An in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device

Abstract

An in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device. The in-situ frequency stabilization of the pumping light is carried out by using the internal alkali metal gas cell of the spin-exchange relaxation-free inertial measurement device, which avoids the defect that the laser frequency detunes from the resonance frequency of the internal alkali metal atoms caused by using an external gas cell for frequency stabilization in the traditional frequency stabilization method. At the same time, the use of the internal alkali metal gas cell for frequency stabilization reduces the volume of the device, saves costs, and facilitates further miniaturization.

Description

Technical Field

[0001] The present invention belongs to the technical field of spin-exchange relaxation-free inertial measurement devices, and relates to an in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device. Background Art

[0002] With the development and progress in the field of quantum physics, spin-exchange relaxation-free inertial measurement devices have become an important development direction for inertial navigation technology in long-range and long-endurance moving carriers. Among them, the pumping laser is a basic component of a spin-exchange relaxation-free inertial measurement device. The most optimal selection of the operating frequency of the pumping laser is a basic requirement for improving measurement sensitivity. Therefore, it is of great significance to achieve the most optimal selection of the operating frequency of the pumping laser.

[0003] Currently, the frequency stabilization methods for the pumping laser of this research object mainly use an external vacuum alkali metal gas cell and employ methods such as saturated absorption spectroscopy frequency stabilization, two-color laser frequency stabilization, and modulation transfer spectroscopy frequency stabilization. The advantages of these frequency stabilization methods are stability and high precision. However, since the gas cell components and working environments in the external vacuum alkali metal gas cell and the spin-exchange relaxation-free inertial measurement device are not the same, the operating frequency of the pumping laser will be detuned from the resonance frequency of the alkali metal in the gas cell of the device, thereby reducing the sensitivity of the inertial measurement of the device.

[0004] In summary, with the development and popularization of the technology of spin-exchange relaxation-free inertial measurement devices and frequency stabilization technology, there is a broad prospect for the design of laser frequency stabilization methods for spin-exchange relaxation-free inertial measurement devices. However, there is still a lack of research and practice in this area. Therefore, it is urgent to design a frequency stabilization method that works at the resonance frequency of the alkali metal gas cell of the device and apply it to spin-exchange relaxation-free inertial measurement devices. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the detuning of the resonance frequency of the alkali metal atoms in the device caused by using an external alkali metal gas cell to stabilize the frequency of the pumping light, and provide an in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device to optimize the operating frequency of the pumping light.

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

[0007] An in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device, characterized by comprising a temperature control system (1), a laser (2), a first half-wave plate (3), a first polarization beam splitter prism (4), a liquid crystal phase retarder (5), a second polarization beam splitter prism (6), a first plano-convex lens (7), a second plano-convex lens (8), a mirror (9), a second half-wave plate (10), a third polarization beam splitter prism (11), a first photodetector (12), a quarter-wave plate (13), a magnetic shielding barrel (14), a three-dimensional magnetic compensation coil (15), an oven (16), an alkali metal gas cell (17), a second photodetector (18), a signal generator (19), a current control system (20), a lock-in amplifier (21), an optical power control system (22), and an optical intensity attenuator (23); the temperature control system (1) controls the temperature of the laser (2), and the current control system (20) controls the current of the laser (2); the laser (2) outputs a beam of monochromatic light that sequentially passes through the first half-wave plate (3), the first polarization beam splitter prism (4), the liquid crystal phase retarder (5), the second polarization beam splitter prism (6), the first plano-convex lens (7), the second plano-convex lens (8), the mirror (9), the second half-wave plate (10), and the third polarization beam splitter prism (11) and is divided into two beams of light with the same size and orthogonal polarization directions. After the first beam of light passes through the first photodetector (12), the optical signal is converted into an electrical signal and fed back to the optical power control system (22); the second beam of light sequentially passes through the quarter-wave plate (13) and the gas cell (17) and then enters the second photodetector (18); the signal generator (19) generates a sine wave signal, which is sent to the current control system (20) on the one hand to modulate the frequency of the light output by the laser (2), and to the lock-in amplifier (21) on the other hand as a reference signal; the current control system (20) processes the output signal of the lock-in amplifier (21) to generate a control signal, and the control signal is added to the modulation signal of the signal generator (19) and then applied to the laser (2) as a control signal.

[0008] The laser (2) is a semiconductor laser.

