Optical rotation angle modulation detection and zero-point closed-loop system of SERF inertial measurement device based on LCVR

Abstract

The invention discloses an optical rotation angle modulation detection and zero point closed-loop system for a SERF inertial measurement device based on LCVR. The system comprises a detection zero point closed-loop control module respectively connected to an output end of a balanced differential detector and an input end of a signal generator. The output end of the signal generator is connected to a second liquid crystal phase retarder as an actuator to adjust the optical rotation angle of its linearly polarized light. The balanced differential detector is connected to the linearly polarized light output end of the second liquid crystal phase retarder via a photodetector, a Wollaston polarization beam splitter and a quarter wave plate in sequence. The system can effectively suppress low-frequency random noise of the detection system, and can make the SERF atomic spin inertial measurement device work at the detection zero point in real time, thereby improving the optical rotation angle detection accuracy, and improving the signal-to-noise ratio and long-term stability of the output signal of the atomic spin inertial measurement device.

Description

Technical Field

[0001] The invention relates to an atomic spin inertial measurement device, in particular to an optical rotation angle modulation detection and zero point closed loop system of a SERF inertial measurement device based on LCVR. By setting a detection zero point closed loop control module connected to a balanced differential detector output end and a signal generator input end respectively, the signal generator output end is connected to a second liquid crystal phase retarder as an actuator to adjust its linear polarization light optical rotation angle, and the balanced differential detector is connected to the linear polarization light output end of the second liquid crystal phase retarder through a photoelectric detector, a Wollaston polarization beam splitter prism and a quarter wave plate in sequence, which can effectively suppress the low-frequency random noise of the detection system, and can make the SERF atomic spin inertial measurement device work at the detection zero point in real time, improve the optical rotation angle detection accuracy, and improve the signal-to-noise ratio and long-term stability of the output signal of the atomic spin inertial measurement device. LCVR is a liquid crystal variable phase retarder. SERF is spin-exchange relaxation-free. Background Art

[0002] The SERF atomic spin inertial measurement device (SERF, Spin-Exchange-Relaxation-Free) based on spin-exchange relaxation-free technology is a new type of inertial measurement device that uses the atomic spin ensemble to sense angular velocity. It uses the coupled precession characteristics of the alkali metal electron spin and the inert gas nuclear spin in the gas chamber under the inertial torque in an extremely weak magnetic field to make the inert gas nuclear spin sensitive to angular velocity changes, thereby achieving high-precision measurement of angular velocity signals. The current detection system of the SERF atomic spin inertial measurement device has problems such as low output signal-to-noise ratio and the detection system not working at the "detection zero point" of the system. Factors such as the system's own low-frequency random noise lead to a low signal-to-noise ratio of the detection output signal; and factors such as optical component defects and long-term drift of the detection laser power make it difficult for the system to work at the detection zero point for a long time; in the process of optical rotation angle detection, these problems will deteriorate the measurement accuracy of the SERF atomic inertial device and affect the long-term stability of the output signal of the SERF inertial measurement device.

[0003] The existing methods for detecting the optical rotation angle include PBS balanced differential DC detection method (PBS, polarized beamsplitter, polarization beam splitter prism), photoelastic modulator PEM (Photoelastic Modulator), electro-optic modulator EOM (Electro-Optic Modulator), acousto-optical modulator AOM (Acousto-optical Modulators) and other AC detection methods. The PBS (polarization beam splitter, polarization beam splitter) balanced differential DC detection method has a simple structure and a small size, but cannot filter out low-frequency random noise, while the PEM, EOM, AOM and other AC detection methods have a complex structure and a large size, which is not conducive to the integration of the SERF atomic spin inertial measurement device, and the above methods cannot realize the system working at the "detection zero point" in real time. Summary of the invention

[0004] The problem solved by the present invention is to overcome the problem that the low-frequency random noise of the detection system of the existing SERF atomic spin inertial measurement device interferes with the output of the detection signal, and the detection system is difficult to work at the "detection zero point" for a long time. The purpose of the present invention is to propose a SERF inertial measurement device optical rotation angle modulation detection and zero point closed-loop system based on LCVR, by setting a detection zero point closed-loop control module connected to the output end of the balanced differential detector and the input end of the signal generator respectively, the output end of the signal generator is connected to the second liquid crystal phase retarder as an actuator to adjust its linear polarization light optical rotation angle, the balanced differential detector is connected to the linear polarization light output end of the second liquid crystal phase retarder through a photoelectric detector, a Wollaston polarization beam splitter and a 1 / 4 wave plate in turn, which can effectively suppress the low-frequency random noise of the detection system, and can make the SERF atomic spin inertial measurement device work at the detection zero point in real time, improve the optical rotation angle detection accuracy, and improve the signal-to-noise ratio and long-term stability of the output signal of the atomic spin inertial measurement device.

