WO2007138576A1 - systÈme d'Éclairage avec intÉgrateur optique pour projecteur d'image - Google Patents

systÈme d'Éclairage avec intÉgrateur optique pour projecteur d'image Download PDF

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Publication number
WO2007138576A1
WO2007138576A1 PCT/IL2007/000636 IL2007000636W WO2007138576A1 WO 2007138576 A1 WO2007138576 A1 WO 2007138576A1 IL 2007000636 W IL2007000636 W IL 2007000636W WO 2007138576 A1 WO2007138576 A1 WO 2007138576A1
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WO
WIPO (PCT)
Prior art keywords
light
image
linear
light beam
optical element
Prior art date
Application number
PCT/IL2007/000636
Other languages
English (en)
Inventor
Naim Konforti
Original Assignee
Mirage Innovations Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mirage Innovations Ltd. filed Critical Mirage Innovations Ltd.
Publication of WO2007138576A1 publication Critical patent/WO2007138576A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
    • G02B27/4205—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
    • G02B27/4272—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having plural diffractive elements positioned sequentially along the optical path
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/0006—Arrays
    • G02B3/0037—Arrays characterized by the distribution or form of lenses
    • G02B3/0056—Arrays characterized by the distribution or form of lenses arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29325—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only
    • G02B6/29329—Diffractive elements operating in transmission
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0081—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 with means for altering, e.g. enlarging, the entrance or exit pupil
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01—Head-up displays
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/0006—Arrays
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
    • G02B6/0015—Means for improving the coupling-in of light from the light source into the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/0016—Grooves, prisms, gratings, scattering particles or rough surfaces
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/0035—Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/0038—Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide

Definitions

  • the present invention relates to optics and, more particularly, to apparatus, method and system for providing light such as to form different linear foci at different longitudinal locations.
  • An electronic display may provide a " real image, the size of which is determined by the physical size of the display device, or a virtual image, the size of which may extend the dimensions of the display device.
  • a real image is defined as an image, projected on or displayed by a viewing surface positioned at the location of the image, and observed by an unaided human eye (to the extent that the viewer does not require corrective glasses).
  • Examples of real image displays include a cathode ray tube (CRT), a liquid crystal display (LCD), an organic light emitting diode array (OLED), or any screen-projected displays.
  • CTR cathode ray tube
  • LCD liquid crystal display
  • OLED organic light emitting diode array
  • a real image could be viewed normally from a distance of about at least 25 cm, the minimal distance at which the human eye can utilize focus onto an object. Unless a person is long-sighted, he may not be able to view a sharp image at a closer distance.
  • CRT display screens typically display images for a user.
  • the CRT displays are heavy, bulky and not easily miniaturized.
  • flat-panel display is typically used.
  • the flat-panel display may use LCD technology implemented as passive matrix or active matrix panel.
  • the passive matrix LCD panel consists of a grid of horizontal and vertical wires. Each intersection of the grid constitutes a single pixel, and controls an LCD element.
  • the LCD element either allows light through or blocks the light.
  • the active matrix panel uses a transistor to control each pixel, and is more expensive.
  • An OLED flat panel display is an array of light emitting diodes, made of organic polymeric materials.
  • Existing OLED flat panel displays are based on both passive and active configurations. Unlike the LCD display, which controls light transmission or reflection, an OLED display emits light, the intensity of which is controlled by the electrical bias applied thereto.
  • Flat-panels are also used for miniature image display systems because of their compactness and energy efficiency compared to the CRT displays. Small size real image displays have a relatively small surface area on which to present a real image, thus have limited capability for providing sufficient information to the user. In other words, because of the limited resolution of the human eye, the amount of details resolved from a small size real image might be insufficient.
  • a virtual image is defined as an image, which is not projected onto or emitted from a viewing surface, and no light ray connects the image and an observer.
  • a virtual image can only be seen through an optic element, for example a typical virtual image can be obtained from an object placed in front of a converging lens, between the lens and its focal point. Light rays, which are reflected from an individual point on the object, diverge when passing through the lens, thus no two rays share two endpoints. An observer, viewing from the other side of the lens would perceive an image, which is located behind the object, hence enlarged.
  • a virtual image of an object, positioned at the focal plane of a lens is said to be projected to infinity.
  • a virtual image display system which includes a miniature display panel and a lens, can enable viewing of a small size, but high content display, from a distance much smaller than 25 cm.
  • Such a display system can provide a viewing capability which is equivalent to a high content, large size real image display system, viewed from much larger distance.
  • U.S. Patent No. 4,711,512 to Upatnieks describes a diffractive planar optics head-up display configured to transmit collimated light wavefronts of an image, as well as to allow light rays coming through the aircraft windscreen to pass and be viewed by the pilot.
  • the light wavefronts enter an elongated optical element located within the aircraft cockpit through a first diffractive element, are diffracted into total internal reflection within the optical element, and are diffracted out of the optical element by means of a second diffractive element into the direction of the pilot's eye while retaining the collimation.
  • Upatnieks does not teach how to transmit a wide field-of-view through the display, or how to transmit a broad spectrum of wavelengths (for providing color images).
  • a major limitation of the head-up display of Upatnieks is the use of thick volume holograms which, albeit their relatively high diffraction efficiency, are known to have narrow angular and chromatic response.
  • U.S. Patent Nos. 5,966,223 and 5,682,255 to Friesem et al. describes a holographic optical device similar to that of Upatnieks, with the additional aspect that the first diffractive optical element acts further as the collimating element that collimates the waves emitted by each data point in a display source and corrects for field aberrations over the entire field-of-view.
  • the field-of-view discussed is ⁇ 6°, and there is a further discussion of low chromatic sensitivity over wavelength shift of ⁇ c of +2 nm around a center wavelength ⁇ c of 632.8 nm.
  • Niv et al. also disclose an optical device incorporating the aforementioned diffractive optical element for transmitting light in general and images in particular into the eye of the user.
  • the above virtual image devices provide a single optical channel, hence allowing the scene of interest to be viewed by one eye. It is recognized that the ability of any virtual image devices to transmit an image without distortions inherently depends on whether or not light rays emanating from all points of the image are successfully transmitted to the eye of the user in their original color. Due to the single optical channel employed by presently known devices, the filed-of-view which can be achieved without distortions or loss of information is rather limited.
  • a binocular device which employs several diffractive optical elements is disclosed in U.S. Patent Application Nos. 10/896,865 and 11/017,920, and in International Patent Application, Publication No. WO 2006/008734, the contents of which are hereby incorporated by reference.
  • An optical relay is formed of a light transmissive substrate, an input diffractive optical element and two output diffractive optical elements. Collimated light is diffracted into the optical relay by the input diffractive optical element, propagates in the substrate via total internal reflection and coupled out of the optical relay by two output diffractive optical elements.
  • the input and output diffractive optical elements preserve relative angles of the light rays to allow transmission of images with minimal or no distortions.
  • the output elements are spaced apart such that light diffracted by one element is directed to one eye of the viewer and light diffracted by the other element is directed to the other eye of the viewer.
  • virtual image display systems include a certain type of image generating apparatus which produce the image being viewed.
  • the apparatus typically projects a light beam constituting the image on an optical relay device which in turn ensures divergence of light rays so as to form the virtual image.
  • Such apparatus typically includes a passive or active miniature display device.
  • Passive display devices include LCD, electrochemical display (ECD), electrophoretic image display (EPID) and digital light processor (DLP).
  • Active display devices include CRT, plasma display panel (PDP), OLED array and electroluminescent display (ELD).
  • each pixel radiates light independently.
  • Passive display devices do not produce light within the pixel and the pixel is only able to block transmission of light generated by a backlight assembly, or alternatively enable reflection of light generated by a front illumination assembly.
  • backlight assemblies are known.
  • the backlight illumination generated can be white or it can be polychromatic, depending on the type of passive display device.
  • Backlight assemblies which employ white illumination include a white light source and color filters such as a color wheel or an arrangement of red, green and blue (RGB) filters at each pixel of the display.
  • Backlight assemblies which employ polychromatic light may operate in a color sequential operation or they can have three separate illumination sources.
  • virtual image display systems employ condenser lens to form a real image of the miniature display device on a projection lens.
  • the clear aperture of the projection lens is larger than the area of the miniature display to allow placing the miniature display adjacent to the condenser lens hence to improve light transmission.
  • the efficiency is far from being optimal and a significant amount of stray light is produced.
  • an apparatus for providing light comprising a light source having a light emitting surface for generating a light beam, a passive modulator configured to modulate the light beam to constitute an image therein; and at least one linear focusing element.
  • the linear focusing element defines a longitudinal optical axis of the apparatus and forms different linear foci at different longitudinal locations along the longitudinal optical axis.
  • the linear focusing element forms two foci: a first linear focus with respect to a first transverse dimension at a first longitudinal location, and a second linear focus with respect to a second transverse dimension at a second longitudinal location.
  • the linear focusing element comprises a first arrangement of lenses characterized by spherical symmetry, and a second arrangement of lenses characterized by a symmetry other than spherical symmetry.
  • the second arrangement of lenses is characterized by a cylindrical symmetry.
  • the first location is at a distance Z 1 from the light source and the second location is at a distance Z 2 from the light source, wherein the ratio between Z 2 and Z 1 is at least 2, more preferably 3.
  • apparatus for providing light comprises: a light source having a light emitting surface for generating a light beam; a passive modulator configured to modulate the light beam to constitute an image therein; and one or more linear focusing elements defining a longitudinal optical axis.
  • the linear focusing element has a first arrangement of lenses characterized by spherical symmetry and a second arrangement of lenses characterized by a symmetry other than spherical symmetry, e.g., cylindrical symmetry.
  • a method of providing light comprises the apparatus described herein.
  • the apparatus further comprises an optical projection element interposed in the light path of the light beam and configured for projecting the light beam in a collimated manner.
  • a system for providing an image to a user comprises: the apparatus described herein and an optical relay device.
  • the apparatus serves as image generating apparatus, and the optical relay device relays the light beam provided by the apparatus in a manner such that the light beam is expanded in a first transverse dimension and relayed to occupy at least one predetermined two-dimensional eye-box region in space.
