WO2000057216A1

WO2000057216A1 - Method and apparatus for illuminating a display

Info

Publication number: WO2000057216A1
Application number: PCT/US2000/007654
Authority: WO
Inventors: Milan M. Popovich; Jonathan D. Waldern
Original assignee: Digilens, Inc.
Priority date: 1999-03-23
Filing date: 2000-03-23
Publication date: 2000-09-28
Also published as: JP2002540447A; KR20010090431A

Abstract

Disclosed is a device for producing colored light and an image generating apparatus including such a device. The device includes a switchable light-directing apparatus (108) configured to receive light and a first control circuit (118) coupled to the switchable light-directing apparatus. The first control circuit provides control signals to the switchable light-directing apparatus. In response to the switchable light-directing apparatus receiving a control signal, the switchable light-directing apparatus directs a first portion of the received light to a first region of a plane. Additionally, the switchable ligth-directing apparatus directs a second portion of the received light to a second region of the plane, and directs a third portion of the received light to a third region of the plane. The second region is positioned between the first and third regions of the plane.

Description

METHOD AND APPARATUS FOR ILLUMINATING A DISPLAY

This application claims priority to Provisional application entitled METHOD AND APPARATUS FOR ILLUMINATING A DISPLAY, Serial Number 60/125,924 filed March 23, 1999; Provisional application entitled DEVICE FOR PRODUCING COLOURED LIGHT AND IMAGE GENERATING APPARATUS INCLUDING SUCH A DEVICE, Serial Number 60/127,898 filed April 5, 1999; and Provisional application entitled DEVICE FOR PRODUCING COLOURED LIGHT AND IMAGE GENERATING APPARATUS INCLUDING SUCH A DEVICE, Serial Number 60/157,796 filed October 5, 1999.

BACKGROUND OF THE INVENTION

Field Of The Invention

The present invention relates generally to a method and apparatus for illuminating an image display, and more particularly to an apparatus and method for illuminating a color sequential image display.

Description of the Related Art

In color sequential displays, a display screen is used to display a sequence of monochrome frames corresponding to what will be the red, green and blue components of a final monochromatic image. A typical color sequential display may take form in a reflective LCD micro display. The images generated by the display are illuminated in succession by a red, green, and blue light so that the red light illuminates the red monochromatic frame of the final monochromatic image, the green light illuminates the green frame of the final monochrome image, and the blue light illuminates the blue frame of the final image. Components of a subsequent monochromatic image are illuminated in the same fashion. Switching from one image to the next is performed very rapidly so that an observer sees what is effectively a full color image.

The successive illumination of image frames by red, green, and blue light is typically achieved using a white light source and a rotating color wheel; such wheels are prone to mechanical failure. Alternatively, the successive illumination of monochromatic frames of an image by red, green, and blue light may be achieved using a white light source and a solid-state device such as a liquid crystal polarization switch. Unfortunately this alternative technique has a disadvantage. More particularly, the solid-state techniques that employ devices such as liquid crystal polarization switches work only with polarized light. Accordingly, at least half of the light available for illuminating a particular monochromatic frame is immediately lost. A more important problem with the mechanical and solid-state techniques for illuminating color sequential displays is that only a third of the available white light is used for illuminating the red, green and blue monochromatic frames of the image collectively. In other words, at least two thirds of the available white light is unused at any given moment. For example, when the red monochromatic frame of a final image is displayed, only red light is used to illuminate, while the green and blue components of the white light source are filtered out and unused. SUMMARY OF THE INVENTION

The present relates to a device for producing colored light and an image generating apparatus including such a device The device includes a switchable light-directing apparatus configured to receive light and a first control circuit coupled to the switchable light-directing apparatus The first control circuit provides control signals to the switchable light-directing apparatus In response to the switchable light-directing apparatus receiving a control signal, the switchable light-directing apparatus directs a first portion of the received light to a first region of a plane Additionally, the switchable light-directing apparatus directs second and third portions of the received light to second and third regions, respectively, of the plane The second region is positioned between the first and third regions of the plane

In one embodiment, the switchable light-directing apparatus comprises a first group of electrically switchable holographic optical elements comprising first, second, and third electrically switchable holographic optical elements each of which is electrically switchable between an active state and an inactive state Each of the first, second, and third electrically switchable holographic optical elements is configured to diffract light incident thereon when operating in the active state, and each of the first, second, and third electrically switchable holographic optical elements transmits light incident thereon without substantial alteration when operating in the deactive state In this embodiment, each of the first, second and third electrically switchable holographic optical elements is activated or deactivated by the first control circuit

BRIEF DESCRIPTION OF THE DRAWINGS While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example and the drawings and will be herein described in detail It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed On the contrary, the mtention is to cover all modifications, equivalents and alternatives falling withm the spirit and scope of the present invention as defined by the appended claims

The present invention may be better understood, and it's numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings

Figure 1 shows a first embodiment of a transmissive type device for producing colored light and an image generating apparatus,

Figure 2 shows a second embodiment of a transmissive type device for producing colored light and an image generating apparatus,

Figure 3 shows a third embodiment of a transmissive tvpe device for producing colored light and an image generating apparatus - j -

Figure 4 shows a first embodiment of a reflective type device for producing colored light and an image generating apparatus:

Figure 5 shows a second embodiment of a transmissive type device for producing colored light and an image generating apparatus;

Figure 6 shows a third embodiment of a transmissive type device for producing colored light and an image generating apparatus;

Figures 7A - 7C illustrate operational aspects of one embodiment of the switchable optics system and image surface employable in the embodiments shown in Figures 1 - 6;

Figure 8 illustrates operational aspects of another embodiment of the switchable optics system and image surface employable in the embodiments shown in Figures 1 - 6;

Figure 9 illustrates operational aspects of still another embodiment of the switchable optics system and image surface employable in the embodiments shown in Figures 1 - 6;

Figure 10A - IOC show alternative embodiments of the filter employable in the embodiments shown in Figures 2 and 5;

Figure 11 is a cross sectional view of an electrically switchable holographic optical element;

Figure 12 is one embodiment of an electrically switchable holographic optical element system employable in the switchable optics system of Figures 2, 3, 5, and 6;

Figure 13 is one embodiment of an electrically switchable holographic optical element system employable in the switchable optics system of Figures 1 and 4;

Figure 14 is one embodiment of an electrically switchable holographic optical element system employable in the switchable optics system of Figures 3 and 6;

Figure 15 is another embodiment of an electrically switchable holographic optical element system employable in the switchable optics system of Figures 2, 3, 5, and 6;

Figure 16 is another embodiment of an electrically switchable holographic optical element system employable in the switchable optics system of Figures 1 and 4;

Figure 17 illustrates one embodiment of the system shown in Figure 2;

Figure 18 illustrates another embodiment of the system shown in Figure 2;

Figure 19 illustrates still another embodiment of the system shown in Figure 2;

Figure 20 illustrates one embodiment of the system shown in Figure 5; Figure 21 illustrates an electrically switchable holographic optical element system and an optical diffuser employable in the embodiments shown in Figures 1 - 6,

Figure 22 illustrates an alternative embodiment of the switchable optics system employable in the embodiment of Figure 2,

Figure 23 illustrates the switchable optics system of Figure 22 with a modification thereto,

Figure 24 illustrates the switchable optics system of Figure 22 with a modification thereto,

Figure 25 shows a fourth embodiment of a transmissive type device for producing colored light and an image generating apparatus,

Figure 26 illustrates operational aspects of the transmissive type device for producmg colored light shown m Figure 25,

Figure 27 shows a fourth embodiment of a reflective type device for producing colored light and an image generating apparatus

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Figure 1 shows one embodiment of a system havmg a light transmissive type device for producmg colored light and an image generatmg apparatus Figure 1 shows a light source 100 for generating white light 102, collimation optics 104, switchable optics system 108, image display system 112 having an image display surface 114 typically comprising an array of pixels for displaying monochromatic data, image control circuit 116, and illumination control circuit 118

White light 102 generated by light source 100 is received by collimation optics 104 Collimation optics 104, in tum, collimates white light 102 to produce collimated white light 106 Switchable optics system 108 receives collimated white light 106 and produces at least three distinct bandwidths of illumination light in response thereto In the preferred embodiment, switchable optics system 108 generates red (R), green (G), and blue (B) bandwidth illumination lights Switchable optics system 108 produces the illumination lights as a result of shaping, filtering, focusing, and/or correcting collimated white light 106 Additionally, switchable optics system 208 selectively directs illumination lights onto subsurfaces of the image display surface

