Patent Publication Number: US-2011062469-A1

Title: Molded lens incorporating a window element

Description:
STATEMENT OF GOVERNMENT SPONSORED RESEARCH 
     One or more embodiments of this invention were made with Government support under contract no. DE-FC26-08NT01583 awarded by Department of Energy. The Government has certain rights in this invention. 
    
    
     FIELD OF INVENTION 
     The present disclosure relates to light emitters with light-emitting devices (LEDs). 
     DESCRIPTION OF RELATED ART 
       FIG. 1  illustrates a cross-sectional view of a light emitter  100 . Light emitter  100  includes a light-emitting device (LED) die  102  and a phosphor layer  104  on the LED die. LED die  102  is mounted on a support  106 . Support  106  may include conductive traces and leads that couple LED die  102  to external components. Support  106  may also include a heat sink to dissipate heat from light emitter  100 . 
     A lens  108  is mounted to support  106  over LED die  102  and phosphor layer  104 , and an encapsulant  110  inside the lens seals the LED die and the phosphor layer. Exposed to light, heat, and/or humidity, lens  108  and/or encapsulant  110  may turn yellow or brown under high power short wavelength blue or ultraviolet (UV) LED operation. 
     SUMMARY 
     In one or more embodiments of the present disclosure, a light emitter includes a light-emitting device (LED) die and an optical element over or proximate to the LED die. The optical element may include a lens, a window element, and a bond at an interface disposed between the lens and the window element. The window element may be a wavelength converting element or an optically flat plate. The window element may be directly bonded or fused to the lens, or the window element may be bonded by one or more intermediate bonding layers to the lens. The bond between the window element and the lens may have a refractive index similar to that of the window element, the lens, or both. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  illustrates a cross-sectional view of a prior art light emitter; 
         FIGS. 2A ,  2 B,  3 A,  3 B,  4 A, and  4 B illustrate cross-sectional views of a light emitter in embodiments of the present disclosure; 
         FIG. 5  illustrates an apparatus that can be used in a process for forming a bond between a lens and a window element in one or more embodiments of the present disclosure; 
         FIGS. 6 to 13  illustrate cross-sectional views of various types of lenses with window elements in embodiments of the present disclosure; 
         FIGS. 14 and 15  illustrate cross-sectional views of light emitters in embodiments of the present disclosure; 
         FIG. 16  illustrates an apparatus that can be used in a process for forming bonding layers on a window element in one or more embodiments of the present disclosure; 
         FIG. 17  illustrates a window element with bonding layers that can be formed in the apparatus of  FIG. 16  in one or more embodiments of the present disclosure; 
         FIG. 18  illustrates an apparatus that can be used in a process for forming a bonding layer on a lens in one or more embodiments of the present disclosure; 
         FIG. 19  illustrates a lens with a bonding layer that can be formed in the apparatus of  FIG. 18  in one or more embodiments of the present disclosure; and 
         FIG. 20  is a cross-sectional view of a lens including grooves in the shape of a Fresnel lens in one or more embodiments of the present disclosure. 
     
    
    
     Use of the same reference numbers in different figures indicates similar or identical elements. 
     DETAILED DESCRIPTION 
       FIG. 2A  illustrates a cross-sectional view of a light emitter  200  in accordance with one or more embodiments of the present disclosure. Light emitter  200  includes an LED die  202  mounted on a support  204 . 
     LED die  202  includes an n-type layer, a light-emitting layer (commonly referred to as the “active region”) proximate the n-type layer, a p-type layer proximate the light-emitting layer, and a conductive reflective layer proximate the p-type layer. In one or more embodiments, a conductive transparent contact layer may be used, such as indium tin oxide, aluminum doped zinc oxide, and zinc doped indium oxide for example. Depending on the embodiment, n- and p-type metal contacts to the n and the p-type layers may be disposed on the same side of LED die  202  in a “flip chip” arrangement. The semiconductor layers are epitaxially grown on a substrate or superstrate, which may be removed so that only the epitaxial layers remain. 
     Support  204  may include a housing  206  with electrical leads, a heat sink  208  in the housing, and a submount  210  mounted on the heat sink. LED die  202  is mounted on submount  210  via contact elements  212 , such as solder, gold, or gold-tin interconnects. Submount  210  may include a substrate with through-vias or may include on-submount redistribution of the metal pattern of LED die  202 . Bond wires may couple bond wire pads on submount  210  to the electrical leads of housing  206 , which pass electrical signals between light emitter  200  and external components. 
     An underfill may be applied between LED die  202  and submount  210 . The underfill may provide mechanical support and may seal voids between LED die  202  and submount  210  from contaminants. The underfill may block any edge emission from the side of LED die  202 . The underfill material may have good thermal conductivity and may have a coefficient of thermal expansion (CTE) that approximately matches at least one of the LED die  202 , submount  210 , and contact elements  212 . Additionally, the underfill material may have a CTE that approximately matches at least one of a lens  214 , a window element  222 , a first silicone  230 , and a second silicone  232  as described later, or at least one of a lens  314 , a bonding layer  330 , and a protective side coating  332  as described later. CTEs may be matched to within 500% or less in one or more embodiments, to within 100% or less in one or more embodiments, to within 50% or less in one or more embodiments, and to within 30% or less of each other in one or more embodiments. The underfill material may be epoxy or silicone, and may have a fill material. 
     More information can be found in U.S. Pat. Nos. 7,462,502, 7,419,839, 7,279,345, 7,064,355, 7,053,419, and 6,946,309, and U.S. Patent App. Pub. No. 20050247944, which are commonly assigned and incorporated by reference in their entirety. 
     An optical element is located over or proximate to LED die  202 . In one or more embodiments of the present disclosure, the optical element includes a high index lens  214  that extracts light from LED die  202 . Lens  214  includes a cavity  216  with a ceiling  218 . Lens  214  has a refractive index (RI) greater than a conventional silicone lens. Lens  214  may have a RI of 1.5 or greater (e.g., 1.7 or greater) at the wavelengths emitted by LED die  202 . Lens  214  may have a shape and a size such that light entering the lens from LED die  202  will intersect a lens exit surface  220  at near normal incidence, thereby increasing light output by reducing total internal reflection at the interface between the lens exit surface and the ambient medium (e.g., air). 
     Lens  214  may be a hemispheric lens or a Fresnel lens. Lens  214  may also be an optical concentrator, which includes total internal reflectors and optical elements having a wall coated with a reflective metal, a dielectric material, or a reflective coating to reflect or redirect incident light. An example of a reflective coating is the Munsell White Reflectance Coating from Munsell Color Services of New York. 
