Patent Publication Number: US-2009231719-A1

Title: Eyebox Shaping Through Virtual Vignetting

Description:
BACKGROUND 
     In a head-up display (HUD), an image is projected into an eyebox region such that the viewer is able to view the displayed image when the viewer&#39;s eyes are positioned within the eyebox, and is unable to view the displayed image when the viewer&#39;s eyes are not positioned within the eyebox. In general, the inpterpupilary distance (IPD), the distance between the pupils of the eyes, tends towards a desire to make the eyebox wider than it is tall so as to provide better viewability of the displayed image. The concept of providing an eyebox with a wider angle viewing aspect ratio may be applicable to scanned beam displays where the viewer&#39;s head is free to move relative to the image displayed in the eyebox. For example, it may be desirable to provide a display system where the eyebox has an aspect ratio on the order of 2:1 or so, and/or which may be based on, for example, the number of pixels in the displayed image such as 800 by 600, a 16 by 9 aspect ratio, and so on. 
    
    
     
       DESCRIPTION OF THE DRAWING FIGURES 
       Claimed subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. However, such subject matter may be understood by reference to the following detailed description when read with the accompanying drawings in which: 
         FIG. 1  is a diagram of a scanned beam display capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments; 
         FIG. 2  is a diagram of a compressed microlens array having respective square and rectangular lenslets for a scanned beam display capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments; 
         FIGS. 3A and 3B  are diagrams of alternative compressed microlens array having compressed hexagonal lenslets as shown in  FIG. 3A  and non-compressed hexagonal lenslets as shown in  FIG. 3B  for a scanned beam display capable of providing a desired aspect ratio in accordance with one or more embodiments; 
         FIG. 4  is a diagram of an example time-averaged diffraction envelope resulting from a beamlet beam profile scanned across a displayed image having a desired eyebox aspect ratio in accordance with one or more embodiments; 
         FIG. 5  is a diagram of an optical system for a scanned beam display system capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments; 
         FIG. 6  is a profile view of a compressed microlens array for a scanned beam display system comprising an array of compressed lenslets for a scanned beam display system capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments; 
         FIG. 7  is a profile view of a compressed dual microlens array for a scanned beam display system comprising an array of compressed lenslets for a scanned beam display system capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments; and 
         FIG. 8  is a diagram of a vehicle having a head-up display comprising a scanned beam display and a compressed microlens array capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments. 
     
    
    
     It will be appreciated that for simplicity and/or clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, if considered appropriate, reference numerals have been repeated among the figures to indicate corresponding and/or analogous elements. 
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components and/or circuits have not been described in detail. 
     In the following description and/or claims, the terms coupled and/or connected, along with their derivatives, may be used. In particular embodiments, connected may be used to indicate that two or more elements are in direct physical and/or electrical contact with each other. Coupled may mean that two or more elements are in direct physical and/or electrical contact. However, coupled may also mean that two or more elements may not be in direct contact with each other, but yet may still cooperate and/or interact with each other. For example, “coupled” may mean that two or more elements do not contact each other but are indirectly joined together via another element or intermediate elements. Finally, the terms “on,” “overlying,” and “over” may be used in the following description and claims. “On,” “overlying,” and “over” may be used to indicate that two or more elements are in direct physical contact with each other. However, “over” may also mean that two or more elements are not in direct contact with each other. For example, “over” may mean that one element is above another element but not contact each other and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean “one”, it may mean “some, but not all”, it may mean “neither”, and/or it may mean “both”, although the scope of claimed subject matter is not limited in this respect. In the following description and/or claims, the terms “comprise” and “include,” along with their derivatives, may be used and are intended as synonyms for each other. 
     Referring now to  FIG. 1 , a diagram of a scanned beam display capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments will be discussed. As shown in  FIG. 1 , a typical scanned beam display  100  may comprise a laser source  110  capable of emitting a laser beam  114  to be scanned into a displayed image by a microelectromechanical system (MEMS) based scanner  116 . Laser source  110  may comprise, for example, a vertical-cavity surface-emitting laser (VCSEL) or the like. MEMS scanner  116  may comprise one or more mirrors disposed on a platform capable of moving in response to an applied voltage to reflect laser beam  114  into a predetermined raster scan  118 . In one or more embodiments, scanned beam display  100  may further include beam shaping optics  112  to shape the laser beam  114  emitted by laser source  110 . For example, the shape of the laser beam  114  emitted from laser source  110  may be generally elliptical in shape, and beam shaping optics  112  may comprise a circularizer for causing the beam profile  112  to be generally circular in shape after being circularized by beam shaping optics  112 . Likewise, beam shaping optics  112  may comprise a top hat lens to cause the profile of the beam, emitted by laser source  110  to be generally flattened in shape from a natural Gaussian type profile as emitted from a typical laser source  110  although the scope of the claimed subject matter is not limited in this respect. In one or more embodiments, other various beam profiles may be utilized, for example an apodized sinc function and/or other arbitrary beam profiles as long as the appropriate size and clipping aperture are determined for best uniformity across eyebox  126 , while maintaining minimized raster ripple. Although a Gaussian beam profile may provide system simplicity, using an apodized sinc may enhance the modulation transfer function (MTF) of scanned beam display  100 , although the scope of the claimed subject matter is not limited in this respect. 
