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WO2009130637A1 - Commande de guide de lumière en fonction de la direction - Google Patents

Commande de guide de lumière en fonction de la direction Download PDF

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Publication number
WO2009130637A1
WO2009130637A1 PCT/IB2009/051582 IB2009051582W WO2009130637A1 WO 2009130637 A1 WO2009130637 A1 WO 2009130637A1 IB 2009051582 W IB2009051582 W IB 2009051582W WO 2009130637 A1 WO2009130637 A1 WO 2009130637A1
Authority
WO
WIPO (PCT)
Prior art keywords
light
guide
propagation
refractive index
controllable
Prior art date
Application number
PCT/IB2009/051582
Other languages
English (en)
Inventor
Jan F. STRÖMER
Erno H. A. Langendijk
Giovanni Cennini
Maarten Sluijter
Original Assignee
Koninklijke Philips Electronics N.V.
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 Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2009130637A1 publication Critical patent/WO2009130637A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/1326—Liquid crystal optical waveguides or liquid crystal cells specially adapted for gating or modulating between optical waveguides
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/011—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  in optical waveguides, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133615—Edge-illuminating devices, i.e. illuminating from the side
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133602—Direct backlight
    • G02F1/133606—Direct backlight including a specially adapted diffusing, scattering or light controlling members
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/13362—Illuminating devices providing polarized light, e.g. by converting a polarisation component into another one

Definitions

  • the present invention relates to a controllable light-guide, and to a light output device and a display device comprising such a controllable light-guide.
  • planar light-guides are used in various applications such as flat-panel displays and light-output devices, for example luminaires.
  • the planar light-guides are typically used in backlights or frontlights for illuminating a pixel array to make an image formed by the pixel array visible to a viewer.
  • light is typically coupled into an edge of the light-guide.
  • one face of the planar light-guide is typically modified through structuring or other modification to enable outcoupling of light through that face and/or the opposite face.
  • the outcoupled light then passes through pixels in the pixel array, which are in a transmissive state, and a corresponding image becomes visible to a viewer.
  • a correspondingly large fraction of the light emitted by the backlight is prevented from reaching the viewer and precious energy is thus wasted.
  • WO 2004079437 discloses an illumination system comprising an optical waveguide and a matrix-addressable light-management member. By modulating a portion of the light-management member between a transparent state and a scattering state, the outcoupling of light from the optical waveguide can be controlled.
  • controllability is limited to a spatial control of the outcoupling of any light present in the light-guide.
  • a general object of the present invention is to provide an improved, controllable light-guide, in particular a light-guide enabling an increased level of controllability of a light-output device including the light-guide.
  • a light-guide configured to guide light within the light-guide through reflections between opposite faces thereof, the light-guide comprising a first light-guide portion controllable to selectively outcouple light traveling in a first direction of propagation within the light-guide through at least one of the faces; and a second light-guide portion controllable to selectively outcouple light traveling in a second direction of propagation, different from the first direction of propagation, within the light-guide through at least one of the faces.
  • the light-guide may advantageously be a planar light-guide, which guides light, through internal reflection, between oppositely located, essentially parallel faces thereof.
  • a planar light-guide may include different optically transparent materials, such as various types of glass, or polymers, for example poly-methyl methacrylate (PMMA) etc.
  • the light-guide may be essentially flat or curved, depending on the application. It may, furthermore, be either substantially rigid, or flexible.
  • an “optically transparent” medium in the present context, a medium which permits passage of at least a fraction of the light (electromagnetic radiation in the visible spectrum) impinging on it.
  • the present invention is based upon the realization that the controllability of a light-output device including a controllable light-guide can be increased by implementing a controllable direction-dependent out-coupling mechanism in the light-guide.
  • output of light that has been injected into the light-guide can be controlled not only through the outcoupling state of a selected portion of the light-guide, but also through the direction of propagation within the light-guide of the injected light.
  • the controllability of a light-output device including the light-guide is increased through the added variables associated with a light-source or light-sources injecting light traveling within the light-guide in different directions of propagation.
  • variables may, for example, include intensity modulation, such as switching or dimming, polarization state, color etc.
  • intensity modulation such as switching or dimming, polarization state, color etc.
  • the light-guide may comprise a controllable light-modulating member sandwiched between first and second optically transparent substrates, the light-modulating member being controllable to exhibit a refractive index gradient in a selected portion thereof, thereby enabling bending of a guided light-beam passing through the selected portion, such that the guided light beam hits one of the faces of the light-guide at a sufficiently small angle with respect to a normal to the face to escape from the light-guide; first control means arranged to control the light-modulating member in a portion thereof corresponding to the first light-guide portion to exhibit a refractive index gradient component, in the first direction of propagation, sufficient to bend light-beams traveling in the first direction of propagation so as to make them escape from the light-guide, and a refractive index gradient component ,in the second direction of propagation, insufficient to bend light-beams traveling in the second direction of propagation so as to make them escape from the light-guide; and second control means arranged to control the light
  • the refractive index gradient is a vector, it can be divided into refractive index components which may or may not be orthogonal.
  • the light-modulating member By controlling the light-modulating member so as to achieve a refractive index gradient having different magnitudes in the first and second directions of propagation (different magnitudes of the first and second refractive index gradient components), selective, direction-dependent outcoupling of light from the light-guide can be achieved.
