Angle-Independent Infrared Filter Assisted by Localized Surface Plasmon Polariton

A plasmonic infrared (IR) filter was experimentally and theoretically investigated. A localized surface plasmon polariton (LSPP) mode which was angle-independent in almost fully incident angle was observed. Through the use of the LSPP mode, an IR reflection-type notch filter with an ultrahigh immunity for the angular deviation was realized. An angle-independent reflection dip was designed at lambda = 6.2 mum with a full-width at half-maximum of 0.5 mum. The experimental result shows that the position and the line shape of the resonant dip at lambda = 6.2 mum remain the same for an increasing incident angle from 20deg to 60deg. The optical properties can be engineered by tuning thickness of the cavity layer. The proposed notch filter presents a large angular tolerance means that the superior angular stability makes it more feasible as it is put into practical applications.