Long-term stabilization of mode-locked Er-fiber lasers with 1.2 fs timing jitter

We demonstrate a new phase-locking technique for long-term and high-precision stabilization of mode-locked Er-fiber lasers by direct optical-microwave phase detection without high-speed photodiodes and mixers. The excellent locking performance reaches 2.1×10
⁻¹⁸
at 4000-s averaging time.