  • the first longitudinal location is defined at the location of the projection optical element
  • the second longitudinal location is defined at the eye- box region.
  • the linear focusing element is designed and constructed such as to form an intermediate virtual image of a first linear segment of the light emitting surface. According to still further features in the described preferred embodiments the linear focusing element also forms a real image of the intermediate virtual image at the first longitudinal location.
  • the linear focusing element is designed and constructed such as to form an intermediate virtual image of a second linear segment of the light emitting surface.
  • the projection optical element is designed and constructed such as to form real image of the intermediate virtual image at the second longitudinal location.
  • the first linear focus is formed at a first transverse plane being at the first longitudinal location, wherein any point on the first transverse plane other than points belonging to the first linear focus is out of focus with respect to the light emitting surface.
  • the second linear focus is formed at a second transverse plane being at the second longitudinal location, and wherein any point on the second transverse plane other than points belonging to the second linear focus is out of focus with respect to the light emitting surface.
  • the optical relay device comprises a light transniissive substrate formed with at least one input optical element for coupling the light beam into the light transmissive substrate, and at least one output optical element for expanding the light beam in the first transverse dimension and coupling the light beam out of the light transmissive substrate to the two-dimensional region.
  • the at least one input optical element and/or the at least one output optical element comprise diffractive optical elements.
  • the at least one linear focusing element comprises a first arrangement of lenses characterized by spherical symmetry and a second arrangement of lenses characterized by a symmetry other than spherical symmetry.
  • the optical relay device comprises an input diffractive optical element, a first output diffractive optical element and a second output diffractive optical element.
  • the input diffractive optical element is designed and constructed for diffracting the light beam to propagate within the light-transmissive substrate via total internal reflection;
  • the first output diffractive optical element is designed and constructed for diffracting light corresponding to a first part of the image out of the light-transmissive substrate;
  • the second output diffractive optical element is designed and constructed for diffracting light corresponding to a second part of the image out of the light- transmissive substrate, such that the combination of the first and the second part substantially reconstructs the image.
  • each of the at least one input optical element and the at least one output optical element is characterized by planar dimensions defined by a length along the first transverse dimension and a width along the second transverse direction, wherein a width of the at least one output optical element is smaller than a width of the at least one input optical element.
  • the linear focusing element is characterized by a first effective focal length in the first transverse dimension and a second effective focal length in the second transverse dimension, the second effective focal length being longer than the first effective focal length.
  • the at least one linear focusing element is a lenslet array.
  • the lenslet array has a first side and a second side opposite the first side, wherein the first arrangement of lenses is an array of spherical lenses arranged on the first side, and wherein the second arrangement of lenses is array of cylindrical lenses arranged on the second side.
  • At least one of the array of cylindrical lenses and the array of spherical lenses is corrugated so as to impart a substantially homogenous intensity distribution across the light beam.
  • the lenslet array is made, at least in part, of a diffractive material.
  • linear focusing element comprises at least one element selected from the group consisting of a condenser lens system, a Fresnel zone plate and a holographic lens.
  • the apparatus further comprises a beam homogenizer interposed in the optical path of the light beam for imparting a substantially homogenous intensity distribution across the light beam.
  • the present invention successfully addresses the shortcomings of the presently known configurations by providing apparatus, method and system for providing light.
  • FIGs. la-b are schematic illustrations of cross-sectional views of an apparatus for providing light, according to various exemplary embodiments of the present invention.
  • FIGs. lc-e are schematic illustrations depicting in perspective manner the operation of a linear focusing element, according to various exemplary embodiments of the present invention.
  • FIG. 2a is a schematic illustration of a cross-sectional view of a light source according to various exemplary embodiments of the present invention
  • FIG. 2b is a schematic illustration of a cross-sectional view of an optical passive modulator according to various exemplary embodiments of the present invention
  • FIGs. 3a-b are schematic illustrations of the linear focusing element in a preferred embodiment in which a lenslet array is employed;
  • FIG. 4 is a schematic cross-sectional illustration of a system for providing an image to a user, according to various exemplary embodiments of the present invention.
  • T/IL2007/000636 is a schematic cross-sectional illustration of a system for providing an image to a user, according to various exemplary embodiments of the present invention.
  • FIGs. 5a-b are schematic illustrations exemplifying ray tracing within the system, according to various exemplary embodiments of the present invention.
  • FIGs. 6a-b are fragmentary schematic illustrations depicting realization of the ray tracing shown in Figures 5a-b;
  • FIG. 7 is a schematic illustration of light diffraction by a linear diffraction grating operating in transmission mode;
  • FIGs. 8a-c are schematic illustrations of cross sectional views of an optical relay device according to various exemplary embodiments of the invention.
  • FIG. 8d is a schematic illustration of a rectangular field-of-view of the optical relay device, according to various exemplary embodiments of the invention.
  • FIGs. 8e-f are schematic illustrations of field-of-view angles of the optical relay device, according to various exemplary embodiments of the invention.
  • FIGs. 9a-b are schematic illustrations of a perspective view ( Figure 3a) and a side view ( Figure 3 b) of the optical relay device, in a preferred embodiment in which the device comprises one input optical element and two output optical elements, according to various exemplary embodiments of the present invention
  • FIGs. 10a-b are fragmentary views schematically illustrating wavefront propagation within the optical relay device, according to preferred embodiments of the present invention.
  • FIG. 11 is a schematic illustration of binocular system, in the preferred embodiment in which the diffraction phenomenon is used for relaying the light.
  • the present embodiments comprise apparatus and method which can be used for providing light. Specifically, but not exclusively, the present embodiments can be used for generating and transmitting an image to an optical relay of a virtual image display system.
  • the present embodiments further comprise a system which employs the apparatus and which can be used for viewing a virtual image.
  • the present embodiments can be used in many applications in which virtual images are viewed, including, without limitation, eyeglasses, binoculars, head mounted displays, head-up displays, cellular telephones, personal digital assistants, aircraft cockpits and the like.
  • Figures la-b are schematic illustrations of cross-sectional views of an apparatus 100 for providing light, according to various exemplary embodiments of the present invention.
  • Apparatus 100 is illustrated in Figures la-b and described below with reference to x-y-z Cartesian coordinate system, where Figure Ia provides a schematic cross-sectional view of apparatus 100 in the x-z plane and Figure Ib provides a schematic cross-sectional view of apparatus 100 in the y-z plane.
  • These cross-sectional views are referred to herein as a "side view" (x-z plane, Figure Ia) and a "top view” (y ⁇ z plane, Figure Ib).
  • apparatus 100 comprises a light source 102 having a light emitting surface 103 for generating a light beam 104, and one or more linear focusing elements 106 which provide linear foci as further detailed hereinbelow.
  • Light source 102 is aligned with linear focusing element 106 such that element 106 is in the optical path of beam 104 or a portion thereof.
  • Linear focusing element 106 has a longitudinal optical axis 108 which, without the loss of generality, is aligned with the z axis.
  • the terms “z axis” and “longitudinal axis” will therefore be used below interchangeably.
  • each of the x and y axes is referred to as a "transverse axis”
  • any linear measure (length) parallel to one of these axis is referred to as a transverse dimension
  • any plane parallel to the x-y plane is referred to as a "transverse plane”.
  • the two transverse dimensions are distinguished by the terms "horizontal” for a transverse dimension which is parallel to the y axis, and "vertical” for a transverse dimension which is parallel to the x axis.
  • a plane parallel to the x-z plane is referred to below as a “vertical plane”
  • a plane parallel to the y-z plane is referred to below as a “horizontal plane.”
  • this terminology describes a situation in which the x axis is directed upwards, but it is not intended to limit the scope of present invention, to any specific orientation of apparatus 100 in space.
  • apparatus 100 is used as an image generating apparatus.
  • light beam 104 is modulated according to image data to constitute an image therein.
  • the modulation of light 104 is preferably by a passive modulator 110.
  • light source 102 serves as a component in a passive display device, which may be a transmissive passive display device, a reflective passive display device or a transflective passive display device.
  • modulator 110 is a transmissive passive display panel and light source provides backlight illumination
  • a reflective passive display device is employed modulator 110 is a reflective passive display panel and light source 102 provides frontlight illumination
  • transflective passive display device is employed modulator 110 is a transflective passive display panel light source 102 provides backlight and/or frontlight illumination.
  • passive display panel refers to any pixelated panel in which the pixels do not produce light and which requires backlight or frontlight for operation.
  • transmissive passive display panels include, without limitation, a transmissive liquid crystal panel and electrophoretic panel.
  • reflective passive display panels include, without limitation, a reflective liquid crystal panel (Liquid Crystal on Silicon or LCOS), and Digital Light Processor (DLPTM) panel.
  • the passive display panel is a liquid crystal panel.
  • FIG. 2a A schematic cross-sectional view of light emitting surface 103 in the transverse plane according to various exemplary embodiments of the present invention is illustrated in Figure 2a.
  • light source 102 comprises a plurality of pixel regions 112 which are arranged over a grid 114 in a plurality of rows along the horizontal dimension and a plurality of columns along the vertical dimensions. But this need not necessarily be the case, since, for some applications, it may not be necessary for the light source to be pixilated.
  • T/IL2007/000636 T/IL2007/000636
  • light source 102 when light source 102 provides a non-modulated light (e.g., for backlighting or for applications in which apparatus serves as illuminating apparatus) light source 102 can be provided as an illumination sheet or any other non pixilated single light source. Yet, from the standpoint of optical efficiency, the use of pixilated light source is favored for the generation of both modulated and non-modulated light beams.
  • a non-modulated light e.g., for backlighting or for applications in which apparatus serves as illuminating apparatus
  • light source 102 can be provided as an illumination sheet or any other non pixilated single light source. Yet, from the standpoint of optical efficiency, the use of pixilated light source is favored for the generation of both modulated and non-modulated light beams.
  • Light source 102 can be embodied as a two-dimensional array of light emitting diodes which may be of any type known in the art, including inorganic light emitting diodes and organic light emitting diodes.
  • the light emitting diodes are surrounded by reflectors so as to gather the light emitted from the semiconductor material and reflect it downstream the longitudinal axis.
