Polarized, multicolor LED-based illumination source

• US 20070146639A1
• Filed: 12/23/2005
• Published: 06/28/2007
• Est. Priority Date: 12/23/2005
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Conner, Arlie
• Granted Patent: US 7,540,616 B2
• Time in Patent Office: Days
• US Class Current: 353/20
• CPC Class Codes: G03B 21/204 using secondary light emission, e.g. luminescence or fluorescence using different colours G03B33/00; if related to video signals H04N9/3197
• CPC Class Codes: G03B 21/2073 Polarisers in the lamp house peculiar to electronic spatial light modulators H04N9/3197
• CPC Class Codes: G03B 33/06 by additive-colour projection apparatus
• CPC Class Codes: G03B 33/12 using beam-splitting or beam-combining systems, e.g. dichroic mirrors
• CPC Class Codes: H04N 9/3167 for polarizing the light beam polarizing optical systems per se G02B27/28

Abstract

Light emitting diodes (LEDs) emit light at a first wavelength. A phosphor material close to LEDs converts at least some of the light to a second wavelength. The light at both wavelengths passes through a light collecting unit. A reflecting polarizer transmits both wavelengths in a first polarization state and reflects light at both wavelengths in a second, orthogonal, polarization state. Light reflected by the reflective polarizer is directed back towards the phosphor material without any substantial increase in angular range. The resulting output light beam contains polarized light at the first and second wavelengths. In some embodiments, an array of LEDs includes LEDs that emit light at a first wavelength and others that emit light at a second wavelength. The phosphor material is disposed on the LEDs emitting the light at the first wavelength.

Claims

1. An illumination source, comprising:

an arrangement of one or more light emitting diodes (LEDs) comprising LEDs capable of generating light at a first wavelength;

phosphor material disposed proximate the one or more LEDs, the phosphor material emitting light at a second wavelength when illuminated by the light at the first wavelength;

a light collecting unit comprising at least a tapered optical element, light at the first and second wavelengths passing through the light collecting unit; and

a reflective polarizer disposed to transmit light at the first and second wavelengths in a first polarization state and to reflect light at the first and second wavelengths in a second polarization state orthogonal to the first polarization state, light at the first and second wavelengths reflected by the reflective polarizer being directed back towards the phosphor material without any substantial increase in angular range, the illumination source producing an output light beam containing polarized light at the first and second wavelengths.

2. A source as recited in claim 1, wherein the light at the first and second wavelength is substantially telecentric at the reflective polarizer.

3. A source as recited in claim 1, wherein the reflective polarizer comprises a curved reflecting polarizer.

4. A source as recited in claim 3, wherein the curved reflecting polarizer has a radius of curvature centered approximately at the phosphor material.

5. A source as recited in claim 1, wherein the first wavelength is a blue wavelength and the second wavelength is a green wavelength.

6. A source as recited in claim 1, wherein the phosphor material comprises Eu-doped SrGa₂S_4.

7. A source as recited in claim 1, wherein the tapered optical element comprises flat reflecting sides.

8. A source as recited in claim 1, wherein the tapered optical element comprises curved reflecting sides.

9. A source as recited in claim 1, wherein light collecting unit comprises a lens disposed proximate the output end of the tapered optical element.

10. A source as recited in claim 1, wherein the tapered optical element comprises a transparent body with internally reflecting sidewalls and a curved output face.

11. A source as recited in claim 1, further comprising a reflective element disposed to reflect a first portion of the light at the first wavelength that has passed through the phosphor material and to transmit a second portion of the light at the first wavelength that has passed through the phosphor material.

12. A source as recited in claim 1, wherein the reflective polarizer comprises a multilayer optical film polarizing beamsplitter and a mirror.

13. A source as recited in claim 1, wherein the reflective polarizer comprises one of a wire grid polarizer and a cholesteric polarizer.

14. A source as recited in claim 1, further comprising a polarization control element disposed between the phosphor and the reflective polarizer.

15. A source as recited in claim 1, wherein the reflective polarizer comprises a multilayer optical film polarizer.

16. A source as recited in claim 1, wherein the one or more LEDS are spaced apart from an input to the a light collecting unit, and further comprising a reflector at least partially surrounding the input so as to reflect light from the one or more LEDS towards the input that would otherwise not pass into the input.

17. A source as recited in claim 1, further comprising a power supply coupled to provide power to the one or more LEDs.

18. A source as recited in claim 1, wherein the arrangement of one or more LEDs further comprises LEDs capable of generating light at a third wavelength.

19. A source as recited in claim 18, wherein the reflective polarizer transmits light at the first, second and third wavelengths in the first polarization state and reflects light at the first, second and third wavelengths in the second polarization state, the output beam further containing polarized light at the third wavelength.

20. A source as recited in claim 1, further comprising an image-forming device, light at the second wavelength being directed to the image-forming device.

21. A source as recited in claim 20, further comprising a projection lens unit disposed to project an image form the image-forming device and a screen on which the image is projected.

22. A source as recited in claim 20, further comprising a controller coupled to control an image formed by the image-forming device.

23. An illumination source, comprising:

an array of one or more light emitting diodes (LEDs) comprising first LEDs capable of emitting light at a first wavelength and second LEDs capable of emitting light at a second wavelength different from the first wavelength; and

a phosphor material disposed on the first LEDs so that light from the first LEDs is incident on the phosphor material, light at the first wavelength being converted to a third wavelength by the phosphor.

24. A source as recited in claim 23, further comprising a light collecting unit disposed to receive the light at the first, second and third wavelengths.

25. A source as recited in claim 23, further comprising a liquid cooled plate having a first surface and a second surface, the first and second LEDs being attached directly to the first surface of the liquid cooled plate, a liquid coolant contacting the second surface of the liquid cooled plate.

26. A source as recited in claim 25, wherein the liquid cooled plate comprises a metal plate having a thickness of less than one millimeter.

27. A source as recited in claim 23, wherein the light at the second wavelength passes through the phosphor.