     Lens  214  may be formed from any combination of optical glass, high index glass, sapphire, diamond, silicon carbide, alumina, III-V semiconductors such as gallium phosphide, II-VI semiconductors such as zinc sulfide, zinc selenide, and zinc telluride, group IV semiconductors and compounds, metal oxides, metal fluorides, an oxide of any of the following: aluminum, antimony, arsenic, bismuth, calcium, copper, gallium, germanium, lanthanum, lead, niobium, phosphorus, tellurium, thallium, titanium, tungsten, zinc, or zirconium, polycrystalline aluminum oxide (transparent alumina), aluminum oxynitride (AlON), cubic zirconia (CZ), gadolinium gallium garnet (GGG), gallium phosphide (GaP), lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT), silicon aluminum oxynitride (SiAlON), silicone carbide (SiC), silicon oxynitride (SiON), strontium titanate, yttrium aluminum garnet (YAG), zinc sulfide (ZnS), spinel, Schott glass LaFN21, LaSFN35, LaF2, LaF3, LaF10, NZK7, NLAF21, LaSFN18, SF59, or LaSF3, Ohara glass SLAM60 or SLAH51, or any combination thereof. Schott glasses are available from Schott Glass Technologies Incorporated, of Duryea, Pa., and Ohara glasses are available from Ohara Corporation in Somerville, N.J. 
     Lens  214  may include luminescent material that converts light of wavelengths emitted by LED die  202  to other wavelengths. In one or more embodiments, a coating on lens exit surface  220  of lens  214  includes the luminescent material. The luminescent material may include conventional phosphor particles, organic semiconductors, II-VI or III-V semiconductors, II-VI or III-V semiconductor quantum dots or nano-crystals, dyes, polymers, or materials such as gallium nitride (GaN) that luminesce. Alternatively, a region of lens  214  near lens exit surface  220  may be doped with a luminescent material. Alternatively, lens  214  may contain a wavelength converting region. Lens  214  may include an anti-reflection coating (AR), either single or multi-layer, on lens exit surface  220  to further suppress reflection at the exit surface. 
     Lens  214  may also comprise any of the materials listed later for window element  222 , bonding layer  219 , bonding layer  330 , bonding layer  1402 , and bonding layer  1410 . 
     More information can be found in U.S. Pat. Nos. 7,279,345, 7,064,355, 7,053,419, 7,009,213, 7,462,502, and 7,419,839, which are commonly assigned and incorporated by reference in their entirety. 
     In one or more embodiments of the present disclosure, the optical element includes a window element  222  that modifies the emission spectrum of LED die  202 , provides a flat optical surface, or both. Window element  222  may be directly bonded or fused to ceiling  218  of lens  214  to form an integral element. Window element  222  may be directly bonded or fused to ceiling  218  of lens  214 , for example, during a molding process. Window element  222  may be placed on ceiling  218  before or while lens  214  becomes solid or hard, for example, by cooling or curing for example in a mold. Window element  222  may also be embedded into lens  214  at ceiling  218  by molding the lens under or over the window element for example in a mold. 
     Alternatively,  FIG. 2B  shows that window element  222  may be bonded to lens  214  with a bonding layer  219  in processes for example described later in reference to  FIGS. 16 to 19 . Bonding layer  219  may comprise any of the materials listed later for a bonding layer  330 , such as lead chloride, lead bromide, potassium fluoride, zinc fluoride, an oxide of aluminum, antimony, arsenic, bismuth, boron, lead, lithium, phosphorus, potassium, silicon, sodium, tellurium, thallium, tungsten, or zinc, or any mixtures thereof. 
     Window element  222  may have a RI of 1.5 or greater (e.g., 1.7 or greater) at the wavelengths emitted by LED die  202 . The bond at the interface disposed between window element  222  and lens  214  may have a RI that substantially matches the RI of either or both of the window element and the lens, a RI that is intermediate to the RIs of the window element and the lens, or a RI that is greater than the RI of the window element or the lens. The RIs substantially match when they are within 100% or less in one or more embodiments, within 50% or less in one or more embodiments, within 25% or less in one or more embodiments, and within 10% or less of each other in one or more embodiments. For example, the RI of the bond and the RI of window element  222  or lens  214  may be within ±0.05 of each other. In one or more embodiments of the present disclosure, lens  214  with window element  222  is mounted on support  204  to enclose LED die  202 . 
     Window element  222  may be formed from any of the materials and material combinations described for lens  214  and bonding layers  219 ,  330 ,  1402 , and  1410 , such as aluminum oxynitride (AlON), polycrystalline alumina oxide (transparent alumina), aluminum nitride, cubic zirconia, diamond, gallium nitride, gallium phosphide, sapphire, silicon carbide, silicon aluminum oxynitride (SiAlON), silicon oxynitride (SiON), spinel, zinc sulfide, or an oxide of tellurium, lead, tungsten, or zinc. 
     Window element  222  may have a CTE approximately matching that of lens  214  to reduce stress in the window element and to prevent the window element from becoming detached from the lens upon heating and cooling. CTE may be matched to within 100% or less in one or more embodiments, to within 50% or less in one or more embodiments, and to within 30% or less of each other in one or more embodiments. 
     In one or more embodiments of the present disclosure, window element  222  is a wavelength converting element that modifies the emission spectrum of LED die  202  to provide one or more desired colors of light. The thickness of the wavelength converting element may be controlled in response to the wavelength of the light produced by the LED die  202 , which results in a highly reproducible correlated color temperature. 
     The wavelength converting element may be a ceramic phosphor plate for generating one color of light or a stack of ceramic phosphor plates for generating different colors of light. A ceramic phosphor plate, also referred to as “luminescent ceramics,” may be a ceramic slab of phosphor. The ceramic phosphor plate may have a RI of 1.4 or greater (e.g., 1.7 or greater) at the wavelengths emitted by LED die  202 . The ceramic phosphor plate may be a Y 3 Al 5 O 12 :Ce 3+ . 
     The ceramic phosphor plate may be an amber to red emitting rare earth metal-activated oxonitridoalumosilicate of the general formula (Ca 1-x-y-z Sr x Ba y Mg z ) 1-n (Al 1-a+b B a )Si 1-b N 3-b O b :RE n , wherein 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦a≦1, 0≦b≦1 and 0.002≦n≦0.2, and RE is selected from europium(II) and cerium(III). The phosphor in the ceramic phosphor plate may also be an oxido-nitrido-silicate of general formula EA 2-z Si 5-a B a N 8-a O a :Ln z , wherein 0&lt;z≦1 and 0&lt;a&lt;5, including at least one element EA selected from the group consisting of Mg, Ca, Sr, Ba and Zn and at least one element B selected from the group consisting of Al, Ga and In, and being activated by a lanthanide selected from the group consisting of cerium, europium, terbium, praseodymium and mixtures thereof. 
