Vol. 30, Issue 1, pp. 151-160

Abstract

Focal plane collection optics consisting of arrays of microlenses may be used to reduce the physical size of an infrared detector without reduction of its apparent optical size and quantum efficiency. This results in reduction of the thermal generation rate in the detector, allowing improvement of performance of infrared devices operating at elevated temperatures. We report on calculations of the optical gain achievable with the use of diffractive microlenses for long-wave (8-22 μm) infrared (LWLR) detectors. Fast diffractive lenses are required for this application, and binary optics is the most popular technology of their fabrication. A large fraction of the binary lens surface relief is built of staircase annular structures whose width is of wavelength-scale. Therefore, the electromagnetic theory of gratings has been applied in the paper to calculate the diffraction efficiency of the Fresnel zones for the multi-phase-level lenses. It is shown that electromagnetic effects limit the speed of the LWIR diffractive lenses.