400%/W second harmonic conversion efficiency in 14 μm-diameter gallium phosphide-on-oxide resonators

Second harmonic conversion from 1550 nm to 775 nm with an efficiency of 400% W−1 is demonstrated in a gallium phosphide (GaP) on oxide integrated photonic platform. The platform consists of doubly-resonant, phase-matched ring resonators with quality factors Q ∼ 104, low mode volumes V ∼ 30(λ/n)3, and high nonlinear mode overlaps. Measurements and simulations indicate that conversion efficiencies can be increased by a factor of 20 by improving the waveguide-cavity coupling to achieve critical coupling in current devices.