Patent Publication Number: US-2023152624-A1

Title: Light Engine Using a Polarization Splitting Lens Unit for Exit Pupil Illumination

Description:
RELATED APPLICATION 
     The present application claims priority to U.S. Provisional Application 63/264,240 filed on Nov. 17, 2021, and incorporates that application in its entirety. 
    
    
     FIELD 
     The present invention relates to an architecture for illuminating a display panel utilizing a polarization splitting lens unit. 
     BACKGROUND 
     A traditional LCOS (liquid crystal on silicon) system is a reflective display technology that requires an external source of polarized illumination. The light is often provided by separate red, green, and blue LEDs (light emitting diodes). The light from the LEDs, in the prior art configuration, are combined using an X-cube to combine the light from the three different LEDs, providing the different colors. In some embodiments, a lens is used in front of the LED to focus the light. The output of the X-cube passes through an MLA (microlens array) which focuses the light to intermediate optics. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG.  1    is an overview diagram of one embodiment of a system in which the polarization splitting lens unit is used. 
         FIG.  2 A  is a diagram of an overview of one embodiment of the polarization splitting lens unit in a light engine, showing light rays and the input and exit pupil overlap. 
         FIG.  2 B  is a perspective view of one embodiment of the polarization splitting lens unit. 
         FIG.  3    is a diagram of an overview of one embodiment of the polarization splitting lens unit in a light engine. 
         FIG.  4 A  is a diagram of an embodiment of the polarization splitting lens unit with a differently angled polarized beam splitter (PBS) in a light engine. 
         FIG.  4 B  is a diagram of one embodiment of the polarization splitting lens unit with offset lenses to create an offset exit pupil in a light engine. 
         FIG.  5 A  is a diagram of an embodiment of the polarization splitting lens unit with a polarization splitting lens unit rotated around the Y-axis in a light engine. 
         FIG.  5 B  is a diagram of an embodiment of the polarization splitting lens unit with a rotated polarization splitting lens unit rotated around the Z-axis in a light engine. 
         FIG.  5 C  is a diagram of an embodiment of the polarization splitting lens unit with a rotated polarization splitting lens unit rotated around the Z-axis in a light engine. 
         FIG.  6 A  is a diagram of one embodiment of the polarization splitting lens unit with the exit pupil in line with the projector element in a light engine. 
         FIG.  6 B  is a diagram of one embodiment of the polarization splitting lens unit with a rotated polarization splitting lens unit in a light engine. 
         FIG.  6 C  is a diagram of one embodiment of the polarization splitting lens unit with offset lenses to create an offset exit pupil in a light engine. 
         FIG.  7 A  is a diagram of one embodiment of the polarization splitting lens unit with the exit pupil in line with the projector element, using a U-fold illumination element in a light engine. 
         FIG.  7 B  is a diagram of one embodiment of the polarization splitting lens unit with the exit pupil in line with the projector element, using a U-fold illumination element with a blazed grating in a light engine. 
         FIG.  8 A  is a diagram of one embodiment of the polarization splitting lens unit using X-cube illumination in a light engine. 
         FIG.  8 B  is a diagram of one embodiment of the polarization splitting lens unit using dichroic plates in a light engine. 
         FIG.  8 C  is a diagram of one embodiment of the polarization splitting lens unit using a dichroic element in a light engine. 
         FIG.  9    is a diagram of one embodiment of the polarization splitting lens unit using RGB illumination in a light engine. 
         FIG.  10    is a diagram of one embodiment of using a polarization conversion element with a polarization splitting lens unit in a light engine. 
         FIG.  11    is a diagram of one embodiment of the polarization splitting lens system with a beam steering prism in a light engine. 
         FIG.  12    is a diagram of one embodiment of the polarization splitting lens system with polarization control in a light engine. 
     
    
    
     DETAILED DESCRIPTION 
     The present application utilizes a light engine that has overlapping input and output pupils, by using a polarization splitting lens unit to spatially separate the input and output pupils, providing industrial design (ID) flexibility. The polarization splitting lens unit is placed in proximity to the top of the optical stack, which permits this flexibility. The polarization splitting lens unit, in some embodiments, may be rotated in two axes, to shift the output pupil relative to the rest of the light engine. This shifts the field of view, and provides additional flexibility for the positioning of the light engine relative to the downstream optical elements, such as a diffractive waveguide combiner. The light may enter the system through an illumination waveguide, in one embodiment. 