     In one or more embodiments, the laser beam  114  is reflected by MEMS scanner  116  to generate a raster scan  118  projected onto an exit pupil expander (EPE)  120 . The maximum total beam deflection angle capable of being produced by MEMS scanner  116  may be referred to as θ. Where MEMS scanner  116  has a scan mirror size of D, which may also refer to the clipping aperture, for a given image size of L, the relationship of θ to the input numerical aperture NA IN  at MEMS scanner  116  may be givens as: 
       2LNA IN =Dθ 
     In one or more embodiments, exit pupil expander  120  may comprise an array of lenses, for example a microlens array (MLA). In one embodiment, the array may comprise any element or cell having a particular transfer function, and is not limited to a microlens array. Likewise, EPE  120  may comprise a dual MLA formed by two adjacent MLAs. In one or more embodiments, the array may comprise a periodic array of elements or cells, also referred to as lenslets, and in one or more alternative embodiments the array may comprise multiple elements that monotonically increase or decrease in spacing across the array, and or otherwise smoothly vary in spacing across the array, along any dimension of the array, and the scope of the claimed subject matter is not limited in this respect. When the reflected beam raster  118  is scanned across exit pupil expander  120 , the image to be displayed from exit pupil expander  120  may be relayed by the projection optics  122  to form a viewing eyebox, or exit pupil, such that the image to be displayed appears at a distance, typically 2-3 meters for a head-up display (HUD), away from the location of the viewer&#39;s eye  128 . In some embodiments, exit pupil expander  120  and/or projection optics  122  may be located at or near the vicinity of MEMS scanner  116 , such as where scanned beam display  100  comprises a head-up display (HUD) in a vehicle or the like, for example where the image is reflected off the windshield of the vehicle and back to the viewer&#39;s eye  128 . In some particular embodiments, exit pupil expander  120  may be disposed in, on, or near the windshield. In one or more alternative embodiments, one or more of exit pupil expander  120  and/or projection optics  122  may be disposed near the viewer&#39;s eye  128 , for example where projection optics  122  comprises an ocular at or near the viewer&#39;s eye, such as suspended by a head band worn by the viewer, and/or disposed in a visor of a head band or helmet worn by the viewer. However, these are merely example arrangements of exit pupil expander  120  and projection optics  122 , and the scope of the claimed subject matter is not limited in these respects. 
     Exit pupil expander  120  is capable of expanding, or converting, the numerical aperture (NA) from the numerical aperture input at MEMS scanner  116 . In such embodiments, exit pupil expander  120  may provide NA conversion at an intermediate image plane to achieve a larger exit pupil. As shown in  FIG. 1 , the full exit cone angle due to the expanded NA output  124  of exit pupil expander can be represented by approximately twice the output NA (2NA OUT ). The size, L, of the image at exit pupil expander  120  is equal to the product of image resolution and pixel size. The expanded NA output  124  is relayed by projection optics  122  to result in an eyebox  126  in which the projected image is capable of being viewed by the viewer&#39;s eye  128 , so that the projected image is generally viewable when the viewer&#39;s eye  128  is located within eyebox  126 , and is generally not viewable when the viewer&#39;s eye  128  is located outside of eyebox  126 . While the viewer&#39;s eye  128  is located within the eyebox  126 , the viewer is capable of viewing the image in a field of view (FOV)  130  defined by, among other things, the projection optics  122 . The relationship between the output numerical aperture, exit pupil diameter (EP) and the field of view is defined as: 
         LNA   OUT   =EPsin ( FOV/ 2) 
     The image is generally viewed by the viewer as a planar image based on a diffraction pattern  132  of beamlets generated by raster scan  118  on exit pupil expander  120 . The resulting diffraction pattern  132  may be based at least in part on the characteristics the beam profile of laser beam  114 , the scanning capabilities and addressability of MEMS scanner  116 , the characteristics of exit pupil expander  120  and the relationships between exit pupil expander  120  and raster scan  118  impinging on the lenses of exit pupil expander  120 , for example beam spot size, Fill Factor, and so on, although the scope of the claimed subject matter is not limited in these respects. In one or more embodiments, scanned beam display  100  may be configured to operate where the beam profile of laser beam  114  is generally Gaussian in shape, which may be a natural beam profile of the laser beam  114  generated by laser source  110 . In such a configuration, beam shaping optics  112  may not require a top hat lens to shape the beam profile of the emitted laser beam  114 . In one or more embodiments, a near field  134  region of the scanned beam display  100  may be defined as the optical pathway in the region comprising exit pupil expander  120 , which can be considered located at a conjugate image plane of the source, and a far field  136  may be defined as a region defined by eyebox  126 , where field of view  130  formed by projection optics  122  can be seen by the viewer&#39;s eye  128 , wherein eyebox  126  is typically at an image conjugate plane of MEMS scanner  116 , although the scope of the claimed subject matter is not limited in this respect. 
