Abstract:
A display system, including: a light source providing illumination; a linear array of electromechanical grating devices of at least two individually operable devices receiving the illumination wherein a grating period is oriented at a predetermined angle with respect to an axis of the linear array wherein the angle is large enough to separate diffracted light beams prior to a projection lens system for projecting light onto a screen; a polarization sensitive element that passes diffracted light beams according to their polarization state; a segmented waveplate for altering the polarization state of a discrete number of selected diffracted light beams wherein the segmented waveplate is located between the linear array and the polarization sensitive element, a scanning element for moving the selectively passed diffracted light beams on the screen; and a controller for providing a data stream to the individually operable devices.

Description:
FIELD OF THE INVENTION 
     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 an electromechanical grating display system that uses a segmented waveplate to select diffracted light beams for projection onto a screen. 
     BACKGROUND OF THE INVENTION 
     Spatial light modulators consisting of an array of high-speed electromechanical phase gratings are important for a variety of systems, including display, optical processing, printing, optical data storage and spectroscopy. Each of the devices on the array can be individually controlled to selectively reflect or diffract an incident light beam into a number of light beams of discrete orders. Depending on the application, one or more of the modulated light beams may be collected and used by the optical system. 
     Electromechanical phase gratings can be formed in metallized elastomer gels. The electrodes below the elastomer are patterned so that the application of a voltage deforms the elastomer producing a nearly sinusoidal phase grating. These types of devices have been successfully used in color projection displays; see  Metallized viscoelastic control layers for light -valve projection displays, by Brinker et al., Displays 16, 1994, pp. 13-20, and  Full - colour diffraction - based optical system for light - valve projection displays,  by 
     Roder et al., Displays 16, 1995, pp. 27-34. 
     An electromechanical phase grating with a much faster response time can be made of suspended micromechanical ribbon elements, as described in U.S. Pat. No. 5,311,360, issued May 10, 1994 to Bloom et al., entitled Method and Apparatus for Modulating a Light Beam. This device, also known as a grating light valve (GLV), can be fabricated with CMOS-like processes on silicon. For display or printing, linear arrays of GLV devices can be used with a scanning Schlieren optical system as described in U.S. Pat. No. 5,982,553, issuedNov. 9, 1999 to Bloom et al., entitled Display Device Incorporating One-Dimensional Grating Light-Valve Array. Alternatively, an interferometric optical system can be used to display an image as disclosed in U.S. Pat. No. 6,088,102, issued Jul. 11, 2000 to Manhart, entitled Display Apparatus Including Grating Light-Valve Array and Interferometric Optical System. In the scanning Schlieren display system of Bloom et al. &#39;553, the plane of diffraction that contains the diffracted light beams is parallel to the axis of the linear GLV array because the grating period is parallel to the axis. This feature increases the cost and complexity of the display system. Specifically, efficient collection of the primary diffracted light beams requires at least one dimension of the optical elements to be significantly larger than the extent of the linear GLV array. Furthermore, the diffracted and reflected light beams overlap spatially throughout most of the optical system. Separation of diffracted light from reflected light is accomplished in close proximity to a Fourier plane of the Schlieren optical system. However, the Fourier plane is also usually the preferred location of a scanning mirror for producing a two-dimensional image. 
     Recently, a linear array of electromechanical conformal grating devices was disclosed by Kowarz, in U.S. Ser. No. 09/491,354, filed Jan. 26, 2000. For this class of devices, it is preferable to have the grating period perpendicular to the axis of the linear array. The diffracted light beams are then spatially separated throughout most of the optical system. In U.S. Ser. No. 09/491,354, it was mentioned that a simplified display system can be designed based on this type of spatial light modulator. However, no specific description of the display system was given. There is a need therefore for a scanning display system that utilizes a linear array of electromechanical conformal grating devices. Furthermore, there is a need for a display system that is simpler and less costly than other known systems. 
