WO2007143347A2 - Volume d'Émission de lumiÈre fluorescente - Google Patents

Volume d'Émission de lumiÈre fluorescente Download PDF

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Publication number
WO2007143347A2
WO2007143347A2 PCT/US2007/068939 US2007068939W WO2007143347A2 WO 2007143347 A2 WO2007143347 A2 WO 2007143347A2 US 2007068939 W US2007068939 W US 2007068939W WO 2007143347 A2 WO2007143347 A2 WO 2007143347A2
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WO
WIPO (PCT)
Prior art keywords
light
extraction surface
recited
wavelength range
disposed
Prior art date
Application number
PCT/US2007/068939
Other languages
English (en)
Other versions
WO2007143347A3 (fr
Inventor
Todd S. Rutherford
Michael Dolgin
Original Assignee
3M Innovative Properties Company
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Publication date
Application filed by 3M Innovative Properties Company filed Critical 3M Innovative Properties Company
Publication of WO2007143347A2 publication Critical patent/WO2007143347A2/fr
Publication of WO2007143347A3 publication Critical patent/WO2007143347A3/fr

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00—Projectors or projection-type viewers; Accessories therefor
    • G03B21/14—Details
    • G03B21/20—Lamp housings
    • G03B21/2006—Lamp housings characterised by the light source
    • G03B21/2033—LED or laser light sources
    • G03B21/204—LED or laser light sources using secondary light emission, e.g. luminescence or fluorescence
    • 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
    • G02B6/0045—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 by shaping at least a portion of the light guide
    • G02B6/0046—Tapered light guide, e.g. wedge-shaped light guide
    • 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
    • G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
    • G02B6/0055—Reflecting element, sheet or layer
    • 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
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4298—Coupling light guides with opto-electronic elements coupling with non-coherent light sources and/or radiation detectors, e.g. lamps, incandescent bulbs, scintillation chambers
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00—Projectors or projection-type viewers; Accessories therefor
    • G03B21/14—Details
    • G03B21/20—Lamp housings
    • G03B21/2006—Lamp housings characterised by the light source
    • G03B21/2013—Plural light sources
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00—Projectors or projection-type viewers; Accessories therefor
    • G03B21/14—Details
    • G03B21/20—Lamp housings
    • G03B21/208—Homogenising, shaping of the illumination light
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
    • H04N9/3141—Constructional details thereof
    • H04N9/315—Modulator illumination systems
    • 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
    • G02F1/133614—Illuminating devices using photoluminescence, e.g. phosphors illuminated by UV or blue light

Definitions

  • the invention relates to light sources, and particularly to light sources that might be used in illumination systems, for example projection systems.
  • the brightness of illumination sources based on a type of light source is typically limited by the brightness of the light source itself.
  • an illumination source that uses light emitting diodes (LEDs) typically has a brightness, measured in power per unit area per unit solid angle), the same as or less than that of the LEDs because the optics that collect the light from the LEDs will, at best, conserve the etendue of the LED source. Accordingly, the brightness of the illumination source is limited.
  • illumination by LEDs is not a competitive option because the brightness of the LEDs that are currently available is too low. This is particularly a problem for the generation of green illumination light, a region of the visible spectrum where the semiconductor materials used in LEDs are less efficient at generating light.
  • a high-pressure mercury lamp is typically able to provide sufficient light for a projection system, but this type of lamp is relatively inefficient, requires a high voltage supply, contains toxic mercury, and has limited lifetime.
  • Solid-state sources, such as LEDs are more efficient, operate at lower voltages, contain no mercury, and are therefore safer, and have longer lifetimes than lamps, often extending to several tens of thousands of hours.
  • An embodiment of the invention is an illumination system including a source of incoherent light capable of generating light in a first wavelength range and an elongate body that emits light in a second wavelength range when illuminated by light in the first wavelength range.
  • the body has a length dimension, a width dimension and a height dimension. At least a portion of the body is tapered so as to increase in width and/or height along the length dimension.
  • the body further includes an extraction surface.
  • a first non-extraction surface extends along at least a portion of the length of the body and is disposed so as to share a common edge with the extraction surface. At least some of the light at the second wavelength is totally internally reflected at the non-extraction surface.
  • At least one external reflector is disposed proximate to the non-extraction surface so as to create a gap between the external reflector and the non-extraction surface.
