Backlighting apparatus employing an array of microprisms

• US 5,396,350 A
• Filed: 11/05/1993
• Issued: 03/07/1995
• Est. Priority Date: 11/05/1993
• Status: Expired due to Term

• Current Assignee: Advanced Display Technologies of Texas LLC (Advanced Display Technologies)
• Original Assignee: Alliedsignal Inc.
• Inventors: Ferm, Paul M., Beeson, Karl W., Zimmerman, Scott M.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US08/149,219
• Time in Patent Office: 487 Days
• Field of Search: 359/40, 359/42, 359/48, 359/49, 359/245, 359/246, 359/247, 359/251, 353/33, 353/81
• US Class Current: 349/62
• CPC Class Codes: F21Y 2103/00 Elongate light sources, e.g. fluorescent tubes
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer

Abstract

An improved backlighting apparatus comprising a slab waveguide that accepts light rays generated by a light source and transmits the light rays via total internal reflection. Attached on one face of the slab waveguide is an array of microprisms, with each microprism having an light input surface parallel to a light output surface and at least one sidewall tilted at an angle from the direction normal to the surface of the waveguide such that light rays escape from the slab waveguide, reflect off the tilted sidewall and emerge from the microprism as a light source substantially perpendicular to the light output surface. An array of microlenses may be positioned to accept the output of the microprisms so that the light exiting from the microlenses is substantially more perpendicular. The backlight apparatus is advantageously used as a backlighting means for flat panel electronic displays.

Claims

1. A backlight assembly for use in a flat panel electronic display, said display having a modulating means capable of providing an image to a remotely positioned observer, and said backlight assembly comprising:

(a) a light generating means for generating a first source of light rays;

(b) a light transmitting means having a first light accepting surface in close proximity to said light generating means, wherein said light transmitting means transports the light rays emanating from said light generating means in a direction substantially parallel to the viewing plane of said modulating means;

(c) reflecting means for collimating said light rays, said reflecting means disposed between said light transmitting means and said modulating means and comprising an array of microprisms and each microprism comprising;

i) a light input surface optically coupled to said light transmitting means

ii) a light output surface distal from and parallel to said light input surface; and

iii) a first sidewall disposed between and contiguous with said light input surface and said light output surface and forming a tilt angle with respect to the normal of the surface of said light transmitting means and further positioned for effecting total reflection of said light rays received by said input surface;

whereby said light rays internally reflected by said sidewall emerge through said light output surface in a direction substantially perpendicular to said modulating means.

2. The backlight assembly of claim 1 wherein said tilt angle is between about 25 degrees to about 40 degrees.

3. The backlight assembly of claim 1 further comprising a second sidewall oppositely disposed from said first sidewall and wherein the surface area of said light output surface is greater than the surface area of said light input surface and both first and second sidewalls form said tilt angle with respect to the normal of the surface of said light transmitting means and further positioned for effecting total reflection of said light rays received by said input surface.

4. The backlight assembly of claim 3 wherein said light generating means further comprises a second light source in close proximity to a second light accepting surface oppositely disposed to said first light accepting surface.

5. The backlight assembly of claim 1 wherein said light generating means further comprises a third light source in close proximity to a third light accepting surface and a fourth light source in close proximity to fourth light accepting surface, said third and fourth light accepting surfaces being generally perpendicular to said first and second light accepting surfaces and said microprisms further comprise a third and fourth sidewall generally perpendicular to said first and second sidewalls and tilted at angles from the direction normal to the surface of said light transmitting means, wherein said light output surface area is greater than the area of said light input surface.

6. The backlight assembly of claim 5 wherein each said angle is between about 25 degrees to about 40 degrees.

7. The backlight assembly of claim 1 further comprising an array of microlenses disposed in close proximity between said reflecting means and said modulating means, wherein the light output of each microprism is directed to a corresponding microlens and said light transmitted through said microlenses emerges as a substantially more collimated light source for said modulating means.

8. The backlight assembly of claim 7 wherein said microprisms and microlenses are constructed from organic polymeric material.

9. The backlight assembly of claim 7 wherein the microprisms possess a height dimension of less than 2 millimeters and further comprise a light input surface and a light output surface with largest dimension of less than 2 millimeters across.

10. The backlight assembly of claim 7 wherein said microprisms, microlenses and light transmitting means have an index of refraction of between about 1.45 and about 1.65.

11. The backlight assembly of claim 10 further comprising an interstitial region between said microprisms having an index of refraction less than the index of refraction of said microprisms.

12. The backlight assembly of claim 1 wherein the summation of said microprism light input surfaces occupy greater than 20 percent of the surface area of said light transmitting means.

13. A backlight assembly for use in a flat panel electronic display, said display having a modulating means capable of providing an image to a remotely positioned observer, and said backlight assembly comprising:

(a) a light generating means for generating a source of light rays;

(b) a light transmitting means substantially related in surface area with said modulating means and having a light accepting surface adjacently positioned next to said light generating means, wherein said light transmitting means transports the light rays emanating from said light generating means via substantially total internal reflection in a direction substantially parallel to the viewing plane of said modulating means;

(c) an array of microprisms disposed between said light transmitting means and said modulating means and each microprism having a light input surface optically coupled to said light transmitting means and a light output surface distal from and parallel to said light input surface and at least one sidewall tilted at an angle from between about 25 degrees to about 40 degrees from the direction normal to the surface of said light transmitting means and positioned for effecting total reflection of said light rays received by said input surface;

wherein, said light rays reflecting through said light transmitting means enter said microprisms through said light input surfaces and emerge through said light output surfaces in a direction substantially perpendicular to said modulating means; and

(d) an array of microlenses disposed in close proximity between said array of microprisms and said modulating means, wherein said output of each microprism is directed to a corresponding microlens and said light transmitted through said microlenses emerges as a substantially more collimated light source for said modulating means.

