Transmissive electromechanical light valve and system

An apparatus, system, and method for a transmissive electromechanical light valve including a gate pivotable between a first position to allow light to pass through a valvelet and a second position to prevent light from passing through the valvelet are disclosed herein. Other embodiments may be described and claimed herein.

FIELD OF THE INVENTION

Embodiments of the invention relate generally to the field of projection systems, and more particularly to a transmissive electromechanical light valve.

BACKGROUND OF THE INVENTION

Multimedia projection systems have become popular for purposes such as conducting sales demonstrations, business meetings, classroom training, and for use in home theaters. In typical operation, multimedia projection systems receive analog video signals from an input device and convert the video signals to digital information to control one or more digitally driven light valves. Depending on the cost, brightness, and image quality goals of the particular projection systems, the light valves may be of various sizes and resolutions and may be employed in single or multiple display configurations.

One type of light valve found in projection systems is a digital micromirror device (DMD). A DMD uses individually controllable mirrors to selectively reflect light either through projection optics or towards a light-absorbing surface, based on image data. Because the DMD operates by selective reflection, the axis of illumination needs to be separated from the axis of projection.

This off-axis illumination could add to the expense and/or sacrifice the compactness of the system. Due to the reflective operation of the DMD, the illumination optics must present light to the same face of the DMD that the projection optics receive light from. This requires either complex optics at the DMD face, or it requires the elements of the two optical systems be placed at distances from the DMD sufficient to allow for unfettered presentation/reception of the light. The physical separation of the components of these prior art systems typically make up a significant portion of the total packaging volume of the system, while necessitating additional optical elements, such as relay lenses, to provide proper illumination at downstream components. Additionally, off-axis illumination could result in oblique illumination of the face of the light valve, which could present additional difficulties.

Other types of light valves, e.g., liquid crystal display (LCD) light valves, operate by selectively rotating polarized light. The light that is incident upon the LCD light valve must be polarized to one polarization state, which could result in increased complexity and decreased light transmission through the system.

DETAILED DESCRIPTION

Illustrative embodiments of the present invention include a transmissive electromechanical light valve and methods practiced thereon.

Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific materials and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. In particular, a wide variety of optical components such as, but not limited to, prisms, mirrors, lenses, and integration elements may be used as appropriate to fold, bend, or modify the illumination for the intended application. Integration of these optical components into illustrated embodiments may not be specifically addressed unless it is necessary to develop relevant discussion of embodiments of the present invention.

FIG. 1illustrates a simplified block diagram of a projection system100with a transmissive electromechanical light valve104in accordance with an embodiment of the present invention. A projection device108may include an illumination arrangement112, coupled to a controller116and optically coupled to the light valve104to provide light along an illumination path120. The illumination arrangement112may provide light with desired characteristics to the light valve104. These characteristics could include, but are not limited to, illumination uniformity, angle, color, and brightness. The illumination arrangement112may include a light source optically coupled to a series of optics including, for example, illumination lenses, integration devices, filters, and/or light-directing components (e.g., mirrors, prisms, light guides, etc.).

In one embodiment the illumination arrangement112may include a polychromatic light source such as, but not limited to, an incandescent lamp (e.g., tungsten halogen) or a gaseous discharge lamp (e.g., a metal halide). In other embodiments, monochromatic light sources such as light-emitting diodes, for example, may be used to produce light of a particular color.

In various embodiments, the system100may also include more than one light valve104. For example, a color-specific light valve may be placed in each of a number of primary colored paths and be used to exclusively modulate the light of these paths. In these embodiments, the illumination arrangement112may include optics to facilitate the presentation of colored light to the appropriate light valves along the appropriate illumination paths.

The controller116, which may include both power and logic circuitry, may be adapted to transmit control signals to the light valve104based, at least in part, upon input signals received from an input device122. The control signals may cause matrix-addressable valvelets to selectively transmit incident light in order to effectuate the rendering of the image conveyed by the input signals. Projection optics124may be positioned adjacent to the light valve104to project the image rendered at the light valve104, conveyed by light rays transmitted along a projection path128, onto a screen or other mechanism for viewing. The rendered image may be, for example, image frames of a video. The projection optics124may include, but are not limited to, projection lenses, filters, and light-directing components.

For the purpose of this description, a still image may be considered as a degenerate or special video where there is only one frame. Accordingly, both still image and video terminologies may be used in the description to follow, and they are not to be construed to limit the embodiments of the present invention to the rendering of one or the other.

The input device122may include a personal or laptop computer, a digital versatile disk (DVD), a set-top box (STB), a video camera, a video recorder, an integrated television tuner, or any other suitable device to transmit signals, e.g., video signals, to the projection device108. In various embodiments, the system100may be, for example, a projector or a projection television.