  • Light source 102 preferably provides a light beam having a substantially homogenous intensity distribution thereacross.
  • light source 102 is a two- dimensional array of light emitting diodes, the diodes are selected with packaging which facilitate homogenous intensity distribution.
  • apparatus 100 can comprise a beam homogenizer 126 interposed in the optical path of light beam 104 for imparting a substantially homogenous intensity distribution across beam 104.
  • Homogenizer 126 can be a diffusive panel, an opal plate, a corrugated plate, ground glass plate and the like.
  • Figure 2b is a schematic cross-sectional view in the transverse plane of modulator 110 in the preferred embodiment in which modulator 110 is an LCD panel.
  • modulator 110 comprises a plurality of pixel regions 116 arranged over a grid 118.
  • Each pixel region 116 is defined by two or more sub-pixel positions 120.
  • the sub-pixel positions correspond to the color channels characterizing the respective pixel region.
  • a pixel region of two color channels has two pixel positions
  • a pixel region of three color channels e.g., RGB channels
  • modulator 110 When modulator 110 is an LCD panel, the pixel regions are typically formed of thin film transistors fabricated on a transparent substrate. Color filters (typically three per pixel region) are fabricated on another transparent substrate to produce colored light by transmitting one third of the light passing therethrough. A liquid crystal layer is sandwiched between the thin film transistors layer and the color filters layer. The optical properties of the liquid crystal in each pixel region are modulated by the thin film transistors to create a light intensity modulation across the area of the T/IL2007/000636
  • a static polarizer can be used to polarize the light produced by the light source, and the liquid crystal pixels can selectively manipulate the polarization of the light passing therethrough.
  • the light intensity modulation is achieved using a static polarizer positioned in front of the liquid crystal pixels which prevents transmission of light of certain polarization.
  • the color filters colorize the intensity- modulated light emitted by the pixels to produce a color output.
  • selected intensities of the three component colors are blended together to selectively control color light output. Selecting the blending of three primary cqlors such as RGB can generally produce a full range of colors suitable for color display purposes. All these designs and operations are well known to those ordinarily skilled in the art of display systems.
  • linear focusing element 106 is preferably designed and constructed to form different linear foci at different longitudinal locations.
  • a real image of a two-dimensional object e.g., a light emitting surface or the like, is the locus of all points at which at least two light rays emanating from the same point (e.g., a pixel) on the light emitting surface intersect.
  • linear focus refers to a line, typically a straight line, which is composed of a plurality of points each defined by the intersection of at least two light rays originating from the same point of the light emitting surface.
  • Linear focusing element 106 forms a linear focus 124 with respect to the horizontal dimension at one location along axis 108, denoted Z 1 , and a linear focus 122 with respect to the vertical dimension at another location along axis 108, denoted Z 2 .
  • focusing element 106 converges the light rays such that projections of the light rays on a horizontal plane are converged at location Z 1 , and projections of the light rays on a vertical plane are converged at location Z 2 .
  • focusing element 106 The operation principles of focusing element 106 are schematically illustrated in Figures lc-e. Shown in Figures lc-e are perspective views of two linear segments of light source 102, one linear segment 102y along the horizontal dimension and one linear segment 102x along the vertical dimensions. Also shown are focusing element 106 and linear foci 122 and 124. Segments 102y and 102x as well as foci 124 and 122 are illustrated in Figures lc-e as arrows.
  • segment 102y is imaged by element 106 on plane 144 and segment 102x is imaged by element 106 on plane 142.
  • segment 102y is a row of pixel regions of light source 102 (see, e.g. , central row 136 in Figure 2a) or a part thereof
  • segment 102x is a column of pixel regions of light source 102 (see, e.g., central column 138 in Figure 2a) or a portion thereof.
  • light rays also emanate from parts of light source 102 which are other than the aforementioned segments 102y and 102x. These parts of the light source, however are not necessarily imaged on any of planes 142 and 144. For example, light rays emanating from a pixel region being on a row other than row 136 and a column other than column 138 do not converge on any of planes 142 and 144.
  • any point on plane 144 other than the points forming focus 124 is out of focus with respect to the light emitting surface of source 102.
  • any point on transverse plane 142 other than the points forming focus 122 is out of focus with respect to the light emitting surface.
  • Figure Ic illustrates both linear foci 122 and 124 along axis 108 and Figures ld-e illustrate convergence of representative light rays emanating from the heads of the arrows illustrating segment 102y ( Figure Id) and segment 102x ( Figure Ie).
  • Figure Id exemplifies four light rays 104-1, 104-2, 104-3 and 104-4 emanating from the head of the arrow representing segment 102y and converging on the transverse plane at location Z 1 the head of the arrow representing focus 124
  • Figure Ie exemplifies four light rays 104-5, 104-6, 104-7 and 104-8 emanating from the head of the arrow representing segment 102x and on the transverse plane at location Z 2 the head of the arrow representing focus 122.
  • Other light rays which emanate from other points of the segments converge on the respective transverse planes to form the linear foci.
  • the ratio Z 2 ZZ 1 is at least 2, more preferably at least 3.
  • apparatus 100 is supplemented with an optical projection element 44 which can be positioned at longitudinal location Z 1 in the optical path of the light beam.
  • Projection element 44 is preferably employed when it is desired to place source 102 near element 106, such that focusing element 106 forms a virtual image of segment 102x, which virtual image is projected by element 106 to forms a real image of segment 102x at plane Z 2 .
  • An exemplified ray tracing of this embodiment is provided in Figures 5a-b hereinunder.
  • Focusing element 106 can be embodied in more than one way.
  • element 106 comprises arrangements of lenses which are constructed and aligned such that the effective focal length in the horizontal dimension differs from that the effective focal length in the vertical dimension.
  • the focal length in the vertical dimension is longer than the focal length in the horizontal dimension.
  • a preferred difference between the focal lengths is of at least 20 %, more preferably at least 25 %.
  • focusing element 106 comprises at least one arrangement of lenses which are characterized by spherical symmetry and at least one arrangement of lenses which are characterized by a symmetry other than spherical symmetry.
  • the combination of spherical and non-spherical lenses results in the desired difference in effective focal length.
  • the non-spherical lenses are optionally and preferably cylindrical lenses. Such non-spherical lenses are favored from the standpoints of availability and design simplicity. Other non-spherical lenses are not excluded from the scope of the present invention.
  • Figures 3a-b are schematic illustrations of linear focusing element 106 in a preferred embodiment in which a lenslet array is employed.
  • Figure 3 a is a side view (parallel to the x-z plane) and
  • Figure 3b is a top view (parallel to the y-z plane).
  • Shown in Figures 3a-b is a lenslet array having a first side 128 and a second side 130 which is opposite to first side 128.
  • An array 132 of spherical lenses is arranged on the first side 128, and an array 134 of cylindrical lenses is arranged on second side 130.
  • the cylindrical lenses are oriented such that their curvature is along the horizontal direction.
  • the focal plane of the spherical lenses in is denoted F 2 and the focal plane of the cylindrical lenses is denoted F 1 .
  • F 2 The focal plane of the spherical lenses in is denoted F 2 and the focal plane of the cylindrical lenses is denoted F 1 .
  • F 1 The focal plane of the spherical lenses in is denoted F 2 and the focal plane of the cylindrical lenses is denoted F 1 .
  • F 2 The focal plane of the spherical lenses in is denoted F 1 .
  • the cylindrical lenses are flat with respect to the x axis ( Figure 3 a), they do not contribute to light ray convergence or divergence in the vertical plane.
  • the light rays are only refracted by the spherical lenses and the effective focal length of lenslet array in this plane is OF 2 where O is the longitudinal location of the effective center of the lenses.
  • the horizontal plane Figure 3b both the cylindrical and the spherical lenses contribute to light ray convergence or divergence, and the effective focal length in the horizontal length is the combination of OF 1 and OF 2 .
  • the homogeneity of intensity distribution across the light beam can be improved by judicious selection of the lenslet array.
  • the array of cylindrical lenses and/or array of spherical lenses is corrugated so as to impart a substantially homogenous intensity distribution across the light beam.
  • the lenslet array is made, at least in part, of a diffractive material, e.g., opal. While the use of lenslet arrays is favored from the standpoints of design simplicity, overall size of apparatus 100 and ability to transmits a plurality of colors, other optical element are not excluded from the scope of the present invention. Thus, 007/000636
  • linear focusing element 106 can also comprise one or more of the following optical elements: a condenser lens system, a Fresnel zone plate and a holographic lens.
  • apparatus 100 can be incorporated in a virtual image display system having an optical relay device which expands a light beam in the horizontal dimension but maintains the linear size of the light beam in the vertical dimension.
  • Figure 4 is a schematic cross-sectional illustration in the horizontal plane of a system 200 for providing an image to a user, according to various exemplary embodiments of the present invention.
  • System 200 can be designed either as a binocular system or as a monocular system for viewing a virtual image.
  • system 200 allows light rays propagations such that when the user places one eye within one two-dimensional eye-box region 20 in space and another eye within another two-dimensional eye-box region 22 in space, the virtual image is perceived.
  • system 200 allows light rays propagations such that the virtual image is perceived when the user places his or her eye within a single region 20.
  • System 200 preferably comprises image generating apparatus 100 for providing light beam 104.
  • apparatus 100 comprises optical projection element 44 interposed in the optical path of the light beam and an optical relay device 10.
  • light beam 104 is modulated to constitute and image therein as described hereinabove.
  • element 44 is positioned at longitudinal location Z 1 along axis 108 and eye-box regions 20, 22 are defined at longitudinal location Z 2 .
  • Optical projection element 44 serves as a collimator which collimates light beam 104 and projects it onto an optical aperture 204 of relay device 10.
  • Any projection element known in the art may be used.
  • a converging lens spherical or non spherical
  • the purpose of the collimating procedure is for improving the imaging ability.
  • a converging lens a light ray going through IL2007/000636
  • a typical converging lens that is normal to the lens and passes through its center, defines the optical axis.
  • the bundle of rays passing through the lens cluster about this axis and may be well imaged by the lens, for example, if the source of the light is located as the focal plane of the lens, the image constituted by the light is projected to infinity.
