Plasmonic Waveguide Ring Resonators with 4 nm Air Gap and λ02/15 000 Mode-Area Fabricated Using Photolithography

Plasmonic air-gap disk resonators with 3.5 mu m diameter and a 4 nm thick, 40 nm wide air gap for a mode area of only lambda(2)(0)/15 000 were fabricated using photolithography only. The resonant modes were clearly identified using tapered fiber coupling method at the resonant wavelengths of 1280-1620 nm. We also demonstrate the advantage of the air-gap structure by using the resonators as label-free biosensors with a sensitivity of 1.6 THz/nm.