Efficient- and Broadband-Coupled Selective Spot-Size Converters With Damage-Free Graphene Integration Process

We report an enhancement of coupling efficiency between an optical fiber and graphene photonic device integrated on a silicon photonics platform. The design and optimization of selective spot-size converters (SSSCs) enables low coupling losses of 1.4 dB/facet for TE and 2.4 dB/facet for TM modes without causing damage to the graphene. In order to maximize the potential of the perfect wavelength independent response in the graphene, ultra-broad-bandwidth coupling from O- to U-bands (1300-1650 nm) is characterized. The bandwidth is over 300 nm (at 3-dB roll off) in both polarization modes. We integrated the SSSCs with a partially graphene integrated silicon-ring resonator to substantiate the wavelength response improvement by a pico-meter-order high-resolution spectroscopy.