T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.
Time and Frequency Division, National Institute of Standards and Technology, Boulder, CO 80305, USA.
Science. 2014 Jul 18;345(6194):309-13. doi: 10.1126/science.1252909. Epub 2014 Jun 19.
Optical frequency division by using frequency combs has revolutionized time keeping and the generation of stable microwave signals. We demonstrate optical frequency division and microwave generation by using a tunable electrical oscillator to create dual combs through phase modulation of two optical signals that have a stable difference frequency. Phase-locked control of the electrical oscillator by means of optical frequency division produces stable microwaves. Our approach transposes the oscillator and frequency reference of a conventional microwave frequency synthesizer. In this way, the oscillator experiences large phase noise reduction relative to the frequency reference. The electro-optical approach additionally relaxes the need for highly linear photodetection of the comb mode spacing. As well as simplicity, the technique is also tunable and scalable to higher division ratios.
利用频率梳进行光频分已经彻底改变了时间测量和稳定微波信号的产生。我们通过使用可调谐电振荡器通过对具有稳定差频的两个光学信号进行相位调制来创建双梳，从而演示了光频分和微波产生。通过光频分对电振荡器进行锁相控制可产生稳定的微波。我们的方法转换了传统微波频率合成器的振荡器和频率基准。通过这种方式，相对于频率基准，振荡器经历了很大的相位噪声降低。光电方法还放宽了对梳模间距进行高线性光电探测的需求。除了简单性之外，该技术还具有可调谐性和可扩展性，可实现更高的分频比。