  • the desired, selective, direction-dependent outcoupling may be achieved by arranging the first control means so as to induce a refractive index gradient that is sufficiently high to enable outcoupling of light beams traveling in the first direction of propagation within the light-guide, but not sufficiently high to enable outcoupling of light beams traveling in the second direction of propagation, and conversely for the second control means.
  • a further effect obtainable through the light-guide according to the present embodiment is that the light outcoupled from the light-guide is coherent, which may be advantageous depending on the field of application of the light-guide.
  • An additional effect obtainable through the light-guide according to the present embodiment is that light can be outcoupled with an essentially unchanged spectral distribution, which is typically not the case for outcoupling by scattering.
  • a light beam bends toward regions of higher refractive index.
  • a refractive index gradient is created by locally modifying the medium to have another refractive index ni .
  • ni refractive index
  • such a local change in refractive index and the accompanying creation of a refractive index gradient can be brought about by various kinds of external stimuli, such as, for example, heat, pressure, an electric field or a magnetic field.
  • the first and second control means may be any means for controllably subjecting the light-modulating member to such various kinds of external stimuli.
  • the first and second control means may or may not be provided in contact with the light-guide.
  • the light-modulating member may include a controllable birefringent material, such as a liquid crystal layer.
  • a birefringent material has an anisotropic refractive index, with an ordinary refractive index no for a ray of light (an ordinary ray) which is polarized perpendicularly to the optical axis of the material, and an extraordinary refractive index n e for a ray of light (an extraordinary ray) which is polarized parallel to the optical axis.
  • an ordinary refractive index no for a ray of light an ordinary ray
  • n e for a ray of light (an extraordinary ray) which is polarized parallel to the optical axis.
  • a local reorientation of the liquid crystal molecules in that portion can be achieved.
  • one linearly polarized component of an unpolarized guided light beam having an electric field which oscillates in the plane in which the reorientation takes place (the extraordinary component) will encounter a refractive index that gradually varies from the ordinary refractive index no to the extraordinary refractive index rie or conversely.
  • this extraordinary component will experience a refractive index gradient and be bent towards an area with a higher refractive index.
  • the other component i.e. the orthogonal linearly polarized component (the ordinary component) typically experiences no change in refractive index, since its electric field oscillates in a plane perpendicular to the long axis of the LC-molecules. Consequently, the ordinary component passes through the LC-layer having reoriented LC-molecules without having its direction changed.
  • the orthogonal linearly polarized component typically experiences no change in refractive index, since its electric field oscillates in a plane perpendicular to the long axis of the LC-molecules. Consequently, the ordinary component passes through the LC-layer having reoriented LC-molecules without having its direction changed.
  • the light-modulating member may be controllable to exhibit a first refractive index gradient with respect to a first polarization component of an unpolarized light beam and a second refractive index gradient with respect to a second polarization component of the light beam, thereby enabling different bending of the polarization components.
  • outcoupling of polarized light can be achieved. This is especially advantageous for applications where only one polarization component is required, such as when the light-guide according to the present invention is used in a backlight for a liquid crystal display (LCD).
  • LCD liquid crystal display
  • a liquid crystal layer is one example of a suitable light-modulating member which is controllable to bend light in a polarization-dependent manner.
  • the liquid crystal molecules can all be made to reorient in a plane perpendicular to the light-guide.
  • the polarization component perpendicular to this plane, and hence perpendicular to the elongated liquid crystal molecules, will experience no change in the refractive index resulting from the reorientation, while the polarization component in the plane of reorientation will be bent when passing through the region with reoriented liquid crystal molecules.
  • the light-modulating member may advantageously comprise a plurality of liquid crystal molecules
  • the first control means may include a first electrode pair arranged in such a way that liquid crystal molecules in the first light-guide portion are redirected through application of a voltage across the first electrode pair
  • the second control means may include a second electrode pair arranged in such a way that liquid crystal molecules in the second light-guide portion are redirected through application of a voltage across the second electrode pair.
  • At least one of the electrodes in the first electrode pair may be arranged to extend essentially perpendicularly to the first direction of propagation, and at least one of the electrodes in the second electrode pair may be arranged to extend essentially perpendicularly to the second direction of propagation.
  • Arranging at least one of the electrodes in each electrode pair so as to extend in a direction that is essentially perpendicular to the respective direction of propagation is one way of redirecting the liquid crystal molecules in the respective portions in such a way that selective, direction-dependent outcoupling is achieved.
  • the electrode(s) it is not necessary for the electrode(s) to extend exactly perpendicularly to the direction of propagation of the light within the light-guide. It is expected that outcoupling with a sufficient degree of direction-dependence (depending on application) can be achieved using electrodes that are arranged to form an angle of, say, 90° ⁇ 10° with respect to the direction of propagation within the light-guide of the light to be outcoupled.
  • the electrode lines need not be completely straight, but may deviate from a straight line without substantially influencing the desired direction-dependent outcoupling.
  • both electrodes in one or both electrode pairs may be provided as essentially parallel lines extending perpendicularly to the respective directions of propagation. It should be noted that the desired selective and direction-dependent outcoupling can be achieved for electrode lines that are not exactly parallel, but are provided at some angle with respect to each other.
  • both electrodes comprised in at least one of the first and second electrode pair may be arranged on a side of the light-modulating member facing the first substrate.
