WO2005029155A1

WO2005029155A1 - Efficient and compact polarization conversion method

Info

Publication number: WO2005029155A1
Application number: PCT/IB2004/051768
Authority: WO
Inventors: Peter J. Janssen
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2003-09-19
Filing date: 2004-09-15
Publication date: 2005-03-31

Abstract

An apparatus for converting an input beam of non-polarized light to polarized light includes first and second light guides. A polarizing surface reflects a first polarized component of the input beam into the first light guide and transmits a second polarized component that is polarized differently from the first polarized component. A reflective surface behind the polarizing surface reflects the second polarized component transmitted through the polarizing surface into the second light guide. The reflective surface is non-parallel to the polarizing surface. A wave-plate intercepts one of the first and second polarized components and converts the polarization of the first or second polarized component to be the same as the other of one.

Description

PHUS030346 1 EFFICIENT AND COMPACT POLARIZATION CONVERSION METHOD

This invention relates generally to methods of converting non-polarized light into polarized light and, more particularly to polarization conversion methods that are particularly useful in providing polarized input beams for high-light applications such as stripe illumination used in scrolling color systems for liquid crystal based displays, projectors, etc. Liquid Crystal (LC) light valves modulate light by changing the polarization of light passing through the birefringent LC medium. In LC systems it is generally desirable to minimize the size of the light valve in order to minimize the cost and/or size of a projector. However, reduction in light valve size results in a concomitant reduction in light output. As a result, with existing polarization conversion techniques, the components must be relatively large and expensive for efficient light collection. Additionally, some polarization conversion techniques, such as those using an embedded tilted polarizing stack, often work well only for a small range of incident angles and wavelengths. Further, the glue used to bond coated elements tends to degraded under intense light exposure such as that necessary for LC light valve projection display and other high-light level systems. To address one or more of the above concerns, in a first aspect of the invention an apparatus for converting an input beam of non-polarized light to polarized light includes a first light guide; a second light guide; a polarizing surface disposed for reflecting a first polarized component of the input beam into the first light guide and transmitting a second polarized component that is polarized differently from the first polarized component; a reflective surface disposed behind the polarizing surface for reflecting the second polarized component transmitted through the polarizing surface into the second light guide, the reflective surface being non-parallel to the polarizing surface; and a wave-plate disposed for intercepting only one of the first and second polarized components and converting the polarization of the one of the first and second polarized components to be the same as the other of the first and second polarized components. PHUSO 30346 2 In another aspect of the invention, an apparatus for converting an input beam of non-polarized light to polarized light includes a first light guide; a second light guide; means disposed for reflecting a first polarized component of the input beam into the first light guide and transmitting a second polarized component that is polarized differently from the first polarized component; a reflective surface disposed behind the polarizing surface for reflecting the second polarized component transmitted through the polarizing surface into the second light guide, the reflective surface being non-parallel to the polarizing surface; and polarization conversion means for converting the polarization of the one of the first and second polarized components to be the same as the other of the first and second polarized components. In a third aspect of the invention, a method of converting an input beam of non-polarized light to an output beam of polarized light includes reflecting a first polarized component of the input beam from a polarizing surface; imaging the first polarized component reflected from the polarizing surface into a first light guide; transmitting a second polarized component of the input beam through the polarizing surface; after transmitting the second polarized component to the polarizing surface, reflecting the second polarized component off a reflective surface disposed behind and being non-parallel to the polarizing surface; imaging the second polarized component reflected off the reflective surface into a second light guide; and converting the polarization of one of the first and second polarized components to be the same as the other of the first and second polarized components.

