Ultralow phase noise microwave generation from mode-locked er-fiber lasers with subfemtosecond integrated timing jitter

Abstract

We demonstrate ultralow phase noise 10-GHz microwave signal generation from a free-running mode-locked Er-fiber laser with-142-and-157-dBc/Hz single-sideband absolute phase noise at 10-and 100-kHz offset frequencies, respectively. The absolute RMS timing jitter is 1.5 fs when integrated from 1-kHz to 5-GHz (Nyquist frequency) offset frequency. In the 10-kHz to 10-MHz integration bandwidth typically used for microwave generators, the RMS integrated jitter is 0.49 fs. The Er-fiber laser is operated in the stretched-pulse regime at close-to-zero dispersion to minimize the phase noise of extracted microwaves. In order to suppress the excess phase noise in the optical-to-electronic conversion process, we synchronize a low-noise voltage-controlled oscillator to the fiber laser using a fiber Sagnac-loop-based optical-microwave phase detector. © 2013 IEEE.