Hollow wedge shaped light guide

[0001] This application is related to Provisional Application Ser. No. 60/336,350, filed Nov. 2, 2000.

[0002] 1. Technical Field

[0003] This invention relates to uniformly distributing collimated light for information display, illumination, and direct lighting applications.

[0004] 2. Background Art

[0005] Present light waveguides, such as those used in personal computers are manufactured from a solid material such as plastic.

[0006] The present invention is a wedge shaped hollow edge-lighted waveguide based on a modular construction technique. This waveguide uses air instead of refractive media. The waveguide is built from optical films that are similar to those commercially available (either sheets or rolls) and can be cut to size to accommodate various display geometries.

List of Reference Numbers for the Major Elements in the Drawing

[0020] The following is a list of the major elements in the drawings in numerical order.

[0021]

5	conical angle (of light ray)
10	top planar sheet
11	total internal reflecting features (top planar sheet)
20	bottom planar sheet
21	reflective light extraction features
100	bottom surface

Mode(s) for Carrying Out the Invention

[0022] Referring first to FIG. 1, a hollow wedge-shaped light guide is formed from a top planar surface 10 and a sloping bottom planar surface 20. The bottom planar surface 20 includes reflective light extraction features 21, which are arranged as a terrace. Advantageously, these terraced extraction features minimize light decollimation effects. The side surfaces 30 of the wedge shaped hollow light guide are specular reflectors.

[0023] The light extraction surfaces 21 of the wedge-shaped waveguide are “clocked” around an axis normal to the light exit plane, where the light exit plane corresponds to the inner surface of top planar sheet 10. I have discovered that a ‘clocking angle’, where the extraction features of a light guide are tilted relative to the input aperture, and rotated (or ‘clocked’) about the normal to the exit aperture is required for a practical hollow wedge shaped light guide in order to deflect the light at preferred angles.

[0024] The light input face is a simple rectangular aperture, defined by top planar sheet 10, bottom planar sheet 20, and specular side surfaces 30.

[0025] The top planar sheet further comprises a top surface having total internal reflecting features 11. In one embodiment of my invention, these total internal reflecting features 11 are formed from a total internal reflection (TIR) film as taught, for example, by Whitehead (U.S. Pat. No. 4,260,22). In certain embodiments of my invention, the total internal reflecting features 11 are substantially less transparent than the bulk material of said top planar sheet 10.

[0026] The top planar sheet 10 structure comprises a transparent structural member supporting one or more films. Films are supported by such techniques as surface lamination or edge fastening. In the case of most transmissive microstuctured films, an air gap must be maintained to ensure proper optical performance. Examples of structural members are optical grade plastic sheet stock, such as those from Ineos Acrylics (Lucite® and Perspex™), ATOFINA Chemicals (Plexiglas® and Tuffak®), GE (Lexan®) and non-birefingent polymers as referenced in this Specification. Also available are glass support structures, such as Corning borosilicate glasses utilized in the manufacture of liquid crystal displays (types 7059, 1737, and EAGLE2000). The plastic sheet offers very good optical clarity, low cost and the ability to withstand more flexure than glass. The glass sheet offers better optical qualities, plus high temperature performance for the application of a variety of functional coatings.

[0027] The sidewalls 30 are opposing, parallel specular reflectors. They may for example, be fabricated from Silverlux, manufactured by the 3M Corporation. Non-optical structural members can support these films, using standard pressure sensitive adhesives, such as those produced by 3M, Nittodenko or Adhesives Research. The supporting members and are located on the non-illuminated side of the reflector. For certain embodiments, the sidewalls 30 are made of optically clear materials, which are coated with a reflective material such as silver or aluminum to from a specular reflector right on the structural member.

[0028] Referring now to FIG. 3, light that enters the input rectangular aperture reflects off the reflective surface of bottom planar sheet 20 or the TIR features 11, until such time that a ray strikes a clocked extraction feature 21. Due to the clocking on the lower extraction film, light is directed off-normal to the TIR film, in order to correct for the tilt that the TIR film would provide to a ray normal to its planar surface and striking its “tread face” (i.e. each stepped feature is comprised of a tread face and a smaller riser face, using the terms from the construction industry related to stair-steps). Due to the riser face of the stepped features on the TIR film, a small percentage of light will form a “ghost image” at a non-desired angle. In certain embodiments, blackening and/or minimizing the height of the riser face eliminates the ghosting.

[0029] Refer to FIG. 4, the light 100 introduced into the inventive wedge shaped hollow light guide have angular distributions 5 that are symmetric about the central axis, where the axis denotes the preferred propagation direction. This direction is parallel to the sidewalls 30, in the plane of the exit aperture, and runs from the input rectangular aperture towards the distal end of the guide.

[0030] FIGS. 5-13 show various cross-sectional views and optical simulation ray-trace results for the hollow wedge-shaped light guide. FIG. 5 depicts the simulation model geometry used to verify the optical performance of one illustrative embodiment of my invention. FIG. 6 illustrates a spot position diagram output, showing uniform light distribution, from a simulation run verifying the performance of the embodiment of FIG. 5.

[0031] FIG. 7 illustrates a spot direction angular profile output, showing the desired rays and ghost images, from a simulation run verifying the performance of the embodiment of FIG. 5. FIG. 8 is a graphical representation of a slice through the spot direction angular profile of FIG. 7.

[0032] FIG. 9 shows detail of some rays from the simulation ray trace for the light guide of FIG. 5. FIG. 10 depicts an additional sectional view of the wedge-shaped light guide of FIG. 5, viewed in the direction of ray propagation. FIG. 11 is a detail of a light ray trace, in the direction of ray propagation, for the wedge-shaped light guide of FIG. 5. FIG. 12 depicts an additional sectional view, viewed in the direction normal to the light propagation direction. FIG. 13 is a detail of a light ray trace, in the direction normal to the light propagation direction.

List of Acronyms used in the Specification

[0033] The following is a list of the acronyms used in the specification in alphabetical order.

[0034]

	LCD	liquid crystal display
	TIR	total internal reflection

Alternate Embodiments

[0035] Alternate embodiments may be devised without departing from the spirit or the scope of the invention. The illumination portion of the invention may be used in a wide variety of applications, including, but not limited to, vehicle lighting, search lights, task lights and projection systems. The display system is utilized in vehicle applications, such as an airplane cockpit, as well as other applications where viewing angles, space, thermal, and/or structural issues are of concern. The wavelengths of light can span on either side of the visible range, as determined by, among other things, material properties and diffraction limits.