Water Cladded Plasmonic Slot Waveguide Vertically Coupled With Si₃N₄ Photonics

We demonstrate, a water cladded plasmo-photonic waveguide, by exploiting the directional coupling scheme to vertically divert light from a 360 $\times$ 800 nm (height $\times$ width) Si$_{3}$N$_{4}$ waveguide to a plasmonic slot waveguide, enabling the excitation of a pure plasmonic mode within a 210 nm wide slot at 1550 nm. The 150 nm thick plasmonic slot waveguide was deposited on top of an oxide cladded Si$_{3}$N$_{4}$ waveguide exhibiting an experimental plasmonic-to-photonic insertion loss of 2.24 $\times$ 0.3 dB and a plasmonic propagation length (L$_{ssp}$) of 10.8 μm at 1550 nm. The proposed plasmo-photonic waveguide holds promise as an optical transducer element for highly sensitive and low cost interferometric biosensors due to the significant phase change achieved per unit propagation length.