Dai Yitang, Cen Qizhuang, Wang Lei, Zhou Yue, Yin Feifei, Dai Jian, Li Jianqiang, Xu Kun
Opt Express. 2015 Dec 14;23(25):31936-44. doi: 10.1364/OE.23.031936.
Extraction of a microwave component from a low-time-jitter femtosecond pulse train has been attractive for current generation of spectrally pure microwave. In order to avoid the transfer from the optical amplitude noise to microwave phase noise (AM-PM), we propose to down-convert the target component to intermediate frequency (IF) before the opto-electronic conversion. Due to the much lower carrier frequency, the AM-PM is greatly suppressed. The target is then recovered by up-conversion with the same microwave local oscillation (LO). As long as the time delay of the second LO matches that of the IF carrier, the phase noise of the LO shows no impact on the extraction process. The residual noise of the proposed extraction is analyzed in theory, which is also experimentally demonstrated as averagely around -155 dBc/Hz under offset frequency larger than 1 kHz when 10-GHz tone is extracted from a home-made femtosecond fiber laser. Large tunable extraction from 1 GHz to 10 GHz is also reported.
从低时间抖动飞秒脉冲序列中提取微波成分，对于当前产生频谱纯净的微波具有吸引力。为了避免光幅度噪声向微波相位噪声的转换（AM-PM），我们建议在光电转换之前将目标成分下变频到中频（IF）。由于载波频率低得多，AM-PM得到了极大抑制。然后通过相同的微波本地振荡（LO）进行上变频来恢复目标。只要第二个LO的时间延迟与IF载波的时间延迟匹配，LO的相位噪声就不会对提取过程产生影响。从理论上分析了所提出提取方法的残余噪声，当从自制的飞秒光纤激光器中提取10 GHz音调时，在大于1 kHz的偏移频率下，实验也证明其平均约为-155 dBc/Hz。还报道了从1 GHz到10 GHz的大可调谐提取。