     The following detailed description of embodiments of the invention makes reference to the accompanying drawings in which like references indicate similar elements, showing by way of illustration specific embodiments of practicing the invention. Description of these embodiments is in sufficient detail to enable those skilled in the art to practice the invention. One skilled in the art understands that other embodiments may be utilized and that logical, mechanical, electrical, functional, and other changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
       FIG.  1    is an overview diagram of one embodiment of a system in which the polarization splitting lens unit is used. The light  110  from illumination subsystem  115  enters the system  120 . The light  110  is generated by a light source which may be one or more of light emitting diodes (LEDs), organic light emitting diodes (OLEDs), lasers, microLEDs, superluminescent diodes (SLEDs), phosphors, quantum dots, or a light source with a different format. In one embodiment, the light from the LEDs forms the entrance pupil  130 . In one embodiment, the illumination subsystem  115  may include light concentrators, an illumination waveguide, mirrors and lenses or other optics, dichroic plates, a dichroic element, a light combiner, or any other set of one or more elements that can produce an entrance pupil image. 
     The entrance pupil  130  defines the dimensions of the light as it enters system  120 , while the exit pupil  135  defines the dimensions of the light as it exits the system  120 . The system  120  includes a polarization splitting lens unit  140 . The polarization splitting lens unit  140  in one embodiment is a cuboid with an angled polarizing beam splitter (PBS)  142 . The light  110  enters the polarization splitting lens unit  140  through an entrance face  144 . Light with a first polarization passes through the PBS toward imaging/illumination optics  150 . Any light with the second polarization, when present, is unused light  145 , and directed out of the polarizations splitting lens unit  140 . In one embodiment, this light is discarded. In another embodiment, this light may be recycled or used in another way. The light exits the polarization splitting lens unit  140  through a double pass face  146 . 
     The light that passes through the PBS then passes through imaging/illumination optics  150 , and is modulated by display element  160 . Display element  160  in one embodiment is a liquid crystal on silicon (LCOS) display. In another embodiment, other types of spatial light modulators may be used. The display element  160  modulates the light, and changes its polarization. The modulated light returned by display element  160  passes through the imaging/illumination optics  150  and enters the polarization splitting lens unit  140  through the double pass face  146 . Because the light is now the opposite polarization when it hits the PBS  142 , it is reflected toward the exit face  148  of the polarization splitting lens unit  140 , and exits the system  120 . Image at the exit pupil  135  may be directed to a user&#39;s eye directly or through a waveguide and/or other optics. 
     The exit pupil  135  is the same size as the entrance pupil  130 , in one embodiment. The entrance pupil  130  and the exit pupil  135  are not offset within the same superpupil. A superpupil is the pupil of an optical system, the area in which the lenses are designed and optimized to image all light. Other designs use two offset subpupils within the superpupil to send the light to the display element and receive the light from the display element  160 , requiring larger size optics  150 . The present system eliminates the need for such subpupils. Furthermore, in one embodiment the system reuses the imaging/illumination optics  150  for both the light directed to the display element  160  and the modulated light directed from the display element  160 , further reducing size. 
     The polarization splitting lens unit  140  is positioned close to the light source, rather than in close proximity to the display element  160 . In one embodiment, an optical power is applied to one or more of its six faces. Note that while the polarization splitting lens unit is shown as a cube, in one embodiment the shape of the three unused faces is irrelevant, as long as it does not interfere with the light transmission. In one embodiment, the polarization splitting lens unit  140  includes a polarized beam splitter  142  at an angle, two substantially parallel faces  144 ,  146 , and one face  148  substantially perpendicular to the parallel faces, and one or more of the three faces have an optical power applied to them. 
     In one embodiment, as shown in  FIGS.  4 B,  5 B,  5 C, and  6 B , the angles of the faces and/or shapes of the lenses may be adjusted when the polarization splitting lens unit is positioned at an angle to the display panel. 
     Although the exit face lenses on the polarization splitting lens unit  140  are illustrated as being convex surfaces, in one embodiment the lenses may be concave or convex. In one embodiment, the optical power on the entrance face  144  and the double pass face  146  effectively act together as a single lens. The optical power on the exit face  148  in one embodiment is matched to the optical power of the entrance face  144 . Because the light passes through the double pass face  144  twice, any changes in the image due to the optical power on that face are negated. In one embodiment, there is only optical power on two faces. In one embodiment, there is only optical power on one face. 
