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Low Power Laser Addressed Liquid Crystal Projection Display Device

IP.com Disclosure Number: IPCOM000053025D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Chang, IF: AUTHOR [+2]

Abstract

Laser-beam-addressed, thermally activated liquid crystal cells have been used for reflective projection displays of high information content. The liquid crystal is sandwiched between two pieces of glass: the front viewing window and the rear writing window. The cell configuration is shown in the drawing, with the proposed layer included. In operation, the liquid crystal cell is thermally biased a few degrees centigrade below the smectic A to nematic transition temperature (T(AN)). In the quiescent state, liquid crystal is transparent. The laser beam is used to selectively heat a portion of liquid crystal to raise its temperature beyond T(AN). After the removal of the laser beam, the liquid crystal is cooled down and transformed into a scattering state.

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Low Power Laser Addressed Liquid Crystal Projection Display Device

Laser-beam-addressed, thermally activated liquid crystal cells have been used for reflective projection displays of high information content. The liquid crystal is sandwiched between two pieces of glass: the front viewing window and the rear writing window. The cell configuration is shown in the drawing, with the proposed layer included. In operation, the liquid crystal cell is thermally biased a few degrees centigrade below the smectic A to nematic transition temperature (T(AN)). In the quiescent state, liquid crystal is transparent. The laser beam is used to selectively heat a portion of liquid crystal to raise its temperature beyond T(AN). After the removal of the laser beam, the liquid crystal is cooled down and transformed into a scattering state.

Most liquid crystals do not have a strong absorption in both visible and near infrared regions. An absorber or anti-reflection coating, such as described in [1], followed by a reflector layer is proposed to absorb the laser beam. The anti- reflection coating consists of three layers, (TiO(2) - SiO(2) - TiO(2)) and is followed by two reflective coatings (300 angstroms Cr and 100 angstroms Al). The laser beam is mainly absorbed by 300 angstroms Cr generates heat propagating toward both the rear glass window and the liquid crystal. The required laser power density to operate the device is fairly large, approximately 100 mJ/cm/2/. With the present device configuration, analysis reveals that most of the heat generated by the absorption of the laser beam is wasted in heating the rear glass window instead of the liquid crystal. A transparent, thermal insulating layer is inserted between the rear glass window and the absorber or anti-reflection coating to reduce the heat loss to the rear glass window. Alternatively, instead of using a glass substrate, a high thermal insulating material may be used.

Either a proper thermal insulating substrate should be used or a laser beam transmitting thermal insulating film should be inserted between the anti-reflecting...