Abstract:
The application of microstructures which improve the quality of light available to the viewer of an optical display system, or any display which works on the concept of moving one surface into direct contact or close proximity of a light guide to extract light through frustrated total internal reflection. Optical microstructures are introduced on one or both of the surfaces of the active layer to enhance its performance. Since the active layer has both an input and an output function, means for enhancing both are presented. The input function to the active layer occurs on the internal surface, so this is where the present invention adds a collector-coupler, a means for facilitating the migration of light from the waveguide into the active layer. The output function occurs on the external surface, where the present invention adds a collimator, a means for both increasing the probability that a light wave will be released from the active layer, and improving the apparent intensity by redirecting light waves so that more of them reach the viewer. Compound microlenses on the internal surface of the active layer can serve as both collector-couplers and collimators, substantially improving light extraction from the light guide and light distribution to the viewer. Depositing a reflective or colored material in the interstitial spaces between these compound microlenses improves the contrast ratio and mitigate pixel cross-talk. The opaque material can be conductive for use in actuating the display.

Description:
TECHNICAL FIELD 
     The present invention primarily relates to the field of displays, and more generally to any display system in which light is extracted from a waveguide through means of selectively controllable contact with its surface. 
     BACKGROUND INFORMATION 
     The present invention addresses certain embodiments for improvement that occur when creating an optical display system, or any device which works on the concept of frustrated total internal reflection (FTIR), an example of which is the Time Multiplexed Optical Shutter (TMOS) display disclosed in U.S. Pat. No. 5,319,491, which is hereby incorporated by reference herein. Embodiments for improvement arise with respect to three basic optical materials in the design of a FTIR display. In a display application, there are defined locations within the architecture where a pixel nominally exists. Where this pixel exists, efficient light coupling from a light guide is desired when FTIR occurs (by controllable switching of the pixel to an “ON” state to frustrate the TIR condition). Where the pixel does not exist (e.g., inactive regions between pixels), very inefficient light coupling is desired. To allow light out of a pixel location when desired, an optical material is moved from a position that is very inefficient at FTIR, to one that is relatively much more efficient at FTIR. In the locations between all of the pixels, the material is inefficient at FTIR at all times. 
     Current approaches to addressing this situation involve three basic materials: (1) a total internal reflection (TIR) light guide, (2) a cladding material which has a lower refractive index than the light guide material, and (3) an optical coupling material that is the active layer. When no light is desired from a pixel (i.e., TIR is to be locally preserved), the optical coupling material is in a position, separated by cladding (which can be air), such that little to no light escapes the light guide since frustration of the TIR is not significant at this pixel location. When light is desired from a pixel (i.e., TIR is not to be locally preserved), the optical coupling material is moved toward the light guide (in which it may or may not come into contact with the light guide) such that the TIR condition is violated and light is released to a viewer due to physical geometry changes that result in FTIR at the pixel. 
     At a center of the implementation of TMOS lies a pixel wherein exists a means of extracting light from an underlying waveguide, generally through advantageous application of forces such that an external structure is caused to move into close proximity or direct contact with the underlying waveguide and light is extracted until the opposite, turning-off motion is generated. Embodiments for enhancing this process have been identified with regard to coupling light out of the underlying waveguide. 
     In particular, several improvement modes have been identified relative to a goal of maximizing the light that is apparent to the viewer. The first of these would be to more optimally capture light when the pixel is in “on” mode and any light that is reflected back into the light guide instead of entering the active layer as intended. Another improvement would be to more optimally capture any light that is reflected from the top surface of the active layer and returns to the light guide traveling the opposite direction across the cladding instead of exiting the active layer toward the viewer as intended. A means of more optimally transferring light waves into the active layer and then out toward the viewer would be advantageous. 
     Another improvement mode considers light within the active layer that is continuously reflected within it, with too shallow of an angle to be released to the viewer. These modes result in some light not reaching the viewer. A slightly different opportunity for improvement occurs when light leaves the external surface, but does so at an angle too shallow to be readily perceived by the viewer—though if it was released, it could more optimally benefit the viewer. A means of redirecting these shallow angle (surface-hugging) light waves more directly toward the viewer would be beneficial. 
