Independent light-trapping cavity for ultra-sensitive plasmonic sensing

The sensing characteristics of an independent-plasmonic-cavity structure that traps light were investigated. The cavity structure traps light by generating self-contained optical vortices in each independent cavity without leakage or propagation of the light; therefore, strong and sharp resonance dips are obtained in a reflectance spectrum. Multiple optical vortices are generated in the independent cavities in higher-order plasmonic cavity modes at shorter wavelengths, realizing the resonance in a wide range from visible to near-infrared. Compared to the propagating surface plasmon resonance, the resonance of plasmonic cavity mode in the independent cavity does not depend on variation of the incident angle of light. The independent-cavity structure was fabricated by a simple process, and it experimentally demonstrated a high sensitivity (above 1500 nm per refractive index unit) and a figure of merit above 20.