[0005] The technical solution of the present invention is as follows:

[0006] The optical rotation angle modulation detection and zero-point closed-loop system of a SERF inertial measurement device based on LCVR is characterized in that it includes a detection zero-point closed-loop control module respectively connected to the output end of a balanced differential detector and the input end of a signal generator, the output end of the signal generator is connected to a second liquid crystal phase retarder as an actuator to adjust the optical rotation angle of its linearly polarized light, the balanced differential detector is connected to the vertical linear polarized light output end of a Wollaston polarization beam splitter prism through a second photodetector, and is connected to the horizontal linear polarized light output end of the Wollaston polarization beam splitter prism through a third photodetector, the Wollaston polarization beam splitter prism is connected to the linear polarized light output end of the second liquid crystal phase retarder through a 1 / 4 wave plate, and the second liquid crystal phase retarder is connected to the alkali metal gas chamber optical path.

[0007] The output end of the balanced differential detector is connected to the first input end of the phase-locked amplifier, the second input end of the phase-locked amplifier is connected to the reference signal input end of the signal generator, and the output end of the phase-locked amplifier is connected to the host computer.

[0008] The alkali metal gas chamber is connected to the detection laser through the second Glan prism, the second 1 / 2 wave plate, the first liquid crystal phase retarder, the first Glan prism and the first 1 / 2 wave plate in sequence; the second Glan prism is connected to the input end of the laser power stabilization control module through the first photodetector; and the output end of the laser power stabilization control module is connected to the first liquid crystal phase retarder.

[0009] The zero point detection closed-loop control module includes a node, a controller and a signal detection module. The node has a positive input terminal of a detection signal set value associated with an expected detection zero point, the negative input terminal of the node is connected to the signal detection module to receive a current value of the detection signal, the output terminal of the node is connected to the controller, the controller is connected to the input terminal of the signal generator receiving an AC signal input, and the input terminal of the signal detection module is connected to the output terminal of the balanced differential detector.

[0010] The Mueller matrix M corresponding to the second liquid crystal phase retarder LCVR for:

[0011]

[0012] In formula (1), δ is the variable phase retardation of the liquid crystal phase retarder;

[0013] The Mueller matrix M corresponding to the 1 / 4 wave plate 1 / 4 for:

[0014]

[0015] In physics, the linearly polarized light with intensity I and angle α with the horizontal axis has the corresponding Stokes matrix S L for:

[0016]

[0017] In physics, the light intensity is I, and the linear polarized light along the horizontal incidence has the corresponding Stokes matrix S i Expressed as:

[0018]

[0019] The Stokes matrix S corresponding to the outgoing polarized light passing through the second liquid crystal phase retarder and the 1 / 4 wave plate is o for:

[0020]

[0021] By combining equations (3) and (5) and setting the corresponding terms equal, we can know that -δ = 2α. It can be seen that the polarized light emitted at this time is linearly polarized light, and the phase delay δ has a linear relationship with the rotation angle α of the linear polarized light emitted from the gas chamber. The rotation angle α can be controlled by the phase delay δ, that is, the polarization direction of the linear polarized light can be controlled to be at the "detection zero point".

[0022] By changing the control voltage V of the second liquid crystal phase retarder LCVR to adjust the magnitude of the LCVR phase delay δ,

[0023] The relationship between the control voltage V and the phase delay δ is expressed as:

[0024]

[0025] In formula (6), δ0 is the maximum phase retardation of the liquid crystal phase retarder, V C is the threshold voltage at which the liquid crystal molecules begin to deflect, e is a natural constant, V0 and M are the characteristic parameters of the liquid crystal, δ0 = 4.7427 rad, V C =0.9234V, V0=1.8442V, M=0.4583.

[0026] The angle between the fast axis and the horizontal axis of the second liquid crystal phase retarder is 45°. The detection zero point closed-loop control module collects the detection output signal of the balanced differential detector through an AD converter, applies an incremental PID calculated control signal, and controls the phase delay amount of the second liquid crystal phase retarder.

