WO2012154446A1

WO2012154446A1 - Optical structure for remote phosphor led

Info

Publication number: WO2012154446A1
Application number: PCT/US2012/035957
Authority: WO
Inventors: Xiaohui Cheng; Andrew J. Ouderkirk; Yarn Chee POON
Original assignee: 3M Innovative Properties Company
Priority date: 2011-05-12
Filing date: 2012-05-01
Publication date: 2012-11-15
Also published as: TW201300697A

Abstract

The disclosure generally relates to broadband solid state illumination sources and image projectors that utilize a phosphor layer or material that is pumped or excited by light from one or more LEDs. In particular, the disclosure provides an efficient and bright source of polarized light. The configuration is compact, efficient, and has especially low etendue.

Description

OPTICAL STRUCTURE FOR REMOTE PHOSPHOR LED

Related Applications

This application is related to the following U.S. Patent Applications, which are incorporated by reference: "REMOTE PHOSPHOR CONVERTED LED" (Attorney Docket No.

67248US002), and "REMOTE PHOSPHOR POLARIZATION CONVERTER" (Attorney Docket No. 67422US002), both filed on an even date herewith.

Technical Field

This disclosure relates generally to light sources, with particular application to solid state light sources that incorporate a light emitting diode (LED) and a phosphor. The disclosure also relates to associated articles, systems, and methods.

Background

Solid state light sources that emit broadband light are known. In some cases, such light sources are made by applying a layer of yellow-emitting phosphor onto a blue LED. As light from the blue LED passes through the phosphor layer, some of the blue light is absorbed, and a substantial portion of the absorbed energy is re-emitted by the phosphor as Stokes-shifted light at longer wavelengths in the visible spectrum, typically, yellow light. The phosphor thickness is small enough so that some of the blue LED light passes all the way through the phosphor layer, and combines with the yellow light from the phosphor to provide broadband output light having a white appearance.

Other LED-pumped phosphor light sources have also been proposed. In U.S. Patent 7,091,653 (Ouderkirk et al.), a light source is discussed in which ultraviolet (UV) light from an LED is reflected by a long-pass reflector onto a phosphor layer. The phosphor layer emits visible (preferably white) light, which light is substantially transmitted by the long-pass reflector. The

LED, phosphor layer, and long-pass filter are arranged in such a way that as UV light travels from the LED to the long-pass reflector it does not pass through the phosphor layer.

There are two primary approaches to increase the polarized output of a light source. One is to position a reflective polarizer to return the light of the undesired polarization state back to the light source. Assuming that the light source is not completely absorbing, and the system can either deterministically or randomly change the polarization state of the light, light will be re-emitted from the source and some of it will pass through the reflective polarizer in the desired state. The other approach is to use a polarization converter, which can almost double the output of the light in the desired polarization state, but can also double the etendue of the illuminator.

While polarization converters are very efficient, the application may have less value in etendue limited systems. Recycling polarizers do not substantially increase etendue, but are limited by the reflectivity of the light source. Since LEDs typically have a reflectivity of 50%, and randomize the polarization state, efficiency is typically less than 15% in a practical system. There is a need for a system that efficiently recycles polarized light, but does not significantly increase etendue

Summary

The disclosure generally relates to broadband solid state illumination sources and image projectors that utilize a phosphor layer or material that is pumped or excited by light from one or more LEDs. In particular, the disclosure provides an efficient and bright source of polarized light.

The configuration is compact, efficient, and has especially low etendue. In one aspect, the present disclosure provides an illumination system that includes a light emitting diode (LED) disposed on a substrate and configured to inject a first light beam along a first propagation direction through a collimating optic; a wavelength selective reflector within the collimating optic to reflect the first light beam back through the collimating optic; and a phosphor disposed immediately adjacent the LED, the phosphor capable of downconverting a major portion of the first light beam to become a second light beam propagating in a second propagation direction back through the collimating optic and through the wavelength selective reflector.

In another aspect, the present disclosure provides an image projector that includes an illumination system, a polarization converter capable of converting the second light beam to a third light beam having a first polarization direction, an imager disposed to intercept the first polarization direction of the second light beam, and projection optics. The illumination system includes a light emitting diode (LED) disposed on a substrate and configured to inject a first light beam along a first propagation direction through a collimating optic; a wavelength selective reflector within the collimating optic to reflect the first light beam back through the collimating optic;and a phosphor disposed immediately adjacent the LED, the phosphor capable of downconverting a major portion of the first light beam to become a second light beam propagating in a second propagation direction back through the collimating optic and through the wavelength selective reflector. The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The figures and the detailed description below more particularly exemplify illustrative embodiments.

Brief Description of the Drawings

Throughout the specification reference is made to the appended drawings, where like reference numerals designate like elements, and wherein:

FIGS. 1A-1D shows cross-section schematics of an illumination system;

FIGS. 2A-2C show schematic views near the light output region of an illumination system; and

FIG. 3 shows a schematic diagram of an image projector.

The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

Detailed Description

The present application provides an efficient and bright source of polarized light. The configuration is compact, efficient, and has especially low etendue. One conventional technique of increasing the polarized light output of an LED illuminator (that is, without consideration of wavelength downconversion) is to use a reflective polarizer to reflect the unused polarization of light back to the source. LED sources generally randomize the polarization state, and a portion of the light is sent back again to the reflective polarizer. Typical conventional recycling polarizer systems increase brightness and output by 10-15%. The illumination system described herein provides a system with a potential of 40-50% improvement over the conventional systems.

The present application describes broadband solid state illumination sources that utilize a phosphor layer or material that is pumped or excited by light from one or more LEDs. The sources also include a reflector and collimating optics. In some cases, the reflector can be a dichroic reflector that reflects at least some of the LED light onto the layer of phosphor. The light exiting the LED propagates within a collimation angle that enters the collimating optic. The light reflects from the reflector and is directed back through the collimating optic to the phosphor layer.

Phosphor converted LEDs is a way of generating different wavelengths and bandwidths than can be efficiently generated directly by an LED. Efficiency in generating light is one of the important attributes of LED illuminator performance, and techniques of increasing efficiency, especially while maintaining a reduced etendue, is important for many applications. Two techniques are typically used to generate light having a longer wavelength from a wavelength downconversion using, for example, a phosphor. In one technique, input light pumps (that is, excites) one side of a phosphor, and downconverted light is emitted from the other side of the phosphor. In another technique, the incident exciting light and useful emitting light come from the same side of the phosphor. In some cases, there are also devices where both modes operate simultaneously. Typically, where excitation and useful emission are both on the same side of the wavelength converter, the converter can be backed with a mirror. Polarization converters can be very efficient, but can also double etendue. Polarization recycling systems can preserve etendue, but generally have low efficiency, particularly with LED-based systems.

For purposes of the description provided herein, "color light" and "wavelength spectrum light" are both intended to mean light having a wavelength spectrum range which may be correlated to a specific color if visible to the human eye. The more general term "wavelength spectrum light" refers to both visible and other wavelength spectrums of light including, for example, infrared light.

