Saturated absorption spectrum and linearly polarized light CPT differential detection time division multiplexing system and method

Abstract

The invention provides a saturated absorption spectrum and linearly polarized light CPT differential detection time division multiplexing system and method. The system comprises a vertical resonant cavity surface emission type VCSEL laser, a lens, a polaroid, a polarization splitting prism, an atomic gas chamber, a mirror surface, an MEMS galvanometer, a photoelectric detector, a control chip and a differential amplifier. The polaroid comprises a first lambda / 2 wave plate, a second lambda / 2 wave plate and a lambda / 4 wave plate; the photoelectric detector comprises a first photoelectric detector, a second photoelectric detector and a third photoelectric detector; the polarization splitting prism comprises a first polarization splitting prism and a second polarization splitting prism; the second lambda / 2 wave plate is used for adjusting the splitting ratio of the second polarization splitting prism; the second polarization splitting prism is used for screening light beams in different polarization directions after being reflected by the mirror surface; the differential amplifier is used for carrying out differential processing on signals generated by the light beams screened by the second polarization splitting prism and received by the second photoelectric detector and the third photoelectric detector, through the system, the utilization rate of a single atomic gas chamber is increased, and the size and power consumption of a miniature atomic clock physical system are reduced.

Description

Technical Field

[0001] The present invention relates to the field of quantum measurement and control technology, and in particular to a saturation absorption spectrum and linear polarized light CPT differential detection time-sharing multiplexing system and method. Background Art

[0002] The atomic clock CPT is currently the most accurate time and frequency standard device. The chip atomic clock is an atomic clock that is as large and heavy as a chip. Because it can guarantee high-precision time and frequency output while being small in size, light in weight and low in power consumption, the micro atomic clock has broad application prospects in scenarios that have strict requirements on volume and power consumption and require high frequency stability. The micro atomic clock is a new generation of autonomous navigation and timing micro terminal, which is widely used in cutting-edge technology fields such as positioning, navigation, surveying, communication, and radar. The basic principle of the micro atomic clock is coherent layout confinement. The micro atomic clock obtains coherent two-color light through microwave modulated lasers and acts on atoms in the atomic gas chamber to achieve CPT resonance, obtain the stable microwave frequency of the specific energy level radiation transition of the atom required by the atomic clock as a spectral line signal, and convert the microwave frequency into a standard frequency output that is convenient to use in practical applications through electronic devices.

[0003] The micro atomic clock is composed of a physical system and a circuit system. The physical system includes lasers, atomic gas chambers, polarization devices, photoelectric sensors, etc. The circuit system includes control chips, microwave chips, electronic circuits, etc. The stable output of the frequency signal of the micro atomic clock requires the precise locking of the laser frequency and the microwave frequency.

[0004] If you want to use the saturated absorption spectrum method to generate a narrow-linewidth laser frequency locking signal, and use the linear polarization light differential detection method to generate a high signal-to-noise ratio microwave frequency locking signal, you often need to use two atomic gas chambers, one of which is used to achieve saturated absorption spectrum and the other is used to achieve CPT resonance. However, using two atomic gas chambers at the same time will increase the size and power consumption of the physical system, which is not suitable for miniature atomic clocks.

[0005] It can be concluded that how to improve the utilization rate of a single atomic gas cell and reduce the volume and power consumption of a miniature atomic clock physical system by using a single atomic gas cell for saturated absorption spectrum and linear polarized light CPT differential detection has become one of the existing technical problems that need to be urgently solved. Summary of the invention

[0006] The present invention provides a saturation absorption spectrum and linear polarized light CPT differential detection time-sharing multiplexing system and method, which are used to improve the utilization rate of a single atomic gas chamber and reduce the volume and power consumption of a micro atomic clock physics system.