     In one or more embodiments, a periodic EPE  120  may be utilized in scanned beam display  100  to result in constant beamlet spacing, however the transmission function of a given lens cell, or lenslet, of EPE  120  determines the resulting diffraction envelope  132  due to the cell and thus the level of beamlet-to-beamlet uniformity. Note that diffraction pattern and diffraction envelope have been used interchangeably herein. In some instances, the diffraction envelope may result from a single cell transmission function, while the interference of overlapping diffraction envelopes coming from neighboring cells gives rise to interferences, thus forming the diffraction orders, or beamlets. For diffraction patterns containing many beamlets, the diffraction envelope can be approximately visualized by drawing an envelope through the peaks of all beamlets. Where scanned beam display  100  is designed to allow the viewer&#39;s head to move freely within the eyebox  126 , the relationship between the input beam profile and shape characteristics and the transmission function of EPE  120  is taken into account in order to achieve a display without significant visible coherent artifacts. A periodic EPE  120  may be utilized in scanned beam display  100  to achieve such a higher level of beamlet-to-beamlet uniformity. While a periodic EPE  120  array is capable of eliminating random speckle artifacts, periodic beamlet diffraction pattern  132  at the eyebox  126  as a result of ordered interference still may be subject to coherent artifacts such as intensity gaps between beamlets and/or beamlet intensity overlap. For head-free type scanned beam display  100 , these coherent artifacts may result in two undesirable visual effects: an intensity tiling pattern, or simply tiling, that appears across the FOV  130 , but is not mapped to the FOV  130 , and/or a Moiré pattern that appears across the FOV  130 , caused by aliasing between the pitch of EPE  120  and the line spacing of raster scan  118 . In general, scanned beam display  100  may be designed to minimize such tiling and/or Moiré artifacts, although the scope of the claimed subject matter is not limited in these respects. 
     In one or more embodiments, once scanned beam display  100  is configured to achieve beamlet-to-beamlet uniformity, beam controls, may be utilized to reduce and/or limit these coherent artifacts of tiling and/or Moiré to achieve a high level of display uniformity and image stability. Such beam controls may involve constraints on the beam parameters and may be summarized as follows: beam shape at the system clipping aperture, beam profile across the system clipping aperture, and/or beam focus NA. In one or more embodiments, the pitch of the elements EPE  120  (EPE pitch), and/or beam wavelength may also be taken into consideration when determining the quantities of these parameters. For instance, exit pupil pattern uniformity may be consistent and independent of spot position for spot sizes larger than the EPE pitch, but may be dependent on spot position for spot sizes smaller than the EPE pitch, or cell size. Moiré can occur for the latter case since exit pupil uniformity from a given spot location, or from a given field point within the image, emanates a different intensity toward the viewer&#39;s eye depending on the spot location within the illuminated cell in EPE  120 . As it typically may be undesirable to require registration of the raster with the EPE  120  due to raster trajectory artifacts, such as raster pinch, aliasing between the pitch layout of EPE  120  and/or the line spacing of raster scan  118  may introduce a Moiré intensity pattern across FOV  130 . Where the spot size of beam  114  is larger than the cell size of EPE  120 , the overall diffraction envelope  132  of the exit pupil pattern is relatively stable versus spot position at the plane of EPE  120 , but intensity gaps may form between beamlets within the exit pupil pattern as the spot grows beyond the cell size. A larger spot size can illuminate more neighboring cells in EPE  120 , thereby increasing the number of exposed equally spaced scatter centers, each of which may be approximately collimated by projection optics  122  at very slightly different, but equally spaced angles toward the viewer&#39;s eye  128 . In an extreme case the result may be considered similar to the N-1 extinctions formed across the interference region of N-equally-spaced beams, forming gaps in the areas exhibiting destructive interference. Consequently, for the case where the spot size of laser beam  114  is larger than the cell size of EPE  120 , each resulting beamlet NA is on the order of the input beam NA. 
     In one or more embodiments, a fill factor of F=1 represents a spot formed by an NA that contains energy out to an angle that matches the NA subtended by a single diffraction order spacing, and thus the spacing of a single beamlet within the exit pupil. Although fill factor is independent of beam profile of laser beam  114 , a typical spot size for the case of F=1 would be on the order of the cell size of EPE  120 . Where intensity gapping occurs, a visible intensity tiling pattern, which is a coherent artifact, appears across FOV  130  that is not mapped to FOV  130  in angle, and so the tiling pattern appears to move in the background of the image upon movement of the viewer&#39;s head. The tiling pattern is formed by intensity variation across beamlets within the exit pupil, and which may appear to be somewhat smoothed to the viewer&#39;s eye  128  due to integration by the eye pupil, which comprises a convolution of the beamlet pattern with eye pupil size. As more beamlets are captured through an eye pupil, uniformity of the image can appear improved. However this may imply that for a given beamlet density uniformity may improve when the brightness is reduced so as to allow the eye pupil to increase in size. Increasing beamlet density at the exit pupil can be achieved by using lower angular resolution. However such a design of scanned beam display  100  may not be acceptable for higher angular resolution specification of scanned beam display  100 . Thus, in one or more embodiments EPE pitch may be selected based at least in part on a desired resolution. Where scanned beam display system  100  is designed to have a higher angular resolution, laser beam  114  may be tailored using beam controls to achieve higher uniformity with reduced coherent artifacts. In one or more embodiments, scanned beam display system  100  may utilize an EPE  120  comprising a compressed microlens array capable of providing a desired eyebox aspect ratio. Such compressed microlens arrays are shown in and described with respect to  FIGS. 2  through  FIG. 7 , below. 