14. A backlight assembly for use in a flat panel electronic display, said display having a modulating means capable of providing an image to a remotely positioned observer, and said backlight assembly comprising:

(a) a light generating means for generating a first and second source of light rays;

(b) a transparent light transmitting means substantially related in surface area with said modulating means and having two light accepting surfaces, each adjacently positioned next to one of said light sources, wherein said light transmitting means transports the light rays emanating from said light generating means via substantially total internal reflection in a direction substantially parallel to the viewing plane of said modulating means;

(c) an array of microprisms disposed between said light transmitting means and said modulating means and each microprism having a light input surface optically coupled to said light transmitting means and a light output surface distal from and parallel to said light input surface and a first and second sidewall tilted at an angle from between about 25 degrees to about 40 degrees from the direction normal to the surface of said light transmitting means and positioned for effecting total reflection of said light rays received by said input surface, wherein said light output surface area is greater than the area of said light input surface;

wherein, said light rays reflecting through said light transmitting means enter said microprisms through said light input surfaces and emerge through said light output surfaces in a direction substantially perpendicular to said modulating means; and

(d) an array of microlenses disposed in close proximity between said array of microprisms and said modulating means, wherein said output of each microprism is directed to a corresponding microlens and said light transmitted through said microlenses emerges as a substantially more collimated light source for said modulating means.

15. A backlight assembly for use in a flat panel electronic display, said display having a modulating means capable of providing an image to a remotely positioned observer, and said backlight assembly comprising:

(a) a light generating means for generating a first, second, third and fourth source of light rays;

(b) a light transmitting means substantially related in surface area with said modulating means having four light accepting surfaces, each adjacently positioned next to one of said light generating means, wherein said light transmitting means transports the light rays emanating from said light generating means via substantially total internal reflection in a direction substantially parallel to the viewing plane of said modulating means;

(c) an array of microprisms disposed between said light transmitting means and said modulating means and each microprism having a light input surface optically coupled to said light transmitting means and a light output surface distal from and parallel to said light input surface and a first, second, third and fourth sidewall tilted at an angle from between about 25 degrees to about 40 degrees from the direction normal to the surface of said light transmitting means and positioned for effecting total reflection of said light rays received by said input surface wherein said light output surface area is greater than the area of said light input surface;

wherein, said light rays reflecting through said light transmitting means enter said microprisms through said light input surfaces and emerge through said light output surfaces in a direction substantially perpendicular to said modulating means; and

(d) an array of microlenses disposed in close proximity between said array of microprisms and said modulating means, wherein said output of each microprism is directed to a corresponding microlens and said light transmitted through said microlenses emerges as a substantially more collimated light source for said modulating means.

16. An assembly for providing substantially collimated light from a light source comprising:

(a) a light transmitting means in close proximity to said light source, wherein said light transmitting means transports the light rays emanating from said light source;

(b) reflecting means for collimating said light rays comprising an array of microprisms with each microprism having a light input surface optically coupled to said light transmitting means, a light output surface distal from and parallel to said light input surface and at least one sidewall positioned for effecting total reflection of said light rays received by said input surface;

wherein, said light rays reflecting through said light transmitting means enter said microprisms through said light input surfaces and emerge through said light output surfaces in a direction substantially perpendicular to said light output surface.

17. The assembly of claim 16 further comprising an array of microlenses disposed in close proximity to said array of microprisms wherein the light output of each microprism is directed to a corresponding microlens and said light transmitted through said microlenses emerges as a substantially more collimated light source.

18. A direct-view flat panel display comprising:

(a) a light generating means for generating light rays;

(b) a modulating means for modulating light from said light generating means to form an image visible to a remote observer;

(c) an image display means for displaying said image from said modulating means positioned adjacent to the light output surface of said modulating means, said display means comprising an array of tapered optical waveguides, the tapered end of each of said waveguides extending outward from said modulating means and having a light input surface optically coupled to said modulating means and a light output surface distal from said light input surface;

(d) a backlight assembly comprising;

(i) a light transmitting means substantially related in surface area with said modulating means and having a light accepting surface positioned adjacent to said light generating means, wherein said light transmitting means transports the light rays emanating from said light generating means via substantially total internal reflection in a direction substantially parallel to the viewing plane of said modulating means;

(ii) reflecting means for collimating said light rays, said reflecting means disposed between said light transmitting means and said modulating means, said reflecting means comprising an array of microprisms with each microprism having a light input surface optically coupled to said light transmitting means and a light output surface distal from and parallel to said light input surface and at least one sidewall positioned for effecting total reflection of said light rays received by said input surface;

wherein, said light rays reflecting through said light transmitting means enter said microprisms through said light input surfaces and exit through said light output surfaces in a direction substantially perpendicular to said modulating means.

19. The direct-view flat panel display of claim 18 further comprising an array of microlenses disposed in close proximity between said reflecting means and said modulating means, wherein the output of each microprism is directed to a corresponding microlens and said light transmitted through said microlenses emerges as a substantially more collimated light source for said modulating means.