  • each of the first and second electrode pairs may, furthermore, comprise a plurality of interleaved electrode segments.
  • Each light-guide portion may, furthermore, comprise several electrodes, which may be arranged on either side or both sides of the liquid crystal layer. Through individual control of these electrodes, the electric field, and hence the refractive index gradient of the liquid crystal layer in the light-guide cell, can be controlled to bend a light-beam traveling through the liquid crystal layer practically at will.
  • a larger refractive index gradient can be obtained than when using in plane switching, which results in increased bending of a beam of light passing through the liquid crystal layer and thus enables a smaller angle of exit from the light-guide with respect to a normal to the light-guide.
  • the light-guide according to the present invention may include a plurality of first light-guide portions, each being controllable to selectively outcouple light traveling in the first direction of propagation within the light-guide through at least one of the faces; and a plurality of second light-guide portions controllable to selectively outcouple light traveling in a second direction of propagation, different from the first direction of propagation, within the light-guide through at least one of the faces.
  • the first and second light- guide portions may be arranged in different configurations, such as, for example, in a striped arrangement for a scanning backlight or in a checkerboard type arrangement for a color controllable light-output device.
  • controllable light-guide including a light-modulating member sandwiched between substrates
  • total internal reflection in either of the substrates should preferably be avoided or at least minimized.
  • both a substrate and the light-modulating member are isotropic at an interface between them, total internal reflection can be avoided by providing a substrate having a refractive index which is lower than or equal to the refractive index of the light- modulating member.
  • the light-modulating member is anisotropic, which makes it more complicated to select parameters for avoiding, or at least minimizing, the occurrence of total internal reflection in a substrate.
  • this can be achieved by matching at least one of the first and second substrates, at least at a boundary between the substrate and the light- modulating member, to the controllable light-modulating member with respect to refractive index and optical axis direction.
  • An anisotropic optical member generally has an ordinary refractive index H 0 , an extraordinary refractive index n eo and an optical axis having a certain direction d.
  • the ordinary refractive index n ⁇ of the substrate equals the ordinary refractive index rio,i of the light-modulating member
  • the extraordinary refractive index n eo , s of the substrate equals the extraordinary refractive index ne O ,i of the light-modulating member
  • the direction d s of the optical axis of the substrate equals the direction di of the light-modulating member.
  • total internal reflection in a substrate can be avoided or at least minimized by configuring the controllable light-guide in such a way that at least one of the first and second substrates has an effective refractive index which is lower than or equal to an effective refractive index of the controllable light-modulating member, at least at a boundary between the substrate and the light-modulating member.
  • the desired relation between the refractive indices of the substrate and the light-modulating member respectively may be achieved by adding a refractive index matching layer between them.
  • the refractive index matching layer should have isotropic characteristics on the side facing the substrate and anisotropic characteristics on the side facing the anisotropic light-modulating member.
  • the refractive index matching layer may have a refractive index transition from, on a side thereof facing the base layer, a first effective refractive index being essentially equal to an effective refractive index of the base layer to, on a side thereof facing the light-modulating member, a second effective refractive index being lower than or equal to the effective refractive index of the light-modulating member.
  • the refractive index-matching layer may, for example, be achieved by manufacturing the refractive index-matching layer of a material having similar characteristics as the anisotropic layer, which, on the side thereof facing the substrate layer, is configured to match the refractive index of the substrate layer.
  • the refractive index-matching layer may be provided in the form of a liquid crystal layer having a pre-tilt on the side thereof facing the substrate.
  • the light-guide may additionally comprise light-recycling means configured to alter the polarization state of light exiting the light-guide after having been guided therethrough, and re-introduce the altered light into the light-guide.
  • Such light-recycling means may, for example, be provided in the form of a suitable retardation plate in combination with a mirror to re-introduce the altered light into the light-guide.
  • the light-guide may, additionally, comprise a light-modifying member for modifying at least one property of light having been outcoupled from the light-guide.
  • a light-modifying member for modifying at least one property of light having been outcoupled from the light-guide.
  • properties include, for example, the spatial, angular, and spectral distributions, and the polarization state of the outcoupled light.
  • one optical element or a combination of optical elements may be used.
  • suitable optical elements include mirrors, lenses, lenticular plates, retardation plates, prisms, in-cell retarder layers, reactive mesogen (RM) cured in LC material, light scattering elements, diffractive gratings, layers of anisotropic media or phosphor layers or polarization layers.
  • RM reactive mesogen
  • the light-guide according to the present invention may, furthermore, advantageously be comprised in a controllable light-output device, further comprising first and second light-sources arranged to inject light into the planar light-guide in the first and second directions of propagation, respectively.
  • the first and second light-sources may be provided in the form of two individually controllable light emitting devices, such as LEDs, or may be provided in the form of a single light emitting device and means for directing light emitted by the light emitting device in such a way that the light is injected into the planar light-guide in the first and second directions of propagation.
  • Such means may, for example, include various optical components, such as optical fibers, mirrors, optical switches etc.
  • Such a controllable light output device may be utilized in a wide variety of applications, including as a backlight in a flat-panel display device, as a luminaire for providing illumination in various settings, such as an office or home environment, and as an ambience-creating device which emits light for decorative purposes rather than for illumination.
  • the first and second light-sources may be adapted to emit differently colored light.
  • the color output by the light-output device can be controlled by controlling the outcoupling of light from the first and second light-guide portions in combination with the differently colored light-sources.