     The ceramic phosphor plate may also be an aluminum garnet phosphors with the general formula (Lu 1-x-y-a-b Y x Gd y ) 3 (Al 1-z Ga z ) 5 O 12 : Ce a Pr b , wherein 0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;z≦0.1, 0&lt;a≦0.2 and 0&lt;b≦0.1, such as Lu 3 Al 5 O 12 :Ce 3+  and Y 3 Al 5 O 12 :Ce 3+ , which emits light in the yellow-green range; and (Sr 1-x-y Ba x Ca y ) 2-z Si 5-a Al a N 8-a O a :Eu z   2+ , wherein 0≦a&lt;5, 0&lt;x≦1, 0≦y≦1, and 0&lt;z≦1 such as Sr 2 Si 5 N 8 :Eu 2+ , which emits light in the red range. Other green, yellow, and red emitting phosphors may also be suitable, including (Sr 1-a-b Ca b Ba c )Si x N y O z :Eu a   2+  (a=0.002-0.2, b=0.0-0.25, c=0.0-0.25, x=1.5-2.5, y=1.5-2.5, 2=1.5-2.5) including, for example, SrSi 2 N 2 O 2 :Eu 2+ ; (Sr 1-u-v-x Mg u Ca v Ba x )(Ga 2-y-z Al y In z S 4 ):Eu 2+  including, for example, SrGa 2 S 4 :Eu 2+ ; Sr 1-x Ba x SiO 4 :Eu 2+ ; and (Ca 1-x Sr x )S:Eu 2+  wherein 0&lt;x≦1 including, for example, CaS:Eu 2+  and SrS:Eu 2+ . Other suitable phosphors include, for example, CaAlSiN 3 :Eu 2+ , (Sr, Ca)AlSiN 3 :Eu 2+ , and (Sr, Ca, Mg, Ba, Zn)(Al, B, In, Ga)(Si, Ge) N 3 :Eu 2+ . 
     The ceramic phosphor plate may also have a general formula (Sr 1-a-b Ca b Ba c Mg d Zn e )Si x N y O z :Eu a   2+ , wherein 0.002≦a≦0.2, 0.0≦b≦0.25, 0.0≦c≦0.25, 0. 0≦d≦0.25, 0.0≦e≦0.25, 1.5≦x≦2.5, 1.5≦y≦2.5 and 1.5≦z≦2.5. The ceramic phosphor plate may also have a general formula of MmAaBbOoNn:Zz where an element M is one or more bivalent elements, an element A is one or more trivalent elements, an element B is one or more tetravalent elements, O is oxygen that is optional and may not be in the phosphor plate, N is nitrogen, an element Z that is an activator, n=2/3m+a+4/3b-2/3o, wherein m, a, b can all be 1 and o can be 0 and n can be 3. M is one or more elements selected from Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium) and Zn (zinc), the element A is one or more elements selected from B (boron), Al (aluminum), In (indium) and Ga (gallium), the element B is Si (silicon) and/or Ge (germanium), and the element Z is one or more elements selected from rare earth or transition metals. The element Z is at least one or more elements selected from Eu (europium), Mn (manganese), Sm (samarium) and Ce (cerium). The element A can be Al (aluminum), the element B can be Si (silicon), and the element Z can be Eu (europium). 
     The ceramic phosphor plate may also be an Eu 2+  activated Sr—SiON having the formula (Sr 1-a-b Ca b Ba c )Si x N y O x :Eu a , wherein a=0.002-0.2, b=0.0-0.25, c=0.0-0.25, x=1.5-2.5, y=1.5-2.5, y=1.5-2.5. 
     The ceramic phosphor plate may also be a chemically-altered Ce:YAG phosphor that is produced by doping the Ce:YAG phosphor with the trivalent ion of praseodymium (Pr). The ceramic phosphor plate may include a main fluorescent material and a supplemental fluorescent material. The main fluorescent material may be a Ce:YAG phosphor and the supplementary fluorescent material may be europium (Eu) activated strontium sulfide (SrS) phosphor (“Eu:SrS”). The main fluorescence material may also be a Ce:YAG phosphor or any other suitable yellow-emitting phosphor, and the supplementary fluorescent material may also be a mixed ternary crystalline material of calcium sulfide (CaS) and strontium sulfide (SrS) activated with europium ((Ca x Sr 1-x )S:Eu 2+ ). The main fluorescent material may also be a Ce:YAG phosphor or any other suitable yellow-emitting phosphor, and the supplementary fluorescent material may also be a nitrido-silicate doped with europium. The nitrido-silicate supplementary fluorescent material may have the chemical formula (Sr 1-x-y-z Ba x Ca y ) 2 Si 5 N 8 :Eu z   2+  where 0≦x, y≦0.5 and 0≦z≦0.1. 
     The ceramic phosphor plate may also have a blend of any of the above described phosphors. 
     More information can be found in U.S. Pat. Nos. 7,462,502, 7,419,839, 7,544,309, 7,361,938, 7,061,024, 7,038,370, 6,717,353, and 6,680,569, and U.S. Pat. App. Pub. No. 20060255710, which are commonly assigned and incorporated by reference in their entirety. 
     In one or more embodiments of the present disclosure, window element  222  is an optically flat plate with an optically flat surface that faces LED die  202 . The optically flat plate may be sapphire, glass, diamond, silicon carbide (SiC), aluminum nitride (AlN), or any transparent, translucent, or scattering ceramic. In one or more embodiments, window element  222  may be any of the materials listed above for lens  214  and bonding layers  219 ,  330 ,  1402 , and  1410 . The optically flat plate may have a RI of 1.5 or greater (e.g., 1.7 or greater) at the wavelengths emitted by LED die  202 . 
     In one or more embodiments of the present disclosure, the optical element may include an optional heat sink  224  for extracting heat from light emitter  200 . Heat sink  224  may have optional fins  226  (only two are labeled). Heat sink  224  may be incorporated by molding, for example, in or on lens  214 . Heat sink  224  may be layers, plates, slabs, or rings. If heat sink  224  is transparent, translucent, or scattering, it may be in the optical path. For example, it may be located directly on window element  222 . Heat sink  224  may be diamond, silicon carbide (SiC), single crystal aluminum nitride (AlN), gallium nitride (GaN), or aluminum gallium nitride (AlGaN), and it may be part of lens  214 , window element  222 , or any part of the optical element. If heat sink  224  is opaque, it may not be in the optical path. For example, it may contact the edge of window element  222 . Heat sink  224  may be silicon, aluminum nitride (polycrystalline, sintered, hot pressed), metals such as silver, aluminum, gold, nickel, vanadium, copper, tungsten, metal oxides, metal nitrides, metal fluorides, thermal greases or any combinations thereof. Heat sink  224  can be reflective to the light being generated and may act as a side coating. 