The invention is explained below with reference to the following drawing figures, of which: Figs. 1A and IB illustrate polarization conversion combined with a lens array homogenizer; Fig. 2 illustrates a polarization conversion unit that can be integrated into a light guide; Figs. 3 A, 3B, and 3C illustrate an example of polarization conversion according to an embodiment of the invention; and PHUS030346 3 Fig. 4 illustrates another possible configuration for polarization conversion according to the invention. Figs. 1A and IB illustrate a polarization conversion method for projection systems. Light is first split into two orthogonally polarized components by an embedded tilted polarizing stack. One of the components passes through a half- wave plate, which rotates the polarization 90 degrees. Thus, the light of both exiting beams have the same polarization. In the illustrated example, collimated light from a parabolic reflector lamp (not shown) is incident on a lens array 2, shown in Fig. 1A. Each lens 4 of the array 2 produces a small spot centered on a corresponding lens 6 of a second lens array 8. As shown in an enlarged partial view in Fig. IB, a polarization coating 10 transmits the p- polarized component 12 of the light ray 14 and reflects the s-polarized component 16. The s-polarized component 16 is converted upon passage through a half- wave plate 18 into p-polarized light 20. Copending U.S. patent application 10/024,775 teaches a polarization conversion unit that can be integrated into a light guide. For example, as shown in Fig. 2, a half-prism 22 and a full prism 24 have total internal reflection (TIR) boundaries 26, 28 that provide light guiding. The polarizing coating on the full prism's TIR boundary 26 reflects one polarization component of the input light and transmits the other polarization component. The reflected component is folded by the half-prism 22. The polarization of the light exiting the full-prism 24 is converted to match the polarization of the other component by a wave-plate 30. In one polarization conversion configuration according to the invention, illustrated in Fig. 3C, light from a light source (not shown) exits a first light guide 32 and passes through a field lens 34 and an imaging lens 36. As most clearly seen in Fig. 3A, a first polarization component is retro- reflected by a reflective polarizer 38 and is imaged by the imaging lens 36 into a second light guide 40. As most clearly seen in Fig. 3B, a second polarization component is transmitted through the reflective polarizer 38 (not shown in Fig. 3B) and is reflected by a mirror 42, which is tilted with respect to the reflective polarizer 38, and is imaged by PHUS030346 4 the imaging lens 36 into a third light guide 44. The polarization of the second component is converted by a wave-plate 46. The field lens 34 helps provide telecentric illumination of the second and third light guides 40, 44. Fig. 4 shows a configuration similar to that of Fig. 3C. Here, a polarizing layer 48 is deposited on the back side of the imaging lens 36 and the exit light guides 40, 44 are merged into a single, larger one 50. It can be appreciated that many similar combinations and modifications can be made. Other embodiments, variations of embodiments, and equivalents, as well as other aspects, objects, and advantages of the invention, will be apparent to those skilled in the art and can be obtained from a study of the drawings, the disclosure, and the appended claims.

Claims

1. An apparatus for converting an input beam of non-polarized light to polarized light, comprising: a first light guide; a second light guide; a polarizing surface disposed for reflecting a first polarized component of the input beam into the first light guide and transmitting a second polarized component that is polarized differently from the first polarized component; a reflective surface disposed behind the polarizing surface for reflecting the second polarized component transmitted through the polarizing surface into the second light guide, the reflective surface being non-parallel to the polarizing surface; and a wave-plate disposed for intercepting only one of the first and second polarized components and converting the polarization of said one of the first and second polarized components to be the same as the other of the first and second polarized components.

2. The apparatus of claim 1, including a field lens disposed at entrances of the first and second light guides.

3. The apparatus of claim 1, including an imaging lens disposed in front of the polarizing surface and the reflective surface.

4. The apparatus of claim 1, wherein the first light guide and the second light guide are portions of a larger light guide.

5. An apparatus for converting an input beam of non-polarized light to polarized light, comprising: a first light guide; a second light guide; means disposed for reflecting a first polarized component of the input beam into the first light guide and transmitting a second polarized component that is polarized differently from the first polarized component; a reflective surface disposed behind the polarizing surface for reflecting the second polarized component transmitted through the polarizing surface into the second light guide, the reflective surface being non-parallel to the polarizing surface; and polarization conversion means for converting the polarization of said one of the first and second polarized components to be the same as the other of the first and second polarized components.

6. The apparatus of claim 5, including means for providing telecentric illumination of the first and second light guides by the first and second polarized components, respectively.

7. The apparatus of claim 5, including means for imaging the first and second polarized components into the first and second light guides, respectively.

8. The apparatus of claim 5, wherein the first light guide and the second light guide are portions of a larger light guide.

9. A method of converting an input beam of non-polarized light to an output beam of polarized light, comprising: reflecting a first polarized component of the input beam from a polarizing surface; imaging the first polarized component reflected from the polarizing surface into a first light guide; transmitting a second polarized component of the input beam through the polarizing surface; after transmitting the second polarized component to the polarizing surface, reflecting the second polarized component off a reflective surface disposed behind and being non-parallel to the polarizing surface; imaging the second polarized component reflected off the reflective surface into a second light guide; and converting the polarization of one of the first and second polarized components to be the same as the other of the first and second polarized components.

10. The method of claim 9, including providing telecentric illumination of the first and second light guides by the first and second polarized components, respectively.