Periodically poled thin film lithium niobate microring resonators with a second-harmonic generation efficiency of 250,000%/W

TL;DR

This paper reports a breakthrough in integrated photonics by demonstrating periodically poled lithium niobate microring resonators with an unprecedented second-harmonic generation efficiency of 250,000%/W, enabling highly efficient nonlinear optical processes on a chip.

Contribution

The authors introduce a novel periodically poled thin film lithium niobate microring resonator with record SHG efficiency, achieved through field-assisted domain engineering and optimized coupling conditions.

Findings

Achieved 250,000%/W SHG efficiency in LN microrings.

Recorded 15% absolute conversion efficiency at low pump power.

Demonstrated dual-band operation via single pulley waveguide.

Abstract

Lithium niobate (LN), dubbed by many as the silicon of photonics, has recently risen to the forefront of chip-scale nonlinear optics research since its demonstration as an ultralow-loss integrated photonics platform. Due to its significant quadratic nonlinearity ($\chi^{(2)}$), LN inspires many important applications such as second-harmonic generation (SHG), spontaneous parametric down-conversion, and optical parametric oscillation. Here, we demonstrate high-efficiency SHG in dual-resonant, periodically poled z-cut LN microrings, where quasi-phase matching is realized by field-assisted domain engineering. Meanwhile, dual-band operation is accessed by optimizing the coupling conditions in fundamental and second-harmonic bands via a single pulley waveguide. As a result, when pumping a periodically poled LN microring in the low power regime at around 1617nm, an on-chip SHG efficiency of 250,000%/W is achieved, a state-of-the-art value reported among current integrated photonics platforms. An absolute conversion efficiency of 15% is recorded with a low pump power of 115$\mu$W in the waveguide. Such periodically poled LN microrings also present a versatile platform for other cavity-enhanced quasi-phase matched $\chi^{(2)}$ nonlinear optical processes.