     SUMMARY OF THE INVENTION 
     The need is met according to the present invention by providing a display system that includes: a light source providing illumination; a linear array of electromechanical grating devices of at least two individually operable devices receiving the illumination wherein a grating period is oriented at a predetermined angle with respect to an axis of the linear array wherein the angle is large enough to separate diffracted light beams prior to a projection lens system for projecting light onto a screen; a polarization sensitive element that passes diffracted light beams according to their polarization state; a segmented waveplate for altering the polarization state of a discrete number of selected diffracted light beams wherein the segmented waveplate is located between the linear array and the polarization sensitive element; a scanning element for moving the selectively passed diffracted light beams on the screen; and a controller for providing a data stream to the individually operable devices. 
     The present invention has several advantages, including: 1) improvement in contrast by eliminating reflections from the projection lens, because such reflections are directed away from the screen; 2) reduction in size of the scanning mirror, because now the scanning mirror can be placed directly at the Fourier plane; 3) increase in design flexibility, because now selection and separation of diffracted orders can take place almost anywhere in the system, rather than solely at the Fourier plane; and 4) reduction in size of lenses and other optical elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective, partially cut-away view of a spatial light modulator with electromechanical conformal grating devices, showing two devices in a linear array; 
     FIG. 2 is a top view of a spatial light modulator with electromechanical conformal grating devices, showing four individually operable devices in a linear array; 
     FIGS. 3 a  and  3   b  are cross-sectional views through line III—III in FIG. 2, showing the operation of an electromechanical conformal grating device in an unactuated state and an actuated state, respectively; 
     FIGS. 4 a  and  4   b  show the operation of a conventional electromechanical two-level grating device in an unactuated state and an actuated state, respectively; 
     FIG. 5 is a top view of a spatial light modulator with conventional GLV devices, showing five individually operable devices in a linear array with deformable ribbon elements oriented perpendicular to the axis of the array and the grating period oriented parallel to the axis; 
     FIG. 6 is a top view of a spatial light modulator with conventional GLV devices, showing five individually operable devices in a linear array with deformable ribbon elements oriented parallel to the axis of the array and the grating period oriented perpendicular to the axis; 
     FIG. 7 is a schematic illustrating a prior art, line-scanned Schleiren display system that includes a light source, illumination optics, a linear array of conventional GLV devices, a projection lens, a scanning mirror, a controller, and a turning mirror located at the Fourier plane of the projection lens; 
     FIG. 8 is a schematic illustrating a line-scanned display system that includes a light source, illumination optics, a linear array of electromechanical conformal grating devices, a projection lens, a scanning mirror, a controller, and a turning mirror located between the linear array and the projection lens; 
     FIG. 9 shows a linear array of electromechanical conformal grating devices illuminated by a line of light; 
     FIG. 10 is a view of the projection screen that illustrates the formation of a two-dimensional image by scanning a line image across the screen; 
     FIGS. 11 a - 11   h  are density plots of the light distribution in different planes of a prior art, line-scanned Schleiren display system in which the modulator is a linear array of conventional GLV devices with deformable ribbon elements oriented perpendicular to the axis of the array; 
     FIGS. 12 a - 12   h  are density plots of the light distribution in different planes of a line-scanned display system in which the modulator is a linear array of electromechanical conformal grating devices; 
     FIG. 13 is a schematic illustrating an embodiment of the display system in which the turning mirror is placed between the first projection lens and the scanning mirror, and an intermediate image plane is formed in the system; 
     FIG. 14 is a schematic illustrating an embodiment of the display system that includes a polarization beamsplitter and a segmented waveplate for separating +1 st  and −1 st  order light beams from the 0 th  order light beam; 
     FIG. 15 a  shows the segmented waveplate for order separation; 
     FIG. 15 b  shows an alternate version of the segmented waveplate for order separation; 
     FIG. 16 is a schematic illustrating a color, line-scanned display system that includes a three-color light source, illumination optics, a color combination cube, three linear arrays of electromechanical conformal grating devices, three projection lenses, a scanning mirror, a polarization beamsplitter, and three segmented waveplates for separating +1 st  and −1 st  order light beams from 0 th  order light beams; 
     FIG. 17 is a schematic illustrating a color, line-scanned display system with a single multi-color segmented waveplate; 
     FIG. 18 shows the multi-color segmented waveplate for order separation; 
     FIG. 19 is a schematic illustrating an alternate embodiment of a color, line-scanned display system with three segmented waveplates; and 
     FIG. 20 is a schematic illustrating a printer system that includes a polarization beamsplitter and a segmented waveplate for separating +1 st  and −1 st  order light beams from the 0 th  order light beam. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The structure and operation of an electromechanical conformal grating device is illustrated in FIGS. 1-3. FIG. 1 shows two side-by-side conformal grating devices  5   a  and  5   b  in an unactuated state. In this embodiment, the devices can be operated by the application of an electrostatic force. The grating 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 conformal grating devices  5   a  and  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  22 . The reflective layer  22  is also a conductor in order to provide electrodes for the actuation of the conformal grating devices  5   a  and  5   b . The reflective and conductive layer  22  is patterned to provide electrodes to the two conformal grating 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 grating 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 four 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 ribbon elements  23   a  and  23   b  sticking when actuated. 
