Extremely confined photons within a gap-mode plasmonic nanocavity for multifunctional applications: nanoimaging and refractive index sensing

The light-matter interaction in plasmonic nanocavities at the sub-diffraction limit has become an important research field in nanophotonics. However, an effective nanocavity platform should not only aim at strong field enhancement, but also provide efficient coupling to the incident light and a high density of the hotspot. Here, we propose an attractive alternative three-dimensionally-tapered plasmonic nanocavity, which is a coupled photonic-plasmonic system consisting of a combination of photonic nanocavity and metallic bowtie-shaped nanoaperture (BNA). Due to its favourable conditions for high energy concentration, large wavevector (k), and efficient energy exchange, the plasmonic BNA nanocavity efficiently transforms the propagating gap-surface plasmon polaritons (GSPPs) into a highly localized catenary-shaped optical field characterized by high-k value and stronger field strength. Simulation results show that the plasmonic BNA nanocavity exhibits multifunctional tunability, due to its considerable localizing ability and low-loss characteristics. When used as a lithographic source generator, it can achieve an 8 nm spatial resolution for arbitrary patterns with high fidelity. Additionally, this approach offers a unique method to enhance plasmonic sensing by allowing the originally confined catenary field to efficiently interact with the surrounding medium. We strongly believe that the liquid-tapered plasmonic BNA nanocavity could pave the way for new research avenues in nanophotonic applications, particularly in high-resolution nanoimaging and highly sensitive chip-based plasmonic sensors.