VCSEL Wavelength Setting by Intra-Cavity Phase Tuning - Numerical Analysis and Experimental Verification

Journal article, 2021

Monolithic multi-wavelength VCSEL arrays, with wavelengths of individual VCSELs precisely set in a post-epitaxial growth process, would enable compact multi-color light sources and transmitters for various sensing and datacom applications. Here we report on a numerical study of the requirements of spectral matching and balancing of DBR reflectances, optical confinement factor, and optical gain for uniformity of threshold current and slope efficiency over wavelength with wavelength set by intra-cavity phase tuning. The requirements are verified by an experimental demonstration of intra-cavity phase tuned VCSELs in the spectral range 1043-1067 nm with a wavelength spacing of 8 ± 1 nm enabled by precise Ar ion-beam etching. Small variations of threshold current and slope efficiency are achieved by close to ideal spectral matching and balancing. The VCSELs are GaAs-based with a dielectric SiO2/TiO2 top-DBR. We conclude that high uniformity of threshold current and slope efficiency is demanding in terms of spectral matching and balancing and requires not only very precise etching for intra-cavity phase tuning and precise thickness of the layers in the dielectric top-DBR, but also precise thickness and composition of the layers in the epitaxial semiconductor part.