Polarized Semiconductor Light Emitting Device

Abstract

A light emitting device includes a light emitting diode (LED), a concentrator element, such as a compound parabolic concentrator, and a wavelength converting material, such as a phosphor. The concentrator element receives light from the LED and emits the light from an exit surface, which is smaller than the entrance surface. The wavelength converting material is, e.g., disposed over the exit surface. The radiance of the light emitting diode is preserved or increased despite the isotropic re-emitted light by the wavelength converting material. In one embodiment, the polarized light from a polarized LED is provided to a polarized optical system, such as a microdisplay. In another embodiment, the orthogonally polarized light from two polarized LEDs is combined, e.g., via a polarizing beamsplitter, and is provided to non-polarized optical system, such as a microdisplay. If desired, a concentrator element may be disposed between the beamsplitter and the microdisplay.

1 . An apparatus comprising:
 a light emitting diode;   a transparent member having an entrance surface coupled to the light emitting diode, the transparent member having reflective surfaces that define an exit surface through which light exits the transparent member, wherein the exit surface is smaller than the entrance surface and wherein the transparent member is shaped such that light emitted from the light emitting diode is directed toward the exit surface; and   a wavelength converting material coupled to the transparent member.   
   
   
       2 . The apparatus of  claim 1 , wherein the transparent member is a compound parabolic concentrator. 
   
   
       3 . The apparatus of  claim 1 , wherein the reflective surfaces of the transparent member are formed from a reflective material overlying a portion of the transparent member. 
   
   
       4 . The apparatus of  claim 3 , further comprising a dielectric layer disposed between the transparent member and reflective material. 
   
   
       5 . The apparatus of  claim 1 , wherein the reflective surfaces of the transparent member are formed from sidewalls of the transparent member. 
   
   
       6 . The apparatus of  claim 1 , further comprising a dichroic filter disposed between the wavelength converting material and the light emitting diode. 
   
   
       7 . The apparatus of  claim 1 , further comprising a polarization filter disposed between the wavelength converting material and the light emitting diode. 
   
   
       8 . The apparatus of  claim 1 , further comprising a filter comprising one of a dichroic filter and a polarization filter, the filter being coupled to the wavelength converting material, wherein the wavelength converting material is disposed between the filter and the light emitting diode. 
   
   
       9 . The apparatus of  claim 1 , wherein the wavelength converting material is disposed on the exit surface. 
   
   
       10 . The apparatus of  claim 1 , further comprising an optical system positioned near the exit surface. 
   
   
       11 . The apparatus of  claim 1 , wherein the light emitting diode is a first light emitting diode with an epitaxial structure comprising an active region sandwiched between an n-type region and a p-type region, the active region configured to emit light that is at least 50% polarized along a first polarization orientation when forward biased, the apparatus further comprising:
 a second light emitting diode with an epitaxial structure comprising an active region sandwiched between an n-type region and a p-type region, the active region of the second light emitting diode configured to emit light that is at least 50% polarized along a second polarization orientation when forward biased; and   a polarizing beamsplitter disposed between the first light emitting diode and the transparent member, the polarizing beamsplitter configured to receive light from the first light emitting diode and light from the second light emitting diode, wherein the polarizing beamsplitter combines the light having a first polarization orientation and the light having a second polarization orientation and emits the combined light to the entrance surface of the transparent member.   
   
   
       12 . A light emitting device comprising:
 a light emitting diode;   a concentrator element coupled to the light emitting diode, the concentrator element having an entrance surface coupled to receive light emitted by the light emitting diode, and an exit surface that is smaller than the entrance surface, the concentrator element being shaped such that light received at the entrance surface is directed toward the exit surface; and   a wavelength converting material disposed over the exit surface.   
   
   
       13 . The light emitting device of  claim 12 , wherein the concentrator element is configured to approximately preserve the radiance of the light emitting diode. 
   
   
       14 . The light emitting device of  claim 12 , wherein the concentrator element is formed from a cavity within a solid body. 
   
   
       15 . A method comprising
 emitting light from an active region of a light emitting diode;   at least partially randomizing the polarization state of the light emitted from the active region; and   transmitting light having a desired polarization orientation and reflecting light that does not have the desired polarization orientation after at least partially randomizing the polarization state of the light emitted from the active region.   
   
   
       16 . The method of  claim 15 , wherein transmitting light having a desired polarization orientation comprises transmitting light having a desired polarization orientation through a non-absorbing polarizer. 
   
   
       17 . The method of  claim 15 , further comprising at least partially randomizing the polarization state of the reflected light. 
   
   
       18 . The method of  claim 15 , further comprising:
 concentrating the light emitted by the active region by transmitting the light through an entrance surface coupled to receive light emitted by the active region, reflecting the light from reflective surfaces that define an exit surface and that are shaped such that light emitted from the active region is directed toward the exit surface, wherein the exit surface is smaller than the entrance surface;   wherein concentrating the light occurs prior to transmitting light having a desired polarization orientation.   
   
   
       19 . The method of  claim 15 , further comprising:
 emitting a second light from a second active region of a second light emitting diode;   at least partially randomizing the polarization state of the second light emitted from the second active region;   transmitting the second light having a second desired polarization orientation and reflecting the second light that does not have the second desired polarization orientation after at least partially randomizing the polarization state of the second light emitted from the second active region;   combining the transmitted light having a desired polarization orientation and the transmitted second light having a second desired polarization orientation;   illuminating a microdisplay with the transmitted light having the desired polarization orientation and the transmitted second light having a second desired orientation.