Optical cell

Details Optical cell Optical cell

1996-11-06

1998-11-17

Epps, Georgia Y.

Optical: systems and elements

Optical modulator

Light wave temporal modulation

359272, 359296, 349153, G02F 103

Patent

active

058384820

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention.
The present invention relates to an optical cell (also known as a light valve) of the type which includes a material orientable by an electrical field to vary the amount of luminous transmission through the cell.
2. Description of the Related Art.
Various techniques have been proposed hitherto for the production of optical cells having variable luminous transmission. The techniques have included suspended particles, electrochromism, electrodeposition and liquid crystal technology. The cell is formed by sandwiching a layer of the sensitive material in a space created between adjacent parallel sheets of rigid, generally transparent material, typically thin sheets of glass.
The optical cells to which the present invention relates are those which incorporate a liquid suspension of solid particles capable of orientation by an electric field, such as described, for example, in U. S. Pat. No. 3,655,267 (Research Frontiers). These optical cells switch rapidly from a clear state, achieved when the electrical field is applied, to a dark state when the field is removed.
The surfaces of the parallel sheets facing the space to receive the liquid suspension are coated with an electrically conducting material and the sheets are held apart by an insulating peripheral gasket which also serves to seal the edges of the space. Electrical contact terminals are attached to the respective coatings.
Optical cells provide a means for variable light transmission in glazing panels or for variable light reflection in mirrors, both for vehicles or buildings. For example they can be used as a glazing panel adjustable between an opaque and clear condition to limit solar transmission or to conceal the interior of a room or vehicle to provide privacy therein. They can be used in a vehicle sun-visor, sunshine roof panel or a rear-view mirror or on an aircraft porthole.
The use of an optical cell on a mirror, and especially for a vehicle, rear-view mirror, demands a very high level of quality of the cell. It is important for the cell to have a highly uniform appearance, since every fault in the cell is much more clearly seen than in other applications such as glazing panels in buildings.
In a vehicle rear view mirror the cell is located adjacent and parallel to a reflective surface and in the line of sight between the reflective surface and the vehicle driver so as to provide a variable level of light reflection from the mirror to the driver. In full daylight the degree of luminous reflectivity from a rear-view mirror is required to be high, generally greater than 50% and more preferably greater than 65%. For very dull or nighttime conditions the reflectivity is limited, for example to 15% or less, in order to avoid dazzling of the driver by lights such as the headlights of following vehicles.
The required configuration of the optical cell is highly variable. It may be flat or curved, for example in a rear view mirror. Internal rear view mirrors are generally rectangular with rounded comers, but external rear view mirrors are generally of an irregular four-sided shape, still with rounded corners, or may be circular.
In a device such as a rear view mirror with an associated optical cell the reflective mirror surface can be applied to the cell sheet most distant from the viewer. The reflective surface, for example a layer of silver, can be deposited on the opposite surface of the sheet to that carrying the electrically conductive coating but alternatively can be deposited on the same face. In this latter configuration either a single layer can be applied which serves the purposes of reflection and electrical conduction or a multiple layer can be applied, comprising for example one or more reflective layers, typically of aluminium, chromium or silver, and one or more electrically conductive layers, typically of indium tin oxide (ITO), tin oxide or zinc oxide.
The variation in light transmission through the liquid suspension is achieved by the orientation of the particles. For most applica

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