Illumination system using a broadband cholesteric polarizer having its surface of maximum helix pitch face the radiation source
First Claim
1. An illumination system comprising a radiation source and a broadband, cholesteric polarizer with a layer of a polymeric material having a cholesteric ordering, said material being ordered such that the axis of the molecular helix is oriented transversely to the layer, and the pitch of the molecular helix increasing from a minimum value at a first surface of the cholesteric layer to a maximum value at the second surface of the layer, and the polarizer being positioned in the illumination system in such a manner that the cholesteric layer faces the radiation source with the second surface.
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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.
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18 Claims
- 1. An illumination system comprising a radiation source and a broadband, cholesteric polarizer with a layer of a polymeric material having a cholesteric ordering, said material being ordered such that the axis of the molecular helix is oriented transversely to the layer, and the pitch of the molecular helix increasing from a minimum value at a first surface of the cholesteric layer to a maximum value at the second surface of the layer, and the polarizer being positioned in the illumination system in such a manner that the cholesteric layer faces the radiation source with the second surface.
Specification