Methods and apparatus for spatial light modulation

Improved apparatus and methods for spatial light modulation are disclosed which utilize optical cavities having both front and rear reflective surfaces. Light-transmissive regions are formed in the front reflective surface for spatially modulating light.

FIELD OF THE INVENTION

In general, the invention relates to the field of spatial light modulation, in particular, the invention relates to displays having improved backlights.

BACKGROUND OF THE INVENTION

Displays built from mechanical light modulators are an attractive alternative to displays based on liquid crystal technology. Mechanical light modulators are fast enough to display video content with good viewing angles and with a wide range of color and grey scale. Mechanical light modulators have been successful in projection display applications. Backlit displays using mechanical light modulators have not yet demonstrated sufficiently attractive combinations of brightness and low power. When operated in transmissive mode many mechanical light modulators, with aperture ratios in the range of 10 and 20%, are only capable of delivering 10 to 20% of available light from the backlight to the viewer for the production of an image. Combining the mechanical apertures with color filters reduces the optical efficiency to about 5%, i.e., no better than the efficiencies available in current color liquid crystal displays. There is a need for a low-powered display having increased luminous efficiency.

SUMMARY OF THE INVENTION

The devices and methods described herein provide for mechanical light modulators having improved luminous efficiency, making mechanical actuators attractive for use in portable and large area displays. In some cases, the transmittance or optical efficiency of mechanical modulators coupled to backlights can be improved to the 40 to 60% level, or 10 times more efficient than what is typical in a liquid crystal display. In addition, the devices and methods described herein can be incorporated into small-size, high resolution displays, regardless of the light modulation mechanism, to improve the brightness of the displays and to reduce the power requirements in a display application.

The light modulators described herein make possible portable video displays that can be both bright and low power. The light modulators can be switched fast enough to provide color images using time sequential color techniques, instead of relying on color filters. The displays can be built using as few as three functional layers to form both a mechanical shutter assembly and the electrical connections necessary for array addressing.

In one aspect, the invention relates to a spatial light modulator which includes a first reflective surface and a second reflective surface. The first reflective surface defines a number of light-transmissive regions, such as apertures, filters, or liquid crystal components. The second reflective surface at least partially faces the first reflective surface and reflects light towards the light-transmissive regions defined by the first reflective surface. The reflective surfaces may be mirrors, dielectric mirrors, or thin functional films. In one embodiment the first reflective surface is parallel or substantially parallel to the second reflective surface. In another embodiment, the reflective surfaces are at least partially transverse to one another. The space between the first and second reflective surfaces defines the area of a substantially transparent optical cavity.

In one embodiment, the spatial light modulator includes an array of light modulators for selectively obstructing the light-transmissive regions. Obstructing may include, without limitation, partially or completely blocking, reflecting, deflecting, absorbing, or otherwise preventing light from reaching an intended viewer of the spatial light modulator. In one embodiment, the array of light modulators includes the first reflective surface. One feature of the light modulating elements in the array of light modulators is that they are individually controllable. In one embodiment, the light modulating elements may be MEMS-based shutter assemblies, and optionally may be bistable or deformable shutters. The shutter assemblies include shutters that, in one implementation, are coated with a first film to absorb light striking the shutter from one direction and coated with a second film to reflect light striking the shutter from another direction. In one embodiment, the shutters move in a plane such that in one position the shutters substantially obstruct passage of light through corresponding light-transmissive regions, and in a second position, they allow light to pass through the light-transmissive regions. In another embodiment, the shutters move at least partially out of a plane defined by the array of shutter assemblies in which they are included. While substantially in the plane, the shutters obstruct passage of light through corresponding light-transmissive regions. While substantially out of the plane, the shutters allow light to pass through the light-transmissive regions. In another embodiment, the array of light modulators includes a plurality of liquid crystal cells.

In another embodiment, the spatial light modulator includes a light guide for distributing light throughout the light cavity. The reflective surfaces may be disposed directly on the front and rear surfaces of the light guide. Alternatively, the front reflective surface may be disposed on a separate substrate on which the array of light modulators is disposed. Similarly, the second reflective surface may be coupled directly to the rear side of the light guide, or it may be attached to a third surface.

The substrate on which the array of light modulators is formed may be transparent or opaque. For opaque substrates, apertures are etched through the substrate to form light-transmissive regions. The substrate may be directly coupled to the light guide, or it may be separated from the light guide with one or more spacers or supports. In still a further embodiment, the spatial light modulator includes a diffuser or brightness enhancing film. The spatial light modulator may also include a light source, such as a light emitting diode.

In another aspect, the invention relates to a method of forming an image. The method includes introducing light into a reflective optical cavity. The reflective cavity includes a plurality of light-transmissive regions through which light can escape the reflective optical cavity. The method further includes forming an image by allowing the introduced light to escape the reflective optical cavity through at least one of the light-transmissive regions. In one embodiment, the escape of light is regulated by an array of light modulators that either obstruct light passing through the light-transmissive regions, or allow it to pass. In another embodiment, the method includes forming a color image by alternately illuminating a plurality of different colored light sources. In a further embodiment, the method includes reflecting at least a portion of ambient light striking unobstructed light-transmissive regions.

In still another aspect, the invention relates to a method of manufacturing a spatial light modulator comprising forming a substantially transparent cavity having first and second opposing sides into which light can be introduced. The method also includes coupling a first reflective surface to the first side of the transparent cavity such that the first reflective surface faces the interior of the transparent cavity. A plurality of light-transmissive regions are formed in the first reflective surface. In addition, the method includes coupling a second reflective surface to the second side of the transparent cavity such that the second reflective surface faces the interior transparent cavity.

In another aspect, the invention relates to a method of forming an image by receiving ambient light and positioning shutters formed on at least one substrate to selectively reflect the received ambient light to form the image.

DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS

To provide an overall understanding of the invention, certain illustrative embodiments will now be described, including apparatus and methods for spatially modulating light. However, it will be understood by one of ordinary skill in the art that the systems and methods described herein may be adapted and modified as is appropriate for the application being addressed and that the systems and methods described herein may be employed in other suitable applications, and that such other additions and modifications will not depart from the scope hereof.

FIG. 1Ais an isometric conceptual view of an array100of light modulators (also referred to as a “light modulation array100”), according to an illustrative embodiment of the invention. The light modulation array100includes a plurality of shutter assemblies102a-102d(generally “shutter assemblies102”) arranged in rows and columns. In general, a shutter assembly102has two states, open and closed (although partial openings can be employed to impart grey scale). Shutter assemblies102aand102dare in the open state, allowing light to pass. Shutter assemblies102band102care in the closed state, obstructing the passage of light. By selectively setting the states of the shutter assemblies102a-102d, the light modulation array100can be utilized to form an image104for a projection or backlit display, illuminated by lamp105. In the light modulation array100, each shutter assembly corresponds to a pixel106in the image104. In alternative implementations, a light modulation array includes three color-specific shutter assemblies for each pixel. By selectively opening one or more of the color-specific shutter assemblies corresponding to the pixel, the shutter assembly can generate a color pixel in the image.

