Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Patent
1995-07-12
1998-04-07
Sikes, William L.
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
349 98, 349117, G02F 11335
Patent
active
057370443
ABSTRACT:
An illumination system comprises a radiation source and a broadband, cholesteric polarizer. Such a polarizer includes a layer of a polymeric material having a cholesteric ordering, the material being ordered such that the axis of the molecular helix is oriented transversely to the layer. The broadband character of the polarizer is obtained by increasing the pitch of the molecular helix from a minimum value at a first surface of the cholesteric layer to a maximum value at the second surface of the layer. The polarizer must be positioned in the illumination system in such a manner that the second surface of the cholesteric layer faces the radiation source. By virtue thereof, the illumination system attains a surprisingly low viewing-angle dependence of the brightness and the colour. This property is further improved by using a quarter lambda plate having a negative an isotropy in the refractive index.
REFERENCES:
patent: 5061042 (1991-10-01), Nakamura et al.
patent: 5344513 (1994-09-01), Takenaka
patent: 5486884 (1996-01-01), De Vaan
patent: 5506704 (1996-04-01), Broer et al.
Broer Dirk J.
Van Haaren Johannes A. M. M.
Egbert Walter M.
Malinowski Walter
Sikes William L.
U.S. Philips Corporation
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