Timing jitter characterization of mode-locked lasers with <1 zs/√Hz resolution using a simple optical heterodyne technique.

Timing jitter characterization of free-running mode-locked lasers with an unprecedented resolution is demonstrated using an optical heterodyne technique. A highly sensitive timing jitter phase-discrimination signal with low-parasitic-amplitude sensitivity is achieved. Analytical and numerical methods are used to analyze the properties of the discrimination signal. For an experimental demonstration, we measure the timing jitter between two loosely synchronized mode-locked Er:Yb:glass lasers with 500-MHz fundamental repetition rates. The timing jitter-detection noise floor for a single mode-locked laser reaches 2.8×10(-13)  fs(2)/Hz (∼530  ys/√Hz), and the integrated timing jitter is 16.3 as from 10 kHz to the Nyquist frequency (250 MHz). These results show that this approach can be a simpler alternative to the well-established balanced optical cross-correlation technique.