1988-04-13
1989-06-20
Arnold, Bruce Y.
350 36, G03H 122
Patent
active
048404446
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to optical elements which can provide holographic images and particularly to composite optical elements which may, for example, be employed in sunglasses or the like to provide a holographic image in reflection to a viewer without substantial detriment to the other optical function or functions of the element.
It is known from articles and work by Claude Pueche (Thomposn CSF) to coat a substrate bearing a surface relief hologram with a substantially transparent coating of a different refractive index to the substrate and thereby to obtain a visible holographic image in reflection.
It is proposed in the specification of U.S. Pat. No. 4,315,665 to provide a composite optical element which comprises a first layer or substrate bearing holographic information in the form of a surface pattern, a thin coating which conforms to the surface pattern and is either partially reflective or is of a transparent material of which the reflection index is different from the reflective index of the said substrate and a third layer which fills in the surface variations of the said coating, the third layer being optically transparent, having a refractive index equal to that of the first layer. It is found however that a hologram produced in reflection by such an element may be rather dim. Moreover if the thin coating or intermediate layer is increased in thickness to enhance the brightness of such a hologram the optical performance of the element in other respects is degraded.
It is accordingly one object of the present invention to provide an improved optical element which can provide a holographic image with substantially no detriment to the optical performance of the element and in particular to provide an improved optical element for sunglasses or eyeshades.
An important feature of the invention is the inclusion, in a composite structure including a substrate which carries a surface relief pattern adapted to produce a holographic image in reflection, of a thin optically absorbent layer. Such a layer may be provided between the surface bearing the relief pattern and a further, partially reflective layer. Additionally or alternatively such an absorbent layer may be provided on the opposite surface of the substrate. The absorbent layer or layers provide a means of substantially reducing visible diffraction or refraction disturbance arising from either light transmission through the element from the side facing the surface relief pattern or from reflection of light incident on the element in the opposite direction.
BRIEF DESCRIPTIONN OF THE DRAWINGS
FIG. 1 is a schematic drawing illustrating a known form of composite element; and
FIGS. 2, 3 and 4 are schematic drawings illustrating various composite elements according to the invention.
DETAILED DESCRIPTION
A surface relief pattern may be formed using known holographic techniques on a substrate. At the present time the use of holography is the only practical method to form images of objects in a reflected light beam from a composite optical element. A pattern of light interference fringes may be formed by the interference of a reference beam or beams of coherent or substantially coherent light with a similar coherent or substantially coherent beam of light identified as an object beam or beams, upon a specially prepared detector. The detector may comprise a substrate which is treated with a photo resist material, silver halide film or a thermoplastic, photopolymer or another medium which may be bleached, etched or developed so as to form a surface relief pattern, constituting a hologram. Multiple copies of the resultant surface relief hologram may be made using known techniques from a master hologram, or for the purposes of making an acceptable copy or copies of this master reference waves may be formed using unconventional or novel optics, resulting in an overall improved resolution of the image to be copied. These techniques include the making of secondary metal masters, embossing and injection moulding.
FIG. 1 illustrates a prior proposal
REFERENCES:
patent: T861026 (1969-04-01), Harper et al.
patent: 4315665 (1982-02-01), Haines
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