Also for the purposes of the description provided herein, the term "aligned to a desired polarization state" is intended to associate the alignment of the pass axis of an optical element to a desired polarization state of light that passes through the optical element, that is, a desired polarization state such as s-polarization, p-polarization, right-circular polarization, left-circular polarization , or the like. In one embodiment described herein with reference to the Figures, an optical element such as a polarizer aligned to the first polarization state means the orientation of the polarizer that passes the p-polarization state of light, and reflects or absorbs the second polarization state (in this case the s-polarization state) of light. It is to be understood that the polarizer can instead be aligned to pass the s-polarization state of light, and reflect or absorb the p- polarization state of light, if desired.

In one particular embodiment, the present disclosure describes a phosphor converted LED having a blue or UV emitting LED, a phosphor that is excited by the blue or UV light and generates light with a longer wavelength, an optical collimator, and a dichroic mirror, where the phosphor is in an optically uniform layer that transmits between 5 and 50% of the excitation light, and the dichroic mirror preferentially reflects the excitation light, and transmits the light with the longer wavelength. The light from the LED is reflected by the dichroic mirror, and is focused by a lens assembly onto the front side of a layer of a phosphor. The phosphor is backed by a mirror, and between 5 and 50% of the light from the LED is transmitted through the phosphor to the mirror, and reflected back through the phosphor layer. Light is depolarized by scattering in the phosphor, becomes collimated through the collimating optics, and a fraction of the scattered light is able to either again be recycled, or be transmitted by the reflective polarizer. In one particular embodiment, an illuminator having an LED generating light in the range of blue to UV light is approximately collimated by at least one first lens assembly, reflected by a long-pass dichroic mirror disposed on a surface of the first lens assembly, and focused by a second lens to illuminate an area of a wavelength converting phosphor. The light emitted by the phosphor is collimated by the first and second lens assembly, passes through the dichroic mirror and passes through a reflective polarizer. The light reflected by the reflective polarizer is focused by the first and second lens to the illuminate area of the phosphor.

In one particular embodiment, an illuminator having an LED generating light in the range of blue to UV light is approximately collimated by at least one first lens assembly, reflected by a long-pass dichroic mirror disposed within the first lens assembly, and focused by a second lens to illuminate an area of a wavelength converting phosphor. The light emitted by the phosphor is collimated by the first and second lens assembly, passes through the dichroic mirror and passes through a reflective polarizer. The light reflected by the reflective polarizer is focused by the first and second lens to the illuminate area of the phosphor.

Of particular interest, the applicants have surprisingly discovered that the polarization conversion efficiency can increase as the phosphor thickness is reduced. Although not wishing to be bound by any particular theory, this is likely in part due to the scattering processes in the phosphor layer that causes less depolarization, and also by taking advantage of the single -pass output potential enabled by disposing an optional quarter- wave retarder adjacent the reflective polarizer. In some cases, the retarder can be disposed at any desired location within the optical path between the phosphor and the reflective polarizer; however, adjacent the reflective polarizer is especially preferred. In some cases, the fast-axis of the quarter-wave retarder can be rotated such that it forms an angle to the fast-axis of the reflective polarizer, such as an angle of from about 5 degrees to about 40 degrees, or from about 15 degrees to about 30 degrees, or from about 20 degrees to about 25 degrees, or about 22.5 degrees. This rotation can be used to simulate random depolarization for cases where the phosphor is very thin and not sufficiently scattering. In some cases, some optimization of the system can include parameters including, for example, the phosphor particle size and distribution, phosphor matrix index of refraction, phosphor layer thickness, birefringence in the phosphor (for example, phosphor glass particles vs. crystalline phosphors), and addition of non-luminescent scattering particles such as titania.

The reflective polarizer can be any known reflective polarizer and may be based on a dielectric multilayer optical film (MOF), for example Vikuiti™ Advanced Polarizing Film (APF) available from 3M Company. It may also be based on a circular polarizer such as a cholesteric reflective polarizer, or a MacNeille polarizer, or a wire grid reflective polarizer. According to one embodiment, a multilayer optical film polarizer can be a preferred reflective polarizer. Polymeric multilayer optical film polarizers can be particularly preferred reflective polarizers that can include packets of film layers. Often, the higher energy wavelengths of light, such as blue light, can adversely affect the aging stability of the film, and at least for this reason it is preferable to minimize the number of interactions of blue light with the reflective polarizer. In addition, the nature of the interaction of blue light with the film affects the severity of the adverse aging. Transmission of blue light through the film is generally less detrimental to the film than reflection of blue light entering from the "blue layers" (that is, thin layers) side. Also, reflection of blue light entering the film from the "blue layers" side is less detrimental to the film than reflection of blue light entering from the "red layers" (that is, thick layers) side. Techniques have been described to reduce the number of interactions of actinic light with the reflective polarizer, as well as to reduce the severity of the interactions.

According to one aspect, the illumination system includes a color-selective dichroic mirror positioned to reflect a blue color light toward the wavelength converting phosphor, and transmit other wavelengths of light to the reflective polarizer. The color-selective dichroic mirror is positioned within a collimating optic, and serves to protect the reflective polarizer from light that can be damaging to the reflective polarizer (that is, actinic light such as higher energy blue or ultraviolet (UV) light). The color-selective dichroic mirror intercepts the blue color light (that is, the potentially damaging light) before intercepting the reflective polarizer. The color-selective dichroic mirror reflects a major portion of the blue color light back for recycling to the phosphor, and can also transmit a minor portion through to the reflective polarizer. In one aspect, the major portion reflected by the color-selective dichroic mirror can be greater than 51%, 60%, 70%, 75%, 80%, 85%, or even greater than 90% of the first color light incident on the color-selective dichroic mirror.

In one aspect, the present disclosure is directed toward further improving the stability of the reflective polarizer in an optical element such as a polarization recycling illuminator, by preventing a majority of the actinic light from ever reaching the reflective polarizer. A color- selective dichroic mirror reflects a major portion of the actinic light, while transmitting the major portions of other wavelengths of light. In one particular embodiment, the color-selective dichroic mirror may be disposed adjacent to the reflective polarizer. In one particular embodiment, the color-selective dichroic mirror can be formed directly on the reflective polarizer. In one particular embodiment, the color-selective dichroic mirror can instead be formed on an optical element such as a diagonal prism face that is then positioned adjacent the reflective polarizer. In one particular embodiment, the color-selective dichroic mirror can be a separate film or plate element that is positioned adjacent the reflective polarizer. In one particular embodiment, the color-selective dichroic mirror can be disposed on or within any optical element of the collimating optic that separates the phosphor from the reflective polarizer, as described elsewhere. The color-selective dichroic mirror can be formed by any known process, such as vacuum deposition of an inorganic dielectric stack. In one aspect of the present disclosure, the blue layers can be eliminated from the reflective polarizer, since a major portion of the blue light is reflected by the color-selective dichroic mirror before the blue light interacts with the reflective polarizer.