  • Device 10 serves for relaying, the collimated beam in a manner such that the light beam is expanded in the horizontal dimension and relayed to occupy eye-box regions 20 and/or 22.
  • Relay device 10 can be any relay device known in the art.
  • relay device 10 can operate according to the principles described in U.S. Patent No. 6,757,105, U.S. Patent Application No. 10/896,865 and U.S. Patent Application No. 11/017,920, all assigned to the same assignee as the present Application.
  • apparatus 100 forms one linear focus of the image on element 44 and another linear focus of image at eye-box region(s) 20, 22.
  • the linear focus on element 44 is preferably with respect to the horizontal dimension, and the linear focus at the eye-box region(s), is preferably with respect to the vertical dimension. This is because in the horizontal dimension the expansion of the light beam is being provided by relay device 10 and there is no need to focus the image at the eye-box region(s).
  • the linear focus at the eye-box region(s), is preferably with respect to the vertical dimension, so as to ensure expansion of the light beam also in the vertical dimension.
  • system 200 provides light expansion in both transverse direction, hence facilitates enlarged eye-box regions.
  • apparatus 100 is designed such that most, and more preferably the entire light beam arrives at the eye-box region(s), with minimal light being directed outside the eye-box.
  • the present embodiments significantly reduce optical losses.
  • the ray tracing illustrations include the well-known and used symbols of geometric optics in which an object or image thereof is illustrated as an arrow and a converging or condensing lens is illustrated as a double sided arrow.
  • the object in the ray tracing illustration represents the light source of the system, and the lenses represent the linear focusing element and the projection element of the system.
  • an object which symbolizes light source 102 is located next to a condensing lens which symbolize linear focusing element 106, within the focal length of the lens.
  • the lens is a spherical lens with a focal length of the order of several millimeters, e.g. , about 4 mm.
  • the focal point of the spherical lens if shown at F 2 .
  • the condensing lens 106 is positioned farther than the focal length of another converging lens which symbolize projection element 44.
  • the focal length of the projection element 44 can be about 25 mm.
  • the focal point of this lens is shown at F 3 .
  • an intermediate virtual image of the object is formed by the condensing lens 106 upstream the optical axis (behind the object) and a real image of the intermediate image is formed by the projection element 44 downstream the optical axis at location Z 1 .
  • the object (the light source) is imaged as a real image onto the eye-box region of system 200.
  • FIG. 6a The fragmentary schematic illustration ( Figure 6a) exemplifies a realization of the optical principles in the vertical plane as follows.
  • An LCD display panel is illuminated by an array of LEDs.
  • the LED array is illustrated as a vertical stack of LEDs. Each LED in the vertical stack thus represents a row of LEDs in a two-dimensional LED array.
  • the vertical dimension H of the LCD panel is 7 mm
  • the horizontal dimension W ⁇ not shown, see Figure 6b) is 9 mm.
  • the LCD is located behind a lenslet array such that each row of LEDs (three shown in Figure 6a) is behind a row of lenslets of the lenslet array.
  • the number of LEDs in the LED array is preferably the same as the number of lenslets in the lenslet array.
  • the lenslet array includes spherical lenslets with a focal length of 4 mm and cylindrical lenslets with a focal length of 5.45 mm.
  • the cylindrical lenslets are not shown because, as stated, they do not contribute to light convergence or divergence in the vertical plane.
  • the lenslet array spans the entire vertical dimension of the LCD.
  • the LEDs are located such that each LED is imaged by the spherical lenses and the projection lens as described above onto the eye-box region.
  • the size of the eye-box region along the vertical dimension is about 8 mm. This can be achieved by ensuring that the distance between the centers of two adjacent LEDs is smaller than the distance between the axes of symmetry of two adjacent lenslets.
  • the projection element 44 is not shown for the clarity of presentation, however it is positioned at location Z 1 , as shown in Figure 5a.
  • the linear focusing element 106 is symbolized as two adjacent converging lenses, a spherical lens which also operates in the vertical plane, and a cylindrical lens which is oriented to operate in the horizontal plane but not in the vertical plane.
  • the focal length of the cylindrical lens is also of order of several millimeters but longer than the focal length of the spherical lens. As a representative example, the focal length of the cylindrical lens is about 5.45 mm.
  • the effective focal length of the two adjacent lens is shorter than the distance between the object and the lenses, and a real image is formed at location Z 1 . More specifically, an intermediate virtual image of the object 102 is formed by the cylindrical lens behind the object between the focal points F 1 and F 2 , and a real image of the intermediate image is formed by the spherical lens downstream the optical axis at location Z 1 .
  • the fragmentary schematic illustration ( Figure 6b) exemplifies a realization of the optical principles in the vertical plane as follows.
  • the two-dimensional LED array is illustrated as horizontal stack of LEDs, each representing a column of LEDs in the array.
  • Figure 6b illustrates four LEDs, representing four columns in the array.
  • the LED array includes four columns and three rows. As described above the LEDs illuminate the LCD panel.
  • the four LEDs are positioned behind the lenslet array.
  • the lenslet array includes four spherical lenslets with a focal length of 4 mm and four cylindrical lenslets with a focal length of 5.45 mm. Each illustrated lenslet represents a column in a two-dimensional lenslet array.
  • the lenslet array can be equal in width or wider than the width W of the LCD panel. 007/000636
  • the effective width of the projection lens 44 is preferably the same as the aperture 204 of the relay device (not shown, see Figure 4). With such configuration, each LED can be imaged onto the projection lens.
  • the projection lens has a focal length of about 25 mm and an effective width of about 10 mm.
  • optical relay device 10 The principles and operations of optical relay device 10, in accordance with preferred embodiments of the present invention will be now described.
  • device 10 When a ray of light moving within a light-transmissive substrate and striking one of its internal surfaces at an angle ⁇ as measured from a normal to the surface, it can be either reflected from the surface or refracted out of the surface into the open air in contact with the substrate.
  • Hs is the index of refraction of the light-transmissive substrate
  • «A is the index of refraction of the medium outside the light transmissive substrate (ns > n A )
  • ⁇ 2 is the angle in which the ray is refracted out, in case of refraction.
  • ⁇ i is measured from a normal to the surface.
  • a typical medium outside the light transmissive substrate is air having an index of refraction of about unity.
  • the term "about” refers to ⁇ 10 %.
  • Equation 1 has a solution for ⁇ 2 only for ⁇ i which is smaller than arcsine of njris often called the critical angle and denoted ⁇ c .
  • ⁇ i above the critical angle
  • no refraction angle ⁇ 2 satisfies Equation 1 and light energy is trapped within the light-transmissive substrate.
  • the light is reflected from the internal surface as if it had stroked a mirror. Under these conditions, total internal reflection is said to take place. Since different wavelengths of light (i.e., light of different colors) correspond to different indices of refraction, the condition for total internal reflection depends not only on the 007/000636
  • diffraction When a sufficiently small object or sufficiently small opening in an object is placed in the optical path of light, the light experiences a phenomenon called diffraction in which light rays change direction as they pass around the edge of the object or at the opening thereof. The amount of direction change depends on the ratio between the wavelength of the light and the size of the object/opening.
  • Such optical elements are typically manufactured as diffraction gratings which are located on a surface of a light- transmissive substrate. Diffraction gratings can operate in transmission mode, in which case the light experiences diffraction by passing through the gratings, or in reflective mode in which case the light experiences diffraction while being reflected off the gratings
  • Figure 7 schematically illustrates diffraction of light by a linear diffraction grating operating in transmission mode.
  • a wavefront 1 of the light propagates along a vector / and impinges upon a grating 2 engaging the x-y plane.
  • the normal to the grating is therefore along the z direction and the angle of incidence of the light ⁇ j is conveniently measured between the vector [ and the z axis.
  • ⁇ is decomposed into two angles, ⁇ j ⁇ and ⁇ / y, where ⁇ ; x is the incidence angle in the z-x plane, and ⁇ , y is the incidence angle in the z-y plane.
  • ⁇ iy is illustrated in Figure 7.
  • the grating has a periodic linear structure along a vector g, forming an angle ⁇ R with the y axis.
  • the period of the grating (also known as the grating pitch) is denoted by D.
  • the grating is formed on a light transmissive substrate having an index of refraction denoted by n ⁇ .
  • wavefront 1 changes its direction of propagation.
  • the principal diffraction direction which corresponds to the first order of diffraction is denoted by d and illustrated as a dashed line in Figure 7.
  • the angle of diffraction ⁇ is measured between the vector d and IL2007/000636
  • ⁇ R 0° or 180°
  • the sign of ⁇ / ⁇ , ⁇ g,, ⁇ and ⁇ is positive, if the angles are measured clockwise from the normal to the grating, and negative otherwise.
  • the dual sign on the RHS of the one-dimensional grating equation relates to two possible orders of diffraction, +1 and -1, corresponding to diffractions in opposite directions, say, "diffraction to the right" and "diffraction to the left,” respectively.
  • Figures 8a-c are schematic illustrations of cross sectional views of an optical relay device 10, according to various exemplary embodiments of the present invention.
  • Figures 8a, 8b and 8c illustrate cross sectional views of device 10 in the x-y plane, y-z plane and the x-z plane, respectively.
  • device 10 comprises a light-transmissive substrate 14, an input optical element 13 and an output optical element 15.
  • the system of coordinates in Figures 8a-c is selected such that substrate 000636
  • 26 14 is orthogonal to the z axis, and optical elements 13 and 15 are laterally displaced along the y axis.
  • the z axis is referred to as the "longitudinal" axis
  • the x and y axes are referred to as the "transverse" axes.
  • substrate 14 engages the transverse plane spanned by the x-y axes.
  • Element 13 redirects the light into substrate 14 such that at least a few light rays experience total internal reflection and propagate within substrate 14.
  • Element 15 serves for redirecting at least a few of the propagating light rays out of substrate 14.
  • Each of elements 13 and 15 can be a refractive element, a reflective element or a diffractive element.
  • element 13 and/or element 15 can comprise a plurality of linearly stretched mini- or micro-prisms, and the redirection of light is generally by the refraction phenomenon described by Snell's law.