     Referring now to  FIG. 2 , a diagram of a compressed microlens array having rectangular lenslets for a scanned beam display capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments will be discussed. As shown in  FIG. 2 , an exit pupil expander  120  may comprise a microlens array  210  comprising an array of generally square shaped lenslets  214  having centers  218  as shown. In such a microlens array  210 , the vertical distance d y  between centers  218  of lenslets  214  is approximately equal to the horizontal distance d x  between centers  218  of lenslets  214 . In general, a microlens array  210  comprising an array of generally square shaped lenslets  214  may result in a corresponding eyebox  126  having a generally square shape  222 . Such an eyebox  126  has an aspect ratio approximately equal to one. 
     In order to provide an eyebox  126  having an aspect ratio closer to a typical display, for example approximately a 2:1 aspect ratio, an 800 by 600 pixel aspect ratio, a 16 by 9 aspect ratio, and so on, an exit pupil expander  120  may be designed to have a compressed microlens array  212 . In one embodiment, rather than using generally square shaped lenslets  214 , compressed microlens array  212  may comprise an array of generally rectangular shaped lenslets  216 . In such an arrangement, the vertical distance d y  between centers  220  of lenslets  216  may in general be less than the horizontal distance d x  between centers  220  of lenslets  216 . In general, a compressed microlens array  212  may result in a corresponding eyebox  126  having a generally rectangular shape  224  in order to provide eyebox  126  with a desired aspect ratio, for example having a width that is generally greater than its height. Thus, in one or more embodiments, the resulting shape of eyebox  126  may be designed to have a desired aspect ratio based at least in part on the shape of the lenslets  216  of the microlens array  212  used in EPE  120 . Since the shape of the lenslets  216  is capable of producing a desired shape and/or aspect ratio of eyebox  126 , other shapes of lenslets  216  may be utilized to provide a resulting eyebox  126  shape, for example as shown in and described with respect to  FIG. 3 , below. 
     In one or more embodiments, the desired shape of eyebox  126  may be based at least in part on the geometry of the lenslets  214  of microlens array  210 . As will be discussed in further detail with respect to  FIG. 4  and  FIG. 5 , below, beam spots from raster scan  118  pass through individual lenslets  210 , the lenslets function as clipping apertures to shape and quantize the beam into beam partitions. It should be noted that beamlets appearing at the eyebox  126  are caused by interference due to the overlap of the envelopes formed by these beam partitions cut up into buckets of energy at the EPE  120  as the beam from the raster scan  118  passes through the individual lenslets  210  wherein the amount and shape of the clipping is a function of the geometry of the lenslets  210 . As a result, when the beam partitions combine in the eyebox  126  to form diffraction patterns, the resulting diffraction patterns combined to form a resulting eyebox  126  shape formed from the combination of clipped beam partitions. Thus, the desired shape of eyebox  126  may be achieved by such vignetting of the resulting beamlets via the clipping function of the individual lenslets when the diffraction patterns are combined at the eyebox  126  while maintaining high efficiency. In one or more embodiments, the term virtual vignetting at utilized herein refers to achieving the effects of physical vignetting for the optical system without suffering clipping losses that may otherwise occur with physical vignetting. The term virtual vignetting may also refer to in general the intentional shaping of eyebox  126 . Thus, the eyebox  126  may be shaped by such vignetting at the exit pupil expander  120  via the design of the microlens array  210  or  212  (or  310  or  312 ) of the EPE  120 . In other words, virtual vignetting of the eyebox  126  may be achieved by only supplying the projection relay optics  122  of the scanned beam display  100  with the desired input acceptance cone NA from all field points from microlens array  210  or  212  (or  310  or  312 ) of EPE  120 , thus enabling only the intended eyebox  126  shape and volume by design. Such an arrangement of eyebox  126  via virtual vignetting may also reduce or eliminate swimming artifacts by eliminating light outside the design angles of the projection relay optics  122 . It may also limit scatter and contrast loss in the display image quality by providing the necessary effects of physical vignetting without actually requiring clipping of the light at some location within the display system. Thus, in one or more embodiments, microlens array  210  or  212  (or  310  or  312 ) may be compressed to have an aspect ratio generally on the order of 2:1, although variations from a 2:1 ratio may also be provided according to the application design, for example where the display may comprise 800 by 600 pixels, where a 16:9 ratio is designed, and so on, and the scope of the claimed subject matter is not limited in this respect. In general, the aspect ratio of the eyebox  126  can be designed independently of the FOV aspect ratio of the display. In general, the resulting eyebox  126  may have an aspect ratio where the horizontal dimension is longer than the vertical dimension. Thus, microlens array  210  or  212  (or  310  or  312 ) may be designed to be compressed to have such an aspect ratio where the width is greater than its height by compressing the layout of the lenslet centers  218  or  220  of the array. In one embodiment, lenslets  214  or  216  may have anamorphic profiles. In one or more alternative embodiments, the focal length of the lenslets  214  or  216  may be the same in both orthogonal horizontal and vertical directions. Furthermore, microlens array  210  or  212  may be transmissive or reflective and may provide non-radially symmetric exit cones  124  from EPE  120  in order to achieve the eyebox  126  to have a desired aspect ratio, for example a 2:1 aspect ratio. Such a designed microlens array  210  or  212  (or  310  or  312 ) may be referred to as a compressed microlens array (MLA). Thus, by using a compressed MLA, the shape of eyebox  126  maybe tailored to a desired aspect ratio having a particular geometry, for example the shape of eyebox  126  may comprise a rectangle, a compressed hexagon, an ellipse, and so on. For elliptical shapes, a true elliptical lenslet shape does not pack 100% by geometry, which may also be true for other shapes as well, however in such an embodiment the unfilled gap regions could be masked off to actually allow the generation of a true, or nearly true, elliptically shaped eyebox output. Examples of such alternative shapes of eyebox  126  achieved via a compressed MLA are shown in and described with respect to  FIG. 3 , below. 
