Non-planar graphene directly synthesized on intracavity optical microresonators for GHz repetition rate mode-locked lasers

Generation of high-speed laser pulses is essential for sustaining today’s global, hyper-connected society. One approach for achieving high spectral and temporal purity is to combine optical nonlinear materials with spectral filtering devices. In this work, a graphene-coated microresonator integrates a nonlinear material and a spectral filtering platform into a single device, creating a tunable GHz repetition rate mode-locked fiber laser. The graphene is directly synthesized on the non-planar surface of microresonator, resulting in a uniform, conformal coating with minimal optical loss in the device. The whispering gallery modes of the resonator filter the propagating modes, and the remaining modes from the interaction with graphene lock their relative phases to form short pulses at an elevated repetition rate relying on inter-modal spectral distance. Additionally, by leveraging the photo-thermal effect, all-optical tuning of the repetition rate is demonstrated. With optimized device parameters, repetition rates of 150 GHz and tuning of 6.1 GHz are achieved.