A rubidium atom interferometer laser system

Abstract

This invention discloses a rubidium atom interferometer laser system, belonging to the field of cold atom interferometry. The invention includes a laser seed source module, a cooling light module, a frequency stabilization module, a Raman beam detuning module, a Raman beam module, and a beat frequency phase-locked loop module. This invention utilizes an electro-optic modulator to frequency modulate the laser to generate Raman beams and a pump-back beam. Large detuning of the Raman beam is achieved using an optical fiber AOM (Analog Optical Optical Unit), an optical fiber circulator, and an optical fiber retroreflector. The modulation frequencies of the two AOMs on the Raman beam path have a certain frequency difference. The carrier wave of one of the two EOMs on the Raman beam path and the sideband of the other are used as two Raman beams. A high-speed fiber optic photodetector detects the beat frequency signal, achieving phase locking between the two Raman beams. The rubidium atoms in this invention can be in the F=1 or F=2 state; the Raman beam detuning is increased fourfold, improving Raman beam power and stability, reducing system requirements; and the phase of the Raman beam is locked to avoid stimulated Raman transitions.

Description

Technical Field

[0001] This invention relates to a rubidium atom interferometer laser system, belonging to the field of cold atom interferometry. Background Technology

[0002] Cold atom interferometers use lasers to manipulate alkali metal atoms, achieving atomic cooling, trapping, and interference. Laser systems are one of the important foundations for realizing atomic interference.

[0003] Currently, there are two main types of laser systems commonly used in rubidium atomic interferometers: The first is a space-light laser system, which utilizes distributed feedback lasers, distributed Bragg reflector lasers, external cavity tunable lasers, or 1560nm fiber lasers to obtain the 780nm laser corresponding to the D2 line of rubidium atoms through frequency doubling. Then, optical devices including waveplates, mirrors, polarizing beam splitters (PBS), spatial acousto-optic modulators (AOM), and fiber couplers are used to achieve laser frequency shifting, switching, and beam splitting. Atomic interferometers require lasers of various frequencies, including cooling light, probe light, pump-back light, blow-away light, and Raman light. The space-light optical path is large, has high optical power loss, and low environmental adaptability. The second type is an all-fiber laser system, which utilizes commercially available communication-band optical devices, such as 1560nm seed sources, electro-optic modulators, and erbium-doped optical fiber amplifiers. Amplifier (EDFA), fiber AOM, periodically polarized lithium niobate crystal (PPLN) – except for the laser frequency stabilization module, all-fiber laser systems are composed of fiber optic devices, which have the characteristics of strong environmental adaptability. However, the electro-optic modulator (EOM) generates multiple sets of sidebands during modulation. The stimulated Raman transition process involves multiple pairs of Raman light interacting with atoms, introducing systematic errors. Although IQ modulators and fiber gratings (FBGs) can suppress the extra sidebands, the suppression ratio is low, and the IQ modulator requires three bias voltages to control the carrier-sideband ratio, which can easily introduce changes in the carrier-sideband ratio.

[0004] Various precision measuring devices based on atomic interferometry, such as gravimeters, gravity gradiometers, and gyroscopes, have extremely high measurement accuracy and are rapidly developing from experimental research to engineering applications, with broad application prospects. Therefore, there is an urgent need for a laser system with low linewidth, high power, and strong environmental applicability. Summary of the Invention

[0005] The purpose of this invention is to provide a rubidium atom interferometer laser system, which uses an electro-optic modulator to frequency modulate the laser to generate Raman light and pump-back light. Large detuning of the Raman light is achieved using fiber AOMs, fiber circulators, and fiber retroreflectors. The modulation frequencies of the two AOMs on the Raman light path have a certain frequency difference. The carrier wave of one of the two EOMs on the Raman light path and the sideband of the other are used as two Raman beams. A high-speed fiber photodetector detects the beat frequency signal, achieving phase locking between the two Raman beams while preventing the redundant sidebands from undergoing stimulated Raman transitions with atoms.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The present invention provides a rubidium atom interferometer laser system, comprising: a laser seed source module, a cooling light module, a frequency stabilization module, a Raman light detuning module, a Raman light module, and a beat frequency phase-locked loop module;

[0008] The laser seed source module includes: a laser seed source, an optical fiber isolator, and a first optical fiber coupler;

[0009] The cooling optical module includes: a first optical fiber EOM, a first EDFA, a first PPLN, a second optical fiber coupler, and a first optical fiber AOM;

[0010] The frequency stabilization module includes: a third fiber coupler, a second fiber EOM, a first fiber collimator, a second fiber collimator, a first polarizer, a first half-wave plate, a first PBS, a second half-wave plate, a first reflector, a second reflector, a rubidium bulb, a second PBS, a first space photodetector, a second polarizer, a third half-wave plate, and a second space photodetector.