     In one or more embodiments of the present disclosure, a first silicone  230  is applied on one or both of the LED die  202  and window element  222  so the first silicone is disposed between them after lens  214  is mounted on support  204 . First silicone  230  helps to extract light from LED die  202  to window element  222 . First silicone  230  may also act as a mechanical buffer to insulate LED die  202  from any external impact to lens  214 , and may make light emitter  200  more robust. First silicone  230  may be a polydimethylsiloxane (PDMS) silicone with a RI of 1.4 or greater at the wavelengths emitted by LED die  202 . 
     A second silicone  232  is introduced into the remaining space in cavity  216  after lens  214  is mounted on support  204 . Second silicone  232  may be filled with reflective or scattering particles. Second silicone  232  may cover the edge of window element  222  to reduce edge emission, which may be important when the window element is a wavelength converting element. Second silicone  232  may also cover the edge of first silicone  230  and LED die  202  to reduce edge emission and to help to channel light from the LED die to window element  222 . Second silicone  232  may also serve as an underfill between LED  202  and support  204  instead of a separate underfill. Second silicone  232  may be a phenyl substituted silicone with a RI of 1.5 or greater at the wavelengths emitted by LED die  202 , and may be filled with reflective particles such as one or more of aluminum nitride, aluminum oxynitride (AlON), barium sulfate, barium titanate, calcium titanate, cubic zirconia, diamond, gadolinium gallium garnet (GGG), lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT), sapphire, silicon aluminum oxynitride (SiAlON), silicon carbide, silicon oxynitride (SiON), strontium titanate, titanium oxide, yttrium aluminum garnet (YAG), zinc selenide, zinc sulfide, and zinc telluride, for example. The interfacial boundary between silicones  230  and  232  may serve as a barrier to prevent contaminants from crossing into the first silicone and accumulating in the optical path or on window element  222 . 
     In one or more alternative embodiments, light emitter  200  does not include second silicone  232 . Instead, the entire cavity  216  is filled with first silicone  230 . 
     In one or more alternative embodiments, light emitter  200  does not include first silicone  230  and second silicone  232 . Instead, an air gap is formed between LED die  202  and window element  222 . Without first silicone  230 , an oversize window element  222  may be used to capture as much emission from LED die  202  as possible. The oversize window element  222  may span across cavity ceiling  218  and may even cover the cavity sidewalls. 
     In one or more embodiments of the present disclosure, the optical element is a lens  214  bonded to LED die  202 . Bonding layer  219  may be used to bond lens  214  to LED die  202 . This is further described in the incorporated references before and after. 
       FIG. 3A  illustrates a cross-sectional view of a light emitter  300  in one or more embodiments of the present disclosure. Light emitter  300  includes LED die  202  mounted on support  204 . An optical element is located over or proximate to LED die  202 . In one or more embodiments of the present disclosure, the optical element includes a high index lens  314  that extracts light from LED die  202 . Lens  314  may have a dome-like shape with a bottom surface  318 . Lens  314  may have a RI of 1.5 or greater (e.g., 1.7 or greater). Lens  314  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  314  may include a luminescent material that converts light of wavelengths emitted by LED die  202  to other wavelengths. 
     In one or more embodiments of the present disclosure, the optical element includes a window element  222  that is directly bonded or fused to bottom surface  318  of lens  314  to form an integral element. Window element  222  may be directly bonded or fused to bottom surface  318  of lens  314 , for example, during a molding process. Window element  222  may be placed on bottom surface  318  before or while lens  314  becomes solid or hard by cooling or curing for example in a mold. Window element  222  may also be embedded into lens  314  at bottom surface  318  by molding the lens under or over the window element for example in a mold. 
     Alternatively,  FIG. 3B  shows that window element  222  may be bonded to lens  314  with a bonding layer  319  in processes for example described later in reference to  FIGS. 16 to 19 . Bonding layer  319  may also be any of the materials listed later for a bonding layer  330 , such as lead chloride, lead bromide, potassium fluoride, zinc fluoride, an oxide of aluminum, antimony, bismuth, boron, lead, lithium, phosphorus, potassium, silicon, sodium, tellurium, thallium, tungsten, or zinc, or any mixtures thereof. 
     As previously discussed, window element  222  may have a RI of 1.5 or greater (e.g., 1.7 or greater) at the wavelengths emitted by LED die  202 . The bond at the interface disposed between window element  222  and lens  314  has a RI that substantially matches the RI of either or both of the window element and the lens, a RI that is intermediate to the RIs of the window element and the lens, or a RI that is greater than the window element or the lens. The RIs substantially match when they are within 100% or less in one or more embodiments, within 50% or less in one or more embodiments, within 25% or less in one or more embodiments, and within 10% or less of each other in one or more embodiments. For example, the RI of the bond and the RI of window element  222  or lens  314  may be within ±0.05 of each other. 
     Window element  222  with lens  314  is then bonded to LED die  202  using a bonding layer  330  between the window element and the LED die. Bonding layer  330  may form a rigid bond between window element  222  and LED die  202 . 
     Bonding layer  330  may be formed from any of the material listed above for lens  214 , bonding layer  219 , window element  222 , bonding layer  1402 , and bonding layer  1410 . 
     Bonding layer  330  may also comprise III-V semiconductors including but not limited to gallium arsenide, gallium nitride, gallium phosphide, and indium gallium phosphide; II-VI semiconductors including but not limited to cadmium selenide, cadmium sulfide, cadmium telluride, zinc sulfide, zinc selenide, and zinc telluride; group IV semiconductors and compounds including but not limited to germanium, silicon, and silicon carbide; organic semiconductors, oxides, metal oxides, and rare earth oxides including but not limited to an oxide of aluminum, antimony, arsenic, bismuth, boron, cadmium, cerium, chromium, cobalt, copper, gallium, germanium, indium, indium tin, lead, lithium, molybdenum, neodymium, nickel, niobium, phosphorous, potassium, silicon, sodium, tellurium, thallium, titanium, tungsten, zinc, or zirconium; oxyhalides such as bismuth oxychloride; fluorides, chlorides, and bromides, including but not limited to fluorides, chlorides, and bromides of calcium, lead, magnesium, potassium, sodium, and zinc; metals including but not limited to indium, magnesium, tin, and zinc; yttrium aluminum garnet (YAG), phosphide compounds, arsenide compounds, antimonide compounds, nitride compounds, high index organic compounds; and mixtures or alloys thereof. 
