用于原子干涉重力仪的小型频率合成器设计与实现

Design and implementation of a compact microwave synthesizer for atomic interference gravimeter

在原子干涉重力实验中,拉曼激光制备常采用光学锁相环方法,即先将主从激光器拍频信号与6.8 GHz微波信号源进行混频,再与直接数字频率合成信号发生器进行鉴频鉴相,得到的反馈信号用以控制激光器实现低噪声拉曼光输出,而拉曼光相噪将直接影响原子干涉重力仪的灵敏度。本设计采用STM32F103C8T6单片机对LMX2594数字锁相环芯片进行编程控制,通过锁相环频率合成技术,最终获得6.8 GHz的微波信号源。测试结果表明,该微波信号源相位噪声分别为−65.2 dB@1 Hz、−95.3 dB@1 kHz,频率稳定度为2.72×10^(-11)@1 s,输出功率大于10 dBm。在脉冲间隔时间为100 ms时,信号源对原子干涉重力仪灵敏度的影响为8×10^(-8) m/s^(2)/Hz^(1/2),分辨率影响为2×10^(-8) m/s2@600 s,具有频率稳定度高、相位噪声低等优点,可以满足原子干涉重力实验。

In atom interferometer gravity experiments,Raman laser preparation commonly uses an optical phase-locked loop method,in which the master and slave laser beat signal is mixed with a 6.8 GHz microwave signal source firstly,then frequency discrimination is performed with direct digital frequency synthesis signal generator,and lastly the feedback signal obtained is used to control the low-noise Raman optical output.So the phase noise of Raman output will directly affect the sensitivity of the atom interference gravimeter.This design uses the STM32F103C8T6 microcontroller to program and control the LMX2594 digital phase-locked loop chip,and obtains a 6.8 GHz microwave signal source through the phase-locked loop frequency synthesis technology.The final experimental results show that the phase 2.72×10^(-11)@1 s,and the output power is greater than 10 dBm.When the pulse interval time(T)is 100 ms,influence of signal source on sensitivity of the atom interference gravimeter is 8×10^(-8) m/s^(2)/Hz^(1/2),and on the resolution of the atom interference gravimeter is 2×10^(-8) g@600 s.It is shown that the design has the advantages of high frequency stability and low phase noise,which can meet the requirements of microwave reference sources for atom interferometer.