A raman laser polarization stabilizing device for a cold atom interferometer

Abstract

The application relates to a Raman laser polarization stabilizing device for a cold atom interferometer, comprising a Raman laser system, an acousto-optic modulator, a fiber coupler, a 1 / 2 wave plate, a polarization beam splitter, a cavity, a liquid crystal retarder, a 0-degree mirror, a first photoelectric probe, a first gain amplifier, a differential amplifier, a second photoelectric probe, a second gain amplifier, a PID controller, a voltage selector, an external voltage and a driving signal source. The application can automatically adjust the Raman light ratio in real time, realize free output of various Raman light ratios, and keep the laser polarization and laser power stable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of quantum optics, atomic physics and laser control technology, and relates to a power adjusting device for Raman light, in particular to a Raman laser polarization stabilizing device and method for a cold atom interferometer. BACKGROUND

[0002] Since the self-implementing cold atom interferometer, the atomic interference inertial measurement technology has gradually matured, and high-sensitivity and high-precision atomic inertial sensors have been widely applied in the fields of fundamental physics and engineering applications. At present, the atomic interference type absolute gravimeter has reached a measurement precision of 10-9g, the zero bias stability of the atomic interference type gyroscope can reach 7x10-5° / h, and the measurement resolution of the atomic accelerometer can reach 10-11g.

[0003] The atomic interference technology is based on the coherence manipulation of atoms by laser, and the Raman laser is a necessary condition for realizing atomic interference. The Raman light is mainly composed of two lasers with a certain frequency difference and a fixed phase difference, and when interfering, the two lasers need to have opposite transmission directions, which are usually realized by the method of incident to the 0° reflector. At the same time, according to the transition rule, the polarization directions of the incident and reflected lasers affect the distribution of atoms in different energy levels, which will eventually introduce different degrees of systematic errors. In order to suppress the measurement errors introduced by the same direction Raman light, the combination of linear polarization of incident light and reflected light is often used in experiments, and the polarization directions of the two are perpendicular.

[0004] The traditional adjusting scheme needs to manually adjust the 1 / 4 wave plate in front of the Raman reflector, and the adjusting efficiency is low, especially when the polarization direction is unstable, repeated adjustment is needed, which limits the environmental adaptability of rapid measurement.

[0005] Through retrieval, no existing technology documents similar to the present application have been found. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a Raman laser polarization stabilizing device and method for a cold atom interferometer, which can automatically adjust the Raman light ratio in real time, realize the free output of various Raman light ratios, and keep the laser polarization and laser power stable.

[0007] The present application solves the practical problems by adopting the following technical scheme:

[0008] A Raman laser polarization stabilizing device for a cold atom interferometer, comprising: a Raman laser system, an acousto-optic modulator, a fiber coupler, a 1 / 2 wave plate, a polarization beam splitter, a cavity, a liquid crystal delay, a 0° reflector, a first photoelectric probe, a first gain amplifier, a differential amplifier, a second photoelectric probe, a second gain amplifier, a PID controller, a voltage selector, an external voltage and a driving signal source.

[0009] The laser emitted by the Raman laser system is incident into the acousto-optic modulator to obtain Raman laser with certain intensity, and then the laser is incident into the fiber coupler, and the laser output is incident into the 1 / 2 wave plate to adjust the intensity of the two beams of light after the polarization beam splitter, and the light emitted in the vertical direction is incident into the first photoelectric probe, and then is incident into the first input end of the differential amplifier through the first gain amplifier, the second beam of light emitted by the polarization beam splitter 5 is incident into the cavity through the liquid crystal delay device, the polarization direction is changed by 90 degrees, and then is reflected by the 0-degree mirror and returns along the original path, and then is incident into the second photoelectric probe through the polarization beam splitter 5 again, and then is incident into the second input end of the differential amplifier through the second gain amplifier, and then the output end of the differential amplifier is connected to the first input end of the voltage selector, and the external voltage is connected to the second input end of the voltage selector, and the output end of the voltage selector is connected to the driving signal source, and the driving signal source is connected to the input end of the liquid crystal delay device.

[0010] Moreover, the Raman laser system is generated by phase locking two lasers or by modulating a laser through an electro-optic crystal.

[0011] Moreover, the cavity is a vacuum cavity for cold atom interference experiments.

[0012] Moreover, the voltage selector selects the signal of the PID controller to realize the polarization closed-loop control of the liquid crystal delay device.

[0013] Moreover, the voltage selector selects the signal of the external voltage to directly adjust the polarization direction of the liquid crystal delay device.

[0014] Moreover, the acousto-optic modulator controls the intensity of the laser output by the fiber coupler, and the 1 / 2 wave plate adjusts the light intensity ratio of the transmitted and reflected light of the polarization beam splitter as the reference voltage of the differential amplifier.