     Bonding layer  330  may include luminescent material that converts light of wavelengths emitted by the active region of LED die  202  to other wavelengths. The luminescent material includes conventional phosphor particles, organic semiconductors, II-VI or III-V semiconductors, II-VI or III-V semiconductor quantum dots or nanocrystals, dyes, polymers, and materials such as GaN that luminesce. If bonding layer  330  includes conventional phosphor particles, then the bonding layer should be thick enough to accommodate particles typically having a size of about 5 microns to about 50 microns. 
     Bonding layer  330  may be substantially free of traditional organic-based adhesives such as epoxies, since such adhesives tend to have a low index of refraction. 
     Bonding layer  330  may also be formed from a low RI bonding material, i.e., a bonding material having a RI less than about 1.5 at the emission wavelengths of LED die  202 . Magnesium fluoride, for example, is one such bonding material. Low index optical glasses, epoxies, and silicones may also be suitable low index bonding materials. 
     Bonding layer  330  may also be formed from a glass bonding material such as Schott glass LaSFN35, LaF10, NZK7, NLAF21, LaSFN18, SF59, or LaSF3, or Ohara glass SLAH51 or SLAM60, or mixtures thereof. Bonding layer  330  may also be formed from a high index glass, such as (Ge, As, Sb, Ga)(S, Se, Te, F, Cl, I, Br) chalcogenide or chalcogen-halogenide glasses, for example. If desired, lower index materials, such as glass and polymers may be used. Both high and low index resins, such as silicone or siloxane, are available from manufactures such as Shin-Etsu Chemical Co., Ltd., Tokyo, Japan. The side chains of the siloxane backbone may be modified to change the refractive index of the silicone. 
     Window element  222  can be thermally bonded to LED die  202  after the LED die is mounted on submount  210 . For example, to bond window element  222  to LED die  202 , the temperature of bonding layer  330  is raised to a temperature between about room temperature and the melting temperature of the contact elements  212 , e.g., between approximately 150° C. to 450° C., and more particularly between about 200° C. and 400° C. Window element  222  and LED die  202  are pressed together at the bonding temperature for a period of time of about one second to about 6 hours, for example for about 30 seconds to about 30 minutes, at a pressure of about 1 pound per square inch (psi) to about 6000 psi. By way of example, a pressure of about 700 psi to about 3000 psi may be applied for between about 3 to 15 minutes. Pressure may be applied during cooling. If desired, other bonding processes may be used. 
     It should be noted that due to the thermal bonding process, a mismatch between the CTE of window element  222  and LED die  202  can cause the window element to delaminate or detach from the LED die upon heating or cooling. Accordingly, window element  222 , and LED  202  should have approximately matching CTEs. 
     A protective side coating  332  may be applied to the edge of window element  222 , bonding layer  330 , and LED die  202  to reduce edge emission. Side coating  332  may be a silicone with scattering particles such as aluminum nitride, aluminum oxynitride (AlON), barium sulfate, barium titanate, calcium titanate, cubic zirconia, diamond, gadolinium gallium garnet (GGG), lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT), sapphire, silicon aluminum oxynitride (SiAlON), silicon carbide, silicon oxynitride (SiON), strontium titanate, titanium oxide, yttrium aluminum garnet (YAG), zinc selenide, zinc sulfide, or zinc telluride, a thermal grease, or a metal film such as aluminum, chromium, gold, nickel, palladium, platinum, silver, vanadium, or a combination thereof. 
     In one or more embodiments of the present disclosure, the optical element may include optional heat sink  224  with optional fins  226 . Heat sink  224  may be thermally coupled to window element  222  to extract heat from the window element. Depending on the material of the optical element, it may function as a heat sink. 
     In one or more embodiments of the present disclosure, the optical element is lens  314  bonded to LED die  202 . Bonding layer  319  or  330  may be used to bond lens  314  to LED die  202 . In other embodiments, the optical element is the window element  222  bonded to LED die  222 . Bonding layer  330  may be used to bond window element  222  to LED die  202 . This is further described in the incorporated references before and after. 
     More information can be found in U.S. Pat. Nos. 7,279,345, 7,064,355, 7,053,419, 7,009,213, 7,462,502, 7,419,839, 6,987,613, 5,502,316, and 5,376,580, which are commonly assigned and incorporated by reference in their entirety. 
       FIG. 4A  illustrates a cross-sectional view of a light emitter  400  in one or more embodiments of the present disclosure. Light emitter  400  includes LED die  202  mounted on support  204 . An optical element is located over or proximate to LED die  202 . In one or more embodiments of the present disclosure, the optical element may include a high index lens  414  that extracts light from LED die  202 . Lens  414  may have a solid dome-like shape with a bottom surface  418 . Lens  414  may have a RI of 1.5 or greater. Lens  414  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  414  may include a luminescent material that converts light of wavelengths emitted by LED die  202  to other wavelengths. 
     In one or more embodiments of the present disclosure, the optical element includes a window element  222  that is directly bonded or fused to lens  414 . Window element  222  is also recessed into lens  414  so the window element is coplanar with the bottom surface  418  of the lens. Window element  222  may be directly bonded or fused to lens  414 , for example, during a molding process. Window element  222  may be recessed into bottom surface  418  before or while lens  414  becomes solid or hard by cooling or curing for example in a mold. Window element  222  may also be recessed into bottom surface  418  by molding lens  418  under or over the window element for example in a mold. A recess may also be premade in lens  414  for window element  222 , and the lens may be heated to directly bond or fuse with the window element. 
     Alternatively,  FIG. 4B  shows that window element  222  may be bonded to lens  414  with a bonding layer  419  in processes for example described later in reference to  FIGS. 16 to 19 . Bonding layer  419  may comprise any of the materials listed above for a bonding layer  330 , such as lead chloride, lead bromide, potassium fluoride, zinc fluoride, an oxide of aluminum, antimony, arsenic, bismuth, boron, lead, lithium, phosphorus, potassium, silicon, sodium, tellurium, thallium, tungsten, or zinc, or any mixtures thereof. The bond between window element  222  and lens  414  has a RI that substantially matches the RI of either or both of the window element and the lens, a RI that is intermediate to the RIs of the window element and the lens, or a RI that is greater than the RI for the window element or the lens. 
     Window element  222  with lens  414  is bonded to LED die  202  using bonding layer  330  between the window element and the LED die. 