In one particular embodiment, the phosphor may be a semiconductor such as II -VI based systems, or phosphors based on nitrides, sulfides, selenides, and aluminum oxides, as described elsewhere. The phosphor may be a broad emitter, including one or more wavelength ranges covering the red, green, or blue spectrum, or it may have a medium bandwidth, covering for example the green portion of the spectrum, or it may be a narrow-band emitter. In some cases, the phosphor layer may be optically thin, meaning that it transmits between 5 and 50% of the excitation wavelength, or more preferably, between 5 and 30% of the light.

The present disclosure describes an LED that remotely illuminates a phosphor, where the LED is coupled to a collimation optic with a material having a relatively low index of refraction, and the phosphor is coupled to the collimation optic with a material having a relatively high index of refraction. In one particular embodiment, the LED and the phosphor may use a common collimation optic; however, separate collimation optics may also be used.

It is generally known that the etendue of a light source is proportional to the square of the refractive index of an encapsulant surrounding the source. Since many optical devices are etendue limited, it is usually preferred that the light source, for example an LED, is encapsulated in a low index material such as air. In some optical devices the LED is used to stimulate a wavelength converting material such as a phosphor or a semiconducting wavelength converter. Many phosphors and semiconducting wavelength converters are much more efficient when immersed in an encapsulant that has a relatively high refractive index. Also, semiconducting wavelength converters may be expensive, or contain hazardous materials, or both. In these cases, it may be desirable to immerse the wavelength converter in a higher index medium to reduce the area required. The disclosed devices have a high optical efficiency, with the LED in a low index encapsulant, and the phosphor in an encapsulant with a higher index, while not substantially increasing the etendue of the system.

In some cases, the LED emits blue light (or UV light), and the reflector reflects the blue

LED light onto the phosphor layer. A portion of the blue LED light can combine with longer wavelength light emitted by the phosphor, to provide a broadband output beam, for example, light having a white appearance. In some cases, the LED and/or the phosphor can be disposed on a substrate, and the LED and phosphor are mounted or attached to the substrate immediately adjacent each other. In one particular embodiment, the substrate can be a flexible substrate or a rigid substrate, and can include a reflective region onto which the phosphor is deposited, as described elsewhere.

In this regard, "light emitting diode" or "LED" refers to a diode that emits light, whether visible, ultraviolet, or infrared. It includes incoherent encased or encapsulated semiconductor devices marketed as "LEDs", whether of the conventional or super radiant variety. An "LED die" is an LED in its most basic form, that is, in the form of an individual component or chip made by semiconductor processing procedures. The pump LED may emit light in the blue or UV range, or both. The LED may include super radiant LEDs, lasers, including laser diodes, as well as conventional LEDs, as described elsewhere.

In some cases, the LED can be a short- wavelength LED capable of emitting UV photons.

In general, the LED may be composed of any suitable materials, such as organic semiconductors or inorganic semiconductors, including Group IV elements such as Si or Ge; III-V compounds such as InAs, AlAs, GaAs, InP, A1P, GaP, InSb, AlSb, GaSb, GaN, A1N, InN and alloys of III-V compounds such as AlGalnP and AlGalnN; II-VI compounds such as ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS and alloys of II-VI compounds, or alloys of any of the compounds listed above.

In some cases, the LED can include one or more p-type and/or n-type semiconductor layers, one or more active layers that may include one or more potential and/or quantum wells, buffer layers, substrate layers, and superstrate layers.

In some cases, the LED can include CdMgZnSe alloys having compounds ZnSe, CdSe, and MgSe as the three constituents of the alloy. In some cases, one or more of Cd, Mg, and Zn, especially Mg, may have zero concentration in the alloy and therefore, may be absent from the alloy. For example, the LCD can further include a light converting element (LCE) that can be used to convert light from one wavelength to another. In some cases, the LCE can include a CdO.70ZnO.30Se quantum well capable of emitting in the red, or a CdO.33ZnO.67Se quantum well capable of emitting in the green. As another example, the LED and/or the LCE can include an alloy of Cd, Zn, Se, and optionally Mg, in which case, the alloy system can be represented by Cd(Mg)ZnSe. As another example, the LED and/or the LCE can include an alloy of Cd, Mg, Se, and optionally Zn. In some cases, a quantum well LCE has a thickness in a range from about 1 nm to about 100 nm, or from about 2 nm to about 35 nm.

In some cases, a semiconductor LED or LCE may be n-doped or p-doped where the doping can be accomplished by any suitable method and by inclusion of any suitable dopant. In some cases, the LED and the LCE are from the same semiconductor group. In some cases, the LED and the LCE are from two different semiconductor groups. For example, in some cases, the LED is a III-V semiconductor device and the LCE is a II-VI semiconductor device. In some cases, the LEDs include AlGalnN semiconductor alloys and the LCEs include Cd(Mg)ZnSe

semiconductor alloys. The LCE may generally be a phosphor such as a phosphor particle in a organic binder, in an inorganic binder, or may be semiconductors such as ZnSe or ZnS compounds.

An LCE can be disposed on or attached to a corresponding electroluminescent element by any suitable method such as by an adhesive such as a hot melt adhesive, welding, pressure, heat or any combinations of such methods. Examples of suitable hot melt adhesives include

semicrystalline polyolefins, thermoplastic polyesters, and acrylic resins.

In one particular embodiment, the LED die may be formed from a combination of one or more Group III elements and of one or more Group V elements (III-V semiconductor). Examples of suitable III-V semiconductor materials include nitrides, such as gallium nitride, and phosphides, such as indium gallium phosphide. Other types of III-V materials can also be used, as well as inorganic materials from other groups of the periodic table. The component or chip can include electrical contacts suitable for application of power to energize the device. Examples include wire bonding, tape automated bonding (TAB), or flip-chip bonding. The individual layers and other functional elements of the component or chip are typically formed on the wafer scale, and the finished wafer can then be diced into individual piece parts to yield a multiplicity of LED dies. The LED die may be configured for surface mount, chip-on-board, or other known mounting configurations. Some packaged LEDs are made by forming a polymer encapsulant over an LED die and an associated reflector cup. An "LED" for purposes of this application should also be considered to include organic light emitting diodes, commonly referred to as OLEDs.

The present disclosure allows etendue matching of an LED source that does not require encapsulation for good efficiency. In some cases, the LED source can be encapsulated in a material having an index of refraction between about 1.0 and about 1.2, or approximately 1.0 (that is, air). In some cases, the LED source may have a limitation in the permissible drive current density. In some cases, a phosphor can operate at a high power density, and for higher efficiency of the pumped system is generally preferred to optically couple the phosphor to a primary optic using an encapsulant.

