WO2001094993A2

WO2001094993A2 - Reflective polarizer

Info

Publication number: WO2001094993A2
Application number: PCT/US2001/018672
Authority: WO
Inventors: Edmund Sandberg; Arthur L. Berman
Original assignee: Digital Reflection, Inc.
Priority date: 2000-06-08
Filing date: 2001-06-07
Publication date: 2001-12-13
Also published as: WO2001094993A3; AU2001266811A1

Abstract

Method and system for providing a reflective linear polarizer for an optical system such as a video projection system to more perfectly polarize the S component of the polarized incoming light from being polluted with the P component of the polarized incoming light by providing a non-absorptive polarization in the light path is provided.

Description

SPECIFICATION

REFLECTIVE POLARIZER

RELATED APPLICATION

The present application claims priority under 35 USC §119 to provisional application no. 60/210,285 filed on June 8, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical systems. More particularly, the present invention relates to method and system for providing a reflective linear polarizer for optical systems including video projection systems.

2. Description of the Related Art

Optical systems such as video projection system may be configured to manipulate linearly polarized light. If the linear polarized light in such optical systems is created using a polarized beam splitting cube, the S component of the polarized light reflected by the beam splitting cube may be polluted with some P component of the polarized light. In one approach, a linear polarizer may be placed in the light path as a "clean-up" polarizer to more accurately polarize the S component of the polarized light. Typically, the linear polarizer is an absorptive type polarizer.

In a star prism kernel such as that used in the system by Digital Reflections, Inc. of Los Gatos, California, the assignee of the present application, the light flux is very high and the conventional polymer based absorptive polarizer may be insufficient particularly in light of the heat load. Thus, a non-absorptive approach to the polarization clean up is necessary. One such non-absorptive polarization approach includes the use of a reflective polarizer.

A wire grid reflective polarizer is generally temperature stable, providing a wide angle and good transmission and contrast ratio. Such wire grid reflective polarizers have a soft surface, and require considerable care in cleaning and handling during optical system assembly. Moreover, the wire grid reflective polarizer may have residual absorption, with both the contrast ratio and the transmission reduced at shorter wavelengths. Furthermore, wire grid reflective polarizers are relatively expensive and presently available only in limited quantities. Other reflective polarizers include cholesteric liquid crystal polarizers which provide good transmission and contrast ratio and reflects circularly polarized light, but is similarly expensive.

The contrast ratio of an optical system is the product of the contrast ratio of the polarizer beam splitting cube multiplied by the contrast ratio of the cleanup polarizer. In other words, the contrast ratio of the clean-up polarizer does not have to be very high to obtain a high system contrast ratio, and a value greater than 50: 1 is generally acceptable. Additionally, the reflective polarizer may be positioned in the optical system such that it only encounters green light. Thus, the design of the reflective polarizer may be optimized for performance in the green light wavelength band. Also, since the position of the reflective polarizer is a considerable distance away from the focal point, any physical structure in the polarizer may be not focused and thus may be invisible in the projected image. Furthermore, due to the position of the reflective polarizer, it encounters a very high intensity light flux. Consequently, the reflective polarizer must have very little residual absorption.

SUMMARY OF THE INVENTION

I-n view of the foregoing, a reflective polarizer for use in an optical system in accordance with one embodiment of the present invention includes a substrate having a body portion and a grooved portion, the grooved portion including a light receiving surface the light receiving surface configured to receive an incoming light, the light receiving surface further configured to reflect back a first portion of the incoming light substantially in the same direction as the incoming light and further, to transmit a second portion of the incoming light through the body portion of the substrate.

The incoming light may be unpolarized, and further, where the reflected first portion of the incoming light may be S component of the incoming light and the transmitted second portion of the incoming light may be P component of the incoming light.

The light receiving surface may include a plurality of grooves, each of the grooves having a pair of grooved surfaces, each of the grooved surface substantially angled at 45 degrees relative to the body portion of the substrate.

The light receiving surface may include a plurality of grooves, each of the grooves substantially V-shaped and the plurality of grooves sequentially positioned along the light receiving surface.

Moreover, each of the adjacent grooves may be positioned substantially 0.1 mm apart, and the body portion of the substrate may be approximately 0.5 mm in thickness.

The substrate may a polycarbonate substrate, or an acrylic substrate.

In particular, the substrate may be made of one of a glass material and a plastic material.

The substrate may be non-birefringent.