[0009] The first polarization beam splitter prism (4), the liquid crystal phase retarder (5), and the second polarization beam splitter prism (6) together constitute a light intensity stabilization module; the first polarization beam splitter prism (4) and the second polarization beam splitter prism (6) are vertically placed to achieve an extinction effect, and the transmitted light intensity of the second polarization beam splitter prism (6) is stably controlled by adjusting the voltage of the liquid crystal phase retarder (5).

[0010] By rotating and adjusting the second half-wave plate (10), the light intensities of the two outgoing beams of the third polarization beam splitter prism (11) are made the same.

[0011] The magnetic shielding barrel (14) is used to shield the external magnetic field and adopts a three-layer structure consisting of two layers of permalloy and one layer of ferrite.

[0012] The gas chamber (17) contains potassium, rubidium or cesium atoms and is filled with nitrogen and helium at the same time.

[0013] The light intensity attenuation sheet (23) attenuates the light intensity entering the first photodetector (12) to the linear region of the working point of the first photodetector (12).

[0014] The second photodetector (18) converts the optical signal after passing through the gas chamber (17) into an electrical signal as the signal to be demodulated and sends it to the lock-in amplifier (21) to obtain the differential signal of the absorption spectrum.

[0015] The technical effects of the present invention are as follows: An in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device according to the present invention. This method takes a spin-exchange relaxation-free inertial measurement device as the research object. Aiming at the problem of in-situ control of the pumping light frequency, by using the method that alkali metal atoms have an absorption effect on photons with resonant frequencies, and combining with the fact that alkali metal atoms have different absorption effects on photons with different frequencies, a scheme for in-situ stable control of the pumping light frequency by using the absorption curve of the alkali metal gas chamber for the pumping light is established, realizing the design effect of in-situ frequency stabilization of the pumping light of a spin-exchange relaxation-free inertial measurement device by using an alkali metal atom gas chamber. The present invention stabilizes the frequency of the pumping light based on the absorption curve of the alkali metal atoms for the pumping light. While meeting the design requirements for stable control of the pumping light frequency, it has the characteristics of saving volume and being convenient for engineering implementation, reducing the disadvantage of volume increase caused by an external frequency stabilization module, solving the problem that the frequency stabilization working point of the external frequency stabilization module is inconsistent with the optimal working point of the pumping light frequency of the spin-exchange relaxation-free inertial measurement device, improving the polarization rate of alkali metal atoms, being applicable to products such as spin-exchange relaxation-free inertial measurement devices, and having a very broad application prospect.

[0016] The advantages of the present invention compared with the prior art are as follows: The present invention uses the internal alkali metal gas chamber of the spin-exchange relaxation-free inertial measurement device for frequency stabilization, avoiding the defect that the laser frequency is detuned from the resonance frequency of the internal alkali metal atoms in the traditional frequency stabilization method. At the same time, by using the internal alkali metal gas chamber for frequency stabilization, the volume of the device is reduced, the cost is saved, and it is convenient for further miniaturization. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of an in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device implementing the present invention.

[0018] The reference numerals are listed as follows: 1 - temperature control system; 2 - laser; 3 - first 1 / 2 wave plate; 4 - first polarization beam splitter prism; 5 - liquid crystal phase retarder; 6 - second polarization beam splitter prism; 7 - first plano-convex lens; 8 - second plano-convex lens; 9 - mirror; 10 - second 1 / 2 wave plate; 11 - third polarization beam splitter prism; 12 - first photodetector; 13 - 1 / 4 wave plate; 14 - magnetic shielding barrel; 15 - three-dimensional magnetic compensation coil; 16 - oven; 17 - alkali metal gas cell; 18 - second photodetector; 19 - signal generator; 20 - current control system; 21 - lock-in amplifier; 22 - optical power control system; 23 - optical intensity attenuator. Detailed implementation manners

[0019] The present invention will be described below in conjunction with the accompanying drawings ( Figure 1 ).) and embodiments.