     Another area of improvement for these types of devices, including TMOS, is to more controllably turn on, and then off, any given pixel within the color cycle, with any delays being predictable and short relative to one component color&#39;s cycle time. Previous embodiments have exhibited imperfect results in turning off the pixel controllably within such a time frame. In particular, occasionally pixels turned on would tend to stay on after the applied force to turn “on” was removed, a behavior known as stiction. It would be advantageous to more optimally control stiction when pixels are on when they should not be (in extreme cases of stiction). It would also be beneficial in shorter duration events that do not exceed the whole cycle&#39;s duration, but are on longer than intended within a cycle, the pixel&#39;s perceived color and/or brightness could be somewhat distorted if one of the component colors in the pixel does not turn off predictably as intended—where color is defined via pulse width modulation, stiction causes undesirable augmentation of pulse widths, thus distorting the color values being transduced. While not all FTIR architectures suffer from stiction, those that do would benefit from any improvement to restrict or eliminate its influence. 
     A related area of improvement involves pixel geometry where the cladding is separate from the active layer. When one pixel is turned “on” and then “off” again, the risk of unintended “crosstalk” is contemplated, wherein the active layer in an adjacent pixel is affected by the change in the adjacent pixel, to “on” or to “off” state, and the material moves relative to the underlying cladding, and thereby moves or creates a change in tension in the adjacent pixel&#39;s active layer. A means of reducing the risk of said “crosstalk” by stopping the relative motion between the cladding and the active layer would be beneficial. 
     SUMMARY 
     Embodiments for improvement outlined above may at least in part be addressed in some embodiments of the present invention by introducing microstructures on one or both of the surfaces where contact (or close proximity) occurs. A wide range of microstructure geometries are contemplated. These microstructures may consist of a semi-random distribution of peaks and valleys, characterized by varying degrees of “roughness.” Or, a more controlled distribution of peaks and valleys of selected dimensions and densities, on one or both sides, may be employed. Under even more precisely controlled conditions, particular geometries, with tightly specified dimensions and distribution, may be employed. 
     The present invention enhances the light extraction process by introducing optical microstructures on one or both surfaces of the active layer. Since the active layer has both an input and an output function, means for enhancing both are envisioned. The input function to the active layer occurs on the internal surface, so this is where an embodiment of the present invention adds a collector-coupler, a means for facilitating migration of light from the waveguide into the active layer. An opaque material may be disposed interstitially between the collector-couplers to improve contrast. This opaque material can be electrically conductive which in turn can be used in actuating the pixel. The output function occurs on the external surface, so at this location an embodiment of the present invention adds a collimator, a means for both increasing the probability that a light wave will be released from the active layer, and improving the apparent intensity by redirecting light waves so that more of them reach the viewer. Issues such as stiction and pixel-to-pixel crosstalk are mitigated through advantageous selection of materials and geometries. 
     The foregoing has outlined rather broadly the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
         FIG. 1  illustrates an external view of a TMOS display, as seen by a viewer, to be used by any of several embodiments of the present invention; 
         FIG. 2  illustrates a side view of the internal pixel geometry in a TMOS display, in “off” and “on” states; 
         FIG. 3  illustrates a side view of two adjacent pixels in a TMOS display, one each in “off” and “on” states; 
         FIG. 4  illustrates a side view of one isolated pixel in a TMOS display, in “off” state; 
         FIG. 5  illustrates a side view of one isolated pixel in a TMOS display, in “on” state with opportunities for enhanced light wave behavior shown; 
         FIG. 6  illustrates a side view of one isolated pixel, in “off” state with beneficial features of the present invention shown; 
         FIG. 7  illustrates a side view of one isolated pixel, in “on” state with beneficial features of the present invention, and corresponding beneficial behavior, shown; 
         FIG. 8  illustrates a side view of one isolated pixel, in “off” state with additional bimodal collector-coupler beneficial features of the present invention shown; 
         FIG. 9  illustrates a side view of one isolated pixel, in a nearly “on” state with additional flexurally biased spring-like collector-coupler beneficial features of the present invention shown; 
         FIG. 10  illustrates a side view of one individual example of the flexurally biased collector-coupler features referenced in  FIG. 9 , here in a completely “on” state with maximum compression; 
         FIG. 11  illustrates a side view of one isolated pixel, in “off” state with additional bimodal collector-coupler beneficial features as shown in  FIG. 8 , here a second population of longer features serves as a distributed standoff and a layer of “springy” highly compliant materials is immediately under the surface features; 
         FIG. 12  illustrates a side view of one isolated pixel, in “off” state with additional beneficial features as shown in  FIG. 8 , here a population of standoff features is shown with a highly compliant supporting material that allows the standoffs to be sufficiently compressed so as to allow broad direct contact of the flat supporting material with the light guide; and 
         FIG. 13  illustrates a data processing system configured in accordance with an embodiment of the present invention; 
         FIG. 14  illustrates a side view of one isolated microlens as used as a collector-coupler on the inside surface of the active layer of a pixel in the “off” state (left), and a side view of the same microlens with the pixel in an “on” state (right); 
         FIG. 15  illustrates a side view of a portion of one isolated pixel wherein the collector-coupler features are surrounded by an opaque material, which may be conductive. Both the “off” and “on” states of the pixel are shown; and 
         FIG. 16  illustrates several geometric shapes used for compound microlens. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without such specific details. In other instances, detailed physical features are idealized in order not to obscure the present invention in unnecessary detail. For the most part, details considering timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art. 
