Switchable color filter

Details Switchable color filter Switchable color filter

2006-09-19

2006-09-19

Schechter, Andrew (Department: 2871)

Liquid crystal cells, elements and systems

Liquid crystal system

Variable or rotatable retarder used with other retarders to...

C349S080000, C349S104000, C349S098000, C349S097000

Reexamination Certificate

active

07110054

ABSTRACT:
The liquid crystal switchable color filter switches between three color bands and is preferably used for time-sequential color devices, as for example projection devices, direct view displays and video cameras. The color filter employs circularly polarizing selective reflection bands of at least four cholesteric filters (89, 91, 93, 95) together with three liquid crystal switches (81, 83, 85) and related retarder layers. Between the first and the second as well as between the third and the fourth cholesteric filter an additional half-wave plate (111, 113) is provided, which makes it possible to use cholesteric filters having all the same handedness. Furthermore, for the blocking state of a color band the optic axis of the corresponding liquid crystal switch is parallel or perpendicular to the polarization direction. This concept simplifies production and still exhibits excellent properties for the color switch. Moreover, it advantageously allows overlapping color transmission bands thus improving the light efficiency.

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Bachels et al: “Advanced Electronic Color Switch for Time Sequential Projection” 2001 Sid International Symposium Digest of Technical Papers. San Jose, CA, Jun. 5-7, 2001, Sid International Symposium Digest of Technical Papers, San Jose, CA: Sid, US, vol. 32, Jun. 2001, XP002227327 Chapter: The Electronic Band Modulation Filter.
Schmitt K et al: “Fast Time-Sequential Color Switch Based on Cholesteric Filters and DHF-LCDS” Eurodisplay, XX, XX, Sep. 6, 1999, pp. 437-440, XP008002141 cited in the application.
Makow DM: “Peak reflectance and color gamut of superimposed left- and right-handed cholesteric liquid crystals” Applies Optic, Apr. 15, 1980, USA, vol. 19, No. 8, pp. 1274-1277, XP002197363 ISSN: 0003-6935 Chapter: III. Experimental Results Figures 1-3.

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