controller design. The advantage of this method is its ability to globally compensate for the nonlinear characteristics of the system, unlike traditional PID controllers which can only achieve approximate linearization near local operating points.

[0072] The stability analysis of the controller employs the Lyapunov direct method. The Lyapunov function V = ½e² is constructed, where e = P. set -P represents the power error signal. V=0 if and only if e=0, and V>0 at all other times. By analyzing the negative definiteness of the time derivative, it can be proven that the closed-loop system is globally asymptotically stable under appropriate selection of controller parameters K. This theoretical guarantee ensures the reliability of the system under various operating conditions.

[0073] Employing a unique diffraction-based beam splitting scheme, the +1st order diffracted light generated by the active liquid crystal polarization grating serves as the main path light, entering the atomic gas cell after passing through a polarizer. The -1st order diffracted light is used for power monitoring and feedback control. The transmission axis of the polarizer is aligned with the desired output polarization direction of the system, ensuring that regardless of the dynamic changes in the polarization state caused by voltage adjustment of the active liquid crystal polarization grating, the output light is always linearly polarized light with a fixed polarization direction and a high extinction ratio.

[0074] The diffraction-based beam splitting scheme is based on the physical properties of a liquid crystal polarization grating. When linearly polarized light is incident at a specific angle, the liquid crystal polarization grating generates multiple diffraction orders, with the 0th and ±1st orders being the dominant diffracted beams. By optimizing the grating parameters, the +1st order diffracted beam can achieve high diffraction efficiency (typically >90%) while maintaining excellent polarization characteristics.

[0075] The selection of the polarizer is crucial to ensuring polarization stability. This invention employs a Glan-Taylor prism as the polarizer, which features a high extinction ratio (better than 30 dB), low insertion loss (less than 0.2 dB), and a high laser damage threshold. The polarizer is mounted on a precision rotating frame, allowing for fine adjustments to ensure that its transmission axis is precisely aligned with the desired polarization direction of the system.

[0076] The polarizer operates based on the principle of polarization-selective absorption. When a light beam from a liquid crystal polarizing grating passes through the polarizer, only the component whose polarization direction is aligned with the polarizer's transmission axis can pass through; components with other polarization directions are absorbed or reflected. This mechanism ensures that regardless of the polarization state of the incident light, the outgoing light is always linearly polarized, and the polarization direction is determined by the polarizer's transmission axis.

[0077] A laser power stabilization control method based on an active liquid crystal polarization grating includes a laser, an active liquid crystal polarization grating, a temperature control system, a detection photodiode, a polarizer, and a control system. The system adopts a modular design, with each functional module relatively independent and connected via standard interfaces, exhibiting good interchangeability and expandability.

[0078] A distributed feedback (DFB) semiconductor laser is selected as the laser source, and the output power is initially stabilized by a built-in photodiode. The active liquid crystal polarization grating is the core component of the system, and its parameters have been carefully optimized. The grating period is 70 μm, the cell thickness is 7 μm, and it is arranged in a parallel orientation. The temperature control system consists of a platinum resistance thermometer (PT1000), a flexible non-magnetic electric heating film, and a temperature control circuit board. The PT1000 is installed at the four corners and one center of the liquid crystal polarization grating, and the average temperature is obtained through five-point measurements. The heating film is divided into four independently controlled areas, and the heating power of each area can be independently adjusted according to the temperature measurement value at the corresponding location to ensure the uniformity of the temperature field. The temperature control circuit board uses an STM32F103 microcontroller as its core, employs a 24-bit analog-to-digital converter (ADC) for temperature signal acquisition, and a 16-bit digital-to-analog converter (DAC) to output the control signal, with a temperature control update rate of 100Hz. The power monitoring system uses a silicon photodiode. The polarizer uses a Glan-Taylor prism with an extinction ratio better than 30 dB and an insertion loss of less than 0.2 dB. The polarizer is mounted on a precision rotating frame, and its transmission axis can be precisely aligned with the desired polarization direction of the system through fine adjustments. The polarizer is installed in the +1st order diffraction path of the active liquid crystal polarization grating, located before entering the atomic gas cell.

[0079] The overall system structure is as follows Figure 1 As shown: The laser (1) serves as the light source, and its emitted light is divided into +1 and -1 order diffracted light after passing through the active liquid crystal polarization grating. The +1 order diffracted light serves as the main path light, which passes through the polarizer to form the output light (6) and then enters the atomic gas cell. The -1 order diffracted light is used for power monitoring. The optical power stabilization controller (2) adjusts the driving voltage of the active liquid crystal polarization grating according to the monitoring signal to achieve stable power control. The liquid crystal heating controller (3) achieves temperature control through a platinum resistance thermometer (4) and a flexible non-magnetic electric heating film (5).

[0080] The specific implementation steps are as follows:

[0081] 1. Establish a physical model for the voltage-diffraction efficiency of an active liquid crystal polarization grating:

[0082]

[0083] The model was designed to identify precise model parameters through step response experiments and differential evolution algorithms. Experiments were conducted at multiple temperature points (15℃, 25℃, 35℃, and 45℃), with 10 sets of step response data of different amplitudes collected at each temperature point. The differential evolution algorithm employed an adaptive parameter adjustment strategy, with a population size of 50 and a maximum number of generations of 200. Multiple independent runs were conducted to ensure the reliability of the results.

