Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2001-08-06
2004-06-15
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C353S034000, C353S037000, C353S052000, C353S119000
Reexamination Certificate
active
06751027
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a spatial light modulator, an image projector apparatus using the modulator and method of operating the same which can handle high light intensities. More specifically, the present invention relates to a cooling mechanism for efficiently cooling the heat-emitting components of such a projection display apparatus.
BACKGROUND OF THE INVENTION
Large-screen, high-brightness (>1000 lumens) electronic projection display apparatuses serve different broad areas of application:
electronic presentations for business, education, advertising,
entertainment, e.g. home theater, electronic cinema.
status and information, e.g. military, utilities, transportation,
simulation in e.g. training and games.
Recently, in response to various limitations of the LCD technologies, high-brightness systems have been developed based on digital light processing (DLP) technology. At the heart of a DLP projection display is provided a spatial light modulator (SLM) unit. A spatial light modulator unit comprises at least one spatial light modulator, which is a device that modulates incident light in a spatial pattern corresponding to an electrical or optical input. The incident light may be modulated in its phase, intensity, polarisation, or direction, and the light modulation may be achieved by a variety of materials exhibiting various electro-optic or magneto-optic effects or by materials that modulate light by surface deformation. An SLM consists of a one- or two-dimensional array of light-modulating elements. Silicon technology used in projection data monitors is capable of producing small-sized, two-dimensional light-valve arrays having several hundred thousand to several million light-modulating elements.
Spatial light modulators are either transmissive or reflective. Transmissive devices modulate the light beam as it passes through the unit. Reflective devices modulate the light as it reflects from a mirror inside the unit.
A deformable mirror device (DMD), also called digital mirror device or digital micro-mirror device, is one embodiment of a reflective SLM, see for example U.S. Pat. No. 5,061,049. It is a semiconductor-based array of fast, reflective digital light switches that precisely control reflection of a light source using, for example, a binary pulse width modulation technique. Combined with image processing, memory, a light source, and optics it forms a DLP system capable of projecting large, bright, seamless, high-contrast color images. A DMD has a matrix of a plurality of individually electrically deformable or moveable mirror cells. In a first state or position, each mirror cell of the deformable mirror device acts as a plane mirror to reflect the light received to one direction (through a lens towards a projection screen for example), while in a second state or position they project the light received to another direction (away from the projection screen).
Reflective spatial light modulators, such as DMDs or reflective LCDs, are heat sensitive, and a hot DMD results a decrease of lifetime and/or in discoloration of the projected image.
A cooling mechanism for cooling the internal parts of a projection display apparatus, is generally built in into it. In general, outside air is introduced into the projector apparatus through an intake opening using an intake fan, and flows over the internal heat-emitting components to cool them. After cooling each of these parts, the air is vented by an exhaust fan to the ambient environment from an air vent opening in an outside case of the projector apparatus. Only one fan can be used for both intake and exhaust.
When air is introduced from outside the apparatus, dust and other foreign matter, such as smoke, oil, may penetrate to the inside of the apparatus. An air filter is generally placed over the intake opening to capture dust and filter the air, but it is still possible for fine particles to penetrate to the inside of the apparatus. When such particles enter the inside of the apparatus with the outside air, they may adhere to the surface of the optical elements. When particulate matter thus adheres to a DMD, it causes decreased light output, or it may hinder the individual mirrors in their movements, resulting in severely deteriorated image quality. A known solution to this problem is to disassemble the projector apparatus and replace the DMOs, as the spaces around a DMD are usually very small, and it is very difficult to clean a DMD in its mounted position.
There has been a long felt need to cool the heat-emitting parts inside the projector apparatus in a way that prevents particulate contamination.
U.S. Pat. No. 6,007,205 describes an LCD projector with an optical lens unit comprising transmission LCD's and other light transmitting heat-emitting components, such as polarising plates. The optical lens unit is enclosed in a substantially airtight internal chamber. A circulating air current is created by force, by means of a circulation fan, inside this chamber, which cools the heat-emitting components. Preferably means are provided for introducing outside air and for directing the outside air around the outside surface of the members separating the substantially airtight chamber. A heat exchange action between the circulating air current created in the airtight chamber and the outside air flowing through the intake air path is thereby accomplished. In this way, the projector is provided with a cooling mechanism such that no dust or foreign matter penetrates to the inside the optical lens unit.
The LCD projector described has a limited ability to operate at high light intensities. It is difficult to implement effective cooling of the optical components at the highest brightness levels. Particularly for LCD's which operate as light valves, i.e. they either pass or absorb light, the absorbence of light energy in the LCD for those parts of the projected image which are dark results in large amounts of light energy being absorbed within the sealed chamber (e.g. in the polariser). It is difficult to remove this heat energy by forced convection cooling inside a sealed chamber which relies on an inefficient air-to-air heat exchanger to remove the heat from the sealed chamber and delivery it to an outer chamber.
U.S. Pat. No. 5,170,195 describes methods of cooling transmission LCD's. These methods involve placing cooling liquid in the light path. It is difficult to guarantee perfect optical clarity of a cooling liquid over the life of a projector. Also, the cooling liquid absorbs some of the transmitted light which reduces the transmitted light intensity and increases the load on the cooling circuit of the LCD. The density of the cooling liquid can change polarisation direction of the light thus causing discolorations of the projected image.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an SLM unit, a projector apparatus and a method of operating the same which can handle high light intensities, without dust or foreign matter penetrating to the sensitive optical components inside of the apparatus and thus deteriorating the quality of the image projected.
According to the present invention, there is provided a spatial light modulating unit for a projector apparatus wherein the spatial light modulating unit is provided with a plurality of SLMs (Spatial Light Modulators, for example, one for each color) and a light splitting unit such as a prismatic device for splitting white light into color components. The spatial light modulating unit also has means for combining the light reflected from the SLMs for projection. This combining device can be the same prismatic unit as used for light splitting. The spatial light modulation unit is enclosed by a substantially sealed chamber. A cooling connection is provided for each SLM, whereby the cooling connection passes through the wall of the substantially sealed chamber and makes contact with each SLM in a heat conductive manner. In this way heat from the main heat sources within the sealed chamber is broug
Maes Geert
Van Den Bossche Bart
Vandorpe Krist
Banes & Thornburg
Barco N.V.
Mack Ricky
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