Optics: image projectors – Composite projected image – Multicolor picture
Patent
1996-10-21
1999-02-02
Dowling, William
Optics: image projectors
Composite projected image
Multicolor picture
353 33, 348771, G03B 2128
Patent
active
058655204
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a projection system. In particular, the invention relates to a projection system in which a projected display is formed by spatially modulating light from a light source by one or more spatial light modulator devices, and then projecting the spatially modulated light on to a display area. The invention has particular, although not exclusive relevance to a colour projection system in which beams of light of different colour are directed onto different spatial light modulator devices, and the modulated beams are combined to form a single projected colour display.
A spatial light modulator is an optical component which is controllable to spatially modulate an incident light beam. One class of spatial light modulators are active matrix devices, which comprise a matrix of individually addressed pixels, each pixel comprising a light modulator. Each light modulator may be a liquid crystal, for example as shown in EP 0401912. Alternatively the active matrix device may comprise an array of the tiltable mirror devices as, for example described in U.S. Pat. No. 4856863, U.S. Pat. No. 4615595 and U.S. Pat. No. 4596992. Such tiltable mirror devices comprise miniature mirrored cantilever beam elements which are electrostaticaly deflectable by electric fields provided across a corresponding array of electrodes. The extent of the deflection can be controlled by means of the applied electrostatic potential to provide variable degrees of deflection. Alternatively the tiltable mirror devices can be operated in a binary manner by applying predetermined electrostatic potentials to switch each mirror device between discrete deflection states. Each mirror device angularly deflects an incident light beam, directing the light beam either towards a projection screen or towards a beam dump.
Using an array of such mirror devices, each device being individually addressable, a two dimensional image can be produced. The small size and fast switching times of the mirror devices make them usable at video picture data rates, enabling the display of television or video moving images on the display screen.
In order to display a colour image three separately illuminated arrays of mirror devices may be provided, each array being responsive to light of a different primary colour or primary colour combination, the modulated beams reflected from each device then being combined optically and projected onto a single optical display. Alternatively a single array may be illuminated with different coloured light in sequence (for example using a colour wheel) and the integrating response of an observer's eyes may be relied on to provide a full colour image to the observer.
In our copending International Application PCT WO093/18620 (the contents of which are incorporated herein by reference) there is described a spatial light modulator system comprising a light source, means for splitting light from the source into different colour component beams, and a plurality of deformable mirror spatial light modulators. The light paths between the light source and the means for splitting light and the spatial light modulators are defined within a single prism on which the spatial light modulators are mounted, thus minimising the size of the optical system and providing stability to the system.
The incident beam does not scan, as does an electron beam in a cathode ray tube, but illuminates the whole array of mirror devices. Thus a projection system including one or more deformable mirror devices suffers the disadvantage that it is necessary to space the light source and the projection system such that the light paths of light from the source to the prism assembly, and the modulated light transmitted by the prism assembly to the projector system do not cross. This produces limitations on the compactness and efficiency of the system which can be produced.
It is an object of the present invention to provide a spatial light modulator system in which this problem can be at least alleviated.
According to a first aspect of the present invention
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Fielding Raymond Gordon
Kavanagh Martin
Moss Graham Harry
Digital Projection Limited
Dowling William
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