The state of each shutter assembly102can be controlled using a passive matrix addressing scheme. Each shutter assembly102is controlled by a column electrode108and two row electrodes110a(a “row open electrode”) and110b(a “row close electrode”). In the light modulation array100, all shutter assemblies102in a given column share a single column electrode108. All shutter assemblies in a row share a common row open electrode110aand a common row close electrode110b. An active matrix addressing scheme is also possible. Active matrix addressing (in which pixel and switching voltages are controlled by means of a thin film transistor array) is useful in situations in which the applied voltage must be maintained in a stable fashion throughout the period of a video frame. An implementation with active matrix addressing can be constructed with only one row electrode per pixel.

In the passive matrix addressing scheme, to change the state of a shutter assembly102from a closed state to an open state, i.e., to open the shutter assembly102, the light modulation array100applies a potential to the column electrode108corresponding to the column of the light modulation array100in which the shutter assembly102is located and applies a second potential, in some cases having an opposite polarity, to the row open electrode110acorresponding to the row in the light modulation array100in which the shutter assembly102is located. To change the state of a shutter assembly102from an open state to a closed state, i.e., to close the shutter assembly102, the light modulation array100applies a potential to the column electrode108corresponding to the column of the light modulation array100in which the shutter assembly102is located and applies a second potential, in some cases having an opposite polarity, to the row close electrode110bcorresponding to the row in the light modulation array100in which the shutter assembly102is located. In one implementation, a shutter assembly changes state in response to the difference in potential applied to the column electrode and one of the row electrodes110aor110bexceeding a predetermined switching threshold.

To form an image, in one implementation, light modulation array100sets the state of each shutter assembly102one row at a time in sequential order. For a given row, the light modulation array100first closes each shutter assembly102in the row by applying a potential to the corresponding row close electrode110band a pulse of potential to all of the column electrodes108. Then, the light modulation array100opens the shutter assemblies102through which light is to pass by applying a potential to the row open electrode110aand applying a potential to the column electrodes108for the columns which include shutter assemblies in the row which are to be opened. In one alternative mode of operation, instead of closing each row of shutter assemblies102sequentially, after all rows in the light modulation array100are set to the proper position to form an image104, the light modulation array100globally resets all shutter assemblies102at the same time by applying a potentials to all row close electrodes110band all column electrodes108concurrently. In another alternative mode of operation, the light modulation array100forgoes resetting the shutter assemblies102and only alters the states of shutter assemblies102that need to change state to display a subsequent image104.

In addition to the column electrode108and the row electrodes110aand110b, each shutter assembly includes a shutter112and an aperture114. To illuminate a pixel106in the image104, the shutter is positioned such that it allows light to pass, without any significant obstruction, through, the aperture114towards a viewer. To keep a pixel unlit, the shutter112is positioned such that it obstructs the passage of light through the aperture114. The aperture114is defined by an area etched through a reflective material in each shutter assembly, such as the column electrode108. The aperture114may be filled with a dielectric material.

FIG. 1Bis a cross sectional diagram (see line A-A′ below inFIG. 1D) of one of the shutter assemblies102ofFIG. 1A, illustrating additional features of the shutter assemblies102. Referring toFIGS. 1A and 1B, the shutter assembly102is built on a substrate116which is shared with other shutter assemblies102of the light modulation array100. The substrate116may support as many as 4,000,000 shutter assemblies, arranged in up to about 2000 rows and up to about 2000 columns.

As described above, the shutter assembly102includes a column electrode108, a row open electrode110a, a row close electrode110b, a shutter112, and an aperture114. The column electrode108is formed from a substantially continuous layer of reflective metal, the column metal layer118, deposited on the substrate116. The column metal layer118serves as the column electrode108for a column of shutter assemblies102in the light modulation array100. The continuity of the column metal layer118is broken to electrically isolate one column electrode108from the column electrodes108of shutter assemblies102in other columns of the light modulation array100. As mentioned above, each shutter assembly102includes an aperture114etched through the column metal layer118to form a light-transmissive region.

The shutter assembly includes a row metal layer120, separated from the column metal layer118by one or more intervening layers of dielectric material or metal. The row metal layer120forms the two row electrodes110aand110bshared by a row of shutter assemblies102in light modulation array100. The row metal layer120also serves to reflect light passing through gaps in the column metal layer118other than over the apertures114. The column metal layer and the row metal layer are between about 0.1 and about 2 microns thick. In alternative implementations, such as depicted inFIG. 1D(described below), the row metal layer120can be located below the column metal layer118in the shutter assembly102.

The shutter102assembly includes a third functional layer, referred to as the shutter layer122, which includes the shutter112. The shutter layer122can be formed from metal or a semiconductor. Metal or semiconductor vias124electrically connect the column metal layer118and the row electrodes110aand110bof the row metal layer120to features on the shutter layer122. The shutter layer122is separated from the row metal layer120by a lubricant, vacuum or air, providing the shutter112freedom of movement.

FIG. 1Cis a isometric view of a shutter layer122, according to an illustrative embodiment of the invention. Referring to bothFIGS. 1B and 1C, the shutter layer122, in addition to the shutter112, includes four shutter anchors126, two row anchors128aand128b, and two actuators130aand130b, each consisting of two opposing compliant beams. The shutter112includes an obstructing portion132and, optionally, as depicted inFIG. 1C, a shutter aperture134. In the open state, the shutter112is either clear of the aperture114, or the shutter aperture134is positioned over the aperture134, thereby allowing light to pass through the shutter assembly102. In the closed state, the obstructing portion132is positioned over the aperture, obstructing the passage of light through the shutter assembly102. In alternative implementations, a shutter assembly102can include additional apertures114and the shutter112can include multiple shutter apertures134. For instance, a shutter112can be designed with a series of narrow slotted shutter apertures134wherein the total area of the shutter apertures134is equivalent to the area of the single shutter aperture134depicted inFIG. 1C. In such implementations, the movement required of the shutter to move between open and closed states can be significantly reduced.

Each actuator130aand130bis formed from two opposing compliant beams. A first pair of compliant beams, shutter actuator beams135, physically and electrically connects each end of the shutter112to the shutter anchors126, located in each corner of the shutter assembly102. The shutter anchors126, in turn, are electrically connected to the column metal layer118. The second pair of compliant beams, row actuator beams136aand136bextends from each row anchor128aand128b. The row anchor128ais electrically connected by a via to the row open electrode110a. The row anchor128bis electrically connected by a via to the row close electrode110b. The shutter actuator beams135and the row actuator beams136aand136b(collectively the “actuator beams135and136”) are formed from a deposited metal, such as Au, Cr or Ni, or a deposited semiconductor, such as polycrystalline silicon, or amorphous silicon, or from single crystal silicon if formed on top of a buried oxide (also known as silicon on insulator). The actuator beams135and136are patterned to dimensions of about 1 to about 20 microns in width, such that the actuator beams135and136are compliant.

FIG. 1Dis a top-view of the various functional layers of a light modulation array100′, according to an illustrative embodiment of the invention. The light modulation array100′ includes twelve shutter assemblies102′a-102′l, in various stages of completion. Shutter assemblies102′aand102′binclude just the column metal layer118′ of the light modulation array100′. Shutter assemblies102′c-102′finclude just the row metal layer120′ (i.e., the row open electrode and the row-close electrode) of the light modulation array100′. Shutter assemblies102′gand102′hinclude the column metal layer118′ and the row metal layer120′. In contrast to the shutter assembly102inFIG. 1B, the column metal layer118′ is deposited on top of the row metal layer120′. Shutter assemblies102′i-ldepict all three functional layers of the shutter assemblies102′, the row metal layer120′, the column metal layer118′, and a shutter metal layer122′. The shutter assemblies102′iand102′kare closed, indicated by the column metal layer118′ being visible through the shutter aperture134′ included in the shutter assemblies102′iand102′k. The shutter assemblies102′jand102′lare in the open position, indicated by the aperture114′ in the column metal layer118′ being visible in the shutter aperture134′.

