Color Mixing Rod Integrator in a Laser-Based Projector

• US 20080278691A1
• Filed: 12/13/2006
• Published: 11/13/2008
• Est. Priority Date: 12/20/2005
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Willemsen, Oscar Hendrikus, Krijn, Marcellinus Petrus Carolus Michael
• Granted Patent: US 8,029,144 B2
• Time in Patent Office: Days
• US Class Current: 353/31
• CPC Class Codes: G02B 27/0994 Fibers, light pipes optical fibers per se G02B6/02
• CPC Class Codes: G02B 27/1006 for splitting or combining different wavelengths G02B27/1086, G02B27/141 take precedence
• CPC Class Codes: G02B 27/102 for generating a colour image from monochromatic image signal sources
• CPC Class Codes: G03B 21/2066 Reflectors in illumination beam in projection beam G03B21/28
• CPC Class Codes: G03B 21/208 Homogenising, shaping of the illumination light
• CPC Class Codes: G03B 33/12 using beam-splitting or beam-combining systems, e.g. dichroic mirrors

Abstract

The present invention provides a system (150) (160), apparatus (100) (200) and method to exploit the high beam quality of a laser light source to lower the cost and decrease the size of a color sequentially operated and laser based projector. Using a color mixing rod integrator (100) (200) (500) (550), laser light is homogenized, thus supplying the proper illumination pattern to a spatial light modulator. The rod integrator is also used to recombine the light of the primary colors, thus obviating dichroic recombination optics. For this purpose all light is coupled into the entrance plane of one and the same color mixing rod integrator. In this way a low cost and compact illumination system is obtained. By adding extra reflective layers to entrance (101) (201) and exit faces (105) of the integrator, the length of the integrator is decreased and/or the F/# in the system is increased. This enables a truly portable projector. When applying a color mixing rod integrator according to the present invention in a light engine with a reflective spatial light modulator, the integrator is very well suited for light recycling, which can increase an image'"'"'s brightness up to a factor of three at average video display load.

Claims

1. A color mixing rod integrator (100) (200) for a plurality of beams of laser light of a plurality of primary display colors, comprising:

a rod-shaped body (106) having an interior that passes laser light therethrough and an interior surface (107) that reflects light incident thereon;

an entrance face (101) covered with a first reflective coating (102) to reflect light incident thereon back into the interior of the rod-shaped body (106) and positioned on a first end of the rod-shaped body having a plurality of holes (103) therein such that each hole of said plurality (103) allows light of at least one beam of said plurality of beams to pass therethrough into the interior of the rod-shaped body (106);

an exit face (105) positioned on a second end of the rod-shaped body (106) opposite to and parallel to the entrance face (101), said exit face (105) to allow a part of light incident thereon to pass therethrough; and

means for diverging each of said beams toward said exit face (105) through said interior, wherein, part of the laser light entering said rod integrator via said holes (103) is forced to pass through the interior thereof several times before passing through said exit face (105) and then exiting through said exit face (105) is homogenized.

2. The color mixing rod (100) (200) of claim 1, wherein the rod-shaped body (106) further comprises a length greater than or equal to the coherence length of the plurality of beams of laser light such that said homogenized light exiting through said exit face (105) has speckle therein reduced.

3. The color mixing rod (100) (200) of claim 1, wherein the laser light passing through said exit face (105) has speckle therein reduced by at least 75% and transmission thereof is greater than 85%.

4. The color mixing rod integrator (100) (200) of claim 1, wherein said means for diverging is a plurality of optical elements positioned at said holes (103) such that the divergence of a beam at the end of a first pass through the integrator (100) (200) is a divergence selected from the group consisting of a spot across the entire exit face (500) and a spot of a predetermined diameter on the exit face (550).

5. The color mixing rod integrator (100) (200) of claim 4, wherein:

said exit face (105) is covered with a partially reflective coating (204) that allows a part of light incident thereon to pass therethrough and reflects a part of light incident thereon back into the rod-shaped body (106) toward a source of said light; and

said reflective coating (102) on said entrance face (101) is a highly reflective coating (202).

6. The rod integrator (100) of claim 5, wherein:

the first reflective coating (102) is a highly reflective material (202) selected from the group consisting of silver and a dielectric stack; and

the plurality of holes (103) are each of a diameter such that the laser light can be focused into said hole and can pass therethrough without significant light loss and diffraction effects.

7. The rod integrator (100) (200) of claim 6, wherein:

said laser light is focused to enter each of the holes (103) with a half angle θ

_1/2<

20 degrees in air;

each of said holes (103) has a diameter ≧

2d where d is determined by the equation

8. The rod integrator (100) (200) of claim 7, wherein said half angle θ

_1/2<

15 degrees in air.