  • the color of the light output by the light-output device can be controlled between the first and the second color by controlling the first and second light-guide portions and the emitted (average) intensities of the light-sources.
  • pulse-width modulation is a possible way of controlling the respective, emitted, average intensities.
  • first and second light-sources may be adapted to emit polarized light with major axes of polarization that are essentially perpendicular to the light-guide, which increases the selectivity with respect to the direction of propagation of the light outcoupled from the light-guide in cases where controllable birefringence is used to achieve controllable outcoupling of light.
  • a particularly favorable case is one in which the first and second light-sources emit linearly polarized light.
  • controllable light output device may be included in a display device, further comprising an image-forming member, and arranged to illuminate the image-forming member.
  • the image quality of the display device can be improved because of the increased controllability of the backlight or frontlight constituted by the light- output device according to the present invention.
  • Figs la-c schematically illustrate a controllable light-output device comprising a controllable light-guide according to an embodiment of the present invention
  • Fig 2a schematically illustrates possible paths of light beams in the light-guide in figs la-c when the refractive indices of the substrates are not matched with that of the light-modulating member sandwiched therebetween;
  • Fig 2b schematically illustrates the controllable light-guide in fig 2a with refractive index-matching layers being inserted between the respective substrates and the light-modulating member;
  • Figs 3a-c schematically illustrate a controllable light-output device including a controllable light-guide according to another embodiment of the present invention;
  • Fig 4 schematically illustrates exemplary paths of light-beams having different polarization states in the light-guide in fig 3b for the case when the lower substrate and the liquid crystal layer are not refractive index-matched to each other;
  • Fig 5a schematically illustrates one exemplary way of implementing a refractive index-matching layer between a substrate and the light-modulating member
  • Fig 5b is a graph schematically illustrating the reflection of light at the interface between the substrate and the refractive index matching layer in fig 5a;
  • Fig 6a schematically illustrates a fast scanning backlight comprising a light- guide according to an embodiment of the present invention
  • Fig 6b shows an addressing scheme for the fast scanning backlight in fig 6a
  • Figs 7 schematically illustrates a color controllable light-output device including a light-guide according to an embodiment of the present invention.
  • the present invention is mainly described with reference to a planar controllable light-guide in which a controllable refractive index gradient is achieved by controlling the orientation of liquid crystal molecules in a liquid crystal layer sandwiched between two substrates. It should be noted that this by no means limits the scope of the present invention, which is equally applicable to any other light-guide that is susceptible to selective, direction-dependent outcoupling of light.
  • a light- modulating member other than a liquid crystal layer may be used.
  • Such a light-modulating member could, for example, include an electrophoretic or magnetophoretic cell, in which a refractive index gradient is achieved by locally controlling the concentration of particles, having a first refractive index, suspended in a fluid having a second refractive index, or an electrowetting cell containing two immiscible fluids having different refractive indices.
  • Figs la-c schematically illustrate a controllable light-output device, which is one exemplary application for a controllable light-guide according to the present invention.
  • a light-output device 1 is shown comprising a controllable planar light-guide 2 with edges 3a-d and oppositely located faces 4a-b.
  • the controllable light-guide 2 comprises a light-modulating member 6 which is sandwiched between first 7 and second 8 transparent substrates.
  • the light-guide 2 is controllable in nine square segments 9a- i, of which the segments 9d-f in the center row emit light (or rather permit light to escape) through the upper face of the light-guide 2 as indicated by the arrows in Fig Ia.
  • the light-guide 2 may have virtually any number of controllable segments having practically any shape, which may be different from application to application.
  • the nine segments 9a-i chosen here are for illustration purposes only.
  • two of the segments 9d and 9f outcouple light that was injected at the top left edge 3a and that travels within the light-guide in a direction of propagation from the top left edge 3a to the opposite edge 3c, and one of the segments, i.e. 9e, outcouples light that was injected at the top right edge 3b and that travels within the light- guide in a direction of propagation from the top right edge 3b to the opposite edge 3d.
  • the illumination of, say, segment 9e requires that the segment 9e is controlled to outcouple light and that light travels in the appropriate direction of propagation within the light-guide 2, that is, from the top right edge 3b to the bottom left edge 3d, or in the opposite direction.
  • This increases the controllability of the light-output device 1, because the illumination of the segment 9e can now be controlled either through control of its associated light-source or through control of the segment itself, depending on what is more suitable in the particular application.
  • Fig Ib is a cross-sectional view of a portion of the light-guide 2 in Fig Ia, taken along the line A-A', one exemplary mechanism behind the controllable outcoupling of light illustrated in Fig Ia will now be explained.
  • Fig Ib four different light beams 10a-d having a direction of propagation within the light-guide 2 from the top right edge 3b to the bottom left edge 3d thereof, with reference to fig Ia, are followed as they pass through the light-guide 2.
  • the light-modulating member 6 has a first, constant refractive index nc Onst in the segments 9d, 9f flanking the center segment 9e, as encountered by the light beams 10a-d. Accordingly, the light beams 10a-d do not experience a refractive index gradient when passing through the light-modulating member 6 in the segments 9d, f.
  • the refractive index is modified to repeatedly vary between a first value no and a second, higher value ni. This is illustrated in Fig Ib by the refractive index curve 11 in the portion of the light-modulating member 6 corresponding to the center segment 9e.