In one particular embodiment, the area of the LED source is significantly larger than the area of the phosphor, and a focusing optic can be used to increase the angular range illuminating the phosphor, which can be coupled to a focusing optic with an encapsulant having a higher refractive index than the refractive index of the material surrounding the LED. In some cases, the encapsulant can have an index of refraction between about 1.2 and about 1.6, or between about 1.4 and about 1.5, or, for example, about a 1.41 refractive index. In some cases, the etendue of the encapsulated phosphor can be matched with an unencapsulated LED, for example, by concentrating the light from the LED source onto the phosphor by using a tapered rod. The tapered rod may be optically coupled to the collimating optic, or may be separated by an air gap. The phosphor can be optically coupled to the narrower base of the tapered rod with an encapsulant material such as dimethyl silicone. In some cases, a Compound Parabolic Concentrator (CPC) can be used in place of the tapered rod. The CPC or tapered rod may be made from glass or plastic. The phosphor may be bonded to the tapered rod or CPC with a material having a refractive index of about 1.2 or higher, preferably 1.4 or higher, such as, for example, dimethyl silicone.

FIG. 1A shows a cross-section schematic of an illumination system 100 according to one aspect of the disclosure. In FIG. 1A, the illumination system 100 includes a light collection optic 105 including a first lens element 1 10 and a second lens element 120. The light collection optic 105 includes a light input surface 1 14 and an optical axis 107 perpendicular to the light input surface 1 14. A first light source 140 is disposed on a light injection surface 104 that faces the light input surface 114. In some cases, the first light source 140 can be an unpolarized light source. A light conversion region 170 is disposed immediately adjacent the first light source 140 on the light injection surface 104. In some cases, one of the light conversion region 170 and the first light source 140 is disposed on the optical axis 107 and immediately adjacent each other. In some cases, the light conversion region 170 and the first light source 140 are each displaced from the optical axis 107, immediately adjacent each other. Generally, however, the first light source 140 and the light conversion region 170 are disposed in close proximity to the optical axis 107, so that the collimation angles of the light emitted from the first light source 140 and directed through to the light conversion region 170 can be maintained. In one particular embodiment, FIG. 1A shows an arrangement of first light source 140 slightly above the optical axis 107, and the light conversion region 170 disposed on the optical axis 107. In some cases, a second light source (not shown) can be disposed at a position removed from light injection surface 104, to direct a second light directly toward the light conversion region 170.

Any suitable substrate can be used for light injection surface 104, and may include conductive layers or traces to carry electrical power to the LED. The substrate also preferably has a relatively high heat conduction and relatively low thermal resistance in order to effectively carry heat away from the LED and/or phosphor layer so as to maintain lower operating temperatures thereof. To promote such lower operating temperatures, the substrate may include or be thermally coupled to a suitable heat sink, for example, a relatively thick layer of copper, aluminum, or other suitable metal or other thermally conductive material (not shown). In some cases the substrate may be or comprise a highly reflective surface such as a metal mirror, a metal mirror with dielectric coatings to enhance reflectivity, or a diffusely reflective surface such as microvoided polyester or titania filled polymer, or a multilayer optical film such as 3M™ Vikuiti™ Enhanced Specular Reflector (ESR) film. The substrate may also be or comprise any of the substrates discussed elsewhere herein.

The substrate can include a dielectric layer. Suitable dielectric layers include polyesters, polycarbonates, liquid crystal polymers, and polyimides. Suitable polyimides include those available under the trade names KAPTON, available from DuPont; APICAL, available from Kaneka Texas corporation; SKC Kolon PI, available from SKC Kolon PI Inc.; and UPILEX and UPISEL, available from Ube Industries. Polyimides available under the trade designations UPILEX S, UPILEX SN, and UPISEL VT, all available from Ube Industries, Japan, are particularly advantageous in many applications. These polyimides are made from monomers such as biphenyl tetracarboxylic dianhydride (BPDA) and phenyl diamine (PDA).

Additional design details of exemplary flexible substrates suitable for use in the disclosed embodiments can be found in the following commonly owned U.S. patent applications: U.S. application 61/409,796, "Flexible LED Device and Method of Making", filed Nov. 3, 2010

(Attorney Docket 66938US003); U.S. application 61/409,801, "Flexible LED Device for Thermal Management and Method of Making", filed Nov. 3, 2010 (Attorney Docket 67018US002); U.S. application 61/428034, "Remote Phosphor LED Constructions", filed Dec. 29, 2010 (Attorney Docket 67006US002); and U.S. application 61/428038, "LED Color Combiner", filed Dec. 29, 2010 (Attorney Docket 67010US002).

In one particular embodiment, illumination system 100 further includes a wavelength- selective reflector 132 disposed within the light collection optics 105 along the optical axis 107. The wavelength-selective reflector is configured such that light emitted from the first light source 140 is reflected to the light conversion region 170, and as such may include a lens shape. The wavelength-selective reflector 132 can be a dichroic reflector capable of reflecting the first color light 141a and transmitting all other colors of light.

In one particular embodiment, light collection optics 105 can be a light collimation optics 105 that serves to collimate the light emitted from the first light source 140. Light collimation optics 105 can include a one lens light collimator (not shown), a two lens light collimator (shown), a diffractive optical element (not shown), or a combination thereof. The two lens light collimator has first lens element 110 including a first lens portion 1 16 that includes the light input surface 1 14, a second lens portion 1 1 1, and a third lens portion 1 13 that includes a first convex surface 1 12 disposed opposite the light input surface 114. The wavelength-selective reflector 132 is disposed between the first lens portion 1 16 and the second lens portion 1 1 1. The wavelength-selective reflector 132 may be disposed on the first lens portion 1 16, disposed on the second lens portion 1 1 1, disposed on both the first and second lens portions 1 16, 1 1 1 , or it may be a free-standing film positioned between them. Second lens element 120 includes a second surface 122 facing the first convex surface 1 12, and a third convex surface 124 opposite the second surface 122. Second surface 122 can be selected from a convex surface, a planar surface, and a concave surface.

The path of the first color light 141a from first light source 140 can be traced through illumination system 100. First color light 141a includes a first central light ray 142a travelling in the first light propagation direction, and a cone of rays within first input light collimation angle ΘΗ, the boundaries of which are represented by first boundary light rays 144a, 146a. The first central light ray 142a and the first and second boundary light rays 144a, 146a, are injected from first light source 140 into light input surface 1 14 in a direction generally parallel to the optical axis 107, and within a first input light collimation angle ΘΗ. Each of the first boundary light rays 144a, 146a, and the first central light ray 142a reflect from wavelength-selective reflector 132such that each of a first boundary reflected light rays 144b, 146b, and the first central reflected light ray 142b are reflected toward light conversion region 170.

In one particular embodiment as shown in FIG. 1A, the reflected light rays 142b, 144b,

146b, converge to the light conversion region 170 where they are wavelength converted and re- emitted into light collimation optics 105 as a first converted light rays 141c. Light conversion region 170 downconverts a major portion of the reflected light rays 142b, 144b, 146b, and redirects both the first converted light rays 141c and a remaining portion of the incident reflected light rays 142b, 144b, 146b, back into the light collimation optics 105, as described elsewhere.

