Optics: image projectors – Composite projected image – Multicolor picture
Patent
1994-09-27
1998-01-06
Dowling, William
Optics: image projectors
Composite projected image
Multicolor picture
353 98, 353 31, 348771, G03B 2128
Patent
active
057047014
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a spatial light modulator system. Particularly, but not exclusively, this invention relates to a projection system in which a projected display is formed by modulating light from a light source by a spatial light modulator device, and then projecting the modulated light on to a display area. Particularly, but not exclusively, the invention relates to a color spatial light modulator system in which beams having different color content are reflected from different spatial light modulator devices each driven in accordance with a different video signal, and the modulated beams are combined to form a single projected color display.
A spatial light modulator is an optical component which is controllable to modulate an incident light beam. A relatively old example is the eidophor, a layer of oil scanned by a cathode ray. One class of spatial light modulators is active matrix devices, comprising a matrix of individually addressed pixel light valves or modulators; the liquid crystal modulator array described in, for example, EP 0401912 is one modulator array of this type. In EP 0401912, a liquid crystal matrix is provided in a light path to variably transmit, and hence amplitude modulate, the incident light beam (without altering its path or optical axis). Another example of such an active matrix comprises an array of the tiltable mirror devices, for example the deformable mirror device (DMD) described in, for example, U.S. Pat. No. 4,856,863, U.S. Pat. No. 4,615,595, and U.S. Pat. No. 4,596,992.
Such devices comprise miniature mirrored cantilever beam elements carrying electrodes so as to be electro statically deflectable between two positions. The extent of the deflection can be controlled by the applied electrostatic potential to provide variable degrees of reflection, or the device can be operated in a binary manner by applying predetermined electro static potentials to switch between discrete deflection states. It thus angularly deflects the incident light beam and hence changes the optical axis of the light beam.
Using an array of such devices, each individually addressable, a two dimensional image can be reproduced by exposing the array to an incident light beam, modulating the incident beam by controlling the individual mirror devices from a picture signal, and collating the beam reflected in a particular direction. The small size and fast switching times of devices of the kind described in the above mentioned patents makes them usable at video picture data rates, enabling the display of television or video moving images on a display screen onto which the collated beam is projected.
The incident beam is not scanned, as is an electron beam, but illuminates the entire device. In order to display a color image, therefore, it is necessary to provide three separately illuminated deflector arrays, one controlled responsively to each primary color or primary color combinations, and to optically combine the modulated beams reflected from each device onto a single optical display.
One example of an applica on of such a system is in large scale displays as disclosed in U.S. Ser. No. 07/934,503,U.S. Pat. No. 5,386,253, and U.S. Pat. No. 5,424,868 and PCT/GB92/00002 (all of which are incorporated herein by reference).
Various optical systems for spatial light modulator projectors are known from, for example, EP 0401912, EP 363763 and EP 0450952. A projection system which includes liquid crystal arrays is described in EP 0395156. In this system, a lenticular array arrangement of a type also known from, for example, U.S. Pat. No. 3,296,923 is adopted in which light from a light source is made parallel and directed through a first array of lenslets, each rectangular in cross section and curved on one face, from which the light is directed through a second array of such lenslets, the spacing and curvature of the lenslets being such that each of the first lenslets focuses light into the center of a corresponding lenslet in the second array, and then light from the second array is directed through a
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Fielding Raymond Gordon
Kavanagh Martin
Dowling William
Rank Brimar Limited
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