The switchable optics system 108 simultaneously illuminates at least three distinct subsurface areas of image display surface 1 14 with the illumination lights R, G, B, respectively Preferably, the three subsurfaces are of equal size With reference to Figure 1 , switchable optics system 108 simultaneously illuminates the entire surface 114 by illuminating each of three adjacent subsurfaces 1 14A- 1 14C with one of the illumination lights R, G, B The switchable optics system 108, or any of the switchable optics systems described below, should not be limited to simultaneously illuminating the entire surface 1 14 with the three illumination lights The switchable optics system 108 may simultaneously illuminate three subsurfaces of lesser size than that shown in Figure 1 For example, the switchable optics svstem 108, or any other switchable optics svstem described herein, mav simultaneously illuminate each of onlv three lines of pixels on the display surface with a respective one of the three illummation lights Additionally, the switchable optics system 108. or any other switchable optics system described herein, may simultaneously illuminate each of only three pixels on the display surface with a respective one of the three illumination lights

Display surface 114 displays monochromatic data of monochromatic images in accordance with signals generated by image control circuit 1 16 Each monochromatic image consists of three monochromatic frames (l e , a red monochromatic frame, a green monochromatic frame, and a blue monochromatic frame) With reference to Figure 1 , each monochromatic image is displayed in a three-stage cycle In each cycle, a portion of each monochromatic frame is displayed on each of the subsurfaces 114A, 114B, and 114C For example, in the first stage, subsurface 1 14A displays the top monochromatic component of the red frame while subsurfaces 1 14B and 1 14C display middle and bottom monochromatic components of the green and blue frames, respectively In the second cycle, subsurface 1 14A displays the top monochromatic component of the green frame while subsurfaces 1 14B and 114C display middle and bottom monochromatic components of the blue and red frames, respectively In the third and last stage of the cycle, subsurface 114A displays the top monochromatic component of the blue frame while subsurfaces 1 14B and 1 14C display middle and bottom monochromatic components of the red and green frames, respectively

Illummation control circuit 1 18 is coupled to image control circuit 116 and switchable optics system 108 Switchable optics system 108, operatmg under command of control circuit 118, selectively directs each of the illummation lights R, G, and B to one of the subsurfaces 114A - 114C Illummation control circuit 118 is linked to image control circuit 116 and operates in sync therewith In the embodiment shown in Figure 1, switchable optics system 108 operates in a three-stage cycle In the first stage, switchable optics system 108 receives one or more control signals from control circuit 118 and, m response thereto, directs illummation light R onto subsurface 1 14A while subsurface 1 14A displays the top component of the red monochromatic frame as described above Switchable optics system 108 also directs illummation lights G and B onto subsurfaces 114B and 114C, respectively, m the first cycle, while subsurfaces 1 14B and 1 14C display the middle and bottom component of the green and blue monochromatic frames, respectively In the second cycle, switchable optics system 108 receives one or more second control signals and, in response thereto, directs illumination light G onto subsurface 1 14A while subsurface 114A displays the top component of the green monochromatic frame as described above Switchable optics system 108 also directs illummation lights B and R onto subsurfaces 1 14B and 1 14C, respectively, in the second cycle, while subsurfaces 114B and 114C display the middle and bottom component of the blue and red frames, respectively In the third cycle, switchable optics system 108 receives one or more third control signals and, m response thereto, directs illumination light B onto subsurface 114A while subsurface 114A displays the top component of the blue monochromatic frame as described above Switchable optics systemlOδ also directs illumination lights R and G onto subsurfaces 114B and 114C, respectively, in the third cycle, while subsurfaces 1 14B and 1 14C display the middle and bottom component of the red and green monochromatic frames, respectively Figure 1 shows the second stage of this three-stage cycle in which subsurface 1 14A is illuminated with green illumination light G as subsurface 1 14A displays the top monochromatic component of the green frame, subsurface 1 14B is illuminated with blue illumination light B as subsurface 114B displays the middle monochromatic component of the blue frame, and, 1 14C is illuminated with red illumination light R as subsurface 114C displays the bottom monochromatic component of the red frame If the monochromatic components displayed in the first and third stages are illuminated in similar fashion, and if the switching rate between the three stages is fast enough, than an observer will be able to eye integrate the illuminated components into the final image

When the three stage cycle has completed, image control circuit 1 16 initiates a new three stage cycle for the next image The present invention should not be limited to displaying the monochromatic image in a three stage cycle The present invention could be implemented with three lines of each monochromatic frame bemg simultaneously displayed on three lines of pixels of the image display surface In this alternative embodiment, the monochromatic image is scrolled down the display surface as it is illuminated with illumination lights R, B, and B Additionally, the present invention could be implemented with three pixels of each monochromatic frame being simultaneously displayed on three pixels of the image display surface In this alternative embodiment, the monochromatic image is scrolled across and down the display surface as it is illuminated with illumination lights R, B, and B

Figures 7A - 7C illustrate front views of display surface 114 of Figure 1 Figures 7A - 7C further illustrates how switchable optics system 108 properly illuminates the monochromatic components of the final image In Figure 7 A, subsection 114A is illuminated with R when subsection 114A displays what will be the red monochrome component of the final image in that subsurface Subsection 114B is illuminated with G when subsection 1 14B displays the green monochrome component of the final image m that section Subsection 1 14C is illuminated with B when subsection 1 14C displays the blue monochrome component of the final image in that section Figures 7B and 7C show illummation of the subsections 114A - 1 14C as the subsurfaces cycle through what will be the monochromatic components of the final image

Figure 2 shows an alternative embodiment of a system having a light transmissive type device for producmg colored light and an image generating apparatus The embodiment shown in Figure 2 mcludes white light source 100 which generates a white light 102, collimation optics 104, filter 202, switchable optics system 206, image display system 1 12 having an display surface 1 14, image control circuit 116, and illummation control circuit 1 18 It is noted that the same reference number identifies similar components in the Figures

Collimation optics 104 in Figure 2 collimates white light 102 into collimated white light 106 Filter 202 receives and filters collimated white light 106 to produce at least three spatially separated and bandwidth distinct output lights 204R, 204G, and 204B In the embodiment shown in Figure 2, output light 204R constitutes the red bandwidth component of collimated white light 106, output light 204G constitutes the green bandwidth component of collimated white light 106, and output the light 204B constitutes the blue bandwidth component of collimated white light 106 Switchable optics system 208 shapes, focuses and or corrects output lights 204R, 204G and 204B to produce illumination lights R, G and B, respectively Additionally, switchable optics svstem 208 selectively directs illumination lights onto subsurfaces of the image display surface Image display system 112 displays monochromatic images in the same fashion described with reference to Figure 1 Illumination control circuit 1 18 controls switchable optics system 208 in synchronization with the monochromatic components displayed on display surface 1 14

Switchable optics system208 operates in a three-stage cycle In the first stage of the three-stage cycle, switchable optics system 208 directs illumination lights R, G, and B onto display surfaces 1 14A, 114B, and 114C, respectively, as image subsurfaces 114A, 1 14B, and 1 14C, display the appropriate monochromatic components of the final image In the second stage of the three-stage cycle, switchable optics system 208 directs illumination lights R, G and B onto image subsurfaces 1 14C, 1 14A and 1 14B, respectively, while image subsurfaces 114C, 1 14A and 114B display the appropriate monochromatic components of the final image In the third stage of the three-stage cycle, switchable optics system 208 directs illummation lights R, G, and B onto subsurfaces 1 14B, 1 14C and 1 14A, respectively, while subsurfaces 1 14B, 114C, and 1 14A display the appropriate monochromatic components of the final image. It is noted in Figures 1 and 2 that all or substantially all of collimated white light 106 is used to illuminate display surface 1 14 as display surface 114 displays the final image

Figure 1 shows another embodiment of a system having a light transmissive type device for producmg colored light and an image generating apparatus. Figure 3 shows light source 100, collimation optics 104, switchable optics system 308, image display system 112 having an display surface 114, image control circuit 116, and illumination control circuit 118 With the exception of switchable optics system 308 the embodiments of Figures 1 and 3 are identical The main difference between the systems of Figures 1 and 3 relates to the intensity of illumination lights R, G, and B produced by switchable optics system 308 Unlike the embodiments shown m Figures land 2, switchable optics system 308 shown m Figure 3 illuminates the entire display surface 114 with less than substantially all available collimated white light 106 at any given time.

