ELECTROOPTIC EFFECT AND BIREFRINGENCE IN SEMICONDUCTOR VERTICAL-CAVITY LASERS

Semiconductor vertical-cavity surface-emitting lasers (VCSELs) are kno wn to exhibit a small amount of birefringence. We present a model that enables us to estimate how much of this is due to the electro-optic e ffect produced by the inevitable internal electric field in working de vices; Of vital importance for this model is the notion that the posit ion-dependent changes in the refractive index should be weighted by th e local optical intensity both in the spacer as well as in the distrib uted Bragg reflectors. index variations in the optical nodes thus go u nnoticed, whereas those in the antinodes can strongly affect the cavit y resonance. This is related to the idea that the active quantum wells in a VCSEL should be positioned in optical antinodes to produce the h ighest; modal gain. The results of our model calculation are compared with statistical data on the magnitude and orientation of the measured birefringence in planar proton-implanted VCSELs. These data show the presence of a systematic contribution to the birefringence, which can presumably be attributed to the electro-optic effect, and a random con tribution, which we attribute to stress and strain.