[0027] The signal generator modulates the output control signal into a sinusoidal driving signal to drive the second liquid crystal phase retarder so that the detection signal is compensated to a zero point.

[0028] The signal generator applies a sinusoidal driving signal with a frequency of ω=780 Hz to the second liquid crystal phase retarder, replacing the traditional rectangular wave voltage driving method, and performs high-frequency modulation on the direction of linear polarized light.

[0029] The lock-in amplifier demodulates the collected signal of the balanced differential detector, removes the low-frequency random noise of the detection system, and sends the detected optical rotation angle signal to the host computer to improve the measurement accuracy of the SERF atomic spin inertial measurement device.

[0030] The technical effects of the present invention are as follows: The present invention is based on the LCVR-based SERF inertial measurement device optical rotation angle modulation detection and zero point closed-loop system. Through the combination of LCVR and specific optical devices, the polarization light rotation angle of the output alkali metal gas chamber is controlled by changing the LCVR control voltage, and a signal generator is added on this basis to modulate the optical rotation angle, thereby realizing high-precision detection of the optical rotation angle of the atomic spin inertial measurement device and real-time "detection zero point" precise closed-loop control, effectively suppressing random errors caused by factors such as optical path placement defects, long-term drift of detection laser power, and low-frequency random noise of the detection system, and improving the optical rotation angle detection accuracy, thereby effectively improving the signal-to-noise ratio and long-term stability of the output signal of the atomic spin inertial measurement device, and can be used as a closed-loop solution for an atomic spin inertial measurement device. The present invention belongs to a new type of "detection zero point" closed-loop control device and method, which can be widely used in inertial navigation, attitude determination, and orientation systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a schematic diagram of the structure of the optical rotation angle modulation detection and zero-point closed-loop system of the SERF inertial measurement device based on LCVR. LCVR is a liquid crystal variable retarder. SERF is spin-exchange relaxation-free.

[0032] Figure 2 is Figure 1 On this basis, the overall structural diagram of the detection laser optical path is supplemented.

[0033] Figure 3 yes Figure 1 or Figure 2 Schematic diagram of the principle of the zero-point detection closed-loop control structure involved.

[0034] The reference numerals are listed as follows: A1-detection laser; A2-first 1 / 2 wave plate; A3-first Glan prism; A4-first liquid crystal phase retarder or first LCVR; A5-second 1 / 2 wave plate; A6-second Glan prism; A7-first photodetector; A8-alkali metal gas chamber; A9-second liquid crystal phase retarder; A10-1 / 4 wave plate; A11-Wollaston polarization splitter prism; A12-balanced differential detector; A13-laser power stabilization control module; A14-detection zero point closed-loop control module; A15-second photodetector; A16-third photodetector; A17-signal generator; A18-phase-locked amplifier; A19-host computer (such as a laptop computer, etc.); REF-reference signal; Add-node (the detection signal set value Vs is used as the positive + signal, and the detection signal current value Vi is used as the negative - signal to realize the addition function). DETAILED DESCRIPTION

[0035] Below is the attached figure ( Figure 1-Figure 3 ) and Examples illustrate the present invention.

[0036] Figure 1 It is a structural schematic diagram of the optical rotation angle modulation detection and zero point closed loop system of the SERF inertial measurement device based on LCVR of the present invention. Figure 2 is Figure 1 On this basis, the overall structural diagram of the detection laser optical path is supplemented. Figure 3 yes Figure 1 or Figure 2 Schematic diagram of the principle of the zero-point detection closed-loop control structure involved in the reference Figures 1 to 3As shown, the optical rotation angle modulation detection and zero point closed-loop system of the SERF inertial measurement device based on LCVR is characterized in that it is arranged on the detection laser optical path, and the detection laser optical path includes a detection laser A1, a first 1 / 2 wave plate A2, a first Glan prism A3, a first liquid crystal phase retarder A4, a second 1 / 2 wave plate A5, a second Glan prism A6, a photodetector A7, an alkali metal gas chamber A8, a second liquid crystal phase retarder A9, a 1 / 4 wave plate A10, a Wollaston polarization beam splitter A11, a balanced differential detector A12, a laser power stabilization control module A13, a "zero point detection" closed-loop control module A14, a signal generator A17, a phase-locked amplifier A18 and a host computer A19 (laptop computer) which are optically connected in sequence, wherein: the optical axis of the first Glan prism A3 is perpendicular to the incident surface, the optical axis of the second Glan prism A6 is parallel to the incident surface, and the liquid crystal phase retarder A9 is optically connected in sequence. The angle between the fast axis of the LCVR phase retarder A9 and the horizontal axis is 45 degrees, and the angle between the fast axis of the 1 / 4 wave plate A10 and the horizontal axis is 90 degrees; the laser power stabilization control module A13 controls the phase delay of the first liquid crystal phase retarder A4 through a 2KHz square wave signal, and collects the light power intensity detection signal of the photodetector A7 through an AD analog-to-digital converter; the "zero point detection" closed-loop control module A14 controls the phase delay of the second liquid crystal phase retarder A9 through an incremental PID algorithm, and collects the optical rotation angle signal of the balanced differential detector A12 through an AD analog-to-digital converter; the signal generator A17 generates a sinusoidal AC voltage signal to replace the square wave signal of the traditional PID control algorithm to drive the LCVR liquid crystal phase retarder. The driving voltage can change the distribution direction of the liquid crystal molecules, thereby modulating the polarization direction of the linearly polarized light; the phase-locked amplifier A18 is used to demodulate the output signal.