  • element 13 when both elements 13 and 15 are refractive elements, element 13 refracts the light into substrate 14 such that at least a few light rays experience total internal reflection and propagate within substrate 14, and element 15 refracts at least a few of the propagating light rays out of substrate 14.
  • Refractive elements in the form of mini- or micro-prisms are known in the art and are found, e.g., in U.S. Patent Nos.
  • element 13 and/or element 15 can comprises a plurality of dielectric mirrors, and the redirection of light is generally by the reflection phenomenon, described by the basic law of reflection.
  • element 13 and 15 when both elements 13 and 15 are reflective elements, element 13 reflects the light into substrate 14 such that at least a few light rays experience total internal reflection and propagate within substrate 14, and element 15 reflects at least a few of the propagating light rays out of substrate 14.
  • Reflective elements in the form of dielectric mirrors are known in the art and are found, e.g., in U.S. Patent Nos.
  • Element 13 and/or element 15 can also combine reflection with refraction.
  • element 13 and/or element 15 can comprise a plurality of partially reflecting surfaces located in substrate 14. In this embodiment, the partially reflecting surfaces are preferably parallel to each other.
  • Optical elements of this type are known in the art and found, e.g., in U.S. Patent No. 6,829,095, the contents of which are hereby incorporated by reference.
  • element 13 and/or 15 can comprise a grating and the redirection of light is generally by the diffraction phenomenon.
  • element 13 diffracts the light into substrate 14 such that at least a few light rays experience total internal reflection and propagate within substrate 14, and element 15 diffracts at least a few of the propagating light rays out of substrate 14.
  • difffracting refers to a change in the propagation direction of a wavefront, in either a transmission mode or a reflection mode.
  • a transmission mode “diffracting” refers to change in the propagation direction of a wavefront while passing through the diffractive element; in a reflection mode, “diffracting” refers to change in the propagation direction of a wavefront while reflecting off the diffractive element in an angle different from the basic reflection angle (which is identical to the angle of incidence).
  • elements 13 and 15 are transmissive elements, i.e., they operates in transmission mode.
  • Input element 13 is preferably designed and constructed such that the angle of light rays redirected thereby is above the critical angle, and the light propagates in the substrate via total internal reflection. The propagated light, after a few reflections within substrate 14, reaches output element 15 which redirects the light out of substrate 14.
  • the linear focusing element 106 is preferably designed and constructed taking into account the optical distance between region 20 and element 106 rather than the Euclidian longitudinal distance therebetween. This is because in addition to the free space propagation of the light rays (e.g., from focusing element 106 to projection element 44 and from projection element 44 to input element 13) they also experience a plurality of total internal reflection within substrate 14 and as a consequence the length of the optical path is longer that the Euclidian distance. For example, when a particular light ray experiences N events of total internal reflection the difference between the Euclidian distance and the optical distance is about Nxt where t is the thickness of substrate 14.
  • the number of total internal reflection events for different light rays may differ (see, e.g., rays 17 and 18 in Figure 8b).
  • the optical path therebetween varies from a minimal optical distance of about ⁇ Z E + N m i n t to a maximal optical distance of about ⁇ Z ⁇ + where JV m , n and JV max are, respectively, the minimal and maximal total internal reflection events which may occur within substrate 14.
  • the thickness t is equal 2mm
  • a typical Euclidian longitudinal distance between element 106 and region 20 is about 52 mm
  • a minimal optical distance is about 64 mm and a typical maximal optical distance is about 88 mm.
  • element 106 is selected such that focus 122 is formed at a distance which equals the average between the minimal and maximal optical distances.
  • the average can be an arithmetic or geometric average. As will be appreciated by one of ordinary skill in the art, this can be ensured, for example, by a judicious selection of F 2 for a given F 3 .
  • F 1 can be calculated based on the desired Euclidian longitudinal distance between element 106 and plane 144, where the effective center of projection element 44 is located.
  • Element 13 and/or element 15 is optionally and preferably a linear diffraction grating, operating according to the principles described above. When both elements 13 and 15 are linear ratings, their periodic linear structures are preferably substantially parallel.
  • Elements 13 and 15 can be formed on or attached to any of the surfaces 23 and 24 of substrate 14.
  • Substrate 14 can be made of any light transmissive material, preferably, but not obligatorily, a martial having a sufficiently low birefringence.
  • Element 15 is laterally displaced from element 13. A preferred lateral separation between the elements is from a few millimeters to a few centimeters.
  • Device 10 is preferably designed to transmit light striking substrate 14 at any striking angle within a predetermined range of angles, which predetermined range of angles is referred to of the field-of-view of the device.
  • the input optical element is designed to trap all light rays in the field-of-view within the substrate.
  • a field-of-view can be expressed either inclusively, in which case its value corresponds to the difference between the minimal and maximal incident 6
  • the minimal and maximal incident angles are also referred to as rightmost and leftmost incident angles or counterclockwise and clockwise field- of-view angles, in any combination.
  • the inclusive and exclusive representations of the field-of-view are used herein interchangeably.
  • Figures 8b-f The field-of-view of device 10 is illustrated in Figures 8b-f by two of its outermost light rays, generally shown at 17 and 18.
  • Figure 8b and 8c illustrate the projections of rays 17 and 18 on two planes which are parallel to the normal axis of device 10.
  • Figure 8b illustrates the projections of rays 17 and 18 on a plane containing the horizontal axis of device 10 (the y-z plane in the present coordinate system)
  • Figure 8c illustrates the projections of rays 17 and 18 on a plane containing the vertical axis of device 10 (the x-z plane in the present coordinate system).
  • Figure 8b schematically illustrates the horizontal field-of-view
  • Figure 8c schematically illustrates the vertical field-of-view of device 10.
  • the projection of ray 18 is the rightmost ray projection which forms with the normal axis an angle denoted ⁇ y ⁇
  • the projection of ray 17 is the leftmost ray projection which forms with the normal axis an angle denoted ⁇ y +
  • the projection of ray 18 is the rightmost ray projection which forms with the normal axis an angle denoted ⁇ x ⁇
  • the projection of ray 17 is the leftmost ray projection which forms with the normal axis an angle denoted G x + .
  • the horizontal field-of-view denoted ⁇ y
  • the vertical field-of-view denoted ⁇ x is [G x " , G x + ].
  • the projections ⁇ x ⁇ , ⁇ y ⁇ are measured anticlockwise from the normal axis (the z axis in Figures 8b and 8c), and the projections ⁇ + x , ⁇ + y are measured clockwise from the normal axis.
  • ⁇ y ⁇ j, and a vertical field-of-view ⁇ x ⁇ x + +
  • Figure 8d schematically illustrates the field-of-view in a plane orthogonal to the normal axis of device 10 (parallel to the x-y plane, in the present coordinate system).
  • Rays 17 and 18 are points on this plane.
  • the field-of-view is illustrated as a rectangle, and the straight light connecting the points is the diagonal of the rectangle.
  • Rays 17 and 18 are referred to as the "lower-left” and "upper-right" light rays of the field-of-view, respectively.
  • the field-of-view can also have a planar shape other than a rectangle, include, without limitation, a square, a circle and an ellipse.
  • a planar shape other than a rectangle, include, without limitation, a square, a circle and an ellipse.
  • Figures 8e and 8f illustrate the diagonal field-of-view angles ⁇ ⁇ and ⁇ + in planes containing ray 17 and ray 18, respectively.
  • the relation between ⁇ * and their projections ⁇ /, ⁇ / are given by Equation 5 above with the substitutions ⁇ d ⁇ *, ⁇ dx — ⁇ / and ⁇ dy — ⁇ - ⁇ y*.
  • the term "field-of-view angle" refers to a diagonal angle, such as ⁇ *.
  • the light rays arriving to device 10 can have one or more wavelength.
  • the shortest wavelength is denoted ⁇ and the longest wavelength is denoted ⁇ R
  • the range of wavelengths from ⁇ to ⁇ R is referred to herein as the spectrum of the light.
  • the light rays in the field-of-view impinge on element 13 they are preferably redirected at an angle (defined relative to the normal) which is larger than the critical angle, such that upon striking the other surface of substrate 14, all the light rays of the field-of- view experiences total internal reflection and propagate within substrate 14.
  • element 13 diffracts leftmost ray 17 and rightmost ray 18 into substrate 14 at diffraction angles denoted ⁇ / and ⁇ ⁇ f , respectively.
  • Shown in Figures 8b-c are ⁇ y/ ( Figure 8b) and B x / ( Figure 8b), which are the projections of ⁇ / on the y-z plane and the x-z plane, respectively.
  • the Euclidian distance between two successive points on the internal surface of the substrate at which a particular light ray experiences total internal reflection is referred to as the "hop length" of the light ray and denoted by "h".
  • the propagated light after a few reflections within substrate 14, generally along the horizontal axis of device 10, reaches output optical element 15 which redirects the light out of substrate 14.
  • Device 10 thus transmits at least a portion of the optical energy carried by each light ray between rays 17 and 18.
  • output optical element 15 is characterized by planar dimensions selected such that at least a portion of one or more outermost light rays within the field-of-view is directed to a two- dimensional region 20 being at a predetermined distance Az from light transmissive substrate 14. More preferably, the planar dimensions of element 15 are selected such that the outgoing light beam enters region 20.
  • the length Lo of element 15 is preferably selected to be larger then a predetermined length threshold, Lo , mm , and the width WQ of element 15 is preferably selected to be larger then a predetermined width threshold, Wo, mm -
  • the length and width thresholds are given by the following expressions:
  • region 20 is the "eye-box" of device 10
  • ⁇ z is approximately the distance between the pupil(s) of the user to substrate 14.
  • the distance ⁇ z is referred to herein as the characteristic eye-relief of device 10.
  • the length Lo and width WQ of element 15 are preferably about Lo 5 min + Op, and about Wo, m i n + O p , respectively, where ⁇ p represents the diameter of the pupil and is typically about 3 millimeters.
  • the eye-box is larger than the diameter of the pupil, so as to allow the user to relocate the eye within the eye-box while still viewing the entire virtual image.
  • the length and width of element 15 are preferably:
  • each of LE B and W ⁇ B is preferably larger than O p , so as to allow the user to relocate the eye within region 20 while still viewing the entire field-of-view.
