Method and apparatus for concentrating optical flux in a focal plane array

A back side illuminated focal plane array (10,20) includes a plurality of radiation detectors (12,26) disposed upon a front surface of the array and further includes a plurality of optical flux concentrating structures (16,22) integrally formed upon or within a back, radiation receiving, surface of the array. Each of the flux concentrating structures is in registration with at least one of the radiation detectors for concentrating optical flux thereon. A method of the invention includes the steps of providing a substrate 30 and preparing a surface of the substrate such that the surface has a faster lateral etch rate than a vertical etch rate when exposed to an etchant. The method further includes a step of providing a mask 32 over the surface of the substrate, the mask having a plurality of openings therethrough individual ones of which are located at a position where a lens element is desired. The method further includes the steps of applying an etchant to the surface of the substrate through the openings within the mask, etching the surface of the substrate such that a plurality of depressions 34 are formed within the surface and depositing a layer 36 of material over the surface of the substrate such that the depressions are filled with the material. The method includes an additional step of removing excess material from the surface of the substrate, the material remaining within each of the depressions forming a lens element.