Patent ID: 8026998

Claim:
High contrast, wide viewing angle LCD light switching filter comprising two electrically controlled LC-cells (LCD 1 , LCD 2 ), two mutually crossed pairs of polarizing films (P 1 , A 1 and P 2 , A 2 ), adjacent to light input and output sides of the said LC cells (LCD 1 , LCD 2 ), each of the said LC-cells (LCD 1 , LCD 2 ) having a thin liquid crystal molecular layer (d a +d b +e) of highly twisted liquid crystal enclosed between two boundary glass plates ( 1 a a , 1 a b ), the said plates ( 1 a a , 1 a b ) being on an inner side covered by transparent electrodes ( 1 b a , 1 b b ) and alignment layers ( 1 c a , 1 c b ), characterized in that the alignment layers ( 1 c a , 1 c b ) on the transparent electrodes ( 1 b a , 1 b b ) covering the boundary glass plates ( 1 a a , 1 a b ) of both LC cells (LCD 1 , LCD 2 ) are oriented in such a way that in an optically open state of the LCD light switching filter, when no driving electric voltage (V=0) is applied to the transparent electrodes ( 1 b a , 1 b b ), the liquid crystal molecular layer (d a +d b +e) adopts a highly twisted molecular orientation with twist angles Φ between 120° to 240° and that the two crossed pairs of polarizing films (P 1 , A 1 and P 2 , A 2 ) are oriented with respect to LC molecular alignment surface directions ( 1 r a , 1 r b respectively 2 r a , 2 r b ) of each of the LC cells (LCD 1 , LCD 2 ) in such a way that the light transmission axes of a first (P 1 , A 1 ) of said pairs of polarizing films are aligned within a small angle α along symmetry axes (S 1 1 , S 2 1 ) of the LC-molecular alignment surface directions ( 1 r a , 1 r b ) in a first LC-cell (LCD 1 ) and that the light transmission axes of a second (P 2 , A 2 ) of said pairs of polarizing films are aligned within a small angle α along symmetry axes (S 1 2 , S 2 2 ) of the LC-molecular alignment surface directions ( 2 r a , 2 r b ) in a second LC-cell (LCD 2 ), wherein said angle α is smaller than 20 degrees, allowing for the expansion of an overall viewing angle of the LCD light switching filter.