     In one or more embodiments of the present disclosure, the optical element may include optional heat sink  224  with optional fins  226 . Heat sink  224  may be thermally coupled to window element  222  to extract heat from the window element. Heat sink  224  may be molded to lens  414  at the same time, before, or after window element  222  is bonded. Depending on the material of the optical element, it may function as a heat sink. 
       FIG. 5  illustrates a molding apparatus  500  that can be used in a molding process for directly bonding or fusing window element  222  to lens  414  in one or more embodiments of the present disclosure. Apparatus  500  may be a thermal compression mold with a lower mold half  502  and an upper mold half  504 . Mold halves  502  and  504  define a mold cavity in the desired shape of lens  414 . Mold halves  502  and  504  may have guide pins and holes that align the mold halves. Heating/cooling elements  506  (only two are labeled) provide the proper heating and cooling to mold halves  502  and  504  during the molding process. Heating/cooling elements  506  may be integral or separate from mold halves  502  and  504 . Alternatively mold halves  502  and  504  may be heated by flowing current directly into the mold where the mold halves are also the heating elements. 
     Window element  222  is placed on lower mold half  502  and a glass chunk or powder  508  is placed on the window element. Heating/cooling elements  506  heat mold halves  502  and  504  to a temperature sufficient to shape glass chunk or powder  508  without damaging window element  222 . Upper mold half  504  is positioned on lower mold half  502  to apply heat and pressure to glass chunk or powder  508 , and the softened glass flows and takes the shape of the mold cavity to form lens  414 . As lens  414  cools and hardens, it is directly bonded or fused with window element  222 . In addition to window element  222 , optional heat sink  224  may also be directly bonded or fused with lens  414 . Heat sink  224  may be molded with lens  414  before, after, or at the same time as window element  222 . Heat sink  224  may also be adhered or glued to lens  414 . 
     Heating/cooling elements  506  may gradually cool mold halves  502  and  504 . CTE of may be matched to within 100% or less in one or more embodiments, to within 50% or less in one or more embodiments, and to within 30% or less of each other in one or more embodiments. An ejector pin may be used to push lens  414  with window element  222  from the mold. 
     Although a molding process has been described for lens  414 , mold halves  502  and  504  may take on different shapes to form lenses  214  and  314  described above, and lenses  614 ,  714 ,  814 ,  914 ,  1014 ,  1114 ,  1314 , and  2014  described later. Instead of the described molding process, other lens molding process may be used to form any of the lens with window element described above, including but not limited to injection molding and insert molding. For example, insert molding can be used to incorporate any optional heat sink  224  with optional fins  226  into the lens. 
       FIGS. 6 to 11 ,  13 , and  20  illustrate various lenses with window elements that may replace lens  214  in module  200 , lens  314  in module  300 , or lens  414  in module  400 . These various lenses with window elements may also replace lens  1414  in light emitters  1400  and  1500  described later. 
       FIG. 6  illustrates a cross-sectional view of a lens  614  in one or more embodiments of the present disclosure. Lens  614  has a dome-like shape with a cavity  616  having a ceiling  618 . Window element  222  is directly bonded or fused to lens  614 . Alternatively window element  222  is bonded to lens  614  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Lens  614  is similar to lens  214  described above except that window element  222  is recessed into ceiling  618  so the bottom of the window element may be substantially coplanar with the ceiling. Lens  614  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  614  may include a luminescent material and/or window element  222 . Light from LED die  202  may be converted to another wavelength by window element  222  and/or lens  614 . The combined generated and converted light may produce a desired color. 
       FIG. 7  illustrates a cross-sectional view of a lens  714  in one or more embodiments of the present disclosure. Lens  714  has a dome-like shape with a bottom surface  718 . Window element  222  is directly bonded or fused to bottom surface  718  of lens  714 . Window element  222  also spans over the entire bottom surface  718 . Alternatively, window element  222  is bonded to lens  714  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Lens  714  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  714  may include a luminescent material and/or window element  222 . Light from LED die  202  may be converted to another wavelength by window element  222  and/or lens  714 . The combined generated and converted light may produce a desired color. 
       FIG. 8  illustrates a cross-sectional view of a lens  814  in one or more embodiments of the present disclosure. Lens  814  is a compound parabolic concentrator (CPC) lens with a reflective surface  819  that directs light toward an emitting surface  820 . Window element  222  is directly bonded or fused to a bottom surface  818  of lens  814 . Alternatively window element  222  is bonded to lens  814  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Lens  814  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  814  may include a luminescent material and/or window element  222 . Light from LED die  202  may be converted to another wavelength by window element  222  and/or lens  814 . The combined generated and converted light may produce a desired color. 
       FIG. 9  illustrates a cross-sectional view of a lens  914  in one or more embodiments of the present disclosure. Lens  914  is a type of side-emitting lens. Window element  222  is directly bonded or fused to lens  914 . Alternatively window element  222  is bonded to lens  914  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Window element  222  is recessed into lens  914  so the bottom of the window element may be coplanar with a bottom surface  918  of the lens as shown. Alternatively window element  222  is bonded to and protrudes from bottom surface  918 . Lens  914  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  914  may include a luminescent material and/or window element  222 . Light from LED die  202  may be converted to another wavelength by window element  222  and/or lens  914 . The combined generated and converted light may produce a desired color. 
       FIG. 10  illustrates a cross-sectional view of a lens  1014  in one or more embodiments of the present disclosure. Lens  1014  is another type of side-emitting lens. Window element  222  is directly bonded or fused to lens  1014 . Alternatively window element  222  is bonded to lens  1014  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Window element  222  is recessed into lens  1014  so the bottom of the window element may be coplanar with a bottom surface  1018  of the lens as shown. Alternatively window element  222  is bonded to and protrudes from bottom surface  1018 . Lens  1014  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  1014  may include a luminescent material and/or window element  222 . Light from LED die  202  may be converted to another wavelength by window element  222  and/or lens  1014 . The combined generated and converted light may produce a desired color. 
       FIG. 20  illustrates a lens  2014  including grooves in the shape of a Fresnel lens in one or more embodiments of the present disclosure. Lens  2014  may have a Fresnel pattern that is etched, molded, embossed, or stamped. The Fresnel pattern includes a set of grooves, often arranged in concentric pattern. The Fresnel pattern can be formed on the whole surface  2020 , or only on the top region, or only on the side region of surface  2020 . 