[0020] Figure 1 is a schematic structural diagram of an in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device according to the present invention. At the same time, Figure 1 illustrates the principle of the in-situ frequency stabilization system of the present invention. Refer to Figure 1As shown in the figure, an in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device, comprising a temperature control system (1), a laser (2), a first half-wave plate (3), a first polarization beam splitter prism (4), a liquid crystal phase retarder (5), a second polarization beam splitter prism (6), a first plano-convex lens (7), a second plano-convex lens (8), a mirror (9), a second half-wave plate (10), a third polarization beam splitter prism (11), a first photodetector (12), a quarter-wave plate (13), a magnetic shielding barrel (14), a three-dimensional magnetic compensation coil (15), an oven (16), an alkali metal gas cell (17), a second photodetector (18), a signal generator (19), a current control system (20), a lock-in amplifier (21), an optical power control system (22), and an optical intensity attenuator (23); the temperature control system (1) controls the temperature of the laser (2), and the current control system (20) controls the current of the laser (2); the laser (2) outputs a beam of monochromatic light that sequentially passes through the first half-wave plate (3), the first polarization beam splitter prism (4), the liquid crystal phase retarder (5), the second polarization beam splitter prism (6), the first plano-convex lens (7), the second plano-convex lens (8), the mirror (9), the second half-wave plate (10), and the third polarization beam splitter prism (11) and is divided into two beams of light with the same size and orthogonal polarization directions. After the first beam of light passes through the first photodetector (12), the optical signal is converted into an electrical current signal and fed back to the optical power control system (22); the second beam of light sequentially passes through the quarter-wave plate (13) and the gas cell (17) and then is sent to the second photodetector (18); the signal generator (19) generates a sine wave signal that is sent to the current control system (20) on the one hand to modulate the frequency of the light output by the laser (2), and to the lock-in amplifier (21) on the other hand as a reference signal; the current control system (20) processes the output signal of the lock-in amplifier (21) to generate a control signal, and the control signal is added to the modulation signal of the signal generator (19) and then applied to the laser (2) as a control signal.

[0021] The laser (2) is a semiconductor laser. The first polarization beam splitter prism (4), the liquid crystal phase retarder (5), and the second polarization beam splitter prism (6) together constitute a light intensity stabilization module; the first polarization beam splitter prism (4) and the second polarization beam splitter prism (6) are vertically placed to achieve the extinction effect, and the transmitted light intensity of the second polarization beam splitter prism (6) is stably controlled by adjusting the voltage of the liquid crystal phase retarder (5). By rotating and adjusting the second 1 / 2 wave plate (10), the light intensities of the two outgoing beams of the third polarization beam splitter prism (11) are made the same. The magnetic shielding barrel (14) is used to shield the external magnetic field and adopts a three-layer structure of two layers of permalloy and one layer of ferrite. The gas chamber (17) contains potassium, rubidium, or cesium atoms and is filled with nitrogen and helium at the same time. The light intensity attenuation sheet (23) attenuates the light intensity entering the first photodetector (12) to the linear region of the operating point of the first photodetector (12). The second photodetector (18) converts the optical signal after passing through the gas chamber (17) into an electrical signal as the signal to be demodulated and sends it to the lock-in amplifier (21) to obtain the differential signal of the absorption spectrum.

[0022] By modulating and demodulating the frequency of the laser beam emitted by the laser (2), the feedback signal required by the current control system can be obtained, that is:

[0023] Define the light intensity after passing through the quarter-wave plate (13) as I0, then the light intensity after passing through the gas chamber (17) is I:

[0024] I = I0f(w)

[0025] where w is the frequency of the laser beam emitted by the laser (2); f(w) is the absorption coefficient of the gas chamber for light intensity and is related to the laser frequency w. By applying a small-amplitude modulation with a frequency of w′ to the current of the laser (2) through the signal generator (19), the frequency of the laser beam emitted by the laser (2) after modulation is:

[0026] w = w0 + A sin(w′t)

[0027] where w0 is the frequency before modulation and A is the modulation depth. Then the light intensity I after modulation is:

[0028] I = I0f(w0 + A sin(w′t))

[0029] Performing a Taylor expansion on the modulated light intensity I, we get:

[0030]

[0031] where f (1) 、f (2)... are the first derivative, second derivative... of the function f respectively. A first harmonic signal in the optical intensity I can be obtained through a lock-in amplifier (21). By locking the frequency of the laser beam emitted by the laser (2) at the zero-crossing point of the first harmonic signal, the in-situ stabilization of the frequency of the laser beam emitted by the laser (2) can be achieved.

[0032] An in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device according to the present invention uses an internal alkali metal gas cell in the spin-exchange relaxation-free inertial measurement device to perform in-situ frequency stabilization of the pumping light, avoiding the defect that the laser frequency detunes from the resonance frequency of the internal alkali metal atoms caused by using an external gas cell for frequency stabilization in the traditional frequency stabilization method. At the same time, by using the internal alkali metal gas cell for frequency stabilization, the volume of the device is reduced, the cost is saved, and it is convenient for further miniaturization.

