Temperature Profiling of VCSELs by Thermoreflectance Microscopy

Surface temperature measurements with submicron spatial resolution are reported for operating vertical-cavity surface-emitting lasers (VCSELs) by means of thermoreflectance microscopy. We measure increasingly convex radial temperature distributions with increasing bias power for three types of VCSELs. The corresponding convex refractive index profiles are consistent with previously observed thermal lensing; this effect is far more prominent for the oxide confined single-mode (SM) VCSEL than for the broader aperture devices. For all samples, the change in the average surface temperature varies linearly with the change in dissipated power. A comparison with the temperature of the top distributed Bragg reflector mirror of an oxide confined SM VCSEL, obtained from the wavelength shift of the spontaneous emission, shows that both methods yield comparable results.