  • each of the light beams 10a-d passes through this portion of the light-modulating member 6, they will each encounter a refractive index gradient, and will be bent there towards regions with a higher refractive index, which is a well-known property of light passing through an inhomogeneous medium.
  • each of the light beams 10a-d is redirected to hit the boundary between either one of the substrates 7, 8 and a respective ambient substance 12, in this case air on both sides of the light-guide 2, at a sufficiently small angle ⁇ with respect to a normal 13 to the light-guide 2 to no longer fulfill the condition for total internal reflection (TIR) and be outcoupled from the light-guide 2.
  • TIR total internal reflection
  • each of the light beams 10a-d travels when passing through the light-modulating member 6 in the central segment 9e, it will be outcoupled on the first 14 or second 15 side of the light-guide 2.
  • Fig Ic which is a view of a cross-section of the light-output device 1 of Fig Ia taken along the line B-B', light beams 17a-c injected at the top left edge 3a and traveling within the light-guide 2 in a direction of propagation that is essentially perpendicular to that of the light beams 10a-d in Fig Ib are followed through the light-guide 2.
  • the light beams 17a-c encounter refractive index gradients when passing through the light-modulating member 6 in segments 9d and f, and are bent as is schematically indicated in Fig Ic.
  • the center segment 9e the light beams 17a-c experience, because of their direction of propagation within the light-guide 2, a constant refractive index and are thus not bent when passing through the light-modulating member 6 in the center segment 9e.
  • the light-guide 2 is in the same state for Fig Ic as for
  • the light-output device 1 includes control means that are arranged to control the light-modulating member 6 to exhibit the refractive index gradient components indicated in Fig Ib and Fig Ic.
  • the first 7 and second 8 substrate each have the same refractive index no as the light-modulating member 6 in its "uncontrolled" state. It should be noted that this selection has been made for illustration purposes only, and that a different selection, such as each of the substrates having a substantially lower refractive index than the light-modulating member, or the substrates 7, 8 having mutually different refractive indices, may be advantageous depending on the application.
  • both substrates 7, 8 and the light-modulating member 6 are not matched with respect to refractive index and/or direction of their respective optical axes.
  • both substrates 7, 8 have higher effective refractive indices than the light-modulating member 6.
  • a first beam of light 20a having a first angle ⁇ i of incidence at the interface between the first substrate 7 and the light-modulating member 6 will pass through the light-modulating member 6 - and possibly be redirected during its passage - and through the second substrate 8 and will either be outcoupled or returned through TIR at the interface between the second substrate 8 and the ambient atmosphere 12.
  • a controllable light-output device 40 including a light-guide 41 will now be described.
  • a controllable light-output device 40 having essentially the same configuration, including nine individually controllable segments 9a-e, as the controllable light-output device 1 in Figs la-c, is schematically shown.
  • the controllable light-output device 40 in Fig 3 a emits light in one direction only, as indicated by the arrows in Fig 3 a. Furthermore, the light-output device 40 comprises a controllable light-guide 41 which is configured to contra llab Iy outcouple polarized light.
  • the light-guide 41 in Fig 3a includes a light-modulating member 42 sandwiched between first 7 and second 8 transparent substrates.
  • the light-modulating member 42 is configured to controllably bend only one polarization component of the guided light.
  • the light-guide 41 is provided with a mirror foil 43 covering the second side 15 of the light-guide 41.
  • the backlight 40 further comprises light-recycling means 44a-b in the form of a pair of ⁇ /4 retardation plates 45a-b and mirrors 46a-b for reversing the polarization state of the light having traveled through the light-guide 41 and re-introducing the light back into the light- guide 41 through the opposite edges 3c,d thereof with respect to the respective in-coupling edges 3a,b.
  • each of the segments 9a-i of the light-guide 41 includes individually controllable control means in the form of an electrode pair 47a-i having a plurality of interleaved electrode segments.
  • the electrode segments are provided in the form of essentially parallel electrode lines, that are arranged perpendicularly to either the direction of propagation of the light that is injected at the top left edge 3 a and is guided by the light-guide 41 towards the opposite edge 3 c or the direction of propagation of the light that is injected at the top right edge 3b and is guided by the light-guide 41 towards the opposite edge 3d.
  • Fig 3b is a cross-sectional view of the light-guide 41 in fig 3a taken along the line A-A', a beam 50 of unpolarized light will be followed as it passes through the light-guide 41 in the first direction of propagation from the top right edge 3b towards the opposite edge 3d and back.
  • the light- modulating member 42 is provided in the form of a liquid crystal (LC) layer having a plurality of elongated liquid crystal molecules 51 which are aligned parallel to the first 7 and second 8 substrates in the absence of an electric field acting on the LC molecules 51.
  • LC liquid crystal
  • the liquid crystal molecules may be ho meo tropically oriented, that is, oriented perpendicularly to the substrates 7, 8.
  • the liquid crystal molecules are aligned to have a direction in the plane of the light-guide 41 that is at an angle of about 45° to the electrode segments.
  • Such an alignment can, for example, be achieved by rubbing the substrate in the desired alignment direction.
  • the different segments 9a-i may have different alignment directions, depending on the direction of the electrode segments in the respective light-guide segments 9a-i. The preferred alignment direction would then be approximately perpendicular to the electrode segments.