  • FIGs. IA, IB, 1C, ID, IE and IF schematically illustrate an embodiment of a volume fluorescent light unit according to principles of the present invention
  • FIG. 2 schematically illustrates another embodiment of a volume fluorescent light unit, with a partially tapered body and tiled reflectors, according to principles of the present invention
  • FIG. 3 schematically illustrates another embodiment of a fluorescent body with a partially tapered body and non-tiled reflectors, according to principles of the present invention
  • FIG. 4A schematically illustrates embodiments of a volume fluorescent light unit with reflectors and heat sinks, according to principles of the present invention
  • FIG. 6 shows a graph of the extraction efficiency at various distances from the small end of the body of an experimental volume fluorescent light unit
  • FIG. 7 shows a graph of the extraction efficiency at various distances from the small end of the body of an experimental volume fluorescent light unit
  • FIG. 8 shows a graph of the extraction efficiency versus external mirror reflectivity
  • FIG. 9 shows a graph of the thermal resistance of various air gap distances.
  • the present invention is applicable to light sources and is more particularly applicable to light sources that are used in illumination systems where a high level of brightness is required.
  • the brightness of a light source is measured in optical power (Watts) divided by the etendue.
  • the etendue is the product of the area of the light beam at the light source times the square of the refractive index times the solid angle of the light beam.
  • the etendue of the light is invariant, i.e. if the solid angle of the light beam is reduced without loss of the light, then the area of the beam is increased, e.g. by increasing the emitting area of the light source. Since the etendue is invariant, the brightness of the light generated by the light source can only be increased by increasing the amount of light extracted from the light source. If the light source is operating at maximum output, then the brightness of that light source can no longer be increased.
  • the optical power of the light beam may be increased through the use of additional light sources. There are limits, however, as to how much the optical power and brightness of the light beam can be increased by simply adding more light sources.
  • the optical system that directs the light beam to the target accepts light that is within certain aperture and cone angle limits only. These limits depend on various factors, such as the size of the lenses and the f-number of the optical system.
  • the addition of more light sources does not provide an unlimited increase in the optical power or brightness of the light beam because, at higher numbers of light sources, an increasingly smaller fraction of the light from an added light source lies within the aperture and cone angle limits of the optical system.
  • the invention is believed to be useful for producing a concentrated light source, having a relatively high brightness, using a number of light sources that have a relatively lower brightness, such as light emitting diodes.
  • the light from the lower brightness light sources is used to optically pump a volume of fluorescent material.
  • the fluorescent material absorbs the light emitted by the low brightness light source and fluorescently emits light at a different wavelength.
  • the fluorescent light is typically emitted isotropically by the fluorescent material. At least some of the fluorescent light can be directed within the volume to a light extraction area.
  • the pump surface area is the area of the fluorescent volume that is used for coupling the relatively low brightness, short wavelength pump light into the volume, and the extraction area is that area of the fluorescent volume from which fluorescent light is extracted. A net increase in brightness can be achieved when the pump surface area is sufficiently large compared to the extraction area.
  • the term fluorescence covers phenomena where a material absorbs light at a first wavelength and subsequently emits light at a second wavelength that is different from the first wavelength.
  • the emitted light may be associated with a quantum mechanically allowed transition, or a quantum mechanically disallowed transition, the latter commonly being referred to as phosphorescence.
  • the fluorescent material absorbs only a single pump photon before emitting the fluorescent light, the fluorescent light typically has a longer wavelength than the pump light. In some fluorescent systems, however, more than one pump photon may be absorbed before the fluorescent light is emitted, in which case the emitted light may have a wavelength shorter than the pump light. Such a phenomenon is commonly referred to as upconversion fluorescence.
  • fluorescent and fluorescent light are intended to cover systems where the pump light energy is absorbed by one species and the energy is re-radiated by the same or by another species.
  • This type of device is illustrated and described in U.S. Patent Application No. 11/092,284.
  • One particular embodiment of the invention is schematically illustrated in FIGs.
  • IA, IB and 1C which show top, cross-sectional, and side views, respectively, of a volume fluorescent light unit (or illumination system) 100 that has a body 102 containing fluorescent material, a number of light emitters 104 that emit light 106 into the body 102, and external reflectors 115 which reflects light emitted from the body 102 back into the body 102.
  • the external reflectors are spaced from body 102 a certain distance forming gaps 216A and 216B.