First boundary converted rays 144c, 146c, and first central converted ray 142c, having a first converted collimation angle Θ 1 o, pass through wavelength-selective reflector 132, travel through light collimation optics 105, pass through an optional retarder 136, and intercept reflective polarizer 134. First converted light rays 141c are split by the reflective polarizer 134 into transmitted converted light rays 142d, 144d, 146d having the first polarization state (for example, p-polarized converted light), and reflected converted light rays 142e, 144e, 146e having the second polarization state (for example, s-polarized converted light). The s-polarized converted light rays 142e, 144e, 146e travel back through optional retarder 136, light collimation optics 105, wavelength-selective reflector 132, and are focused again on light conversion region 170 where they are reflected (and possibly de -polarized by the scattering in the phosphor layer) back along the same path as the first converted light rays 141c. In one particular embodiment, the optional retarder can aid depolarization of the converted light recycled back to the phosphor by partial rotation of the polarization state, as described elsewhere.

In one particular embodiment, the input collimation angles ΘΗ can be the same as the converted collimation angle θΐο, and injection optics (not shown) associated with the first light source 140 can restrict these input collimation angles to angles between about 10 degrees and about 80 degrees, or between about 10 degrees to about 70 degrees, or between about 10 degrees to about 60 degrees, or between about 10 degrees to about 50 degrees, or between about 10 degrees to about 40 degrees, or between about 10 degrees to about 30 degrees or less. In some cases, the light collimation optics 105 and the wavelength-selective reflector 132 can be fabricated such that the converted collimation angle Θ 1 o can be the same, and also substantially equal to the input collimation angle ΘΗ. In one particular embodiment, each of the input collimation angle ranges from about 60 to about 70 degrees, and the converted collimation angles also ranges from about 60 to about 70 degrees.

FIG. IB shows a cross-section schematic of an illumination system 101 according to one aspect of the disclosure. Each of the elements 104-170 shown in FIG. IB correspond to like- numbered elements shown in FIG. 1 A, which have been described previously.

In one particular embodiment, light collection optics 105 can be a light collimation optics 105 that serves to collimate the light emitted from the first light source 140. Light collimation optics 105 can include a one lens light collimator (not shown), a two lens light collimator (shown), a diffractive optical element (not shown), or a combination thereof. The two lens light collimator has first lens element 1 10 that includes a first convex surface 1 12 disposed opposite the light input surface 1 14. The wavelength-selective reflector 132 is disposed on first convex surface 1 12. Second lens element 120 includes a second surface 122 facing the first convex surface 1 12, and a third convex surface 124 opposite the second surface 122. Second surface 122 can be selected from a convex surface, a planar surface, and a concave surface.

In one particular embodiment as shown in FIG. IB, the reflected light rays 142b, 144b, 146b, converge to the light conversion region 170 where they are wavelength converted and re- emitted into light collimation optics 105 as a first converted light rays 141c. Light conversion region 170 downconverts a major portion of the reflected light rays 142b, 144b, 146b, and re- directs both the first converted light rays 141c and a remaining portion of the incident reflected light rays 142b, 144b, 146b, back into the light collimation optics 105, as described elsewhere.

FIG. 1 C shows a cross-section schematic of an illumination system 102 according to one aspect of the disclosure. Each of the elements 104- 170 shown in FIG. 1 C correspond to like- numbered elements shown in FIG. 1 A, which have been described previously.

In one particular embodiment, light collection optics 105 can be a light collimation optics 105 that serves to collimate the light emitted from the first light source 140. Light collimation optics 105 can include a one lens light collimator (not shown), a two lens light collimator (shown), a diffractive optical element (not shown), or a combination thereof. The two lens light collimator has first lens element 1 10 that includes a first convex surface 1 12 disposed opposite the light input surface 1 14. Second lens element 120 has a fourth lens portion 121 that includes a second surface 122 facing the first convex surface 1 12, a fifth lens portion 125 disposed adjacent the fourth lens portion 121, and a sixth lens portion 123 disposed adjacent the fifth lens portion 125 and having a third convex surface 124 opposite the second surface 122. The wavelength-selective reflector 132 is disposed between the fifth lens portion 125 and the sixth lens portion 123. The wavelength- selective reflector 132 may be disposed on the fifth lens portion 125, disposed on the sixth lens portion 123, disposed on both the fifth and sixth lens portions 125, 123, or it may be a freestanding film positioned between them. Second surface 122 can be selected from a convex surface, a planar surface, and a concave surface.

The path of the first color light 141a from first light source 140 can be traced through illumination system 100. First color light 141a includes a first central light ray 142a travelling in the first light propagation direction, and a cone of rays within first input light collimation angle ΘΗ, the boundaries of which are represented by first boundary light rays 144a, 146a. The first central light ray 142a and the first and second boundary light rays 144a, 146a,are injected from first light source 140 into light input surface 1 14 in a direction generally parallel to the optical axis 107, and within a first input light collimation angle ΘΗ. Each of the first boundary light rays 144a, 146a, and the first central light ray 142a reflect from wavelength-selective reflector 132such that each of a first boundary reflected light rays 144b, 146b, and the first central reflected light ray 142b are reflected toward light conversion region 170.

In one particular embodiment as shown in FIG. 1C, the reflected light rays 142b, 144b, 146b, converge to the light conversion region 170 where they are wavelength converted and re- emitted into light collimation optics 105 as a first converted light rays 141c. Light conversion region 170 downconverts a major portion of the reflected light rays 142b, 144b, 146b, and redirects both the first converted light rays 141c and a remaining portion of the incident reflected light rays 142b, 144b, 146b, back into the light collimation optics 105, as described elsewhere.

First converted light rays 141c include first boundary converted rays 144c, 146c, and first central converted ray 142c having a first converted collimation angle θΐο. First central converted ray 142c travels back through light collimation optics 105 generally along the same path (but in the opposite propagation direction) as central reflected light ray 142b. In one particular embodiment, light conversion region 170 can be configured so that first boundary converted rays 144c, 146c also travel back through light collimation optics 105 generally along the same path (but in the opposite propagation direction) as first boundary reflected light rays 144b, 146b.

First boundary converted rays 144c, 146c, and first central converted ray 142c, having a first converted collimation angle Θ 1 o, travel through light collimation optics 105 passing through wavelength-selective reflector 132, pass through an optional retarder 136, and intercept reflective polarizer 134. First converted light rays 141c are split by the reflective polarizer 134 into transmitted converted light rays 142d, 144d, 146d having the first polarization state (for example, p-polarized converted light), and reflected converted light rays 142e, 144e, 146e having the second polarization state (for example, s-polarized converted light). The s-polarized converted light rays 142e, 144e, 146e travel back through optional retarder 136, light collimation optics 105, wavelength-selective reflector 132, and are focused again on light conversion region 170 where they are reflected (and possibly de -polarized by the scattering in the phosphor layer) back along the same path as the first converted light rays 141c. In one particular embodiment, the optional retarder can aid depolarization of the converted light recycled back to the phosphor by partial rotation of the polarization state, as described elsewhere. FIG. ID shows a cross-section schematic of an illumination system 103 according to one aspect of the disclosure. Each of the elements 104-170 shown in FIG. ID correspond to like- numbered elements shown in FIG. 1 A, which have been described previously.

