Plasmonic Hybrid Cavity-Channel Structure for Tunable Narrow-Band Optical Absorption

A hybrid plasmonic structure consisting of adjacent U-shaped cavities separated by a nanochannel is proposed for tunable and narrow-band selection of light. The hybrid cavity-channel structure achieves absorption resonance with a bandwidth, defined as the full-width at half-maximum, of 1.5 nm and tunable property in the near-infrared and infrared regions. The hybrid structure resonance originates in the coupling of horizontal surface plasmon mode of the U-cavity with channel mode, which sustains stationary-surface-plasmons in the channel with antinodes at the channel entrances enabling light concentration and nodes at the channel exits enabling light confinement. As a result of the coupling, a sharp and strong absorption resonance is readily adjustable by varying the geometrical parameters of the U-cavity while keeping the channel parameters unchanged.