Conception and realization of spectral sorters

The advancement and scaling effect in complementary metal oxide semiconductor (CMOS) and micro-electro-mechanical system (MEMS) technology has made possible to make smaller image sensors with higher density of imaging pixels to respond at the demand of low cost imagers. Generally, the higher pixel density in imaging system is achieved by shrinking the size of each pixel in an array. The shrinking of pixel dimension however deteriorates the optical efficiency and therefore impose the tradeoff between the performance and minimum achievable pixel size. As the pixel size continues to shrink and approach the dimensions comparable to the wavelength, the spectral separation techniques used in current generation imaging system should be revised and new design methodologies have to be explored. This dissertation explored different techniques that could be used to efficiently sort the band of different wavelengths, mainly in far-infrared (8µm - 12µm) and visible (0.4 µm – 0.7 µm) spectrum in different spatial locations. We introduced the concept of spectral sorting based on normalized optical efficiency (NOE). For given number of pixels (N) or detectors, we define the phenomenon of sorting if NOE of individual pixels, considering incidence power from all pixel domain, is greater than 1/N. First we study differently sized optical patch antenna to efficiently sort the infrared light in different spatial locations using numerical techniques. Using array of such antennas we find the near perfect absorption of multiple wavelengths in infrared spectrum. The antenna arrays are fabricated and characterized in CEA-LETI platform to validate our study. We also report our study on using two differently sized Metal-Semiconductor-Metal (MSM) nanostructures to achieve absorption higher than 50% in individual silicon detector for visible spectrum. Finally we present our study on grating based dielectric multilayer structure for sorting of visible light which could enable to shrink the pixel size of visible imaging system to submicron dimension. We derived the comprehensive design strategy of such sorting structure and present the sorting structure designed to achieve optical efficiency as high as 80% in pixel size of as less as 0.5µm.