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 = 6:2 m with a full-width at half-maximum of 0.5 m. The experimental result shows that the position and the line shape of the resonant dip at = 6:2 m remain the same for an increasing incident angle from 20 to 60 . 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.

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