Super-mode noise suppression for coupled optoelectronic oscillator with optoelectronic hybrid filter

A novel scheme to implement the super-mode noise suppression for coupled optoelectronic oscillator (COEO) utilizing an optoelectronic hybrid filter (OEF) is proposed and experimentally demonstrated. The OEF is made up of a multi-mode optoelectronic oscillator, incorporated in the COEO loop to serve as a channelized RF filter, while the fiber laser in the COEO can be viewed as another channelized RF filter of high Q. The cascading of the two equivalent channelized RF filters can greatly improve the out-of-band rejection ratio of the combined filter and restrain the adjacent mismatched modes in the oscillating loop. In the experiment, a 9.955 GHz RF signal with the side mode suppression ratio of larger than 82.6 dB is obtained, and the super-mode noise spur at an offset frequency of 5.9 MHz is suppressed 15 dB to -145 dBc/Hz level compared with the conventional COEO.