The embodiments shown m Figures 1 through 3 include a transmissive-type switchable optics system The present invention can be employed with a reflective type switchable optics system Figure 4 shows the embodiment of Figure 1 with switchable optics system 108 replaced by switchable optics system 408, and with image display system 112 repositioned to take advantage of the reflective properties of switchable optics system 408 Except for its reflective properties, switchable optics system 408 operates in a manner substantially similar to switchable optics system 108 shown in Figure 1

In Figure 1, switchable optics system 108 emits illumination lights R - B from a surface opposite a surface that receives collimated white light 106 In contrast, reflective-type switchable optics system 408 emits illumination lights R - G from the same surface that receives collimated white light 106 Figure 5 shows the system of Figure 2 with switchable optics system 208 replaced by switchable optics system 508, and with image display system 112 repositioned to take advantage of the reflective properties of switchable optics system 508 Switchable optics svstem 508 is a reflective-type system, whereas switchable optics system 208 shown in Figure 2 is a transmissive-type system Figure 6 shows the system of Figure 3 with the transmissive switchable optics svstem 308 replaced by reflective-type switchable optics system 608 Again, like the system shown in Figure 3, switchable optics system 608 shown in Figure 6 illuminates surface 1 14 with less than substantially all of collimated white light 106

Figures 7 A through 7C illustrate one mode in which monochromatic components of the final image image are displayed and illuminated on image surface 114 As shown display surface 114 is divided mto three areas of equal size, each of which is cyclically and sequentially illuminated with red, green, and blue illumination light as the appropriate monochromatic component is displayed thereon The present invention should not be limited thereto Figure 8 shows a front-view of display surface 1 14 which is divided mto six subsurfaces 114A through 114F In this embodiment subsurfaces 114A and 114D sequentially and cyclically display in monochrome what will be red, blue and green components of the final image in those subsurfaces, subsurfaces 114B and 114E sequentially and cyclically display in monochrome what will be green, red and blue components of the final image in those regions, and subsurfaces 1 14C and 1 14F sequentially and cyclically display in monochrome what will be blue, green and red components of the final image in those regions Moreover, when subsurfaces 114A and 114D are displaying their red monochromatic components, subsurfaces 114B and 1 14E display their green monochromatic components and subsurfaces 114C and 114F display their blue monochromatic components, and so on To illuminate the monochromatic components of the final image displayed in the subsurfaces 114A through 114F, as shown m Figure 8, the switchable optics system of Figures 1 through 6 must be modified to produce two separate groups of red, green, and blue illumination lights In this embodiment, the first group of red, green and blue illummation lights are selectively directed to each of the subsurfaces 114A through 114C, while the second group of red, green and blue illumination lights are selectively directed to each of the subsurfaces 1 14D through 114F Thus, the modified switchable optics system directs the red illumination lights to the two subsurfaces which display their red monochromatic components of the image at that tune, while directing the green illummation lights to the two subsurfaces displaying their green monochromatic subcomponent image and the blue illummation lights to the two subsurfaces displaying their blue monochromatic subcomponent of the image at the time The modified switchable optics systems operate m a cyclic manner so that the red, green, and blue illummation lights of the first group are directed to subsurfaces 14A through 14C in synchronism with the display thereon of red, green, and blue monochromatic components of the final image Similarly the modified switchable optics systems operate m a cyclic manner so that the red, green, and blue illummation lights of the second group are directed to subsurfaces 1 14D through 114F in synchronism with the display thereon of red, green, and blue monochromatic components of the final image

Figures 9A through 9F show a front-view of image display surface 1 14 operating in accordance with another embodiment In this embodiment, surface 114 is divided mto six subsurfaces 1 14 A through 114F of equal size It is noted that display surface 1 14 can be further divided into regions each of which occupies a line of pixels However the present invention will be illustrated with the image display divided into six distinct but equal-sized subsurfaces Whereas the display surface described above operate in a three-stage cycle to complete a full image, surface 1 14 shown in Figures 9A through 9F, operates in a six-stage cycle to completely display a final monochromatic image Each subsurface 1 14A through 1 14F displays in monochrome what will be the red, green, and blue components of the final image in that section However, the display of the red, blue, and green components does not occur sequentially or cyclically as described above In this embodiment only three of the subsurfaces 1 14A through 1 14F at any given point m time display a red, green, and blue component of the final image The display of the components of the final unage scrolls down the display surfaces 1 14A through 1 14F as shown in Figures 9A through 9F Figure 9A illustrates the first stage of the six-stage cycle In Figure 9 A, subsurfaces 14A through 14C display in monochrome what will be the red, green, and blue components of the final image, respectively, in those subsurfaces In the second stage of the six-stage cycle as shown Figure 9B, subsurfaces 114B through 114D display the red, green, and blue components of the final image, respectively, in those sections In the third stage of the six-stage cycle, as shown in Figure 9C, subsurfaces 1 14C through 1 14E display in monochrome what will be the red, green, and blue components of the final image, respectively, in those sections In the fourth stage, as shown in Figure 9D, subsurfaces 14D through 14F display in monochrome what will be the red, green, and blue components of the final image, respectively, in those sections In Figure 9E, subsurfaces 114E, 1 14F, and 1 14A display in monochrome what will be the red, green, and blue components of the final image, respectively, in those sections In the last stage, as shown in Figure 9F, subsurfaces 1 14F, 1 14A, and 114B display the red, green, and blue components of the final unage, respectively, m those sections

Figures 9A through 9F represent snapshots of the display surface 1 14 during each stage of the six- stage cycle Switchable optics systems 108, 208, 308, 408, 508 and 608 (described above) can be modified in order to illuminate only those subsurfaces 1 14A through 1 14F which display monochromatic components of the final unage with the appropriate illummation light at any given time More particularly, the modified switchable optics systems in this embodiment operate m a six-stage cycle In the first stage of the six-stage cycle, the switchable optics systems direct the red, green, and blue illumination lights to subsurfaces 114A through 114C, respectively, as subsurfaces 114A through 114C display their red, green, and blue monochromatic components of the final image, respectively, as shown m Figure 9A In the second stage, the modified switchable optics systems direct the red, green, and blue illummation lights to subsurfaces 114B, 1 14C, and 114D, respectively, as subsurfaces 114B, 1 14C, and 1 14D display their red, green, and blue monochromatic components of the final image, respectively as shown in Figure 9B In the third stage of the six-stage cycle, the modified switchable optics systems direct red, green, and blue illumination lights to subsurfaces 1 14C, 114D and 114E, respectively, as subsurfaces 1 14C, 1 14D and 1 14E display their red, green, and blue monochromatic components of the final unage, respectively as shown in Figure 9C In the fourth stage of the six-stage cycle, a modified switchable optics systems direct the red, green, and blue illumination lights to subsurfaces 1 14D, 1 14E and 114F, respectively, as subsurfaces 1 14D, 1 14E and 114F display their red, green, and blue monochromatic components of the final image, respectively as shown in Figure 9D In the fifth stage of the six-stage cycle, the modified switchable optics systems direct the red, green, and blue illumination lights onto subsurfaces 114E, 1 14F, and 1 14A, respectively, as subsurfaces 1 14E, 1 14F, and 1 14A display their red green and blue monochromatic components of the final image, respectively as shown ιn Figure 9E In the last stage of the six-stage cycle modified switchable optics systems direct their red, green, and blue illumination lights onto subsurfaces 1 14F 1 14A and 1 14B respectively, as subsurfaces 1 14F, 1 14A, and 1 14B display their respective red, green, and blue components of the final image, respectively as shown in Figure 9F The switching or cycling of the modified switchable optics svstem and the display surface is such that an observer sees what is effectively the final image without anv visible divisions between the subsurfaces 114A through 114F

Figures 10A through IOC show alternative embodiments of the filter 202 employed in Figures 2 and 5 In Figure 10A, filter 202 includes three dichroic filters 1002, 1004, and 1006 arranged in sequence along an optical path from the light source 100 (not shown in Figures 10A through 10C) More particularly, filter 1002 receives collimated white light 106 and reflects the red bandwidth component thereof sideways to produce output light 204R Remaining components of collimated white light 106 pass through filter 1002 substantially unaltered Filter 1004 receives the light transmitted through filter 1002 and reflects the green bandwidth component thereof sideways to produce green output light 204G while transmitting the blue bandwidth component without substantial alteration The remaining blue bandwidth component of collimated white light is reflected sideways by filter 1006 to produce output light 204B

