Ultralow Phase Noise Microwave Generation From Mode-Locked Er-Fiber Lasers With Subfemtosecond Integrated Timing Jitter

TL;DR

This paper reports the generation of ultralow phase noise 10-GHz microwave signals using a mode-locked Er-fiber laser, achieving subfemtosecond timing jitter through optimized laser operation and optical-to-electronic phase noise suppression techniques.

Contribution

It introduces a method to produce ultralow phase noise microwaves from an Er-fiber laser with integrated timing jitter below 1 femtosecond.

Findings

Achieved -142 and -157 dBc/Hz phase noise at 10 and 100 kHz offsets.

Measured RMS timing jitter of 1.5 fs from 1 kHz to 5 GHz.

Demonstrated effective suppression of excess phase noise via fiber Sagnac-loop-based phase detection.

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.