Simplified and improved diffractive subtractive color filtering technique
AssigneeRCA Corporation
InventorKarl Knop
Life of this patent
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Abstract
The present invention takes advantage of the fact that the first and second optical depths of a diffractive subtractive color filter respectively manifesting cyan and yellow zero-order diffraction light may be so selected that an optical depth equal to the sum of the first and second optical depths manifests green zero-order diffraction light. This permits a variable optical amplitude first grating, manifesting cyan, yellow and green, to be combined with a fixed optical amplitude second grating, manifesting magenta, to provide a full gamut of colors.
Claims11
A diffractive substractive color filter responsive to illumination thereof with white light for deriving colored zero order diffraction light, said filter comprising:
- a variable optical amplitude binary phase delay diffractive structure selectively comprising no more than three different optical amplitudes consisting of a given first optical amplitude corresponding to cyan zero order diffraction light, a given second optical amplitude corresponding to yellow zero order diffraction light, and a third optical amplitude substantially equal to the sum of said first and second amplitudes and corresponding to green zero order diffraction light, and
- wherein said structure comprises a plurality of separate regions including a first region, having said third optical amplitude and a second region having solely one of said first and second optical amplitudes.
In a method for fabricating a diffractive subtractive color filter which includes the recording of a diffraction grating structure in photoresist for use in embossing a surface relief pattern diffractive structure in a medium having a certain difference in index of refraction from its surroundings;
- the improvement comprising the steps of:
- providing a recording blank composed of a substrate sheet supporting a layer of positive photoresist where the substrate sheet has a square-wave diffraction grating of a given line spacing and a given physical depth embossed in a face thereof with said layer of photoresist having a thickness which fills the grooves of said grating and extends a given distance beyond the ridges of said grating,
- illuminating at least a first portion of said photoresist layer with cyan-manifesting light to provide a first given exposure of said photoresist layer, and
- then illuminating at least a second portion of said photoresist layer with yellow manifesting light to provide a second given exposure of said photoresist layer,
- said given distance being at least equal to the depth of unexposed areas of said photoresist layer dissolved during development, said first given exposure alone being that required to reveal after development of said photoresist layer a first part of said physical depth of said square wave grating equal to an optical amplitude for said diffractive subtractive color filter manifesting cyan zero order diffraction light divided by said certain difference in index of refraction, said second given exposure alone being that required to reveal after development of said photoresist layer a second part of said physical depth of said square wave grating equal to an optical amplitude for said diffractive subtractive color filter manifesting yellow zero order diffraction light divided by said certain difference in index of refraction, and said given physical depth being substantially equal to the sum of said first and second parts thereof.
Dependencies are inferred from the claim text.