  • FIGs. IA, IB and 1C A Cartesian coordinate system is provided in FIGs. IA, IB and 1C to aid in the description of the volume fluorescent light unit 100.
  • the directions of the coordinate system have been arbitrarily assigned so that the output fluorescent light propagates generally along the z-direction, which is parallel to the longitudinal dimension of the body, having a length, L.
  • the width of the body 102, w is measured in the x-direction and the height of the body 102, h, is measured in the y-direction.
  • the body 102 is tapered along its length.
  • the height of the body 102, h, along the y-direction increases in size along the length of the body 102, L, i.e., along the z-direction.
  • the pump light enters the body 102 through pump surfaces 110 and fluorescent output light 109 passes out the body 102 through an extraction face 112.
  • External reflectors 115A and 115B are positioned immediately adjacent non-extraction surfaces 113A-113D (referred to generally as “non-extraction surfaces 113").
  • the pump surfaces 110 are also non-extraction surfaces 113. While four non-extraction surfaces 113 are illustrated in the current embodiment it should be understood that any number of non- extraction surfaces 113 as well as any number of pump surfaces 110 may be included in the current invention.
  • non-extraction surfaces 113 extend along length L of body 102.
  • the body 102 is tapered so that the largest cross sectional area of the body occurs at the extraction face 112.
  • a rear surface 150 is also illustrated and may or may not be orthogonal to one or more of the non-extraction surfaces 113 and may or may not be substantially parallel to the extraction surface.
  • TIR total internal reflection
  • some portions of the fluorescent light may be transmitted through non-extraction surface 113A of the body 102.
  • Other portions of the fluorescent light exemplified by ray 108B, are reflected within the body 102.
  • gaps 216A and 216B There are several practical reasons for leaving gaps 216A and 216B referred to generally as “gaps 216") between the external reflectors 115 and the body 102, instead of placing reflectors 115 directly against body 102.
  • gaps 216 allow for efficient TIR conditions.
  • the residual loss of a TIR reflection can be very low (less than 0.1% per bounce).
  • this TIR effect is caused by the movement from the high index material of the body 102 into low index material (e.g., air, having refractive index approximately 1.0).
  • a low index material such as air (or other material) can fill the gap 216.
  • Utilizing the TIR effect is better than placing the reflectors 115 directly against the body 102 because unless the reflectivity of the reflector is very high over a wide range of angles, it will increase the overall loss after the many reflections needed to reach the end of the body 102. Additionally, coating the sides of the body with a reflective surface would be expensive since the coating would need to come very close to the body edges and have >99.5% reflectivity (requiring many layers for a dielectric stack reflector, and multiple coating cycles would be needed to coat all of the non-extractions faces).
  • ⁇ cp sin 1 (Vn), (5) where n p is the refractive index on the outside of the non-extraction surface 113A (in this case within gap 216A) and n is the refractive index of the body 102.
  • This angle ⁇ cp is known as the "critical angle”. Hatched region 117 shows the range of angles that are less than ⁇ cp . If the non-extraction surface 113A is in air (i.e., if the substance filling gap 216A is air), the value of n p is approximately equal to 1.
  • n is larger.
  • ray 208 A If light, for example ray 208 A, is incident at the non-extraction surface 113A so as to form an angle with a line normal to non-extraction surface (its Angle of Incidence, or AOI) and this angle is less than the critical angle, ⁇ cp , then the light 208 A is transmitted through the non-extraction surface 113 A.
  • AOI Angle of Incidence
  • FIG. ID is a schematic of light unit 100 (illustrated without light emitters for clarity) showing an example of how this works.
  • Light ray 208C which initially does not meet the TIR condition is reflected from the external reflector 115. After reflection and re-entry through non-extraction surface 113 A, it has a larger AOI at the body/air interface at non-extraction surface 113C than it did at the previous interaction with the body/air interface at non-extraction surface 113 A, and is closer to TIR.
  • Light ray 208C is refracted away from normal as it passes into gap 216A.
  • Gap 216A is the space between external reflector 115 and non-extraction surface 113 A.
  • Light ray 208C reflects off of external reflector 115 at point 214B.
  • the light ray 208C re- enters body 102 at point 214C creating an angle of refraction G 1 .
  • the angle of incidence at point 214A and the angle of refraction at point 214C of light ray 208C are substantially equal.
  • Light ray 208C travels through body 102 until it encounters non-extraction surface 113C at point 214D.
