Browse Prior Art Database

LCD GLARE AVOIDANCE USING A SURFACERELIEF DIFFRACTIVE OPTICAL ELEMENT

IP.com Disclosure Number: IPCOM000009839D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-23
Document File: 2 page(s) / 106K

Publishing Venue

Motorola

Related People

Zane Coleman: AUTHOR [+2]

Abstract

Reflective liquid crystal displays (LCD), such as those used in low power portable products, rely on reflected ambient light to illuminate the display. The position of the display, in relation to the light source and the viewer, that provides the brightest image is also the position of glare from the front of the display. This makes the display unreadable and consequently it is viewed at a position just off glare, the position which is not as bright. This approach intentionally mis-aligns the glare light from the useful light reflected from the display to improve considerably the brightness and readability.

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MOTOROLA

Technical Developments

LCD GLARE AVOIDANCE USING A SURFACERELIEF DIFFRACTIVE OPTICAL ELEMENT

by Zane Coleman and George Valliath

Reflective liquid crystal displays (LCD), such as those used in low power portable products, rely on reflected ambient light to illuminate the display.

The position of the display, in relation to the light source and the viewer, that provides the brightest image is also the position of glare from the front of the display. This makes the display unreadable and consequently it is viewed at a position just off glare, the position which is not as bright. This approach intentionally mis-aligns the glare light from the useful light reflected from the display to improve considerably the brightness and readability.

Motorola has previously developed reflective holographic approachesl.2 and transmission holographic approaches3.4 to improve the glare avoidance in the displays for our products. Reflective Holographic Optical Elements (HOE) are not compatible with reflective LCD's with internal reflective electrodes. In the case of external reflectors, the additional thickness introduced with the rear glass substrate causes a significant amount of incident light to pass through two different color filters, thus reducing the brightness. Most color LCD manufacturers have moved the reflective component of the display inside the cell to alleviate this problem.

However, the manufacturing and processing requirements currently prohibit the implementation of the reflective holographic optical element inside the liquid crystal cell.

Transmission HOE's are a viable method, however, they have several limitations. ~anufacturing the holographic transmission films is expensive, the light control is limited, there is a significant amount of noise inherent with mass manufacture, and it is not as environmentally stable as some plastics.

The approach taken here is the combination of a conventional reflective (or transflective) LCD that has a transmissive diffractive optical element on the front viewing side of the display that provides glare avoidance by steering the incoming light away from where refraction would guide it. On the path out, however, it does not significantly deflect the light further. The net effect of the diffractive optical element and reflective LCD is to cause the reflected light to be off the glare angle. The diffractive optical element may also diffract light through a defined angular range at each location on the film, thus simulating a diffuser (light scattering element) as well as a beam steering optic (Figure I).

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