On-Chip Hybrid Photonic-Plasmonic Waveguides with Ultrathin Titanium Nitride Films

A solid-state hybrid photonic-plasmonic (HPP) waveguide geometry has been experimentally demonstrated with plasmonic titanium nitride. The configuration is made with robust fabrication techniques, CMOS-compatible materials, and features a straightforward design with dielectric cladding layers that exhibit a significant index mismatch with the substrate. The resulting waveguide is shown to reduce both the propagation loss (0.6 dB/mm) and mode size (7.7 mu m) when compared to previously reported long-range surface plasmon polariton (LRSPP) waveguides using both noble metal and alternative metals of similar configurations. In addition, the structure removes the need to match the cladding indices with the substrate index, allowing for a thin film superstrate cladding (similar to 300 nm) that can be readily deposited using numerous methods. This flexibility allows for additional optimization factors to be considered in the design, such as metal film epitaxy, etching selectivity, device function, and compatibility with subsequent fabrication steps. For example, the top cladding layer can be made of silicon nitride for photonic circuits, a gain medium for loss compensation, as well as lithium niobate or zinc oxide for electrical or optical modulation, without sacrificing performance.