  • the dimensions of input optical element 13 are preferably selected to allow all light rays within the field-of-view to propagate in substrate 14 such as to impinge on the area of element 15.
  • the length Li of input element 13 equals from about X to about 3X where X is preferably a unit hop-length characterizing the propagation of light rays within substrate 14.
  • X equals the hop-length of the light-ray with the minimal hop-length, which is one of the outermost light-rays in the field-of-view (ray 18 in the exemplified illustration of IL2007/000636
  • X is typically the hop- length of one of the outermost light-rays which has the shortest wavelength of the spectrum.
  • the width Wo of element 15 is smaller than the width W 1 of element 13.
  • W ⁇ is preferably calculated based on the relative arrangement of elements 13 and 15.
  • elements 13 and 15 are centrally aligned with respect to the vertical axis of device 10 (but laterally displaced along the horizontal axis and optionally displaced also along the normal axis). In the present coordinate system this central alignment correspond to equal x coordinate for a central width line 130 (connecting half width points of element 13) and a central width line 150 (connecting half width points of element 15).
  • the relation between W ⁇ is preferably given by the following expression:
  • W 1 2 (L 0 + Ay) tan ⁇ + W 0 , (EQ. 8)
  • ⁇ y is the lateral separation between element 13 and element 15 along the horizontal axis of device 10
  • ⁇ is a predetermined angular parameter.
  • ⁇ is the angle formed between the horizontal axis and a straight line connecting the corner of element 13 which is closest to element 15 and the corner of element 15 which is farthest from element 13 (see, e.g., line 12 in Figure 8a).
  • ⁇ relates to the propagation direction of one or more of the outermost light rays of the field-of-view within the substrate, as projected on a plane parallel to the substrate.
  • ⁇ equals the angle formed between the horizontal axis of the substrate and the propagation direction of an outermost light ray of the field-of-view, as projected on a plane parallel to the substrate.
  • a typical value for the absolute value of ⁇ is, without limitation, from about 6° to about 15°.
  • a viewer placing his or her eye in region 20 of dimensions W ⁇ Q receives at least a portion of any light ray within the field-of-view, provided the distance between the eye and element 15 equals ⁇ z or is smaller than ⁇ z.
  • the preferred value for ⁇ z is, without limitation, from about 15 millimeters to about 35 millimeters, the preferred value for Ay is, without limitation, from a few millimeters to a few centimeters, the preferred value for Z,E B is, without limitation, from about 5 millimeters to about 13 millimeters, and the preferred value for W E B is, without limitation, is from about 4 millimeters to about 9 millimeters.
  • selection of large ⁇ z results in smaller eye-box dimensions Z EB and W E B, as known in the art.
  • small ⁇ z allows for larger eye-box dimensions L EB and JP-EB-
  • Lo, m in and Wo, m ⁇ n are preferably calculated using Equation 6, and together with the selected dimensions of region 20 (£E B and Wm), the dimensions of element 15 (Zo and Wo) can be calculated using Equation 7.
  • the vertical dimension W ⁇ of input element 13 is preferably calculated by selecting values for Ay and ⁇ and using Equation 8.
  • the horizontal dimension L ⁇ is generally selected from about 3 millimeters and about 15 millimeters.
  • elements 13 and 15 can be designed, for a given spectrum, solely based on the value of ⁇ ⁇ and the value of the shortest wavelength ⁇ .
  • the period, D, of the gratings can be selected based on ⁇ ⁇ and ⁇ , irrespectively of the optical properties of substrate 14 or any wavelength longer than ⁇ .
  • D is selected such that the ratio ⁇ /D is from about 1 to about 2.
  • D is a maximal grating period.
  • D in order to accomplish total internal reflection D can also be smaller than ⁇ B /[n A (l-sm ⁇ ⁇ )].
  • Substrate 14 is preferably selected such as to allow light having any wavelength within the spectrum and any striking angle within the field-of-view to propagate in substrate 14 via total internal reflection.
  • the refraction index of substrate 14 is larger than ⁇ p/D + / ⁇ Sm(G + ). More preferably, the refraction index, ns, of substrate 14 satisfies the following equation: n s > [ ⁇ R /D + « A sin( ⁇ + )]/sin( ⁇ D MAX ). (EQ. 10) where ⁇ D MAX is the largest diffraction angle, e.g., the diffraction angle of the light ray 17. There are no theoretical limitations on ⁇ D MAX , except from a requirement that it is positive and smaller than 90 degrees. ⁇ D MAX can therefore have any positive value smaller than 90°. Various considerations for the value ⁇ D MAX are found in U.S. Patent No. 6,757,105, the contents of which are hereby incorporated by reference.
  • the thickness, t, of substrate 14 is preferably from about 0.1 mm to about 5 mm, more preferably from about 1 mm to about 3 mm, even more preferably from about 1 to about 2.5 mm.
  • t is preferably selected to allow simultaneous propagation of plurality of wavelengths, e.g., t > 10 X R .
  • the width/length of substrate 14 is preferably from about 10 mm to about 100 mm.
  • a typical width/length of the diffractive optical elements depends on the application for which device 10 is used.
  • device 10 can be employed in a near eye display, such as the display described in U.S. Patent No.
  • the length of substrate 14 can be 1000 mm or more, and the length of diffractive optical element 15 can have a similar size.
  • the length of the substrate is longer than T/IL2007/000636
  • t is preferably larger than 5 millimeters. This embodiment is advantageous because it reduces the number of hops and maintains the substrate within reasonable structural/mechanical conditions.
  • Device 10 is capable of transmitting light having a spectrum spanning over at least 100 nm. More specifically, the shortest wavelength, ⁇ , generally corresponds to a blue light having a typical wavelength of between about 400 to about 500 nm and the longest wavelength, ⁇ , generally corresponds to a red light having a typical wavelength of between about 600 to about 700 nm.
  • the angles at which light rays 18 and 17 are redirected can differ.
  • the angles of redirection depend on the incident angles (see, e.g., Equations 2-5 for the case of diffraction)
  • the allowed clockwise ( ⁇ + ) and anticlockwise ( ⁇ ⁇ ) field-of-view angles are also different.
  • device 10 supports transmission of asymmetric field-of-view in which, say, the clockwise field-of-view angle is greater than the anticlockwise field- of- view angle.
  • the difference between the absolute values of the clockwise and anticlockwise field-of-view angles can reach more than 70 % of the total field-of-view.
  • a light- transmissive substrate can be formed with at least one input optical element and two or more output optical elements.
  • the input optical element(s) serve for redirecting the light into the light-transmissive substrate in a manner such that different portions of the light, corresponding to different partial field-of-views, propagate within the substrate in different directions to thereby reach the output optical elements.
  • the output optical elements redirect the different portions of the light out of the light- transmissive substrate.
  • the planar dimensions of the output and/or input optical elements can be selected to facilitate the transmission of the partial field-of- views.
  • the output optical elements can also be designed and constructed such that the redirection of the different portions of the light is in complementary manner.
  • any number of input/output optical elements can be used. Additionally, the number of input optical elements and the number of output optical elements may be different, as two or more output optical elements may share the same input optical element by optically communicating therewith.
  • the input and output optical elements can be formed on a single substrate or a plurality of substrates, as desired.
  • the input and output optical elements comprise linear diffraction gratings of identical periods, formed on a single substrate, preferably in a parallel orientation.
  • input/output optical elements can engage any side of the substrate, in any combination.
  • transmissive and reflective optical elements For example, suppose that there is one input optical element, formed on surface 23 of substrate 14 and two output optical elements formed on surface 24. Suppose further that the light impinges on surface 23 and it is desired to diffract the light out of surface 24.
  • the input optical element and the two output optical elements are all transmissive, so as to ensure that entrance of the light through the input optical element, and the exit of the light through the output optical elements.
  • Figures 9a-b are schematic illustrations of a perspective view ( Figure 9a) and a side view ( Figure 9b) of device 10, in a preferred embodiment in which one input optical element 13 and two output optical elements 15 L2007/000636
  • device 10 can be used as a binocular device for transmitting light to a first eye 25 and a second eye 30 of a user.
  • first 15 and second 19 output optical elements are formed, together with input optical element 13, on surface 23 of substrate 14.
  • Element 13 preferably redirects the incoming light into substrate 14 in a manner such that different portions of the light, corresponding to different partial fields-of-view, propagate in different directions within substrate 14.
  • element 13 redirects light rays within one asymmetric partial field-of-view, designated by reference numeral 26, leftwards to impinge on element 15, and another asymmetric partial field-of-view, designated by reference numeral 32, to impinge on element 19.
  • Elements 15 and 19 complementarily redirect the respective portions of the light, or portions thereof, out of substrate 14, to provide first eye 25 with partial field-of-view 26 and second eye 30 with partial field-of-view 32.
  • Partial field-of- views 26 and 32 form together the field-of-view 27 of device
  • elements 15 and 19 are characterized by planar dimensions selected such that at least a portion of one or more outermost light rays within partial field-of-view 26 is directed to two-dimensional region 20, and at least a portion of one or more outermost light rays within partial field-of-view 32 is directed to another two- dimensional region 22. This can be achieved by selecting the lengths and widths of elements 15 and 19 to be larger then predetermined length and width thresholds, as described above (see Equations 6-7).
  • the planar dimensions of region 20 equal the planar dimensions of region 22.
  • the planar dimensions of each of regions 20 and 22 as well as the distance ⁇ z are preferably within the aforementioned ranges.
  • the lateral separation between the horizontal centers of regions 20 and 22 is at least 40 millimeters.
  • the lateral separation between the horizontal centers of regions 20 and 22 is less than 80 millimeters.
  • the planar dimensions of elements 15 and 19 are selected such that the portions of outermost light rays are respectively directed to regions 20 and 22, for any lateral separation between the regions which is larger than 40 millimeters and smaller than 80 millimeters.
  • the planar dimensions of elements 15 and 19 are preferably selected such that eyes 25 and 30 are respectively provided with partial field-of-views 26 and 32 for any interpupillary distance IPD satisfying IPD min ⁇ IPD ⁇ IPD max .
  • the lengths and widths of output elements 15 and 19 can be set according to Equations 7 substantially as described hereinabove.