     The general concept of TMOS, as originally expressed in U.S. Pat. No. 5,319,491, is briefly illustrated in  FIGS. 2 and 3 . In  FIG. 2 , a side view  200  of one pixel  101  is shown, first in the “off” position  211 , and second in the “on” position  212 . An internal light guide  201 , and the light waves  204  contained therein, are shown relative to the active layer  202 , with “off” cladding  203  in the space between the two. As described previously, “off”  211  represents TIR and no light emission, and “on”  212  represents FTIR with light waves  206  released from the active layer  202 . The mechanical change in position of the active layer  202  toward the light guide  201  causes the cladding thickness to decrease to “on” cladding  213 . 
       FIG. 3  shows a simplified side view representation  300  of two adjacent pixels, to more clearly contrast the “off”  311  geometry with the “on”  312  geometry. Of particular note is the special case for the “on” cladding  313  (corresponding to  213  in  FIG. 2 ) shown here where contact takes place and therefore the cladding thickness  313  is zero. In this direct contact case, additional modes of coupling may become available and hence light coupling can be enhanced beyond the proximity case. 
       FIG. 1  illustrates a TMOS display  100  configured to operate with pixels  101  described below in accordance with embodiments of the present invention. A top or plan view of display  100  is shown from a viewer&#39;s point of view. For simplicity, only a select number of pixels  101  are shown in a matrix format. Any number of pixels  101  may be implemented in accordance with principles of the present invention. 
       FIGS. 4 through 7  show a more detailed side view of one pixel  101 , to further illustrate embodiments of the present invention.  FIG. 4  shows an isolated view  400  of a pixel  101 , in the “off” geometry as in  FIG. 3  “off”  311 , with two particular surfaces of a light coupling layer  404  (similar to  202  in  FIG. 2 ) identified—an internal surface  401  that faces a light guide  403  (similar to  201  in  FIG. 2 ), and an external surface  402  that faces a viewer (not shown). 
     In  FIG. 5 , a more detailed view  500  of pixel  101  is now shown in the “on” position. Three opportunities are illustrated with respect to optimizing the amount and direction of light that passes out of the active layer  506  (corresponding to  404  in  FIG. 4 ), each can individually or in combination improve conditions so a viewer can more fully benefit from that available light. A first enhancement opportunity occurs at the interface between the active layer  506  and the light guide  505  (corresponding to  403  in  FIG. 4 ), wherein even though the geometry is in the “on” position, light in the light guide is still reflected  501  from internal surface  507  (corresponding to  401  in  FIG. 4 ) back into the light guide instead of entering the active layer  506  as intended. A second enhancement opportunity is similar in that a light wave  502  is reflected back into the light guide  505 , but in this case, the outer surface  508  (corresponding to  402  in  FIG. 4 ) is where non-beneficial reflection occurs, and light wave  502  is shown having re-entered the light guide  505  as  504 . A third enhancement opportunity occurs when the light wave has entered the active layer with too shallow of an angle and is hence continuously reflected  503  within the active layer  506  without beneficially exiting. 
