Tunable white light based on polarization sensitive light-emitting diodes

Abstract

A lighting apparatus for emitting polarized white light, which includes at least a first light source for emitting primary light comprised of one or more first wavelengths and having a first polarization direction; and at least a second light source for emitting secondary light in the first polarization direction, comprised of one or more secondary wavelengths, wherein the first light and the secondary light are combined to produce a polarized white light. The lighting apparatus may further comprise a polarizer for controlling the primary light's intensity, wherein a rotation of the polarizer varies an alignment of its polarization axis with respect to the first polarization direction, which varies transmission of the primary light through the polarizer, which controls a color co-ordinate or hue of the white light.

1 . A white light-emitting device for emitting polarized white light, comprising:
 one or more Light Emitting Diodes (LEDs), Super Luminescent Diodes (SLDs), or Laser Diodes (LDs) that emit polarized light.   
   
   
       2 . The device of  claim 1 , wherein the LEDs, SLDs, or LDs are nonpolar or semipolar LEDs, SLDs, or LDs comprised of III-nitride based materials. 
   
   
       3 . The device of  claim 2 , wherein the nonpolar LEDs, SLDs, or LDs are fabricated on an m-plane or an a-plane of a wurtzite III-nitride based substrate or a III-nitride hetero-epitaxial template. 
   
   
       4 . The device of  claim 2 , wherein the semipolar LEDs, SLDs, or LDs are fabricated on any crystallographic plane other than a c-plane, m-plane or a-plane of a wurtzite III-nitride based substrate or a III-nitride hetero-epitaxial template. 
   
   
       5 . The device of  claim 2 , further comprising a light emitting active layer of the nonpolar or semipolar LEDs, SLDs, or LDs that experiences reduced polarization induced fields and a reduced quantum confined stark effect as compared to a light emitting active layer of a polar light emitting device grown along a c-axis of III-nitride. 
   
   
       6 . The device of  claim 5 , wherein the polarization induced fields are reduced at interfaces with the active layer. 
   
   
       7 . The device of  claim 1 , further comprising:
 a plurality of the LEDs, SLDs, or LDs, wherein each LED, SLD, or LD is for emitting the polarized light having a different color or wavelength from light emitted by the other LEDs, SLDs, or LDs, and a combination of the light having different color or wavelength is the polarized white light.   
   
   
       8 . The device of  claim 1 , wherein the one or more LEDs, SLDs, or LDs emit a single color of primary light, and further comprising:
 one or more phosphors for emitting secondary light when optically pumped by the primary light, wherein a combination of the primary light and secondary light is the polarized white light having a same polarization as the primary light.   
   
   
       9 . The device of  claim 8 , wherein the phosphors have a structure that maintains a polarization of the primary light, so that the secondary light has the polarization of the primary light. 
   
   
       10 . The device of  claim 8 , wherein the phosphors are sufficiently crystalline to emit secondary light having a polarization ratio greater than 0.5. 
   
   
       11 . The device of  claim 1 , wherein the device utilizes a polarization property of the LEDs, LDs, or SLDs to emit the polarized white light. 
   
   
       12 . A method of emitting polarized white light, comprising:
 (a) providing one or more Light Emitting Diodes (LEDs) that emit polarized LED light that excites one or more phosphors to emit phosphor light, wherein polarization of the LED light and polarization of the phosphor light is in a same direction.   
   
   
       13 . A method of fabricating a white light-emitting device for emitting polarized white light, comprising:
 (a) providing one or more Light Emitting Diodes (LEDs) that emit a shorter wavelength of polarized light that is converted into a longer wavelength of polarized light by one or more phosphors, wherein a resulting mixture of the shorter wavelength of polarized light and the longer wavelength of polarized light appears as white light.   
   
   
       14 . A lighting apparatus for emitting white light, comprising:
 (a) a first light source for emitting a primary light comprised of one or more first wavelengths and having a first polarization direction;   (b) a second light source for emitting secondary light comprised of one or more second wavelengths, wherein the primary light and the secondary light are combined to produce a white light; and   (c) a polarizer for controlling the primary light's intensity, wherein a rotation of the polarizer varies an alignment of its polarization axis with respect to the first polarization direction, which varies transmission of the primary light through the polarizer, which controls a color co-ordinate or hue of the white light.   
   
   
       15 . The lighting apparatus of  claim 14 , wherein the first light source is a light emitting diode (LED). 
   
   
       16 . The lighting apparatus of  claim 15 , wherein the LED is a nonpolar or semipolar III-nitride based LED. 
   
   
       17 . The lighting apparatus of  claim 14 , wherein the second light source is a light emitting diode (LED). 
   
   
       18 . The lighting apparatus of  claim 17 , wherein the LED is a nonpolar or semipolar III-nitride based LED. 
   
   
       19 . The lighting apparatus of  claim 14 , wherein the second light source is a phosphor optically pumped by the first light source. 
   
   
       20 . The lighting apparatus of  claim 14 , wherein the first light source emits blue light, and the second light source emits yellow light. 
   
   
       21 . The lighting apparatus of  claim 20 , wherein the first wavelengths are between 400 nm and 500 nm and the second wavelengths are above 500 nm. 
   
   
       22 . The lighting apparatus of  claim 14 , wherein the secondary light has a second polarization direction, and the apparatus further comprises:
 an additional polarizer for controlling the secondary light's intensity, wherein a rotation of the additional polarizer varies an alignment of its polarization axis with respect to a second polarization direction of the secondary light, which varies transmission of the secondary light through the additional polarizer, which controls the color co-ordinate or hue of the white light.   
   
   
       23 . The lighting apparatus of  claim 14 , further comprising
 one or more additional light sources for emitting additional light comprised of one or more additional wavelengths, wherein the primary light, the secondary light, and the additional light are combined to produce the white light with improved color rendering properties.   
   
   
       24 . The lighting apparatus of  claim 23 , wherein the additional light source has an additional polarization direction, and the apparatus further comprises
 an additional polarizer for controlling the additional light's intensity, wherein a rotation of the additional polarizer varies an alignment of its polarization axis with respect to the additional polarization direction, which varies transmission of the additional light through the additional polarizer, which controls the color co-ordinate or hue of the white light.   
   
   
       25 . A method for emitting white light, comprising:
 (a) emitting a primary light from a first light source, wherein the primary light is comprised of one or more first wavelengths and has a first polarization direction;   (b) emitting a secondary light from a second light source, wherein the secondary light is comprised of one or more second wavelengths, and the primary light and the secondary light are combined to produce a white light; and   (c) controlling the primary light's intensity using a polarizer, wherein a rotation of the polarizer varies an alignment of its polarization axis with respect to the first polarization direction, which varies transmission of the primary light through the polarizer, which controls a color co-ordinate or hue of the white light.   
   
   
       26 . A method of fabricating a lighting apparatus for emitting white light comprising:
 (a) providing a first light source for emitting primary light comprised of one or more first wavelengths and having a first polarization direction;   (b) providing a second light source for emitting secondary light comprised of one or more second wavelengths, wherein the primary light and the secondary light are combined to produce a white light; and   (c) providing a polarizer for controlling the primary light's intensity, wherein a rotation of the polarizer varies an alignment of its polarization axis with respect to the first polarization direction, which varies transmission of the primary light through the polarizer, which controls a color co-ordinate or hue of the white light.