     Window element  222  is directly bonded or fused to a bottom surface  2018  of lens  2014 . Alternatively window element  222  is bonded to lens  2014  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Window element  222  is bonded to and protrudes from bottom surface  2018  as shown. Alternatively window element  222  is recessed into lens  2014  so the bottom of the window element may be coplanar with a bottom surface  2018  of the lens. Lens  2014  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  2014  may include a luminescent material and/or window element  222 . Light from LED die  202  may be converted to another wavelength by window element  222  and/or lens  2014 . The combined generated and converted light may produce a desired color. 
       FIG. 11  illustrates a cross-sectional view of a lens  1114  in one or more embodiments of the present disclosure. Lens  1114  is a right angle lens or prism. One window element  222  (labeled  222 A) may be directly bonded or fused to one leg of prism  1114 , and a second window element  222  (labeled  222 B) may be directly bonded or fused to another leg of the prism. Alternatively one or both window elements  222 A and  222 B may be bonded to lens  1114  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Window element  222 A is recessed into prism  1114  so the bottom of the window element may be coplanar with a surface  1118 A of the lens as shown, and window element  222 B is recessed into the prism so the bottom of the window element may be coplanar with a surface  1118 B of the lens as shown. Alternatively at least one or both window elements  222 A and window element  222 B protrude from surfaces  1118 A and  1118 B. Lens  1114  may be made from any material described above for lens  214 . As similarly described above for lens  214 , lens  1114  may include a luminescent material and/or window element  222 . Light from LED die  202  may be converted to another wavelength by window element  222  and/or lens  1114 . The combined generated and converted light may produce a desired color. 
       FIG. 12  illustrates a light emitter  1200  with prism  1114  in one or more embodiments of the present disclosure. LED die structures  1202  and  1204  are bonded to respective window elements  222 A and  222 B. Each LED dies structure includes an LED die and a support. Prism  1114  combines lights  1206  and  1208  from respective LED die structures  1202  and  1204  and window elements  222 A and  222 B to emit a light  1210 . Light  1206  and  1208  may be the same or different wavelength. 
       FIG. 13  illustrates a cross-sectional view of a lens  1314  in one or more embodiments of the present disclosure. Lens  1314  has a dome-like shape with a bottom surface  1318 . A first window element  222  (labeled  222 C) is encapsulated or embedded within lens  1314 , and a second window element  222  (labeled  222 D) is directly bonded or fused to the lens. Alternatively window element  222 D is bonded to lens  1314  with a bonding layer in processes for example described later in reference to  FIGS. 16 to 19 . Window element  222 D is recessed into lens  1314  so the bottom of the window element may be coplanar with bottom surface  1318  as shown. Alternatively window element  222 D protrudes from bottom surface  1318 . Window element  222 C may be a wavelength converting element (e.g., a ceramic phosphor plate) and window element  222 D may be an optically flat plate or another wavelength converting element (e.g., a ceramic phosphor plate). Lens  1314  may be made from any material described above for lens  214 . Light from LED die  202  may be converted to another wavelength by window elements  222 C,  222 D, and/or lens  1314 . The combined generated and converted light may produce a desired color. 
     Additional lenses, such as top-emitter, elongated optical concentrator, top-emitter with reflectors, side-emitter, side-emitter with reflector, asymmetric elongated side-emitter, and top-emitter with light guide, may be adopted with window element  222  as described in the present disclosure. These lenses are described in U.S. Pat. Nos. 7,009,213 and 7,276,737, which are commonly owned and incorporated by reference. 
       FIG. 14  illustrates a cross-sectional view of a light emitter  1400  in one or more embodiments of the present disclosure. Light emitter  1400  includes LED die  202  mounted on support  206 . An optical element is located over or proximate to LED die  202 . In one or more embodiments of the present disclosure, the optical element includes a window element  222  is bonded by a bonding layer  1402  to LED die  202 . Bonding layer  1402  may be a silicone, an epoxy, a sol-gel material, a glass, or a high index material similar to a later described bonding layer  1410 . Bonding layer  1402  may also be a material described earlier for bonding layer  330 . An optional side coating  1404  may be applied to the edge of window element  222 , bonding layer  1402 , and LED die  202  to reduce edge emission. Side coating  1404  may be a silicone, epoxy, or sol-gel derived material filled with reflective or scattering particles such as aluminum nitride, aluminum oxynitride (AlON), barium sulfate, barium titanate, calcium titanate, cubic zirconia, diamond, gadolinium gallium garnet (GGG), hafnium oxide, indium oxide, lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT), sapphire, silicon aluminum oxynitride (SiAlON), silicon carbide, silicon oxynitride (SiON), strontium titanate, tantalum oxide, titanium oxide, yttrium aluminum garnet (YAG), zinc selenide, zinc sulfide, or zinc telluride, thermal greases, or a metal film such as aluminum, chromium, gold, nickel, palladium, platinum, silver, or vanadium, or a combination of any of the above. 
     In one or more embodiments of the present disclosure, the optical element includes a high index lens  1414  that extracts light from LED die  202 . Lens  1414  may have a dome-like shape with a bottom surface  1408 . Lens  1414  may have a RI of 1.5 or greater (e.g., 1.7 or greater) at the light emitting device&#39;s emission wavelengths. Lens  1414  may be made from glass, sapphire, diamond, alumina, or any material described above for lens  214 . Lens  1414  is bonded by a high index bond layer  1410  to window element  222 . Although bottom surface  1408  is shown as being a flat surface, a recess may be provided in the bottom surface that at least partly receive window element  222 . This may help to position window element  222  and lens  1414  in the bonding process. 
     High index bond layer  1410  has a RI that substantially matches the RI of either or both of window element  222  and lens  1414 , a RI that is intermediate to the RIs of the window element and the lens, or a RI that is greater than the window element or the lens. The RIs substantially match when they are within 100% or less in one or more embodiments, within 50% or less in one or more embodiments, within 25% or less in one or more embodiments, and within 10% or less of each other in one or more embodiments. For example, the RI of the bond and the RI of window element  222  or lens  1414  may be within ±0.05. 