[0015] Advantages and beneficial effects of the present application:

[0016] 1. The present application provides a Raman laser polarization stabilizing device for a cold atom interferometer, which is based on a closed-loop control scheme of Raman light polarization, improves the stability of Raman light polarization, and effectively improves the adjustment efficiency. The present application is different from the traditional manual adjustment, and the driving voltage of the liquid crystal delay device is actively scanned to obtain the light intensity change of the reflected Raman light, so that the optimal polarization direction corresponding to the maximum light intensity can be quickly obtained, the adjustment efficiency is faster, and the long-term stability of the polarization is better through the closed-loop control.

[0017] 2. The Raman laser polarization stabilizing device for a cold atom interferometer according to the present application can be applied to the field of cold atom interferometric inertial measurement technology, such as a cold atom interferometric gravimeter, a gyroscope, an accelerometer, and a gravity gradiometer, and can also be applied to cold atom related experiments. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Figure 1 is a schematic diagram of the device structure of the present application.

[0019] Figure 1 is a schematic diagram of the device structure of the present application.

[0020] 1 - Raman laser system; 2 - acousto-optic modulator; 3 - fiber coupler; 4 - 1 / 2 wave plate; 5 - polarization beam splitter; 6 - cavity; 7 - liquid crystal retarder; 8 - 0° mirror; 9 - first photodetector; 10 - first gain amplifier; 11 - differential amplifier; 12 - second photodetector; 13 - second gain amplifier; 14 - PID controller; 15 - voltage selector; 16 - external voltage; 17 - driving signal source. DETAILED DESCRIPTION

[0021] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and cannot be understood as a limitation of the present application.

[0022] A Raman laser polarization stabilizing device for a cold atom interferometer, as shown in Figure 1 Figure 1, comprises a Raman laser system, an acousto-optic modulator, a fiber coupler, a 1 / 2 wave plate, a polarization beam splitter, a cavity, a liquid crystal retarder, a 0° mirror, a first photodetector, a first gain amplifier, a differential amplifier, a second photodetector, a second gain amplifier, a PID controller, a voltage selector, an external voltage, and a driving signal source.

[0023] The laser emitted by the Raman laser system 1 is incident into the acousto-optic modulator 2 to obtain Raman laser with certain intensity, and then the laser is incident into the fiber coupler 3, and the laser output from the fiber coupler 3 is incident into the 1 / 2 wave plate 4 to adjust the intensity of two beams of light output from the polarization beam splitter 5, and the light output from the polarization beam splitter 5 in the direction perpendicular to the incident direction is incident into the first photoelectric probe 9, and then the light is incident into the first input end of the differential amplifier 11 through the first gain amplifier 10, the second beam of light output from the polarization beam splitter 5 is incident into the cavity 6 through the liquid crystal delay 7, and then the polarization direction of the light is changed by 90°, and then the light is reflected by the 0° mirror 8 and returns along the original path, and then the light is incident into the polarization beam splitter 5 again, and only the light in the direction perpendicular to the incident light by 90° is output to the second photoelectric probe 12, and then the light is incident into the second input end of the differential amplifier 11 through the second gain amplifier 13, and then the output of the differential amplifier 11 is input into the PID controller 14, and then the output of the PID controller 14 is input into the first input end of the voltage selector 15, and then the external voltage 16 is connected to the second input end of the voltage selector 15, and then the output of the voltage selector 15 is connected to the driving signal source 17, and then the driving signal source 17 is connected to the input end of the liquid crystal delay 7.

[0024] In the embodiment, the Raman laser system is generated by phase locking two lasers or by modulating one laser through an electro-optic crystal.

[0025] In the embodiment, the cavity 6 is a vacuum cavity for cold atom interference experiment.

[0026] In the embodiment, the polarization closed loop control of the liquid crystal delay 7 is realized by selecting the signal of the PID controller 14 to be conducted by the voltage selector 15.

[0027] In the embodiment, the polarization direction of the liquid crystal delay 7 is adjusted directly by the external voltage 16 by selecting the signal of the external voltage 16 to be conducted by the voltage selector 15.

[0028] In the embodiment, the intensity of the laser output from the fiber coupler 3 is controlled by the acousto-optic modulator 2, the intensity ratio of the transmitted light and the reflected light of the polarization beam splitter 5 is adjusted by the 1 / 2 wave plate 4, and the intensity ratio is used as the reference voltage of the differential amplifier.

[0029] The application will be further described below in combination with specific examples.

