Post-fabrication trimming of gallium phosphide ring resonators for quantum frequency conversion

Abstract

Post-fabrication resonator trimming will be a critical tool in realizing long distance transmission of quantum states via frequency conversion with photonic ring resonators. Two trimming mechanisms are investigated: digital etching via separated diffusion-limited formation and removal of an oxide layer to modify resonator dimensions, and hydrogen silsesquioxane (HSQ) electron-beam exposure to modify cladding refractive index. Controlled etch cycles with resonant wavelength shifts of -0.379 ± 0.163 nm are demonstrated with digital etching. HSQ cladding electron-beam exposure shows a clear relationship between dose and wavelength shift that enables deterministic trimming of individual devices with quality factors on the order of 104 to within 0.03 nm of a target wavelength. HSQ electron-beam exposure is used to demonstrate target-wavelength-trimmed second harmonic generation from telecom to near infra-red wavelengths.