       FIG.  2 A  is a diagram of an overview of one embodiment of the polarization splitting lens unit in a light engine, showing light rays and the entrance and exit pupils split from each other by the polarization splitting lens unit. The illustration shows the light source as illumination waveguide  220 , which guides the light from LEDs  210  to the polarization splitting lens unit  230 . The out-coupler of illumination waveguide  220  is positioned in close proximity to the input face of the polarization splitting lens unit  230 . The polarization splitting lens unit  230  passes the light through to the illumination and imaging stack  240 , which focuses the light onto the LCOS  250 . 
     The light is modulated by the LCOS  250 , and the polarization of the light is reversed, and then the light is redirected back through the illumination and imaging lens stack  240 . When the light hits the PBS in the polarization splitting lens unit  230 , it is reflected toward the exit pupil. From the exit pupil, the image may be guided through a waveguide or other combiners or elements (not shown) to the user&#39;s eyes. 
       FIG.  2 B  is a perspective view of one embodiment of the polarization splitting lens unit. In one embodiment, the polarization splitting lens unit  230  includes a polarizing beam splitter (PBS)  235  at an angle, to reflect the light to the exit face of the polarization splitting lens unit  230 . In one embodiment, the polarization splitting lens unit  230  is a single element with integrated lenses. In another embodiment, the polarization splitting lens unit  230  may include a structure to support the polarizing beam splitter (PBS)  235 , and one or more lenses positioned at the locations shown, e.g., potentially one or two lenses parallel to the entrance pupil on either side of the PBS  235 , and a lens parallel to the exit pupil, but separate from the structure supporting the PBS  235 . 
     In one embodiment, the polarization splitting lens unit  230  is made of optical glass. In another embodiment, the polarization splitting lens unit is made of optical plastic. In another embodiment, any other optically clear material may be used. In one embodiment, the polarization splitting lens unit  230  is manufactured by gluing together two triangular prisms to form a cuboid, with a grating or other material disposed on the interfacing surfaces of the prisms to form PBS  235 . 
     The polarization splitting lens unit  230  in one embodiment has lenses  265 ,  275 ,  285  on three of its faces, the entry face  260 , the exit face  270 , and the double pass face  280 . In another embodiment, only one surface may include a lens—in one embodiment the double pass face  280 —or on two surfaces—in one embodiment the entry face  260  and exit face  270 , may include lenses. The lenses may be shaped to provide an offset to the light exiting the lens. The shaping, on one embodiment, may include the use of a wedge to angle the lens. In one embodiment, the shaping may be a freeform lens. 
     The lenses can vary from convex to concave. The lenses may be spherical or aspherical, or freeform lenses. The lenses may be plano (flat) lenses, in one embodiment, applying no optical power. In one embodiment, the lenses are made from the same material as the polarization splitting lens unit. In another embodiment, they are made from a different optical material. In one embodiment, the lenses are manufactured on the polarization splitting lens unit  230 . In one embodiment, the lenses are glued onto the polarization splitting lens unit  230 . In another embodiment, the lens shapes are manufactured as part of the two prisms which form the polarization splitting lens unit  230 . 
       FIG.  3    is a diagram of an overview of one embodiment of the polarization splitting lens unit in a light engine. The light from LEDs  310  passes through light concentrators  315 , into an illumination waveguide  320 . In one embodiment, each color LED  310  has a separate in-coupler into waveguide  320 . Although the in-couplers are illustrated as being horizontally displaced, in one embodiment the LEDs  310  and associated in-couplers are displaced along any of the axes, including the Z-axis. In one embodiment, the LEDs are arranged in a circular pattern. 
     The out-coupler of the illumination waveguide  320  defines the illumination entrance pupil  330 . The entrance pupil  330  defines the size and orientation of the light entering the system. The light from the out-coupler enters the entry surface of polarization splitting lens unit  340 . The light passes through the PBS  345 . In one embodiment, light of a second polarization is reflected out of the polarization splitting lens unit  340 . In one embodiment, that light is discarded. 
     The light exiting the polarization splitting lens unit  340  passes through imaging/illumination optics  350 , to LCOS panel  360 . The light modulated by LCOS panel  360  is reflected back through imaging/illumination optics  350 , and enters the polarization splitting lens unit  340 . The light is then reflected by the PBS  345 , out of the polarization splitting lens unit  340 . The light exiting the polarization splitting lens unit  340  forms the exit pupil  370 . The light exiting polarization splitting lens unit  340  may be coupled into another waveguide (not shown). 