The light receiving surface may be provided with a polarized beam splitting thin film coating.

The substrate may have an index of refraction of approximately 1.58.

The polarizer may also include a cover plate, and an optical adhesive provided between the cover plate and the light receiving surface of the substrate groove portion.

The optical adhesive may be index matched to the substrate, while the cover plate may include a polycarbonate substrate.

The cover plate may include a body portion and a grooved portion, the grooved portion provided with the optical adhesive, the grooved portion of the cover plate substantially configured to receive the light receiving surface of the substrate groove portion.

Additionally, the grooved portion of the cover plate may be provided with a plurality of V-shaped grooves, the V-shaped grooves substantially configured to mate to a corresponding groove of the light receiving surface of the substrate groove portion.

Also, a layer of green dichroic may be deposited on an outer surface of the cover plate opposite a surface facing the substrate.

Additionally, an anti-reflection layer may be provided on a light exiting surface of the substrate body portion, where the light exiting surface of the substrate body portion may be not laminated.

A reflective polarizer for use in an optical system in accordance with another embodiment of the present invention includes a substrate including a grooved surface, a polarized beamsplitting coating deposited on the substrate groove surface, a cover plate, an optical adhesive provided between the cover plate and the substrate grooved surface, where an unpolarized light received on the substrate grooved surface is decomposed into a transmitted portion and a reflected portion.

The received unpolarized light may be decomposed into S component and P component, the S component corresponding to the reflected portion and the P component corresponding to the transmitted portion.

The grooved surface may be substantially triangular shaped, and the substrate may be made of polycarbonate or acrylic, and may be non- birefringent. Moreover, the substrate may have an index of refraction of 1.58, while the optical adhesive may be index matched to the substrate.

A method of providing a reflective polarizer for use in an optical system in accordance with yet another embodiment of the present invention includes providing a substrate including a grooved surface, depositing a polarized beamsplitting coating on the substrate groove surface, providing a cover plate, and providing an optical adhesive between the cover plate and the substrate grooved surface, where an unpolarized light received on the substrate grooved surface is decomposed into a transmitted portion and a reflected portion.

The grooved surface may be substantially triangular shaped, the step of providing the substrate may include the step of providing one of a polycarbonate substrate and an acrylic substrate, and the substrate may be non- birefringent, and may have an index of refraction of approximately 1.58. The method in one aspect may further include the step of index matching the optical adhesive to the substrate.

These and other features and advantages of the various aspects and embodiments of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a reflective polarizer in accordance with one embodiment of the present invention.

Figure 2 illustrates the physical dimensions of the reflective polarizer of Figure 1.

Figure 3 illustrates the reflective polarizer of Figure 1 configured for use in a star prism kernel of an optical system in accordance with one embodiment of the present invention.

Figure 4 illustrates the reflective polarizer of Figure 1 configured for use in a star prism kernel of an optical system in accordance with another embodiment of the present invention.

INCORPORATION BY REFERENCE What follows is a cite list of references each of which is, in addition to those references that may be cited above and below herein, including that which is described as background, and the above invention summary, are hereby incorporated by reference into the detailed description of the preferred embodiment below, as disclosing alternative embodiments of elements or features of the preferred embodiments not otherwise set forth in detail below. A single one or a combination of two or more of these references may be consulted to obtain a variation of the preferred embodiments described in the detailed description below. Further patent, patent application and non-patent references may be cited in the written description and are also incorporated by reference into the detailed description of the preferred embodiment with the same effect as just described with respect to the following references: United States patent applications no. 60/192,258, 60/192,732, 60/194,735, 60/198,436, 60/200,094, 60/202,265, 60/208,603, 60/210,784, 60/210,285, 60/213,334, 60/214,574, 60/215,932, 60/217,758, 60/220,979, 60/224,617, 60/224,961, 60/224,257, 60/224,503, 60/224,291, 60/224,290, 60/224,060, 60/224,059, 60/224,061, 60/224,289, 60/227,229, 60/229,666, 60/230,330, 60/230,326, 60/232,281, 60/234,415, 60/245,807 and 60/249,815, each of which is assigned to the same assignee as the present application.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 illustrates a reflective polarizer in accordance with one embodiment of the present invention. Referring to Figure 1, a configuration of a reflective polarizer 100 is provided with a polycarbonate substrate 110 with 45° grooves on the light receiving surface forming a triangular grooved surface. The light receiving surface of the substrate 110 is provided with a thin film of polarized beamsplitting coating 120 such as that used is polarized beamsplitting cubes, along the triangular grooved surface.