In other alternate implementations, a shutter assembly can include multiple apertures and corresponding shutters and actuators (for example, between, 1 and 10) per pixel. In changing the state of this shutter assembly, the number of actuators activated can depend on the switching voltage that is applied or on the particular combination of row and column electrodes that are chosen for receipt of a switching voltage. Implementations are also possible in which partial openings of an aperture is made possible in an analog fashion by providing a switching voltages partway between a minimum and a maximum switching voltage. These alternative implementations provide an improved means of generating a grey scale.

With respect to actuation of shutter assemblies102, in response to applying a potential to the column electrode108of the shutter assembly102, the shutter anchors126, the shutter112and the shutter actuator beams135become likewise energized with the applied potential. In energizing one of the row electrodes110aor10b, the corresponding row anchor128aor128band the corresponding row actuator beam136aor136balso becomes energized. If the resulting potential difference between a row actuator beam136aor136band its opposing shutter actuator beam135exceeds a predetermined switching threshold, the row actuator beam136aor136battracts its opposing shutter actuator beam135, thereby changing the state of the shutter assembly102.

As the actuator beams135and136are pulled together, they bend or change shape. Each pair of actuator beams135and136(i.e., a row actuator beam134aor134band its opposing shutter actuator beam135) can have one of two alternate and stable forms of curvature, either drawn together with parallel shapes or curvature, or held apart in a stable fashion with opposite signs to their of curvature. Thus, each pair is mechanically bi-stable. Each pair of actuator beams135and136is stable in two positions, one with the shutter112in an “open” position, and a second with the shutter112in a “closed” position. Once the actuator beams135and136reach one of the stable positions, no power and no applied voltage need be applied to the column electrode108or either row electrode110aor10bto keep the shutter112in that stable position. Voltage above a predetermined threshold needs to be applied to move the shutter112out of the stable position.

While both the open and closed positions of the shutter assembly102are energetically stable, one stable position may have a lower energy state than the other stable position. In one implementation, the shutter assemblies102are designed such that the closed position has a lower energy state than the open position. A low energy reset pulse can therefore be applied to any or all pixels in order to return the entire array to its lowest stress state, corresponding also to an all-black image.

The light modulation array100and its component shutter assemblies102are formed using standard micromachining techniques known in the art, including lithography; etching techniques, such as wet chemical, dry, and photoresist removal; thermal oxidation of silicon; electroplating and electroless plating; diffusion processes, such as boron, phosphorus, arsenic, and antimony diffusion; ion implantation; film deposition, such as evaporation (filament, electron beam, flash, and shadowing and step coverage), sputtering, chemical vapor deposition (CVD), epitaxy (vapor phase, liquid phase, and molecular beam), electroplating, screen printing, and lamination. See generally Jaeger, Introduction to Microelectronic Fabrication (Addison-Wesley Publishing Co., Reading Mass. 1988); Runyan, et al., Semiconductor Integrated Circuit Processing Technology (Addison-Wesley Publishing Co., Reading Mass. 1990); Proceedings of the IEEE Micro Electro Mechanical Systems Conference 1987-1998; Rai-Choudhury, ed., Handbook of Microlithography, Micromachining & Microfabrication (SPIE Optical Engineering Press, Bellingham, Wash. 1997).

More specifically, multiple layers of material (typically alternating between metals and dielectrics) are deposited on top of a substrate forming a stack. After one or more layers of material are added to the stack, patterns are applied to a top most layer of the stack marking material either to be removed from, or to remain on, the stack. Various etching techniques, including wet and/or dry etches, are then applied to the patterned stack to remove unwanted material. The etch process may remove material from one or more layers of the stack based on the chemistry of the etch, the layers in the stack, and the amount of time the etch is applied. The manufacturing process may include multiple iterations of layering, patterning, and etching.

The process also includes a release step. To provide freedom for parts to move in the resulting device, sacrificial material is interdisposed in the stack proximate to material that will form moving parts in the completed device. An etch removes much of the sacrificial material, thereby freeing the parts to move.

After release the surfaces of the moving shutter are insulated so that charge does not transfer between moving parts upon contact. This can be accomplished by thermal oxidation and/or by conformal chemical vapor deposition of an insulator such as Al2O3, Cr2O3, TiO2, HfO2, V2O5, Nb2O5, Ta2O5, SiO2, or Si3N4 or by depositing similar materials using techniques such as atomic layer deposition. The insulated surfaces are chemically passivated to prevent problems such as stiction between surfaces in contact by chemical conversion processes such as fluoridation or hydrogenation of the insulated surfaces.

FIG. 2is a cross-section of an optical cavity200for use in a spatial light modulator, according to an illustrative embodiment of the invention. The optical cavity200includes a front reflective surface202and a rear reflective surface204. The front reflective surface202includes an array of light-transmissive regions206through which light208can escape the optical cavity200. Light208enters the optical cavity200from one or more light sources210. The light206reflects between the front and rear reflective surfaces202and204until it reflects through one of the light-transmissive regions206. Additional reflective surfaces may be added along the sides of the optical cavity200.

The front and rear reflective surfaces202and204, in one implementation, are formed by depositing a metal or semiconductor onto either a glass or plastic substrate. In other implementations, the reflective surfaces202and204are formed by depositing metal or semiconductor on top of a dielectric film that is deposited as one of a series of thin films built-up on a substrate. The reflective surfaces202and204have reflectivities above about 50%. For example, the reflective surfaces202and204may have reflectivities of 70%, 85%, 96%, or higher.

Smoother substrates and finer grained metals yield higher reflectivities. Smooth surfaces may be obtained by polishing a glass substrate or by molding plastic into smooth-walled forms. Alternatively, glass or plastic can be cast such that a smooth surface is formed by the settling of a liquid/air interface. Fine grained metal films without inclusions can be formed by a number of vapor deposition techniques including sputtering, evaporation, ion plating, laser ablation, or chemical vapor deposition. Metals that are effective for this reflective application include, without limitation, Al, Cr, Au, Ag, Cu, Ni, Ta, Ti, Nd, Nb, Si, Mo and/or alloys thereof.

Alternatively, the reflective surface can be formed by interposing a dielectric material of low refractive index between a light guide in the optical cavity200and any of a series of thin films deposited on top of it. The change in refractive index between the light guide and the thin film leads to a condition of total internal reflection within the light guide, whereby incident light of sufficiently low incidence angle can be reflected with nearly 100% efficiency.

In the alternative, the reflective surfaces202or204can be formed from a mirror, such as a dielectric mirror. A dielectric mirror is fabricated as a stack of dielectric thin films which alternate between materials of high and low refractive index. A portion of the incident light is reflected from each interface where the refractive index changes. By controlling the thickness of the dielectric layers to some fixed fraction or multiple of the wavelength and by adding reflections from multiple parallel interfaces, it is possible to produce a net reflective surface having a reflectivity exceeding 98%. Some dielectric mirrors have reflectivities greater than 99.8%. Dielectric mirrors can be custom-designed to accept a pre-specified range of wavelengths in the visible range and to accept a pre-specified range of incident angles. Reflectivities in excess of 99% under these conditions are possible as long as the fabricator is able to control the smoothness in the dielectric film stacks. The stacks can include between about 20 and about 500 films.

