Using graphene to tune vertical-cavity surface-emitting lasers

A novel approach for enhancing the tuning speed of vertical-cavity surface-emitting lasers (VCSEL) is presented. The design is based on incorporating gated multiple graphene flakes in one of the DBR layers that is adjacent to the cavity to tune the resonance wavelength of the device. Different design structures have been studied. By applying a gate voltage on the graphene flakes, the effective refractive index of the cavity is changed which detunes the resonant wavelength of the cavity. The unique features of graphene ensure fast tuning speed. Our analysis on a 1.3 μm InAs quantum dot-based VCSELs predicts that inserting double graphene flakes separated by 20 nm SiO₂ spacer in a λ/4 layer yields ~ 0.6 nm wavelength tuning range and ~ 6.3 GHz tuning speed. The threshold current variation within the tuning range is less than 43%. The wavelength tuning range can be increased to 1.2 nm by using 4 graphene flakes which reduces the tuning speed to ~ 1.9 GHz and increases the threshold current variation to 84%. In another design, we find that inserting 4 graphene flakes separated by 80 nm SiO₂ spacer in a 3λ/4 layer yields ~ 0.8 nm tuning range and 14.5 GHz tuning speed. For fine wavelength tuning, the device is capable of providing > 39 GHz tuning speed.