  • the horizontal center of each of elements 15 and 19 is located at a distance of (IPD ma x + IPD m i n )/4 from the horizontal center element 13.
  • the width Wi of element 13 is preferably larger than width of each of elements 15 and 19.
  • the calculation of W ⁇ is preferably, but not obligatorily, performed using a procedure similar to the procedure described above, see Equation 8.
  • the same planar dimensions Io x WQ are used for both output elements 15 and 19, and the same lateral separation ⁇ y is used between elements 13 and 15 and between elements 13 and 19.
  • the width W ⁇ of the input element can be set according to Equation 8 using the angular parameter ⁇ as described above. Equation 8 can also be used in for configuration in which the lateral separation between elements 13 and 15 differs from the lateral separation between elements 13 and 19.
  • field-of-view 27 preferably includes substantially all light rays originated from image 34. Partial fields-of-view 26 and 32 can therefore correspond to different parts of image 34, which different parts are designated in Figure 9b by numerals 36 and 38.
  • the partial field-of-views hence also the parts of the image arriving to each eye depend on the wavelength of the light. Therefore, it is not intended to limit the scope of the present embodiments to a configuration in which part 36 is viewed by eye 25 and part 38 viewed by eye 30. In other words, for different wavelengths, part 36 is viewed by eye 30 and part 38 viewed by eye 25.
  • device 10 can be constructed such that eye 25 sees part 38 for the blue light and part 36 for the red light, while eye 30 sees part 36 for the blue light and part 38 for the red light. In such configuration, both eyes see an almost symmetric field-of-view for the green light. Thus, for every color, the two partial fields-of-view compliment each other.
  • the human visual system is known to possess a physiological mechanism capable of inferring a complete image based on several parts thereof, provided sufficient information reaches the retinas.
  • This physiological mechanism operates on monochromatic as well as chromatic information received from the rod cells and cone cells of the retinas.
  • the two asymmetric field-of-views reaching each individual eye, form a combined field-of-view perceived by the user, which combined field-of-view is wider than each individual asymmetric field-of-view.
  • first 26 and second 32 partial fields-of-view there is a predetermined overlap between first 26 and second 32 partial fields-of-view, which overlap allows the user's visual system to combine parts 36 and 38 of image 34, thereby to perceive the image, as if it has been fully observed by each individual eye.
  • the optical elements can be constructed such that the exclusive representations of partial fields-of-view 26 and 32 are, respectively, [- ⁇ , ⁇ ] and [- ⁇ , ⁇ ], resulting in a symmetric combined field-of-view 27 of [- ⁇ , ⁇ ]. It will be appreciated that when ⁇ » ⁇ > 0, the combined field-of-view is considerably wider than each of the asymmetric field-of-views.
  • Device 10 is capable of transmitting a field-of-view of at least 20 degrees, more preferably at least 30 degrees most preferably at least 40 degrees, in inclusive representation. 000636
  • different sub-spectra correspond to different, wavelength-dependent, asymmetric partial field-of-views, which, in different combinations, form different wavelength- dependent combined fields-of-view.
  • a red light can correspond to a first red asymmetric partial field-of-view, and a second red asymmetric partial field-of- view, which combine to a red combined field-of-view.
  • a blue light can correspond to a first blue asymmetric partial field-of-view, and a second blue asymmetric partial field-of-view, which combine to a blue combined field-of-view, and so on.
  • a multicolor configuration is characterized by a plurality of wavelength-dependent combined field-of-views.
  • the optical elements are designed and constructed so as to maximize the overlap between two or more of the wavelength-dependent combined field-of-views.
  • element 15 provides eye 25 with, say, a first sub- spectrum which originates from part 36 of image 34, and a second sub-spectrum which originates from part 38 of image 34.
  • Element 19 preferably provides the complementary information, so as to allow the aforementioned physiological mechanism to infer the complete spectrum of the image.
  • element 19 preferably provides eye 30 with the first sub-spectrum originating from part 38, and the second sub-spectrum originating from part 36.
  • a multicolor image is a spectrum as a function of wavelength, measured at a plurality of image elements.
  • This ideal input is rarely attainable in practical systems. Therefore, the present embodiment also addresses other forms of imagery information.
  • a large percentage of the visible spectrum can be represented by mixing red, green, and blue colored light in various proportions, while different intensities provide different saturation levels.
  • other colors are used in addition to red, green and blue, in order to increase the color gamut.
  • different combinations of colored light are used in order to represent certain partial spectral ranges within the human visible spectrum.
  • a wide-spectrum light source is used, with the imagery information provided by the use of color filters.
  • the multicolored image can be displayed by three or more channels, such as, but not limited to, Red-Green-Blue (RGB) or Cyan-Magenta- Yellow-Black (CMYK) channels.
  • RGB channels are typically used for active display systems (e.g., CRT or OLED) or light shutter systems (e.g., Digital Light ProcessingTM (DLPTM) or LCD illuminated with RGB light sources such as LEDs).
  • CMYK images are typically used for passive display systems (e.g., print). Other forms are also contemplated within the scope of the present invention.
  • the sub-spectra can be discrete values of wavelength.
  • a multicolor image can be provided by an OLED array having red, green and blue organic diodes (or white diodes used with red, green and blue filters) which are viewed by the eye as continues spectrum of colors due to many different combinations of relative proportions of intensities between the wavelengths of light emitted thereby.
  • the first and the second sub-spectra can correspond to the wavelengths emitted by two of the blue, green and red diodes of the OLED array, for example the blue and red.
  • Device 10 can be constructed such that, say, eye 30 is provided with blue light from part 36 and red light from part 38 whereas eye 25 is provided with red light from part 36 and blue light from part 38, such that the entire spectral range of the image is transmitted into the two eyes and the physiological mechanism reconstructs the image.
  • the light arriving at the input optical element of device 10 is preferably collimated, by a projection element or collimator 44 as described above.
  • Collimator 44 can be, for example, a converging lens (spherical or non spherical), an arrangement of lenses and the like.
  • Collimator 44 can also be a diffractive optical element, which may be spaced apart, carried by or formed in substrate 14.
  • a diffractive collimator may be positioned either on the entry surface of substrate 14, as a transmissive diffractive element or on the opposite surface as a reflective diffractive element.
  • Figures 10a-b are schematic illustrations of wavefront propagation within substrate 14, according to preferred embodiments in which diffractive elements are employed. Shown in Figures 10a-b are four principal light rays, 51, 52, 53 and 54, respectively emitted from four points, A, B, C and D, of image 34. The illustrations in Figures 10a-b lie in the y-z plane. The projections of the incident angles of rays 51, 52, 53 and 54 onto the y-z plane relative to the normal axis are denoted ⁇ f " , ⁇ f + , ⁇ f ⁇ and ⁇ f + , respectively.
  • the first superscript index refer to the position of the respective ray relative to the center of the field-of-view
  • the second superscript index refer to the position of the respective ray relative to the normal from which the angle is measured, according to the aforementioned sign convention.
  • Equation 4 The relation between each incident angle, ⁇ , and its respective diffraction angle, ⁇ D ' j , is given by Equation 4, above, with the replacements ⁇ iy — > aj 1' , and ⁇ dy -> ⁇ D ij .
  • Points A and D represent the left end and the right end of image 34, and points B and C are located between points A and D.
  • rays 51 and 53 are the leftmost and the rightmost light rays of a first asymmetric field-of-view, corresponding to a part A-C of image 34
  • rays 52 and 54 are the leftmost and the rightmost light rays of a second asymmetric field-of-view corresponding to a part B-D of image 34.
  • the first and second asymmetric field-of- views are, respectively, [ ⁇ f ⁇ , Oc 1 +" ] and [ ⁇ f + , Ct 1 + + ] (exclusive representations).
  • an overlap field-of-view between the two asymmetric field-of-views is defined between rays 52 and 53, which overlap equals [ ⁇ f + , ⁇ f ⁇ ] and corresponds to an overlap B-C between parts A-C and B-D of image 34.
  • lens 45 magnifies image 34 and collimates the wavefronts emanating therefrom. For example, light rays 51-54 pass 6
  • each diffracted light ray experiences a total internal reflection upon impinging on the inner surfaces of substrate 14 if
  • ⁇ ⁇ c do not experience a total internal reflection hence escape from substrate 14.
  • a light ray may, in principle, split into two secondary rays each propagating in an opposite direction within substrate 14, provided the diffraction angle of each of the two secondary rays is larger than ⁇ c .
  • secondary rays diffracting leftward and rightward are designated by a single and double prime, respectively.
  • FIG. 10a showing a particular and preferred embodiment in which
  • ⁇ c .
  • Shown in Figure 10a are rightward propagating rays 51" and 53", and leftward propagating rays 52' and 54'.
  • element 13 split all light rays between ray 51 and ray 52 into two secondary rays, a left secondary ray, impinging on the inner surface of substrate 14 at an angle which is smaller than ⁇ c , and a right secondary ray, impinging on the inner surface of substrate 14 at an angle which is larger than ⁇ c .
  • light rays between ray 51 and ray 52 can only propagate rightward within substrate 14.
  • light rays between ray 53 and ray 54 can only propagate leftward.
  • light rays between rays 52 and 53 corresponding to the overlap between the asymmetric field-of-views, propagate in both directions, because element 13 split each such ray into two secondary rays, both impinging the inner surface of substrate 14 at an angle larger than the critical angle, ⁇ c .
  • light rays of the asymmetrical f ⁇ eld-of-view defined between rays 51 and
  • Ray 54 splits into two secondary rays, ray 54' (not shown) and ray 54" diffracting leftward and rightward, respectively.
  • leftward propagating ray 54' either diffracts at an angle which is too large to successfully reach element 15, or evanesces.
  • ray 52 splits into two secondary rays, 52' (not shown) and 52" diffracting leftward and rightward, respectively.
  • rightward propagating ray 52" diffracts at an angle ⁇ D ⁇ + > ⁇ c .
  • Both secondary rays diffract at an angle which is larger than ⁇ c experience one or a few reflections within substrate 14 and reach output optical element 15 and 19 respectively (not shown).
