Picosecond Electro-Optic Comb With Multi-GHz Repetition-Rate Sweeping Range

Abstract

Conventional electro-optic (EO) combs are known for their repetition-rate agility. However, due to a nonzero time delay between the driving signals for the cascaded phase and intensity modulators, such systems can rarely withstand multi-GHz tuning range while maintaining high-quality temporal shapes. In this letter, we establish that a diminishing modulator delay time is the single most important factor impacting the repetition-rate sweeping performance of a short-pulsed EO comb. By reducing the modulator delay time to zero, we demonstrate an EO comb that is capable of frequency sweeping across an ultrabroad frequency span (6-10 GHz) while consistently outputting high-quality $\sim ~5$ ps pulses. Importantly, the ‘zero modulator delay time’ strategy inherently ensures phase matching for all frequencies and the limitation on sweeping speed is completely eliminated. The pulse duration and temporal shape are highly stable and reproducible, and the timing jitters are under 125 fs for all repetition rates within the tuning range. We also demonstrate wavelength-agility in such a system, by tuning the center wavelength of the seed semiconductor laser from 1535 to 1565 nm. Across the tuning range, optical signal-to-noise ratios of over 40 dB are achieved. This simple approach provides an effective solution for stabilizing the pulse duration for EO combs and may find applications in asynchronous optical sampling or other time-resolved experiments.