High-Contrast Gratings Performance Issues in Tunable VCSELs

Tunable vertical-cavity surface-emitting lasers (VCSELs) are becoming key components in several sensing applications, where single-mode, single polarization light is required. In such devices, high-contrast gratings (HCGs) are very promising mirrors, because of their high reflectivity, strong polarization discrimination, and low-volume occupation. However, their introduction might lead to unexpected increases in the threshold gain, destroying the tuning performance. In this paper, these phenomena are investigated and explained in detail. Although VCSEL modes are computed by means of our full 3-D vectorial code, a Gaussian beam model is used to obtain deeper insight into the HCG reflectivity mechanism in the presence of a finite beam.