Screens having graded refractive index lenses

Details Screens having graded refractive index lenses Screens having graded refractive index lenses

1996-04-22

1999-07-20

Epps, Georgia

Optical: systems and elements

Single channel simultaneously to or from plural channels

By surface composed of lenticular elements

359619, G02B 2710

Patent

active

059263199

DESCRIPTION:

BRIEF SUMMARY
THIS INVENTION relates to light diffusing and depixelating screens or layers incorporating graded refractive index (GRIN) microlenses or other optical features. Screens of this type, made from photopolymerized material are disclosed, for example, in European Patent Specification No. 0294122, International (WO) Published Specifications Nos. WO91/18304 and WO92/1605 and in co-pending International Patent Application PCT/GB94/01281 to which reference should be had.
European Patent No. 0294111 discloses a microlens screen comprising a sheet of transparent material formed with an array of integral microlenses which are spaced apart from one another in the plane of the sheet with each microlens having an optical axis extending through the sheet material from one major face thereof to another, for example extending normal to the plane of the sheet material or inclined relatively slightly to a normal to such plane.
In the microlens screen disclosed in European Patent No. 0294122 the transparent material is a variable refractive index polymer and the individual lenses, forming said array of microlenses, are graded refractive index (GRIN) lenses or which owe at least a substantial part of their optical power to graded refractive index effects in the polymer.
The present invention relates to light diffusing screens having graded refractive index features which are not, strictly speaking, lens-like in character, as well as to screens having graded refractive index microlenses.
According to one aspect of the invention there is provided a microlens screen which is provided, on at least one surface thereof, with an opaque coating extending over the regions between adjoining microlenses in the array but not occluding the microlenses themselves.
Preferably the opaque layer is black.
European Patent No. 0294122 describes a method of making a graded refractive index microlens screen in which a photopolymerizable monomer, for example an acrylamide monomer, Provo ed in the f ore of a sheet or layer of viscous fluid or tacky gel, is exposed selectively at each of a plurality of spots (corresponding to the eventual microlenses) to ultraviolet light to cause polymerization selectively in the spots illuminated. Subsequently, after polymerization in the region of the spots so illuminated, the material is subjected to a blanketing exposure to ultraviolet light to cure the remainder of the material unexposed during the initial, selective exposure. The material may be heated before or after the selective exposure.
In a preferred embodiment of the above-noted aspect of the present invention, in which the microlens screen comprises a sheet of photopolymer material substantially as disclosed in Eur opean Patent No. 0294122, advantage is taken of the fact that, at a time after the selective exposure and before the blanketing exposure, the unpolymerized material (monomer) is significantly tacky, whereas the photopolymerized material, which forms the individual microlenses, is substantially dry and non-tacky, by applying to one surface of the material, after it has been selectively exposed in the regions where microlenses or analogous features are desired to be formed but before the subsequent blanketing exposure, a layer of a black opaque material, such as Chromalin, which adheres to the tacky regions but not the dry polymerized regions defining the microlenses. Subsequently the Chromalin material is removed from the non-adhesive regions. The same technique may be applied to certain other photopolymers. For example, the photopolymer used may be that supplied by Du Pont under the Registered Trade Mark OMNIDEX and having the type designation HRF150 or HRF600. The monomer in the HRF series photopolymers is fluorescent N-vinyl-carbazole (NVC) dispersed in a plasticized polyvinyl acetate (PVAC), cellulose acetate butyrate (CAB) or polyvinyl butyrate (PVB) as the polymeric binder. The material may be initiated either by photoinitiators or by a photosensitizing dye/initiator combination.
The OMNIDEX materials are available in sheet form, comprisi

REFERENCES:
patent: 3552822 (1971-01-01), Altman
patent: 3609000 (1971-09-01), Miyano et al.
patent: 4068922 (1978-01-01), Dotsko
patent: 4111695 (1978-09-01), Yevick
patent: 4877717 (1989-10-01), Suzuki et al.
patent: 5471881 (1995-12-01), Hochstein
patent: 5473454 (1995-12-01), Blanchard
patent: 5568313 (1996-10-01), Steenblik et al.

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