Optical frequency combs have become revolutionary tools in high-precision applications. Timing jitter of optical pulse trains is an important property for optical frequency comb applications, including time/frequency metrology, low phase noise microwave generation, photonic analog-to-digital converters, photonics-based radars, dual-comb ranging, and timing synchronization and distribution, to name a few. For high-resolution timing jitter characterization of mode-locked lasers, optical cross-correlation method [1] using nonlinear optic processes has been used in the last decade. However, the complexity of the method and the requirement of reference lasers (with matched repetition-rate and lower timing jitter) have limited the applicability of this method.