       FIG.  4 A  is a diagram of an embodiment of the polarization splitting lens unit with a differently angled polarized beam splitter (PBS). In this configuration, the angle of the PBS  445  is not 45 degrees, but rather a different angle. Displacing the PBS  445  changes the output angle of the exit pupil  470  from the normal angle. This is useful to change the optical axis up or down, which provides industrial design flexibility. It also offsets the field of view. In one embodiment, the PBS  445  angle may vary from 20° to 70° (45°±25°). 
     In addition to the increased industrial design flexibility, displacing the exit pupil  470  also reduces ghosting from a reflected image from a combining waveguide into which the exit pupil  470  is directed (not shown). As the light from the exit pupil  470  enters the in-coupling grating of the combining waveguide, a portion of it is diffracted back as if the light had hit a mirror. Angling the exit pupil as shown in FIG.  4 A causes that reflected image from this diffractive order to either miss the PBS  445  or to enter the PBS  445  at an off-axis angle; this reduces the amount of light that makes it back through the system to the LCOS panel  460 . Without the angle, in some embodiments this diffracted light enters the system on-axis, hits the LCOS panel which reflects it back to the exit pupil, which can cause a noticeable ghost in the final image. The angled exit pupil reduces or eliminates the ghost image from the bounce-back (diffractive order). 
       FIG.  4 B  is a diagram of one embodiment of the polarization splitting lens unit with offset lenses to create an offset exit pupil. In this configuration, the PBS  485  in the polarization splitting lens unit  480  is at a standard 45 degree angle, and the off-set exit pupil  470  is produced by a shaped exit face lens  495 . In one embodiment, the optical power and shape of the entrance face lens  490  is matched to the optical power and shape exit face lens  495 , to avoid distortion, having a corresponding offset angle. In one embodiment, because the entrance face lens  490  is angled with respect to the polarization splitting lens unit  480 , the illumination waveguide  420 , or its out-coupler, is also positioned at an angle, so the light enters the entrance face lens  490  of polarization splitting lens unit  480  at an angle. The entrance face lens  490  alters the angle of the light, so the light impacting the PBS  485  is correctly oriented to be directed to the LCOS panel  460 , and modulated. This configuration also provides an offset exit pupil  470 , with its attendant benefits, while using polarization splitting lens unit  480  with a PBS  485  at a 45 degree angle. 
       FIG.  5 A  is a diagram of an embodiment of the polarization splitting lens unit with a polarization splitting lens unit rotated around the Y-axis. In this configuration, the polarization splitting lens unit  540  may be rotated to shift the angle of the exit pupil  570 . By rotating the polarization splitting lens unit  540 , the angle of impact of light returning from LCOS  560  changes, which displaces the exit pupil  570 . In the configuration where the angle of the PBS  545  is different from 45° and the polarization splitting lens unit  540  is rotated around the Y-axis, the output optical axis, and thus the angle of the exit pupil  570  is rotated in two axes and the final rotated angle isn&#39;t contained in a single axis plane. This enables the positioning of the exit pupil  570  more flexibly for the configuration of a wearable system. In one embodiment, the rotation of the polarization splitting lens unit  540  may be between 0.1 degree and 25 degrees in either direction. 
       FIG.  5 B  is a diagram of an embodiment of the polarization splitting lens unit with a rotated polarization splitting lens unit tilted and rotated around the Z-axis. In this configuration, the polarization splitting lens unit  540  is tilted, and the PBS  575  is off-angle, that is not at a 45 degree angle in one or both directions. This produces a more significant displacement of the exit pupil  570 . As noted above, the displacement of the exit pupil  570  provides more positioning flexibility and may reduce ghost images. In one embodiment, the shapes and/or lenses on the entrance face  542 , between face  544 , and the exit face  546  of the polarization splitting lens unit  540  are adjusted so that the optical axis is normal to the surface of the polarization splitting lens unit  540 . In one embodiment, this may be done by inserting an angled element between the face of the polarization splitting lens unit cube and the lens, in one or more of the faces  542 ,  544 ,  546 . In one embodiment, this may be done by using a free form lens shape to provide the angle change needed. In another embodiment, as shown in  FIG.  5 C , the underlying polarization splitting lens unit shape is changed, to provide this alignment. 