FIG. 2illustrates various components of the illumination arrangement112disposed relative to the light valve104and projection optics124, in accordance with an embodiment of this invention. A light source204may generate polychromatic light that is directed towards color filter segments of a color wheel208. The color wheel208may have color filter segments, e.g., red, green, and blue, as well as other filter segments to provide additional brightness (e.g., white) or desired color balance (e.g., light-purple to correct for the red deficient nature of typical polychromatic light). The color wheel208may transmit color sequential light into an integrating device such as an integrating tunnel212. In various embodiments, other color-filtering devices may be used. Additionally, other embodiments, e.g., ones employing monochromatic light sources, may not have a color-filtering device.

The integrating tunnel212may be composed of a solid glass rod that relies on total internal reflection to transfer light through it and to create, at its output end, a substantially uniform illumination field. The integrating tunnel212may include a cladding or reflective mirrored sidewalls that may protect internal reflection. The integrating tunnel212may have a tapered output end having an aspect ratio that corresponds to an aspect ratio of the light valve104. The shaped and integrated light may then be presented to the light valve104along an illumination path that is substantially orthogonal to the face of the light valve104, in accordance with an embodiment of the present invention. In various embodiments, other integrating devices such as, but not limited to, a hollow integrating tunnel with reflective sidewalls or a flyseye-lens integrator may be used.

This orthogonal arrangement of this embodiment may prevent the oblique illumination of the transmissive electromechanical light valve104. Additionally, because the illumination arrangement112is presenting light to a different face of the light valve104than the projection optics124are receiving light from, elements from both of these components may be placed closer to the light valve104. This may, in turn, facilitate smaller elements being used. For example, in a prior art system, the first element of the projection lens would need a back focal length that was long enough to allow light to be presented to a DMD unobstructed. However, the further that the element is placed from the DMD, the larger the element has to be in order to accept diverging light rays. Unlike the prior art system, the positioning of the projection optics124relative to the light valve104of the present embodiment is not constrained by the positioning of the elements of the illumination arrangement112relative to the light valve104. Therefore a smaller, more compact system may be enabled by the use of the transmissive electromechanical light valve104of embodiments of this invention.

FIG. 3illustrates valvelets300and304of a transmissive electromagnetic light valve308in accordance with an embodiment of the present invention. The valvelets300and304may operate to selectively control the passage of light through portions of the light valve308. The light valve308may have a transparent substrate312, which is common to both valvelets300and304, that has a surface316facing illumination optics and a surface320facing projection optics.

The valvelet300may include a transparent electrode322, a hinge324, and a landing328coupled to the surface320as shown. The valvelet300may also include a gate332that is coupled to the hinge324in a pivotable relationship. The gate332may be made of a conductive material and have a reflective surface. As shown inFIG. 3, the gate332of the valvelet300may be in a closed position such that light transmitted through the substrate312(and possibly the electrode322as well) at the area of the valvelet300may be reflected by the gate332back through the substrate312and out from the surface316. In another embodiment, the gate332may have a non-reflective surface to absorb the light.

In one embodiment, the gate332may be biased to the closed position by a rotational force applied to the gate332through the hinge324. In other embodiments, the gate332may be biased to an open position.

Valvelet304may include elements similar to those found in valvelet300including a transparent electrode336, a hinge340, a landing344, and a gate348. As shown, the gate348of the valvelet304may be in an open position such that light transmitted through the substrate312(and possibly the electrode336as well) at the area of the valvelet304may be emitted out towards projection optics that face the surface320.

Light that is transmitted through the valvelet304may not be completely collimated, with some of the light drifting from one side of the valvelet304to the other as it passes through. Light having this lateral drift may be reflected off of the open gate348and out towards the projection optics in order to prevent an effective reduction of the aperture ratio caused by the gate348.

In one embodiment, the valvelet304may be operated by applying an electrical charge to the electrode336such that a repulsive electromagnetic force exists between the gate348and the electrode336. This repulsive force may overcome the rotational bias applied by the hinge340and cause the gate348to rotate around the hinge340and away from the electrode336. Releasing the charge to the electrode336may allow for the rotational force to restore the hinge to the closed position.

In one embodiment, the electrodes322and336may be electrically coupled to an underlying memory circuit. This memory circuit may be capable of independently addressing the electrodes322and336in a manner to dictate their respective charges. In one embodiment, the electrodes322and336may be embedded and/or disposed within the substrate312.

In other embodiments, an electrical charge may be applied to the gate348through the hinge340and the electrodes322and336may be part of a conductive plane disposed within the substrate312.

The landings328and344may provide a station for proper disposition of the gates332and348, respectively, while in the closed position. In various embodiments, the landings328and344may be electrodes with the same potential as the gates332and348to facilitate the electrical biasing of the gates332and348. In other embodiments, the landings328and344may be made of a dielectric material.