As shown in Figure 1, when the incoming unpolarized combined S component and P component input light 130 is received at the light receiving surface of the substrate 110 with polarized beamsplitting coating 120, the transmitted light is the P component of the polarized input light as shown by light pathl31 and transmitted through the reflective polarizer 100, while the reflected light is the S component of the polarized input light and reflected back towards the direction of the input light as substantially shown by path 132 in Figure 1.

In the manner described above, the incoming light may be decomposed into two components, the P component transmitted without alteration, and the S component which is reflected back towards the direction of the light source. In particular, as shown in Figure 1, the S component of the incoming light is reflected first on the polarized beamsplitting coated light receiving surface 111 and then onto the adjacent beamsplitting coated light receiving surface 112 of the substrate 110 such that the direction of travel of the S component of the incoming light is substantially completely reversed.

Figure 2 illustrates the physical dimensions of the reflective polarizer of Figure 1. Referring to Figure 2, the physical dimensions of the reflective polarizer 110 in one embodiment is shown. As can be seen, the grooves on the light receiving surface of the reflective polarizer 110 is angled substantially at 45° forming a series of V-shaped grooves, with the distance between the center of the adjacent V-shaped grooves being approximately 0.1 mm. Furthermore, in one aspect, the substrate 110 may be composed of a material such as glass or plastic with index of refraction of 1.58. In the case the substrate 110 is made from plastic, the material may be non-birefringent such that the substrate 110 does not effect the polarization. Examples of plastic material for the substrate 110 include acrylic and polycarbonate.

Figure 3 illustrates the reflective polarizer of Figure 1 configured for use in a star prism kernel of an optical system in accordance with one embodiment of the present invention. Referring to Figure 3, a mated configuration of a reflective polarizer mated to a grooved substrate is shown. In particular, a second grooved substrate 310 provided with a layer of optical adhesive coating 320 on the grooved surface forming a cover plate for the grooved substrate 110 is provided on the complementary grooved surface of the substrate 110. The optical adhesive coating in one embodiment may be index matched to the substrate 110.

Figure 4 illustrates the reflective polarizer of Figure 1 configured for use in a star prism kernel of an optical system in accordance with another embodiment of the present invention. Referring to the Figure, a flat cover plate for the substrate 110 is provided. In particular, a flat substrate 410 may be provided with a deposit of optical adhesive 420 between the flat substrate 410 and the grooved substrate 110 such that the optical adhesive 420 substantially fills the grooves of the substrate 110 between the flat substrate 410 and the triangular grooved substrate 110. Additionally, in one aspect of the present invention, a layer of green dichroic 430 may be provided on the outer surface of the flat substrate 410 opposite the surface facing the grooved substrate 110. In this manner, in one approach, the thin film coating of green dichroic 430 may be combined with the reflective polarizer substrate 410 rather than being provided as a separate substrate layer in the prism assembly of the video projection system. Moreover, the outer surface of the polarizer substrate 110 may be provided with a layer of anti-reflection coating 440 in particular, in cases where the outer surface of the substrate 110 is not laminated.

In the manner described above, in accordance with various embodiments of the present invention, method and system for providing a reflective linear polarizer for an optical system such as a video projection system to more accurately polarize the S component of the polarized incoming light from being polluted with the P component of the polarized incoming light by providing a non-absorptive polarization in the light path is provided. In particular, the reflective linear polarizer of the various embodiments of the present invention described above is provided with high contrast and throughput, a wide acceptance angle, while being physically robust and relatively inexpensive and easy to manufacture.

Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.

Claims

WHAT IS CLAIMED IS:

1. A reflective polarizer for use in an optical system, comprising: a substrate having a body portion and a grooved portion, said grooved portion including a light receiving surface said light receiving surface . configured to receive an incoming light, said light receiving surface further configured to reflect back a first portion of said incoming light substantially in the same direction as the incoming light and further, to transmit a second portion of said incoming light through said body portion of said substrate.

2. The polarizer of claim 1 wherein said incoming light is unpolarized.

3. The polarizer of claim 1 wherein said reflected first portion of said incoming light is an S component of said incoming light and said transmitted second portion of said incoming light is a P component of said incoming light.