Filter 202 shown in Figure 10B is similar to that shown in Figure 10A However, dichroic filter 108 receives collimated white light and transmits the red bandwidth component thereof to produce output beam 204R while deflecting sideways the remaining blue and green bandwidth components of collimated white light Filters 1004 and 1006 reflect the green and blue bandwidth components, respectively, of the light deflected by filter 1008 to produce output beams 204G and 204B, respectively, m the same fashion as shown in Figure 10A

Figure 10C shows filter 202 including a dichroic prism 1012 with dichroic layers on its interfaces and a pair of plane mirrors 1014 and 1016 One example of the dichroic prism which can be employed in Figure 10C, is manufactured by Nitto Optical of Japan under the name Cross Dichroic Prism Such a prism is typically fabricated from glass such as DK7, and operates over the visible band from 420nm to 680nm and has a reflectivity of at least 94% for polarized light at normal mcidence It is also possible to employ prisms that have high transmission and are relatively insensitive to the polarization state of the incident light Pπsm 1012 has an input face 1018 that receives collimated white light 106, and three output faces 1020, 1022, and 1024 The red bandwidth component of collimated white light 106 is deflected to one side by reflection and filtration at the prism interfaces, to emerge from output face 1020 as output light 204R This light is then deflected 90 degrees by plane mirror 1014 towards the switchable optics system The green bandwidth component of collimated white light 106 passes straight through prism 1 12 without substantial alteration to emerge as output light 204G from surface 1022 The blue bandwidth component of collimated white light 106 is deflected to one side by reflection and filtration at the prism interfaces to emerge from output face 1024 as illumination light 204B 204B is deflected through 90 degrees bv plane mirror 1026

As noted above switchable optics svstems 108. 208, 308 408, 508, and 608 can direct the red, green and blue illumination lights onto display surfaces 1 14A -1 14C Typically, switchable optics systems 108 208. 308. 408, 508, and 608 also focus illumination lights onto the subsurfaces. Additionally switchable optics systems 108, 308, 408 and 608 may filter collimated white light 106. The switchable optics systems may be base on solid state switching techniques using acousto-optic materials, liquid crystals or alternatively, opto mechanical devices such as rotating prisims, mirrors, or gratings. In the preferred embodiment, the switchable optics systems are based on electrically switchable holographic optical technology.

Accordingly, the switchable optics systems described above includes an electrically switchable holographic optical element (ESHOE) system having at least three groups of three electrically switchable holographic elements that perform the illumination light directing functions described above. The ESHOE system may additionally perform the functions of filtering the collimated white light 106 to produce separated red, green, and blue illumination lights, or focusing the illuminations lights onto the subsurfaces of display surface 1 14. Additionally, the ESHOE system may perform the functions of light shaping and light correction. However, these last functions are preferably performed by conventional optics embodied in glass or plastic separate and apart from the ESHOE system. The function of focusing the illumination light onto the subsurfaces of the image display may also be performed by conventional optics.

Figure 11 shows the cross-sectional view of an exemplary switchable holographic optical element that can be used in the ESHOE system. The switchable holographic optical element of Figure 11 includes a pair of substantially transparent and electrically non-conductive layers 1102, a pair of substantially transparent and electrically conductive layers 1104, and a switchable holographic layer 1 106 formed, in one embodiment, from the polymer dispersed liquid crystal material described in U.S. Patent Application 09/478,150 entitled Optical Filter Employing Holographic Optical Elements And Image Generating System Incorporating The Optical

Filter, filed January 5, 2000, which is incoφorated herein by reference. In one embodiment, the substantially transparent, electrically non-conductive layers 1102 comprise glass, while the substantially transparent, electrically conductive layers 1 104 comprise indium tin oxide (ITO). An anti-reflection coating (not shown) may be applied to selected surfaces of the switchable holographic optical element, including surfaces of the ITO and the electrically nonconductive layers, to improve the overall transmissive efficiency of the optical element and to reduce stray light. As shown in the embodiment of Figure 11, all layers 1102-1 106 are arranged like a stack of pancakes on a common axis 408. The layers may be flexible.

Layers 1102-1106 may have substantially thin cross-sectional widths, thereby providing a substantially thin aggregate in cross-section. More particularly, switchable holographic layer 1 106 may have a cross-sectional width of 5 - 12 microns (the precise width depending on a spectral bandwidth and required diffraction efficiency), while non-conductive glass layers 1 102 may have a cross-sectional width of .4 - .8 millimeters. Obviously, ITO layers 1 104 must be substantially thin to be transparent. It should be noted that holographic layers may be deposited on thin plastic substrates. The plastic substrates may also be flexible.

With ITO layers 1 104 coupled to a first voltage, an electric field is established within the switchable holographic layer 1106, and the switchable holographic element operates in the inactive state described above. However, when the ITO layers 1 104 are coupled to a voltage below the first voltage, the switchable holographic optical element operates in the active state as described above. When active, the electrically switchable holographic optical element diffracts, for example, the red bandwidth component of collimated incident light 1 12 while passing the remaining components of collimated incident light 1 12, including green and blue bandwidth components without substantial alteration

The switchable holographic optical element shown in Figure 1 1 may be reflective or transmissive type Figure 1 1 shows the switchable holographic optical element with oppositely facmg front and back surfaces 1 1 10 and 1 1 12 Whether reflective or transmissive type, collimated white light 106 falls mcident on the front surface 11 10 at normal mcidence angle If the switchable holographic optical element is configured as transmissive type, diffracted light components emerge from back surface 1 112 In contrast, if the electrically switchable holographic optical element is configured as reflective type hologram, diffracted light components emerge from front surface 1 1 10 Transmissive type electrically switchable holographic optical elements can be employed m the switchable optics systems shown Figures 1, 2 and 3, while reflective type electrically switchable holographic optical elements can be employed in the switchable optics systems shown in Figures 4, 5 and 6

Switchable holographic layer 1 106 records a hologram using conventional techniques In one embodiment, the resultmg hologram is characterized by a high diffraction efficiency and a fast rate at which the optical element can be switched between active and inactive states In the embodiment of switchable holographic layer 1 106 formed from polymer dispersed liquid crystal (PDLC) material, the recorded hologram can be switched from a diffracting state to a transmitting state with the creation and elimination of the electric field mentioned above Preferably, the holograms recorded in the switchable holographic layer 1106 would be Bragg (also know as thick or volume phase) type in order to achieve high diffraction efficiency Raman-Nath or thm phase type holograms may also be employed

The hologram recorded m switchable holographic layer 1106 can be based on PDLC materials described in the 09/478,150 application which, as noted above, is incoφorated herein by reference The hologram, in one embodiment, results m an interference pattern created by recording beams, I e , a reference beam and an object beam, mteractmg withm switchable holographic layer 1106 Interaction of the beams with the PDLC material causes photopolymeπzation Liquid crystal droplets become embedded in the dark regions of the fringe patterns that are formed by the intersection of the recordmg beams during the recording process Stated differently, the recording material may be a polymer dispersed liquid crystal mixture which undergoes safe separation during the recordmg process, creating regions densely populated by liquid crystal microdroplets, mterspersed by regions of clear photopolymer When a voltage of sufficient magnitude is supplied to ITO layers 1 104, the liquid crystal droplets reorient and change the refractive mdex of the switchable holographic layer 1 106, thereby essentially erasing the hologram recorded therein so that all collimated white light 106 incident thereon passes without noticeable alteration The material used within switchable holographic layer 1 106 is configured to operate at a high switching rate (e g , the material can be switched in tens of microseconds which is very fast when compared with conventional liquid crvstal display materials) and a high diffraction efficiency Figure 12 is a block diagrams representing an embodiment of an ESHOE system employable in the switchable optics svstem used in Figures 2 and 3 More particularly, the ESHOE svstem shown in Figure 12 includes three groups of three electrically switchable holographic optical elements The first group, designated 1202, consists of three holographic optical elements 1202A - 1202C stacked one upon another The second group of holographic optical elements, designated 1204, consists of three holographic optical elements 1204A - 1204C stacked one upon another The third group of holographic elements, designated 1208, consists of three holographic optical elements 1208A - 1208C stacked one upon another

