Sub-femtosecond synchronization of microwave oscillators with mode-locked Er-fiber lasers

TL;DR

This paper demonstrates sub-femtosecond synchronization of microwave oscillators with mode-locked Er-fiber lasers, achieving extremely low phase noise and long-term stability through fiber-based optical-microwave phase detection.

Contribution

It introduces a fiber-based phase detection method enabling ultra-precise synchronization of microwave signals with optical pulse trains.

Findings

Residual phase noise of -133 dBc/Hz at 1 Hz offset

Integrated rms timing jitter of 838 as

Long-term phase drift of 847 as over 2 hours

Abstract

We synchronize a 8.06-GHz microwave signal from a voltage-controlled oscillator with an optical pulse train from a 77.5- MHz mode-locked Er-fiber laser using a fiber-based optical-microwave phase detector. The residual phase noise between the optical pulse train and the synchronized microwave signal is -133 dBc/Hz (-154 dBc/Hz) at 1 Hz (5 kHz) offset frequency, which results in 838 as integrated rms timing jitter [1 Hz - 1 MHz]. The long-term residual phase drift is 847 as (rms) measured over 2 hours, which reaches 4\times10^{-19} fractional frequency instability at 1800 s averaging time. This method has a potential to provide both sub-fs-level short-term phase noise and long-term phase stability in microwave extraction from mode-locked fiber lasers.