     Embodiments of the present invention are illustrated in  FIG. 6 , where the detailed model  400  has new features added in view  600 . Collector-coupler features  601  are added to the internal surface  603  (corresponding to  401  in  FIG. 4 ). The collector-coupler features interact with light waves that approach the vicinity of the light guide and “on” active layer interface, increasing the probability of light waves to exit the light guide and enter the active layer, to become available to the external surface  604  (corresponding to  402  in  FIG. 4 ) of the active layer for release to the viewer. This release to the viewer may be further enhanced by another embodiment of the present invention. More particularly, on the external surface  604 , collimator features  602  may be added. It is an object of said collimator features  602  to create benefits in two ways. A first of these is to interact with light waves as they approach the vicinity of the interface between the active layer&#39;s external surface  604  and the collimator features  602 . Through said interaction, a probability of light waves to exit the external surface  604  and enter the collimator features  602  is increased, whereby the quantity of light waves that are available to be guided to the viewer is increased. A second benefit of the collimator features  602  relates to this guidance process once light waves have entered the collimator features  602 . Optical properties of said structures  602  are advantageously chosen so as to redirect the light waves that would otherwise tend to leave the surface  604  at a shallow angle, nearly parallel to said surface  604 , and instead cause them to leave the collimator feature&#39;s external surface more nearly in the direction of the viewer, which is more nearly perpendicular to surface  604 . 
     One embodiment for fabricating collector-couplers  601 , collimator features  602  and other similar features disclosed herein on the active layer involves processing of the unadjusted active layer using a roll-to-roll processing machine available from Nanoventions, Inc. (address: 1050 Northfield Court, Suite 280, Roswell, Ga., 30076). Using the Nanoventions roll-to-roll processes, which enable high-speed chemical lithography of acrylate nanofeatures on thin film polymer substrates, structures  601  and  602  may be fabricated on raw active layer polymer sheets that give rise to a desired performance hereunder, both with respect to optical output and mechanical integrity. Such structures may also be formed via roll-to-roll deployment using continuous deposition and monolithic integration, as implemented by Iowa Thin Films, Inc., while similar proven strategies for volume sheet polymer fabrication have enjoyed years of success with industry giants such as 3M, DuPont, and GE Plastics. Structures  601  and  602  may also be formed via negative mold topologies etched into a metal cylinder designed to impress the desired geometry into a suitably interactive polymer (e.g., a thermoplastic with sufficiently low viscoelastic behavior). 
       FIG. 7  shows model  600  now in the “on” mode  700 . In first illustrated embodiment, the collector-coupler features  707  (corresponding to  601  in  FIG. 6 ), improve the probability of a light wave coupling into the active layer  704  and being transmitted to the viewer. Through advantageous selection of these geometries, mechanisms of enhanced coupling are implemented, including, but not limited to, antenna effects of interactions and optical amplifications through mutually reinforcing electromagnetic behaviors, whisper gallery mode resonance and reinforcement at desired wavelengths, complementary surface plasmon effects and associated reinforcing interactions with the previous resonances, and other beneficial mechanisms that will be apparent to one skilled in the art. These secondary effects arise due to geometry-enabled amplification not unlike the amplification effects attained by careful design of antennas, excepting that the wavelength range is that of visible light. In the case of surface plasmon resonances, the electromagnetic field traveling across the surface is in similar manner subject to amplification due to pseudo-antenna-like effects stemming from a strategically-chosen system geometry that is properly optimized. 
     An example of said collector-coupler features is the compound microlens  1400  shown in  FIG. 14 . The shape of the microlens  1400  is designed so that light coupled into the aperture  1406  will contact a side  1401  under conditions sufficient for total internal reflection within the microlens  1400  before it contacts the internal surface of the active layer  1402 . The light will then be reflected at an angle sufficient to cross the external surface of the active layer  604  and exit the display. 
       FIG. 16  illustrates several exemplary shapes of the compound microlens  1400 . The microlens  1400  can have any desired shape known to the art of non-imaging optics, such as pyramidal frustum  1601 , conical frustum  1602 , compound parabolic  1603 , compound elliptical, polyobject or any conic section revolved to form a solid. A portion of the end of the microlens that faces the light guide surface  1403  is flat, giving the microlens the shape of a frustum. This flat surface area is the aperture  1406  through which light is coupled out of the light guide  1408  and into the microlens  1400 . The relationship of the upper diameter  1405  of the microlens  1400  to the aperture diameter  1406  and the height  1411  of the microlens  1400 , is determined by the refractive index of the light guide  1408  and the refractive index of the material comprising the microlens  1400 . The refractive index of the light guide  1408  determines the critical angle for TIR light within the light guide  1408  (i.e., range of angles of available TIR light). When light is coupled from the light guide  1408  into the microlens  1400  it will change angle according to the refractive index of the microlens material. The angle of the side of the microlens  1401  is constructed such that the light coupled from the light guide  1408  remains TIR with respect to the sides  1401  of the microlens  1400 . The height  1411  of the microlens  1400  is determined so that all or substantially all light that is coupled into the microlens  1400  strike a side  1401  of the microlens  1400  before it strikes the upper surface  1405 . For example, a light guide  1408  of refractive index 1.52 and a microlens  1400  of refractive index 1.6 will require the diameter of the aperture  1406  to be approximately one-half the dimension of the upper diameter  1405  of the microlens. The height  1411  of the microlens  1400 , in this example, would be approximately 60% of the upper diameter  1405 . In this example, the microlens  1400  will redirect more than 96% of the light  1410  coupled into it across internal surface of the active layer  1402  and out the top surface of the active layer (to the viewer). 
     A benefit may also be realized from the addition of the collimator features  703  (corresponding to  602  in  FIG. 6 ) at the external surface  702  (corresponding to  604  in  FIG. 6 ). This benefit addresses the opportunity for enhancement  502  discussed previously. Through an advantageous selection of collimator features  703 , the probability of the undesired reflection  705  (corresponding to  502  in  FIG. 5 ) back into the light guide  706  is reduced, and more light passes out through surface  702 . 
     A benefit may be realized with an addition of the collimator features  703 —the features are chosen to advantageously redirect the released light wave  701  to a more desirable angle of emission, so that it is more available to the viewer. Released light waves at angles nearly parallel to the surface  702  are advantageously redirected to be more perpendicular to said surface  702 , and thereby more apparent to a viewer. It should be noted that this improvement is in addition to the internal examples mentioned above. 
     The microlens  1400  in  FIG. 14  can also function as a collimator. The shape of the microlens can be designed in a manner known to non-imaging optics so that light exits the active layer at desired angles, and not at angles nearly parallel to the external surface of the active layer  604  ( FIG. 6 ). 
       FIG. 8  shows a magnified view  800  of “off” side view  600 , including collector-coupler beneficial features  802  (corresponding to  601  in  FIG. 6 ), and an additional set of features  801 . By adding this second population of collector-coupler features  801 , creating a bi-modal population, an additional benefit is attained that addresses the stiction issue mentioned in the Background Information. The simplified illustration shows a feature of this additional population  801 , namely that it is longer than the other mode  802  in the overall population. When this surface  801  comes in contact with the light guide  806 , the longer population  801  will contact first, and then be compressed as the surfaces  803 ,  807  move closer together, until the first population also reaches close proximity or direct contact. When the “off” mechanism is engaged and the surfaces  803 ,  807  are intended to separate, the compressed second population  801  acts as compressed springs, creating a brief but strong force to help initiate the separation movement. Said separating force is strongest at the very position when stiction is at its worst, the very start of separation. Of course, for purposes of this simplified illustration, two populations are described, but this should not be considered to limit the present invention, rather the present invention further envisions a plurality of varying populations, two or greater than two modes, with a range of heights to advantageously achieve said benefits with regard to overcoming stiction and also improving light coupling as previously described. 
       FIG. 9  is a magnified view  900  of a side view of an embodiment of a pixel  101 , nearly in the “on” position shown in  700 , but shown in the position just prior to contact to more clearly illustrate details of the geometry, though it should be understood that they are simplified to help illustrate an embodiment the intention of the present invention. The angled features  901  are similar in optical behavior to the collector-coupler features  601 , and derive similar benefits accordingly, but in this additional detail create a benefit. As the angled features  901  come into contact with the light guide  902 , they are elastically deformed in such a manner as to build potential energy like a compressed spring (See  FIG. 10 ). When the “on” period is over and the “off” mode initiates, these features  901  can advantageously release the potential energy in the form of an initial separation force, similar to the features  801  described above, that can beneficially increase the force available to overcome stiction. 
       FIG. 10  illustrates a side view of one individual example  1000  of the flexurally biased collector-coupler features  901  referenced in  FIG. 9 , here in a completely “on” state with maximum compression  1001 . The illustration is simplified and exaggerated to more clearly show an embodiment of the present invention. It should be appreciated that the illustrated compression is elastic in nature, and therefore will provide a force in the direction of separation, thereby beneficially increasing the overall force available to overcome stiction issues. 
       FIG. 11  illustrates a side view  1100  of an embodiment of one isolated pixel  101 , in “off” state with additional bimodal collector-coupler features of the present invention as shown in  FIG. 8 , here the second population of longer features  1107  (corresponding to  801  in  FIG. 8 ) serves as a distributed standoff with distributed points of contact  1102  and a layer of “springy” highly compliant material  1101  immediately under the surface features  1106  (corresponding to  802  in  FIG. 8 ), and  1107 . Several mechanisms are contemplated for overcoming stiction, including but not limited to: the active layer itself  1104  may have some compliance that could provide restorative force after “on” compression; likewise the longer standoff features  1107  are intended to be elastically compressed while “on” and also provide restorative force to overcome stiction; and the highly compliant layer  1101  is chosen to provide compliance and then a restorative force to overcome stiction. 
       FIG. 12  illustrates a side view  1200  of one isolated pixel  101 , in “off” state with additional beneficial features of the present invention as shown in  FIG. 8 ; here only a population of standoff features  1201  is shown with a highly compliant supporting material  1205  (similar to  1101 ) that allows the standoff&#39;s  1201  to be sufficiently compressed so as to allow broad direct contact of the flat supporting material  1205  with the light guide  1202 . Said highly compliant material  1205  and the compressed standoff&#39;s  1202  could both provide restorative force to overcome stiction when “on” switches to “off.” 
     It should be understood that not only is the geometry shown a simplification to illustrate the concept, but that it is possible to combine advantageously the different beneficial embodiments. For example, multi-modal population, as in  801  in  FIG. 8  could also incorporate angled or other advantageously chosen geometries that create spring-like separation forces, within the non-longer population so as to overcome stiction through multiple means. 
     An additional embodiment of the present invention is shown in  FIG. 15 . Since light is coupled out of the light guide by the collector-coupler features  1503 , an opaque material  1504  can be disposed between the collector-coupler features  1503 . The opaque material  1504  prevents light from entering the active layer at undesired locations, improving the overall contrast ratio of the display and mitigating pixel cross-talk. The opaque material  1504  can substantially fill the interstitial area between the collector-coupler features  1503  of each pixel, or it can comprise a conformal coating of these features and the interstitial spaces between them. The aperture  1508  (corresponding to  1406  of  FIG. 14 ) of each collector-coupler  1503  remains uncoated so that light can be coupled into the collector-coupler  1503 . Depending on the desired use of the display, the opaque material  1504  may be either a specific color (i.e., black) or reflective. 
     For electrostatically actuated pixels, such as those disclosed in U.S. Pat. No. 5,319,491, a deposition of opaque material  1504  which is conductive serves as one plate of a parallel plate capacitor. A layer of transparent conductor  1505 , such as indium tin oxide (ITO) is disposed on the light guide, forming the other plate of the capacitor. By placing a voltage differential across these conductors, the flexible active layer  1501  is drawn toward the light guide  1502  by means of electrostatic attraction, thereby placing the pixel in the “ON” state. A layer of dielectric  1506  may be disposed on top of the transparent conductor  1505  to prevent short circuits between the two conductor layers. Deposition of conductor in this manner eliminates the need to deposit a layer of transparent conductor on the active layer (within the optical path of the viewer). This improves display efficiency while reducing the costs associated with transparent conductors relative to opaque conductors. 
     A representative hardware environment for practicing the present invention is depicted in  FIG. 13 , which illustrates an exemplary hardware configuration of data processing system  1313  in accordance with the subject invention having central processing unit (CPU)  1310 , such as a conventional microprocessor, and a number of other units interconnected via system bus  1312 . Data processing system  1313  includes random access memory (RAM)  1314 , read only memory (ROM)  1316 , and input/output (I/O) adapter  1318  for connecting peripheral devices such as disk units  1320  and tape drives  1340  to bus  1312 , user interface adapter  1322  for connecting keyboard  1324 , mouse  1326 , and/or other user interface devices such as a touch screen device (not shown) to bus  1312 , communication adapter  1334  for connecting data processing system  1313  to a data processing network, and display adapter  1336  for connecting bus  1312  to display device  1338 . CPU  1310  may include other circuitry not shown herein, which will include circuitry commonly found within a microprocessor, e.g., execution unit, bus interface unit, arithmetic logic unit, etc. CPU  1310  may also reside on a single integrated circuit. 
     Display device  1338  may incorporate display  100  and any of the various embodiments, or any other display technology capable of utilizing embodiments of the present invention. Control circuitry within display adapter  1336  is not disclosed herein for the sake of simplicity.