In operation, the ESHOE system shown in Figure 12 is used to direct the red, green, and blue illumination lights onto the subsurfaces 114A - 114C, as shown in Figures 7 A through 7C During each stage in the three-stage cycle described with reference to Figures 7 A through 7C, each of the electrically switchable holographic optical elements in one of the three groups 1202 through 1208 is activated More particularly, stage one described above is implemented by activatmg the electrically switchable holographic optical elements 1202A through 1202C of group 1202 The second stage of the illumination cycle described above is implemented by activating the electrically switchable holographic optical elements 1204A - 1204C of group 1204 The third stage in the three-stage cycle described above is implemented by activating each of the electrically switchable holographic optical elements 1208A - 1208C of the third group 1208 Illummation control circuit 1 18 sequentially and cyclically activates and deactivates groups 1202 through 1208 by providmg the appropπate activation or deactivation voltages thereto so that only one group is activated at any

With reference to Figure 2, electrically switchable holographic optical elements 1202 A, 1204A and

1208A diffract output light 204R when activated onto subsurfaces 1 14A, 114B and 1 14C, respectively Electrically switchable holographic optical elements 1202B, 1204B and 1208B, when activated, diffract the output light 204G onto subsurfaces 114B, 114C and 1 14A, respectively Activated holographic optical elements 1202C, 1204C, and 1208C diffract output light 204B onto subsurfaces 1 14C, 114B and 1 14A, respectively

With contmuing reference to Figure 12 and with further reference to Figure 3, electrically switchable holographic optical elements 1202A, 1204A and 1204A diffract the red bandwidth component of collimated white light 106 onto subsurface 114 A, 114B and 114C, respectively, while passing the remaining components of collimated white light 106 incident thereon without substantial alteration The portions of collimated white light 106 which pass through activated electrically switchable holographic optical elements enter free space and do not fall incident upon the display surface 1 14 This is because diffracted light emerges from the electrically switchable holographic optical element at an angle with respect to the light that passes without substantial alteration, and the display surface is positioned to take advantage of this fact Electrically switchable holographic optical elements 1202B, 1204B and 1208B diffract the green bandwidth portion of collimated white light 106 incident thereon the diffracted light falling incident upon subsurfaces 1 14B, 114C and 1 14A, respectively The remammg portions of collimated white light 106 incident upon activated optical elements 1202B, 1204B and 1208B, transmit therethrough without substantial alteration and enter free space Likewise activated optical elements 1202C 1204C, and 1208C diffract the blue bandwidth component of collimated white light 106 incident thereon, the diffracted blue bandwidth component falling incident upon subsurfaces 1 14C, 1 14B and 1 14A, respectively.

Figure 13 shows an ESHOE system for use in the embodiments of Figures 1 and 4. The ESHOE system of Figure 13 includes three groups of three electrically switchable holographic optical elements. The first group 1302 includes three electrically switchable holographic optical elements 1302A, 1302B and 1302C, each of which is configured to diffract red bandwidth light when active while transmitting green and blue bandwidth light without alteration. When deactivated, each of the electrically switchable holographic optical elements 1302A, 1302B, and 1302C passes the red, green, and blue bandwidths without alteration. Diffracted red bandwidth light emerges from electrically switchable holographic optical elements 1302A, 1302B and 1302C at distinct exit angles to illuminate subsurfaces 114A - 1 14C, respectively.

The second group 1304 includes three electrically switchable holographic optical elements 1304A, 1304B and 1304C, each of which is configured to diffract green bandwidth light when active while transmitting red and blue bandwidth light without alteration. When deactivated, each of the electrically switchable holographic optical elements 1304A, 1304B and 1304C passes the red, green, and blue bandwidths without alteration. The second group 1304 includes three electrically switchable holographic optical elements 1304A, 1304B and 1304C, each of which is configured to diffract green bandwidth light when active while transmitting red and blue bandwidth light without alteration. When deactivated, each of the electrically switchable holographic optical elements 1304A, 1304B and 1304C passes the red, green, and blue bandwidths without alteration. Diffracted green bandwidth light emerges from electrically switchable holographic optical elements 1304A, 1304B, and 1304C at distinct exit angles to illuminate subsurfaces 1 14A through 114C, respectively.

The third group 1306 includes three electrically switchable holographic optical elements 1306A, 1306B and 1306C, each of which is configured to diffract blue bandwidth light when active while transmitting red and green bandwidth light without alteration. When deactivated, each of the electrically switchable holographic optical elements 1306A, 1306B, and 1306C passes the red, green, and blue bandwidths without alteration. Diffracted blue bandwidth light emerges from electrically switchable holographic optical elements 1306A, 1306B, and 1306C at distinct exit angles to illuminate subsurfaces 114A through 114C, respectively.

The ESHOE system shown in Figure 13, acting under control of control circuit 1 18, operates to illuminate the display surface 114 as shown in Figures 7A through 7C. In this mode, control circuit activates only one electrically switchable holographic optical element in each of the groups 1302 through 1306. More particularly, the control circuit in the first cycle activates electrically switchable holographic optical elements 1302A, 1304B, and 1306C to illuminate display surface 1 14 as shown in Figure 7A. Control circuit in the second cycle activates electrically switchable holographic optical elements 1302C, 1304A, and 1306B to illuminate display surface 1 14 as shown in Figure 7B. Control circuit in the third cycle activates electrically switchable holographic optical elements 1302B, 1304C, and 1306A to illuminate display surface 1 14 as shown in Figure 7C. Figure 14 shows the ESHOE system of Figure 12 with the electrically switchable holographic optical elements stagered The ESHOE of Figure 14 can be used to direct collimated white light 106

The switchable optics systems can employ a pair of the ESHOE systems described in Figures 12 and

13 to increase the intensity of illumination lights for illuminating the monochromatic components of the display surface More particularly, the ESHOE system of Figure 13 or 14 could be duplicated, the two

ESHOE systems placed side by side with a polarization rotator in between In this arrangement, each of the s and p polarized components of collimated light 106 or the output lights 204R - -204B will be diffracted by one of the two ESHOE systems with the rotator therebetween Alternatively, the ESHOE system of Figure 13 or

14 could be duplicated and placed side by side, with the diffraction gratings in each of the electrically switchable holographic optical elements of one of the ESHOE systems aligned orthogonal to the diffraction gratings of each electrically switchable holographic optical elements of the other ESHOE system These arrangements are more fully described m U S Patent Application 09/478, 150 which is incoφorated herein in its entirety

The ESHOE systems above are employable to illuminate a display surface divided mto three separate subsurfaces with R, G, and B illumination lights Alternative ESHOE systems may be employed, for example, to illuminate a display surface divided into six separate subsurfaces as shown in Figures 9A - 9F Figures 15 and 16 show ESHOE systems which can be employed to produce the illumination patterns shown in Figures 9 A - 9F The ESHOE system of Figure 15 is employable in the systems of Figures 2 and 5 while the ESHOE system of Figure 15 is employable m the systems of Figure 1, 3, 4 and 6 In general, the total number of electrically switchable holographic optical elements needed in each ESHOE system (configured to diffract only one of the s or p polarization components of collimated light 106 or output lights 204R - 204B) equals the number of distinct illumination lights (normally three) multiplied by the number of subsurfaces of the display surface 114 that display monochromatic components of the final image

Figure 17 shows one embodiment of the system shown in Figure 2 Figure 17 shows 202B receiving collimated white light 106 from collimation lens 104 Filtered output lights 20R - 204B are subsequently received by ESHOE system 1200 As noted in Figure 12, ESHOE system 1200 comprises three stacks of electrically switchable holographic optical elements stacked one upon another Each of these elements directs and focuses a respective wavelength band of output light received from the filter 202B onto one of the subsurfaces 114A - 114C The situation shown in Figure 17 is achieved by illummation control circuit 118 activating the electrically switchable holographic optical elements 1202A - 1202C (see Figure 12) and deactivatmg electrically switchable holographic optical elements 1204A - 1204C and 1206 A - 1206C