     Referring now to  FIGS. 3A and 3B , diagrams of alternative compressed microlens arrays having hexagonal lenslets as shown in  FIG. 3A  and non-compressed microlens arrays having hexagonal lenslets as shown in FIG. B for a scanned beam display capable of providing a desired aspect ratio in accordance with one or more embodiments will be discussed. As an alternative to using rectangular shaped lenslets  216  in a compressed microlens array  212 , other shapes of lenslets may be utilized such as hexagonal shaped lenslets  314  or rotated hexagonal shaped lenslets  316  as shown in  FIG. 3 . For example, EPE  120  may comprise a microlens array  310  comprising a compressed array of hexagonal shaped lenslets  314  to result in eyebox  126  having a general compressed hexagonal shape  318 . As with the rectangular shaped lenslets  216  as shown in  FIG. 2 , hexagonal shaped lenslets  314  may be compressed in one direction with respect to another orthogonal direction to provide a compressed hexagonal shape  318  to eyebox  126 . Thus, the vertical spacing d y  between centers  322  of lenslets  314  may be less than the horizontal spacing between centers  322  of lenslets  314  to provide a generally compressed hexagonal shape  318  to eyebox  126  such that eyebox  126  has an aspect ratio where its horizontal width is longer than its vertical height. 
     Similarly, exit pupil expander  120  may comprise a compressed microlens array  312  comprising an array of rotated hexagonal shaped lenslets  316 . The resulting eyebox  126  may then generally comprise a generally rotated hexagonal shape  320 . Likewise, the overall aspect ratio of the resulting compressed rotated hexagonal eyebox  320  may be designed by selecting the ratio of the vertical spacing d y  between centers  324  of rotated hexagonal lenslets  316  to the horizontal spacing d x  between centers  324  of rotated hexagonal lenslets. In general, any shape of lenslet and ratio of vertical distance to horizontal distance between the centers of the lenslets may be selected to result in a desired shape and/or aspect ratio of the eyebox  126 , and the scope of the claimed subject matter is not limited to any particular lenslet shape, vertical and/or horizontal spacing, and/or aspect ratio. For example, the lenslets of the microlens array may comprise elliptical shaped elements, octagonal shaped elements, and so on, and the scope of the claimed subject matter is not limited in these respects. For comparison with the compressed hexagonal arrays  310  and  312  as shown in  FIG. 3A ,  FIG. 3B  shows resulting eyeboxes  126  having a non-compressed hexagonal shape  328  and a non-compressed rotated hexagonal shape  336  from respective non-compressed hexagonal array  322  of non-compressed hexagonal lenslets  324  and non-compressed rotated hexagonal array  330  of non-compressed rotated hexagonal lenslets  332 . In such arrangements as shown in  FIG. 3B , centers  326  of lenslets  324  and/or centers  334  of lenslets  332  may be generally equidistantly spaced with respect to the nearest neighboring centers  326 . 