[0030] Take the line polarization adjustment of Raman laser for rubidium 87 atom interferometer as an example, the requirement is that the polarization direction of Raman laser incident on both sides of the cavity 6 is perpendicular to each other. The power of Raman light is set to P0 after modulation by the acousto-optic modulator 2, and becomes ηP0 after passing through the fiber coupler, where η is the coupling efficiency. By adjusting the 1 / 2 wave plate 4, the polarization direction of the transmitted light can be changed, thereby changing the intensity ratio of the reflection direction and the projection direction of the polarization beam splitter 5. At this time, the light reflected by the polarization beam splitter 5 forms a photocurrent after passing through the probe 9, and is converted into a voltage signal V1 after passing through the first gain amplifier.

[0031] The light transmitted out of the polarization beam splitter 5 enters the liquid crystal retarder 7 after passing through the cavity 6, at this time the mirror 8 returns the incident laser to the original path and changes the polarization direction again after passing through the liquid crystal retarder 7 again. By scanning the external voltage 16, the driving signal source 17 can be dynamically adjusted to quickly adjust the polarization direction of the incident light of the liquid crystal retarder 7. At this time, the second photodetector 12 is used to monitor the light intensity of the light reflected from the polarization beam splitter 5, and the second gain amplifier 13 converts the photocurrent signal of the second photodetector 12 into a voltage signal V2. When the external voltage 16 is adjusted to monitor that V2 reaches the maximum value, the corresponding polarization direction can meet the requirement, at this time the value of the external voltage 16 is fixed to complete the polarization adjustment, at this time the system is in an open loop working mode.

[0032] In order to realize the long-term stability of the polarization stability, when the external voltage 16 reaches the maximum value of V2, the PID controller 14 connects the conditioned signal to the driving signal source 17 after the voltage selector 15 is turned on, at this time the external voltage 16 stops scanning, at this time the system is in a closed loop state. The light reflected by the polarization beam splitter 5 always outputs the maximum light intensity, which means that the polarization direction of the Raman laser incident on both sides of the cavity 6 is always perpendicular to each other.

[0033] The present application is described with reference to flowcharts and / or block diagrams according to the methods, devices (systems), and computer program products of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as combinations of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the computer or other programmable data processing apparatus generate a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The device that implements the functions specified in the flowcharts and / or block diagrams.

[0034] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0035] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the functions specified in one or more boxes. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Raman laser polarization stabilisation apparatus for a cold atom interferometer, characterised in that: Comprise: Raman laser system, acousto-optic modulator, fiber coupler, 1 / 2 wave plate, polarization beam splitter, cavity, liquid crystal delay, 0° mirror, first photoelectric probe, first gain amplifier, differential amplifier, second photoelectric probe, second gain amplifier, PID controller, voltage selector, external voltage and drive signal source; The laser emitted by the Raman laser system is incident into the acousto-optic modulator to obtain a certain intensity of Raman laser. Then the laser enters the fiber coupler, and the output laser enters the 1 / 2 wave plate to adjust the intensity of the two beams of light after the polarization beam splitter. The outgoing light in the vertical incidence direction enters the first photoelectric probe, passes through the first gain amplifier, and enters the first input end of the differential amplifier. The second beam of light emitted by the polarization beam splitter is incident into the cavity after passing through the liquid crystal delay, and the polarization direction changes by 90°. Then it is reflected by the 0° mirror and returns along the original path. After passing through the polarization beam splitter again, only the light in the direction perpendicular to the incident light by 90° is emitted to the second photoelectric probe. After passing through the second gain amplifier, it enters the second input end of the differential amplifier. The output end of the differential amplifier enters the PID controller, and then outputs to the first input end of the voltage selector. The external voltage is connected to the second input end of the voltage selector. The output end of the voltage selector is connected to the drive signal source, and the drive signal source is connected to the input end of the liquid crystal delay.

2. The Raman laser polarization stabilizing device for cold atom interferometer according to claim 1, characterized in that: The Raman laser system is generated by phase locking two lasers or by modulating a laser through an electro-optic crystal.

3. The Raman laser polarization stabilizing device for cold atom interferometer according to claim 1, characterized in that: The cavity is a vacuum cavity for cold atom interference experiments.

4. The Raman laser polarization stabilizing device for cold atom interferometer according to claim 1, characterized in that: After the voltage selector selects the signal of the PID controller to be conducted, the polarization closed-loop control of the liquid crystal delay is realized.

5. The Raman laser polarization stabilizing device for cold atom interferometer according to claim 1, characterized in that: After the voltage selector selects the signal of the external voltage to be conducted, the polarization direction of the liquid crystal delay is directly adjusted by the external voltage.

6. The Raman laser polarization stabilizing device for cold atom interferometer according to claim 1, characterized in that: The intensity of the output laser of the fiber coupler is adjusted by the acousto-optic modulator. The ratio of the transmitted and reflected light intensity of the polarization beam splitter is adjusted by the 1 / 2 wave plate, which is used as the reference voltage of the differential amplifier.

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