Improved selectivity of optical transmission through cascaded waveguide-metal-grating filters

We analyze the resonant transmission of two near-field coupled, cascaded bandpass filters, based on metallic stripe or patch gratings. The response, in terms of both maximum efficiency and light rejection out of the resonance, overpasses the simple convolution of the responses of two isolated filters, while keeping good angular tolerance. Illustrations are given in the infrared and visible ranges where the technological integration of such compact structures is particularly relevant for detection applications.