  • Light ray 208C defines an AOI of ⁇ i+n, which is larger than that of the AOI at points 214A and 214C. This is due to the non-parallel relationship between the normal line 215A at non-extraction surface 113A and a normal line 215B at non- extraction surface 113C. The skewed relationship between the normals (215A and 215B) is due to the non-parallel relationship of the sides of tapered body 102.
  • the AOI increases with each successive encounter by light ray 208C as it exits either non-extraction surface 113A or non-extraction surface 113C, and passes into gap 216A or 216B. Eventually the AOI is large enough that it is greater than the Critical Angle, and light ray 208C begins to TIR within the body 102, such as is shown at point 212.
  • some backward propagating rays i.e. rays that propagate towards narrowing portion of body 102 as illustrated by ray 208D
  • ray 208D some backward propagating rays (i.e. rays that propagate towards narrowing portion of body 102 as illustrated by ray 208D) that initially meet the TIR condition are eventually coupled out of the slab sides (since the AOI of the light ray falls below the Critical Angle).
  • light ray 208D initially has an AOI greater than the Critical Angle as it encounters non-extraction surfaces 113A or 113C, but after each reflection from the non-extraction surfaces 113A or 113C, the angle of incidence decreases. This occurs since light ray 208D is traveling opposite that of light ray 208C (discussed previously with respect to FIG. IE).
  • light unit (or illumination system) 300 includes external reflectors 315 that can be used with a body 302 having at least a portion of which is not tapered.
  • FIG. 2 is a schematic illustration of light unit 300 shown without light emitters, for clarity.
  • reflectors 315 confine light ray 308C that does not meet the TIR condition (i.e. its AOI is not greater than the Critical Angle) until it is coupled into tapered portion 320.
  • External reflectors 315 can run parallel to the entirety of non-extraction surfaces 313A and 313B of non-tapered portion 324 and tapered portion 320 of body 302 (in other words the reflectors 315 are "tiled").
  • FIG. 1 illustrates the entirety of non-extraction surfaces 313A and 313B of non-tapered portion 324 and tapered portion 320 of body 302.
  • external reflectors 415 can have a single slope with respect to the entire body 302, including the tapered portion 320 and non-tapered portion 324.
  • the transition point between tapered portion 320 and non-tapered portion 324 will be referred to as a non-tapered output 326 and tapered input 328. It should be understood that this is an arbitrary reference, and alternatively, this point could, for example, refer to the "extraction surface" of the non-tapered portion.
  • light ray 308C which has escaped body 302 (due to an AOI of less than the critical angle) continually reflects off of reflectors 315 and propagates through body 302 with substantially no change in the AOI as it exits body 302 into one of air gaps 316A or 316B.
  • Light ray 308C does not begin to approach the TIR condition until after it encounters tapered portion 320. This is due to the fact that normal lines exemplified by 322A and 322B on opposing non-extractor surfaces 313A and 313B at non-tapered portion 324 are substantially parallel. The result is that the AOI of light ray 308C does not significantly change.
  • Tapered portion 320 of body 302 additionally has an advantage of functioning as an output extractor, reducing the amount of fluorescent light that would otherwise be totally internally reflected at the extraction surface 312 (versus using a non-tapered body.)
  • different types of tapered portions 320 in the form of output extractors may be coupled to the non-tapered portion 324.
  • a tapered, transmissive rod or tunnel is coupled to the non-tapered output 326 for use as an output extractor and to form tapered portion 320 of body 302.
  • the tunnel is shaped to closely couple to the non-tapered output 326.
  • non-tapered output 326 and the extractor are sufficiently matched (i.e., in size, shape, and refractive index), then light can be efficiently coupled from non-tapered portion 324 into the tapered portion 320 by placing the tapered input 328 against, or within less than one wavelength of, the non- tapered output 326, preferably around or less than one-quarter of a wavelength.
  • An index matching material for example an index matching oil or an optical adhesive, may also be used between the extractor and the non-tapered output 326.
  • the extractor may be made of any suitable transparent material, for example a glass or a polymer.
  • Reflection of fluorescent light in the extractor tends to direct the fluorescent light along the z-direction, and so the angular spread of the fluorescent light at the output of the tunnel (i.e., the extraction face 312) is less than the angular spread of the light as it enters the tapered portion 320 from the non-tapered portion 324.
  • the reduced angular spread reduces the amount of fluorescent light that is totally internally reflected at the output surface (i.e., the extraction face 312).
