一种应用于CPT原子钟的低相噪微波频率合成器

A low phase noise microwave frequency synthesizer applied to CPT atomic clock

在微波原子钟里,微波用于激励原子的钟跃迁以获得鉴频信号,微波的相位噪声是限制微波原子钟短期频率稳定度的主要因素之一。在本工作中,实现了一种用于相干布居囚禁(CPT)原子钟的低噪声、结构简单的微波频率合成器,以满足高性能CPT原子钟需要。合成器主要由100 MHz恒温晶体振荡器(OCXO)、声表面滤波器、带锁相的介质振荡器(PDRO)和直接数字合成器(DDS)组成。经测量,对于1 Hz、100 Hz、1 kHz和10 kHz频率偏移处,其输出的3.417 GHz信号的绝对相位噪声分别为-61、-107、-118.6和-124 dBc/Hz。在1 s平均时间处,预期的交调效应对原子钟短期频率稳定的限制仅为5.8×10^(14)。该设计不仅为小型化高性能CPT原子钟提供一种结构简单的微波合成器,还可应用于POP、冷原子CPT等微波原子钟。

In the microwave atomic clock, the microwave is used to excite the clock transition of the atom to obtain the frequency discrimination signal, and the phase noise of the microwave is one of the main factors that limit the short-term frequency stability of the microwave atomic clock.In this work, a low-noise, simple-structure microwave frequency synthesizer for coherent population trap(CPT) atomic clocks was realized to meet the requirements of high-performance CPT atomic clocks.The synthesizer is mainly composed of a 100 MHz oven-controlled crystal oscillator(OCXO),a surface acoustic filter, a phase-locked dielectric oscillator(PDRO) and a direct digital synthesizer(DDS).The absolute phase noises of 3.417 GHz signal are measured to be-61,-107,-118.6 and-124 dBc/Hz for 1 Hz, 100 Hz, 1 kHz and 10 kHz offset frequencies, respectively.The expected intermodulation effect limits the short-term frequency stability of the atomic clock to only 5.8×10^(14) at 1 s average time.This design not only provides a simple structure microwave synthesizer for miniaturized high-performance CPT atomic clocks, but can also be applied to microwave atomic clocks such as POP and cold atom CPT.