       FIG.  5 C  is a diagram of an embodiment of the polarization splitting lens unit with a polarization splitting lens unit that produces an off-angled exit pupil. Rather than tilting the entire polarization splitting lens unit  580 , in this configuration the exit surface  590  where the light exits the polarization splitting lens unit  580  is angled. This also creates an off-angle exit pupil  570 , with the exit face  590  of the polarization splitting lens unit  580  aligned to an output optical axis, so that the optical axis  595  is normal to the exit surface  590  and aligned with the optical axis  595  of the lens on that surface  590 . The shape of the polarization splitting lens unit  580  in this configuration is a cuboid with the exit face displaced to create an effective tilt. The entrance face  582  and between face  584  of the polarization splitting lens unit  580  are parallel. 
       FIG.  6 A  is a diagram of one embodiment of the polarization splitting lens unit with the exit pupil in line with the projector element. In this configuration, the light from LEDs  610  is input through light concentrators  615  into illumination waveguide  620 . The light exiting the illumination waveguide  620  forms illumination entrance pupil  630 , and enters the polarization splitting lens unit  640  through its entry face  642 . In this configuration, the light with a first polarization is reflected by PBS  645  toward the LCOS panel  660 . The portion of light that is polarized in a second direction, if any, passes through the polarization splitting lens unit  640 . In one embodiment, this light is discarded. In another embodiment, the light may be recycled. 
     The reflected light passes through imaging/illumination optics  650  to LCOS panel  660 . The light is modulated by the LCOS panel  660 , and returned through imaging/illumination optics  650  to the between face  644  of the polarization splitting lens unit  640 . This light re-enters the polarization splitting lens unit  640  through the between face  644 , and passes through the PBS  645  to form exit pupil  670 . This aligns the LCOS panel  660  with the exit pupil, rather than offsetting it by 90 degrees. This configuration may be useful in some designs, based on the available positions for the optics  650  and LCOS panel  660 . 
       FIG.  6 B  is a diagram of one embodiment of the polarization splitting lens unit with a rotated polarization splitting lens unit. In this embodiment, the polarization splitting lens unit  640  is rotated about an axis normal to the LCOS panel  660 . Because this rotation shifts the angle of the PBS  645  to the incoming light, illumination sub-system is rotated to correctly position the illumination entrance pupil  630  for the rotated polarization splitting lens unit  640 . The illumination subsystem includes the illumination waveguide  620 , LEDs  610 , and light concentrators  615  which work together to output the light in an illumination entrance pupil  630 . The rotation of the illumination subsystem ensures that the light illuminates the active area of the LCOS panel  660 . Alternatively, or additionally, the LCOS panel  660  can be rotated to ensure that the light reflected by the polarization splitting lens unit  640  hits the active area of the LCOS panel  660 . In one embodiment, when the LCOS  660  is rotated, the system may include a polarization management method, such as additional retarder films, to ensure the incoming polarization state is aligned to the preferred state of the display panel  660  to ensure contrast. 
       FIG.  6 C  is a diagram of one embodiment of the polarization splitting lens unit with offset lenses to create an offset exit pupil. In this configuration, the shape of the entrance face lens  690  and the shape of the exit face lens  695  on the polarization splitting lens unit  680  are shaped to offset the exit pupil. By using a shaped exit face lens  695 , the exit pupil  670  is offset. As noted above, this has advantages in reducing ghosting, and providing positioning flexibility for the system. To match the offset of the exit face lens  695 , the entrance face lens  690  is offset as well. In one embodiment, the offsets are matching. Because the entrance face lens  690  is offset, in one embodiment, the illumination waveguide  620  and/or the out-coupler of the illumination waveguide is angled or positioned, so is the light exiting the illumination waveguide  620  is at an angle so the offset entrance face lens  690  corrects for the angling of the light. Thus, the light impacts the PBS  685  at a 45 degree angle, despite the offset of the entrance face lens  690 . 
       FIG.  7 A  is a diagram of one embodiment of the polarization splitting lens unit with the exit pupil in line with the projector element, using a U-fold illumination configuration. The U-fold illumination configuration positions the imaging/illumination optics  750  and the illumination waveguide  720  in parallel. This reduces the area required for the system. This configuration also has the exit pupil  765  in-line with the LCOS panel  760 . 