[0011] The Raman optical detuning module includes: an optical fiber circulator, a second optical fiber AOM, and an optical fiber retroreflector.

[0012] The Raman optical module includes: a second EDFA, a fourth fiber coupler, a third fiber EOM, a fourth fiber EOM, a third fiber AOM, a fourth fiber AOM, a third EDFA, a fourth EDFA, a second PPLN, a third PPLN, a fiber polarization combiner, and a fifth fiber AOM.

[0013] The beat frequency phase-locked module includes: a fiber optic high-speed photodetector, a pre-stage low-noise amplifier, a 603 frequency and phase detector, a filter, a post-stage low-noise amplifier, and a PID module.

[0014] The laser seed source module is provided by fiber DFB or fiber ECDL, and the laser output is split into two paths after passing through the fiber isolator and the first fiber coupler.

[0015] One output of the first fiber coupler is connected to the input of the cooling optical module, and passes through the first fiber EOM, the first EDFA, the first PPLN and the second fiber coupler in sequence. One output of the second fiber coupler is connected to the input of the first fiber AOM. The output of the first fiber AOM serves as the cooling light, the probe light and the return pump light.

[0016] When the first fiber EOM is modulated, its carrier and positive first-order sideband serve as the cooling light and pump-back light of the interferometer, respectively. When the first fiber EOM is not modulated, its output serves as the probe light. The first fiber AOM serves as an optical switch.

[0017] Another output of the second fiber coupler is connected to the input of the third fiber coupler of the frequency stabilization module. The first output of the third fiber coupler is connected to the input of the second fiber EOM. The second output of the third fiber coupler and the output of the second fiber EOM are respectively expanded and collimated by the first fiber collimator and the second fiber collimator. The laser beam expanded and collimated by the first fiber collimator passes sequentially through the first polarizer, the first half-wave plate, the first PBS, the second half-wave plate, the first mirror, the second mirror, the rubidium bulb, and the second PBS, and is detected by the first space photodetector. The laser beam expanded and collimated by the second fiber collimator passes sequentially through the second polarizer, the third half-wave plate, the second PBS, the rubidium bulb, the second mirror, the first mirror, the second half-wave plate, and the first PBS, and is detected by the second space photodetector. The signal from the first space photodetector is used for modulation-transfer frequency stabilization, and the signal from the second space photodetector is used to observe saturated absorption signals or wavelength modulation-transfer frequency stabilization.

[0018] The frequency stabilization module can lock the wavelength corresponding to the sideband of the first optical fiber EOM, and achieve frequency modulation of the laser output frequency by changing the driving frequency of the first optical fiber EOM.

[0019] The other output of the first fiber coupler is connected to the input of the Raman optical detuning module, and passes through the fiber circulator, the second fiber AOM, the fiber retroreflector, the second fiber AOM, and the fiber circulator in sequence.

[0020] The Raman optical detuning module utilizes the fiber AOM dual-pass mode to achieve Raman optical detuning, and after frequency doubling, the detuning is four times the fiber AOM driving frequency.

[0021] The output of the fiber optic circulator is connected to the input of the Raman optical module, passing sequentially through the second EDFA and the fourth fiber optic coupler. One output of the fourth fiber optic coupler passes sequentially through the third fiber EOM, the third fiber AOM, the third EDFA, and the second PPLN. The other output of the fourth fiber optic coupler passes sequentially through the fourth fiber EOM, the fourth fiber AOM, the fourth EDFA, and the third PPLN. The outputs of the second and third PPLNs are respectively connected to the two inputs of the fiber polarization combiner. The higher-power output of the fiber polarization combiner is connected to the fifth fiber AOM as the Raman light. The EDFA performs optical power pre-amplification. The carrier of the third fiber EOM and the positive first-order sideband of the fourth fiber EOM are used as two Raman beams. The driving frequencies of the third fiber AOM and the fourth fiber AOM are different to avoid the multi-order sidebands of the fourth fiber EOM resonating with atoms. The driving frequencies of the third fiber AOM and the fourth fiber AOM are compensated for the Doppler detuning of atoms by frequency sweeping. During the frequency sweeping process of the third fiber AOM and the fourth fiber AOM, the third EDFA and the fourth EDFA can always remain in saturation due to the prevention of the second EDFA. The fiber polarization combiner realizes Raman beam combining, and the fifth fiber AOM realizes the switching of Raman beams.