Figure 18 shows a another embodiment of the system shown in Figure 2 In this embodiment, light from an source 100 is collimated and projected onto filter 202A The output lights 204R - 204B are received and redirected by ESHOE system 1200 mounted on the front surface of a transparent (e g glass) plate 1802 to produce illumination lights After bemg redirected, the illumination lights are totally internally reflected by a rear face of the plate 1802 and are incident upon a device 1804 (also mounted on the front of the plate 1802) which focuses the illumination lights and corrects chromatic dispersion in the latter The illumination lights are then projected on to subsurfaces 1 14A - 114C With reference to Figure 12, the ESHOE system 1200 of Figure 18 includes three stacks of three electrically switchable holographic optical elements Illummation control circuit (not shown in Figure 18) activates the electrically switchable holographic optical elements in only one stack to illuminate the subsurfaces

Because the electrically switchable holographic optical elements of ESHOE system 1200 operate off- axis and over appreciable spectral bandwidths, some correction of chromatic and geometrical aberration will be necessary, and this function is performed by the device 1804 In a particular example, device 1804 comprises a stack of holographic diffraction elements which are designed to act on red, green and blue bandwidth light, respectively Because the angular separation between R, G, and B illummation lights is relatively large (indeed, larger than the angular bandwidth of the Bragg holograms in these elements), the Bragg angular and wavelength selectivity will be sufficient to ensure that there is no appreciable cross-talk between the red, green and blue wavelengths Under these circumstances, there is no need for these elements of device 1804 to be made switchable on and off

As noted above, electrically switchable holographic optical elements will act efficiently only on the p- polarised component of the incident light, with the s-polarised component being substantially unaffected, I e undiffracted by the electrically switchable holographic optical elements As a consequence, half of the available light power will be lost To prevent this from happening, the smgle ESHOE system 1200 of Figure 18 can be replaced with a pair of ESHOE systems 1200 and a polarisation rotator optically mteφosed therebetween In this alternative embodiment, the p-polaπsed component of the light mcident upon the electrically switchable holographic optical elements of the first ESHOE system is diffracted whilst the s- polaπsed component passes therethrough substantially unaffected The polarisation rotator ( which can be an achromatic half-wave plate) is designed to rotate by 90 degrees the polarisation direction of light passmg therethrough Thus, the p-polarised light diffracted by the first ESHOE system becomes s-polarised, whilst the undiffracted s-polarised light becomes p-polarised On encountering the second ESHOE svstem, the (now) p- polarised component is diffracted whilst the (now) s-polaπsed component passes therethrough substantially unaffected The properties of electrically switchable holographic optical elements the two ESHOE systems are chosen such that the emission angle of diffracted light is the same m each case, so that both the p- and the s-polaπsed components are emitted m the same direction

In an alternative arrangement, the polarisation rotator is omitted and mstead the fringes of the holograms recorded m the electrically switchable holographic optical elements m the two ESHOE systems are arranged to be mutually crossed, so that the electrically switchable holographic optical elements m the first ESHOE system act on the p-polaπsed component whereas those in the second ESHOE system act on the s- polaπsed component Agam, the properties of the holograms in each ESHOE system are chosen such that the diffracted p- and s- polarised components are emitted m the same direction

Figure 19 shows a further embodiment of the system shown in Figure 2 Here filter 202C of Figure

10C is employed to filter collimated white light received from collimation lens 104 Additionally, the switchable optics svstem includes the ESHOE 1200 and an optical corrector 1902 is optically inteφosed between the filter 202C and the ESHOE 1200, its puφose being to correct for aberrations introduced by the latter.

Figure 20 shows a side view and a top view of an embodiment of the system shown in Figure 5 in which a reflective ESHOE 1200. The system shown in Figure 20 is similar to that shown in Figure 19 in that filter 202C is employed to filter collimated light from collimation lens 104. The top view shows how output lights 204GR, G, and B are diffracted by ESHOE 1200 to produce illumination lights R, G, and B which subsequently illuminate display surface 114. Further, the top view shows that illumination lights (i.e. the diffracted output lights) emerge from ESHOE system at angle measured with respect to the angle at which output lights fall incident on the input surface of ESHOE system 1200. An appreciable diffraction angle is needed for the electrically switchable holographic optical elements to achieve high diffraction efficiency.

Further, it is noted that reflective type electrically switchable holographic optical elements are not sensitive to the polarization state of the incident light at moderate incidence and diffraction angles. Accordingly, no special measures are needed to avoid polarization loses.

Figure 21 shows an arrangement where, instead of being directed to an image surface, illumination lights R, G, and B are projected on to an intermediate optical diffuser 2102. The diffuser can be used to control the beam characteristics to generate identical polar diagrams for the illumination light. The diffuser can be conventional, but is preferably a holographic light-shaping diffuser, which can be composed of a stack of non-switchable holographic optical elements.

Figure 22 shows an alternative embodiment of the system shown in Figure 2. The switchable optics system of Figure 22 employs the ESHOE system 1200 of Figure 12. However, the groups of electrically switchable holographic optical elements not arranged side by side. Rather, the groups of electrically switchable holographic optical elements 1202, 1204, and 1206 are individually positioned adjacent input faces of a dichroic prism. Collimated light 106 is filtered into output lights 204R - 204B by filter 202B. Output light 204R is deflected 90 degrees by a plane mirror 2204 and falls incident upon an input face of the dichroic prism after being diffracted by one of the activated electrically switchable holographic optical elements in group 1202. Similarly, output light 204B is deflected 90 degrees by a plane mirror 2206 and falls incident upon another input face of the dichroic prism after being diffracted by. Output light 204G falls incident on a third input face of the dichroic prism after being diffracted by one of the activated electrically switchable holographic optical elements in group 1204. The dichroic prism redirects the diffracted lights (i.e., the illumination lights R, G, and B) to a color correction element 2202, disposed optically immediately after the output face of the dichroic prism, before illuminating image surface 1 14. Figure 23 depicts a modification of the system shown in Figure 22 in which the plane mirrors 2204 and 2206 are replaced by total internal reflection prisms 2304 and 2306. Figure 24 illustrates a further embodiment of Figure 22 in which the dichroic filter elements of filter 202B and the plane mirror2206 are rearranged so that output lights 204R - 204B fall incident on the groups of electrically switchable holographic optical elements 1202 - 1206. respectively, at an angle greater than 90 degrees. It is noted that plane mirror 2204 is removed from this alternative. In each case the output beams are angled so that diffracted light is emmitted normally to the output surfaces of the electrically switchable holographic optical elements. The arrangement shown in Figure 18 is such that the illumination lights incident at any point on the dιspla> surface overlap exactly and appear to have been generated from a common point This is an important requirement in many reflective display devices, where the brightness of the final projected image depends o specular reflection at the display rather than diffusion (as would be the case, for example, with transmissive LCDs) In embodiments described above the output lights are not matched in this way and may need to be modified using diffusion screens (such as shown in Figure 21) before they could be used to illuminate a reflective non-diffusmg display

Figure 25 shows an alternative embodiment employing the present invention Figure 25 shows image surface 114 comprises an array of pixels 2502 The pixels are divided among three sets, with pixels in each set being evenly distributed across the image surface 1 14 Figure 25 shows is a cross sectional view of one line of pixels in the arrayed image surface Image control circuit controls the display of monochrome images on surface 114 so that, at any time, the pixels in each set display (in monochrome) either the red, green, or blue component of the final image, and also such that the pixels in each set display these final image components in succession

Figure 25 also shows an ESHOE system 2504 having groups of three electrically switchable holographic optical elements 2504A - 2504C used for illuminating the pixels with illumination lights R, G, or B Although not shown, the number of groups of three electrically switchable holographic optical elements 2504A - 2504C equals the number of pixels in a line of pixels Figure 25 shows one group of three electrically switchable holographic optical elements 2504A - 2504C Essentially, the ESHOE system 2504 receives collimated white light 106 from a collimation lens (not shown) ESHOE 2504 filters, directs, and focuses the collimated white light 106 by diffraction to illuminate each of pixels with R, G, or B illumination light The red illumination lights R are directed to those pixels 2502 which are, at the time, displaying red monochromatic components of the final image The green illumination lights G are directed to those pixels 2502 which are, at the time, display g green monochromatic components of the final image The blue illumination lights B are directed to those pixels 2502 which are, at the time, displaying blue monochromatic components of the final image

ESHOE system 2504 is controlled by circuit 118 so that only one of the electrically switchable holographic optical elements 2504A - 2504C in each group is active at a given point in time Moreover, control circuit is in synchronism with unage control circuit 116 so that only those pixels 2502 displaying red, green, or blue monochrome components of the final image are illummated with R, G, or B illumination light

