  Gallium nitride (GaN) as a wide-band gap material has been 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 have rarely been studied due to the relatively high optical
loss of GaN waveguides (2 dB/cm). In this letter, we report GaNOI
microresonator with intrinsic quality factor over 2 million, corresponding to
an optical loss of 0.26 dB/cm. Parametric oscillation threshold power as low as
8.8 mW is demonstrated, and the experimentally extracted nonlinear index of GaN
at telecom wavelengths is estimated to be n2 = 1.2*10 -18 m2W-1, which is
comparable with silicon. 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 most balanced platform for chip-scale nonlinear applications.