9. A method for integrating a plurality of laser beams of light each beam comprising one of a plurality of primary display colors, comprising:

providing a rod-shaped body (106) that includes an entrance face (101) positioned on a first end and an exit face (105) positioned on a second end (106) opposite to and parallel to the entrance face (101) and having an interior that passes the laser beams of light therethrough and an interior surface (107) that reflects light incident thereon back into the interior of the rod-shaped body (106);

covering the entrance face (101) of the provided rod-shaped body with a first reflective coating (102) having a plurality of holes (103) therein to allow light of said laser beams to pass therethrough into the interior of the rod-shaped body, said first reflective coating to reflect light incident thereon back into the interior of the rod-shaped body (106); and

diverging each of said beams toward said exit face (105) through said interior, wherein part of the light of said laser beams entering said rod-shaped body (106) via said holes (103) is forced to pass through the interior thereof a plurality of times before passing through said exit face (105) and then exiting through said exit face (105), is homogenized.

10. The method of claim 9, wherein said rod-shaped body (106) a length greater than or equal to the coherence lengths of the beams of laser light such that said light exiting through said exit face (105) has speckle therein reduced.

11. The method of claim 9, wherein said light exiting through said exit face (105) has speckle therein reduced by at least 75% and transmission thereof is greater than 85%.

12. The method of claim 11, further comprising the step of providing a partially reflective coating (204) covering the exit face (105) that reflects a part of the light incident thereon back into the interior of the color mixing rod integrator (200) and allows a remaining part of the light incident thereon to pass therethrough;

13. The method of claim 12, wherein each hole of the plurality of holes (103) is of such a diameter d that the beams of laser light, which have an extremely low é

tendue and thus can be focused to a very small spot, can pass through the holes (103) without significant light loss or diffraction effects.

14. The method of claim 13, wherein said diverging step further comprises the step of providing a plurality of optical elements positioned at said holes (103) such that the divergence of a beam at the end of a first pass through the integrator (100) (200) is a divergence selected from the group consisting of a spot across the entire exit face (500) and a spot of a predetermined diameter on the exit face (550).

15. The method of claim 14, further comprising the steps of:

focusing each of said beams of light to enter a hole of said plurality of holes (103) with a half angle θ

_1/2<

20 degrees in air;

sizing each said hole of said plurality of holes (103) to have a diameter ≧

2d where d is determined by the equation

16. The method of claim 15, wherein said half angle θ

_1/2<

15 degrees in air.

17. A projection engine (160), comprising:

a color mixing rod integrator (100) (200) including;

a rod-shaped body (106) having an interior that passes a plurality of beams of laser light of a plurality of primary display colors therethrough and an interior surface (107) that reflects light incident thereon back into the interior of the rod-shaped body (106),

an entrance face (101) positioned on a first end of the rod-shaped body covered with a first reflective coating (101) having a plurality of holes (103) therein to allow the laser beams of light to pass therethrough into the interior of the rod-shaped body, said first reflective coating to reflect light incident thereon back into the interior of the rod-shaped body (106),

means for diverging each of said beams of said plurality of beams toward said exit face (105) through said interior, said means being positioned in proximity to said plurality of holes (103), and

an exit face (105), positioned on a second end of the rod-shaped body (106) opposite to and parallel to the entrance face (101),

wherein part of the beams of laser light entering said rod integrator via said plurality of holes (103) at a given half angle is forced to pass through the interior thereof several times before passing through said exit face (105) and then exiting through said exit face (105) is homogenized;

a display panel (108) configured in proximity to said exit face (105) of said color mixing rod integrator (100) (200) such that illumination of said display panel (108) is by the homogenized light exiting through said exit face (105).

18. The engine (160) of claim 17 wherein the rod-shaped body (160) has a length greater than or equal to the coherence lengths of the plurality beams of laser light of a plurality of primary display colors such that said light exiting through said exit face (105) has speckle therein reduced.

19. The engine (160) of claim 17, wherein the beams of laser light exiting through said exit face (105) have speckle therein reduced by at least 75% and transmission thereof is greater than 85%.

20. The engine (150) of claim 17, further comprising a second reflective coating (204) that is a partially reflective coating (204), covering the exit face (105), wherein, a part of the beams of laser light is reflected back toward the sources thereof by the partially reflective coating (204) and a remaining part of the beams of light exits therethrough.

21. The engine (150) of claim 20, wherein said means for diverging is a plurality of optical elements positioned at said holes (103) such that the divergence of a beam at the end of a first pass through the integrator (100) (200) is a divergence selected from the group consisting of across the entire exit face (500) and a spot of a predetermined diameter on the exit face (550).

22. The engine (150) of claim 21, wherein said first reflective coating (102) on said entrance face (101) is a highly reflective coating (202).

23. The engine (150) of claim 22, wherein:

the highly reflective coating (202) is a material selected from the group consisting of silver and a dielectric stack;

the plurality of holes (103) are each of a diameter such that each of the beams of laser light can be focused into one of said holes (103) and can pass therethrough without significant light loss and diffraction effects.

24. The engine (150) of claim 23, wherein:

each said beam of laser light is focused to enter one of said holes (103) with a half angle θ

_1/2<

20 degrees in air;

each of said holes (103) has a diameter ≧

2d where d is determined by the equation

25. The engine (160) of claim 24, wherein said half angle θ

_1/2<

15 degrees in air.

26. The engine (160) of claim 24, further comprising a relay optics 109 configured in proximity to said exit face (105) to accomplish illumination of said display panel (108).