2 μm optics frequency comb generation via optical parametric oscillation from a lithium niobate optical superlattice box resonator

Optical parametric oscillators (OPOs) can downconvert the pump laser to longer wavelengths with octave separation via chi((2)), which is widely used for laser wavelength extension including mid-infrared (MIR) generation. Such a process can be integrated in monolithic resonators, being compact and low in threshold. In this work, we show that the monolithic chi((2)) mini-OPO can also be used for optical frequency comb generation around 2096 nm and enters the boundary of MIR range. A new geometry called an optical superlattice box resonator is developed for this realization with near-material-limited quality factor of 4.0 x 10(7). Only a continuous-wave near-infrared pump laser is required, with OPO threshold of 80 mW and output power up to 340 mW. Revival temporal profiles are measured at a detectable repetition frequency of 1.426 GHz, and narrow beat note linewidth of less than 10 Hz shows high comb coherence. These results are in good agreement with our simulation for a stable comb generation. Such an OPO-based comb source is useful for carbon dioxide sensing or the mine prospect applications and can be generalized to longer MIR wavelengths for general gas spectroscopy. (C) 2022 Chinese Laser Press

Automated summary

This work explores the feasibility of generating optical frequency combs using a monolithic chi((2)) mini-OPO and applies it to the mid-infrared range. A new geometry called an optical superlattice box resonator is developed for this purpose. Experimental results demonstrate that, through measuring the revival temporal profiles and narrow beat note linewidths at a detectable repetition frequency, this OPO-based comb source exhibits high coherence.