Planar light source device having polarization separator formed of two sheets with mating triangular prisms and different indices of refraction

• US 6,239,851 B1
• Filed: 07/06/1998
• Issued: 05/29/2001
• Est. Priority Date: 10/12/1995
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation, Sekisui Kagaku Kogyo Kabushiki Kaisha (Sekisui)
• Original Assignee: International Business Machines Corporation, Sekisui Kagaku Kogyo Kabushiki Kaisha (Sekisui)
• Inventors: Nakamura, Kozo, Hatazawa, Tsuyonobu, Mamiya, Johji, Tanase, Hiroshi, Watanabe, Takashi, Hayashi, Hideki, Suzuki, Masaru
• Primary Examiner(s): MALINOWSKI, WALTER J
• Application Number:
  US09/051,504
• Time in Patent Office: 1,058 Days
• Field of Search: 349/62, 349/65, 362/26, 362/31, 359/487, 359/488
• US Class Current: 349/62
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/13355 Polarising beam splitters [PBS]
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

The purpose of the invention is to provide a light guide of a variety of forms having a uniform distribution of brightness in the plane and a planer light source device for a liquid crystal display device which uses such light guide. The light guide comprises a first surface which is a surface to which a natural polarization light is incident and a second surface other than the first surface which is an exit surface of a specific polarization light into which, said natural polarization light is modulated, wherein;

said light guide has an interface of two materials of different indices of refraction oriented at an angle of θB+/−α degrees relative to the primary propagation direction of said incident light, said θB being an angle satisfying Brewster'"'"'s condition, more than two orientations of said interface exist in a single light guide, and the difference between the indices of refraction of the two materials of different indices of refraction is between 0.001 and 1.0. θB is typically about 45 degrees. The light guide comprises a first transparent member having a plurality of upwardly convex right angle isosceles triangles on a first surface thereof and a first index of refraction and a second transparent member having a plurality of downwardly convex right angle isosceles triangles on a second surface thereof and a second index of refraction, and said first surface and said second surface contact each other.

Claims

1. A planar light guide, comprising:

a polarization separator having a planar light entrance surface upon which unpolarized light that travels in a propagation direction is incident at a generally a right angle;

said polarization separator having a planar light exit surface that extends perpendicular to said light entrance surface and parallel to said propagation direction, and from which polarized light exits said polarization separator;

said polarization separator having a plurality of planar light-refracting interfaces that are located below said light exit surface;

said light-refracting interfaces comprising a plurality of planes that are inclined to said light exit surface;

said light-refracting interfaces being formed by a physical engagement of a first and a second sheet of light-transparent material that extend parallel to said light exit surface;

said first and second sheets of material having different index of refractions;

said refracting interfaces being formed by a first series of isosceles triangle columns whose apices are directed upward toward said light exit surface, each triangle column within said first series of triangle columns alternating with a second series of isosceles triangle columns whose apices are directed downward and away from said light exit surface;

with height lines that equally divide said apices extending perpendicular to said light exit surface, and with opposite equal length sides of each triangle column extending at an angle of θ

_B, +/−

20-degrees relative to said propagation direction;

said angle θ

_B being an angle that satisfies Brewster condition; and

a difference between the said index of refraction of said two materials being between 0.001 and 1.0.

2. The light guide of claim 1 wherein:

said opposite equal length sides of each triangle column extending at an angle of θ

_B, +/−

10-degrees relative to said propagation direction; and

a difference between the said index of refraction of said two materials is between 0.001 and 0.2.

3. The light guide of claim 1 in which said triangle columns are right-angle isosceles triangle columns such that said angle θ

_B is 45-degrees.

4. The light guide of claim 3 wherein:

said first sheet includes a first plurality of upwardly-directed, right angle, triangle columns having a first index of refraction;

said second sheet includes a second plurality of downward-directed, right angle, triangle columns having a second and different index of refraction; and

said first and second sheets physically contacting each ovhther in a column interlocking manner to thereby form said plurality of interfaces.

5. The light guide of claim 4 wherein:

said first sheet is formed of a transparent acrylic resin having an index of refraction of about 1.49; and

said second sheet is formed of a transparent photo-setting resin having an index of refraction of about 1.53.

6. The light guide of claim 4, including:

a light source emitting said unpolarized light; and

a light-collimating member located intermediate said light source and said light entrance surface.

7. The light guide of claim 4, including:

a first light reflector located adjacent to a first surface of said polarization separator that is opposite to and parallel with said light entrance surface;

a polarization converting member located intermediate said light reflector and said first surface; and

a second light reflector located adjacent to a second surface of said polarization separator that is opposite to and parallel with said light exit surface.

8. The light guide of claim 1 including:

a liquid crystal cell located adjacent to said light exit surface, said liquid crystal cell having a plurality of picture elements;

a modulating filter located intermediate said light exit surface and said liquid crystal cell; and

a voltage applying mechanism connected to apply a voltage to said picture elements.

9. The light guide of claim 1 wherein said first and second series of isosceles triangle columns form an elongated light-refracting interface having a shape selected from the group W-shape and sine wave shape.

10. The light guide of claim 1 including:

a third series of isosceles triangle columns underlying said second series of isosceles triangle columns and aligned with said first series of isosceles triangle columns, apices of said third series of triangle columns being directed upward toward said light exit surface;

each triangle column within said third series of triangle columns alternating with a fourth series of isosceles triangle columns that underlie said third series of isosceles triangle columns and are aligned with said second series of isosceles triangle columns and whose apices are directed downward and away from said light exit surface.

11. The light guide of claim 1 wherein said difference between the index of refraction of said two materials is less adjacent to said light entrance surface and an opposite end surface of said light guide than it is therebetween.

12. The light guide of claim 1 wherein:

said height lines of said first and second triangle columns are relatively long adjacent to said light entrance surface and an opposite end surface of said light guide and are relatively short therebetween,

thereby providing relatively large surface refracting interface surfaces adjacent to said light entrance surface and said opposite end surface of said light guide and relatively small surface refracting interface surfaces therebetween.

13. The light guide of claim 1 including:

a third light transparent sheet of uniform thickness having an index of refraction different than said first and second sheets and positioned between said first and second sheets, said third sheet physically conforming to said apices.