[0033] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. It is hereby pointed out that the above description helps those skilled in the art to understand the present invention, but does not limit the protection scope of the present invention. Any implementation that is an equivalent replacement, modification, improvement, and / or simplification of the above description without departing from the substantial content of the present invention falls within the protection scope of the present invention.

Claims

1. An in-situ frequency stabilization system for the pumping light of a spin-exchange relaxation-free inertial measurement device, characterized in that, It includes a temperature control system (1), a laser (2), a first half-wave plate (3), a first polarization beam splitter prism (4), a liquid crystal phase retarder (5), a second polarization beam splitter prism (6), a first plano-convex lens (7), a second plano-convex lens (8), a mirror (9), a second half-wave plate (10), a third polarization beam splitter prism (11), a first photodetector (12), a quarter-wave plate (13), a magnetic shielding barrel (14), a three-dimensional magnetic compensation coil (15), an oven (16), an alkali metal gas cell (17), a second photodetector (18), a signal generator (19), a current control system (20), a lock-in amplifier (21), an optical power control system (22), and an optical intensity attenuator (23); the temperature control system (1) controls the temperature of the laser (2), and the current control system (20) controls the current of the laser (2); the laser (2) outputs a beam of monochromatic light that sequentially passes through the first half-wave plate (3), the first polarization beam splitter prism (4), the liquid crystal phase retarder (5), the second polarization beam splitter prism (6), the first plano-convex lens (7), the second plano-convex lens (8), the mirror (9), the second half-wave plate (10), and the third polarization beam splitter prism (11) and is divided into two beams of light with the same size and orthogonal polarization directions. After the first beam of light passes through the first photodetector (12), the optical signal is converted into an electrical current signal and fed back to the optical power control system (22); the second beam of light sequentially passes through the quarter-wave plate (13) and the gas cell (17) and then enters the second photodetector (18); the signal generator (19) generates a sine wave signal that is sent to the current control system (20) on the one hand to modulate the frequency of the light output by the laser (2), and to the lock-in amplifier (21) on the other hand as a reference signal; the current control system (20) processes the output signal of the lock-in amplifier (21) to generate a control signal, and the control signal is added to the modulation signal of the signal generator (19) and then applied to the laser (2) as a control signal.

2. The in-situ frequency stabilization system for the pumping light of the spin-exchange relaxation-free inertial measurement device according to claim 1, characterized in that The laser (2) is a semiconductor laser.

3. The in-situ frequency stabilization system for the pumping light of the spin-exchange relaxation-free inertial measurement device according to claim 1, wherein The first polarization beam splitter prism (4), the liquid crystal phase retarder (5), and the second polarization beam splitter prism (6) together constitute a stable optical intensity module; the first polarization beam splitter prism (4) and the second polarization beam splitter prism (6) are vertically placed to achieve an extinction effect, and the transmitted optical intensity of the second polarization beam splitter prism (6) is stably controlled by adjusting the voltage of the liquid crystal phase retarder (5).

4. The in-situ frequency stabilization system for the pumping light of the spin-exchange-relaxation-free inertial measurement device according to claim 1, characterized in that, By rotating and adjusting the second half-wave plate (10), the optical intensities of the two output beams of the third polarization beam splitter prism (11) are made the same.

5. The in-situ frequency stabilization system for the pumping light of the spin-exchange relaxation-free inertial measurement device according to claim 1, characterized in that, The magnetic shielding barrel (14) is used to shield the external magnetic field and adopts a three-layer structure of two layers of permalloy and one layer of ferrite.

6. The in-situ frequency stabilization system for the pumping light of the spin-exchange relaxation-free inertial measurement device according to claim 1, wherein, The gas cell (17) contains potassium, rubidium, or cesium atoms and is filled with nitrogen and helium at the same time.

7. The in-situ frequency stabilization system for the pumping light of the spin-exchange-relaxation-free inertial measurement device according to claim 1, wherein The optical intensity attenuator (23) attenuates the optical intensity entering the first photodetector (12) to the linear region of the operating point of the first photodetector (12).

8. The in-situ frequency stabilization system for the pumping light of the spin-exchange relaxation-free inertial measurement device according to claim 1, characterized in that, The second photodetector (18) converts the optical signal after passing through the gas cell (17) into an electrical current signal as the signal to be demodulated and sends it to the lock-in amplifier (21) to obtain the differential signal of the absorption spectrum.

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