In one particular embodiment, light collection optics 105 can be a light collimation optics 105 that serves to collimate the light emitted from the first light source 140. Light collimation optics 105 can include a one lens light collimator (not shown), a two lens light collimator (shown), a diffractive optical element (not shown), or a combination thereof. The two lens light collimator has first lens element 1 10 that includes a first convex surface 1 12 disposed opposite the light input surface 1 14. Second lens element 120 includes a second surface 122 facing the first convex surface 1 12, and a third convex surface 124 opposite the second surface 122. The wavelength- selective reflector 132 is disposed on the third convex surface 124. Second surface 122 can be selected from a convex surface, a planar surface, and a concave surface.

The path of the first color light 141a from first light source 140 can be traced through illumination system 100. First color light 141a includes a first central light ray 142a travelling in the first light propagation direction, and a cone of rays within first input light collimation angle ΘΗ, the boundaries of which are represented by first boundary light rays 144a, 146a. The first central light ray 142a is injected from first light source 140 into light input surface 114 in a direction generally parallel to the optical axis 107, and within a first input light collimation angle ΘΗ. The first central light ray 142a passes through first lens element 1 10, second lens element 120, and reflects from wavelength-selective reflector 132 such that the first central reflected light ray 142b is coincident with the optical axis 107 as shown in FIG. 1. Each of the first boundary light rays 144a, 146a, are injected into the light input surface 1 14 in a direction generally at the first input light collimation angle ΘΗ to the optical axis 107, pass through first lens element 110, second lens element 120, and reflects from wavelength-selective reflector 132 such that the first boundary reflected light rays 144b, 146b, respectively, are generally parallel to the optical axis 107 as shown, before re-entering light collimation optics 105. As can be seen from FIG. ID, the light collimation optics 105 can serve to collimate the first color light 141a passing from the first light source 140 to the wavelength-selective reflector 132.

Each of the first central light ray 142a and the first boundary light rays 144a, 146a, reflect from the wavelength-selective reflector 132 and travel back through the light collimation optics 105 as central reflected light ray 142b and a first and a second boundary reflected light rays 144b, 146b that are collimated and essentially parallel to, and in some cases centered upon (for example, as shown in FIG. 1), the optical axis 107. In one particular embodiment as shown in FIG. ID, the reflected light rays 142b, 144b, 146b, converge to the light conversion region 170 where they are wavelength converted and re-emitted into light collimation optics 105 as a first converted light rays 141c. Light conversion region 170 downconverts a major portion of the reflected light rays 142b, 144b, 146b, and re-directs both the first converted light rays 141c and a remaining portion of the incident reflected light rays 142b, 144b, 146b, back into the light collimation optics 105, as described elsewhere.

First boundary converted rays 144c, 146c, and first central converted ray 142c, having a first converted collimation angle Θ 1 o, travel through light collimation optics 105 passing through wavelength-selective reflector 132, pass through an optional retarder 136, and intercept reflective polarizer 134. First converted light rays 141c are split by the reflective polarizer 134 into transmitted converted light rays 142d, 144d, 146d having the first polarization state (for example, p-polarized converted light), and reflected converted light rays 142e, 144e, 146e having the second polarization state (for example, s-polarized converted light). The s-polarized converted light rays 142e, 144e, 146e travel back through optional retarder 136, light collimation optics 105, wavelength-selective reflector 132, and are focused again on light conversion region 170 where they are reflected (and possibly de -polarized by the scattering in the phosphor layer) back along the same path as the first converted light rays 141c. In one particular embodiment, the optional retarder can aid depolarization of the converted light recycled back to the phosphor by partial rotation of the polarization state, as described elsewhere.

Although the foregoing description has been directed toward an illuminator that generates polarized light, it is to be understood that the illuminator can also be used effectively to generate unpolarized light by eliminating the reflective polarizer 134 (and also the optional retarder 136). Such elimination can reduce polarization recycling and therefore also reduce the light conversion efficiency. The unpolarized light can be converted to polarized light by other techniques, such as described elsewhere and as known to one of skill in the art.

FIG. 2A shows a schematic view near the light conversion region 170 of the illumination systems 100- 103 shown in FIGS. 1A- 1D, according to one aspect of the disclosure. Each of the elements 104-170 shown in FIG. 2A correspond to like -numbered elements shown in FIGS. 1A- 1D, which have been described previously. In FIG. 2A, the light conversion region 170 includes a phosphor 150 disposed on a reflective region 106 of light injection surface 104 and surrounded by an encapsulant 155. Encapsulant 155 has an index of refraction greater than the index of refraction of the material surrounding the first light source 140, as described elsewhere. Encapsulant 155 can be any of the encapsulating materials described previously, such as, for example, dimethyl silicone. In some cases, encapsulant 155 can completely fill the separation between the light injection surface 104 and the light input surface 114.

In some cases, encapsulant 155 can instead be fabricated as a lens that includes a curved surface 156 (as shown in FIG. 2A), to focus the reflected light rays 142b, 144b, 146b that exit light input surface 1 14 onto the phosphor 150. Upon intercepting phosphor 150, a major portion of reflected light rays 142b, 144b, 146b, are wavelength downconverted to become converted light rays 142c, 144c, 146c, and are emitted to re-enter illumination system 100 as converted light rays 142c, 144c, 146c having the converted collimation angle θΐο. In some cases, converted collimation angle θ2ο may be the same as input collimation angle ΘΗ.

FIG. 2B shows a schematic view near the light conversion region 170 of the illumination systems 100- 103 shown in FIGS. 1A- 1D, according to one aspect of the disclosure. Each of the elements 104-170 shown in FIG. 2B correspond to like-numbered elements shown in FIGS. 1A-

1D, which have been described previously. In FIG. 2B, the light conversion region 170 includes a phosphor 150 disposed on a reflective region 106 of light injection surface 104 and surrounded by an encapsulant 155. Encapsulant 155 has an index of refraction greater than the index of refraction of the material surrounding the first light source 140, as described elsewhere. Encapsulant 155 can be any of the encapsulating materials described previously, such as, for example, dimethyl silicone. In some cases, encapsulant 155 can completely fill the separation between the light injection surface 104 and the light input surface 114.

In some cases, encapsulant 155 can be fabricated as a tapered rod 157 (as shown in FIG. 2B), to focus the reflected light rays 142b, 144b, 146b that exit light input surface 1 14 onto the phosphor 150. Tapered rod 157 can be any of the tapered rods described elsewhere, and may have reflective surfaces or polished surfaces to enable TIR from the surfaces. Tapered rod 157 is configured to transport and further concentrate output light rays 141c. Upon intercepting phosphor 150, a major portion of reflected light rays 142b, 144b, 146b, are wavelength downconverted to become converted light rays 142c, 144c, 146c, and are emitted to re-enter illumination system 100 as converted light rays 142c, 144c, 146c having the converted collimation angle θΐο. In some cases, converted collimation angle θ2ο may be the same as input collimation angle ΘΗ.

