LAUSR

A novel approach for achieving ultrafast and wide tunable vertical-cavity surface-emitting lasers (VCSELs) is presented. The design is based on incorporating multiple graphene flakes separated by SiO 2 dielectric in a λ/2 cavity and placing multiquantum wells in one of the quarter wave layers of the bottom mirrors. The device concept enhances both the wavelength tuning range and tuning speed which is attractive for many photonic applications. By applying a gate voltage on the graphene flakes, the effective refractive index of the cavity can be changed with ultrahigh speed. We have shown that 2 graphene flakes inside a 5 µm-diameter passive cavity provides tuning speed as high as 32 GHz and wavelength tuning range of 3.8 nm. The tuning speed increases to 52 GHz when the device diameter is reduced to 3 µm. The effect of spacer thickness and the number of graphene flakes on the performance characteristics of the device is investigated. Our analysis shows that tuning speed as high as 2 GHz and wavelength tuning range of ~ 12 nm is obtained for VCSEL that incorporates 6 graphene flakes separated by 10 nm SiO 2 spacers and biased in parallel. The tuning speed can be increased to ~ 16 GHz when the flakes are biased in series at the expense of higher gate voltage. A tradeoff between the wavelength tuning range and the tuning speed is obtained.