     A top view of a four-device linear array of conformal grating devices  6   a ,  6   b ,  6   c , and  5   d  is shown in FIG.  2 . The elongated ribbon elements  23   a ,  23   b ,  23   c , and  23   d  are depicted partially removed over the portion of the diagram below the line III—III in order to show the underlying structure. For best optical performance and maximum contrast, the intermediate supports  27  must 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  must not be visible in the gaps  28  between the conformal grating devices  5   a - 5   d . Here each of the conformal grating 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 grating devices  5   a - 5   d  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 grating devices  5   a - 5   d . The bottom conductive layer  12  of FIG. 1 can be common to all of the devices. 
     FIG. 3 a  is a side view, through line III—III of FIG. 2, of two channels of the conformal grating device  5   b  (as shown and described in FIG. 1) in the unactuated state. FIG. 3 b  shows the same view of the 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, conducting 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 end supports  24   a  and  24   b . In this state, an incident light beam  30  is primarily diffracted into a 0th order light beam  32  in the mirror direction. To obtain the actuated state, a voltage is applied to the conformal grating device  6   b , which deforms the elongated ribbon element  23   b  and produces a partially conformal grating with period Λ. FIG. 3 b  shows the conformal grating device  5   b  (as shown and described in FIG. 1) in the fully actuated state with the elongated ribbon element  23   b  in contact with the 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 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  36   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 is diffracted into the 0th order. One or more of the diffracted beams can be collected and used by the optical system, depending on the application. When the applied voltage is removed, the forces due to the tensile stress and bending restores the ribbon element  23   b  to its original unactuated state. 
     A linear array of conformal grating devices is formed by arranging the devices as illustrated in FIGS. 1-3 with the direction of the grating period A along the y direction and perpendicular to the axis of the array (i.e., the x direction). For a given incident angle, the planes containing the various diffracted light beams are distinct. These planes all intersect in a line at 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 over a relatively short distance. This feature simplifies the optical system design and enables feasible designs in which the separation of diffracted light beams can be done spatially without Schlieren optics. 
     A conventional Grating Light Valve (GLV) is shown in FIGS. 4 a  and  4   b . FIG. 4 a  depicts the ribbon structure of the device in the unactuated state and FIG. 4 b  in the actuated state. For operation of the device, an attractive electrostatic force is produced by a voltage difference between the bottom conductive layer  42  and the reflective and conductive layer  48  atop the ribbon element  46 . In the unactuated state, with no voltage difference, all of the ribbon elements  46  in the GLV device are suspended above the substrate  40  at the same height. In this state, an incident light beam  54  is primarily reflected as from a mirror to form a 0th order diffracted light beam  55 . To obtain the actuated state (see FIG. 4 b ), a voltage is applied to every other ribbon element  46  producing a grating. In the fully actuated state, every other ribbon element  46  is in contact with the protective layer  44 . When the height difference between adjacent ribbon elements is ¼ of the wavelength of an incident light beam  56 , the light beam is primarily diffracted into a +1st order light beam  57  and a −1st order light beam  58 . One or more of the diffracted beams can be collected and used by an optical system, depending on the application. When the applied voltage is removed, the force due to the tensile stress restores the ribbon elements  46  to their original unactuated state (see FIG. 4 a ). 