  • the reorientation of the LC molecules 51 in the center segment 9e results in areas with varying refractive index in the section plane and, consequently, in the formation of refractive index gradients.
  • the LC molecules 51 Due to the electrode configuration in the light-output device 40 in Figs 3a-c, the LC molecules 51 are reoriented in a plane perpendicular to the light-guide 41. Therefore, only the polarization component 53 of the unpolarized light beam 50, which is polarized in the plane of reorientation of the LC molecules 51, experiences the refractive index gradient(s) and is bent.
  • the other polarization component 54 which is polarized in a plane perpendicular to the reorientation plane of the LC molecules 51, will pass through the LC layer 42 without encountering a refractive index gradient, and will accordingly not be bent.
  • the perpendicular polarization component 54 passes through the light-guide 41 from the incoupling edge 3b and exits through the opposite edge 3d. After exiting the light-guide 41 through this edge 3d, the light beam 54 passes through the ⁇ /4 retardation plate 45a a first time, is reflected in the mirror 46a, and then passes the ⁇ /4 retardation plate 45 a a second time before again entering the light-guide 41. Due to the resulting polarization reversal, the light beam 54 will have been transformed to a parallel-polarized light beam 55 traveling in the opposite direction.
  • this beam 54 When passing through the LC-layer 42 in the center segment 9e, this beam 54 is bent by the refractive index gradient and is outcoupled, following reflection in the mirror 43, on the second side 15 as indicated in Fig 3b. Furthermore, since the electrode segments 47a-b in the center segment 9e are parallel to the light injected at the top left edge 3a of the light-guide 41 and perpendicular to the light injected at the top right edge 3b, only light-beams having a direction of propagation from the top right edge 3b towards the bottom left edge 3d will experience a refractive index gradient and be bent when passing through the light-modulating member 6 in the center segment 9e.
  • Fig 3 c shows a section of the light-guide 41 taken along the line B-B' in Fig 3 a.
  • the extraordinary polarization component 62a of the unpolarized beam 61 of light will be contained in the first substrate 7 as is indicated in fig 4.
  • the ordinary polarization component 62b will pass the interface between the substrate 7 and the liquid crystal layer 42 practically without refraction or reflection, since the refractive indices n g i ass and n 0 essentially match. Consequently, there will be no controllable outcoupling of light from the light-guide 65 in this case, as is also indicated in fig 4.
  • an exemplary light-guide configuration for achieving a simultaneous match between the first substrate 7 and the liquid crystal layer 42 is schematically shown, said light-guide configuration having a refractive index matching layer 64 provided between the first substrate 7 and the controllable liquid crystal layer 42.
  • the refractive index matching layer 64 is, in this exemplary embodiment, made of the same or similar material as the controllable liquid crystal layer 42.
  • the liquid crystal molecules 65 (only one is indicated here) have a pre-tilt of 18.5° at the interface between the first substrate 7 and the refractive index matching layer 64.
  • the liquid crystal molecules 66 At the interface between the refractive index matching layer 64 and the controllable liquid crystal layer 42, the liquid crystal molecules 66 (only one is indicated here) are aligned with the interface.
  • the thickness D of the refractive index matching layer 64 should preferably be large enough for the layer to be continuous, i.e. the material properties of the refractive index matching layer 64 should change slowly over a distance corresponding to one wavelength of the light. This means that the thickness of the refractive index matching layer 64 should preferably be of the same order of magnitude as the thickness of the controllable liquid crystal layer 42, which may typically be about 5 ⁇ m.
  • the intensity reflectance coefficient R calculated as a function of the angle of incidence is schematically shown for the light-guides in Figs 4 and 5 a, respectively.
  • the intensity reflectance coefficient is an indication of the percentage of the incident energy flux that is reflected.
  • the pre-tilt referred to above can, for example, be achieved using a polymer network that stabilizes the director profile of the liquid crystal layer forming the refractive index matching layer 64.
  • the first step would be to make a cell with a cell gap of the desired thickness of the refractive index matching layer 64.
  • This cell is then filled with a mixture of the liquid crystal material and a reactive mesogen material.
  • the top surface of the cell would be a planar alignment layer and the opposite surface would have the required 18.5° pre-tilt.
  • a UV-exposure step will freeze this alignment, so that an electric field will only insignificantly change the director profile.
  • the top substrate is removed in such a way that the polymer network remains on the bottom surface.
  • another top substrate having a planar alignment layer, is applied to the cell.
  • the new cell is filled with the same liquid crystal material as in the previous cell, but without the reactive mesogen material.
  • a light-output device in the form of a fast scanning backlight 80 comprising a light-guide 81 according to an embodiment of the present invention will be described with reference to Figs 6a-b.
  • the light-guide 81 in Fig 6a has a number of individually controllable segments 82a-g by means of which selective, direction-dependent outcoupling of light from the light-guide 81 can be achieved.
  • the fast scanning backlight 80 further comprises a first set 83 of LEDs arranged to inject light at the left edge 3a of the light-guide 81 and a second set 84 of LEDs arranged to inject light at the top edge 3b of the light-guide 81.
  • the segments 82a-g are provided in the form of segments extending across the entire width of the light-guide. Furthermore, every other segment, i.e.
  • 82 a, c, e, g is adapted to outcouple light having a direction of propagation within the light-guide 81 from the left edge 3 a to the right edge 3 c (or the opposite direction), while the remaining segments 82b, d, f are adapted to outcouple light having a direction of propagation within the light-guide 81 from the top edge 3b to the bottom edge 3d (or the opposite direction).
