Single-mode, single-polarization VCSELs via elliptical surface etching: experiments and theory

Polarization control in vertical-cavity surface-emitting lasers (VCSELs) has attracted a lot of interest and different techniques have been proposed to achieve it. Among them, one of the most attractive relies on slight modifications of existing and well-behaving devices, i.e., by introducing a noncircular transverse section layer somewhere in the device. Even though experimental verifications of this principle have already been carried out, a theoretical framework to better understand and possibly optimize such devices is still missing. This mainly originates from the need of a fully vectorial and three-dimensional approach. In this paper, we will undertake a joint experimental and theoretical effort: first, we give experimental evidence of polarization control by applying elliptical surface etching. Then, after having validated the vectorial electromagnetic model by comparing numerical and experimental results, we are able for the first time to explain and compare the polarization selection mechanisms and, consequently, to provide guidelines for optimized structures.