Polarized, LED-based illumination source

• US 7,445,340 B2
• Filed: 08/31/2005
• Issued: 11/04/2008
• Est. Priority Date: 05/19/2005
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Oehler, Peter R., Donnelly, Sean M., Conner, Arlie R
• Primary Examiner(s): Lee; Diane I.
• Assistant Examiner(s): Cruz; Magda
• Application Number:
  US11/216,258
• Publication Number:
  US 20060262514A1
• Time in Patent Office: 1,161 Days
• Field of Search: 353/20, 353/37, 353/50, 353/81, 353/94, 362/551, 362/555
• US Class Current: 353/20
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G03B 21/16 Cooling; Preventing overheating
• CPC Class Codes: G03B 21/2033 LED or laser light sources
• 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: H04N 9/3141 Constructional details thereof details not peculiar to the presence of an electronic spatial light modulator G03B21/14

Abstract

An illumination source includes a number of light emitting diodes (LEDs) operating at a first wavelength. Light from the LEDs illuminates a phosphor material that generates light at a second wavelength. A reflective polarizer transmits light at the second wavelength in a first polarization state and reflects light at the second wavelength in a second polarization state orthogonal to the first polarization state. The light at the second wavelength reflected by the reflective polarizer is directed back towards the phosphor material without an increase in angular range. In some embodiments the LEDs, having a conformal layer of phosphor material, are attached directly to the first surface of a liquid cooled plate. A liquid coolant contacts a second surface of the plate.

Claims

1. An illumination source, comprising:

an arrangement of one or more light emitting diodes (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/focusing unit comprising at least a tapered optical element;

a reflective element disposed to reflect light at the first wavelength that has passed through the phosphor material; and

a reflective polarizer disposed to transmit telecentric light at the second wavelength in a first polarization state and to reflect telecentric light at the second wavelength in a second polarization state orthogonal to the first polarization state, light at the second wavelength reflected by the reflective polarizer being directed back towards the phosphor material without an increase in angular range.

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

3. A source as recited in claim 1, wherein the light at the second wavelength is not telecentric at the second polarizer, and the reflective polarizer comprises a curved reflecting element.

4. A source as recited in claim 3, wherein the curved reflecting element 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 SrGa₂S₄.

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 the collimating element 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 the collimating element.

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

12. A source as recited in claim 10, wherein the collimating element comprises curved reflecting sidewalls.

13. A source as recited in claim 1, wherein the reflective element comprises a long pass reflective filter.

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

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

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

17. A source as recited in claim 1, wherein the one or more LEDS are spaced apart from an input to the a light collecting/focusing 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.

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

19. 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.

20. A source as recited in claim 19, 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.

21. A source as recited in claim 19, further comprising a controller coupled to control an image formed by the image-forming device.