  • OC 1 T + is the largest angle for which the diffracted light ray will successfully reach the optical output element 19
  • all light rays emitted from part A-B of the image do not reach element 19 and all light rays emitted from part B-D successfully reach element 19.
  • angle Ot 0 4" is the largest angle (in absolute value) for which the diffracted light ray will successfully reach optical output element 15, then all light rays emitted from part C-D of the image do not reach element 15 and all light rays emitted from part A-C successfully reach element 15.
  • the input and output optical elements can be linear diffraction gratings having identical periods and being in a parallel orientation.
  • This embodiment is advantageous because it is angle-preserving.
  • the identical periods and parallelism of the linear gratings ensure that the relative orientation between light rays exiting the substrate is similar to their relative orientation before the impingement on the input optical element. Consequently, light rays emanating from a particular point of the overlap part B-C of image 34, hence reaching both eyes, are parallel to each other. Thus, such light rays can be viewed by both eyes as arriving from the same angle in space. It will be appreciated that with such configuration viewing convergence is easily obtained without eye-strain or any other inconvenience to the viewer, unlike the prior art binocular devices in which relative positioning and/or relative alignment of the optical elements is necessary.
  • the period, D, of the gratings and/or the refraction index, n s , of the substrate can be selected so to provide the two asymmetrical field-of-views, while ensuring a predetermined overlap therebetween. This can be achieved in more than one way.
  • a ratio between the wavelength, ⁇ , of the light and the period D is larger than or equal a unity: ⁇ /D ⁇ l. (EQ. 12)
  • This embodiment can be used to provide an optical device operating according to the aforementioned principle in which there is no mixing between light rays of the non- overlapping parts of the field-of-view (see Figure 10a).
  • the ratio XID is smaller than the refraction index, n s , of the substrate. More specifically, D and n s can be selected to comply with the following inequality:
  • the value of p is preferably selected so as to ensure operation of the device according to the principle in which some mixing is allowed between light rays of the non-overlapping parts of the field-of-view, as further detailed hereinabove (see Figure 000636
  • ⁇ D MAX is selected so as to allow at least one reflection within a predetermined distance x which may vary from about 30 mm to about 80 mm.
  • ⁇ D MAX is selected so as to reduce the number of reflection events within the substrate, e.g., by imposing a requirement that all the diffraction angles will be sufficiently small, say, below 80°.
  • device 10 can transmit light having a plurality of wavelengths.
  • the gratings period is preferably selected to comply with Equation 12, for the shortest wavelength, and with Equation 13, for the longest wavelength. Specifically: ⁇ ⁇ /(n s p) ⁇ D ⁇ ⁇ B , (EQ. 14) where ⁇ and XR are, respectively, the shortest and longest wavelengths of the multicolor spectrum. Note that it follows from Equation 12 that the index of refraction of the substrate should satisfy, under these conditions, n s p ⁇ X R /X B .
  • the grating period can also be smaller than the sum ⁇ + ⁇ R , for example:
  • a apparatus 100 for providing an image to a user in a wide field-of-view there is provided a apparatus 100 for providing an image to a user in a wide field-of-view.
  • FIG. 11 is a schematic illustration of system 300, which, in its simplest configuration, comprises optical relay device 10 for transmitting image 34 into first eye 25 and second eye 30 of the user, an image generating apparatus, which can be, for example, apparatus 100 as described above or a modification thereof as described hereinunder and a projection element or collimator 44.
  • Apparatus 100 provides optical relay device 10 with a light beam modulated to constitute the image.
  • Image generating apparatus 100 can be either analog or digital.
  • An analog image generating apparatus typically comprises a light source 327 and at least one image carrier 29.
  • Representative examples for light source 327 include, without limitation, a lamp (incandescent or fluorescent), one or more LEDs or OLEDs, and the like.
  • Representative examples for image carrier 29 include, without limitation, a miniature slide, a reflective or transparent microfilm and a hologram.
  • apparatus 100 comprises a miniature CRT.
  • Miniature CRTs are known in the art and are commercially available, for example, from Kaiser Electronics, a Rockwell Collins business, of San Jose, California.
  • a digital image generating apparatus can comprise passive display panel 330 such as modulator 100 described above, which modulates light emitted from source 327.
  • Light sources suitable for a digital image generating system include, without limitation, a lamp (incandescent or fluorescent), one or more LEDs (e.g., red, green and blue LEDs) or OLEDs, and the like.
  • Suitable passive display panels include, without limitation, rear-illuminated transmissive or front-illuminated reflective LCD, Digital Light ProcessingTM (DLPTM) units, and the like.
  • Transparent miniature LCDs are commercially available, for example, from Kopin Corporation, Taunton, Massachusetts.
  • Reflective LCDs are are commercially available, for example, from Brillian Corporation, Tempe, Arizona.
  • Miniature OLED arrays are commercially available, for example, from eMagin Corporation, Hopewell Junction, New York. IL2007/000636
  • the pixel resolution of the digital miniature displays varies from QVGA (320 x 240 pixels) or smaller, to WQUXGA (3840 x 2400 pixels).
  • System 300 is particularly useful for enlarging a field-of-view of devices having relatively small screens.
  • PDAs personal digital assistants
  • Pocket PC such as the trade name iPAQTM manufactured by Hewlett- Packard Company, Palo Alto, California.
  • the above devices although capable of storing and downloading a substantial amount of information in a form of single frames or moving images, fail to provide the user with sufficient field-of-view due to their small size displays.
  • system 300 comprises a data source 325 which can communicate with apparatus 100 via a data source interface 323.
  • a data source interface 323 Any type of communication can be established between interface 323 and data source 325, including, without limitation, wired communication, wireless communication, optical communication or any combination thereof.
  • data source 325 and source interface 323 are operatively associated with wireless transceivers 332 and 334, respectively, to establish wireless communication thereamongst.
  • Interface 323 is preferably configured to receive a stream of imagery data (e.g., video, graphics, etc.) from data source 325 and to input the data into apparatus 100.
  • imagery data e.g., video, graphics, etc.
  • data source 325 is a communication device, such as, but not limited to, a cellular telephone, a personal digital assistant device (PDA) and a portable computer (laptop).
  • PDA personal digital assistant device
  • portable computer laptop
  • Additional examples for data source 325 include, without limitation, television apparatus, portable television device, satellite receiver, video cassette recorder, digital versatile disc (DVD) player, digital moving picture player (e.g., MP4 player), digital camera, video graphic array (VGA) card, and many medical imaging apparatus, e.g., ultrasound imaging apparatus, digital X-ray apparatus (e.g., for computed tomography) and magnetic resonance imaging apparatus.
  • DVD digital versatile disc
  • VGA video graphic array
  • data source 325 may generates also audio information.
  • the audio information can be received by interface 323 and provided to the user, using an audio unit 31 (speaker, one or more earphones, etc.).
  • data source 325 provides the stream of data in an encoded and/or compressed form.
  • system 300 further comprises a decoder 33 and/or a decompression unit 35 for decoding and/or decompressing the stream of data to a format which can be recognized by apparatus 100.
  • Decoder 33 and decompression unit 35 can be supplied as two separate units or an integrated unit as desired.
  • System 300 preferably comprises a controller 37 for controlling the functionality of apparatus 100 and, optionally and preferably, the information transfer between data source 325 and apparatus 100.
  • Controller 37 can control any of the display characteristics of apparatus 100, such as, but not limited to, brightness, hue, contrast, pixel resolution and the like.
  • controller 37 can transmit signals to data source 325 for controlling its operation. More specifically, controller 37 can activate, deactivate and select the operation mode of data source 325.
  • controller 37 can select the displayed channel; when data source 325 is a DVD or MP4 player, controller 37 can select the track from which the stream of data is read; when audio information is transmitted, controller 37 can control the volume of audio unit 31 and/or data source 325.
  • System 300 or a portion thereof can be integrated with a wearable device, such as, but not limited to, a helmet or spectacles, to allow the user to view the image, preferably without having to hold optical relay device 10 by hand.
  • a wearable device such as, but not limited to, a helmet or spectacles
  • system 300 or a portion thereof can be adapted to be mounted on an existing wearable device.
  • device 10 is manufactured as a spectacles clip which can be mounted on the user's spectacles
  • device 10 is manufactured as a helmet accessory which can be mounted on a helmet's screen.
  • the present embodiments can also be provided as add-ons to the data source or any other device capable of transmitting imagery data. Additionally, the present embodiments can also be used as a kit which includes the data source, the image generating system, the binocular device and optionally the wearable device. For example, when the data source is a communication device, the present embodiments can be used as a communication kit. IL2007/000636
  • planar dimension calculations are performed in accordance with the teachings of the preferred embodiments of the invention for the diffraction of red light.
  • the present calculations are for 509 nm period gratings formed in a light transmissive substrate having index of refraction of 1.522 and thickness of 2 mm. As a representative example for red light, a wavelength of 615 nm was assumed.
  • a hop-length of h 3.5 mm which is then used to set the length L ⁇ of the input element to be from about 3.5 mm to about 10.5 mm.
  • the above values of ⁇ x and ⁇ , y correspond to an outermost propagation angle
  • the value of the angular parameter ⁇ is 8.8°.
  • planar dimension calculations are performed in accordance with the teachings of the preferred embodiments of the invention for the diffraction of blue light.
  • the present calculations are for 389 nm period gratings formed in a light transmissive substrate having index of refraction of 1.529 and thickness of 1.8 mm. As a representative example for blue light, a wavelength of 465 nm was assumed.

Abstract

L'invention concerne un appareil pour produire une lumière. L'appareil comprend une source lumineuse présentant une surface électroluminescente conçue pour générer un faisceau lumineux, et au moins un élément de concentration linéaire définissant un axe optique longitudinal. L'élément de concentration linéaire forme des foyers linéaires différents à des emplacements longitudinaux différents le long de l'axe optique longitudinal. L'appareil est particulièrement utile comme appareil de génération d'images dans un système qui obtient des rapports d'expansion linéaire différents dans des dimensions transversales différentes.
PCT/IL2007/000636 2006-05-25 2007-05-27 systÈme d'Éclairage avec intÉgrateur optique pour projecteur d'image WO2007138576A1 (fr)

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