[0037] The outgoing laser of the detection laser A1 passes through the first 1 / 2 wave plate A2 and the first Glan prism A3 to emit vertical linear polarized light, and then passes through the second 1 / 2 wave plate A5 and the second Glan prism A6 for splitting, and then emits horizontal linear polarized light to enter the alkali metal gas chamber, and emits another path of light to enter the photodetector A7. After the laser power stabilization control module A13 collects data, stable light intensity control is performed. After passing through the second liquid crystal phase retarder A9, the quarter wave plate A10 and the Wollaston polarization beam splitter A11, the polarized light from the exiting air chamber is decomposed into two orthogonal beams of linear polarized light, namely horizontal polarization and vertical polarization, and detected by the balanced differential detector A12. After differential amplification calculation, an optical rotation angle signal can be obtained. After being processed by the incremental PID algorithm using the "zero point detection" closed-loop control module A14, an analog control signal is output through D / A (digital / analog) conversion, and the bias error of the detection signal is compensated, thereby realizing closed-loop control of the zero point detection. The signal generator A17 generates a sinusoidal signal, which is driven by the LCVR liquid crystal phase retarder to modulate the polarization direction of the linear polarized light. After the phase-locked amplifier demodulates the output signal, an optical rotation angle signal with the low-frequency random noise of the detection system removed is obtained.

[0038] The laser power stabilization control module A13 refers to a circuit system with the STMicroelectronics STM32F103 control chip as the core, which contains functions such as analog-to-digital conversion and digital-to-analog conversion.

[0039] The "zero point detection" closed-loop control module A14 refers to a circuit system with the STMicroelectronics STM32F103 control chip as the core, which contains functions such as analog-to-digital conversion and digital-to-analog conversion.

[0040] The LCVR-based SERF inertial measurement device optical rotation angle modulation detection and zero point closed-loop system is characterized by including an alkali metal gas chamber A8, a second liquid crystal phase retarder A9, a 1 / 4 wave plate A10, a Wollaston polarization splitter prism A11, a balanced differential detector A12, a "zero point detection" closed-loop control module A14, a signal generator A17, a phase-locked amplifier A18 and a host computer A19 (laptop computer); the balanced differential detector A12 includes two photodetectors, namely a photodetector A15 and a photodetector A16.

[0041] Due to jitter and other problems in the background of the detection system, the balanced differential detector A12 will simultaneously detect the low-frequency noise of the detection system when detecting the output optical rotation angle signal of the SERF atomic spin inertial measurement device, affecting the detection accuracy of the inertial measurement device.

[0042] The linear polarization direction of the exit gas chamber determines the output signal of the balanced differential detector A12. Ideally, when the initial exit linear polarization direction is horizontal, the output signal of the balanced differential detector A12 is zero. When the linear polarization direction of the exit gas chamber is non-horizontal, the initial detection signal is not zero. This is a system error caused by factors such as defects in optical components and long-term drift of the detection laser power. The realization of "detection zero point" closed-loop control can effectively suppress the above system error.

[0043] The clever combination of the second liquid crystal phase retarder A9 and the 1 / 4 wave plate A10 placed at the designated position can realize the function of a non-mechanical, electrically controlled, fast-axis variable 1 / 2 wave plate, and can achieve precise control of the polarization direction of linear polarized light, thereby realizing "zero point detection" closed-loop control. The theoretical principle of its function realization is as follows:

[0044] The second liquid crystal phase retarder A9 has a corresponding Mueller matrix M LCVR for:

[0045]

[0046] In the above formula, δ is the variable phase retardation of the liquid crystal retarder.