     The table below summarizes the key differences between a conformal grating device and a conventional GLV for a single device of each type. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Conformal grating device 
                 Conventional GLV 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 # of moving ribbons 
                 1 
                 3-6 
               
               
                 # of stationary ribbons 
                 none 
                 3-6 
               
               
                 Number of channels 
                 &gt;5 
                 1 
               
               
                 Grating period direction 
                 Parallel to ribbon length 
                 Perpendicular to 
               
               
                   
                   
                 ribbon length 
               
               
                 Grating profile 
                 Smoothly varying 
                 Square (binary) 
               
               
                   
               
             
          
         
       
     
     It should be noted that the parameters above pertain to the preferred forms of each of the devices. 
     In a linear array made from conventional GLV devices, the ribbon elements are usually all arranged parallel to each other. FIG. 5 shows the top view of a portion of such a linear array. In this example, each of 5 devices  45   a ,  45   b ,  45   c ,  45   d  and  45   e  contains 4 movable ribbon elements  46   a  that are electrically connected to each other and 4 stationary ribbon elements  46   b  that are connected to ground. The application of a voltage to a device causes the movable ribbon elements  46   a  belonging to that device to actuate in unison into the channel  50 . The grating period Λformed by the actuated ribbons is parallel to the axis of the array and perpendicular to the length of the ribbon elements  46   a  and  46   b . The diffracted light beams then overlap spatially over a relatively long distance. 
     As a comparative example between the two types of linear arrays, let us consider an array of conformal grating devices that is 4 cm long (2000 devices 20 μm wide) illuminated by a 100 μm wide line of light. For devices with a period chosen such that the diffracted orders are angularly separated by 1 degree, the orders will become spatially separated in approximately 6 mm. This rapid separation of diffracted orders occurs because the grating period is perpendicular to the axis of the linear array of conformal grating devices and is parallel to the length of the ribbon elements. A similar 4 cm linear array of prior art GLV devices with a 4 degree angular separation between diffracted orders would require at least 60 cm for spatial separation, without the use of a Schlieren optical system. This relatively slow order separation occurs because the grating period is parallel to the axis of the linear array of GLV devices. 
     A linear array of GLV devices can also be constructed with the ribbon elements perpendicular to the axis of the array as illustrated in FIG.  6 . Each of the 5 devices  62   a ,  62   b ,  62   c ,  62   d  and  62   e  is individually operable and has its own channel  60   a ,  60   b ,  60   c ,  60   d  and  60   e . For such a GLV array, the grating period Λis perpendicular to the axis of the array and the diffracted light beams become spatially separated over a relatively short distance. However, this type of GLV array suffers from the existence of significant gaps between devices that cause some pixelation in the display. 
     FIG. 7 shows a GLV-based display system of the prior art that has a Schlieren optical system. The linear array  85  consists of GLV devices of the type shown in FIG.  5 . Light is emitted from a source  70  and passes through a spherical lens  72  and a cylindrical lens  74  before hitting a turning mirror  82 . The turning mirror  82  is placed at the Fourier (focal) plane of a projection lens system  75 . Although only a single lens element is shown, in practice, the projection lens system will consist of multiple elements. Light reflected by the turning mirror  82  is focused by the projection lens system  75  into a line illuminating the linear array  85 . A small portion of the illumination that strikes the projection lens system  75  will be reflected. In order to avoid a reduction in the contrast of the display system from such reflections, the projection lens system  75  needs to have very good optical coatings and/or needs to be used off-axis. The GLV devices of the linear array  85  are selectively activated by the controller  80  to correspond to a line of pixels. If a particular device of the array is actuated by application of a voltage to the ribbon elements, it diffracts light primarily into +1st order and −1st order light beams. If a particular device is not actuated, it diffracts light primarily into the 0th order light beam. These three primary light beams are collected by the same projection lens  75 , which focuses the three light beams into distinct spots at the Fourier plane. The 0th order light beam hits the turning mirror  82  and is reflected towards the light source  70 . The +1st and −1st order light beams pass above and below the turning mirror  82  and strike a scanning mirror  77  that sweeps the light beams across a screen  90  to form a viewable two-dimensional image. Higher-order light beams also show up as spots in the Fourier plane and can be blocked from reaching the screen  90  by a stop in the Fourier plane (not shown). The controller  80  synchronizes the sweep of the scanning mirror  77  with the actuation of the devices of the linear array  85 . 