[0022] Another output of the fiber polarization combiner is connected to the input of the beat frequency phase-locked module. The optical beat frequency signal is converted into an electrical signal by the fiber high-speed photodetector, amplified by the pre-stage low-noise amplifier, and compared with the reference signal in the frequency and phase discriminator. The error signal of the frequency and phase discriminator passes through the filter, the post-stage low-noise amplifier, and the PID module in sequence. The feedback signal output by the PID module is fed back to the fourth fiber EOM to achieve laser phase locking.

[0023] Beneficial effects:

[0024] 1. The present invention discloses a rubidium atom interferometer laser system, which uses an electro-optic modulator to frequency modulate the laser to generate Raman light and pump back light. The pump back light can be generated by modulation through a first fiber EOM or a third fiber EOM. During the polarization gradient cooling process, the first fiber EOM turns off the cooling light and the pump back light at the same time. After the polarization gradient cooling is completed, the rubidium atoms are in the F=1 state. The third fiber EOM turns off both the cooling light and the pump back light. After the polarization gradient cooling is completed, the atoms are in the F=2 state.

[0025] 2. The rubidium atom interferometer laser system disclosed in this invention utilizes fiber AOM, fiber circulator and fiber retroreflector to achieve large detuning of Raman light. After laser frequency doubling, the detuning of Raman light can be increased to four times the modulation frequency of fiber AOM. Compared with the use of high frequency spatial AOM, the power and stability of Raman light are improved. Compared with the frequency shifting method of sideband locking and beat frequency lock phase-locking, the requirements for control system are reduced.

[0026] 3. The rubidium atom interferometer laser system disclosed in this invention has a frequency difference between the modulation frequencies of the two AOMs in the Raman optical path. Then, the carrier of one of the two EOMs in the Raman optical path and the sideband of the other are used as two Raman beams respectively. Finally, the beat frequency signal is detected by the fiber optic high-speed photodetector to achieve phase locking between the two Raman beams, while avoiding the unnecessary sidebands from undergoing stimulated Raman transitions with atoms. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall composition of a rubidium atom interferometer laser system according to the present invention;

[0028] Figure 2 This is a schematic diagram of a rubidium atom interferometer laser system according to the present invention;

[0029] Figure 3 This is a schematic diagram of the frequency stabilization module of a rubidium atom interferometer laser system according to the present invention;

[0030] Among them, 1-laser seed source module, 2-cooling light module, 3-frequency stabilization module, 4-Raman light large detuning module, 5-Raman light module, 6-beat frequency phase-locked loop module, 101-laser seed source, 102-fiber isolator, 103-first fiber coupler, 201-first fiber EOM, 202-first EDFA, 203-first PPLN, 204-second fiber coupler, 205-first fiber AOM, 301-third fiber coupler, 302-second fiber EOM, 303-first fiber collimator, 304-second fiber collimator, 305-first polarizer, 306-first half-wave plate, 307-first PBS, 308-second half-wave plate, 309-first reflector, 310-second reflector, 311-rubidium bulb, 312-second PBS, 313-first space Photodetector, 314-Second polarizer, 315-Third half-wave plate, 316-Second space photodetector, 401-Fiber circulator, 402-Second fiber AOM, 403-Fiber retroreflector, 501-Second EDFA, 502-Fourth fiber coupler, 503-Third fiber EOM, 504-Fourth fiber EOM, 505-Third fiber AOM, 506-Fourth fiber AOM, 507-Third EDFA, 508-Fourth EDFA, 509-Second PPLN, 510-Third PPLN, 511-Fiber polarization combiner, 512-Fiber AOM, 601-Fiber high-speed photodetector, 602-Pre-stage low-noise amplifier, 603-Frequency and phase detector, 604-Filter, 605-Post-stage low-noise amplifier, 606-PID module. Detailed Implementation

[0031] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0032] Example 1:

[0033] like Figure 1 As shown, an embodiment of a rubidium atom interferometer laser system includes: a laser seed source module 1, a cooling light module 2, a frequency stabilization module 3, a Raman light detuning module 4, a Raman light module 5, and a beat frequency phase-locked loop module 6;

[0034] like Figure 2 As shown, the laser seed source module 1 includes: a laser seed source 101, an optical fiber isolator 102, and a first optical fiber coupler 103.

