用于可移动量子重力仪的光纤拉曼激光源研究

Research on Fiber Raman Laser Source for Mobile Quantum Gravimeter

基于两个窄线宽光纤激光器和自制的锁相控制系统,研制了一个低相位噪声窄线宽拉曼光纤激光源,建立了拉曼光纤激光系统的相位噪声模型,研究了拍频光功率、不同频率参考源对拉曼激光相位噪声的影响。实验结果表明,该拉曼光纤激光源在10 Hz~1 MHz范围内相位噪声功率谱密度可达到^(-11)8 dBc/√Hz,相应的相位噪声为22.7 mrad,将其应用到重力仪中获得的重力测量灵敏度为10.93μGal/√Hz。对拉曼激光源进行连续3 h的相位噪声稳定性测试和连续25 min的频率稳定性测试,得到的相位噪声标准差为0.734 mrad,相应的重力灵敏度标准差仅为0.349μGal/√Hz。当积分时间为1 s时,相位锁定时频率稳定度为2.675×10^(-11),验证了该激光源具有低相位噪声和高稳定性。利用相位噪声模型得到的理论结果与实验结果一致,证实了理论模型的正确性。

With the development of atomic manipulation technology,the cold atom interferometry is widely used to measure astronomical and physical parameters such as gravitational acceleration,gravitational constant,fine structure constant and gravitational wave.Among them,the quantum gravimeter based on the cold atomic interference has developed rapidly due to advantages of small size,strong mobility,high sensitivity and high stability.As an impact on the performance of cold quantum gravimeters,the phase noise of Raman light directly affects the sensitivity of quantum gravimeter.Therefore,the study of low phase noise Raman laser source for quantum gravimeter has become one of the research hotspots.The schemes of Raman laser generation include the electro-optic modulation method,the acousto-optic modulation method and optical locking method.The electro-optic modulation method loses a lot of power during the modulation process,and the modulation sideband is easy to introduce unstable system effects.In the acousto-optic modulation method,the change of the external environment causes the instability of the mirror in the spatial optical path to introduce additional errors,and the high-frequency AOM diffraction efficiency is very low,it is difficult to generate high-frequency signals,and it is expensive.The optical phase-locked method generates a phase error signal after the beat frequency detection of the master and slave lasers,the error signal is fed back to the master laser through the circuit control system to maintain phase synchronization,and a Raman laser is generated finally.Compared with the other two methods,the all-fiber optical phase-locked method does not require complex spatial optical paths,have high reliability and does not generate excess sidebands.Therefore,this paper constructs a low phase noise Raman fiber laser system with low phase noise,high stability,strong environmental adaptability,and can be used for field gravity measurement.A complete phase noise analysis model for Raman laser system is established,and its phase noise characteristics are theoretically analyzed and optimized.The phase noise power spectral density can reach^(-11)8 dBc/√Hz in the range of 10 Hz~1 MHz,and the corresponding phase noise is 22.7 mrad,and the gravity measurement sensitivity obtained by applying it to the gravimeter is 10.93μGal/√Hz.The effects of beat frequency optical power and different frequency reference sources on the phase noise of Raman laser are studied,and when the output optical power of the master and slave lasers P1∶P2=1∶1,the frequency stability of the Raman laser source is the best.By testing the phase noise stability of the Raman laser source for three hours and the frequency stability for 25 minutes,the calculated standard deviation of the phase noise is 0.734 mrad and the corresponding standard deviation of the gravity sensitivity is only 0.349μGal/√Hz,and when the integration time is 1 s,the frequency stability of the phase locking is 2.675×10^(-11),which verifies that the laser source has low phase noise and high stability.Moreover,the theoretical results obtained by using the phase noise model are highly consistent with the experimental results,which confirms the correctness of the theoretical model.