     In the prior art display system of FIG. 7, in order to effectively separate the +1st and −1st order light beams from the 0th order light beam, the turning mirror  82  must be placed near the Fourier plane of the projection lens system  75 , i.e., it must be located at approximately the focal distance f from the lens. However, this location is also best for placing the scanning mirror  77  because the +1st and −1st order light beams are tightly focused here, allowing for a reduction in the size and weight of the scanning mirror  77 . 
     FIGS. 8-10 illustrate a display system with a turning mirror  82  placed between the linear array  85  and the projection lens system  75 . Light emitted by source  70  is conditioned by a spherical lens  72  and a cylindrical lens  74  before hitting the turning mirror  82  and focusing on the linear array  85 . In this system, the axis of the cylindrical lens  74  is rotated 90 degrees with respect to the cylindrical lens  74  in FIG.  7 . By placing the turning mirror  82  between the linear array  85  and the projection lens system  75 , the contrast-reducing reflections of the prior art system of FIG. 7 are eliminated because the illuminating light beam never passes through the projection lens system  75 . FIG. 9 shows the linear array  85  illuminated by a line of light  88 . In this particular example there are 17 electromechanical conformal grating devices shown. In practice, there would be hundreds or thousands of devices. The controller  80  selects the devices to be actuated based on the desired pixel pattern for a given line of a two-dimensional image. If a particular device is not actuated, it diffracts the incident light beam primarily into the 0th order light beam, which subsequently hits the turning mirror  82  and is reflected towards the source  70 . If the device is actuated, it diffracts the incident light beams primarily into +1st order and −1st order light beams. These two first-order diffracted light beams pass around the turning mirror  82  and are projected on the screen  90  by the projection lens system  75 . Higher-order diffracted light beams can be blocked by the addition of a stop  83 . The scanning mirror  77  sweeps the line image across the screen  90  to form the two-dimensional image. Preferably, the scanning mirror  77  is placed near the Fourier plane of the projection lens system  75 . FIG. 10 is a view facing the screen  90  showing the formation of a two-dimensional image from a series of 1080 sequential line scans. 
     Clearly, there are two kinds of diffracted light beams in this display system: those that are blocked by obstructing elements from reaching the screen  90  and those that pass around obstructing elements to form an image on the screen  90 . In this particular system, the obstructing elements are the turning mirror  82  that blocks the 0th order light beam and the stops  83  that block the ±2nd, ±3rd, ±4th . . . orders of light. As will be explained later, according to the present invention, the combination of a polarization sensitive element, such as a beamsplitter, and a segmented waveplate can be used as an alternate method for choosing the diffracted light beams that are allowed to reach the screen  90 . 
     The linear array  85  is preferably constructed of electromechanical conformal grating devices of the type shown in FIGS. 1-3. It may also be constructed of GLV devices of the type shown in FIG. 6, or of other kinds of electromechanical grating devices. However, in order to place the turning mirror  82  before the projection lens system  75 , the grating period Λmust be rotated at a sufficiently large angle with respect to the long axis of the linear array  85 . For the electromechanical conformal grating devices of FIGS. 1-3 and the GLV devices of FIG. 6, this angle is 90 degrees. A lesser angle can also be used so long as the diffracted orders become separated before reaching the projection lens system  75 . It is impractical, however, to make this type of display system with no rotation between the grating period and the axis of the linear array  85 . Therefore, a conventional linear array of GLV devices of the type shown in FIG. 5 cannot be used with this kind of system. 