  • any controlled outcoupling of light from a light-guide can be used to implement a scanning backlight.
  • the scanning frequency can be increased, because the switching time from one scanning state to the next scanning state becomes limited to the switching time of a light-source rather than to the switching time of the light-guide.
  • Fig 6b schematically shows an exemplary addressing scheme for the fast scanning backlight in Fig 6a.
  • the first set 83 of LEDs (Left LEDs) and the second set 84 of LEDs (Top LEDs) are switched in an alternating fashion. This leads to continuous light incoupling into the backlight (from alternating sides).
  • the backlight will be OFF.
  • the first 82a and the last 82g row, seen from the top are addressed and switched ON.
  • the top LEDs 84 are switched on and the first 82a and the second 82b rows, seen from the top, are addressed, but only the first row 82a outcouples light, since the second row 82b can only couple out light that is injected from the left edge 3a.
  • the left LEDs 83 are switched on and the second 82b and the third 82c row, seen from the top, are addressed, but only the second row 82b outcouples light. This cycle continuous until the last backlight segment has coupled out light and one full backlight frame is completed.
  • Fig 7 a further embodiment of the present invention, in the form of a color-controllable light-output device will be described.
  • the direction-dependent, selective outcoupling properties of the light-guide according to the present invention can be used to achieve a color-controllable light-output device 90 as schematically shown in Fig 7.
  • a color-controllable light-output device 90 differently colored light-sources (not shown in Fig 7) are provided to inject differently colored light at the top left edge 3a and the top right edge 3b, respectively, of the light-guide 91, as indicated by the different arrows in Fig 7.
  • differently colored light-sources are provided to inject differently colored light at the top left edge 3a and the top right edge 3b, respectively, of the light-guide 91, as indicated by the different arrows in Fig 7.
  • the light-output device 90 in Fig 7 includes a number of segments 9a-i. Furthermore, each segment 9a-i comprises a number of sub-segments.
  • the 36 sub-segments comprised in the center segment 9e are schematically illustrated in the enlarged portion of the light-guide 91 shown in Fig 7.
  • half of the number of sub-segments have control electrodes that are perpendicular to the direction of propagation of light injected into the light-guide 91 at the top left edge 3 a, while the remaining electrodes are perpendicular to the direction of propagation of light injected into the light-guide 91 at the top right edge 3b.
  • half of the number of sub-segments can be individually controlled to outcouple the color of light that is injected at the top left edge 3a, while the remaining half of the number of sub-segments can be individually controlled to outcouple the color of light that is injected at the top right edge 3b.
  • the color of the center segment 9e as perceived by a user can be controlled by controlling which sub-segments outcouple light and/or how much light is outcoupled by each "active" sub-segment.
  • 91 may be configured to outcouple linearly polarized light, for example through an embodiment similar to that described in connection with Figs 3a-c, and the light injected into the light-guide 91 may have different linear polarizations such that the direction-dependent outcoupling is supported polarization-dependent outcoupling.
  • a color-controllable light-output device using the selective direction-dependent outcoupling of light through the light-guide 91 light of two different colors is mixed by controlling the sub-segments as discussed above. The accessible colors are then limited to a line in a color space between the first and the second colors.
  • the frame rate of the light- output device 90 should then be at least 120 Hz (for switching between two colors, using the configuration of Fig 7) to ensure flicker- free color mixing.
  • the present invention is by no means limited to the preferred embodiments.
  • many other configurations of electrodes, or control means other than those described herein, are feasible, such as the electrodes or other control means being provided on opposite sides of the light-modulating member or as a combination of a transverse and an in-plane electrode configuration.
  • the light-source can be provided in the form of any other suitable light-source configuration, such as an electroluminescent (EL) light-source.
  • EL electroluminescent
  • many other segment shapes and configurations are conceivable, and may be advantageous, depending on application.
  • the segments may be hexagonally shaped.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mathematical Physics (AREA)
  • Liquid Crystal (AREA)

Abstract

La présente invention concerne un guide de lumière (2 ; 41 ; 81 ; 91) configuré pour guider la lumière dans le guide de lumière à travers des réflexions entre ses faces opposées (14, 15). Le guide de lumière comprend une première partie guide de lumière (9e) pouvant être commandée pour découpler sélectivement de la lumière se propageant dans une première direction de propagation dans le guide de lumière (2 ; 81 ; 91) à travers au moins une des faces (14, 15) ; et une seconde partie guide de lumière (9d, 9f) pouvant être commandée pour découpler sélectivement de la lumière se propageant dans une seconde direction de propagation, différente de la première, dans le guide de lumière (2 ; 41 ; 81 ; 91) à travers au moins une des faces (14, 15). Ainsi, il est possible de commander l'émission de la lumière qui a été injectée dans le guide de lumière non seulement par l'intermédiaire de l'état de découplage d'une partie sélectionnée du guide de lumière mais également par l'intermédiaire de la direction de propagation dans le guide de lumière de la lumière injectée.