     High index bond layer  1410  may be a silicone resin or silicate binder filled with properly dispersed high index nano-particles with particle sizes &lt;100 nm (e.g., &lt;50 nm). To facilitate dispersability of the nano-particles, a small amount of suitable dispersing agent may be used as a compatibilizer between the nano-particles and the dispersion medium. The volume ratio of dispersed nano-particles and binder matrix may be tuned to control the refractive index of bond layer  1410 , i.e., a higher volume concentration of the high refractive index nano-particles increases the effective refractive index of the bond layer. The silicone resin may be a methyl polysiloxane, a phenyl polysiloxane, a methyl phenyl polysiloxane, or mixtures thereof. The silicate binder may be of a type forming a silicate, a methylsilicate, or phenylsilicate upon curing, or a mixture thereof, and may be derived from precursor monomers and/or oligomers in a sol-gel process. The high index nano-particles may be a high refractive index nano-particle, such as aluminum oxide, aluminum nitride, aluminum oxynitride (AlON), barium sulfate, barium titanate, calcium titanate, cubic zirconia, diamond, gadolinium gallium garnet (GGG), gadolinium oxide, hafnium oxide, indium oxide, lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT), strontium titanate, silicon aluminum oxynitride (SiAlON), silicon carbide, silicon oxynitride (SiON), tantalum pentoxide, titanium oxide, yttrium aluminum garnet (YAG), yttrium aluminum oxide, yttrium oxide, zirconium oxide, yttria stabilized zirconium oxide, or a mixture thereof. 
     A thin layer of the high index bond material may be applied to window element  222 , lens  1414 , or both. The thickness of the high index bond material may be several microns (e.g., &lt;10 microns). The high index bond material may be applied in various ways, such as by dispensing, printing, spray coating, spin coating, or blade coating. The high index bond material is typically deposited in fluid form, and may remain fluid up to the moment of connection of window element  222  and lens  1414 , or may be partially solidified or gelled at the moment of connection, or may be a solid that tackifies upon heating to enable easy connection. Usually the high index bond material reacts to form a solidified bond that may range from a gelled state to a hard resin. 
     For example, the high index bond material precursor may consist of a methyl substituted silicone resin with dispersed nano-TiO 2  particles that is spin or blade coated from a solution onto window element  222 . The spin coating or blade coating may be applied on a large scale, e.g., a substrate of window elements  222  that is subsequently diced into smaller parts and used as individual window elements. The silicone resin is of a type that is solid at room temperature but when heated at a temperature of 70 to 150° C. will tackify to enable a bonding contact between lens  1414  that is brought into contact with window element  222 . The high index bond material is then cured at a higher temperature (e.g., 1 hour at 200° C.) to form high index bond layer  1410  between window element  222  and lens  1414 . Alternatively the high index bond material is dispensed in liquid form on window element  222  or lens  1414  and both components are connected. The bond is then cured to a high index solid at elevated temperature, e.g., 150° C. for 1 hour. 
     A solvent may be present in the high index bonding precursor fluid. The solvent may be removed prior to bonding or during the bonding process or may remain (partially) present to facilitate optical contact and may be removed further from the bond through evaporation. The remaining gap between lens  1414  and support  204  may be filled with an underfill material  1412  such as silicone. The underfill material may contain a particulate filler to enhance thermal conductivity and/or reflectivity. 
       FIG. 15  illustrates a cross-sectional view of a light emitter  1500  in one or more embodiments of the present disclosure. Light emitter  1500  is similar to light emitter  1400  except that side coating  1404  is not present because underfill material  1412  is replaced with a reflective underfill material  1512 . The underfill material may also fill a gap between LED die  202  and support  204 . The reflective underfill material may be a silicone filled with a reflective thermal grease, a metal film, reflective or scattering particles, or a combination thereof may also be used. The reflective or scattering particles may be aluminum nitride, aluminum oxynitride (AlON), barium sulfate, barium titanate, calcium titanate, cubic zirconia, diamond, hafnium oxide, indium oxide, gadolinium gallium garnet (GGG), lead lanthanum zirconate titanate (PLZT), lead zirconate titanate (PZT), sapphire, silicon aluminum oxynitride (SiAlON), silicon carbide, silicon oxynitride (SiON), strontium titanate, tantalum oxide, titanium oxide, yttrium aluminum garnet (YAG), zinc selenide, zinc sulfide, zinc telluride, or a combination thereof. 
     Instead of filling the gap between lens  1414  and support  204  after the lens bonding, underfill material  1412  or  1512  may be deposited on support  204  until it is level or planarized with window element  222  before the lens bonding. If so, material of high index bond layer  1410  may be applied over the entire top surface of window element  222  and underfill material  1412  or  1512 . 
     Instead of being a silicone or a sol-gel material, high index bond layer  1410  may also be made of the same material as bonding layer  330  described above. In one or more embodiments of the present disclosure, bonding layer  1410  is made of an optical glass having a lower melting temperature than window element  222  and lens  1414 . The glass may be formed on top of window element  222 , on the bottom of lens  1414 , or both. The glass is heated until it softens, and pressure may be applied to during the bonding process and cool down. The glass forms a high index bond layer  1410  between window element  222  and lens  1414 . 
       FIG. 16  illustrates an apparatus for a process to form a glass high index bonding layer on window element  222  in one or more embodiments of the present disclosure. Window element  222  is held by supports in a lower mold half  1602  and an upper mold half  1604  is positioned on the lower mold. Mold halves  1602  and  1604  may have guide pins and holes for proper alignment of the mold halves. Heating/cooling elements  1606  (only two are labeled) provide the proper heating and cooling to mold halves  1602  and  1604  during the molding process. Heating/cooling elements  1606  may be integral or separate from mold halves  1602  and  1604 . 
     Glass is introduced through a mold inlet  1608  over the top and the bottom surfaces of window element  222 . As the glass hardens, it bonds with window element  222  to form bonding layers  1402  and  1410  as shown in  FIG. 17 . Window element  222  is later heated and bonded to the bottom of lens  1414  and the top of LED die  202 . Although bonding layers  1402  and  1410  are formed on both sides of window element  222 , the above process may be modified to form one bonding layer on one side of the window element. 
       FIG. 18  illustrates an apparatus for a process to form a glass high index bond material on the bottom of lens  1414  in one or more embodiments of the present disclosure. Lens  1414  is first molded and placed in a lower mold half  1802 , and an upper mold  1804  is positioned on the lower mold. Mold halves  1802  and  1804  may have guide pins and holes for proper alignment of the mold halves. Heating/cooling elements  1808  (only two are labeled) provide the proper heating and cooling to mold halves  1802  and  1804  during the molding process. Heating/cooling elements  1808  may be integral or separate from mold halves  1802  and  1804 . Alternatively, an apparatus similar to that shown in  FIG. 5  with an appropriate shape may be used with bonding glass chunks or powder to form a bonding glass layer on a lens or window element. 
     Glass is introduced through a mold inlet  1806  over the bottom surface of lens  1414 . As the glass hardens, it bonds with lens  1414  to form a bonding layer  1410  as shown in  FIG. 19 . Lens  1414  with bonding layer  1410  is later heated and bonded to window element  222  or LED die  202 . 
     Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. Numerous embodiments are encompassed by the following claims.