  • the tapered portion 320 may be formed integrally with the non-tapered portion 324, for example the tapered portion 320 and the non-tapered portion 324 may be molded from a single piece of material, such as polymer material. Additionally, the tapered portion 320 may or may not contain fluorescent material.
  • the extraction face 312 of the tapered portion 320 may be perpendicular to the z- axis, or may be tilted, for example as is further described in published U.S. Patent Application No. 2005-0135761 -Al .
  • a tilted extraction face 312 may be useful, for example, where the extraction face 312 is being imaged by an image relay system to a tilted target.
  • DMD digital multimirror device
  • Texas Instruments Piano, Texas
  • a DMD has many mirrors positioned in a plane, each mirror being individually addressable to tilt between two positions.
  • the DMD is typically illuminated by a light beam that is non-normal to the DMD mirror plane, i.e. the mirror plane is tilted relative to the direction of propagation of the illumination light, and the image light reflected by the DMD is reflected in a direction normal to the mirror plane.
  • the body of the present invention may take on many different shapes.
  • body 102 has a rectangular cross- section, parallel to the x-y plane.
  • the cross-section of the body (102, 302) may be different, for example, circular, triangular, elliptical, or polygonal, and may also be irregular.
  • the cross-sectional area (in the x-y plane) of the body 102 illustrated in FIG.s 1A-1F and tapered portion 320 in FIG.s 2 and 3 can increase (i.e. the "taper" can occur) in just one dimension, or in two.
  • Reflectors 115, 315 and 415 shown in FIG.'s 1-3 include a large air gap for illustration purposes.
  • the air space preferably is kept small. Keeping the gaps small minimizes light escaping from the sides of the reflectors.
  • the air gap is preferably ⁇ 10% of the width of the body 102, 302 at its small end. For typical designs this means that the air gap is less than 100 microns. While air is the typical substance in gap, the invention contemplates the use of other substances such as filling gaps 216 with a low refractive index dielectric or gas other than air.
  • the thickness of the gaps 416A and 416B can be chosen to assure that the thermal resistance of the layer of material in the gaps 416A and 416B (e.g. air) does not exceed heat transfer requirements.
  • the gaps 416A and 416B can be filled with gasses (or other materials) other than air, especially those that have higher thermal conductivity than air, such as those in the following table:
  • the gas in the gap can be at a pressure that is higher than atmospheric pressure which can further increase thermal conductivity.
  • light output effectiveness can be increased. This occurs due to the decreased loss of TIR light (when a tapered body is used), potential increase in light absorption since light from light emitters can be directed into slab, and controlling the temperature of body 402 to limit quenching.
  • the distance of gaps 416A and 416B is held at 100 microns or less. Other preferred gap distances include distances of 0.075 mm and 0.03 mm.
  • Light emitters 404 are illustrated as the "pump light" source to illuminate body 402. These light emitters 404 are illustrated at being attached to heat sinks 430C and 430D.
  • Additional reflective surfaces can be attached to heat sinks 430C and 430D, or placed between light emitters 404 and body 402 to further provide cooling to body 402. It may be useful to make these reflective surfaces dichroic to allow passing of the pump light through the reflector, while reflecting the fluorescing light.
  • the current invention includes utilizing a minimal gap distance between the body 402 and the reflectors 415 to cool the body 402, regardless of whether body 402 is tapered (or includes a tapered portion) or is not tapered.
  • One embodiment of the current invention utilizes a curved reflector 515A, as shown in FIG. 4B. Although shown contacting body 502 only on one edge, a curved reflector could be provided which contacts the body on both reflector edges as shown in dotted lines at 515B.
  • reflector 515 A is primarily a reflector used to direct pump light generated by light emitters 504, whereas reflector 515B is primarily used to reflect fluorescent light (as discussed and described previously). If both reflectors 515A and 515B are used together, reflector 515B would preferably be dichroic, allowing light from light emitters 504 to pass through, while reflecting fluorescent light from body 502.
  • the curved reflector configuration can provide a different air flow space which may be desirable when designing a cooling system for the inventive light unit. Also illustrated are light emitters 504, reflector 515, gap 516 and heatsink 530.
  • reflectors can serve to confine the pump light as well as the fluorescent light. If external reflectors are placed on all side of the body, (i.e., between the light emitters and the body) it may be beneficial to make the reflectors dichroic, so that the pump light can pass through with a minimum loss.
