Wavelength-selective phase-type optical low-antialiasing filter and fabrication methods

A wavelength-selective optical low-pass filter for use with an optical imaging system of a solid-state color imager, comprising a transparent substrate and a plurality of transparent spots randomly placed on the substrate for producing a phase difference between a wavefront transmitted through the spots and that portion of the substrate other than the spots to define a filter having a spatial sampling cut-off frequency which varies depending on wavelength of light, the phase difference satisfying the following conditions where phi alpha , phi beta , and phi gamma are the phase differences due to the spots at certain specific wavelengths in the visible through infrared portion of the optical spectrum, and are given by the following relationship where i = alpha , beta , or gamma ; ni; is the index of refraction of the material comprising the spots at the specific wavelength lambda i; ni' is the index of refraction of the medium surrounding the spots at the specific wavelength lambda i; and t is the physical thickness of the spots.