[0035] like Figure 2 As shown, the cooling optical module 2 includes: a first optical fiber EOM 201, a first EDFA 202, a first PPLN 203, a second optical fiber coupler 204, and a first optical fiber AOM 205;

[0036] like Figure 3 As shown, the frequency stabilization module 3 includes: a third fiber coupler 301, a second fiber EOM 302, a first fiber collimator 303, a second fiber collimator 304, a first polarizer 305, a first half-wave plate 306, a first PBS 307, a second half-wave plate 308, a first reflector 309, a second reflector 310, a rubidium bulb 311, a second PBS 312, a first space photodetector 313, a second polarizer 314, a third half-wave plate 315, and a second space photodetector 316.

[0037] like Figure 2 As shown, the Raman optical detuning module 4 includes: an optical fiber circulator 401, a second optical fiber AOM 402, and an optical fiber retroreflector 403.

[0038] like Figure 2 As shown, the Raman optical module 5 includes: a second EDFA 501, a fourth fiber coupler 502, a third fiber EOM 503, a fourth fiber EOM 504, a third fiber AOM 505, a fourth fiber AOM 506, a third EDFA 507, a fourth EDFA 508, a second PPLN 509, a third PPLN 510, a fiber polarization combiner 511, and a fifth fiber AOM 512.

[0039] like Figure 2 As shown, the beat frequency phase-locked loop module 6 includes: a fiber optic high-speed photodetector 601, a pre-stage low-noise amplifier 602, a frequency and phase detector 603, a filter 604, a post-stage low-noise amplifier 605, and a PID module 606.

[0040] In this embodiment, the laser seed source module 1 is provided with a laser seed source 101 by a 1560nm band fiber DFB, which passes through a fiber isolator 102 and a first fiber coupler 103 in sequence, and the output laser is split into two outputs.

[0041] One output of the first fiber coupler 103 is connected to the input of the cooling optical module 2, and then passes through the first fiber EOM 201, the first EDFA 202, the first PPLN 203 and the second fiber coupler 204 in sequence. One output of the second fiber coupler 204 is connected to the input of the first fiber AOM 205. The output of the first fiber AOM 205 serves as the cooling light, the probe light and the return pump light.

[0042] When the first fiber EOM201 is modulated, its carrier and positive first-order sideband serve as the cooling light and pump back light of the interferometer, respectively. When the first fiber EOM201 is not modulated, its output serves as the probe light. The first fiber AOM205 serves as an optical switch.

[0043] Another output of the second fiber coupler 204 is connected to the input of the third fiber coupler 301 of the frequency stabilization module 3. The first output of the third fiber coupler 301 is connected to the input of the second fiber EOM 302. The second output of the third fiber coupler 301 and the output of the second fiber EOM 302 are respectively expanded and collimated by the first 303 and the second fiber collimator 304. After being expanded and collimated by the first fiber collimator 303, the laser beam passes sequentially through the first polarizer 305, the first half-wave plate 306, the first PBS 307, the second half-wave plate 308, the first reflector 309, and the second reflector 304. The first space photodetector 313 detects the laser beam after it has been expanded and collimated by the second fiber collimator 304, through the second polarizer 314, the third half-wave plate 315, the second PBS 312, the rubidium bulb 311, the second mirror 310, the first mirror 309, the second half-wave plate 308, and the first PBS 307. The laser beam is then detected by the second space photodetector 316. The signal from the first space photodetector 313 is used for modulation transfer frequency stabilization, and the signal from the second space photodetector 316 is used to observe saturated absorption signals or wavelength modulation transfer frequency stabilization.

[0044] The frequency stabilization module 3 can lock the wavelength corresponding to the sideband of the first optical fiber EOM201, and achieve frequency modulation of the laser output frequency by changing the driving frequency of the first optical fiber EOM201.

[0045] The other output of the first fiber coupler 103 is connected to the input of the Raman optical detuning module 4, and passes through the fiber circulator 401, the second fiber AOM 402, the fiber retroreflector 403, the second fiber AOM 402, and the fiber circulator 401 in sequence.