In another alternative, the first and second reflective surfaces202or204are included in the optical cavity200as separate components. A thin sheet of polished stainless steel or aluminum can suffice for this purpose. Also, it is possible to produce a reflective metal surface or a dielectric mirror on the surface of a continuous sheet or roll of plastic. The sheet of reflective plastic can then be attached or adhered to other components in the optical cavity200.

The light-transmissive regions206are arranged in an array to form pixels from which an image is formed. In the illustrative embodiment, the light-transmissive regions206are spaced between about 100 and about 350 microns apart. The light transmissive regions are oblong or rectangular in shape, wherein the greater dimension is between about 50 and about 300 microns while the narrower dimension is between 2 and 100 microns, though other shapes and sizes may be suitable. For projection displays the pitch can be as small as 20 microns, with aperture widths as small as 5 microns. The ratio between the area of the front reflective surface202taken up by light-transmissive regions206and the total area of the front reflective surface202is referred to herein as the transmissiveness ratio. Illustrative implementations of the optical cavity200have transmissiveness ratios of between about 5% and about 50%. Normally, spatial light modulators having such low transmissiveness ratios would emit insufficient light to form a usable image. To ensure greater light208emission from the optical cavity200, the front and rear reflective surfaces202and204reflect the light208back and forth a number of times until the reflected light208passes through a light-transmissive region206, or until the light208loses its energy from the reflections. Higher reflectivity surfaces result in more light208escaping from the optical cavity200to form an image. Table 1, below, lists the percentage of light208introduced into the optical cavity200that escapes through the light-transmissive regions206(in terms of efficiency) for several transmissiveness ratio/reflectivity pairings.

When the optical cavity200is used to form the basis of a transmissive display, one or more light sources210introduce light into the optical cavity200. The light source(s)210may be of any suitable type, including, for example, any of the types disclosed in U.S. Pat. Nos. 4,897,771 and 5,005,108, the entire disclosures of which are incorporated herein by reference. In particular, the light source(s)210may be an arc lamp, an incandescent bulb which also may be colored, filtered or painted, a lens end bulb, a line light, a halogen lamp, a light emitting diode (LED), a chip from an LED, a neon bulb, a fluorescent tube, a fiber optic light pipe transmitting from a remote source, a laser or laser diode, or any other suitable light source. Additionally, the light sources may be a multiple colored LED, or a combination of multiple colored radiation sources210in order to provide a desired colored or white light output distribution. For example, a plurality of colored lights such as LEDs of different colors (red, blue, green) or a single LED with multiple colored chips may be employed to create white light or any other colored light output distribution by varying the intensities of each individual colored light. A reflector may be positioned proximate to the light source210to reflect light208emitted away from the optical cavity200towards the optical cavity200. In one implementation, three light sources210, one red light source210, one green light source210, and one blue light source210, sequentially introduce light208into the optical cavity200, alternating at frequencies in the range of 20 to 600 Hz. A rate in excess of 100 Hz is generally faster than what the human eye can detect, thus providing a color image.

FIG. 3Ais a linear cross-sectional view of a shutter assembly300in an open position. The shutter assembly300is formed on transparent substrate302having a thickness of from about 0.3 mm to about 2 mm. The substrate302can be, for example, made of a glass or a plastic. Suitable glasses include borosilicate glasses, or other glasses that can withstand processing temperatures up to or exceeding 400 degrees Centigrade. Suitable plastics for the substrate302include, for example, polyethyleneterephthalate (PET), or polytetrafluoroethylene (PETF), or other substantially transparent plastics that can withstand processing temperatures in excess of 200° C. Other candidate substrate materials include quartz and sapphire, which are understood to withstand processing temperatures in excess of 800° C.

The lowest layer, referred to as the “column metal layer”304, of the shutter assembly300serves as the front reflective surface202of the optical cavity ofFIG. 2. During the process of manufacturing the shutter assembly300, an aperture306is etched through the column metal layer304to form a light-transmissive region, such as the light transmissive regions206ofFIG. 2. The aperture306can be generally circular, elliptical, polygonal, serpentine, or irregular in shape. The aperture occupies about 5% to about 25% of the area dedicated to the particular shutter assembly300in the light modulation array. Other than at the aperture306, the column metal layer304is substantially unbroken. The aperture306is filled with a dielectric material307. Example dielectrics suitable for inclusion in the shutter assembly300include SiO2, Si3N4, and Al2O3.

The next layer is composed mostly of a dielectric material307, separating the column metal layer304from the row electrodes308aand308bdisposed a layer above. The dielectric layers316may be between 0.3 and 10 microns thick. The top layer of the shutter assembly300includes a shutter anchor312, two row anchors313, two actuators, and a shutter310. The beams of the actuators are not shown as the cross section of the shutter assembly300is taken at a position in which the row actuator beams meet the row anchors313and the shutter actuator beams meet the shutter310(see, for example, line B-B′ onFIG. 1D). The top layer is supported above the lower layers by the anchors312so that the shutter310is free to move.

In alternative implementations, the row electrodes308aand308bare located at a lower layer in the shutter assembly300than the column metal layer304. In another implementation the shutter310and actuators can be located at a layer below either of the column metal layer304or the row electrodes308aand308b.

As described in relation toFIG. 1B, the actuators included in the shutter assembly may be designed to be mechanically bi-stable. Alternatively, the actuators can be designed to have only one stable position. That is, absent the application of some form of actuation force, such actuators return to a predetermined position, either open or closed. In such implementations, the shutter assembly300includes a single row electrode308, which, when energized, causes the actuator to push or pull the shutter310out of its stable position.

FIG. 3Bis a cross-sectional view of a second alternative shutter assembly300′ in an open position according to an illustrative embodiment of the invention. The second shutter assembly300′ includes a substrate302′, a column metal layer304′, an aperture306′, row electrodes308a′ and308b′, a shutter310′, two actuators, a shutter anchor312′, and two row anchors313′. The beams of the actuators are not shown as the cross section of the shutter assembly300′ is taken at a position in which the row actuator beams meet the row anchors313′ and the shutter actuator beams meet the shutter310′. (See, for example, line B-B′ onFIG. 1D).

In the shutter assembly300′, additional gaps are etched into the column metal layer304′. The gaps electrically separate different portions of the column metal layer304′ such that different voltages can be applied to each portion. For instance, in order to reduce parasitic capacitances that can arise between the column metal layer304′ and the row electrodes308a′ and308b′ resulting from their overlap, a voltage can be selectively applied to the sections314of the column metal layer304′ that immediately underlies the row electrodes308a′ and308b′ and the anchor312′.

FIG. 3Cis a cross-sectional view of another third alternative shutter assembly300″ according to an illustrative embodiment of the invention. The shutter assembly300″ includes a substrate302″, a column metal layer304″, an aperture306″, row electrodes308a″ and308b″, a shutter310″, two actuators, a shutter anchor312″, and two row anchors313″. The beams of the actuators are not shown as the cross section of the shutter assembly300″ is taken at a position in which the row actuator beams meet the row anchors313″ and the shutter actuator beams meet the shutter310″. (See, for example, line B-B′ onFIG. 1D). The shutter assembly300″ includes a reflective film316deposited on the substrate302″. The reflective film316serves as a front reflective surface for an optical cavity incorporating the shutter assembly300″. With the exception of an aperture306″ formed in the reflective film316to provide a light transmissive region, the reflective film316is substantially unbroken. A dielectric layer318separates the reflective film316from the column metal layer304″. At least one additional dielectric layer318separates the column metal layer304″ from the two row electrodes308a″ and308b″. During the process of the manufacturing of the third alternative shutter assembly300″, the column metal layer304″ is etched to remove metal located below the row electrodes308a″ and308b″ to reduce potential capacitances that can form between the row electrodes308a″ and308b″ and the column metal layer304″. Gaps320formed in the column metal layer304″ are filled in with a dielectric.

FIG. 3Dis a cross-sectional view of a further alternative shutter assembly300′″ in a closed position according to an illustrative embodiment of the invention. The fourth alternative shutter assembly300′″ includes a substrate302′″, a column metal layer304′″, an aperture306′″, row electrodes308a′″ and308b′″, a shutter310′″, two actuators, a shutter anchors312′″, and two row anchors313′″. The beams of the actuators are not shown as the cross section of the shutter assembly300′″ is taken at a position in which the row actuator beams meet the row anchors313′″ and the shutter actuator beams meet the shutter310′″. (See, for example, line B-B′ onFIG. 1D). In contrast to the previously depicted shutter assemblies102,300,300′, and300″, much of the dielectric material used in building the fourth alternative shutter assembly300′″ is removed by one or more etching steps.

The space previously occupied by the dielectric material can be filled with a lubricant to reduce friction and prevent stiction between the moving parts of the shutter assembly300′″. The lubricant fluid is engineered with viscosities preferably below about 10 centipoise and with relative dielectric constant preferably above about 2.0, and dielectric breakdown strengths above about 104V/cm. Such mechanical and electrical properties are effective at reducing the voltage necessary for moving the shutter between open and closed positions. In one implementation, the lubricant preferably has a low refractive index, preferably less than about 1.5. In another implementation the lubricant has a refractive index that matches that of the substrate302. Suitable lubricants include, without limitation, de-ionized water, methanol, ethanol, silicone oils, fluorinated silicone oils, dimethylsiloxane, polydimethylsiloxane, hexamethyldisiloxane, and diethylbenzene.

FIG. 4is a cross sectional view of a shutter assembly400with a coated shutter402, according to an illustrative embodiment of the invention. The shutter assembly400is depicted as having the general structure of the shutter assembly300ofFIG. 3A. However, the shutter assembly400can take the form of any of the shutter assemblies102,300,300′,300″, or300′″ described above or any other shutter assembly described below.

A reflective film404coats the bottom of the shutter402to reflect light406back through the shutter assembly400when the shutter402is in the closed position. Suitable reflective films404include, without limitation, smooth depositions of Al, Cr, or Ni. The deposition of such a film404, if the film404is greater than about 0.2 microns thick, provides a reflectivity for the shutter of 95% or higher. Alternatively, amorphous or polycrystalline Si, when deposited onto a smooth dielectric surface, can provide reflectivity high enough to be useful in this application

The top of the shutter402is coated with a light absorbing film408to reduce reflection of ambient light410striking the top of the shutter assembly400. The light absorbing film408can be formed from the deposition and/or anodization of a number of metals, such as Cr, Ni, or Au or Si in a manner that creates a rough or porous surface. Alternatively, the light absorbing film408can include an acrylic or vinyl resin which includes light absorbing pigments. In alternative implementations of the shutter assembly400, the absorbing film408is applied to the entire, or substantially the entire top surface of the shutter assembly400.

FIG. 5is a cross sectional view of a shutter assembly500with a second coated shutter502, according to an illustrative embodiment of the invention. The shutter assembly500is depicted as having the general structure of the first alternative shutter assembly300ofFIG. 3A. However, the shutter assembly can take the form of any of the shutter assemblies describes above102,300,300′,300″, and300′″ or any other shutter assembly described below. In the shutter assembly500, both the top and the bottom of the shutter502are coated with a light absorbing film504such as a light absorbing film408. The light absorbing film504on the bottom of the shutter502absorbs light impacting the shutter502in a closed position. For an optical cavity, such as optical cavity200ofFIG. 2, including the shutter assembly500, the intensity of light exiting the optical cavity is independent of the image being formed. That is, light intensity is independent of the fraction of shutters that may be in the open or the closed position.

FIG. 6is cross-sectional view of an elastically actuated shutter assembly600for use in a light modulation array, such as light modulation array102, according to an illustrative embodiment of the invention. The elastically actuated shutter assembly600includes a metal column layer602, a single row electrode604, an elastic element606, and a shutter608. The elastic element606provides a restoring force which keeps the shutter608in an open position, away from a corresponding aperture610in the column metal layer602. In the open position, light612can pass through the aperture610. Provision of a switching voltage to the single row electrode604counters the force of the elastic element606, thereby putting the shutter608into a closed position over the aperture610. In the closed position, the shutter608blocks light612from exiting through the aperture610. In an alternative implementation, the shutter assembly600may include a latch to lock the shutter608into a closed position such that after the shutter608closes, the row electrode604can be de-energized without the shutter608opening. To open the shutter608, the latch is released. In still another implementation of the shutter assembly600, the elastic actuator tends to keep the shutter608in a closed position. Applying a voltage to the row electrode604moves the shutter608into an open position. Suitable spring-like elastic actuators for displays have been described in U.S. Pat. No. 5,062,689, the entirety of which is incorporated herein by reference.

FIG. 7is a cross-sectional view of a shutter assembly700with a deformable shutter701for use in a light modulation array, according to an illustrative embodiment of the invention. The shutter assembly700includes a column metal layer702, and one row electrode704formed on a substrate708. The deforming shutter701, instead of translating from one side of the shutter assembly700to the other side of the shutter assembly700to open and close, deforms in response to the energizing of the row electrode704. The deforming shutter701is formed such that the deforming shutter701retains residual stress, resulting in the deforming shutter701tending to curl up out of the plane of the light modulation array in which it is included. By imposing a switching voltage between the row electrode704and the column metal layer702, the deforming shutter701is attracted towards the substrate708, thereby covering an aperture710formed in the column metal layer702. Deformable or hinge type actuators have been described in the art, for instance in U.S. Pat. Nos. 4,564,836 and 6,731,492, the entireties of which are incorporated herein by reference.

FIG. 8Ais a cross-sectional view of a shutter assembly800with an opaque substrate802, such as silicon, for use in a light modulation array, according to an illustrative embodiment of the invention. The opaque substrate802has a thickness in the range of about 200 microns to about 1 mm. Though the shutter assembly800resembles the shutter assembly300ofFIG. 3A, the shutter assembly800can take substantially the same form of any of the shutter assemblies300,300′,300″,300′″,400,500,600, or700described inFIGS. 3-7. An aperture804is etched through the entirety of the opaque substrate802. In one implementation, the aperture804is formed using an anisotropic dry etch such as in a CFCl3gas with plasma or ion assist. The shutter assembly800may also include a reflective coating810deposited on the side of the opaque substrate802opposite the column metal layer.

FIG. 8Bis a cross-sectional view of a second shutter assembly800′ with an opaque substrate802′ for use in a light modulation array, according to an illustrative embodiment of the invention. In comparison to the shutter assembly800inFIG. 8A, the underside of the opaque substrate800′ is etched away forming cavities806beneath the apertures804′ of the shutter assembly800′. The cavities806allow light from a larger range of angles to escape through the aperture804′. The larger range provides for a brighter image and a larger viewing angle.

The shutter assemblies described in FIGS.1and3-8depend on electrostatic forces for actuation. A number of alternative actuator forcing mechanisms can be designed into shutter assemblies, including without limitation the use of electromagnetic actuators, thermoelastic actuators, piezoelectric actuators, and electrostiction actuators. Other shutter motions which can be used to controllably obstruct an aperture include without limitation sliding, rotating, bending, pivoting, hinging, or flapping; all motions which are either within the plane of the reflective surface or transverse to that plane.

FIG. 9is a cross-sectional view of a liquid crystal-based spatial light modulator900. The liquid crystal-based spatial light modulator900includes an array901of liquid crystal cells902. The liquid crystal cells902include pairs of opposing transparent electrodes904on either side of a layer of liquid crystal molecules906. On one side of the liquid crystal array901, the liquid crystal-based spatial light modulator900includes a polarizer908. On the opposite side of the array901, the liquid crystal-based spatial light modulator900includes an analyzer910. Thus, without intervention, light passing through the polarizer908would be filtered blocked by the analyzer910. When a voltage is imposed between the transparent electrodes904, the liquid crystal molecules906between the electrodes904align themselves with the resultant electric field reorienting the light passing through the polarizer908such that it can pass through the analyzer910. The polarizer908is positioned on top of a front reflective surface911, which defines a plurality of light-transmission regions913. The array901is attached to an optical cavity, such as optical cavity200and includes a cover plate912. Cover plates are described in further detail in relation toFIG. 11.

Each liquid crystal cell902may have a corresponding red, green, or blue color specific filter. Alternatively, color differentiation can be provided by multiple lamps operating in sequence as described above in relation toFIG. 2.

Most liquid crystal displays (LCDS) are designed with resolutions of 80 to 110 dots per inch, wherein pixel widths are in the range of 250 to 330 microns. For such an LCD display, even with active matrix or thin-film transistor (TFT) addressing or switching, the transmissiveness ratio of the liquid-crystal display is in the range of 75 to 90%. For high-resolution applications (e.g. for document displays or projection displays) in which the desired image resolution is 300 to 500 dots per inch, however, and where pixels are only 50 microns in diameter, the overhead required for TFT addressing can limit the available transmissiveness ratio to about 30 or 50%. Such high-resolution displays, therefore, typically suffer from a lower luminous efficiency than their lower-resolution counterparts due to a loss of aperture ratio. By constructing the liquid crystal display using an optical cavity as described above, greater luminous efficiency can be achieved even in high-definition LCD displays.

FIG. 10is a cross sectional view of a first shutter-based spatial light modulator1000according to an illustrative embodiment of the invention. The shutter-based spatial light modulator1000includes a light modulation array1002, an optical cavity1004, and a light source1006. The light modulation array1002can include any of the shutter assemblies300,300′,300″,300′″,400,500,600,700,800, or800′ described above inFIGS. 3-8. The optical cavity1004, in the first shutter-based spatial light modulator1000, is formed from a light guide1008having front and rear surfaces. A front reflective surface1010is deposited directly on the front surface of the light guide1008and a second reflective surface1012is deposited directly on the rear surface of the light guide1008.

The light guide1008can be formed from glass or a transparent plastic such as polycarbonate or polyethylene. The light guide1008is about 300 microns to about 2 mm thick. The light guide1008distributes light1014introduced into the optical cavity1004substantially uniformly across the surface of the front reflective surface1010. The light guide1008achieves such distribution by means of a set of total internal reflections as well as by the judicial placement of light scattering elements1016. The light scattering elements1016can be formed in or on the rear side of the light guide1018to aid in redirecting light1014out of the light guide1008and through light-transmissive regions1019formed in the front reflective surface1010.

FIG. 11is a cross sectional view of a second shutter-based spatial light modulator1100, according to the illustrative embodiment of the invention. As with the first shutter-based spatial light modulator1000inFIG. 10, the second shutter-based spatial light modulator1100includes a light modulation array1102, an optical cavity1104, and a light source1106. In addition, the second spatial light modulator includes a cover plate1108.

The cover plate1108serves several functions, including protecting the light modulation array1102from mechanical and environmental damage. The cover plate1108is a thin transparent plastic, such as polycarbonate, or a glass sheet. The cover plate can be coated and patterned with a light absorbing material, also referred to as a black matrix1110. The black matrix can be deposited onto the cover plate as a thick film acrylic or vinyl resin that contains light absorbing pigments.

The black matrix1110absorbs substantially all incident ambient light1112—ambient light is light that originates from outside the spatial light modulator1100, from the vicinity of the viewer—except in patterned light-transmissive regions1114positioned substantially proximate to light-transmissive regions1116formed in the optical cavity1104. The black matrix1110thereby increases the contrast of an image formed by the spatial light modulator1100. The black matrix1110can also function to absorb light escaping the optical cavity1104that may be emitted, in a leaky or time-continuous fashion.

In one implementation, color filters, for example, in the form of acrylic or vinyl resins are deposited on the cover plate1108. The filters may be deposited in a fashion similar to that used to form the black matrix1110, but instead, the filters are patterned over the open apertures light transmissive regions1116of the optical cavity1104. The resins can be doped alternately with red, green, or blue pigments.

The spacing between the light modulation array1102and the cover plate1108is less than 100 microns, and may be as little as 10 microns or less. The light modulation array1102and the cover plate1108preferably do not touch, except, in some cases, at predetermined points, as this may interfere with the operation of the light modulation array1102. The spacing can be maintained by means of lithographically defined spacers or posts, 2 to 20 microns tall, which are placed in between the individual right modulators in the light modulators array1102, or the spacing can be maintained by a sheet metal spacer inserted around the edges of the combined device.

FIG. 12Ais a cross sectional view of a third shutter-based spatial light modulator1200, according to an illustrative embodiment of the invention. The third shutter-based spatial light modulator1200includes an optical cavity1202, a light source1204, and a light modulation array1206. In addition, the third shutter-based spatial light modulator1204includes a cover plate1207, such as the cover plate1108described in relation toFIG. 11.

The optical cavity1202, in the third shutter-based spatial light modulator1200, includes a light guide1208and the rear-facing portion of the light modulation array1206. The light modulation array1206is formed on its own substrate1210. Both the light guide1208and the substrate1210each have front and rear sides. The light modulation array1206is formed on the front side of the substrate1210. A front-facing, rear-reflective surface1212, in the form of a second metal layer, is deposited on the rear side of the light guide1208to form the second reflective surface of the optical cavity1202. Alternatively, the optical cavity1202includes a third surface located behind and substantially facing the rear side of the light guide1208. In such implementations, the front-facing, rear-reflective surface1212is deposited on the third surface facing the front of the spatial light modulator1200, instead of directly on the rear side of the light guide1208. The light guide1208includes a plurality of light scattering elements1209, such as the light scattering elements1016described in relation toFIG. 10. As inFIG. 10, the light scattering elements are distributed in a predetermined pattern on the rear-facing side of the light guide1208to create a more uniform distribution of light throughout the optical cavity.

In one implementation, the light guide1208and the substrate1210are held in intimate contact with one another. They are preferably formed of materials having similar refractive indices so that reflections are avoided at their interface. In another implementation small standoffs or spacer materials keep the light guide1208and the substrate1210a predetermined distance apart, thereby optically de-coupling the light guide1208and substrate1210from each other. The spacing apart of the light guide1208and the substrate1210results in an air gap1213forming between the light guide1208and the substrate1210. The air gap promotes total internal reflections within the light guide1208at its front-facing surface, thereby facilitating the distribution of light1214within the light guide before one of the light scattering elements1209causes the light1214to be directed toward the light modulator array1206shutter assembly. Alternatively, the gap between the light guide1208and the substrate1210can be filled by a vacuum, one or more selected gasses, or a liquid.

FIG. 12Bis a cross sectional view of a fourth shutter-based spatial light modulator1200′, according to an illustrative embodiment of the invention. As with the spatial light modulator1200ofFIG. 12A, the fourth spatial light modulator1200′ includes an optical cavity1202′, a light source1204′, a light modulation array1206′, and a cover plate1207′, such as the cover plate1108described in relation toFIG. 11. The optical cavity1202′ includes a rear-facing reflective surface in the light modulation array1206′, a light guide1208′, and a front-facing rear-reflective surface1212′. As with the third spatial light modulator1200, the light modulation array1206′ of the fourth spatial light modulator1200′ is formed on a substrate1210′, which is separate from the light guide1208′.

In the fourth spatial light modulator1200′, the light guide1208′ and the substrate1210′ are separated by a light diffuser1218and a brightness enhancing film1220. The diffuser1218helps to randomize the optical angles of scattered light1214′ to improve uniformity and reduce the formation of ghost images from the light source1204or the light modulation array1206. In one implementation, the brightness enhancement film1220includes an array of optical prisms that are molded into a thin plastic sheet, and which act to funnel light into a narrow cone of illumination. The brightness enhancing film1220re-directs light leaving the light guide1208′ through light-transmissive regions1222at an oblique angle towards the viewer, thus resulting in an apparent increases in brightness along the optical axis for the same input power.

FIG. 12Cis a cross sectional view of a fifth shutter-based spatial light modulator1200″, according to an illustrative embodiment of the invention. As with the spatial light modulator1200ofFIG. 12A, the fifth spatial light modulator1200″ includes an optical cavity1202″, a light source1204″, a light modulation array1206″, and a cover plate1207″, such as the cover plate1108described in relation toFIG. 11. The optical cavity1202″ includes a rear-facing reflective surface in the light modulation array1206″, a light guide1208″, and a front-facing rear-reflective surface1212″. As with the third spatial light modulator1200, the light modulation array1206″ of the fifth spatial light modulator1200″ is formed on a substrate1210″, which is separate from the light guide1208″.

In the fifth spatial light modulator1200″, the light guide1208″ and the substrate1210″ are separated by a microlens array1224. The microlens array1224re-directs light1214″ leaving the light guide1208″ through light-transmissive regions1222′ at an oblique angle towards the viewer, thus resulting in an apparent increases in brightness for the same input power.

In addition, since the light modulation array1206″ in the fifth shutter-based spatial light modulator1200″ is formed on its own substrate1210″, separate from the light guide1208″, the light guide1208″ can be constructed of a moldable plastic, without the transition temperature of the plastic limiting the manufacturing processes available for constructing the light modulation array1210″. Thus, the light guide1208″ can be molded to substantially encapsulate the light source1204″ used to introduce light1214″ into the optical cavity1202″. The encapsulation of the light source1204″ into the light guide1208″ provides improved coupling of light1214″ into the light guide1208″. Similarly, scattering elements1209″ can be incorporated directly in the mold for the light guide1208″.

FIG. 12Dis a cross-sectional view of a sixth illustrative embodiment of a shutter-based light modulation array1200′″. As with the spatial light modulator1200ofFIG. 12A, the sixth spatial light modulator1200′″ includes an optical cavity1202′″, a light source1204′″, a light modulation array1206′″, and a cover plate1207′″, such as the cover plate1108described in relation toFIG. 11. The optical cavity1202′″ includes a rear-facing reflective surface in the light modulation array1206′″, a light guide1208′″, a front-facing rear-reflective surface1212′″, a diffuser1218′″, and a brightness enhancing film1220′″.

The space between the light modulation array1206′″ and the cover plate1207′″ is filled with a lubricant1224, such as the lubricant described in relation toFIG. 3D. The cover plate1207′″ is attached to the shutter assembly1206with an epoxy1225. The epoxy should have a curing temperature preferably below about 200 C, it should have a coefficient of thermal expansion preferably below about 50 ppm per degree C. and should be moisture resistant. An exemplary epoxy is EPO-TEK B9021-1, sold by Epoxy Technology, Inc. The epoxy also serves to seal in the lubricant1224.

A sheet metal or molded plastic assembly bracket1226holds the cover plate1207′″, the light modulation array1206′″, and the optical cavity1202′″ together around the edges. The assembly bracket1226is fastened with screws or indent tabs to add rigidity to the combined device. In some implementations, the light source1204′″ is molded in place by an epoxy potting compound.

FIG. 13is a cross-sectional view of a seventh shutter-based spatial light modulator1300according to an illustrative embodiment of the invention. The seventh shutter-based spatial light modulator1300includes a substrate1302on which a light modulation array1304is formed, and a light guide1306. The light modulation array1304includes a front reflective surface for the optical cavity1310of the spatial light modulator1300. A reflective material is deposited or adhered to the rear side of the light guide to serve as a rear reflective surface1308. The rear side of the light guide1306is angled or shaped with respect to the front side of the light guide1308to promote uniform distribution of light in the light modulation array1304. The rear reflective surface1308, however, is still partially facing the front reflective surface.

FIG. 14Ais a cross-sectional view of another spatial light modulator1400, according to an illustrative embodiment of the invention. The spatial light modulator1400includes a substrate1402on which a light modulation array1404is formed. The light modulation array includes a reflective surface serving as a front reflective surface1405of an optical cavity. The spatial light modulation1400also includes a rear reflective surface1406substantially facing the rear side of the light modulation array1404. A light source1408is positioned within the space formed between the substrate1402on which the light modulation array1404is formed and the rear reflective surface1406. The space may also be filled with a substantially transparent plastic into which the light source1408is embedded.

FIG. 14Bis a cross-sectional view of another spatial light modulator1400′, similar to the spatial light modulator1400ofFIG. 14A. The spatial light modulator1400′ includes a substrate1402′ on which a light modulation array1404′ is formed. The light modulation array1404′ includes a reflective surface serving as a front reflective surface1405of an optical cavity. The spatial light modulation1400′ also includes a rear reflective surface1406′. The rear reflective surface1406′ is corrugated, textured, or shaped to promote light distribution in the optical cavity formed by the reflective surfaces (i.e., the rear reflective surface1406′ and a reflective surface incorporated into the light modulation array1404′ of the spatial light modulator1400′.

FIG. 15is a cross-sectional view of another shutter assembly1500for use in a light modulation array, according to an illustrative embodiment of the invention. The shutter assembly1500includes a metal column layer1502, two row electrodes1504aand1504b, a shutter1506, built on a substrate1509. The shutter assembly1500also includes one or more light scattering elements1508. As with other implementations of the shutter assemblies described above, an aperture1510is etched through the column metal layer1502. The light scattering elements1510can include any change in the shape or geometry of the substrate1509, such as by roughening, coating, or treating the surface of the substrate1509. For example, the light scattering elements can include patterned remnants of the column metal1502having dimensions of about 1 to about 5 microns. The light scattering elements1508aid in extracting light1512trapped in the substrate1508due to total internal reflection. When such trapped light1512strikes one of the scattering elements1508, the angle of the light's1512path changes. If the angle of the light's1512path becomes sufficiently acute, it passes out of the substrate1509. If the shutter1506is in the open position, the scattered light1512can exit the aperture1510, and proceed to a viewer as part of an image.