[0007] In the first aspect, a saturation absorption spectrum and linear polarization light CPT differential detection time-sharing multiplexing system is provided, comprising: a vertical cavity surface emitting VCSEL laser, a lens, a polarizer, a polarization beam splitter prism, an atomic gas chamber, a mirror, a MEMS galvanometer, a photodetector, a control chip and a differential amplifier; wherein the polarizer comprises a first λ / 2 wave plate, a second λ / 2 wave plate and a λ / 4 wave plate; the photodetector comprises a first, a second and a third photodetector; the polarization beam splitter prism comprises a first and a second polarization beam splitter prism; wherein,

[0008] The first λ / 2 wave plate is used to adjust the polarization direction of the linearly polarized light emitted by the VCSEL laser passing through the lens;

[0009] The second λ / 2 wave plate is used to adjust the polarization direction of the linearly polarized light passing through the first polarization beam splitter prism, thereby adjusting the splitting ratio of the second polarization beam splitter prism;

[0010] The λ / 4 wave plate is used to convert the linearly polarized light passing through the second λ / 2 wave plate and the atomic gas chamber into circularly polarized light and then into linearly polarized light, and rotate the polarization angle of the light by 90°;

[0011] The MEMS galvanometer is used to electrically control the angle of the mirror surface, so that the mirror surface deflects within ±15°, thereby controlling the reflection direction of light;

[0012] The second polarization beam splitter prism is used to screen light beams with different polarization directions after being reflected by the mirror;

[0013] The differential amplifier is used to perform differential processing on the signals generated by the second photodetector and the third photodetector after receiving the light beam screened by the second polarization beam splitter prism;

[0014] The control chip is used to periodically control the angle of the MEMS galvanometer according to usage requirements.

[0015] In one embodiment, if the angle between the polarization direction of the laser beam passing through the first polarization beam splitter prism and the fast axis of the second λ / 2 wave plate is a set angle θ, the λ / 4 wave plate and the polarization direction of the laser beam passing through the first polarization beam splitter prism are set at an angle of (2×θ+45) degrees.

[0016] In one embodiment, if the control chip controls the angle of the MEM galvanometer to be -15°, the MEMS galvanometer reflects the laser back to the first polarization beam splitter prism along the original transmission path, and adjusts the position of the first photodetector so that the first photodetector detects the reflected laser.

[0017] In one embodiment, if the control chip controls the angle of the MEM galvanometer to +15°, the MEMS galvanometer will reflect the laser beam to the second mirror, and under the condition that no CPT resonance occurs, the angle of the second λ / 2 wave plate is adjusted, and the angle of the λ / 4 wave plate is adjusted synchronously following the second λ / 2 wave plate, so that the signal intensities detected by the second photodetector and the third photodetector are equal, and the differential value is zero.

[0018] In one embodiment, the atomic gas chamber is used to provide gaseous 87 Rb atoms, which contain a micro rubidium bubble, a magnetic field coil, a magnetic shielding shell, a heating module, and a heat preservation module; the rubidium bubble is coated with a layer of paraffin film and filled with a certain set pressure. 87 Rb atoms, no buffer gas.

[0019] In one embodiment, the VCSEL laser is used to output laser light with a wavelength of 795 nm.

[0020] In a second aspect, a method for time-division multiplexing of saturated absorption spectrum and linear polarized light CPT differential detection is provided, and the method is applied to the above-mentioned system, comprising:

[0021] The angle of the second λ / 2 wave plate is adjusted so that it forms an angle of a set angle θ with the linear polarized light passing through the lens, the first λ / 2 wave plate and the first polarization beam splitter prism, and the angle of the λ / 4 wave plate is adjusted so that its fast axis forms an angle of (2×θ+45) degrees with the direction of the linear polarized light transmitted through the first polarization beam splitter prism;

[0022] Adjust the position of the lens to collimate the laser beam emitted by the VCSEL laser, and control the chip to apply voltage to the MEMS galvanometer so that the angle of the MEMS galvanometer is -15°, so that the reflected light hits the first photodetector;

[0023] The control chip applies voltage to the MEMS galvanometer, making the angle of the MEMS galvanometer +15°, so that the reflected light hits the second mirror, adjusts the microwave frequency to make it detuned, does not generate CPT resonance, and adjusts the angle θ until the differential signal value of the second photodetector and the third photodetector is zero;

[0024] Among them, in the period when the MEMS galvanometer angle is -15°, the VCSEL laser current is subjected to the first set Hz modulation and demodulation to lock the laser frequency at the saturation absorption peak; in the period when the MEMS galvanometer angle is 15°, the microwave frequency is subjected to the second set Hz modulation and demodulation to lock the microwave frequency at the CPT resonance peak, and the two periods are performed alternately.

