基于光学腔的超稳微波源

Now, all domestic fountain clocks employ quartz-based microwave sources as the local oscillators, whose best stability is about 1E-13@1s, which limits short-term frequency stability of these clocks. We plan to study and develop an optically-generated ultra-stable microwave source. This frequency source is reference to the length of an ultra-stable optical cavity with a stability of E-15 @ 1s. It includes four part: an ultra-stable CW laser, an optical frequency comb, low noise optical detection part and a low noise microwave synthesizer. The ultra-stable laser reads out the stability of the cavity length; the optical frequency comb transfers the stability of ultra-stable laser frequency into stability of comb`s pulse rate; the optical detection part converts comb`s pulse rate into electric frequency signal; the low noise synthesizer produces microwave signal which can be used directly in fountain clocks for transition interrogation. This 9.192 GHz microwave source is expected to be exhibiting frequency stability of below 5E-15@1s and phase noise of below -90dBc/Hz@1Hz,and it is able to run continuously over a month. With such a local oscillator, these domestic fountain clocks could improve their short-term frequency stability an order of magnitude.

目前国内基准喷泉钟普遍采用基于晶振的微波频率源，其秒级稳定度为1E-13，这种微波源的相位噪声导致的原子钟稳定度恶化已经成为制约我国基准喷泉钟性能的主要因素之一。本项目拟采用光生微波的办法，以超稳光学谐振腔长度为基准，将单频激光频率稳定到超稳光学腔上、然后利用飞秒光梳将单频超稳激光频率合成到微波频段，最后通过低噪声光电转换和低噪声微波频率综合产生基准喷泉钟的本地频率信号。预期9.192 GHz微波源秒级稳定度优于5E-15@1s，相位噪声优于-90 dBc/Hz@1Hz，能够连续运行一月以上。应用该微波源，喷泉钟的短期频率稳定度将提高一个数量级。

国内基准喷泉钟普遍采用基于晶振的微波频率源，其秒级稳定度为1E-13，这种微波源的相位噪声导致的原子钟稳定度恶化已经成为制约我国基准喷泉钟性能的主要因素之一。本项目采用光生微波的办法，以超稳光学谐振腔长度为基准，将单频激光频率稳定到超稳光学腔上、然后利用飞秒光梳将单频超稳激光频率合成到微波频段，最后通过低噪声光电转换和低噪声微波频率综合产生基准喷泉钟的本地频率信号。9.192 GHz微波源样机秒级稳定度为3.3E-15@1s，相位噪声优于-90 dBc/Hz@1Hz，能够连续运行一月以上；系统已经应用于基准喷泉钟，使其秒级频率稳定度从E-13提升到E-14。