       FIG.  7 B  is a diagram of one embodiment of the polarization splitting lens unit with the exit pupil in line with the projector element, using a U-fold illumination configuration with a blazed grating. In this configuration the illumination waveguide  770  is in parallel with the imaging/illumination optics  750 . The out-coupler  775  of illumination waveguide  770  is a blazed grating  775 . A blazed grating  775  is a diffraction grating, in one embodiment formed using a sawtooth pattern with metallization. This provides a more compact design for the illumination waveguide  770 , because the illumination waveguide  770  can be positioned in closer proximity to the polarization splitting lens unit  740 . In one embodiment, the blazed grating  775  may be replaced by a holographic, diffractive, or other optical surface to out-couple the light from illumination waveguide  720 . 
       FIG.  8 A  is a diagram of one embodiment of the polarization splitting lens unit using X-cube illumination. In this configuration the light sources, LEDs  810 A- 810 C are combined by X-cube light combiner  820 , before entering the polarization splitting lens unit  840 . The polarization splitting lens unit  840  passes the light of a first polarization through to imaging/illumination optics  850 , and discards light of the opposite polarization. The LCOS panel  860  modulates the light and flips its polarization before passing it back through imaging/illumination optics  850 . On the second pass, the polarization splitting lens unit  840  reflects the light from the LCOS  860 , to exit pupil  870 . 
       FIG.  8 B  is a diagram of one embodiment of the polarization splitting lens unit using dichroic plates in a light engine. In this embodiment, the illumination subsystem includes dichroic plates  882 , to direct the light to the polarization splitting lens unit  840 . One of the dichroic plates  882  in one embodiment, reflects red light from red light source  880 B, and passes through light from green light source  880 C. The other dichroic plate  882  reflects blue light from blue light source  880 A, and passes through light from green light source  880 C. The light lines are displaced to show the reflection v. pass-through aspect, the lights are not displayed in a real display system. In one embodiment, each light source  880 A- 880 C includes an LED, a reflective light concentrator, and one or more lenses. 
       FIG.  8 C  is a diagram of one embodiment of the polarization splitting lens unit using a dichroic element in a light engine. In this embodiment, the illumination subsystem includes a dichroic element  892 , to direct the light to the polarization splitting lens unit  840 . The dichroic element  892  in one embodiment has different coatings on the two sides of a dichroic shape, with both sides designed to pass through some colors of light, while reflecting other colors of light. In one embodiment, the nearer side is designed to pass through light from a blue light source  890 A, with the interior surface of the further side reflecting the blue light toward the polarization splitting lens unit  840 . The nearer side is also designed to reflect the light from the red light source  890 B. Both sides pass through light from the light source  890 C. This enables the system to use a small dichroic element  892  to direct light from the light sources to the polarization splitting lens unit  840 . In one embodiment, each light source  890 A- 890 C includes an LED, a reflective light concentrator, and one or more lenses. 
       FIG.  9    is a diagram of one embodiment of the polarization splitting lens unit using RGB illumination. The RGB LED(s)  910  are concentrated by light concentrator  915 , and are in-coupled into the polarization splitting lens unit  940 &#39;s entrance surface. The light with the first polarization passes through the polarization splitting lens unit  940 , and passes through imaging/illumination optics  950  to LCOS panel  960 . The light with the second polarization is reflected, and discarded. After the LCOS panel  960  modulates the light, it passes back through the imaging/illumination optics  950 , and into the polarization splitting lens unit  940 . The light, now having the opposite polarization is reflected by the PBS in the polarization splitting lens unit  940  to exit pupil  970 . 
       FIG.  10    is a diagram of one embodiment of the polarization splitting lens unit using a polarization conversion element  1080  to convert the light from illumination waveguide  1020  to a single polarization state. The light exiting the illumination waveguide  1020  contains light in both polarization states, shown by the solid-line arrow. After passing through the polarization conversion element  1080 , the light is converted into a single polarization state shown by the dash-dot lined arrow. This state passes through the PBS  1045  and is modulated by the LCOS panel  1060 . The LCOS panel  1060  flips the polarization of the light, as shown by the dashed line, before passing it back through imaging/illumination optics  1050 . The modulated light reflects off of the PBS  1045  just as in the other embodiments, to form exit pupil  1070 . On the first pass through the polarization splitting lens unit  1040 , there is almost no light in the second polarization state, due to polarization conversion element  1080 , so it is not illustrated in the diagram. In one embodiment, the polarization conversion element  1080  is made up of one or more micro lens arrays and geometric phase lenses. In another embodiment the polarization conversion element  1080  utilizes Bragg reflection and a diffuse surface to convert the light into a single polarization state. Other polarization conversion configurations or recycling elements may be used. 