  • the particular selection of fluorescent material depends on the desired fluorescent wavelength and the wavelength of the light emitted from the light emitter 104. It is preferred that the fluorescent material absorb the pump light 106 emitted by the light emitter 104 efficiently, so that the pump light 106 is mostly, if not all, absorbed within the body 102. This enhances the efficiency of converting pump light 106 to useful fluorescent output light 109.
  • the light emitters 104 may be any suitable type of device that emits incoherent light. The present invention is believed to be particularly useful for producing a relatively bright beam using light from less bright light emitters.
  • the light 106 emitted from the light emitters 104 is in a wavelength range that overlaps well with an absorption wavelength band of the fluorescent material. Also, it is useful if the light emitters 104 can be oriented so that there is a high degree of optical coupling of the emitted light 106 into the body 102.
  • One suitable type of light emitter is the LED, which typically generates light 106 having a bandwidth in the range of about 20 nm to about 50 nm, although the light bandwidth may be outside this range.
  • the radiation pattern from an LED is, in many cases, approximately Lambertian, and so relatively efficient coupling of the light 106 into the body 102 is possible.
  • Other types of light emitter may also be used, for example a gas discharge lamp, a filament lamp and the like.
  • the light emitters 104 may optionally be provided on a substrate (shown optionally in dotted lines at 220).
  • substrate 220 may make electrical and thermal connections to the LEDs for providing power and cooling respectively.
  • the substrate 220 may be reflective so that some light, exemplified by light ray 106A, directed from the light emitter 104 in direction away from the body 102 may be redirected towards the body 102.
  • the substrate 220 may reflect pump light that has passed through the body 102 without being absorbed, exemplified by light ray 106B.
  • the maximum efficiency for coupling fluorescent light out of a body using total internal reflection may be calculated. As discussed above, generally it is preferred that the body has a higher refractive index, so that a greater fraction of the fluorescent light is totally internally reflected within the body.
  • the body 102 may be formed of any suitable material.
  • the body 102 may be formed of the fluorescent material itself, or may be formed of some dielectric material that is transparent to the fluorescent light and that contains the fluorescent material.
  • dielectric material include inorganic crystals, glasses and polymer materials.
  • fluorescent materials that may be doped into the dielectric material include rare-earth ions, transition metal ions, organic dye molecules and phosphors.
  • One suitable class of dielectric and fluorescent materials includes inorganic crystals doped with rare-earth ions, such as cerium-doped yttrium aluminum garnet (Ce:YAG), or doped with transition metal ions, such as chromium-doped sapphire or titanium-doped sapphire.
  • Rare-earth and transition metal ions may also be doped into glasses.
  • Another suitable class of material includes a fluorescent dye doped into a polymer body.
  • fluorescent dyes are available, for example from Sigma- Aldrich, St. Louis, Missouri, and from Exciton Inc., Dayton, Ohio.
  • Common types of fluorescent dye include fluorescein; rhodamines, such as Rhodamine 6G and Rhodamine B; and coumarins such as Coumarin 343 and Coumarin 6.
  • the particular choice of dye depends on the desired wavelength range of the fluorescent light and the wavelength of the pump light.
  • Many types of polymers are suitable as hosts for fluorescent dyes including, but not limited to, polymethylmethacrylate and polyvinylalcohol.
  • Phosphors include particles of crystalline or ceramic material that include a fluorescent species.
  • a phosphor is often included in a matrix, such as a polymer matrix.
  • the refractive index of the matrix may be substantially matched, within at least 0.02, to that of the phosphor so as to reduce scattering.
  • the phosphor may be provided as nanoparticles within the matrix: there is little scattering of light within the resulting matrix due to the small size of the particles, even if the refractive indices are not well matched.
  • fluorescent materials include doped semiconductor materials, for example doped II-VI semiconductor materials such as zinc selenide and zinc sulfide.
  • doped II-VI semiconductor materials such as zinc selenide and zinc sulfide.
  • an upconversion fluorescent material is a thulium-doped silicate glass, described in greater detail in co-owned U.S. Patent Publication No. 2004/0037538 Al . In this material, two, three or even four pump light photons are absorbed in a thulium ion (Tm + ) to excite the ion to different excited states that subsequently fluoresce.
  • Tm + thulium ion
  • the particular examples of fluorescent species described above are presented for illustrative purposes only, and are not intended to be limiting.