     Referring now to  FIG. 4 , a diagram of an example time-averaged diffraction envelope resulting from a beamlet beam profile scanned across a displayed image having a desired eyebox aspect ration in accordance with one or more embodiments will be discussed.  FIG. 4  illustrates how individual beamlets  424  having corresponding spot profiles  410 ,  412 , and  414  from raster scan  118  are affected by microlens array  410  of EPE  120  to form individual diffraction patterns  416 ,  418 , and  420  that combine in exit cone  124  into an overall diffraction pattern  132  based at least in part on the geometry of lenslets  422  of which microlens array  410  comprises. As shown in  FIG. 4 , raster scan  118  may address one or more lenslets  422  of microlens array  410  in exit pupil expander  120 , for example by scanning across MLA  410  two or more scan lines for a given lenslet  422 . The beam profile of laser beam  114  used to generate raster scan  118  may comprise, for example, a Gaussian beam profile to generate near-Gaussian shaped spot profiles  410 ,  412 , and  414  for each scan line per lenslet  422 . The resulting diffraction pattern for any single one of spot profiles  410 ,  412 , and/or  414 , when considered alone, may result in underfilling the diffraction envelope with energy in such a way that is spot position dependent, and as a result an aliasing, or beating pattern, may occur between the array pitch of EPE  120  the line spacing of raster scan  118 , thereby causing Moiré artifacts across the displayed image. For example, spot profile  410  may result in a corresponding diffraction pattern  416  which exhibits a skew in intensity toward the lower end of diffraction pattern  132 , with less intensity toward the middle or upper end of diffraction pattern  132 . For a given eye location within the eyebox  126 , this intensity skew may result in an apparent ripple, or fringe, in the Moiré pattern in the displayed image. Likewise, spot profile  412  results in a diffraction pattern  418  having greater intensity in the middle and less intensity in the lower or upper ends of diffraction pattern. Similarly, spot profile  414  may result in diffraction pattern  420  having greater intensity at the upper end of diffraction pattern  132 , and less intensity at the middle or lower end of diffraction pattern. Thus, if Gaussian beams are used having Fill factor greater than F=1, such that the spot profiles formed at the raster scan  118  are smaller than the lenslet pitch, and the addressability A=d/l s  for EPE pitch d and line spacing l s , is set to A=1, meaning on average there is only about a single scan line per lenslet  412  in EPE  120 , the resulting diffraction pattern  132  may not be even and thereby generate Moiré artifacts in the displayed image. However, in one or more embodiments, the spot energy may be distributed evenly within a cell or lenslet  422  over time so that raster scan  118  may provide more than one scan line per lenslet  422  to provide an addressability of A&gt;1. An addressability of A&gt;1 may be accomplished by providing additional addressability with MEMS scanner  116  when defining display pixel size p on order of EPE pitch d. By doing so, raster scan  118  will result in two or more scan lines per lenslet  422  so that over time, individual corresponding diffraction patterns  416 ,  418 , and  420  resulting from spot profiles  410 ,  412 , and  416  will combine to result in an overall diffraction pattern  132  that is sufficiently constant over the entire diffraction envelope  132  to reduce or minimize the Moiré effect in the displayed image. Thus, in one or more embodiments, if a Gaussian beam profile is utilized, Moiré artifacts may be effectively reduced or eliminated by utilizing additional addressability of MEMS scanner  116  to cause raster scan  118  to provide more than one scan line per lenslet  312  to have an addressability of A&gt;1, however the scope of the claimed subject matter is not limited in this respect. Thus, the overall shape of diffraction pattern  132 , and thus the resulting shape of eyebox  126 , may be tailored via shaping of the individual diffraction patterns  416 ,  418 , and  420 , via shaping of the geometry of lenslets  422  of MLA  410 , and/or via shaping of the beam profiles  410 ,  412 , and  414  as discussed with respect to  FIG. 5 , below. 
     Referring now to  FIG. 5 , a diagram of an optical system for a scanned beam display system capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments will be discussed. The basic concept of a compressed MLA solves the eyebox shape problem to result in an eyebox  126  having a shape tailored to a desired aspect ratio. However, if the beam shaping optics  112  of the light source module, comprising laser source  110  and beam shaping optics  112 , include a round top-hat output optic, efficiency may suffer. Thus, beam shaping optics  112  can be designed such that a top-hat output correlates to the desired aspect ratio of high Fill factor beamlets formed within eyebox  126  at the output of beam shaping optics  112  so that the efficiency loss due to an appropriately shaped system-clipping-aperture, for example a compressed hexagon, ellipse, or rectangle, may be minimized. Depending on uniformity requirements, a moderate truncation ratio can be considered for use in laser source  110  as well as in the top-hat converter optic of beam shaping optics  112 . Beam cone NAs can be defined according to the diffraction pattern beamlet NAs and beamlet layout within the eyebox resulting from the interference of diffraction envelopes due to layout and shape of lenslets  314  in order to maintain high Fill Factor F. 
     An example of the lenslet shape, eyebox shape, and resulting beamlet layout is illustrated in  FIG. 5 . Note that the beamlet layout can now be used to dictate a desirable system clipping aperture and orientation which will help increase high Fill Factor F. For example, EPE  120  may include a compressed MLA  310  as shown in  FIG. 3  comprising an array of compressed lenslets  314  generally having a hexagonal shape. The hexagonal lenslets  414  my provide a hexagonally shaped clipping aperture  516  which when applied to a laser beam  114  having a circularly shaped profile may clip some of the power of the laser beam having a circular cross section  514 . Thus, power of the laser beam  114  in its circular cross section  514  falling outside the hexagonally shaped clipping aperture  516  may be wasted power. In one or more embodiments it may be possible to capitalize on a dynamic Moiré condition in such an arrangement in order to reduce or minimize Moiré and/or tiling artifacts. Such embodiments would allow a spotsize in the faster scan dimension of laser beam  114  in raster scan  118  to be reduced to less than optimum for higher Fill Factor F while maintaining the spotsize along the slower scan dimension. Such an arrangement would be beneficial for efficiency since it would not be required to force an elliptically shaped spot system clipping aperture  516 , and thus no changes in the beam shaping optics would be required. In addition such an arrangement would also result in increased light efficiency without the requiring an elliptically shaped clipping aperture  516 . 
     In one or more embodiments wherein a higher Fill Factor and higher uniformity are provided, higher efficiency can be regained via utilization of an elliptical top-hat output element  514  in beam shaping optics  112 , or and/or by providing an output element  514  in beam shaping optics  112  having a shape closer to that of an ideal clipping aperture dictated by beamlet layout within eyebox  126 . Note that when the desired aspect ratio of an eyebox  126 , and thus beamlet and clipping aperture shape, approximate that of a laser diode in laser source  110  having and elliptical NA output aspect ratio, it may be possible to capitalize on the resulting output exit cone shape and therefore simplify the beam shaping optics  112  needed to achieve a higher Fill Factor F. In one or more embodiments, the aspect ratios of the profiles  510  and/or  512  of the laser beam  114 , could be sufficiently matched with the aspect ratio of the lenslets  314  and thus the resulting eyebox  126  may result in an arrangement in which a circularizer optic in beam shaping optics  112  is not required. In other words, typically a laser diode emits a beam having an elliptical shaped cross section that is circularized by a circularizer optic in beam shaping optics  112 . However, since it is desired to provide an eyebox  126  having an aspect ratio where the width is greater than its height, the scanned beam display  100  may take advantage of the elliptical shape of the laser beam  114  to provide a higher efficiency by eliminating the circularizer optic from the beam shaping optics  112 , although the scope of the claimed subject matter is not limited in this respect. In one or more embodiments, although the aspect ratio of the input beam may be similar to the lenslet and thus eyebox shape, the input beam typically needs to be oriented orthogonal to the lenslet orientation wherein longer axis of beam at MEMS will be taller than wide, while at the lenslet the beam will be wider than tall, and then the spotsize formed from the beam focused from the MEMS scanner at the EPE will be wider than tall and thus be generally aligned with the shape of the lenslets to prove a higher fill factor in the lenslets. 
     In one or more embodiments, a variety of top-hat converters and combinations thereof may be considered for utilization in beam shaping optics  112 : a 1-dimensional top-hat converter  514  may be used for capitalizing on dynamic Moiré; a 2-dimensional elliptical Gaussian-to-elliptical top-hat output converter  514  may be utilized with a compressed MLA  310  in EPE  120  for HUD type applications; a 2-dimensional circularized-Gaussian-to-elliptical top-hat converter  514 ; two crossed 1-dimensional top-hat converters  514 ; 1-dimensional top-hat converter  514  with orthogonal clipping, and so on. Note also that conjugate focus effects on either or both ends of the converter  514  can be implemented, for example using a Gaussian-to-top-hat converter. However, these are merely examples of the types of converters  415  that may be utilized in beam shaping optics to achieve a desired amount of efficiency with a compressed MLA  310 , and the scope of the claimed subject matter is not limited in these respects. 
     In one or more embodiments, when using the arrangements as described, above, the spot shape at EPE  120  may become somewhat elliptical due to the aspect ratio of the exit cone forming the spot. Furthermore, an ideal shape of the beamlets as defined by beamlet layout centroids may also become compressed. Relative orientations of compressed microlens arrays  310  and the corresponding output eyebox shapes  318  of both hexagonal as well as rectangular are shown in and described with respect to  FIG. 2  and  FIG. 3  for a given focal length, and are shown as relative indicators of expected relative output size of eyebox  126  for a given focal length of the compressed MLA. The focal length of the given MLA and/or the shape of the lenslets of the MLA may be selected according to the type of application, for example to be tailored to a HUD type display application, however many combinations are possible depending on the desired application, and the scope of the claimed subject matter is not limited in these respects. 
     Referring now to  FIG. 6 , a profile view of a compressed microlens array for a scanned beam display system comprising an array of compressed lenslets for a scanned beam display system capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments will be discussed. As shown in  FIG. 6 , EPE  120  may comprise a microlens array  410  having a plurality of lenslets  414  wherein the lenslets are shaped and/or spaced to provide a compressed MLA  410 . Thus, the vertical spacing of the centers of lenslets  414  may be compressed with respect to the horizontal spacing of the centers of lenslets  414  as shown in and described with respect to  FIG. 2  and  FIG. 3 . Furthermore, lenslets  414  may be designed with a desired radius (R), flat-top width (d W ), seam radius (r S ), diagonal sag (t d ), and/or grid sag (t g ) to appropriately shape the resulting diffraction patterns  416 ,  418 , and  420  as shown in  FIG. 4  to result in an overall diffraction pattern  132  that provides a desired shape of eyebox  126 . In one or more embodiments, for a dual MLA case, minimized seam radius r S  and/or flat-top width d w  may help achieve greater performance. Typically, deviations from and ideal lenslet profile may result in non-uniform intensity fluctuation across the eyebox  126 . In some embodiments, having non-minimized seams radius and/or flat-top width may be a useful design parameter, for example in applications in which moderate uniformity may be achieved from an EPE having a single MLA. As but one example, compressed MLA  410  may be about 130 mm in a horizontal direction and may be about 100 mm in a vertical direction, and have a thickness of about 1.1 mm, although the scope of the claimed subject matter is not limited in this respect. In one or more embodiments EPE  120  may comprise a single compressed MLA  410 . In one or more alternative embodiments, EPE  120  may comprise a dual MLA, where one or both of the MLAs comprises a compressed MLA  410 . A dual MLA arrangement is shown in and described with respect to  FIG. 7 , below. 
