An enhanced model for the modulated reflectance spectra of vertical-cavity surface-emitting laser structures

Modulation spectroscopy has proved to be unique in being able to probe the vital active-layer quantum well (QW) transitions in vertical-cavity surface-emitting lasers (VCSELs). We have been characterising an all-AlGaAs-based VCSEL structure designed to operate at high temperatures, using photo-modulated reflectance (PR) as a function of temperature up to 180 degrees C. We previously developed an empirical model to fit VCSEL PR spectra when the features from the QW transitions and the Fabry-Perot cavity mode (CM) overlap and interact, and this fitting function has, so far, proved to be very successful. However, the present VCSEL has a particularly high finesse cavity and our established model is unable to fit the unusually detailed interacting CM/QW PR spectra. Here, we perform new reflectivity calculations for this VCSEL structure. These provide new insight into the Seraphin coefficients of the CM, and their inter-relationship, when they lie near the QW transitions. This deepens our understanding of VCSEL PR lineshapes, yielding an enhanced model which we successfully fit to the temperature-dependent PR spectra of the present VCSEL. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim