Patent Document

FIELD OF THE INVENTION  
         [0001]    This invention relates to a display system with a linear array of electromechanical grating devices that is scanned in order to generate a two-dimensional image. More particularly, the invention relates to a high-contrast laser display system containing electromechanical conformal grating devices.  
         BACKGROUND OF THE INVENTION  
         [0002]    Spatial light modulators based on electromechanical grating devices are important for a wide range of applications, including display, data storage, spectroscopy and printing. Such systems require large numbers of individually addressable devices in either a linear or area array, with over a million addressable devices desirable for an area modulator array in a high-quality display.  
           [0003]    Recently, an electromechanical conformal grating device consisting of ribbon elements suspended above a substrate by a periodic sequence of intermediate supports was disclosed by Kowarz in U.S. Pat. No. 6,307,663, entitled “Spatial Light Modulator With Conformal Grating Device” issued Oct. 23, 2001. The electromechanical conformal grating device is operated by electrostatic actuation, which causes the ribbon elements to conform around the support substructure, thereby producing a grating. The device of &#39;663 has more recently become known as the conformal GEMS device, with GEMS standing for grating electromechanical system. The conformal GEMS device possesses a number of attractive features. It provides high-speed digital light modulation with high contrast and good efficiency. In addition, in a linear array of conformal GEMS devices, the active region is relatively large and the grating period is oriented perpendicular to the array direction. This orientation of the grating period causes diffracted light beams to separate in close proximity to the linear array and to remain spatially separated throughout most of an optical system.  
           [0004]    While ideal conformal GEMS devices have perfectly planar ribbon elements, fabrication, processing, and material selection can result in actual ribbon elements having an appreciable curvature. Since the ribbon elements are periodic, the ribbon curvature is also a periodic sequence. In a display system, this periodic ribbon curvature produces unintended diffracted light beams that can potentially reduce image contrast if allowed to pass through the optical system and reach the display screen. These unintended beams, referred to as diffracted cross-orders, reduce contrast because they are present even when the conformal GEMS device is in the non-actuated state. There is a need, therefore, for a high-contrast display system, based on conformal GEMS devices, that does not allow diffracted cross-orders to pass through the optical system.  
         SUMMARY OF THE INVENTION  
         [0005]    The need is met according to the present invention by providing an improved projection system that includes a conformal grating electromechanical system (GEMS) device for forming an image on a medium, and also including: a light source providing illumination; a linear array of conformal GEMS devices receiving the illumination; an obstructing element for blocking a zeroth order reflected light beam from reaching the medium; a cross-order filter placed substantially near a Fourier plane of a lens system for blocking a plurality of diffracted cross-order light beams from reaching the medium; a scanning element for moving non-obstructed diffracted light beams relative to the medium; and a controller for providing a data stream to the individually operable devices. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a perspective, partially cut-away view of two conformal GEMS devices in a linear array;  
         [0007]    [0007]FIG. 2 is a top view of four conformal GEMS devices in a linear array;  
         [0008]    [0008]FIGS. 3 a  and  3   b  are cross-sectional views through line  3 , 5 - 3 , 5  in FIG. 2, showing the operation of a conformal GEMS device in an unactuated state and an actuated state, respectively;  
         [0009]    [0009]FIGS. 4 a  and  4   b  are cross-sectional views through line  4 - 4  in FIG. 2 showing the conformal GEMS device in an unactuated state and an actuated state, respectively;  
         [0010]    [0010]FIG. 5 a  is a cross-sectional view through line  3 , 5 - 3 , 5  in FIG. 2, showing an unactuated conformal GEMS device that contains residual ribbon curvature;  
         [0011]    [0011]FIG. 5 b  is a cross-sectional view through line  4 - 4  in FIG. 2, showing an unactuated conformal GEMS device that contains residual ribbon curvature;  
         [0012]    [0012]FIG. 6 is a top view of four conformal GEMS devices in a linear array, wherein each of the devices contains two ribbon elements;  
         [0013]    [0013]FIG. 7 is a topographical representation of residual ribbon curvature in conformal GEMS devices;  
         [0014]    [0014]FIG. 8 is a three-dimensional plot of residual ribbon curvature in a single cell of FIG. 7;  
         [0015]    [0015]FIG. 9 is a schematic illustrating a line-scanned display system with high contrast according to the present invention;  
         [0016]    [0016]FIG. 10 shows a linear array of conformal GEMS devices illuminated by a line of light;  
         [0017]    [0017]FIG. 11 is a view of the projection screen that illustrates the formation of a two-dimensional image by scanning a line image across the screen;  
         [0018]    [0018]FIGS. 12 a - 12   d  are density plots of the light distribution in different planes of FIG. 9 between the linear array of conformal GEMS devices and the projection lens, wherein the devices are actuated;  
         [0019]    [0019]FIGS. 13 a - 13   d  are density plots of the light distribution in different planes of FIG. 9 after the projection lens, wherein the conformal GEMS devices are actuated;  
         [0020]    [0020]FIGS. 14 a - 14   d  are density plots 4  of the light distribution in different planes of FIG. 9 after the projection lens, wherein the conformal GEMS devices are not actuated and the ribbons have residual curvature;  
         [0021]    [0021]FIG. 15 is a schematic illustrating a three-color embodiment of a line-scanned display system with high contrast;  
         [0022]    [0022]FIG. 16 is a schematic illustrating a second three-color embodiment of a line-scanned display system with high contrast;  
         [0023]    [0023]FIG. 17 is a schematic illustrating a third three-color embodiment of a line-scanned display system with high contrast; and  
         [0024]    [0024]FIG. 18 illustrates the spatial filter used in the third three-color embodiment of FIG. 17. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    The conformal Grating Electromechanical System (GEMS) devices are illustrated in FIGS.  1 - 3 . FIG. 1 shows two side-by-side conformal GEMS devices  5   a  and  5   b  in an unactuated state. The conformal GEMS devices  5   a  and  5   b  are formed on top of a substrate  10  covered by a bottom conductive layer  12 , which acts as an electrode to actuate the devices  5   a ,  5   b . The bottom conductive layer  12  is covered by a dielectric protective layer  14  followed by a standoff layer  16  and a spacer layer  18 . On top of the spacer layer  18 , a ribbon layer  20  is formed which is covered by a reflective layer and conductive layer  22 . The reflective and conductive layer  22  provides electrodes for the actuation of the conformal GEMS devices  5   a  and  5   b . Accordingly, the reflective and conductive layer  22  is patterned to provide electrodes for the two conformal GEMS devices  5   a  and  5   b . The ribbon layer  20 , preferably, comprises a material with a sufficient tensile stress to provide a large restoring force. Each of the two conformal GEMS devices  5   a  and  5   b  has an associated elongated ribbon element  23   a  and  23   b , respectively, patterned from the reflective and conductive layer  22  and the ribbon layer  20 . The elongated ribbon elements  23   a  and  23   b  are supported by end supports  24   a  and  24   b , formed from the spacer layer  18 , and by one or more intermediate supports  27  that are uniformly separated in order to form equal-width channels  25 . The elongated ribbon elements  23   a  and  23   b  are secured to the end supports  24   a  and  24   b  and to the intermediate supports  27 . A plurality of square standoffs  29  is patterned at the bottom of the channels  25  from the standoff layer  16 . These standoffs  29  reduce the possibility of the elongated ribbon elements  23   a  and  23   b  sticking when actuated.  
         [0026]    A top view of a four-device linear array of conformal GEMS devices  5   a ,  5   b ,  5   c  and  5   d  is shown in FIG. 2. The elongated ribbon elements  23   a ,  23   b ,  23   c , and  23   d  (respectively) are depicted partially removed over the portion of the diagram below the line A-A in order to show the underlying structure. For best optical performance and maximum contrast, the intermediate supports  27  should preferably be completely hidden below the elongated ribbon elements  23   a ,  23   b ,  23   c , and  23   d . Therefore, when viewed from the top, the intermediate supports  27  should not be visible in the gaps  28  between the conformal GEMS devices  5   a - 5   d . Here, each of the conformal GEMS devices  5   a - 5   d  has three intermediate supports  27  with four equal-width channels  25 . The center-to-center separation A of the intermediate supports  27  defines the period of the conformal GEMS devices in the actuated state. The elongated ribbon elements  23   a - 23   d  are mechanically and electrically isolated from one another, allowing independent operation of the four conformal GEMS devices  5   a - 5   d . The bottom conductive layer  12  of FIG. 1 can be common to all of the conformal GEMS devices  5   a - 5   d.    
         [0027]    [0027]FIG. 3 a  is a side view, through line  3 , 5 - 3 , 5  of FIG. 2, of two channels  25  of the conformal GEMS device  5   b  (as shown and described in FIGS. 1 and 2) in an unactuated state. FIG. 3 b  shows the same view for an actuated state. For operation of the device, an attractive electrostatic force is produced by applying a voltage difference between the bottom conductive layer  12  and the reflective and conductive layer  22  of the elongated ribbon element  23   b . In the unactuated state (see FIG. 3 a ), with no voltage difference, the ribbon element  23   b  is suspended flat between the supports. In this state, an incident light beam  30  is primarily reflected into a 0th order light beam  32 , as in a simple planar mirror. To obtain the actuated state, a voltage is applied to the conformal GEMS device  5   b , which deforms the elongated ribbon element  23   b  and produces a partially conformal GEMS with period Λ. FIG. 3 b  shows the device  5   b  (as shown and described in FIGS. 1 and 2) in the fully actuated state with the elongated ribbon element  23   b  in contact with standoffs  29 . The height difference between the bottom of element  23   b  and the top of the standoffs  29  is chosen to be approximately ¼ of the wavelength λ of the incident light. The optimum height depends on the specific conformal shape of the actuated device. In the actuated state, the incident light beam  30  is primarily diffracted into the +1st order light beam  35   a  and −1st order light beam  35   b , with additional light diffracted into the +2nd order  36   a  and −2nd order  36   b . A small amount of light is diffracted into even higher orders and some light remains in the 0th order. In general, one or more of the various beams can be collected and used by an optical system, 44  depending on the application. When the applied voltage is removed, the forces due to tensile stress and bending restores the ribbon element  23   b  to its original unactuated state, as shown in FIG. 3 a.    
         [0028]    [0028]FIGS. 4 a  and  4   b  show a side view through line  4 - 4  of FIG. 2 of the conformal GEMS device  5   b  in the unactuated and actuated states, respectively. The conductive reflective ribbon element  23   b  is suspended by the end support  24   b  and the adjacent intermediate support  27  (not shown in this perspective). The application of a voltage actuates the device as illustrated in FIG. 4 b.    
         [0029]    In one embodiment, a linear array of conformal GEMS devices is formed by arranging the devices as illustrated in FIGS.  1 - 2  with the direction of the grating period Λ perpendicular to the axis of the array. The planes containing the various diffracted light beams then intersect in a line at the linear array and are distinct away from the linear array. Even with a large linear array consisting, possibly, of several thousand devices illuminated by a narrow line of light, the diffracted light beams become spatially separated in close proximity to the linear array. This feature simplifies the optical system design and allows for the selection of specific diffracted light beams without the use of Schlieren optics.  
         [0030]    The conformal GEMS devices illustrated in FIGS.  1 - 4  would, when actuated, produce non-zero diffracted orders (+1 st  order  35   a , −1 st  order  35   b , +2 nd  order  36   a  and −2 nd  order  36   b ) that have very high contrast. This ideal situation arises if, in the unactuated state, the ribbon elements  23   a ,  23   b ,  23   c  and  23   d  are suspended perfectly flat between the intermediate supports  27  and, hence, do not cause any diffraction of light into non-zero diffracted orders. In practice, ribbon elements  23   a ,  23   b ,  23   c  and  23   d  will have a certain amount of curvature because of stress differences between the ribbon layer  20 , which is typically silicon nitride, and the reflective and conductive layer  22 , which is typically aluminum. This problem is illustrated in FIGS. 5 a  and  5   b , which are similar to FIGS. 3 a  and  4   a , respectively. FIG. 5 a  is a side view, through line  3 , 5 - 3 , 5  of FIG. 2, of two channels  25  of the conformal GEMS device  5   b , with the addition of ribbon curvature. FIG. 5 b  shows a rotated side view of the same device along the direction of the ribbon width w. The ribbon curvature causes a weak grating to be present even when the conformal GEMS device  5   b  is not actuated, thus reducing system contrast. For high-quality projection displays, such as digital cinema projectors, a contrast above 1000:1 is often required. (Contrast is defined as the ratio of diffracted light intensity with the device actuated to diffracted light intensity with the device unactuated.)  
         [0031]    An alternate embodiment of conformal GEMS devices is shown in FIG. 6, which depicts a top view of a four-device linear array similar to FIG. 2. Each of the conformal GEMS devices  5   a ,  5   b ,  5   c , and  5   d  now has an associated pair of subdivided elongated conductive reflective ribbon elements ( 51   a ,  52   a ), ( 51   b ,  52   b ), ( 51   c ,  52   c ), and ( 51   d ,  52   d ), respectively. This subdivision of each conformal GEMS device  5   a ,  5   b ,  5   c , and  5   d  permits fabrication of wider conformal GEMS devices, without significantly impacting optical performance. The preferred method of fabrication is to etch a sacrificial layer (not shown) from the channel  25 , thus releasing the elongated conductive ribbon elements ( 51   a ,  52   a ), ( 51   b ,  52   b ), ( 51   c ,  52   c ), and ( 51   d ,  52   d ). The subdivided gaps  55  between the elongated conductive elements ( 51   a ,  52   a ), ( 51   b ,  52   b ), ( 51   c ,  52   c ), and ( 51   d ,  52   d ) allow the etchant to access this sacrificial layer. Increasing the number of subdivided gaps  55  can therefore improve the etching process. In practice, it may be necessary to further subdivide the conformal GEMS devices  5   a ,  5   b ,  5   c , and  5   d  into more than two. The elongated-conductive reflective ribbon elements ( 51   a ,  52   a ), ( 51   b ,  52   b ), ( 51   c ,  52   c ), and ( 51   d ,  52   d ) are depicted partially removed over the portion of the diagram below the line A-A in order to show the underlying structure. For best optical performance and maximum contrast, the intermediate supports  27  should be completely hidden below the elongated-conductive reflective ribbon elements  51   a ,  52   a ,  51   b ,  52   b ,  51   c ,  52   c ,  51   d , and  52   d . Therefore, when viewed from the top, the intermediate supports  27  should not penetrate into the subdivided gaps  55 . In general, the ribbon elements within a single conformal GEMS device are mechanically isolated, but electrically coupled. They therefore operate in unison when a voltage is applied.  
         [0032]    [0032]FIG. 7 is a top view illustration of an unactuated linear array of conformal GEMS devices  5   a - 5   d , similar to FIG. 6, with a contour map overlay of the ribbon elements&#39; surface profile showing ribbon curvature. Each cell  54  within the elongated-conductive ribbon elements  51   a ,  52   a ,  51   b ,  52   b ,  51   c ,  52   c ,  51   d , and  52   d  has a saddle-like shape, shown in more detail in the three-dimensional plot of FIG. 8. As visible in the top view of FIG. 7, cells  54  form a two-dimensional periodic pattern that acts as a reflective crossed grating. Typically, in manufactured conformal GEMS devices, the peak-to-peak height of the crossed grating is less than 40 nm, i.e., less than a tenth of a wavelength for visible wavelengths. The period of the crossed grating along the length of the elongated-conductive reflective ribbon elements  51   a - 51   d  and  52   a - 52   d  is equal to the conformal GEMS period Λ, as determined by the placement of the intermediate supports  27 . The period of the crossed grating in the perpendicular direction is the ribbon period p.  
         [0033]    As described in co-pending U.S. patent application Ser. No. Docket #80,511B (CIP), the saddle-like shape of each cell  54  can be significantly flattened by careful refinement of the manufacturing process, thus reducing the peak-to-peak height of the weak crossed grating. A display system based on a linear array of conformal GEMS devices was described by Kowarz et al. in U.S. patent application Ser. No. 09/671,040, entitled Electromechanical Grating Display System with Spatially Separated Light Beam, filed Sep. 27, 2000. However, when conformal GEMS devices with appreciable ribbon curvature are used in the display system of U.S. Ser. No. 09/671,040, the diffracted cross-orders reduce image contrast. To further improve image contrast in a system, the diffracted light (cross-orders) generated by the crossed grating can be prevented from reaching the image plane.  
         [0034]    [0034]FIG. 9 shows a high-contrast display system  900  containing a linear array  85  of conformal GEMS devices that eliminates the contrast-reducing cross-orders. Light emitted from a source  70  is conditioned by a pair of lenses  72  and  74 , before hitting a turning mirror  82  and illuminating the linear array  85 . The display system  900  forms an entire two-dimensional scene from a scan of a one-dimensional line image of the linear array  85  across the screen  90 . The conformal GEMS devices of the linear array  85  are capable of rapidly modulating incident light to produce multiple lines of pixels with gray levels. The controller  80  selectively activates the linear array  85  to obtain the desired pixel pattern for a given line of a two-dimensional scene. If a particular conformal GEMS device is not actuated, it reflects the incident light beam primarily into the 0th order light beam, which is directed back towards the source  70  by the turning mirror  82 . If a particular conformal GEMS device is actuated, it diffracts the incident light beams primarily into +2 nd , +1 st , −1 st  and −2 nd  order light beams. These diffracted light beams pass around the turning mirror  82  and are projected on the screen  90  by the projection lens system  75 . A cross-order filter  110  placed near the Fourier (focal) plane “f” of the projection lens system  75  prevents the undesirable diffracted cross-orders from reaching the screen  90 . The function of the cross-order filter  110  is described later in more detail. The scanning mirror  77  sweeps the line image across the screen  90  to form the two-dimensional scene. The controller  80  provides synchronization between the sweep of the scanning mirror  77  and a data stream that provides the scene content.  
         [0035]    [0035]FIG. 10 depicts a linear array  85  of conformal GEMS devices (P1 . . . P1080) illuminated by a line of light  88  parallel to the long axis of the linear array  85 . For illustration purposes, there are 1080 individually operable conformal GEMS devices shown, labeled P1 through P1080. The grating period Λ (not shown) is preferably perpendicular to the long axis of the linear array  85  and to the line of light  88 . FIG. 11 is a view facing the screen  90  of the display system  900 , shown in FIG. 9, and depicts the formation of the two-dimensional scene. In this illustration, HDTV resolution is obtained by scanning the image of the linear array  85  of 1080 conformal GEMS devices to generate 1920 sequential lines, thereby producing a scene with 1080 by 1920 pixels.  
         [0036]    [0036]FIGS. 12 a - 12   d  illustrate the propagation of the diffracted light beams through the display system  900  of FIG. 9 in several planes prior to the projection lens system  75 . Continuing, FIGS. 13 a - 13   d  show the light distribution after the projection lens system  75 . In this example, the light source  70  is a laser, the lens has a focal length f of 50 mm, the linear array is 1 cm long and all of the conformal GEMS devices on the linear array  85  are turned on. As the various diffracted light beams propagate from one plane to the next, they spread out in a direction perpendicular to the axis of the linear array  85 . Here D refers to the distance between the linear array  85  to the plane of interest. The diffracted beams become spatially separated within a few millimeters from the linear array  85  and remain spatially separated throughout the display system  900 , except near the screen  90  (and any intermediate image planes of the linear array  85 ). FIG. 12 d  shows the light distribution at the turning mirror  82 , which is located close to the projection lens system  75 . The turning mirror 82 blocks the unwanted 0 th  diffracted order and reflects it back towards the source  70 . In this example, six diffracted orders from −3 rd  to −1 st  and +1 st  to +3 rd  are allowed to pass through the projection lens system  75 . FIGS. 13 a - 13   d  show these diffracted orders after they have gone through the projection lens system  75 . Near the Fourier plane (D=100 mm), the diffracted orders are tightly focused into six spots. It is, therefore, preferable to place the scanning mirror  77  close to the Fourier plane to minimize its size and weight. Eventually, as the six diffracted orders continue propagating towards the screen  90 , they again become overlapping spatially near the image plane at the screen  90 .  
         [0037]    [0037]FIGS. 12 a - 12   d  and  13   a - 13   d  describe light propagation through the display system  900  of FIG. 9 when all of the conformal GEMS devices of the linear array  85  are turned on. Obviously, when the conformal GEMS devices are turned off, any light that is not obstructed will reduce the contrast and quality of the image on the screen  90 . FIGS. 14 a - 14   d  illustrate the off-state light distribution in several planes after the projection lens system  75  of FIG. 9. The conformal GEMS devices modeled in FIGS. 14 a - 14   d  have ribbon curvature that produces a weak crossed grating. Some light is still present in the primary +1 st  and −1 st  orders. However, because the conformal GEMS devices are off, the intensity of these orders is substantially less, often by a factor of 1000 or more, than the corresponding orders in FIGS. 12 a - 12   d  and  13   a - 13   d . The higher orders, 3 rd , −2 nd , +2 nd  and +3 rd , are now reduced to the point that they are not visible in the figures. The crossed grating generates four dominant diffracted cross-orders labeled (+1, +1), (+1, −1), (−1, +1) and (−1, −1) in FIGS. 14 b  and  14   c . As shown in FIG. 14 c , by placing a cross-order filter  110  substantially near the Fourier plane of the projection lens system  75 , the aforementioned four cross-orders can be separated and blocked while leaving the desired diffracted orders unaffected. In order to effectively separate the diffracted cross-orders from the primary +1 st  and −1 st  orders, the cross-order filter should be placed at a distance less than approximately (f 2 λ)/(L Λ) from the Fourier plane, where λ is the wavelength and L is the length of the linear array  85 . The cross-order filter  110  increases system contrast without substantially decreasing optical efficiency. The contrast improvement enabled by the addition of the cross-order filter  110  depends on the exact profile of the crossed grating, i.e., on the specific saddle-like shape of each cell  54 .  
         [0038]    Clearly, there are two kinds of light beams in display system  900 : (1) those that are blocked by obstructing elements from reaching the screen  90 , and (2) those that pass around obstructing elements to form an image on the screen  90 . In the system of FIG. 9, the obstructing elements are the turning mirror  82  that blocks the 0 th  order light beam and the cross-order filter  110  that blocks the (+1, +1), (+1, −1), (−1, +1) and (−1, −1) diffracted cross-orders. In subsequent embodiments, similar obstructing elements are used to prevent unwanted diffracted light beams from reaching the screen. As is well known to those skilled in the art, a variety of elements may be used for this purpose. For example, cross-order filter  110  could be an absorbing stop or a pair of tilted mirrors. Alternatively, the scanning mirror  77  could be designed so that the diffracted cross-orders pass above and below the mirror edges, therefore, never becoming part of the image. This appropriately-sized scanning mirror  77  would then also function as a cross-order filter.  
         [0039]    In general, to effectively separate and obstruct the various diffracted light beams, the light illuminating the linear array of conformal GEMS devices needs to have a relatively small spread in angles of incidence. For example, if the conformal GEMS devices have a period of 30 microns and the illuminating wavelength is 532 nm, the angular separation between the 0 th  order light beam and the +1 st  order light beam is approximately 1 degree. Therefore, the total angular spread of the light incident upon the linear array should be less than 1 degree, in the plane perpendicular to the linear array. Similarly, in order to create distinct diffracted cross-orders at the Fourier plane of the projection lens, the angular spread of the incident light should also be sufficiently narrow in the plane parallel to the linear array. A coherent laser is the most optically efficient source for generating light with such a narrow range of incident angles. For incoherent sources, such as filament lamps and light emitting diodes, a vast majority of the optical power would be wasted by the illumination system in the process of generating the required illumination.  
         [0040]    The embodiment of FIG. 9 can be used either for single color or for color-sequential display systems. For a color-sequential display, the light source  70  produces a plurality of colors that are sequential in time and the controller  80  is synchronized with the light source  70 . For example, if the light source  70  consists of three combined red, green, and blue lasers, these are turned on sequentially to produce overlapping red, green, and blue images on the screen  90 . The image data sent by the controller  80  to the linear array  85  is synchronized with the respective turned-on laser color.  
         [0041]    Color-sequential display systems waste two-thirds of the available light because only one color is used at a time. FIGS. 15, 16, and  17  depict embodiments of the invention that project three colors simultaneously, (for example, red, green, and blue). In FIG. 15, three separate light sources  70   r ,  70   g ,  70   b , each with their own illumination optics  72   r ,  72   g ,  72   b ,  74   r ,  74   g ,  74   b , provide light to the three linear arrays  85   r ,  85   g ,  85   b  via three turning mirrors  82   r ,  82   g ,  82   b . Red light illuminates linear array  85   r , green light linear array  85   g  and blue light linear array  85   b . The −3 rd , −2 nd , −1 st , +1 st , +2 nd , and +3 rd  order light beams emerging from the three linear arrays  85   r ,  85   g ,  85   b , are combined by a color-combining element, shown as a color-combining cube  100  in FIG. 15. The 0 th  order light beams are directed towards their respective sources by the turning mirrors  82   r ,  82   g ,  82   b . A single projection lens system  75  forms a three-color line image of the three linear arrays  85   r ,  85   g ,  85   b  on the screen  90  (not shown in figure). As before, the sweep of the scanning mirror  77  (not shown in figure) generates a two-dimensional image from the line image. To increase system contrast, cross-orders are removed by the cross-order filter  110  at the Fourier plane of the projection lens  75 .  
         [0042]    [0042]FIG. 16 shows an alternate color-simultaneous embodiment in which the three turning mirrors  82   r ,  82   g ,  82   b  of FIG. 15 are replaced by polarization beam splitters  114   r ,  114   g ,  114   b  with ¼ wave plates  116   r ,  116   g ,  116   b  and 0 th  order stops  118   r ,  118   g ,  118   b . The combination of polarization beam splitter, ¼ wave plate and 0 th  order stop provides easier alignment tolerances than when the illumination and obstruction functions are combined, as in the turning mirror solution. For further system flexibility, the system of FIG. 16 contains three separate projection lenses  75   r ,  75   g ,  75   b.    
         [0043]    [0043]FIG. 17 shows a variation of the system in FIG. 16 in which a single spatial filter  111  placed at the Fourier plane of the projection lenses  75   r ,  75   g ,  75   b  replaces the three 0 th  order stops  118   r ,  118   g ,  118   b  and the cross-order filter  110 . As shown in FIG. 18, the spatial filter  111  has a 0 th  order portion  111   b  to block 0 th  order light beams and a cross-order portion  111   a  to block cross-orders.  
         [0044]    Although the above embodiments describe display systems, the same principles can be used to implement high-contrast printing systems based on linear arrays of conformal GEMS devices. Instead of a screen  90 , the image medium would be a light reactive material, such as photographic paper, thermally activated media, or thermal transfer media. Furthermore, the scanning mirror  77  would typically be replaced by a paper transport system that serves as the scanning element. A more detailed description of conformal GEMS printing systems is found in U.S. patent application Ser. No. 09/671,040.  
         [0045]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       Parts List  
       [0046]    [0046] 5   a  conformal GEMS device  
         [0047]    [0047] 5   b  conformal GEMS device  
         [0048]    [0048] 5   c  conformal GEMS device  
         [0049]    [0049] 5   d  conformal GEMS device  
         [0050]    [0050] 10  substrate  
         [0051]    [0051] 12  bottom conductive layer  
         [0052]    [0052] 14  dielectric protective layer  
         [0053]    [0053] 16  standoff layer  
         [0054]    [0054] 18  spacer layer  
         [0055]    [0055] 20  ribbon layer  
         [0056]    [0056] 22  reflective and conductive layer  
         [0057]    [0057] 23   a  elongated ribbon element  
         [0058]    [0058] 23   b  elongated ribbon element  
         [0059]    [0059] 23   c  elongated ribbon element  
         [0060]    [0060] 23   d  elongated ribbon element  
         [0061]    [0061] 24   a  end support  
         [0062]    [0062] 24   b  end support  
         [0063]    [0063] 25  channel  
         [0064]    [0064] 27  intermediate support  
         [0065]    [0065] 28  gap  
         [0066]    [0066] 29  standoff  
         [0067]    [0067] 30  incident light beam  
         [0068]    [0068] 32  0 th  order light beam  
         [0069]    [0069] 35   a  +1 st  order light beam  
         [0070]    [0070] 35   b  1 st  order light beam  
         [0071]    [0071] 36   a  +2 nd  order light beam  
         [0072]    [0072] 36   b  −2 nd  order light beam  
         [0073]    [0073] 51   a  elongated conductive ribbon element  
         [0074]    [0074] 51   b  elongated conductive ribbon element  
         [0075]    [0075] 51   c  elongated conductive ribbon element  
         [0076]    [0076] 51   d  elongated conductive ribbon element  
         [0077]    [0077] 52   a  elongated conductive ribbon element  
         [0078]    [0078] 52   b  elongated conductive ribbon element  
         [0079]    [0079] 52   c  elongated conductive ribbon element  
         [0080]    [0080] 52   d  elongated conductive ribbon element  
         [0081]    [0081] 54  cell  
         [0082]    [0082] 55  subdivided gaps  
         [0083]    [0083] 70  light source  
         [0084]    [0084] 70   r  light source  
         [0085]    [0085] 70   g  light source  
         [0086]    [0086] 70   b  light source  
         [0087]    [0087] 72  lens  
         [0088]    [0088] 72   r  illumination optics  
         [0089]    [0089] 72   g  illumination optics  
         [0090]    [0090] 72   b  illumination optics  
         [0091]    [0091] 74  lens  
         [0092]    [0092] 74   r  illumination optics  
         [0093]    [0093] 74   g  illumination optics  
         [0094]    [0094] 74   b  illumination optics  
         [0095]    [0095] 75  projection lens system  
         [0096]    [0096] 75   r  projection lens  
         [0097]    [0097] 75   g  projection lens  
         [0098]    [0098] 75   b  projection lens  
         [0099]    [0099] 77  scanning mirror  
         [0100]    [0100] 80  controller  
         [0101]    [0101] 82  turning mirror  
         [0102]    [0102] 82   r  turning mirror  
         [0103]    [0103] 82   g  turning mirror  
         [0104]    [0104] 82   b  turning mirror  
         [0105]    [0105] 85  linear array  
         [0106]    [0106] 85   r  linear array  
         [0107]    [0107] 85   g  linear array  
         [0108]    [0108] 82   b  linear array  
         [0109]    [0109] 88  line of light  
         [0110]    [0110] 90  screen  
         [0111]    [0111] 100  color-combining cube  
         [0112]    [0112] 110  cross-order filter  
         [0113]    [0113] 111  spatial filter  
         [0114]    [0114] 111   a  cross-order portion of spatial filter  
         [0115]    [0115] 111   b  zeroth-order portion of spatial filter  
         [0116]    [0116] 114   r  polarization beam splitter  
         [0117]    [0117] 114   g  polarization beam splitter  
         [0118]    [0118] 114   b  polarization beam splitter  
         [0119]    [0119] 116   r  ¼ waveplate  
         [0120]    [0120] 116   g ¼ waveplate  
         [0121]    [0121] 116   b ¼ waveplate  
         [0122]    [0122] 118   r  zeroth-order stop  
         [0123]    [0123] 118   g  zeroth-order stop  
         [0124]    [0124] 118   b  zeroth-order stop  
         [0125]    [0125] 900  display system

Technology Category: 3