     Referring now to  FIG. 7 , a profile view of a compressed dual microlens array for a scanned beam display system comprising an array of compressed lenslets for a scanned beam display system capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments will be discussed. In one or more embodiments, two compressed MLAs  710  and  712  may be utilized in a double-pass dual MLA arrangement in a single EPE  700  as shown in  FIG. 7 . In one or more particular embodiments, the dual microlens arrays  710  and  712  may be tangibly embodied in the form of a double-sided molded single element wherein MLA  710  and MLA  712  are formed from the same piece of material such as a molded polymer or the like. Alternatively, MLA  710  and MLA  712  may be fabricated as separate units that are combined together into a single unit via an optically transparent adhesive or the like. In one or more embodiments, such a dual MLA EPE  120  may provide a hopped eyebox effect via utilization of a relative tilt of the input scan angle bias (θ)  714  as shown. In one or more embodiments, eyebox hopping may refer to a characteristic of the dual MLA EPE which occurs when an input beam has angle of incidence just outside the exit NA of the EPE, dual MLA or reflective double-pass MLA over reflector. In one or more embodiments, the input scan angle bias  714  may involve a relative transverse shift of MLAs  710  and  712  and/or a bias relative tilt of the scan input with respect to EPE  700 , or a combination of both. Such a hopped eyebox effect may be utilized, for example, to diminish ambient reflections such as sunlight where scanned beam display  100  is deployed in a HUD display of vehicle, an example of which is shown in and described with respect to  FIG. 8 , below. Both single MLA and dual MLA configurations may be utilized in EPE  700 . In general, uniformity of the displayed image may be better with a dual MLA EPE  700 . Also, a dual MLA EPE  700  is capable of trading off beam-steering with input angle bias  714  of the full scan. In one or more embodiments, a prism shaped substrate (not shown) may be provided for the scan-side MLA  710 , and a flat shaped substrate may be provided for the output side MLA  712  so as to simplify the mechanics of the MEMS scan engine  116  while providing a bias angle on the output cone chief ray as input to the projection relay optics  122 , although the scope of the claimed subject matter is not limited in these respects. In one or more alternative embodiments, a non-telecentric EPE (not shown) can be created with a compressed MLA EPE in a similar fashion as a regular-tiled EPE. In addition, the two dissimilar pitch MLAs required for forming a non-telecentric dual MLA EPE can be appropriately spaced in tandem, or molded appropriately on each side of a single element. Furthermore, a compressed MLA arrangement as discussed herein may also incorporate phase shifting by providing a periodic MLA with ordered phase shifts, although the scope of the claimed subject matter is not limited in these respects. 
     Referring now to  FIG. 8 , a diagram of a vehicle having a head-up display comprising a scanned beam display and a compressed microlens array capable of providing a desired eyebox aspect ratio in accordance with one or more embodiments will be discussed. As shown in  FIG.8 , vehicle  800  may deploy scanned beam display  100  in a HUD-type arrangement, for example so that the operator of vehicle can view vehicle instrument data while simultaneously looking through windshield  810  of vehicle  800 . In one or more embodiments, display  100  may be mounted in the dashboard  814  of vehicle  800  and project a raster scan  118  of a displayed image onto EPE  120 . In the embodiment shown, EPE  120  may be partially reflective to reflect the raster scan  118  via output cone into eyebox  126 , and partially transmissive so that the viewer may see through EPE  120  and through windshield  810  into the environment outside of vehicle  800 . In alternative embodiments, EPE  120  may be transmissive and disposed within dashboard  814  and/or otherwise in or proximate to display  100  wherein windshield  810  itself is used as a reflective surface to reflect raster scan  118  off windshield  810  and into eyebox  126  so that the image is viewable by the viewer&#39;s eye  128 . Thus, in one or more embodiments, EPE  120  may comprise one or more compressed MLAs, for example MLA  310  of  FIG. 3  comprising an array of compressed hexagonally shaped lenslets  314  to result in an eyebox  126  having an aspect ratio wherein the width of eyebox  126  is greater than the height of eyebox  126  as discussed herein. As a result, vehicle  800  may comprise a scanned beam display having a compressed MLA to result in an eyebox having a desired shape and/or aspect ratio via virtual vignetting. However, this is merely one example deployment of a compressed MLA to achieve a desired eyebox shape in a scanned beam display, and the scope of the claimed subject matter is not limited in this respect. 
     Although the claimed subject matter has been described with a certain degree of particularity, it should be recognized that elements thereof may be altered by persons skilled in the art without departing from the spirit and/or scope of claimed subject matter. It is believed that the subject matter pertaining to eyebox shaping through virtual vignetting and/or many of its attendant utilities will be understood by the forgoing description, and it will be apparent that various changes may be made in the form, construction and/or arrangement of the components thereof without departing from the scope and/or spirit of the claimed subject matter or without sacrificing all of its material advantages, the form herein before described being merely an explanatory embodiment thereof, and/or further without providing substantial change thereto. It is the intention of the claims to encompass and/or include such changes.