[0025] In one embodiment, before adjusting the angle of the second λ / 2 wave plate, the method further includes: controlling the temperature of the control atomic gas chamber according to usage requirements to stabilize the temperature.

[0026] In one embodiment, the MEMS galvanometer is electromagnetically driven based on MEMS and optoelectronic semiconductor technology. The galvanometer is driven in a two-dimensional manner by a combination of two springs formed by MEMS processing. The normal direction of the mirror surface is changed by applying voltage, thereby changing the reflection direction of light.

[0027] In one implementation, the first set Hz is 5 kHz; the second set Hz is 156 Hz.

[0028] An embodiment of the present invention provides a saturation absorption spectrum and linear polarization light CPT differential detection time-sharing multiplexing system and method, the system comprising: a vertical cavity surface emitting VCSEL laser, a lens, a polarizer, a polarization beam splitter prism, an atomic gas chamber, a mirror, a MEMS galvanometer, a photodetector, a control chip and a differential amplifier; wherein the polarizer comprises a first λ / 2 wave plate, a second λ / 2 wave plate and a λ / 4 wave plate; the photodetector comprises a first, a second and a third photodetector; the polarization beam splitter prism comprises a first and a second polarization beam splitter prism; wherein the first λ / 2 wave plate is used to adjust the polarization direction of the linear polarized light emitted by the VCSEL laser passing through the lens; the second λ / 2 wave plate is used to adjust the polarization direction of the linear polarized light passing through the first polarization beam splitter prism, and then adjust the second polarization beam splitter prism. The λ / 4 wave plate is used to convert the linearly polarized light passing through the second λ / 2 wave plate and the atomic gas chamber into circularly polarized light and then into linearly polarized light, and rotate the polarization angle of the light by 90°; the MEMS galvanometer is used to electrically control the angle of the mirror surface, so that the mirror surface deflects within ±15°, thereby controlling the reflection direction of the light; the second polarization beam splitter prism is used to screen the light beams with different polarization directions after being reflected by the mirror surface; the differential amplifier is used to perform differential processing on the signals generated by the second photodetector and the third photodetector when the light beam is screened by the second polarization beam splitter prism; the control chip is used to periodically control the angle of the MEMS galvanometer according to the use requirements. Through the above system, the utilization rate of a single atomic gas chamber is improved, and the volume and power consumption of the miniature atomic clock physics system are reduced.

[0029] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structure particularly pointed out in the written description, claims, and drawings thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0031] Figure 1 A schematic diagram of the specific structure of a saturation absorption spectrum physical system according to an embodiment of the present invention;

[0032] Figure 2 A schematic diagram of a specific structure of differential detection of CPT resonance based on linearly polarized light according to an embodiment of the present invention;

[0033] Figure 3 It is a schematic diagram of the structure of a time-division multiplexing system for saturation absorption spectrum and linear polarized light CPT differential detection according to an embodiment of the present invention;

[0034] Figure 4 The figure is a flow chart of the steps of a method for time-division multiplexing of saturated absorption spectrum and linear polarized light CPT differential detection according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to improve the utilization rate of a single atomic gas chamber and reduce the volume and power consumption of a micro-atomic clock physical system, a saturation absorption spectrum and linear polarized light CPT differential detection time-sharing multiplexing system and method are provided.

[0036] The preferred embodiments of the present invention are described below in conjunction with the drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In addition, the embodiments of the present invention and the features in the embodiments may be combined with each other if there is no conflict.