Each of the electrically switchable holographic optical elements 2504A - 2504C in each group, includes three stacks of holographic lenses (preferably microlenses) formed in the holographic recordmg medium therein The lenses in each stack operate on the red, green, and blue bandwidth components, respectively of collimated light 106 when activated by the appropriate signal generated by illumination control circuit 1 18 In Figure 25, each of the holographic lenses that diffract red bandwidth light is shown cross hatched, each of the holographic lenses that diffract green bandwidth light is shown plain, and each of the holographic lenses that diffract blue bandwidth light is shown dotted The three stacks of lenses in each electrically switchable holographic optical element are positioned between a pair of electrode (ITO) layers so that all lenses therebetween are activated bv the control signal provided to the pair of electrodes by the control circuit 1 18 Alternatively, each stack of lenses, or each lens in the electrically switchable holographic optical elements may be separately switchable into or out of the active state However, such an alternative embodiment requires that each separate lens or each separate stack of lenses by sandwiched between its own set of ITO layers

Figures 26A - -26C illustrate operational aspects of the ESHOE system 2504 shown in Figure 25 Figures 26 A - 26C show only pixels 2502 A - 2502C and one holographic lens from the lens stack of each of the electrically switchable holographic optical elements of groups 2504 A - 2504C Figure 26A shows a first stage of a three stage cycle in which pixels 2502 A - 2502C display green, red, and blue monochrome components, respectively, of the final image Also in this stage, the holographic lenses m the first group 2504A are all activated by control circuit 118 so that the red lens contained m first group 2504A directs and focuses the red bandwidth component of collimated white light 106 incident thereon onto pixels 2502A while passing light of other bandwidths incident thereon without noticeable alteration, the green lens contained in first group 2504A directs and focuses the green bandwidth component of collimated white light 106 incident thereon onto pixels 2502B while passmg light of other bandwidths incident thereon without noticeable alteration, and the blue lens contamed in first group 2504A directs and focuses the blue bandwidth component of collimated white light 106 incident thereon onto pixels 2502C while passmg light of other bandwidths mcident thereon without noticeable alteration Lenses shown in broken lmes are deactivated by control circuit 118 These lenses pass all incident light with out substantial alteration

In the second stage of the three stage cycle illustrated in Figure 26B, pixels 2502 A - 2502C display red, blue, and green monochrome components, respectively, of the final image Also in this stage, the holographic lenses in the second group 2504B are all activated by control circuit 1 18 so that the red lens contained in first group 2504B directs and focuses the red bandwidth component of collimated white light 106 incident thereon of pixels 2502A while passmg light of other bandwidths mcident thereon without noticeable alteration, the green lens contained in first group 2504B directs and focuses the green bandwidth component of collimated white light 106 incident thereon onto pixels 2502C while passing light of other bandwidths incident thereon without noticeable alteration, and the blue lens contamed in first group 2504B directs and focuses the blue bandwidth component of collunated white light 106 mcident thereon onto pixels 2502B while passing light of other bandwidths incident thereon without noticeable alteration

In the last stage of the three stage cycle illustrated in Figure 26C, pixels 2502 A - 2502C display blue, green, and red monochrome components, respectively, of the final image Also in this stage, the holographic lenses in the second group 2504C are all activated by control circuit 1 18 so that the red lens contained in first group 2504C directs and focuses the red bandwidth component of collimated white light 106 incident thereon onto pixels 2502C while passing light of other bandwidths incident thereon without noticeable alteration, the green lens contained in first group 2504C directs and focuses the green bandwidth component of collimated white light 106 incident thereon onto pixels 2502B while passing light of other bandwidths incident thereon without noticeable alteration, and the blue lens contained in first group 2504C directs and focuses the blue bandwidth component of collimated white light 106 incident thereon onto pixels 2502A while passmg light of other bandwidths incident thereon without noticeable alteration

The three stage cycle is then repeated for the next final images, with the switching between the various stages being performed rapidly In this fashion the image surface 1 14 is perceived by a viewer as displaying a full color image, and with the red, green and blue components of collimated white light 1 14 being fully used at all times It is to be understood that, where a particular pixel displays at any given tune a part of the final image where one or more of the monochromatic components are missing, then no illumination light is directed and focused onto that pixel during that particular operation, then no light of those particular color(s) is focused onto that pixel during that particular cycle For example, if a given pixel displays a part of the image having only a red spectral component, then no green or blue illummation light is focused thereon

A further embodiment of the image generating apparatus is shown in figure 27, where the image surface 1 14 is pixellated like that described in Figure 25 and operates under the action of control circuit 116 In this embodiment, however, collimated light 106 is reflected by ESHOE system 2702 towards a directing device 2704, which then directs red, green and blue illummation lights onto the pixels 2502

More particularly, the ESHOE system 2702 is composed of three reflective, electrically switchable holographic optical elements In one embodiment, electrically switchable holographic optical elements 2702A-2702C can be arranged similar to that shown in Figure 25 save that each group of electrically switchable holographic optical element consists of three arrays of holographic mirrors In an alternative each electrically switchable holographic optical element can be embedded as three large holographic mirrors It should be understood that reflective electrically switchable holographic optical elements operate m a manner similar to mirrors m that light emits from the same surface that receives the incident light However, reflective electrically switchable holographic optical elements operate by diffracting mcident light, the diffracted light emitting from the same surface that receives the incident light

Each of the electrically switchable holographic optical elements is arranged to diffract the red, green and blue components of the light 106 at three predetermmed emission angles, as indicated by arrows A, B and

C Control circuit 1 18 activates each of the electrically switchable holographic optical elements 2702 A - 2702C in sequence, I e so that when one element is activated while the other two are deactivated When the element 2702 A is activated, red illummation light is emitted in the direction of arrow A whilst green and blue illumination light is emitted respectively in the direction of arrows B and C When the element 2702B is activated, red illummation light is emitted m the direction of arrow B whilst green and blue illummation lights are emitted respectively m the direction of arrows C and A When the element 2702C is activated, red light is emitted in the direction of arrow C whilst green and blue light is emitted respectively in the direction of arrows A and B

The directing device 2704 comprises essentially a passive optical element (such as an array ot prismatic elements, lens-like elements or holographic device) which deflects light incident thereon to a degree dependent upon its wavelength The device 2704 is arranged to direct light received in the direction of arrow A onto one set of pixels 2502, and to direct light received in the direction of arrows B and C onto second and third sets of the pixels. These sets of pixels are controlled by the control circuit 1 16 such that each set displays at any given time either a "red", "green" or "blue" monochromatic component of the final image, with each set displaying all of these image components in sequence. Operation of the control circuits 1 16 and 1 18 is synchronized such that, by way of example, when electrically switchable holographic optical element 2702A is activated, device 2704 directs red light onto those pixels which are at the time displaying a red monochromatic component of the final image, and so on. Otherwise, operation of the apparatus of this embodiment is analogous to that described above with reference to Figure 25.

In a preferred example of the above apparatus, the directing device 2704 is composed of a stack of three holographic elements each of which is optimised to act upon the re, green and blue wavelengths, respectively.

Whereas the invention has been described in relation to what are presently considered to be the most practicable and preferred embodiments, it is to be understood that the invention is not limited to the disclosed arrangements but rather is intended to cover various modification and equivalent construction included within the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS

1. An apparatus comprising: a switchable optics system comprising a first group of electrically switchable holographic optical elements comprising first, second, and third electrically switchable holographic optical elements each of which is electrically switchable between an active state and an inactive state, wherein each of the first, second, and third electrically switchable holographic optical elements is configured to diffract light incident thereon when operating in the active state, wherein each of the first, second, and third electrically switchable holographic optical elements transmits light incident thereon without substantial alteration when operating in the deactive state, and; a first control circuit coupled to the first, second and third electrically switchable holographic optical elements, wherein each of the first, second and third electrically switchable holographic optical elements is activated or deactivated by the control circuit; wherein light diffracted by the first electrically switchable holographic optical element passes through a first region of a plane; wherein light diffracted by the second electrically switchable holographic optical element passes through a second region of the plane; wherein light diffracted by the third electrically switchable holographic optical element passes through a third region of the plane; wherein the second region is positioned between the first and third regions of the plane.

2. The apparatus of claim 1 wherein each of the first, second and third electrically switchable holographic optical elements is configured to diffract first bandwidth light incident thereon.

3. The apparatus of claim 2 wherein each of the first, second and third electrically switchable holographic optical elements is configured to be separately activated or deactivated by the first control circuit.

