High-brightness LED-phosphor coupling
View Patent ↗A high brightness LED phosphor coupling device. A semiconductor light source is encapsulated by a medium of first index of refraction, a layer of phosphor surrounded by a second medium of second index of refraction of optical index less than the first index and a light coupler for redirecting most of the light from the light source to an area of the phosphor about equal to the area of the light source multiplied by the square of the ratio of the first to the second index of refraction.
1. A light source comprising:
a semiconductor light source surrounded by an encapsulating first medium having a first optical index of refraction n encapsulant ;
a layer of phosphor surrounded by a second medium having a second optical index of refraction n 2 less than said first index of refraction of said encapsulating first medium; and
a light coupler redirecting the majority of light from said semiconductor light source to an area of said layer of phosphor approximately equal to the area of said semiconductor light source multiplied by (n encapsulant/n 2 ) 2 .
2. The device of claim 1 where said light coupler is a non-imaging reflector.
3. The device of claim 2 where said non-imaging reflector is a compound parabolic concentrator.
4. The device of claim 3 where said compound parabolic concentrator has a light output angle approximately equal to arcsine(n 2 /n encapsulant ) for light inside said encapsulating first medium.
5. The device of claim 2 where said light coupler comprises a first portion nearer to said semiconductor light source and a second portion farther from said semiconductor light source than said first portion, said first and second portions separated by a ledge region about parallel to the top surface of said semiconductor light source and situated at a level intermediate between the bottom surface of said semiconductor light source and the output aperture of said light coupler.
6. The device of claim 5 where said ledge region is about 0.2 mm or more in extent.
7. The device of claim 5 including a bond wire connecting said semiconductor light source to said ledge region.
8. The device of claim 1 where said first optical index of refraction is between 1.4 and 1.7 and said second optical index of refraction is less than 1.2.
9. The device of claim 8 where said area of said phosphor layer is less than three times the area of said semiconductor light source.
10. The device of claim 1 where said second medium is air.
11. A light source comprising,
a semiconductor light source surrounded by an encapsulating first medium having a first optical index of refraction n encapsulant ;
a layer of phosphor surrounded by a second medium having a second optical index of refraction n 2 less than said first index of refraction of said encapsulating first medium; and
a light coupler having a structure which substantially conserves etendue for redirecting the majority of light from said semiconductor light source to said layer of phosphor and said coupler having an output light angle inside said first medium arcsine (n 2 /n encapsulant ).
12. The device of claim 11 where said non-imaging coupler is a compound parabolic concentrator.
13. The device of claim 11 where said coupler has input diameter D in , an output diameter D out , and an output angle in said second medium θ 2 , such that D out is about equal to
n
encapsulant
n
2
D
i
n
sin
θ
2
14. The device of claim 13 where said coupler comprises a first portion nearer to said semiconductor light source and a second portion farther from said semiconductor light source than said first portion, said first and second portions separated by a ledge region, where said first portion blocks light ray paths from said semiconductor light source from reaching said ledge region.