[0037] It should be noted that the terms "first", "second", etc. in the description and claims of the embodiments of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0038] For laser frequency locking, saturation absorption spectroscopy is a technique for measuring atomic absorption spectra. Its characteristic is that the half-width of the absorption spectrum signal is not Doppler broadened, but is only determined by the line width of the atomic energy level transition involved and the laser intensity. The specific structure of the saturation absorption spectroscopy physical system is as follows Figure 1 As shown. VCSEL laser is used to generate linear polarized light of a specific frequency; the lens is used to converge the divergent light beam into a parallel light beam; the red laser is the pump light, and the blue laser is the probe light; the atomic gas chamber contains gaseous 87Rb atoms; the reflector is used to reflect the pump light back as the detection light; the λ / 4 wave plate is used to change the polarization state of the laser; the polarization beam splitter prism is used to screen the light beams with different polarization angles. The laser emitted by the VCSEL is converged into parallel light by the lens. By adjusting the λ / 2 wave plate, the light completely passes through the polarization beam splitter prism, and the pump light and the atomic gas chamber are 87 After the Rb atom acts, it is reflected by the reflector. The reflected light is used as the detection light and passes through the atomic gas chamber along the same path and in the opposite direction, achieving the condition of producing a saturated absorption spectrum. Since the laser passes through the λ / 4 wave plate twice, the polarization direction rotates 90 degrees and is completely reflected by the polarization splitter prism. The photoelectric sensor can detect the saturated absorption spectrum signal, and the saturated absorption spectrum signal can be modulated and demodulated to PID lock the laser frequency.

[0039] For microwave frequency locking, using linear polarized light differential detection method with linear polarized light as pump source will not lead to the generation of polarization dark state, and differential detection technology can use Faraday rotation effect to eliminate useless common mode signals and retain differential mode signals with high signal-to-noise ratio. The specific structure of CPT resonance based on linear polarized light differential detection is as follows: Figure 2 As shown. VCSEL laser is used to generate linear polarized light of a specific frequency; lens is used to converge divergent light beam into parallel light beam; λ / 2 wave plate is used to adjust the splitting ratio of polarization beam splitter prism; polarization beam splitter prism is used to transmit or reflect light beams of different polarization directions for differential detection later; two photodetectors are used to detect light intensity signals of different polarization directions; differential amplifier is used to perform differential and amplification processing on the signals of two photodetectors. After the laser emitted by VCSEL is converged into parallel light by lens, at the microwave frequency that does not generate CPT resonance, by adjusting the angle of λ / 2 wave plate, the signals measured by the two photodetectors are equal and the differential value is zero, and the angle of λ / 2 wave plate is maintained. At this time, at the microwave frequency that generates CPT resonance, the differential amplifier can output a differential mode CPT resonance signal with a high signal-to-noise ratio, and the microwave frequency can be locked by modulation and demodulation.

[0040] like Figure 3 As shown, embodiment 1 provides a saturated absorption spectrum and linear polarized light CPT differential detection time-sharing multiplexing system, including: a vertical cavity surface-emitting VCSEL laser, a lens, a polarizer, a polarization beam splitter prism, an atomic gas chamber, a mirror, a MEMS galvanometer, a photodetector, a control chip and a differential amplifier; wherein the polarizer includes a first λ / 2 wave plate, a second λ / 2 wave plate and a λ / 4 wave plate; the photodetector includes first, second and third photodetectors; the polarization beam splitter prism includes first and second polarization beam splitter prisms; the mirror includes first and second mirrors.

[0041] VCSEL lasers are used to generate linearly polarized light of a specific frequency;

[0042] Lenses are used to converge diverging light beams into parallel beams;

[0043] The first λ / 2 wave plate is used to adjust the polarization direction of the linearly polarized light emitted by the VCSEL laser passing through the lens;

[0044] The second λ / 2 wave plate is used to adjust the polarization direction of the linearly polarized light passing through the first polarization beam splitter prism, thereby adjusting the splitting ratio of the second polarization beam splitter prism;

[0045] The λ / 4 wave plate is used to convert the linearly polarized light passing through the second λ / 2 wave plate and the atomic gas chamber into circularly polarized light and then into linearly polarized light, and rotate the polarization angle of the light by 90°;

[0046] The MEMS galvanometer can electrically control the angle of the mirror surface, and can deflect the mirror surface within ±15 degrees, thereby controlling the reflection direction of light;

[0047] The second polarization beam splitter prism is used to screen light beams with different polarization directions after being reflected by the mirror;

[0048] The photodetector is used to detect the signal of the transmitted light; the differential amplifier is used to perform differential processing on the signal generated by the second photodetector and the third photodetector after receiving the light beam screened by the second polarization beam splitter prism;

[0049] The control chip is used to periodically control the angle of the MEMS galvanometer according to usage requirements.