  • An exemplary embodiment of a projection system that might use a fluorescent volume light unit as described herein is schematically illustrated in FIG.
  • the projection system 500 is a three-panel projection system, having light sources 502a, 502b, 502c that generate differently colored illumination light beams 506a, 506b, 506c, for example red, green and blue light beams.
  • the green light source 502b includes a fluorescent volume light unit.
  • any, or all of the light source 502a, 502b, 502c may include fluorescent volume light units.
  • the light sources 502a, 502b, 502c may also include beam steering elements, for example mirrors or prisms, to steer any of the colored illumination light beams 506a, 506b, 506c to their respective image-forming devices 504a, 504b, 504c.
  • the image-forming devices 504a, 504b, 504c may be any kind of image-forming device.
  • the image-forming devices 504a, 504b, 504c may be transmissive or reflective image-forming devices. Liquid crystal display (LCD) panels, both transmissive and reflective, may be used as image-forming devices.
  • LCD liquid crystal display
  • a suitable type of transmissive LCD image-forming panel is a high temperature polysilicon (HTPS) LCD.
  • An example of a suitable type of reflective LCD panel is the liquid crystal on silicon (LCoS) panel.
  • the LCD panels modulate an illumination light beam by polarization modulating light associated with selected pixels, and then separating the modulated light from the unmodulated light using a polarizer.
  • Another type of image-forming device referred to a digital multimirror device (DMD), and supplied by Texas Instruments, Piano, Texas, under the brand name DLPTM, uses an array of individually addressable mirrors, which either deflect the illumination light towards the projection lens or away from the projection lens.
  • the image-forming devices 504a, 504b, 504c are of the LCoS type.
  • the light sources 502a, 502b, 502c may also include various elements such as polarizers, integrators, lenses, mirrors and the like for dressing the illumination light beams 506a, 506b, 506c.
  • the colored illumination light beams 506a, 506b, 506c are directed to their respective image forming devices 504a, 504b and 504c via respective polarizing beamsplitters (PBSs) 510a, 510b and 510c.
  • PBSs polarizing beamsplitters
  • the colored image light beams 508a, 508b and 508c may be combined into a single, full color image beam 516 that is projected by a projection lens unit 511 to the screen 512.
  • the image-forming devices 504a, 504b, 504c may be coupled to a controller 520 (dashed lines) that controls the image displayed on the screen 512.
  • the controller may be, for example, the tuning and image control circuit of a television, a computer or the like.
  • the colored illumination light beams 506a, 506b, 506c are reflected by the PBSs 510a, 510b and 510c to the image-forming devices 504a, 504b and 504c and the resulting image light beams 508a, 508b and 508c are transmitted through the PBSs 510a, 510b and 510c.
  • the illumination light may be transmitted through the PBSs to the image-forming devices, while the image light is reflected by the PBSs.
  • Other embodiments of projection systems may use a different number of image- forming devices, either a greater or smaller number. Some embodiments of projection systems use a single image-forming device while other embodiments employ two image- forming devices.
  • projection systems using a single image-forming device are discussed in more detail in co-owned U.S. Patent Application Serial No. 10/895,705 and projection systems using two image-forming devices are described in co-owned U.S. Patent Application Serial No. 10/914,596.
  • the illumination light is incident on only a single image-forming panel.
  • the incident light is modulated, so that light of only one color is incident on a part of the image-forming device at any one time.
  • the color of the light incident on the image-forming device changes, for example, from red to green to blue and back to red, at which point the cycle repeats. This is often referred to as a "field sequential color" mode of operation.
  • differently colored bands of light may be scrolled across the single panel, so that the panel is illuminated by the illumination system with more than one color at any one time, although any particular point on the panel is instantaneously illuminated with only a single color.
  • two colors are directed sequentially to a first image-forming device panel that sequentially displays an image for the two colors.
  • the second panel is typically illuminated continuously by light of the third color.
  • the image beams from the first and second panels are combined and projected. The viewer sees a full color image, due to integration in the eye.
  • 22 mm of the body are excited by blue LEDs to produce fluorescence.
  • the efficiency of light extraction varies along the 22 mm of the body that are generating fluorescent light.
  • FIG. 6 illustrates the efficiency (the amount of light extracted from the extraction face versus the pumped light) as a function of the position where the fluorescent light is generated for a body with two external reflectors close to the two large faces of the body.