       FIG.  11    is a diagram of one embodiment of the polarization splitting lens system with a beam steering prism. The light from LEDs  1110  is focused by light concentrators  1115  into illumination waveguide  1120 . The output of illumination waveguide  1120  is the illumination entrance pupil  1130 , directed into an entrance face of the polarization splitting lens unit  1140 . The polarizing beam splitter (PBS)  1145  in polarization splitting lens unit  1140  directs light with the first polarization to LCOS panel  1160 . The modulated light, with the opposite polarization, passes through the polarization splitting lens unit  1140 , to beam steering prism  1180 . Beam steering prism  1180  is used to direct the light to an exit pupil  1170 . 
     In one embodiment, the beam steering prism  1180  may have an optical power applied to its entrance surface  1182 , its exit surface  1184 , or both surfaces  1182 ,  1184 . The reflective surface  1186  of the beam steering prism  1180  in one embodiment is polarization sensitive, to reflect only light with one polarization. This may be used to clean up the outgoing light. The reflective surface  1186  in one embodiment is a TIR (total internal reflection) surface. The reflective surface  1186  in one embodiment may apply an optical power as well. The beam steering prism  1180  enables configuration flexibility, to direct the exit pupil  1170 . Beam steering prism&#39;s interface angle, the angle between the entrance surface  1182  and the reflective surface  1186 , in one embodiment is 45 degrees. In another embodiment, the interface angle may be set at another angle depending on face wrap angle or pantoscopic/retroscopic tilt. In one embodiment, the angle of the reflective surface  1186  may be a compound angle. The beam steering prism  1180  in one embodiment can also be rotated around the optical axis normal to the LCOS panel, to angle the exit pupil. The use of beam steering prism  1180  provides another degree of freedom in positioning the exit pupil  1170 . 
       FIG.  12    is a diagram of one embodiment of the polarization splitting lens system with polarization control. The light from LEDs  1210  is focused by light concentrators  1215  into illumination waveguide  1220 . The output of illumination waveguide  1220  is the illumination entrance pupil  1230 , directed into an entrance face of the polarization splitting lens unit  1240 . The polarizing beam splitter (PBS)  1245  in polarization splitting lens unit  1240  passes the light with the first polarization to LCOS panel  1260 . The modulated light, with the opposite polarization, is reflected by the PBS  1245 , out of the polarization splitting lens unit  1240 , to form exit pupil  1270 . 
     In one embodiment, polarization control system includes near-pupil polarization control element  1280  and near-panel polarization control element  1285 . In one embodiment, the polarization control system converts the light into circularly polarized light. Because the light is circularly polarized, it does not have alignment issues with the LCOS panel  1260 . The light returning from the LCOS panel  1260  is converted back to linear polarization, in one embodiment, to be directed by the PBS  1245  to the exit pupil. 
     While the various embodiments showed different illumination subsystems, such as an illumination waveguide, X-cube light combiner, dichroic plates, dichroic elements, and RGB LEDs, one of skill in the art would understand that other methods to generate and direct light to the entrance pupil may be used. Similarly, the modifications and variations among the various embodiments shown may be combined in different ways. For example, the X-cube illuminator may be combined with the offset lens, or the U-fold design may be combined with the offset lens, a polarization conversion element or polarization control elements may be inserted into any of the configurations, etc. Furthermore, the change in the angle of the PBS in the polarization splitting lens unit, the rotation of the polarization splitting lens unit, and other configuration changes may be combined across the various embodiments illustrated. 
     Additionally, while the diagrams show lenses on all three faces of the polarization splitting lens unit, in some embodiments, some of the sides may have planar lenses, or no lenses. In some embodiments, the polarization splitting lens unit may apply no optical power to the light passing through it. Additionally, while the lenses on the face of the polarization splitting lens unit are illustrated as convex, the lenses may be convex or concave, spherical or aspherical, plano, or freeform. In one embodiment, some or all of the faces or lenses of the polarization splitting lens unit may be polarization or wavelength sensitive. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the disclosure as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.