[0047] 1 / 4 wave plate A10, corresponding Mueller matrix M 1 / 4 for:

[0048]

[0049] In physics, the linearly polarized light with intensity I and angle α with the horizontal axis has the corresponding Stokes matrix S L for:

[0050]

[0051] The light intensity is I, and the linear polarized light is incident horizontally. The corresponding Stokes matrix S i Expressed as:

[0052]

[0053] The outgoing polarized light passing through the second liquid crystal phase retarder A9 and the 1 / 4 wave plate A10 has a corresponding Stokes matrix S o for:

[0054]

[0055] By combining equations (3) and (5) and setting the corresponding terms equal, we can know that -δ = 2α. It can be seen that the polarized light emitted at this time is linearly polarized light. The phase delay δ has a linear relationship with the rotation angle α of the linear polarized light emitted from the gas chamber. The phase delay δ can be used to control the size of the rotation angle α, that is, the polarization direction of the linear polarized light can be controlled to be at the "detection zero point".

[0056] By changing the LCVR control voltage V, the LCVR phase delay δ can be adjusted. The relationship between the liquid crystal control voltage V and the phase delay δ is expressed as:

[0057]

[0058] In the above formula, δ0 is the maximum phase delay of the liquid crystal phase retarder, V C is the threshold voltage at which the liquid crystal molecules begin to deflect, e is a natural constant, V0 and M are characteristic parameters of the liquid crystal. According to the empirical formula and product parameters, δ0 = 4.7427 rad,

[0059] V C =0.9234V, V0=1.8442V, M=0.4583.

[0060] According to the above relationship, by changing the liquid crystal control voltage V, the LCVR phase delay δ is adjusted, thereby changing the polarization direction of the linear polarized light exiting the gas cell.

[0061] The angle between the fast axis and the horizontal axis of the liquid crystal phase retarder A9 is 45°; the "zero point detection" closed-loop control module A14 collects the detection output signal of the balanced differential detector A12 through an AD converter, applies an incremental PID calculated control signal, and controls the phase delay amount of the second liquid crystal phase retarder A9.

[0062] The signal generator A17 applies a sinusoidal drive signal with a frequency of ω=780 Hz, replacing the traditional rectangular wave voltage drive mode, and performs high-frequency modulation on the direction of the linearly polarized light.

[0063] The phase-locked amplifier A18 demodulates the collected signal of the balanced differential detector A12, removes the low-frequency random noise of the detection system, and sends the detected optical rotation angle signal to the host computer.

[0064] The invention discloses a SERF inertial measurement device optical rotation angle modulation detection and zero point closed loop system based on LCVR, comprising the following steps:

[0065] Collecting the detection output signal output by the balanced differential detector A12;

[0066] Amplifying and A / D converting the detection output signal of the inertial measurement device to obtain detection signal output data; performing differential operation processing on the collected data and a preset inertial measurement device detection signal value to obtain a digital error signal;

[0067] The digital error signal is processed by an incremental PID algorithm and then outputted as an analog control signal through D / A conversion;

[0068] The output control signal is modulated into a sinusoidal driving signal to drive the LCVR liquid crystal phase retarder, so that the detection signal is compensated to zero point;

[0069] The feedback signal is demodulated by a phase-locked amplifier, which effectively suppresses the low-frequency random noise of the detection system, realizes the detection of the optical rotation angle signal, and improves the measurement accuracy of the SERF atomic spin inertial measurement device.

[0070] Figure 1 It includes an alkali metal gas chamber A8, a second liquid crystal phase retarder A9, a 1 / 4 wave plate A10, a Wollaston polarization splitter prism A11, a balanced differential detector A12, a "zero point detection" closed-loop control module A14, a signal generator A17, a phase-locked amplifier A18 and a host computer A19 (laptop computer).

[0071] Figure 2 The detection laser optical path includes a detection laser A1, a first 1 / 2 wave plate A2, a first Glan prism A3, a first liquid crystal phase retarder A4, a second 1 / 2 wave plate A5, a second Glan prism A6, a photodetector A7, an alkali metal gas chamber A8, a second liquid crystal phase retarder A9, a 1 / 4 wave plate A10, a Wollaston polarization beam splitter prism A11, a balanced differential detector A12, a laser power stabilization control module A13, a "detection zero point" closed-loop control module A14, a signal generator A17, a phase-locked amplifier A18 and a host computer A19 (laptop computer) which are optically connected in sequence.

