Transverse modes in thermally detuned oxide-confined vertical-cavity surface-emitting lasers

We present joint experimental and theoretical investigations of the emission characteristics of oxide-confined vertical-cavity surface-emitting lasers (VCSEL's). The transverse mode formation in medium-sized VCSEL's is determined by the interaction between spatial cavity characteristics and spectral properties of the optical gain: depending on a detuning between the cavity fundamental resonance and the spectral gain maximum, we find the VCSEL's emitting either on the fundamental transverse mode or on modes of particularly high radial order. For a quantitative interpretation of these characteristics, we adopt a model that considers the detailed electromagnetic structure of the VCSEL and yields wavelength, spatial field distribution, and threshold gains of all supported cavity modes. Combining these solutions with the quantum-well optical response provides the laser threshold operation conditions. The theoretical results are in excellent quantitative agreement with the experimental observations. Thus, our work identifies the relevant mechanisms and offers the perspective to control and to utilize high-order mode emission from oxide-confined VCSEL's.