Thermal Coupling in Vertical-Cavity Surface-Emitting Laser Arrays

Thermal coupling in an operating vertical-cavity surface-emitting laser (VCSEL) array is investigated by using thermoreflectance microscopy to obtain two-dimensional thermal maps with very high spatial and thermal resolution. In contrast with existing techniques for estimating average cavity temperatures, thermoreflectance microscopy enables surface thermal imaging of the entire array while simultaneously resolving surface temperature distributions across individual VCSEL apertures. We quantify the significant thermal coupling between neighboring VCSELs in the array and compare the results to those obtained using the traditional technique of estimating average operating temperature of a laser cavity by monitoring the temperature- dependent shift in the lasing wavelength. A time gated wavelength shift experiment is performed to measure the thermal diffusivity of the array. We report a thermal conductivity (??_th) and thermal diffusivity (??) for the VCSEL array of ??_th = 0.31 W/(cm??K) and ?? = 1.47 ?? 10^-5 m²??s^-1, respectively.