Experimental investigation of guiding mechanisms in large area VCSELs

We report on a novel technique involving spatially and spectrally resolved measurements of the spontaneous and stimulated emission from a VCSEL, which allows the mode structure, carrier density, and nett cavity loss to be mapped. The measurements allow ready assessment of optical guiding in the structure. It is found that in large area devices with low ohmic heating, the guiding is dominated by free carrier effects.