[0050] For the angle of the polarizer, if the angle between the polarization direction of the laser beam passing through the first polarization beam splitter and the fast axis of the second λ / 2 wave plate is the set angle θ, then the λ / 4 wave plate needs to be at an angle of (2×θ+45) degrees with the polarization direction of the laser beam passing through the polarization beam splitter. Let the control chip control the angle of the MEM galvanometer to -15°, such as Figure 3 As shown by the blue line, at this time, the MEMS galvanometer reflects the laser back along the original path and adjusts the position of the first photodetector so that the reflected laser can just hit the first photodetector.

[0051] Let the control chip control the angle of the MEM galvanometer to +15°, such as Figure 3 As shown by the red line, at this time, the MEMS galvanometer reflects the laser beam to the second mirror. Under the condition that no CPT resonance occurs, the angle of the second λ / 2 wave plate is adjusted (the angle of the λ / 4 wave plate is adjusted following the second λ / 2 wave plate) so that the signal intensities detected by the second photodetector and the third photodetector are the same and the differential value is zero. At this time, all initial settings are completed.

[0052] The light emitted by the VCSEL is converted into parallel light through the lens, and the angle of the first λ / 2 wave plate is adjusted to change the direction of the linearly polarized light so that the light completely passes through the first polarization beam splitter prism. In the laser frequency locking stage, the control chip controls the angle of the MEMS galvanometer to -15°, so that the MEMS galvanometer reflects the light back along the original path. After the light passes through the second λ / 2 wave plate, the atomic gas chamber, and the λ / 4 wave plate, it is reflected by the MEMS galvanometer. The reflected light passes through the λ / 4 wave plate twice, and the polarization direction of the light is rotated 90 degrees. After the light passes through the atomic gas chamber twice, a saturated absorption spectrum is generated, and after being reflected by the polarization beam splitter prism, it is observed by the first photodetector.

[0053] During the microwave frequency locking stage, the control chip controls the angle of the MEMS galvanometer to +15° so that the light is reflected to the second mirror. The light reflected by the MEMS galvanometer passes through the λ / 4 wave plate again. Since the light has passed through the λ / 4 wave plate once when it enters the galvanometer, the linearly polarized light is still linearly polarized light after passing through the λ / 4 wave plate twice. The angles of the second λ / 2 wave plate and the λ / 4 wave plate are adjusted in a linked manner so that the signal intensities detected by the second photodetector and the third photodetector are equal when there is no interaction between light and atoms. Differential detection can be used to obtain a differential mode signal that eliminates common mode noise.

[0054] In the second embodiment, the VCSEL laser, namely Vertical-Cavity Surface-Emitting Laser (VCSEL), is a semiconductor laser that can output laser light with a wavelength of 795 nm.

[0055] The lens is used to converge the laser light, so that the divergent laser light is converged into a parallel light beam.

[0056] The polarizer is used to change the polarization direction of light and is generally divided into a λ / 2 wave plate or a λ / 4 wave plate. The difference is that the λ / 2 wave plate delays light by Π phases along the slow axis, while the λ / 4 wave plate delays light by Π / 2 phases along the slow axis.

[0057] The polarization beam splitter prism is used to split light along two mutually perpendicular polarization directions.

[0058] The atomic gas chamber is used to provide gaseous 87 Rb atoms, which contain a micro rubidium bubble, a magnetic field coil, a magnetic shielding shell, a heating module, and a heat preservation module. The rubidium bubble is coated with a layer of paraffin film and filled with a certain pressure of 87 Rb atoms, no buffer gas;

[0059] The MEMS galvanometer is electromagnetically driven based on MEMS and optoelectronic semiconductor technology. The galvanometer can be driven in a two-dimensional manner by a combination of two springs formed by MEMS processing, and the normal direction of the mirror surface is changed by applying voltage, thereby changing the reflection direction of light.

[0060] The photoelectric sensor is used to detect the intensity of the light signal;

[0061] The differential amplifier has two signal input ports, one positive and one negative. The operational amplifier inside it subtracts the positive and negative signals and amplifies them before outputting them.

[0062] The control chip can be programmed so that the pins of the control chip can output designated signals according to the requirements of the program.

