Coherent, Inc.

Stephen D Vincent

Bruce E Perilloux

A short-wave-pass optical filter, including a partially absorbing or transparent substrate coated by a set of layers having different quarter-wave optical thicknesses, which is designed to reflect visible radiation of a selected color white transmitting visible radiation and maintaining a neutral color balance. The inventive filter is designed so that the desired reflected color (and the transmitted neutral color balance) is substantially independent of viewing angle (i.e., the incidence angle). In a preferred embodiment, the substrate is composed of UV-absorbing glass, and the coating is substantially a double quarter-wave stack of alternating layers of SiO.sub.2 and TiO.sub.2, TiO or Ti.sub.2 O.sub.3. The reflectance of the inventive filter (as a function of wavelength) is designed to have a ripple in at least one segment of the visible spectrum, but to have no significant ripples in all other segments of the visible spectrum. The partial reflection represented by the one or more rippled regions is sufficient to give the filter a desired aesthetic color, such as violet, orange, or blue. In a preferred embodiment, the visible light reflected by the inventive filter corresponds not only to a first rippled region, but also to a second rippled region or 'partial second-order stopband' (or both), where each rippled region and partial second-order stopband is positioned so that, as the reflected light is viewed with changing incidence angle, the reflected color will not significantly change.

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Grass Valley, CA, United States of America

Stephen D Vincent