Polarization properties in the transition from below to above lasing threshold in broad-area vertical-cavity surface-emitting lasers

TL;DR

This paper investigates how the polarization of broad-area VCSELs changes dramatically from below to above lasing threshold, revealing two distinct transition types influenced by cavity mirror properties.

Contribution

It identifies and characterizes two different polarization transition behaviors in broad-area VCSELs near the lasing threshold, linking them to cavity mirror properties.

Findings

Polarization rotates up to 90 degrees near threshold.

Two types of polarization transition: abrupt and smooth.

Polarization behavior depends on cavity mirror properties.

Abstract

For highly divergent emission of broad-area vertical-cavity surface-emitting lasers (VCSELs) a rotation of the polarization direction by up to 90 degrees occurs when the pump rate approaches the lasing threshold. Well below threshold the polarization is parallel to the direction of the transverse wave vector and is determined by the transmissive properties of the Bragg reflectors that form the cavity mirrors. In contrast, near-threshold and above-threshold emission is more affected by the reflective properties of the reflectors and is predominantly perpendicular to the direction of transverse wave vectors. Two qualitatively different types of polarization transition are demonstrated: an abrupt transition, where the light polarization vanishes at the point of the transition, and a smooth one, where it is significantly nonzero during the transition.