4. The polarizer of claim 1 wherein said light receiving surface includes a plurality of grooves, each of said grooves having a pair of grooved surfaces, each of said grooved surface substantially angled at 45 degrees relative to said body portion of said substrate.

5. The polarizer of claim 1 wherein said light receiving surface includes a plurality of grooves, each of said grooves substantially V-shaped and said plurality of grooves sequentially positioned along said light receiving surface.

6. The polarizer of claim 4 wherein each of said adjacent grooves is positioned substantially 0.1 mm apart.

7. The polarizer of claim 1 wherein said body portion of said substrate is approximately 0.5 mm in thickness.

8. The polarizer of claim 1 wherein said substrate is a polycarbonate substrate.

9. The polarizer of claim 1 wherein said substrate is an acrylic substrate.

10. The polarizer of claim 1 wherein said substrate is made of one of a glass material and a plastic material.

11. The polarizer of claim 1 wherein said substrate is non-birefringent.

12. The polarizer of claim 1 wherein said light receiving surface is provided with a polarized beam splitting thin film coating.

13. The polarizer of claim 1 wherein said substrate has an index of refraction of approximately 1.58.

14. The polarizer of claim 1 further including: a cover plate; and an optical adhesive provided between said cover plate and said light receiving surface of said substrate groove portion.

15. The polarizer of claim 13 wherein said optical adhesive is index matched to said substrate.

16. The polarizer of claim 13 wherein said cover plate includes a polycarbonate substrate.

17. The polarizer of claim 13 wherein said cover plate includes a body portion and a grooved portion, said grooved portion provided with said optical adhesive, said grooved portion of said cover plate substantially configured to receive said light receiving surface of said substrate groove portion.

18. The polarizer of claim 13 wherein said grooved portion of said cover plate is provided with a plurality of V-shaped grooves, said V-shaped grooves substantially configured to mate to a corresponding groove of said light receiving surface of said substrate groove portion.

19. The polarizer of claim 13 further including a layer of green dichroic deposited on an outer surface of said cover plate opposite a surface facing said substrate.

20. The polarizer of claim 13 further including an anti-reflection layer provided on a light exiting surface of said substrate body portion.

21. The polarizer of claim 19 wherein said light exiting surface of said substrate body portion is not laminated.

22. A reflective polarizer for use in an optical system, comprising: a substrate including a grooved surface; a polarized beamsplitting coating deposited on said substrate groove surface; a cover plate; and an optical adhesive provided between said cover plate and said substrate grooved surface; wherein an unpolarized light received on said substrate grooved surface is decomposed into a transmitted portion and a reflected portion.

23. The polarizer of claim 21 wherein received unpolarized light is decomposed into S component and P component, said S component corresponding to said reflected portion and said P component corresponding to said transmitted portion.

24. . The polarizer of claim 21 wherein said grooved surface is substantially triangular shaped.

25. The polarizer of claim 21 wherein said substrate is a polycarbonate substrate.

26. The polarizer of claim 21 wherein said substrate is an acrylic substrate.

27. The polarizer of claim 21 wherein said substrate is made of one of a glass material and a plastic material.

28. The polarizer of claim 21 wherein said substrate is non-birefringent.

29. The polarizer of claim 21 wherein said substrate has an index of refraction of approximately 1.58.

30. The polarizer of claim 21 wherein said optical adhesive is index matched to said substrate.

31. The polarizer of claim 21 wherein said cover plate includes a polycarbonate substrate.

32. A method of providing a reflective polarizer for use in an optical system, comprising the steps of: providing a substrate including a grooved surface; depositing a polarized beamsplitting coating on said substrate groove surface; providing a cover plate; and providing an optical adhesive between said cover plate and said substrate grooved surface; wherein an unpolarized light received on said substrate grooved surface is decomposed into a transmitted portion and a reflected portion.

33. The method of claim 31 wherein received unpolarized light is decomposed into S component and P component, said S component corresponding to said reflected portion and said P component corresponding to said transmitted portion.

34. The method of claim 31 wherein said grooved surface is substantially triangular shaped.

35. The method of claim 31 wherein said step of providing said substrate includes the step of providing one of a polycarbonate substrate and an acrylic substrate.

36. The method of claim 31 wherein said substrate is non-birefringent.

37. The method of claim 31 wherein said substrate has an index of refraction of approximately 1.58.

38. The method of claim 31 further including the step of index matching said optical adhesive to said substrate.