     The significant differences between the display system of the prior art (FIG. 7) and the display system of FIG. 8 can be understood by examining the propagation of the diffracted light beams throughout the two systems. FIGS. 11 a - 11   h  show the amplitude of the diffracted light beams along several parallel planes between the linear array  85  and the screen  90  for the prior art system of FIG.  7 . In this modeled example, the lens has a focal length f of 50 mm, the linear array is 1 cm long. D refers to the distance between the linear array  85  to the plane of interest. As the diffracted light beams emerge from the linear array  85 , they begin to spread along the direction of the axis of the linear array as illustrated in FIGS. 11 a - 11   d . The interference between the various diffracted beams causes a rapid variation in the intensity known to those skilled in the art as tilt fringes. At the plane just before the projection lens (see FIG. 11 d ), the diffracted light beams have spread to about twice the length of the linear array. The lens must be large enough to avoid truncating the diffracted light beams to be projected on the screen, which are the −1st and +1st order light beams in this case. After passing through the projection lens system  75 , the beams begin to focus. At a distance of D=90 mm from the linear array  85 , the various diffracted orders are spatially separated. Distinct spots are visible that correspond to the +3rd, +2nd, +1st, 0th , −1st, −2nd and −3rd orders (see FIG. 11 g ). At the Fourier plane (D=100 mm), the turning mirror  82  blocks the 0th order light beam and a stop blocks the +3rd, +2nd, −2nd and −3rd orders. The +1st and −1st order light beams continue towards the screen  90  where they overlap spatially to form the line image. It is important to note that the various order light beams are only spatially separated near the Fourier plane (near D=100 mm). Therefore, only the vicinity of this plane is available for separating the +1st and −1st order light beams from the rest of the diffracted orders. 
     FIGS. 12 a - 12   h  show the amplitude of the diffracted light beams along several parallel planes for the display system of FIG.  8 . In contrast to the prior art display system, 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 . They become spatially separated a few millimeters from the linear array  85  and remain spatially separated throughout the system, except near the screen  90  and any intermediate image planes. FIG. 12 d  shows the light distribution just before the turning mirror  82  and the stop  83 , which block the unwanted diffracted orders. Only the +1st and −1st order light beams pass through the projection lens system  75 . For better optical efficiency, higher diffracted orders could also be allowed through. FIGS. 12 e - 12   h  show the +1st and −1st order light beams after they have gone through the projection lens system and pass through focus at the Fourier plane (D=100 mm). Near the Fourier plane, the two first order light beams are tightly focused into two spots. Therefore, by placing the scanning mirror  77  here, it can be kept small and light. The +1st and −1st order light beams overlap spatially when they finally reach the screen  90 . 
     An alternate embodiment of the display system is shown in FIG.  13 . The projection lens system now consists of  3  separate lens groups  75   a ,  75   b  and  75   c . The turning mirror  82  is placed between the first lens group  75   a  and the scanning mirror  77  adjacent to the first lens group  75   a . This location for the turning mirror  82  can be beneficial because the diffracted light beams are collimated along one axis in this space. The cylindrical lens  74  axis is rotated 90 degrees with respect to the cylinder lens of FIG.  8 . The scanning mirror  77  is preferably placed at the Fourier plane (focal plane) of the first lens group  75   a . The second lens group  75   b  creates an intermediate image  92  of the linear array  85  that can be used to modify the image appearing on the screen  90 . For example, an aperture can be placed in this plane to create a sharp boundary for the image. The third lens group  75   c  projects the intermediate image  92  onto the screen  90 . 
     In the embodiments of FIGS. 8 and 13, the turning mirror  82  is used both for providing illumination to the linear array  85  and for blocking the 0 th  order light beam from reaching the screen  90 . This requires precise positioning of a small turning mirror  82 , which can be difficult for the case of conformal grating devices where the diffracted orders may only be separated by 1 degree. Furthermore, the embodiment of FIG. 13 can have a reduction in contrast of the projected image caused by weak reflections of the incident light from the first lens group  75   a.    
     According to the present invention, a display system that incorporates a segmented waveplate  120  can be used to eliminate these two problems as illustrated in FIGS. 14 and 15 a . Referring to FIG. 14, the source  70  emits linearly polarized light that is reflected by a polarization element, here shown as a polarization beamsplitter  96  and focuses on the linear array  85 . For optimum illumination and light efficiency, the source is preferably a linearly polarized laser. Unpolarized sources may also be used since the polarization beamsplitter  96  will render the reflected light linearly polarized. Referring to FIG. 15 a , the incident light illuminating the linear array  85  passes unmodified through the central portion  124  of the segmented waveplate  120 . If a particular device on the linear array  85  of FIG. 14 is not actuated, it diffracts the incident light beam primarily into the 0th order light beam. The 0th order passes back through the central portion  124 , hits the polarization beamsplitter  96  of FIG.  14  and is reflected towards the source  70  of FIG.  14 . On the other hand, if a particular device is actuated, it diffracts the incident light beam primarily into +1st order and −1st order light beams. These two first-order diffracted light beams pass through the half-wave segments  122  of the segmented waveplate  120  of FIG. 16 a , which then rotates the linear polarization by 90 degrees. Specifically in FIG. 14, the polarization beamsplitter  96  allows this state of polarization to be projected onto a screen  90  by a projection lens system  75 . Higher-order diffracted light beams can be blocked by the addition of a stop  83  or by adding additional clear portions to the segmented waveplate  120 . 
     FIG. 15 b  shows an alternative embodiment of the segmented waveplate  120  in which the central portion  124  is replaced by a full-wave segment  126 . In practice this solution may be more easily manufacturable, since it can be implemented by merely overlapping two half-wave plates. The optical subsystem  140  of FIG. 14 that combines the linear array  85 , the segmented waveplate  120  and the polarization beamsplitter  96  is a basic block that can be incorporated into other types of systems. The specific example of a printer will be discussed later. If higher efficiency is desired, the segmented waveplate  120  can be selected so that higher order light beams pass through the system. 
     The above embodiments 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 lasers 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 turned-on laser color. 
     Color-sequential display systems waste two-thirds of the available light because only one color is projected at a time. FIG. 16 depicts an embodiment of the invention that projects three colors simultaneously. In FIG. 16, the light source  70  emits linearly-polarized red, green and blue beams. After these three beams strike polarization beamsplitter  96 , they are separated by a color combination cube  100  and are focused onto distinct linear arrays by three projection lenses  72   r ,  72   g  and  72   b . Red light illuminates linear array  85   r , green light illuminates linear array  85   g  and blue light illuminates linear array  85   b . The 0 th  order light beams emerging from the three linear arrays pass unmodified through the central portions of three segmented waveplates  120   r ,  120   g  and  120   b . However, the +1 st  and −1 st  order light beams pass through the half-wave portions of the segmented waveplates, which rotates the beam polarization by 90 degrees. Each of the waveplates is chosen to match the color of interest. All of the +1 st , 0 st  and −1 st  order light beams are combined by the color combination cube  100  and subsequently strike the polarization beamsplitter  96 . Because of the difference in the state of polarization, the polarization beamsplitter  96  reflects the red, green and blue 0 th  order beams back towards the source and allows the red, green and blue +1 st  and −1 st  order light beams to project onto a screen  90 . 
     Alternatively, a color-simultaneous display system can be made with a single multi-color segmented waveplate  130  located between a polarization beamsplitter  96  and a color combination cube  100 , as shown in FIGS. 17 and 18. In this embodiment, each of the linear arrays  85   r ,  85   g  and  85   b  has the same period Λ, or a period chosen so that the red, green and blue +1 th  and −1 st  order light beams do not spatially overlap as they pass through the multi-color segmented waveplate  130 . Referring to FIG. 18, the red, green and blue 0 th  order light beams are transmitted unmodified through a central opening  134  and are reflected towards a light source  70  of FIG. 17 by the polarization beamsplitter  96 . The red, green and blue +1 st  and −1 st  order light beams each pass through a corresponding half-wave segment  132   r ,  132   g  and  132   b , which causes the beams to be projected onto the screen  90 . 
     In practice, because color combination cubes usually only work well with a particular state of linear polarization, the embodiment of FIG. 17 allows for a better design than the one of FIG.  16 . In the display system of FIG. 17 all of the +1 st  and −1 st  order light beams traveling through the color combination cube  100  have the same state of polarization as their 0 th  order counterparts. On the other hand, in the display system of FIG. 16, the state of polarization of the +1 st  and −1 st  order light beams in the color combination cube  100  is rotated with respect to the 0 th  order. Therefore, the system of FIG. 16 requires good performance from the color combination cube  100  for both states of linear polarization of each color, whereas the one of FIG. 17 only requires good performance for a single state of linear polarization. 
     The color-simultaneous display systems of FIGS. 16 and 17 each require three projection lens systems  72   r ,  72   g ,  72   b . A lower-cost color-simultaneous display system with a single projection lens system  75  is illustrated in FIG.  19 . 
     The embodiments described above can readily be altered to obtain printing systems. For example, FIG. 20 shows a printer that is fashioned from the optical subsystem  140  from FIG.  14 . An imaging lens  105  is used at finite conjugates to create a line image of a linear array  85  on light sensitive media  110 . This line image is formed from the +1 st  order and −1 st  order light beams that pass through the polarization beamsplitter  96 . Although a scanning mirror  77 , as shown in FIG. 14, could be used to create a two-dimensional image from the line image, it is usually preferable to use a media transport system to move the light sensitive media  110  with respect to the line image. In FIG. 20, the media transport system is a rotating drum  107 . The motion of the media must be synchronized with the actuation of the electromechanical conformal grating devices of the linear array  85  by the controller  80 . This embodiment can be used for either a monochrome or a color-sequential printer. To obtain a high-speed printer that can print three colors simultaneously on photographic paper, three linear arrays would be needed. 
     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 
       5   a  conformal grating device 
       5   b  conformal grating device 
       5   c  conformal grating device 
       5   d  conformal grating device 
       10  substrate 
       12  bottom conductive layer 
       14  protective layer 
       16  standoff layer 
       18  spacer layer 
       20  ribbon layer 
       22  reflective, conductive layer 
       23   a  elongated ribbon element 
       23   b  elongated ribbon element 
       23   c  elongated ribbon element 
       23   d  elongated ribbon element 
       24   a  end support 
       24   b  end support 
       25  channel 
       27  intermediate support 
       28  gap 
       29  standoff 
       30  incident light beam 
       32  0 th  order light beam 
       35   a  +1 st  order light beam 
       35   b  −1 st  order light beam 
       36   a  +2 nd  order light beam 
       36   b  −2 nd  order light beam 
       40  substrate 
       42  bottom conductive layer 
       44  protective layer 
       45   a  GLV device 
       45   b  GLV device 
       45   c  GLV device 
       45   d  GLV device 
       45   e  GLV device 
       46  ribbon element 
       46   a  movable ribbon element 
       46   b  stationary ribbon element 
       48  reflective and conductive layer 
       50  channel 
       54  incident light beam 
       55  0th order light beam 
       56  incident light beam 
       57  +1st order light beam 
       58  −1st order light beam 
       60   a  channel 
       60   b  channel 
       60   c  channel 
       60   d  channel 
       60   e  channel 
       62   a  GLV device 
       62   b  GLV device 
       62   c  GLV device 
       62   d  GLV device 
       62   e  GLV device 
       70  light source 
       72  spherical lens 
       72   r  projection lens 
       72   g  projection lens 
       72   b  projection lens 
       74  cylindrical lens 
       75  projection lens system 
       75   a  first lens group 
       75   b  second lens group 
       75   c  third lens group 
       77  scanning mirror 
       80  controller 
       82  turning mirror 
       83  stop 
       85  linear array 
       85   r  linear array 
       85   g  linear array 
       85   b  linear array 
       88  line of light 
       90  screen 
       92  intermediate image 
       96  polarization beamsplitter 
       100  color combination cube 
       105  imaging lens 
       107  rotating drum 
       110  light sensitive media 
       120  segmented waveplate 
       120   r  segmented waveplate 
       120   g  segmented waveplate 
       120   b  segmented waveplate 
       122  half-wave segment 
       124  central portion 
       126  full-wave segment 
       130  multi-color segmented waveplate 
       132   r  half-wave segment for red 
       132   g  half-wave segment for green 
       132   b  half-wave segment for blue 
       134  central opening 
       140  optical subsystem 
     f focal distance