[0046] Raman optical detuning module 4 utilizes fiber optic AOM dual-pass mode to achieve Raman optical detuning;

[0047] In the embodiment, the detuning after frequency doubling is four times the fiber AOM drive frequency;

[0048] The output of fiber optic circulator 401 is connected to the input of Raman optical module 5, and then sequentially passes through second EDFA 501 and fourth fiber optic coupler 502. One output of fourth fiber optic coupler 502 sequentially passes through third fiber EOM 503, third fiber AOM 505, third EDFA 507, and second PPLN 509. The other output of fourth fiber optic coupler 502 sequentially passes through fourth fiber EOM 504, fourth fiber AOM 506, fourth EDFA 508, and third PPLN 510. The outputs of second PPLN 509 and third PPLN 510 are respectively connected to fiber polarization combiner 51. The two input ends of 1 are connected. The higher-power output of the fiber polarization combiner 511 is connected to the fifth fiber AOM 512 as Raman light. The second EDFA 501 performs optical power pre-amplification. The carrier of the third fiber EOM 503 and the positive first-order sideband of the fourth fiber EOM 504 serve as two Raman beams. The driving frequencies of the third fiber AOM 505 and the fourth fiber AOM 506 are different to avoid the multi-order sidebands of the fourth fiber EOM 504 resonating with the atoms. The driving frequencies of the third fiber AOM 505 and the fourth fiber AOM 506 are compensated for the Doppler detuning of the atoms by frequency sweeping. During the frequency sweeping process of the third fiber AOM 505 and the fourth fiber AOM 506, the third EDFA 507 and the fourth EDFA 508 can always remain in saturation due to the prevention of the second EDFA 501. The fiber polarization combiner 511 realizes Raman beam combining, and the fifth fiber AOM 512 realizes the switching of Raman light.

[0049] Another output of the fiber polarization combiner 511 is connected to the input of the beat frequency phase-locked module 6. The optical beat frequency signal is converted into an electrical signal by the fiber high-speed photodetector 601, amplified by the pre-stage low-noise amplifier 602, and compared with the reference signal in the frequency and phase discriminator 603. The error signal of the frequency and phase discriminator passes through the filter 604, the post-stage low-noise amplifier 605 and the PID module 606 in sequence. The feedback signal output by the PID module 606 is fed back to the fourth fiber EOM 504 to achieve laser phase locking.

