Abstract: A cholesteric film is formed into an optical device comprising a plurality of layers. The cholesteric film is initially placed in a first predetermined state, for instance heating to a first predetermined temperature, and is then irradiated with narrow band UV radiation. The properties of an upper layer of the film are fixed, for instance for reflecting normally incident infrared radiation of a particular handedness. This process is repeated for different wavelengths of UV fixing radiation so as to penetrate to different depths from the surface of the film in order to form the layers. This method may be used to produce a filter of reduced sensitivity to angle of incidence. In addition to the infrared reflecting layer, red and green reflecting layers are provided. For normally incident radiation, the red and green layers reflect red and green parts R and G, whereas the blue part B of the spectrum is transmitted.

Abstract: A cholesteric film is formed into an optical device comprising a plurality of layers. The cholesteric film is initially placed in a first predetermined state, for instance heating to a first predetermined temperature, and is then irradiated with narrow band UV radiation. The properties of an upper layer of the film are fixed, for instance for reflecting normally incident infrared radiation of a particular handedness. This process is repeated for different wavelengths of UV fixing radiation so as to penetrate to different depths from the surface of the film in order to form the layers. This method may be used to produce a filter of reduced sensitivity to angle of incidence. In addition to the infrared reflecting layer, red and green reflecting layers are provided. For normally incident radiation, the red and green layers reflect red and green parts R and G, whereas the blue part B of the spectrum is transmitted.

Abstract: A cholesteric film is formed into an optical device comprising a plurality of layers. The cholesteric film is initially placed in a first predetermined state, for instance heating to a first predetermined temperature, and is then irradiated with narrow band UV radiation. The properties of an upper layer of the film are fixed, for instance for reflecting normally incident infrared radiation of a particular handedness. This process is repeated for different wavelengths of UV fixing radiation so as to penetrate to different depths from the surface of the film in order to form the layers. This method may be used to produce a filter of reduced sensitivity to angle of incidence. In addition to the infrared reflecting layer, red and green reflecting layers are provided. For normally incident radiation, the red and green layers reflect red and green parts R and G, whereas the blue part B of the spectrum is transmitted.

Abstract: A broadband cholesteric optical device such as a polarizer or a spectral filter includes a broadband cholesteric layer, for instance, of a graded pitch type such that the cholesteric pitch increases monotonically from one surface of the film to the other surface. In order to improve the off-axis performance, a compensator is provided in the form of a positive birefringence film whose optic axis is substantially perpendicular to the film. Another negative birefringence film whose optic axis is also perpendicular to the film may also be provided.

Abstract: A broadband cholesteric polariser includes at least one pair of adjacent layers. The at least one pair includes a cholesteric layer and a compensating layer. The compensating layer has a refractive index perpendicular to the compensating layer greater than a refractive index oriented within the compensating layer.

Abstract: An illumination system includes a polarization selective holographic element, which includes at least one optically anisotropic material, arranged to separate light of a first polarization type from light of a second polarization type, and converting section for converting light of at least one of the first and second polarization types to light of a common polarization type. Where the polarization selective holographic element separates two orthogonal components of plane polarized light from one another, the converting section can include a polarization rotator, for example a half wave plate, or alternatively a quarter wave plate and a reflector arranged to reflect light back through the quarter wave plate. Where the polarization selective holographic element separates opposite handed components of circularly polarized light, the converting section can include a reflector.

Abstract: An illumination system includes a polarized light source which emits circularly polarized light of a particular handedness and a cholesteric filter having a region arranged to transmit circularly polarized light falling within a first wavelength band and to reflect other wavelengths of circularly polarized light. A reflector redirects the reflected light back towards the cholesteric filter. The cholesteric filter can include a first layer having portions which reflect red, green and blue light while transmitting other colors, and a second layer identical to the first layer but out of alignment therewith so that each region of the filter transmits only one color of light, the other colors being reflected.

Abstract: A film of photosensitive material is illuminated from first and second sides with coherent polarized light so as to form an interference pattern within the film. Regions of cyclicly varying refractive index are provided in the film in accordance with the intensity of the interference patten, thereby forming an polarization sensitive refractive index grating. The refractive index grating may be used as a polarization and wavelength dependent mirror, patterned polarizer, beamsplitter or filter.

Abstract: A birefringent element is patterned such that for light of a first polarisation the element acts as a first refractive optical element and for light of a second polarisation the optical response of the element changes. The element can be used in conjunction with a polarisation selecting means, such as a liquid crystal device, to provide an electrically controllable optical element that can be used in light beam manipulation applications.