[0072] Figure 3 In the control closed-loop circuit, the "zero point detection" closed-loop control module A14 mainly includes a preset SERF inertial measurement device desired detection zero point (S=0), a control circuit with STMicroelectronics STM32F103 control chip as the core as a controller, and a digital-to-analog converter with signal acquisition function; A17 signal generator to realize the input of AC signal; A9 liquid crystal phase retarder as an actuator; linearly polarized light passing through A9 as the controlled object; then gradually passing through A10~A12 to convert the optical signal into a voltage signal; the voltage signal is sent to the A14 "zero point detection" closed-loop control module, thereby realizing the "zero point detection" closed-loop control.

[0073] like Figure 1As shown, the LCVR-based SERF inertial measurement device optical rotation angle modulation detection and zero-point closed-loop system of the present invention includes an alkali metal gas chamber A8, a second liquid crystal phase retarder A9, a 1 / 4 wave plate A10, a Wollaston polarization beam splitter prism A11, a balanced differential detector A12, a detection control module A14, a signal generator A17 and a phase-locked amplifier A18. The polarization direction of the linear polarized light of the exit chamber is approximately horizontal before closed-loop control. The linear polarization direction of the exit chamber determines the initial output signal of the balanced differential detector A12. The angle with the horizontal direction causes the initial detection signal of the balanced differential detector A12 to be non-zero. The angle between the fast axis of the liquid crystal phase retarder A9 and the horizontal axis is 45 degrees, and the angle between the fast axis of the 1 / 4 wave plate A10 and the horizontal axis is 90 degrees. The "zero point detection" closed-loop control module A14 calculates the required control voltage through an incremental PID algorithm, and the signal generator A17 modulates the control voltage signal into a sinusoidal AC signal to control the phase delay δ of the second liquid crystal phase retarder A9. The change of δ causes the angle between the linear polarized light and the horizontal axis to change. According to the preset value of the control quantity, that is, the initial output signal of the SERF inertial measurement device is zero, the "1 / 2 wave plate" with variable fast axis is formed by the ingenious combination of LCVR and 1 / 4 wave plate, which realizes the precise control of the polarization direction of linear polarized light and controls the initial output signal at the "detection zero point" in real time; and after the detection signal is demodulated by the phase-locked amplifier A18, the low-frequency random noise is effectively suppressed, and the optical rotation angle signal detection is realized.

[0074] The second liquid crystal phase retarder A9 is used to change the phase delay control of the linearly polarized light passing through the alkali metal gas chamber and serves as an actuator of the control loop.

[0075] The 1 / 4 wave plate A10 is used to adjust the elliptically polarized light passing through the second liquid crystal phase retarder A9 and convert it back into linearly polarized light.

[0076] The Wollaston polarization beam splitter A11 has an optical axis that forms an angle of 45° with the polarization direction of the incident linear polarized light, so that the outgoing light is two beams of linear polarized light with orthogonal polarization directions.

[0077] The balanced differential detector A12 includes two photodetectors, namely a photodetector A15 and a photodetector A16.

[0078] The signal generator A17 generates a sinusoidal AC voltage signal to drive the LCVR liquid crystal phase retarder instead of the square wave signal of the traditional PID control algorithm. The driving voltage can change the distribution direction of the liquid crystal molecules, thereby modulating the polarization direction of the linear polarized light.

[0079] The output voltage signal of the SERF atomic inertial measurement device is defined as S; the REF signal is a reference signal generated by the signal generator A17, and the REF signal is transmitted to the phase-locked amplifier A18; the SERF inertial measurement device expects to detect the zero point, and the output voltage signal S=0 of the SERF atomic inertial measurement device is taken as the expected signal value. The phase-locked amplifier A18 is used to demodulate the output signal.

[0080] Modulation refers to the process in which the lock-in amplifier A18 uses the REF signal as a reference signal to extract the SERF atomic inertial measurement device output voltage signal S from the modulation signal.

[0081] When stationary, the angular velocity sensed by the atomic spin measurement device should be the speed of the earth's rotation. At this time, the detection signal is approximately 0. The measured data is a system measurement error caused by a combination of factors such as the optical path placement, long-term drift of the detection laser power, and low-frequency random noise of the detection system.