[0050] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rubidium atom interferometer laser system, characterized in that: include: Laser seed source module (1), cooling light module (2), frequency stabilization module (3), Raman light detuning module (4), Raman light module (5), and beat frequency phase-locked module (6); The laser seed source module (1) includes: a laser seed source (101), an optical fiber isolator (102), and a first optical fiber coupler (103); The cooling optical module (2) includes: a first optical fiber EOM (201), a first EDFA (202), a first PPLN (203), a second optical fiber coupler (204), and a first optical fiber AOM (205); The frequency stabilization module (3) includes: a third fiber coupler (301), a second fiber EOM (302), a first fiber collimator (303), a second fiber collimator (304), a first polarizer (305), a first half-wave plate (306), a first PBS (307), a second half-wave plate (308), a first reflector (309), a second reflector (310), a rubidium bulb (311), a second PBS (312), a first space photodetector (313), a second polarizer (314), a third half-wave plate (315), and a second space photodetector (316); The Raman optical detuning module (4) includes: an optical fiber circulator (401), a second optical fiber AOM (402), and an optical fiber retroreflector (403); The Raman optical module (5) includes: a second EDFA (501), a fourth fiber coupler (502), a third fiber EOM (503), a fourth fiber EOM (504), a third fiber AOM (505), a fourth fiber AOM (506), a third EDFA (507), a fourth EDFA (508), a second PPLN (509), a third PPLN (510), a fiber polarization combiner (511), and a fifth fiber AOM (512); The beat frequency phase-locked module (6) includes: fiber optic high-speed photodetector (601), pre-stage low-noise amplifier (602), 603 frequency and phase detector (603), filter (604), post-stage low-noise amplifier (605) and PID module (606); The laser seed source (101) module (1) is provided by fiber DFB or fiber ECDL, and passes through fiber isolator (102) and first fiber coupler (103) in sequence, and the output laser is split into two outputs; One output of the first fiber coupler (103) is connected to the input of the cooling optical module (2), and sequentially through the first fiber EOM (201), the first EDFA (202), the first PPLN (203) and the second fiber coupler (204). One output of the second fiber coupler (204) is connected to the input of the first fiber AOM (205). The output of the first fiber AOM (205) serves as the cooling light, the probe light and the return pump light. When the first fiber EOM (201) is modulated, its carrier and positive first-order sideband serve as the cooling light and pump back light of the interferometer, respectively. When the first fiber EOM (201) is not modulated, its output serves as the probe light. The first fiber AOM (205) serves as the optical switch. The other output of the second fiber coupler (204) is connected to the input of the third fiber coupler (301) of the frequency stabilization module (3). The first output of the third fiber coupler (301) is connected to the input of the second fiber EOM (302). The second output of the third fiber coupler (301) and the output of the second fiber EOM (302) are respectively expanded and collimated by the first fiber collimator (303) and the second fiber collimator (304). After being expanded and collimated by the first fiber collimator (303), the laser beam is sequentially passed through the first polarizer (305), the first half-wave plate (306), the first PBS (307), the second half-wave plate (308), the first reflector (309), and the second half-wave plate (308). The laser beam, after being expanded and collimated by the second fiber collimator (304), passes sequentially through the second polarizer (314), the third half-wave plate (315), the second PBS (312), the rubidium bulb (311), the second mirror (310), the first mirror (309), the second half-wave plate (308), and the first PBS (307), and is detected by the second space photodetector (316). The signal from the first space photodetector (313) is used for modulation transfer frequency stabilization, and the signal from the second space photodetector (316) is used to observe saturated absorption signals or wavelength modulation transfer frequency stabilization. The frequency stabilization module (3) can lock the wavelength corresponding to the sideband of the first fiber EOM (201) and achieve frequency modulation of the laser output frequency by changing the driving frequency of the first fiber EOM (201). The other output of the first fiber coupler (103) is connected to the input of the Raman optical detuning module (4), and passes through the fiber circulator (401), the second fiber AOM (402), the fiber retroreflector (403), the second fiber AOM (402), and the fiber circulator (401) in sequence. Raman optical detuning module (4) uses fiber AOM dual-pass mode to achieve Raman optical detuning. After frequency doubling, the detuning is four times the fiber AOM driving frequency. The output of the fiber optic circulator (401) is connected to the input of the Raman optical module (5), and then sequentially passes through the second EDFA (501) and the fourth fiber optic coupler (502). One output of the fourth fiber optic coupler (502) sequentially passes through the third fiber EOM (503), the third fiber AOM (505), the third EDFA (507), and the second PPLN (509). The other output of the fourth fiber optic coupler (502) sequentially passes through the fourth fiber EOM (504), the fourth fiber AOM (506), the fourth EDFA (508), and the third PPLN (510). The outputs of the second PPLN (509) and the third PPLN (510) are respectively connected to the two inputs of the fiber polarization combiner (511). The higher-power output of the fiber polarization combiner (511) is connected to the fifth fiber AOM (512) as the Raman optical output. The second EDFA (501) performs optical power pre-amplification. The carrier of the third fiber EOM (503) and the positive first-order sideband of the fourth fiber EOM (504) serve as two Raman beams. The driving frequencies of the third fiber AOM (505) and the fourth fiber AOM (506) are different to avoid the multi-order sideband of the fourth fiber EOM (504) from resonating with the atom. The driving frequencies of the third fiber AOM (505) and the fourth fiber AOM (506) are compensated for the Doppler detuning of the atom by frequency sweeping. During the frequency sweeping process of the third fiber AOM (505) and the fourth fiber AOM (506), the third EDFA (507) and the fourth EDFA (508) can always remain in saturation due to the prevention of the second EDFA (501). The fiber polarization combiner (511) realizes Raman beam combining. The fifth fiber AOM (512) realizes the switching of Raman beams. Another output of the fiber polarization combiner (511) is connected to the input of the beat frequency phase-locked module (6). The optical beat frequency signal is converted into an electrical signal by the fiber high-speed photodetector (601), and amplified by the pre-stage low-noise amplifier (602). The signal is then compared with the reference signal in the frequency and phase discriminator (603). The error signal of the frequency and phase discriminator passes through the filter (604), the post-stage low-noise amplifier (605), and the PID module (606) in sequence. The feedback signal output by the PID module (606) is fed back to the fourth fiber EOM (504) to achieve laser phase locking.

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