FIG. 2C shows a schematic view near the light conversion region 170 of the illumination systems 100- 103 shown in FIGS. 1A- 1D, according to one aspect of the disclosure. Each of the elements 104-170 shown in FIG. 2C correspond to like-numbered elements shown in FIGS. 1A- ID, which have been described previously. In FIG. 2C, the light conversion region 170 includes a phosphor 150 disposed on a reflective region 106 of light injection surface 104 and surrounded by an encapsulant 155. Encapsulant 155 has an index of refraction greater than the index of refraction of the material surrounding the first light source 140, as described elsewhere. Encapsulant 155 can be any of the encapsulating materials described previously, such as, for example, dimethyl silicone. In some cases, encapsulant 155 can completely fill the separation between the light injection surface 104 and the light input surface 114.

In some cases, encapsulant 155 can be fabricated as a CPC 158 (as shown in FIG. 2C), to focus the reflected light rays 142b, 144b, 146b that exit light input surface 1 14 onto the phosphor 150. CPC 158 can be any of the CPCs described elsewhere, and may have reflective surfaces or polished surfaces to enable TIR from the surfaces. CPC 158 is configured to transport and further concentrate output light rays 141c. Upon intercepting phosphor 150, a major portion of reflected light rays 142b, 144b, 146b, are wavelength downconverted to become converted light rays 142c, 144c, 146c, and are emitted to re-enter illumination system 100 as converted light rays 142c, 144c, 146c having the converted collimation angle θΐο. In some cases, converted collimation angle θ2ο may be the same as input collimation angle ΘΗ.

Phosphor 150 can be any of the phosphors described elsewhere, and in some cases, can include more than one type of phosphor so that the downconverted light includes more than one wavelength of light. In some cases (not shown), the downconverted light from a first phosphor can be used to excite a second phosphor to further downconvert the light to a different wavelength light. In some cases (also not shown), a portion of the downconverted light from a first phosphor can reflect from a dichroic mirror in a manner similar to the first color light 141a as described with reference to any of FIGS. 1A- 1D, and excite a second phosphor to further downconvert the light to a different wavelength light.

FIG. 3 shows a schematic diagram of an image projector 1, according to one aspect of the disclosure. Image projector 1 includes an illuminator module 10 that is capable of injecting a partially collimated polarized light output 24 into an optional homogenizing polarization converter module 30 where the partially collimated polarized light output 24 becomes converted to a homogenized polarized light 45 that exits the optional homogenizing polarization converter module 30 and enters an image generator module 50. The image generator module 50 outputs an imaged light 65 that enters a projection module 70 where the imaged light 65 becomes a projected imaged light 80.

In one aspect, illuminator module 10 includes an input light source that is input through a light collimation optics 105 in illumination system 100, as described elsewhere. The illumination system 100 produces a light output that exits illuminator module 10 as partially collimated polarized light output 24, as described elsewhere. The partially collimated polarized light output 24 can be a polychromatic combined polarized light that comprises more than one wavelength spectrum of light. For purposes of the description provided herein, "color light" and "wavelength spectrum light" are both intended to mean light having a wavelength spectrum range which may be correlated to a specific color if visible to the human eye. The more general term "wavelength spectrum light" refers to both visible and other wavelength spectrums of light including, for example, infrared light.

According to one aspect, each input light source comprises one or more light emitting diodes (LED's). Various light sources can be used such as lasers, laser diodes, organic LED's (OLED's), and non solid state light sources such as ultra high pressure (UHP), halogen or xenon lamps with appropriate collectors or reflectors. Light sources, light collimators, lenses, and light integrators useful in the present invention are further described, for example, in Published U.S. Patent Application No. US 2008/0285129, the disclosure of which is herein included in its entirety.

In one aspect, optional homogenizing polarization converter module 30 includes a polarization converter 40 that is capable of converting partially collimated light output 24 into homogenized polarized light 45. Optional homogenizing polarization converter module 30 further can include a monolithic array of lenses 42, such as a optional monolithic FEA of lenses described elsewhere that can homogenize and improve the uniformity of the partially collimated polarized light output 24 that exits the optional homogenizing polarization converter module 30 as homogenized polarized light 45. Representative arrangements of optional FEA associated with the optional homogenizing polarization converter module 30 are described, for example, in co-pending U.S. Patent Serial Nos. 61/346183 entitled FLY EYE INTEGRATOR POLARIZATION

CONVERTER (Attorney Docket No. 66247US002, filed May 19, 2010); 61/346190 entitled POLARIZED PROJECTION ILLUMINATOR (Attorney Docket No. 66249US002, filed May 19, 2010); and 61/346193 entitled COMPACT ILLUMINATOR (Attorney Docket No. 66360US002, filed May 19, 2010). In some cases (not shown), optional homogenizing polarization converter module 30 can be eliminated, wholly or in part, since the output of illuminator module 10 can include a partially collimated polarized light output 24 which can be suitable for input into image generator module 50, described below.

In one aspect, image generator module 50 includes a polarizing beam splitter (PBS) 56, representative imaging optics 52, 54, and a spatial light modulator 58 that cooperate to convert the homogenized polarized light 45 into an imaged light 65. Suitable spatial light modulators (that is, image generators) have been described previously, for example, in U.S. Patent Nos. 7,362,507 (Duncan et al.), 7,529,029 (Duncan et al.); in U.S. Publication No. 2008-0285129-A1 (Magarill et al.); and also in PCT Publication No. WO2007/016015 (Duncan et al.). In one particular embodiment, homogenized polarized light 45 is a divergent light originating from each lens of the optional FEA. After passing through imaging optics 52, 54 and PBS 56, homogenized polarized light 45 becomes imaging light 60 that uniformly illuminates the spatial light modulator. In one particular embodiment, each of the divergent light ray bundles from each of the lenses in the optional FEA illuminates a major portion of the spatial light modulator 58 so that the individual divergent ray bundles overlap each other.

In one aspect, projection module 70 includes representative projection optics 72, 74, 76, that can be used to project imaged light 65 as projected light 80. Suitable projection optics 72, 74, 76 have been described previously, and are well known to those of skill in the art.

Following are a list of embodiments of the present disclosure.

Item 1 is an illumination system, comprising: a light emitting diode (LED) disposed on a substrate and configured to inject a first light beam along a first propagation direction through a collimating optic; a wavelength selective reflector within the collimating optic to reflect the first light beam back through the collimating optic; and a phosphor disposed immediately adjacent the LED, the phosphor capable of downconverting a major portion of the first light beam to become a second light beam propagating in a second propagation direction back through the collimating optic and through the wavelength selective reflector.

Item 2 is the illumination system of item 1 , wherein the collimating optic comprises a first lens element adjacent the substrate and a second lens element adjacent the first lens element and opposite the substrate, the wavelength selective reflector being disposed on an outer surface of the first or second lens element, or embedded within the first or second lens element.

Item 3 is the illumination system of item 1 or item 2, wherein the wavelength selective reflector comprises a curved surface capable of focusing the first light beam on the phosphor.

Item 4 is the illumination system of item 1 to item 3, further comprising a reflective polarizer disposed adjacent the collimating optic and opposite the substrate, wherein the reflective polarizer is configured to reflect a second polarization direction of the second light beam back through the collimating optic to focus on the phosphor, and transmit a first polarization direction of the second light beam.