[0082] The detection signal of the SERF atomic spin measurement device can be considered as an optical rotation angle signal, recorded as θ. The linearly polarized light with a light intensity of I0 is incident on the Wollaston spectrometer A11. Considering the high-frequency modulation of the signal generator A17, θ2 = θ*βsin(ωt), where θ2 is the detection laser optical rotation angle signal incident on the balanced differential detector A12, β is the amplitude of the modulation signal, ω is the frequency of the modulation signal, and t is time.

[0083] The photodetector A15 detects light intensity of I0cos 2 (θ2-π / 4) (7)

[0084] The photodetector A16 detects light intensity I0sin 2 (θ2-π / 4) (8)

[0085] Define the output voltage signal of the SERF atomic inertial measurement device as S. Considering that the phase-locked amplifier A18 demodulates the signal, the output voltage signal S of the SERF atomic inertial measurement device is obtained by differential calculation as follows:

[0086] S=I0(cos 2 (θ-π / 4)-sin 2 (θ-π / 4))=I0cos(2θ-π / 2)=I0sin(2θ) (9)

[0087] In the small angle range, sin(θ)=θ

[0088] At this time, the SERF atomic inertial measurement device outputs a voltage signal of S = 2I0θ (10)

[0089] At this time, the output voltage signal of the SERF atomic spin measurement device and the optical rotation angle signal are in direct proportion.

[0090] Definition: The AD analog-to-digital converter of the detection signal samples the output voltage signal as U, and the error value between the current output value and the previous output value is ΔU i , i is a positive integer (i=1, 2, 3..., n)

[0091] The incremental PID (Proportion-Integration-Differentiation) algorithm is very different from the traditional PID algorithm. Unlike the traditional PID algorithm, which accumulates all errors, the incremental PID only determines the control increment based on the most recent sampling. It mainly processes the error between the current output value and the previous output value through feedback. It has a simpler structure, is easier to implement, and has good robustness. The expression of the incremental PID algorithm for this system is:

[0092] ΔU i =k p (err i -err i-1 )+k i err i +k d (err i -2err i-1 +err i-2 ) (11)

[0093] err i =v s -v i (12)

[0094] Where: U i k is the increment of the error change measured by the SERF atomic spin inertial measurement device system; p is the proportionality coefficient; k i is the integral coefficient; k d is the differential coefficient; err i The difference between the set value of the output voltage signal of the atomic spin measurement device and the current acquisition; err i-1 for err i The last deviation; err i-2 for err i-1 The last deviation; v s v is the detection signal setting value (SERF inertial measurement device expects to detect zero point S = 0); i is the current value of the detection signal, i is a positive integer, referring to the number of signal acquisition times (i=1, 2, 3..., n).

[0095] It can be seen from formula (6) that the output signal of the incremental PID control algorithm is only related to the sampling output errors of the last three times, and is not affected by the global sampling signal, which effectively suppresses the signal error accumulated over time.

[0096] In the control closed loop, the A14 "zero detection" closed-loop control module mainly includes the pre-set SERF inertial measurement device expected detection zero point (S=0), the control circuit with STMicroelectronics STM32F103 control chip as the core as the controller, and a digital-to-analog converter with signal acquisition function; A17 signal generator to realize the input of AC signal; A9 liquid crystal phase retarder as an actuator; linearly polarized light passing through A9 as the controlled object; then gradually passing through A10~A12 to convert the optical signal into a voltage signal; the voltage signal is sent to the A14 "zero detection" closed-loop control module, thereby realizing the "zero detection" closed-loop control; at the same time, the voltage signal is also sent to the A18 phase-locked amplifier, and the processed signal is transmitted to the A19 host computer (laptop computer). Figure 3 Add in the code is used as a node to implement the addition function, which means: node output = +v s -v i .