[0063] The embodiment provides a time-sharing multiplexing system for saturated absorption spectrum and linear polarized light CPT differential detection. The beneficial effects of this patent include: time-sharing multiplexing of a single atomic gas chamber to alternately realize saturated absorption spectrum and linear polarized light differential detection; the time-sharing multiplexing system will not cause the generation of saturated absorption spectrum lines under the condition of a single atomic gas chamber. 87 Rb atoms and the CPT resonance spectrum of linearly polarized light 87 Rb atoms influence each other, which reduces the volume and power consumption of the physical system when building both the saturated absorption spectrum system and the linear polarized light differential detection system.

[0064] Based on the same technical concept, an embodiment of the present application also provides a time-sharing multiplexing method for saturated absorption spectrum and linear polarized light CPT differential detection. Since the method is applied to the above-mentioned system, the implementation of the method can refer to the implementation of the system, and the repeated parts will not be repeated.

[0065] like Figure 4 As shown, the embodiment provides a time-division multiplexing method for saturated absorption spectrum and linear polarized light CPT differential detection, and the specific implementation steps include:

[0066] S41, adjusting the angle of the second λ / 2 wave plate so that it forms an angle of a set angle θ with the linear polarized light passing through the lens, the first λ / 2 wave plate and the first polarization beam splitter prism, and adjusting the angle of the λ / 4 wave plate so that its fast axis forms an angle of (2×θ+45) degrees with the direction of the linear polarized light transmitted through the first polarization beam splitter prism;

[0067] S42, adjusting the position of the lens to collimate the laser beam emitted by the VCSEL laser, and controlling the chip to apply voltage to the MEMS galvanometer to make the angle of the MEMS galvanometer -15° so that the reflected light hits the first photodetector;

[0068] S43, the control chip applies voltage to the MEMS galvanometer to make the angle of the MEMS galvanometer +15°, so that the reflected light hits the second mirror, adjusts the microwave frequency to make it detuned and does not generate CPT resonance, and adjusts the angle θ until the differential signal value of the second photodetector and the third photodetector is zero;

[0069] Among them, in the period when the MEMS galvanometer angle is -15°, the VCSEL laser current is subjected to the first set Hz modulation and demodulation to lock the laser frequency at the saturation absorption peak; in the period when the MEMS galvanometer angle is 15°, the microwave frequency is subjected to the second set Hz modulation and demodulation to lock the microwave frequency at the CPT resonance peak, and the two periods are performed alternately.

[0070] In one embodiment, before adjusting the angle of the second λ / 2 wave plate, the method further includes: controlling the temperature of the control atomic gas chamber according to usage requirements to stabilize the temperature.

[0071] In one embodiment, the MEMS galvanometer is electromagnetically driven based on MEMS and optoelectronic semiconductor technology. The galvanometer is driven in a two-dimensional manner by a combination of two springs formed by MEMS processing. The normal direction of the mirror surface is changed by applying voltage, thereby changing the reflection direction of light.

[0072] In one implementation, the first set Hz is 5 kHz; the second set Hz is 156 Hz.

[0073] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0074] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A saturation absorption spectrum and linear polarized light CPT differential detection time-division multiplexing system, characterized in that: include: A vertical cavity surface emitting VCSEL laser, a lens, a polarizer, a polarization beam splitter prism, an atomic gas chamber, a mirror, a MEMS galvanometer, a photodetector, a control chip and a differential amplifier; wherein the polarizer comprises a first λ / 2 wave plate, a second λ / 2 wave plate and a λ / 4 wave plate; the photodetector comprises a first, a second and a third photodetector; the polarization beam splitter prism comprises a first and a second polarization beam splitter prism; wherein, The first λ / 2 wave plate is used to adjust the polarization direction of the linearly polarized light emitted by the VCSEL laser passing through the lens; The second λ / 2 wave plate is used to adjust the polarization direction of the linearly polarized light passing through the first polarization beam splitter prism, thereby adjusting the splitting ratio of the second polarization beam splitter prism; The λ / 4 wave plate is used to convert the linearly polarized light passing through the second λ / 2 wave plate and the atomic gas chamber into circularly polarized light and then into linearly polarized light, and rotate the polarization angle of the light by 90°; The MEMS galvanometer is used to electrically control the angle of the mirror surface, so that the mirror surface deflects within ±15°, thereby controlling the reflection direction of light; The second polarization beam splitter prism is used to screen light beams with different polarization directions after being reflected by the mirror; The differential amplifier is used to perform differential processing on the signals generated by the second photodetector and the third photodetector after receiving the light beam screened by the second polarization beam splitter prism; The control chip is used to periodically control the angle of the MEMS galvanometer according to usage requirements.

