Fabrication and evaluation of rib-waveguide-type wavelength conversion devices using GaN-QPM crystals

Abstract

A GaN crystal comprises two polar structures along the c-axis direction, and functions as a quasi-phase-matching (QPM) crystal by fabricating a periodic inversion structure. We fabricated GaN-QPM crystals to design rib-waveguide-type devices for achieving highly efficient wavelength conversion. The QPM period required for wavelength conversion was calculated in the design phase of the device structure. GaN-QPM crystals with the obtained period were fabricated using double-polarity selective-area growth (DP-SAG). The GaN-QPM crystal was then used to fabricate a second-harmonic generation (SHG) device with a rib waveguide structure. Optical measurements revealed that the device achieved wavelength conversion from 840 to 420 nm. Further, the SHG device exhibited a wavelength conversion efficiency of 1.5 × 10-4% W-1. These results indicated that GaN-QPM crystals fabricated by DP-SAG can be used for wavelength conversion.