FIG. 16is a cross sectional view of yet another spatial light modulator1600according to an illustrative embodiment of the invention. The spatial light modulator1600includes a light modulation array1602formed on the rear surface of a substrate1604, facing the interior of an optical cavity1606. The individual light modulation elements1608, such as the shutter assemblies300,300′,300″,300′″,400,500,600,700,800, and800′ described inFIGS. 3-8or the liquid-crystal cells902described inFIG. 9, making up the light modulation array1602are modified to reverse the sides of the light modulation elements1608that reflect or absorb light as compared to what is described with reference toFIGS. 4 and 5.

The optical cavity1606includes both a front reflective surface1610, a rear reflective surface1612, and a light guide1614. Light is introduced into the optical cavity by a light source1613. The front reflective surface1610is disposed on front-facing surface of the light guide1614, providing a substantially continuous layer of high reflectivity and also defining light transmissive region1616. The front reflective surface1610is separated from the light modulation array1602by a transparent gap1618. The gap1618is preferably narrower than width of the light transmissive regions1616, less than, for example, about 100 microns. The gap1618may be as narrow as about 10 microns wide, or even narrower.

In one implementation, the gap1618is filled with a lubricant1620, such as the lubricant described in relation toFIG. 3D. The lubricant1620may have a refractive index that substantially matches that of the light guide1614to facilitate the extraction of light from the light guide1614.

The spatial light modulator1600can optionally forego a cover plate, since the shutter assembly is protected by the environment by the substrate1604. If a cover plate is omitted, a black matrix, such as the black matrix1110ofFIG. 11, can be applied to the front-facing surface of the substrate1604.

FIG. 17is a cross-sectional view of a transflective shutter assembly1700, according to an illustrative embodiment of the invention, which can be incorporated into the spatial light modulators1000,1100,1200,1300,1400, and1500described inFIGS. 10-15. The transflective shutter assembly1700forms images from both light1701emitted by a light source positioned behind the shutter assembly1700and from ambient light1703. The transflective shutter assembly1700includes a metal column layer1702, two row electrodes1704aand1704b, and a shutter1706. The transflective shutter assembly1700includes an aperture1708etched through the column metal layer1702. Portions of the column metal layer1702, having dimensions of from about 1 to about 5 microns, are left on the surface of the aperture1708to serve as transflection elements1710. A light absorbing film1712covers the top surface of the shutter1706.

While the shutter is in the closed position, the light absorbing film1712absorbs ambient light1703impinging on the top surface of the shutter1706. While the shutter1706is in the open position as depicted inFIG. 17, the transflective shutter assembly1700contributes to the formation of an image both by allowing light1701to pass through the transflective shutter assembly originating from the dedicated light source and from reflected ambient light1703. The small size of the transflective elements1710results in a somewhat random pattern of ambient light1703reflection.

The transflective shutter assembly1700is covered with a cover plate1714, which includes a black matrix1716. The black matrix absorbs light, thereby substantially preventing ambient light1703from reflecting back to a viewer unless the ambient light1703reflects off of an uncovered aperture1708.

FIG. 18is a cross-sectional view of a second transflective shutter assembly1800according to an illustrative embodiment of the invention, which can be incorporated into the spatial light modulators1000,1100,1200,1300,1400, and1500described inFIGS. 10-15. The transflective shutter assembly1800includes a metal column layer1802, two row electrodes1804aand1804b, and a shutter1806. The transflective shutter assembly1800includes an aperture1808etched through the column metal layer1702. At least one portion of the column metal layer1802, having dimensions of from about 5 to about 20 microns, remains on the surface of the aperture1808to serve as a transflection element1810. A light absorbing film1812covers the top surface of the shutter1806. While the shutter is in the closed position, the light absorbing film1812absorbs ambient light1803impinging on the top surface of the shutter1806. While the shutter1806is in the open position, the transflective element1810reflects a portion of ambient light1803striking the aperture1808back towards a viewer. The larger dimensions of the transflective element1810in comparison to the transflective elements1710yield a a more specular mode of reflection, such that ambient light originating from behind the viewer is substantially reflected directly back to the viewer.

The transflective shutter assembly1800is covered with a cover plate1814, which includes a black matrix1816. The black matrix absorbs light, thereby substantially preventing ambient light1803from reflecting back to a viewer unless the ambient light1803reflects off of an uncovered aperture1808.

Referring to bothFIGS. 17 and 18, even with the transflective elements1710and1810positioned in the apertures1708and1808, some portion of the ambient light1703and1803passes through the apertures1708and1808of the corresponding transflective shutter assemblies1700and1800. When the transflective shutter assemblies1700and1800are incorporated into spatial light modulators having optical cavities and light sources, as described above, the ambient light1703and1803passing through the apertures1708and1808enters the optical cavity and is recycled along with the light introduced by the light source. In alternative transflective shutter assemblies, the apertures in the column metal are at least partially filled with a semi-reflective-semitransmissive material.

FIG. 19is a cross sectional view of a front reflective shutter assembly1900according to an illustrative embodiment of the invention. The front reflective shutter assembly1900can be used in a reflective light modulation array. The front reflective shutter assembly1900reflects ambient light1902towards a viewer. Thus, use of arrays of the front reflective shutter assembly1900in spatial light modulators obviates the need for a dedicated light source in viewing environments having high amounts of ambient light1902. The front reflective shutter assembly1900can take substantially the same form of the shutter assemblies300,300′,300″,300′″,400,500,600,700,800or800′ ofFIGS. 3-8. However, instead of the column metal layer of the shutter assemblies300,400,500,600,700, or800including an aperture to allow passage of light, the column metal layer includes a reflective surface beneath the position of a closed shutter1904. The front-most layer of the reflective shutter assembly1900, including at least the front surface of the shutter1904, is coated in a light absorbing film1908. Thus, when the shutter1904is closed, light1902impinging on the reflective shutter assembly1900is absorbed. When the shutter1904is open, at least a fraction of the light1902impinging on the reflective shutter assembly1900reflects off the exposed column metal layer1910back towards a viewer. Alternately the column metal layer1910can be covered with an absorbing film while the front surface of shutter1908can be covered in a reflective film. In this fashion light is reflected back to the viewer only when the shutter is closed.

As with the other shutter assemblies and light modulators described above, the reflective shutter assembly1900can be covered with a cove rplate1910having a black matrix1912applied thereto. The black matrix1912covers portions of the cover plate1910not opposing the open position of the shutter.

FIG. 20is an isometric view of a spatial light modulator2000including multiple light modulation arrays2002, according to an illustrative embodiment of the invention. The size of several of the light modulation arrays2002described above is limited, somewhat, by the semiconductor manufacturing techniques used to construct them. However, light guides2004and reflective films2006can be formed on a significantly larger scale. A spatial light modulator which includes multiple, adjacently disposed light modulation arrays2002, arranged over one or more light guides2004, can generate a larger image, thereby circumventing these limitations.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The forgoing embodiments are therefore to be considered in all respects illustrative, rather than limiting of the invention.