Abstract: An optical scanning device comprising means for scanning optical record carriers of predetermined different formats, such as CDs and DVDs, using scanning at different numerical apertures provided by an optical diaphragm. The optical diaphragm comprises cholesteric liquid crystal material of one or more selected helical pitches which provide the diaphragm with desired wavelength- and/or polarization-selective characteristics.

Abstract: In the case of a twisted nematic LCD of the dual-domain type, a better viewing-angle dependence is achieved by providing a birefringent retardation foil on the side where the liquid crystal molecules are uniformly oriented, the optical axis of said retardation foil extending in a plane parallel to said orientation.

Abstract: A reflective liquid crystal (R-LCD) display device in which both the residual retardance of an R-LCD and the skew-angle effect of the analyzer may be compensated by a single compensator which has its optical axis oriented at an angle of from 1 to 30 degrees to the plane of polarization of the incident beam, eliminating the need for two separate compensators.

Abstract: An optical wavefront modifier (27) is adapted for modifying a wavefront of an optical beam passing through the modifier. The modifier comprises a first and a second transparent electrode layer (42, 43) and a flat medium (46) for modifying the wavefront in dependence on electrical excitation of the medium and arranged between the electrode layers. The electrode layers are adapted to impress a first wavefront modification of a first order of a radius in the cross-section of the beam in the plane of the medium and to impress simultaneously a second wavefront modification of a second order of the radius different from the first order.

Abstract: A compensator (for example, for a liquid-crystal display device) comprising a retardation foil with a tilted optical main axis and, in addition, a second optically active layer, can be manufactured in a simple manner by providing the retardation foil and the second layer on different sides of a transparent support.