Subfemtosecond synchronization of microwave oscillators with mode-locked Er-fiber lasers

Abstract

We synchronize an 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 $-133\mathrm{dBc}/\mathrm{Hz}$ ($-154\mathrm{dBc}/\mathrm{Hz}$) 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 h, which reaches $4\times {10}^{-19}$ fractional frequency instability at 1800 s averaging time. This method has a potential to provide both subfemtosecond-level short-term phase noise and long-term phase stability in microwave extraction from mode-locked fiber lasers.

© 2012 Optical Society of America

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