  • FIG. 6 also illustrates the comparative case of a body where no reflectors are utilized.
  • FIG. 7 illustrates the extraction efficiency as a function of slab position for a slab with external reflectors on all four sides.
  • the extraction is perfect until the point at 16 mm where TIR begins to occur on the exit face.
  • the case where no reflectors are used is included for comparison.
  • the improvement in extraction efficiency will be limited by the reflectivity of the external reflectors.
  • FIG. 8 illustrates the calculated effect of reduction in reflectivity of the external reflector. Substantial increases in efficiency are realized for reflectivities above 95%, which is within the range of relatively simple enhanced metallic reflectors. This is compared to the case of a reflector placed directly on the slab, where the efficiency drops off extremely rapidly and >99% reflectivity is needed for any enhancement.
  • the surface area of the two large sides of the slab is 3.1 sq cm.
  • thermal resistance of the heat sink for example UBC60-25B from "Alphanovatech” with forced air convection with velocity 2m/sec, will be about 9 °K/W. Therefore thermal resistance of the air gap must not exceed 8.2 °K/W (i.e. 17.2-9). Calculation of the thermal resistance of the air gap as shown in FIG. 9 confirms that an air gap less than 0.075 mm will be sufficient to cool down the slab as required.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Non-Portable Lighting Devices Or Systems Thereof (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)

Abstract

Un mode de réalisation de l'invention consiste en un système d'éclairage qui contient une source de lumière non cohérente capable d'émettre de la lumière dans une première plage de longueur d'onde et un corps allongé qui émet de la lumière dans une deuxième plage de longueur d'onde lorsqu'il est éclairé par la lumière de la première plage de longueur d'onde. Le corps présente une dimension de longueur, une dimension de largeur et une dimension de hauteur. Au moins une partie du corps se rétrécit de telle sorte que sa largeur et/ou sa hauteur augmentent dans le sens de la longueur. Le corps comprend en outre une surface d'extraction. Une première surface de non-extraction s'étend sur au moins une partie de la longueur du corps et est disposée de manière à partager un bord commun avec la surface d'extraction. Au moins une partie de la lumière à la deuxième longueur d'onde subit une réflexion interne totale sur la surface de non-extraction. Au moins un réflecteur externe est disposé à proximité de la surface de non-extraction de manière à créer un interstice entre le réflecteur externe et la surface de non-extraction.
PCT/US2007/068939 2006-06-02 2007-05-15 Volume d'Émission de lumiÈre fluorescente WO2007143347A2 (fr)

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US80382106P 2006-06-02 2006-06-02
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2749943A4 (fr) * 2011-08-27 2015-08-19 Appotronics Corp Ltd Système de projection et dispositif électroluminescent de celui-ci
GB2552379A (en) * 2016-07-22 2018-01-24 Univ Oxford Innovation Ltd A receiver assembly and a data communications method

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US5949933A (en) * 1998-03-03 1999-09-07 Alliedsignal Inc. Lenticular illumination system
US6272269B1 (en) * 1999-11-16 2001-08-07 Dn Labs Inc. Optical fiber/waveguide illumination system
US6418252B1 (en) * 2001-01-16 2002-07-09 The Regents Of The University Of California Light diffusing fiber optic chamber
US6687436B2 (en) * 1998-09-01 2004-02-03 Stephen Griffin Optical fiber with numerical aperture compression

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Publication number Priority date Publication date Assignee Title
US5949933A (en) * 1998-03-03 1999-09-07 Alliedsignal Inc. Lenticular illumination system
US6687436B2 (en) * 1998-09-01 2004-02-03 Stephen Griffin Optical fiber with numerical aperture compression
US6272269B1 (en) * 1999-11-16 2001-08-07 Dn Labs Inc. Optical fiber/waveguide illumination system
US6418252B1 (en) * 2001-01-16 2002-07-09 The Regents Of The University Of California Light diffusing fiber optic chamber

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2749943A4 (fr) * 2011-08-27 2015-08-19 Appotronics Corp Ltd Système de projection et dispositif électroluminescent de celui-ci
EP3382451A1 (fr) * 2011-08-27 2018-10-03 Appotronics Corporation Limited Système de projection et dispositif électroluminescent associé
GB2552379A (en) * 2016-07-22 2018-01-24 Univ Oxford Innovation Ltd A receiver assembly and a data communications method

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TW200807137A (en) 2008-02-01

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