Passive high efficiency variable reflectivity image display device

• US 5,959,777 A
• Filed: 06/10/1997
• Issued: 09/28/1999
• Est. Priority Date: 06/10/1997
• Status: Expired due to Term

• Current Assignee: Concord HK International Education Limited
• Original Assignee: University of British Columbia
• Inventors: Whitehead, Lorne A.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Lucas, Michael A
• Application Number:
  US08/872,161
• Time in Patent Office: 840 Days
• Field of Search: 359/618, 359/263, 385/901, 349/62, 356/71
• US Class Current: 359/618
• CPC Class Codes: G02B 26/02 for controlling the intensity of light G02B26/004 takes precedence
• CPC Class Codes: G02F 1/315 based on the use of controlled internal reflection
• CPC Class Codes: G02F 2203/026 attenuated or frustrated internal reflection
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

A variably reflective display device amenable to multiple pixel display applications. Each pixel has at least one element having a reflective state in which incident light undergoes total internal reflection, and having a non-reflective state in which total internal reflection is prevented. Such prevention is achieved by interfering with (scattering and/or absorbing) the evanescent wave adjacent the surface of the element. For example, a member can be positioned adjacent the element and deformed between first and second positions. In the first position a gap remains between the member and the element to allow the evanescent wave to behave normally. In the second position the member is in optical (but not atomic) contact with the element, such that the member interferes with the evanescent wave and thereby prevents total internal reflection. In one embodiment, each pixel is a grouping of retro-reflective elements, such as corner reflectors. An elastomeric material is provided adjacent each grouping. If a gap is left between the grouping and the elastomeric material, the grouping continues to exhibit total internal reflection. But, if the elastomeric material makes optical contact with the grouping, the evanescent wave is absorbed or scattered and hence total internal reflection is prevented, which in turn prevents reflection of incident light. Thus, the "pixel" formed by the corner reflector grouping is "off" if it makes optical contact with the elastomeric material, and "on" if a gap is left between the two.

Claims

1. A multiple pixel image display device, comprising:

(a) each said pixel formed by at least one element having a reflective state in which light incident upon a front surface of said element undergoes total internal reflection and an absorptive state in which said total internal reflection is prevented, said total internal reflection being characterized by an evanescent wave adjacent a rearward surface of said element; and

,

(b) switching means for controllably switching said elements between said states, said switching means further comprising a member positioned adjacent said rearward surface and deformable between a first position in which a gap remains between said member and said rearward surface and a second position in which said member is in optical contact with said rearward surface to provide a separation distance between said member and said rearward surface of substantially less than 0.5 microns and substantially more than 10^-4 microns, said member not interfering with said evanescent wave in said first position, said member interfering with said evanescent wave in said second position and thereby preventing said total internal reflection, said second position not permitting substantial atomic contact between said member and said rearward surface.

5. An image display device as defined in claim 1, wherein each of said elements is retro-reflective, and wherein each of said pixels further comprises a grouping of said elements.

6. An image display device as defined in claim 5, wherein said retro-reflective elements are corner reflectors.

7. An image display device as defined in claim 5, wherein said retro-reflective element grouping is diffuse.

8. An image display device as defined in claim 1, wherein said member further comprises an elastomeric material.

9. An image display device as defined in claim 8, wherein said elastomeric material has a thin, comparatively hard outer surface coating.

10. An image display device as defined in claim 1, each of said pixels comprising at least one three-faceted corner reflector, said image display device further comprising a coloured reflective contact element for each one of said three corner reflector facets, each one of said contact elements deformable between a first position in which a gap remains between said one contact element and said corresponding corner reflector facet, and a second position in which said one contact element is in optical contact with said corresponding corner reflector facet.

2. An image display method, comprising:

(a) forming a plurality of image pixels, each of said pixels having a reflective state in which light incident upon a front surface of said pixel undergoes total internal reflection, said total internal reflection being characterized by an evanescent wave adjacent a rearward surface of said element; and

,

(b) preventing said total internal reflection at selected ones of said pixels to switch said selected pixels from said reflective state to an absorptive state, said preventing comprising positioning a member adjacent a rearward surface of said selected pixels and deforming said member between a first position in which a gap remains between said member and said rearward surface and a second position in which said member is in optical contact with said rearward surface with a separation distance between said member and said rearward surface of substantially less than 0.5 microns and substantially more than 10^-4 microns, said second position not permitting substantial atomic contact between said member and said rearward surface, said member not interfering with said evanescent wave in said first position, said member interfering with said evanescent wave in said second position and thereby preventing said total internal reflection.

3. An image display method as defined in claim 2, wherein said member is an elastomeric material.

4. An image display method as defined in claim 2, wherein said image pixels each comprise a three-faceted corner reflector, said preventing further comprising, for each one of said pixels, deforming a coloured contact element with respect to a corresponding one of said facets between first and second positions which respectively do not and do interfere with said evanescent wave at said corresponding facet.