Fabrication-Tolerant and Low-Loss Hybrid Plasmonic Slot Waveguide Mode Converter

Integrated plasmonic structures can concentrate light to deep-subwavelength volumes below the diffraction limit and have been explored in many applications including label-free nanophotonic sensing with single molecule sensitivity, nonlinear conversion, and lasing. However, conversion between the dielectric waveguide mode and the plasmonic mode typically suffers from large mode conversion loss and requires high nanofabrication precision because of the mode mismatch and the precise alignment requirements with the plasmonic slot structure, respectively. Here, we report low-loss conversion between a dielectric waveguide mode and a hybrid plasmonic slot waveguide mode in a structure with a large fabrication tolerance. The measured conversion loss between the dielectric waveguide mode to the hybrid plasmonic slot waveguide mode can be <; 2 dB in the wavelength range of 1.54-1.60 μm under the optimal phase match condition. The loss remains low with a lateral misalignment tolerance of >500 nm. We confirmed enhanced light-matter interaction in the plasmonic slot waveguide region by measuring the enhancement in optical absorption of graphene with and without the plasmonic slot structure. Our results demonstrate a new approach to achieve deep-subwavelength light concentration by using an easy-to-fabricate interface with dielectric waveguides.