Localized surface plasmon induced transparency and spatial resolution enhancement of nanosensors

Resonances in micrometer metallic cavities are very important for the interactions between materials and light. Triangular, trapezoidal and W-shaped cavities are investigated through the finite difference time domain (FDTD) method. Surface plasmon polariton resonant (SPPR) dark and bright modes are excited on the sides of triangular and trapezoidal cavities. When the trapezoidal cavity is shaped to W-shaped cavity, localized surface plasmon resonance (LSPR) is excited at the tip of wedge. The LSPR with narrow bandwidth interferes destructively with SPPR dark and bright modes with wide bandwidth on the sides of cavity, forming localized surface plasmon induced transparency (LSPIT) and Fano resonance (LSPFR), respectively. Comparative to general cavity-resonance (CR) modes with at least one dimension larger than half of wavelength in 2D structures, the LSPR can be confined to an ultra-small scale with both two dimensions less than half of wavelength. The LSPIT and LSPFR can be applied to enhance the spatial resolution of sensor and design sensors to sense particle's size, position and refractive index in several-nm scale.