Optics and photonics have made possible many modern-day technologies and enhanced the quality of life in many areas. Just like the indispensible roles of their counterparts in electronics, optical frequency synthesizer and optical function generator can be versatile test equipments to characterize and understand future photonics devices.
Optical frequency comb is a new time and frequency standard with unprecedented precision and is key to the development of optical frequency synthesizer and optical function generator. The current benchmark laser systems for optical frequency combs are self-referenced femtosecond mode-locked lasers. However, continuous-wave pumped microresonators recently emerge as promising alternative platforms for optical frequency comb generation. Microresonator-based optical frequency combs, or Kerr frequency combs, are unique in their compact footprints and offer the potential for monolithic electronic and feedback integration, thereby expanding the already remarkable applications of optical frequency combs.
In this talk I will report two recent progresses on optical frequency combs from on-chip Si3N4 microresonators: 1) generation of mode-locked ultrashort pulses from a ring resonator; and 2) stabilization of 18 GHz optical frequency comb from a spiral resonator. I will first describe the generation of stable mode-locked pulse trains from normal dispersion microresonators. The importance of pump detuning and wavelength-dependent quality factors in stabilizing and shaping the pulse structure will be discussed. Then I will present a low-phase-noise on-chip optical frequency comb with 18 GHz comb spacing, compatible with high-speed silicon optoelectronics. Both the pump frequency and the comb spacing can be stabilized using standard phase locked loop technique. Finally, future endeavour towards next-generation optical frequency synthesizer and optical function generator will be discussed.