[0084] 2. Based on the cascading relationship of temperature, viscosity, and response speed: Temperature change → Liquid crystal viscosity change → Response speed change → Decreased system stability. A temperature control system was designed and implemented to indirectly stabilize the system's dynamic characteristics by stabilizing the temperature. An improved PID control algorithm was used to stabilize the temperature of the active liquid crystal polarization grating at the set value, reducing the impact of temperature fluctuations on system performance. The temperature control system was first tested under open-loop conditions, measuring the system's step response and frequency response, and the PID parameters were tuned based on the test results.

[0085] 3. Design of nonlinear controllers based on accurate physical models:

[0086]

[0087] The controller program is burned into the power control circuit board to achieve real-time and precise control of laser power.

[0088] 4. The system monitors the power change of the -1st order diffracted light and adjusts the driving voltage of the active liquid crystal polarization grating in real time to change the power of the +1st order diffracted light, thereby stabilizing the main path light power. The +1st order diffracted light enters the atomic gas cell after passing through the polarizer, which ensures the polarization stability of the output light.

[0089] This invention achieves high-precision and stable control of laser power and polarization by organically combining the voltage control characteristics of an active liquid crystal polarization grating, a precision temperature control system, a physical model-based nonlinear controller, and a post-polarizer, providing a reliable laser source for atomic spin inertial measurement devices. The successful development of this system demonstrates the effectiveness of the physical model-based design method in optical control systems and provides a valuable reference for similar applications.

[0090] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A laser power stabilization control method based on an active liquid crystal polarization grating, characterized in that, Includes the following steps: Step 1: For the active liquid crystal polarization grating located between the laser and the polarizer, establish a voltage-diffraction efficiency physical model based on the diffraction characteristics of the active liquid crystal polarization grating. Step 2: A flexible non-magnetic electric heating film is attached to the surface of the active liquid crystal polarization grating, and a heating temperature control system for the active liquid crystal polarization grating is designed to control the time constant of the active liquid crystal polarization grating by controlling the rotational viscosity of the liquid crystal material which is related to temperature. Step 3: Design a nonlinear controller based on the voltage-diffraction efficiency physical model to transform the nonlinear system into an equivalent linear system through compensation. Step 4: The output light of the active liquid crystal polarization grating is split into a main path light and a secondary path light. The secondary path light is used for laser power monitoring and feedback control. The main path light is polarized and filtered by a polarizer to obtain polarization-stable output light.

2. The laser power stabilization control method based on an active liquid crystal polarization grating according to claim 1, characterized in that, In step 1, the output feedback terminal of the active liquid crystal polarization grating is connected to the negative input terminal of the second adder through a photodiode. The positive input terminal of the second adder is connected to a set input power. The output terminal of the second adder is connected to the input terminal of the active liquid crystal polarization grating through a nonlinear controller.

3. The laser power stabilization control method based on an active liquid crystal polarization grating according to claim 1, characterized in that, In step 2, the flexible non-magnetic electric heating film is connected to the negative input terminal of the first adder through a platinum resistance thermometer. The set temperature is input to the positive input terminal of the first adder. The output terminal of the first adder is connected to the flexible non-magnetic electric heating film through a PID controller and a heating film drive in sequence.

4. The laser power stabilization control method based on an active liquid crystal polarization grating according to claim 1, characterized in that, The expression for the voltage-diffraction efficiency physical model in step 1 is as follows: Where P is the laser power, t is the time, τ is the time constant of the active liquid crystal polarization grating, τ is related to the rotational viscosity of the liquid crystal material, the rotational viscosity of the liquid crystal material is related to the temperature, g is the gain coefficient, u is the control voltage, s is the saturation coefficient, c is the damping coefficient, and cP is the damping term reflecting the inherent energy dissipation mechanism of the system.

5. The laser power stabilization control method based on an active liquid crystal polarization grating according to claim 1, characterized in that, The expression for the nonlinear controller in step 3 is as follows: Where u is the nonlinear controller to be designed, k is the saturation characteristic coefficient, x is the state variable related to the laser power P, a is an intermediate quantity, a=c / τ, K is the controller parameter, e is the laser power error signal, and b is an intermediate quantity, b=g / τ.

6. The laser power stabilization control method based on an active liquid crystal polarization grating according to claim 1, characterized in that, In step 4, the main path light is the +1st order diffraction light generated by an active liquid crystal polarization grating. The main path light enters the atomic gas cell after passing through a polarizer, and the secondary path light is the -1st order diffraction light generated by an active liquid crystal polarization grating.

7. The laser power stabilization control method based on an active liquid crystal polarization grating according to claim 1, characterized in that, The polarizer uses a high extinction ratio polarizing prism or thin-film polarizer with an extinction ratio better than 30dB and an insertion loss of less than 0.2dB.

Images