In one embodiment, a proper closed disposition may hold the gates332and348apart from the respective electrodes322and336by a distance. The distance may be large enough to prevent arcing between the two conductors but small enough to allow a sufficient electromagnetic force to effectuate a rotation from the closed position to an open position.

Separation between a gate and an electrode may not be needed in an embodiment with electrodes embedded or disposed within a substrate. However, a landing may still be used in these embodiments for other reasons, such as, but not limited to, electrically biasing the gate and/or preventing contact between the gate and the transparent surface which may compromise one or both of the surfaces.

The magnitude of the electromagnetic force between a gate and an electrode may determine the rotation of the gate. In one embodiment, the gates may be driven digitally between a fully open and a fully closed position. Grayscale imaging may be provided through pulse width modulation in this digital fashion. In another embodiment, the electromagnetic force may be exerted to partially rotate the gate. This could allow an analog grayscale to be used by only allowing a portion of the light to pass.

FIG. 4illustrates a valvelet400of a light valve404in accordance with an embodiment of the present invention. The valvelet400may have elements similar to comparable elements of valvelets300and304, including a gate assembly having a hinge408, a landing412, and a gate416. In this embodiment the gate assembly may be coupled to a transparent substrate420while a transparent electrode424is coupled to another transparent substrate428. In this embodiment, an electrical charge may be applied to the electrode424such that an attractive electromagnetic force is exerted between the gate416and the electrode424. Releasing the charge applied to the electrode424may allow the restoring force, exerted by the hinge408, to transition the gate416into the closed position.

In this embodiment, the substrate420may be separated a distance from the substrate428that would provide the gate416sufficient clearance to transition between the open and closed positions. Additionally, the distance may be small enough such that an electromagnetic relationship exists between the two conductors. The substrates420and428may facilitate the encasing of the movable parts of the light valve404in order to protect the parts from particulates and other environmental interference.

FIG. 5illustrates valvelets500and504of light valve508in accordance with an embodiment of the present invention. This embodiment may have spacers512and516coupled between substrates520and524. Electrodes528and532and landings536and540may be respectively coupled to the spacers512and516as shown. The spacers512and516may have a reflective surface opposite the surface coupled with the electrodes528and532. When a gate544of the valvelet504is in the open position, light striking the reflective surface of the spacer512may be reflected. Likewise, light striking the reflective surface of the open gate544may also be reflected. By providing for these complementary reflections through the valvelet504the cone angle of the illumination may be substantially unchanged throughout transmission. That is, the distribution of angles of the incoming light may be approximately the same as the distribution of the angles of the transmitted light. For similar reasons, gates of other embodiments may have reflective surfaces on both sides.

In one embodiment, the spacer512may be made of a dielectric material that may facilitate the prevention of interference from the electrode528with the gate544.

FIG. 6illustrates a top-view of a valvelet600of a light valve604in accordance with an embodiment of the present invention. The valvelet600may include gates608and612coupled to a substrate616by respective hinges620and624. An electrode628is embedded in substrate632. In this embodiment, the elements may be similar to like-named elements discussed with reference to earlier embodiments. However, in this embodiment, the transmission of light through the valvelet600is modulated by the pair of gates608and612. The embedded electrode628may have a central portion636that is overlaid with a dielectric material, which could be a similar material as that found in the remaining substrate632. This design could facilitate the attractive electromagnetic force between the gates608and612and the electrode628being greater at the periphery of the valvelet600than at the center. This could, in turn, facilitate a full extension of the gates608and612while in the open position.

FIG. 7illustrates a top-view of valvelets700and704of a light valve708in accordance with an embodiment of the present invention. Valvelets700and704may include gates712and716that are coupled to hinges720and724, respectively. The hinges720and724may be located approximately at the centerlines of the respective gates712and716.

In this embodiment, the gates712and716may cooperate with the addressing electrodes728,732, and736to effectuate an electromagnetic force resulting in the valvelet700being in a closed position, and the valvelet704being in an open position. One or more substrates (not shown) may be coupled to the valvelets700and704to provide sufficient structure while allowing the rotation of the gates712and716through the open and closed positions.

FIG. 8illustrates a front-view of a rectangular array of valvelets800of a light valve804in accordance with an embodiment of the present invention. The valvelets800may be similar to the valvelets700and704described and discussed above with reference toFIG. 7. Additionally, some or all of the valvelets800may be interchanged with any of the valvelets discussed and described with reference to earlier embodiments.

Referring also toFIGS. 1-2, the face of the light valve804may be illuminated by illumination arrangement112. The valvelets800may be individually controlled to allow or prevent the transmission of light through the light valve804to effectuate an image pattern conveyed by control signals from the controller116. The pattern of transmitted light may then be imaged onto a viewing device through projection optics124.