Sub-Femtosecond Timing Jitter From a SESAM Mode-Locked Yb-Fiber Laser

We demonstrate sub-femtosecond timing jitter of ultrashort pulses from a dispersion managed Yb-fiber laser mode-locked by a SESAM. Timing jitters of the mode-locked Yb-laser under different dispersion conditions (when the intra-cavity dispersions are −0.005 ps², +0.001 ps², +0.006 ps²) are characterized by the single-crystal balanced optical cross-correlator. In our experiment, an ultra-low timing jitter of 48 attoseconds is achieved when the jitter spectral density is integrated from 3 kHz to 1 MHz offset frequency. We think that the obtained timing jitter level is the lowest for fiber lasers mode-locked by real saturable absorbers. This ultra-low timing-jitter, stably mode-locked fiber laser source is expected to be used for high precision applications outside of the laboratory.

I. Introduction

Passively mode-locked fiber lasers, which produce equally spaced ultrashort pulses in the time domain, can be applied in various areas, such as photonic radar [1], [2], absolute distance measurement [3], [4], photonic analog-to-digital converters (ADCs) [5], [6], remote timing distribution [7], [8], microwave signal generation [9], [10], to name a few. In these application scenarios, minimizing the timing jitter of the ultrashort pulses is preferred, because the resolution and accuracy can be greatly improved if low timing-jitter pulses are used. Accurate assessment of the timing jitter of passively mode-locked fiber lasers is a prerequisite for further advances in those high precision application fields. The traditional optical-to-electrical method is introduced to characterize the timing jitter of ultrashort pulses by analyzing the radio frequency (RF) noise of the repetition-rate signal [11]. However, this photodetection method suffers from the amplitude-to-phase conversion noise and the measurement sensitivity is limited by the highest harmonic order of the repetition-rate signal. Thus, the resolution of this method is usually restrained to ~10 fs. To overcome the resolution limit, the balanced optical cross-correlator (BOC) is invented in 2003 [12]. This technique not only has a simple experimental setup but also is immune to laser intensity noise, which can provide a jitter measurement resolution towards attosecond (as) level.