Integrated Gallium Nitride Nonlinear Photonics

Abstract

Gallium nitride (GaN) as a wide bandgap material is widely used in solid-state lighting. Thanks to its high nonlinearity and high refractive index contrast, GaN-on-insulator (GaNOI) is also a promising platform for nonlinear optical applications. Despite its intriguing optical proprieties, nonlinear applications of GaN are rarely studied owing to the relatively high optical loss of GaN waveguides (typically ≈2 dB cm−1). In this paper, GaNOI microresonators with intrinsic quality factor over 2.5 million are reported, corresponding to an optical loss of 0.17 dB cm−1. Parametric oscillation threshold power as low as 6.2 mW is demonstrated, and the experimentally extracted nonlinear index of GaN at telecom wavelengths is estimated to be n2 = 1.4 × 10−18 m2 W−1, which is several times larger than that of commonly used platform such as Si3N4, LiNbO3, and AlN. Single soliton generation in GaN is implemented by an auxiliary laser pumping scheme, so as to mitigate the high thermorefractive effect in GaN. The large intrinsic nonlinear refractive index, together with its broadband transparency window and high refractive index contrast, make GaNOI a promising platform for chip-scale nonlinear applications.