Pixel-sized infrared filters for a multispectral focal plane array.

We present a theoretical study of guided-mode-resonance filters made of two sub-wavelength metallic gratings and a dielectric waveguide, with lateral geometries compatible with the size of infrared focal plane array pixels. Contrary to most of the studies described in the literature, we consider here a focused beam on finite-sized filters, and we investigate the optical properties of a mosaic of 30 µm-long filters. We demonstrate the spectral filtering ability and low crosstalk of such components. We also study the impact of an oblique beam onto a filtering mosaic. We finally discuss the opportunities offered by these results for a new generation of multispectral infrared cameras, and we give an example of a simple architecture.

Field extension inside guided-mode-resonance filters under a focused beam.

We present a theoretical study of the mid-infrared guided mode resonance spectral filters made of two subwavelength metallic gratings and a dielectric waveguide under a focused beam with a finite spot size. This Letter shows that, at the resonant wavelength, the lateral extension of the electromagnetic field in the waveguide is close to the width of the beam. We compare the performance of filters using gratings with a one-slit pattern and gratings with a two-slit pattern, and we show that the latter gratings (biatom gratings) provide a higher transmission and a better limitation of field extension, due to an improved angular acceptance. These results open new perspectives for pixel-sized infrared filters.