[0097] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. The optical rotation angle modulation detection and zero point closed loop system of SERF inertial measurement device based on LCVR is characterized by: It includes a detection zero point closed-loop control module connected to the output end of a balanced differential detector and the input end of a signal generator respectively, the output end of the signal generator is connected to a second liquid crystal phase retarder as an actuator to adjust the optical rotation angle of its linear polarized light, the balanced differential detector is connected to the vertical linear polarized light output end of a Wollaston polarization beam splitter prism through a second photodetector, and is connected to the horizontal linear polarized light output end of the Wollaston polarization beam splitter prism through a third photodetector, the Wollaston polarization beam splitter prism is connected to the linear polarized light output end of the second liquid crystal phase retarder through a 1 / 4 wave plate, and the second liquid crystal phase retarder is connected to the alkali metal gas chamber optical path; The signal generator applies a sinusoidal driving signal with a frequency of ω=780 Hz to the second liquid crystal phase retarder, replacing the traditional rectangular wave voltage driving mode, and performs high frequency modulation on the direction of the linear polarized light; The detection zero point closed-loop control module comprises a node, a controller and a signal detection module, wherein the node has a detection signal setting value positive input terminal associated with the desired detection zero point, the negative input terminal of the node is connected to the signal detection module to receive the current value of the detection signal, the output terminal of the node is connected to the controller, the controller is connected to the input terminal of the signal generator receiving the AC signal input, and the input terminal of the signal detection module is connected to the output terminal of the balanced differential detector; The signal generator modulates the output control signal into a sinusoidal driving signal to drive the second liquid crystal phase retarder so that the detection signal is compensated to a zero point.

2. The optical rotation angle modulation detection and zero point closed loop system of SERF inertial measurement device based on LCVR according to claim 1, characterized in that: The output end of the balanced differential detector is connected to the first input end of the phase-locked amplifier, the second input end of the phase-locked amplifier is connected to the reference signal input end of the signal generator, and the output end of the phase-locked amplifier is connected to the host computer.

3. The optical rotation angle modulation detection and zero point closed loop system of SERF inertial measurement device based on LCVR according to claim 1, characterized in that: The alkali metal gas chamber is connected to the detection laser through the second Glan prism, the second 1 / 2 wave plate, the first liquid crystal phase retarder, the first Glan prism and the first 1 / 2 wave plate in sequence; the second Glan prism is connected to the input end of the laser power stabilization control module through the first photodetector; and the output end of the laser power stabilization control module is connected to the first liquid crystal phase retarder.

4. The optical rotation angle modulation detection and zero point closed loop system of SERF inertial measurement device based on LCVR according to claim 1, characterized in that: The Mueller matrix M corresponding to the second liquid crystal phase retarder LCVR for: In formula (1), δ is the variable phase retardation of the liquid crystal phase retarder; The Mueller matrix M corresponding to the 1 / 4 wave plate 1 / 4 for: In physics, the linearly polarized light with intensity I and angle α with the horizontal axis has the corresponding Stokes matrix S L for: In physics, the light intensity is I, and the linear polarized light along the horizontal incidence has the corresponding Stokes matrix S i Expressed as: The Stokes matrix S corresponding to the outgoing polarized light passing through the second liquid crystal phase retarder and the 1 / 4 wave plate is o for: By combining equations (3) and (5) and making the corresponding terms equal, we can know that -δ=2α. It can be seen that the polarized light emitted at this time is linearly polarized light, and the phase delay δ has a linear relationship with the rotation angle α of the linear polarized light emitted from the gas chamber. The rotation angle α can be controlled by the phase delay δ, that is, the polarization direction of the linear polarized light can be controlled to be at the "detection zero point".

5. The optical rotation angle modulation detection and zero point closed loop system of SERF inertial measurement device based on LCVR according to claim 1, characterized in that: By changing the control voltage V of the second liquid crystal phase retarder LCVR to adjust the magnitude of the LCVR phase delay δ, the relationship between the control voltage V and the phase delay δ is expressed as follows: In formula (6), δ0 is the maximum phase retardation of the liquid crystal phase retarder, V C is the threshold voltage at which the liquid crystal molecules begin to deflect, e is a natural constant, V0 and M are the characteristic parameters of the liquid crystal, δ0 = 4.7427 rad, V C =0.9234V, V0=1.8442V, M=0.4583.

6. The optical rotation angle modulation detection and zero point closed loop system of SERF inertial measurement device based on LCVR according to claim 1, characterized in that: The angle between the fast axis and the horizontal axis of the second liquid crystal phase retarder is 45°. The detection zero point closed-loop control module collects the detection output signal of the balanced differential detector through an AD converter, applies an incremental PID calculated control signal, and controls the phase delay amount of the second liquid crystal phase retarder.

7. The LCVR-based SERF inertial measurement device optical rotation angle modulation detection and zero-point closed-loop system according to claim 2, characterized in that: The lock-in amplifier demodulates the collected signal of the balanced differential detector, removes the low-frequency random noise of the detection system, and sends the detected optical rotation angle signal to the host computer to improve the measurement accuracy of the SERF atomic spin inertial measurement device.

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