4. The apparatus of claim 3 wherein the first control circuit is configured to sequentially and cyclically activate and deactivate the first, second and third electrically switchable holographic optical elements so that only one of the first, second, and third electrically switchable holographic optical elements is active at any point in time.

5. The apparatus of claim 1 wherein each of the first, second and third electrically switchable holographic optical elements is configured to diffract first, second, and third bandwidth light incident thereon, respectively, wherein the first, second, and third bandwidth lights are distinct from each other.

6. The apparatus of claim 5 wherein the first, second, and third electrically switchable holographic optical elements are configured to be collectively activated or deactivated by the first control circuit. 7 The apparatus of claim 1 wherein each of the electrically switchable holographic optical elements comprises a holographic recording medium that records a hologram, wherein the holographic recording medium comprises a monomer dipentaervthritol hydroxypentaacrylate, a liquid crystal a cross-linking monomer, a coinitiator. and a photoimtiator dye

8 The apparatus of claim 1 wherein each of the electrically switchable holographic optical elements comprises a hologram made by exposing an mterference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure a polymeπzable monomer, a liquid crystal, a cross-linking monomer, a coinitiator, and a photoimtiator dye

9 The apparatus of claim 1 wherein the directing apparatus further comprises a second group of electrically switchable holographic optical elements comprising first, second and third electrically switchable holographic optical elements coupled to the first control circuit, wherein each of the first, second and third electrically switchable holographic optical elements of the second group is electrically switchable between an active state and an inactive state, wherein each of the first, second and third electrically switchable holographic optical elements of the second group is activated or deactivated by the control circuit, wherem each of the first, second and third electrically switchable holographic optical elements of the second group is configured to diffract light incident thereon when operatmg m the active state, wherem each of the first, second and third electrically switchable holographic optical elements of the second group transmits light incident thereon without substantial alteration when operating in the deactive state, wherein light diffracted by the first electrically switchable holographic optical element of the second group passes through the third region of the plane, wherem light diffracted by the second electrically switchable holographic optical element of the second group passes through the first region of the plane wherem light diffracted by the third electrically switchable holographic optical element of the second group passes through the second region of the plane, a third group of electrically switchable holographic optical elements comprising first, second and third electrically switchable holographic optical elements coupled to the first control circuit wherein each of the first, second and third electrically switchable holographic optical elements of the third group is electrically switchable between an active state and an inactive state, wherein each of the first, second and third electrically switchable holographic optical elements of the third group is activated or deactivated by the control circuit, wherein each of the first, second, and third electrically switchable holographic optical elements of the third group is configured to diffract light mcident thereon when operating in the active state, wherem each of the first, second, and third electrically switchable holographic optical elements of the third group transmits light mcident thereon without substantial alteration when operating in the deactive state, wherein light diffracted by the first electrically switchable holographic optical element of the third group passes through the second region of the plane, wherem light diffracted by the second electrically switchable holographic optical element of the third group passes through the third region of the plane, wherem light diffracted by the third electrically switchable holographic optical element of the third group passes through the first region of the plane

10 The apparatus of claim 9 wherein each of the first, second and third electrically switchable holographic optical elements of the first group is configured to diffract first bandwidth light incident thereon, wherein each of the first, second and third electrically switchable holographic optical elements of the second group is configured to diffract second bandwidth light mcident thereon, wherein each of the first, second, and third electrically switchable holographic optical elements of the third group is configured to diffract third bandwidth light mcident thereon, wherein the first, second, and third bandwidths are distinct from each other

1 1 The apparatus of claim 10 wherein each of the first electrically switchable holographic optical elements is configured to be separately activated or deactivated by the first control circuit, wherein each of the second electrically switchable holographic optical elements is configured to be separately activated or deactivated by the first control circuit, and wherem each of the third electrically switchable holographic optical elements is configured to be separately activated or deactivated by the first control circuit

12 The apparatus of claim 11 wherein the first control circuit is configured to sequentially and cyclically activate and deactivate the first electrically switchable holographic optical elements so that only one of the first electrically switchable holographic optical elements is active at any point m time, wherein the first control circuit is configured to sequentially and cyclically activate and deactivate the second electrically switchable holographic optical elements so that only one of the second electrically switchable holographic optical elements is active at anv point in time, wherem the first control circuit is configured to sequentially and cyclically activate and deactivate the third electrically switchable holographic optical elements so that only one of the third electrically switchable holographic optical elements is active at any point in time, wherein the control circuit is configured to activate only one of the electrically switchable holographic optical elements in each of the first, second, and third groups of electrically switchable holographic optical elements at any point in tune

13 The apparatus of claim 9 wherein each of the first, second, and third electrically switchable holographic optical elements is configured to diffract first, second, and third bandwidth light mcident thereon, respectively, wherein the first, second, and third bandwidth lights are distinct from each other

14 The apparatus of claim 13 wherein the first control circuit is configured to sequentially and cyclically activate and deactivate the first, second, and third electrically switchable holographic optical elements of the first, second, and third groups of electrically switchable holographic optical elements, respectively, so that only the first, second, and third groups electrically switchable holographic optical elements of only one of the first, second, and third groups of electrically switchable holographic optical elements are active at any point m time

15 The apparatus of claim 1 further comprising a light source for generating light comprising first, second and third bandwidth light, a collimatmg lens for receivmg and collimating light generated by the light source, a filter for receivmg and filtering light collimated by the collimat g lens, wherein the filter filters the received collimated light into spatially separate first, second, and third bandwidth lights

16 The apparatus of claim 15 wherein the first electrically switchable holographic optical element is configured to receive and diffract the first bandwidth light, wherem the second electrically switchable holographic optical element is configured to receive and diffract the second bandwidth light, and wherem the third electrically switchable holographic optical element is configured to receive and diffract the third bandwidth light

17 The apparatus of claim 1 further compπsmg a light source for generatmg light compπsmg first, second, and third bandwidth light, a collimatmg lens for receiving and collimatmg light generated by the light source, wherem each of the first, second, and third electrically switchable holographic optical elements is configured to receive the collunated light generated by the light source, wherem the first electrically switchable holographic optical element is configured to diffract the first bandwidth light of the collimated light received by the first electrically switchable holographic optical element when active while transmitting the second and third bandwidth light of the collimated light received by the first electrically switchable holographic optical element, wherein the second electrically switchable holographic optical element is configured to diffract the second bandwidth light of the collimated light received by the second electrically switchable holographic optical element when active while transmitting the first and third bandwidth light of the collimated light received by the second electrically switchable holographic optical element wherein the third electrically switchable holographic optical element is configured to diffract the third bandwidth light of the collimated light received by the third electrically switchable holographic optical element when active while transmitting the second and first bandwidth light of the collimated light received by the third electrically switchable holographic optical element

18 The apparatus of claim 1 further comprising a display device comprising a display surface configured to display a monochrome image, wherem the display surface is configured to receive the first, second and third diffracted lights

19 The apparatus of claim 18 wherem the monochrome image comprises first, second, and third monochrome components, wherem the first monochrome image is configured to receive the first diffracted light, wherein the second monochrome image is configured to receive the second diffracted light, and wherem the third monochrome image is configured to receive the third diffracted light

20 The apparatus of claim 19 wherem the display surface is configured to simultaneously display the first, second, and third monochromatic components on first, second, and third subsurfaces, respectively, of the display surface, wherem the second subsurface is positioned between and adjacent to the first and third subsurfaces

21 The apparatus of claim 19 wherein the display surface is configured to sequentially display the first, second and third monochromatic components on a subsurface of the display surface

22 An apparatus compπsmg a switchable light-directing apparatus configured to receive light, a first control circuit coupled to the switchable light-directing apparatus, wherem the switchable light-directing apparatus is configured to receive a control signal from the first control circuit, wherem the switchable light-directing apparatus directs a first portion of received light to a first region of a plane in response to receiving the control signal, wherein the switchable light-directing apparatus directs a second portion of received light to a second region of the plane in response to receiving the control signal, wherem the switchable light-directing apparatus directs a third portion of received light to a third region of the plane in response to receiving the control signal, wherein the second region is positioned between the first and third regions

23 An apparatus comprising a light directing having a first surface and a second surface, wherein the first surface is configured to receive light, and wherein the second surface is configured to emit at least two portions of light received on the first surface, wherein the apparatus is configured to direct the at least two portions of light to separate positions in an output plane