Item 5 is the illumination system of item 1 to item 4, wherein the collimating optic comprises an optical axis and at most one of the LED or the phosphor are disposed on the optical axis.

Item 6 is the illumination system of item 1 to item 5, wherein the phosphor comprises an encapsulated phosphor.

Item 7 is the illumination system of item 6, wherein the encapsulated phosphor comprises an encapsulant having an index of refraction between about 1.2 and about 1.6. Item 8 is the illumination system of item 6 or item 7, wherein the encapsulated phosphor comprises an encapsulant having an index of refraction between about 1.4 and about 1.5.

Item 9 is the illumination system of item 1 to item 8, further comprising a low-index material having an index of refraction between about 1.0 and about 1.2 between the LED and the collimating optic.

Item 10 is the illumination system of item 9, wherein the low index material is air.

Item 1 1 is the illumination system of item 1 to item 10, wherein the first light beam comprises first light rays propagating within a first collimation angle of the first propagation direction.

Item 12 is the illumination system of item 1 to item 11, wherein the second light beam comprises second light rays propagating within a second collimation angle of a second propagation direction opposite the first propagation direction.

Item 13 is the illumination system of item 6 to item 12, wherein the encapsulated phosphor comprises dimethyl silicone encapsulant.

Item 14 is the illumination system of item 1 to item 13, further comprising a second LED disposed to inject a third light beam directly toward the phosphor.

Item 15 is the illumination system of item 1 to item 14, wherein the phosphor is disposed on a reflective substrate.

Item 16 is the illumination system of item 1 to item 15, further comprising a focusing optical element disposed between the phosphor and the collimating optic, the focusing optical element capable of concentrating the first light beam.

Item 17 is the illumination system of item 16, wherein the focusing optical element comprises a tapered glass rod or a Compound Parabolic Concentrator (CPC).

Item 18 is the illumination system of item 4 to item 17, further comprising a retarder disposed between the phosphor and the reflective polarizer.

Item 19 is the illumination system of item 18, wherein the retarder is a quarter- wave retarder having a fast axis oriented at an angle of 22.5 degrees to the fast-axis of the reflective polarizer.

Item 20 is the illumination system of item 4 to item 19, wherein the reflective polarizer comprises a cholesteric reflective polarizer, a MacNeille reflective polarizer, a wire grid reflective polarizer, or a multilayer optical film (MOF) reflective polarizer.

Item 21 is the illumination system of item 1 to item 20, wherein the wavelength selective reflector comprises a blue light reflector or an ultraviolet light reflector.

Item 22 is an image projector, comprising: an illumination system, comprising: a light emitting diode (LED) disposed on a substrate and configured to inject a first light beam along a first propagation direction through a collimating optic; a wavelength selective reflector within the collimating optic to reflect the first light beam back through the collimating optic; a phosphor disposed immediately adjacent the LED, the phosphor capable of downconverting a major portion of the first light beam to become a second light beam propagating in a second propagation direction back through the collimating optic and through the wavelength selective reflector; a polarization converter capable of converting the second light beam to a third light beam having a first polarization direction; an imager disposed to intercept the first polarization direction of the second light beam; and projection optics.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. An illumination system, comprising:

a light emitting diode (LED) disposed on a substrate and configured to inject a first light beam along a first propagation direction through a collimating optic;

a wavelength selective reflector within the collimating optic to reflect the first light beam back through the collimating optic; and a phosphor disposed immediately adjacent the LED, the phosphor capable of downconverting a major portion of the first light beam to become a second light beam propagating in a second propagation direction back through the collimating optic and through the wavelength selective reflector.

2. The illumination system of claim 1, wherein the collimating optic comprises a first lens element adjacent the substrate and a second lens element adjacent the first lens element and opposite the substrate, the wavelength selective reflector being disposed on an outer surface of the first or second lens element, or embedded within the first or second lens element.

3. The illumination system of claim 1, wherein the wavelength selective reflector comprises a curved surface capable of focusing the first light beam on the phosphor.

4. The illumination system of claim 1, further comprising a reflective polarizer disposed adjacent the collimating optic and opposite the substrate, wherein the reflective polarizer is configured to reflect a second polarization direction of the second light beam back through the collimating optic to focus on the phosphor, and transmit a first polarization direction of the second light beam.

5. The illumination system of claim 1, wherein the collimating optic comprises an optical axis and at most one of the LED or the phosphor are disposed on the optical axis.

6. The illumination system of claim 1, wherein the phosphor comprises an encapsulated phosphor.

7. The illumination system of claim 6, wherein the encapsulated phosphor comprises an encapsulant having an index of refraction between about 1.2 and about 1.6.

8. The illumination system of claim 6, wherein the encapsulated phosphor comprises an encapsulant having an index of refraction between about 1.4 and about 1.5.

9. The illumination system of claim 1, further comprising a low- index material having an index of refraction between about 1.0 and about 1.2 between the LED and the collimating optic.

10. The illumination system of claim 9, wherein the low- index material is air.

1 1. The illumination system of claim 1 , wherein the first light beam comprises first light rays propagating within a first collimation angle of the first propagation direction.

12. The illumination system of claim 1, wherein the second light beam comprises second light rays propagating within a second collimation angle of the second propagation direction opposite the first propagation direction.

13. The illumination system of claim 6, wherein the encapsulated phosphor comprises dimethyl silicone encapsulant.

14. The illumination system of claim 1, further comprising a second LED disposed to inject a third light beam directly toward the phosphor.

15. The illumination system of claim 1, wherein the phosphor is disposed on a reflective substrate.

16. The illumination system of claim 1, further comprising a focusing optical element disposed between the phosphor and the collimating optic, the focusing optical element capable of concentrating the first light beam.

17. The illumination system of claim 16, wherein the focusing optical element comprises a tapered glass rod or a Compound Parabolic Concentrator (CPC).

18. The illumination system of claim 4, further comprising a retarder disposed between the phosphor and the reflective polarizer.

19. The illumination system of claim 18, wherein the retarder is a quarter- wave retarder having a fast axis oriented at an angle of 22.5 degrees to the fast-axis of the reflective polarizer.

20. The illumination system of claim 4, wherein the reflective polarizer comprises a cholesteric reflective polarizer, a MacNeille reflective polarizer, a wire grid reflective polarizer, or a multilayer optical film (MOF) reflective polarizer.

21. The illumination system of claim 1 , wherein the wavelength selective reflector comprises a blue light reflector or an ultraviolet light reflector.

22. An image projector, comprising:

an illumination system, comprising:

a wavelength selective reflector within the collimating optic to reflect the first light beam back through the collimating optic;

a phosphor disposed immediately adjacent the LED, the phosphor capable of downconverting a major portion of the first light beam to become a second light beam propagating in a second propagation direction back through the collimating optic and through the wavelength selective reflector;

a polarization converter capable of converting the second light beam to a third light beam having a first polarization direction;

an imager disposed to intercept the first polarization direction of the second light beam; and

projection optics.