2. The system according to claim 1, characterized in that If the angle between the polarization direction of the laser beam passing through the first polarization beam splitter prism and the fast axis of the second λ / 2 wave plate is a set angle θ, the angle between the λ / 4 wave plate and the polarization direction of the laser beam passing through the first polarization beam splitter prism is (2×θ+45) degrees.

3. The system according to claim 2, characterized in that If the control chip controls the angle of the MEM galvanometer to be -15°, the MEMS galvanometer reflects the laser back to the first polarization beam splitter prism along the original transmission path, and adjusts the position of the first photodetector so that the first photodetector detects the reflected laser.

4. The system according to claim 2, characterized in that If the control chip controls the angle of the MEM galvanometer to +15°, the MEMS galvanometer will reflect the laser beam to the second mirror, and under the condition that no CPT resonance occurs, the angle of the second λ / 2 wave plate is adjusted, and the angle of the λ / 4 wave plate is adjusted synchronously following the second λ / 2 wave plate, so that the signal intensities detected by the second photodetector and the third photodetector are equal, and the differential value is zero.

5. A system according to any one of claims 3 or 4, characterized in that: The atomic gas chamber is used to provide gaseous 87 Rb atoms, which contain a micro rubidium bubble, a magnetic field coil, a magnetic shielding shell, a heating module, and a heat preservation module; the rubidium bubble is coated with a layer of paraffin film and filled with a certain set pressure. 87 Rb atoms, no buffer gas.

6. The system according to claim 1, characterized in that The VCSEL laser is used to output laser light with a wavelength of 795 nm.

7. A time-division multiplexing method for saturation absorption spectrum and linear polarization light CPT differential detection, the method is applied to the system described in 1 to 6, characterized in that: include: The angle of the second λ / 2 wave plate is adjusted so that it forms an angle of a set angle θ with the linear polarized light passing through the lens, the first λ / 2 wave plate and the first polarization beam splitter prism, and the angle of the λ / 4 wave plate is adjusted so that its fast axis forms an angle of (2×θ+45) degrees with the direction of the linear polarized light transmitted through the first polarization beam splitter prism; Adjust the position of the lens to collimate the laser beam emitted by the VCSEL laser, and control the chip to apply voltage to the MEMS galvanometer so that the angle of the MEMS galvanometer is -15°, so that the reflected light hits the first photodetector; The control chip applies voltage to the MEMS galvanometer, making the angle of the MEMS galvanometer +15°, so that the reflected light hits the second mirror, adjusts the microwave frequency to make it detuned, does not generate CPT resonance, and adjusts the angle θ until the differential signal value of the second photodetector and the third photodetector is zero; Among them, in the period when the MEMS galvanometer angle is -15°, the VCSEL laser current is subjected to the first set Hz modulation and demodulation to lock the laser frequency at the saturation absorption peak; in the period when the MEMS galvanometer angle is 15°, the microwave frequency is subjected to the second set Hz modulation and demodulation to lock the microwave frequency at the CPT resonance peak, and the two periods are performed alternately.

8. The method according to claim 7, characterized in that Before adjusting the angle of the second λ / 2 wave plate, the method further includes: controlling the temperature of the control atomic gas chamber according to use requirements to stabilize the temperature.

9. The method according to claim 7, characterized in that: The MEMS galvanometer is electromagnetically driven based on MEMS and optoelectronic semiconductor technology. The galvanometer is driven in a two-dimensional manner by a combination of two springs formed by MEMS processing. The normal direction of the mirror surface is changed by applying voltage, thereby changing the reflection direction of light.

10. The method according to claim 7, characterized in that The first setting hertz is 5 kHz; the second setting hertz is 156 Hz.

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