Diffractive microstructures for color separation and fusing

Claim 1

Optical apparatus for dispersing a visible light spectrum into primary color bands and directing each color band into a specified pixelated cell of a passive display comprising: a display including pixelated cells; an array of refractive microlenses arranged parallel to the plane of the display to receive visible light; a diffraction grating arranged parallel, and in close proximity, to the array of refractive microlenses to separate the visible light into primary color bands, wherein said microlenses focus the visible light onto the display, while said diffraction grating separates the visible light into the primary color bands in different diffraction orders such that each color band is directed to the specified pixelated cell for transmission therethrough, wherein said diffraction grating comprises an optical material having a periodic echelle structure, wherein each period has a profile of discrete optical thicknesses and each profile begins with an minimum optical thickness, and increases stepwise in optical thickness to a maximum optical thickness, wherein said profiles are arranged such that the optical thickness of the profiles increases in the same direction across a surface of the optical material, with the maximum optical thickness of at least one profile abutting the minimum optical thickness of an adjacent profile, and wherein the physical difference in depth between adjacent steps within said profile is ##EQU7## where λ is the design wavelength and n is the index of refraction of the material.