PCT/IB2009/051582 2008-04-23 2009-04-16 Commande de guide de lumière en fonction de la direction WO2009130637A1 (fr)

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EP08154992.5 2008-04-23

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US7826698B1 (en) 2007-12-19 2010-11-02 Oree, Inc. Elimination of stitch artifacts in a planar illumination area
US8128272B2 (en) 2005-06-07 2012-03-06 Oree, Inc. Illumination apparatus
US8182128B2 (en) 2007-12-19 2012-05-22 Oree, Inc. Planar white illumination apparatus
US8215815B2 (en) 2005-06-07 2012-07-10 Oree, Inc. Illumination apparatus and methods of forming the same
US8231237B2 (en) 2008-03-05 2012-07-31 Oree, Inc. Sub-assembly and methods for forming the same
US8272758B2 (en) 2005-06-07 2012-09-25 Oree, Inc. Illumination apparatus and methods of forming the same
US8301002B2 (en) 2008-07-10 2012-10-30 Oree, Inc. Slim waveguide coupling apparatus and method
US8297786B2 (en) 2008-07-10 2012-10-30 Oree, Inc. Slim waveguide coupling apparatus and method
US8328406B2 (en) 2009-05-13 2012-12-11 Oree, Inc. Low-profile illumination device
US8591072B2 (en) 2011-11-16 2013-11-26 Oree, Inc. Illumination apparatus confining light by total internal reflection and methods of forming the same
US8624527B1 (en) 2009-03-27 2014-01-07 Oree, Inc. Independently controllable illumination device
US8727597B2 (en) 2009-06-24 2014-05-20 Oree, Inc. Illumination apparatus with high conversion efficiency and methods of forming the same
US9857519B2 (en) 2012-07-03 2018-01-02 Oree Advanced Illumination Solutions Ltd. Planar remote phosphor illumination apparatus

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EP0144375A1 (fr) * 1983-05-16 1985-06-19 King Leighton Hanna Guide d'onde optique reglable.
WO2008125926A1 (fr) * 2007-04-17 2008-10-23 Koninklijke Philips Electronics N.V. Guide de lumière réglable et dispositif d'affichage

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EP0144375A1 (fr) * 1983-05-16 1985-06-19 King Leighton Hanna Guide d'onde optique reglable.
WO2008125926A1 (fr) * 2007-04-17 2008-10-23 Koninklijke Philips Electronics N.V. Guide de lumière réglable et dispositif d'affichage

Cited By (24)

* Cited by examiner, † Cited by third party
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US8641254B2 (en) 2005-06-07 2014-02-04 Oree, Inc. Illumination apparatus
US8128272B2 (en) 2005-06-07 2012-03-06 Oree, Inc. Illumination apparatus
US8215815B2 (en) 2005-06-07 2012-07-10 Oree, Inc. Illumination apparatus and methods of forming the same
US8272758B2 (en) 2005-06-07 2012-09-25 Oree, Inc. Illumination apparatus and methods of forming the same
US8414174B2 (en) 2005-06-07 2013-04-09 Oree, Inc. Illumination apparatus
US8579466B2 (en) 2005-06-07 2013-11-12 Oree, Inc. Illumination apparatus and methods of forming the same
US8459856B2 (en) 2007-12-19 2013-06-11 Oree, Inc. Planar white illumination apparatus
US8172447B2 (en) 2007-12-19 2012-05-08 Oree, Inc. Discrete lighting elements and planar assembly thereof
US8182128B2 (en) 2007-12-19 2012-05-22 Oree, Inc. Planar white illumination apparatus
US7826698B1 (en) 2007-12-19 2010-11-02 Oree, Inc. Elimination of stitch artifacts in a planar illumination area
US8238703B2 (en) 2007-12-19 2012-08-07 Oree Inc. Waveguide sheet containing in-coupling, propagation, and out-coupling regions
US8064743B2 (en) 2007-12-19 2011-11-22 Oree, Inc. Discrete light guide-based planar illumination area
US8550684B2 (en) 2007-12-19 2013-10-08 Oree, Inc. Waveguide-based packaging structures and methods for discrete lighting elements
US8231237B2 (en) 2008-03-05 2012-07-31 Oree, Inc. Sub-assembly and methods for forming the same
US8297786B2 (en) 2008-07-10 2012-10-30 Oree, Inc. Slim waveguide coupling apparatus and method
US8301002B2 (en) 2008-07-10 2012-10-30 Oree, Inc. Slim waveguide coupling apparatus and method
US9164218B2 (en) 2008-07-10 2015-10-20 Oree, Inc. Slim waveguide coupling apparatus and method
US8624527B1 (en) 2009-03-27 2014-01-07 Oree, Inc. Independently controllable illumination device
US8328406B2 (en) 2009-05-13 2012-12-11 Oree, Inc. Low-profile illumination device
US8727597B2 (en) 2009-06-24 2014-05-20 Oree, Inc. Illumination apparatus with high conversion efficiency and methods of forming the same
US8591072B2 (en) 2011-11-16 2013-11-26 Oree, Inc. Illumination apparatus confining light by total internal reflection and methods of forming the same
US8840276B2 (en) 2011-11-16 2014-09-23 Oree, Inc. Illumination apparatus confining light by total internal reflection and methods of forming the same
US9039244B2 (en) 2011-11-16 2015-05-26 Oree, Inc. Illumination apparatus confining light by total internal reflection and methods of forming the same
US9857519B2 (en) 2012-07-03 2018-01-02 Oree Advanced Illumination Solutions Ltd. Planar remote phosphor illumination apparatus

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