Planar, Ultrathin, Subwavelength Spectral Light Separator for Efficient, Wide-Angle Spectral Imaging

We propose a planar, ultrathin, subwavelength spectral light separator that enables efficient, angularly robust, spatially coregistered decomposition of light into its spectral components. The device consists of a collection of spectrally tuned "meta-atoms" and achieves spectral selectivity by utilizing strong localized resonance supported by each individual meta-atom. The three-dimensional meta-atoms are formed by resonant subwavelength-size rectangular apertures in a planar metallic film of deep-subwavelength thickness. The overall physical cross-sectional area of the device is subwavelength, and its thickness is deep-subwavelength. Different spectral components of light are simultaneously separated and collected in different subwavelength-size aperture pairs, where each aperture pair is composed of two perpendicularly oriented, same-size apertures; and different aperture pairs collect their light from overlapping cross-sectional regions. Hence, spatial coregistration errors between different spectral channels are quite reduced, which is an attractive feature for multispectral imaging systems. The operation of the device is polarization-independent; however, the device also simultaneously separates different linear polarization components of light and collects their power in different apertures of aperture pairs. The device also exhibits angular robustness for obliquely incident light, that is, spectral selectivity is largely angle-independent. Both features are appealing for imaging applications.