LIGHT GUIDE PLATE AND BACKLIGHT MODULE THEREWITH

• US 20070076432A1
• Filed: 07/17/2006
• Published: 04/05/2007
• Est. Priority Date: 07/20/2005
• Status: Active Grant

• Current Assignee: Hon Hai Precision Industry Co., Ltd., Tsinghua University
• Original Assignee: Hon Hai Precision Industry Co., Ltd., Tsinghua University
• Inventors: Jin, Guo-Fan, Yang, Xing-Peng, Yan, Ying-Bai
• Granted Patent: US 7,806,537 B2
• Time in Patent Office: Days
• US Class Current: 362/615
• 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 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements

Abstract

backlight module includes a light guide plate (52), a light source (51), a reflecting sheet (53), a diffusion sheet (54), and a reflective polarizing beam splitter (57). The light guide plate includes a light input surface (521), a light output surface (522) adjacent to the light input surface, a reflecting surface (523) opposite the light output surface, and a number of microstructures (524) located on the reflecting surface. In the light guide plate, stress-induced birefringence is introduced to achieve a polarization state conversion, thereby facilitating efficient use of the light generated by the light source.

Claims

1. A light guide plate, comprising:

a light input surface, a light output surface adjacent to the light input surface, and a reflective surface opposite to the light output surface;

two orthogonal stresses/strains existing in the light guide plate, the two orthogonal stresses/strains having an angle in the range more than about 0 and less than about 90 degrees between one stress/strain and the light input surface of the light guide plate, a stress/strain difference existing between the two orthogonal stresses/strains;

a phase retardation due to the stress/strain difference, the phase retardation being defined by the equation;

δ

=2π

Δ

σ

L/λ

=2Kπ

+π

wherein δ

represents the phase retardation value, L represents double the thickness of the light guide plate, C represents the stress/strain-optical coefficient, Δ

σ

represents the stress/strain difference, and λ

represents wavelength of an incident light.

2. The light guide plate as defined in claim 1, wherein the angle between one stress/strain and the light input surface is about 45 degrees.

3. The light guide plate as defined in claim 1, wherein the stress/strain is defined by the minimum of an objective function:

$y=\underset{\mathrm{\Delta <br><br>\sigma <br><br>}}{\min }<br><br>\left\{w_R\times <br><br>\mathrm{abs}<br><br>\left[\mathrm{mod}<br><br>\left({\mathrm{\delta <br><br>}}_R,2<br><br>\mathrm{\pi <br><br>}\right)-\mathrm{\pi <br><br>}\right]+w_G\times <br><br>\mathrm{abs}<br><br>\left[\mathrm{mod}<br><br>\left({\mathrm{\delta <br><br>}}_G,2<br><br>\mathrm{\pi <br><br>}\right)-\mathrm{\pi <br><br>}\right]+w_B\times <br><br>\mathrm{abs}<br><br>\left[\mathrm{mod}\left({\mathrm{\delta <br><br>}}_B,2<br><br>\mathrm{\pi <br><br>}\right)-\mathrm{\pi <br><br>}\right]\right\}$

wherein mod denotes modules after division, abs indicates an absolute value, δ

_R, δ

_G, and δ

_B denote the phase retardation values for wavelengths of λ

_R, λ

_G, and λ

_B, respectively, and W_R, W_G and W_B denote statistical weight factors for wavelengths of λ

_R, λ

_G, and λ

_B, respectively.

4. The light guide plate as defined in claim 1, wherein a plurality of microstructures is formed on the reflective surface of the light guide plate.

5. The light guide plate as defined in claim 4, wherein at least one microstructure is in the shape of a V-shaped groove.

6. A backlight module, comprising:

a light source for emitting light;

a light guide plate adjacent to the light source, the light guide plate having a light input surface, a light output surface adjacent to the light input surface, and a reflective surface opposite to the light output surface;

a reflecting sheet on the reflective surface of the light guide plate; and

a reflective polarizing beam splitter on the light input surface of the light guide plate;

wherein two orthogonal stresses/strains exist in the light guide plate, the two orthogonal stresses/strains having an angle in the range from above 0 degree to less than about 90 degrees between one stress/strain and the light input surface of the light guide plate, a stress/strain difference existing between the two orthogonal stresses/strains;

the phase retardation due to the stress/strain difference being defined by the equation;

δ

=2π

C Δ

σ

L/λ

=2K+π

wherein δ

represents the phase retardation value, L represents the twice thickness of the light guide plate, C represent the stress/strain-optical coefficient, Δ

σ

represents the stress/strain difference, and λ

represents wavelength of a incident light.

7. The backlight module as define in claim 6, wherein the angle between one stress/strain and the light input surface is about 45 degrees.

8. The backlight module as define in claim 6, wherein the stress/strain is defined by the minimum of objective function:

$y=\underset{\mathrm{\Delta <br><br>\sigma <br><br>}}{\min }<br><br>\left\{w_R\times <br><br>\mathrm{abs}<br><br>\left[\mathrm{mod}<br><br>\left({\mathrm{\delta <br><br>}}_R,2<br><br>\mathrm{\pi <br><br>}\right)-\mathrm{\pi <br><br>}\right]+w_G\times <br><br>\mathrm{abs}<br><br>\left[\mathrm{mod}<br><br>\left({\mathrm{\delta <br><br>}}_G,2<br><br>\mathrm{\pi <br><br>}\right)-\mathrm{\pi <br><br>}\right]+w_B\times <br><br>\mathrm{abs}<br><br>\left[\mathrm{mod}\left({\mathrm{\delta <br><br>}}_B,2<br><br>\mathrm{\pi <br><br>}\right)-\mathrm{\pi <br><br>}\right]\right\}$

wherein mod denotes modules after division, abs indicates an absolute value, δ

_R,, δ

_G, δ

_B denote the phase retardation values for wavelengths of λ

_R,, λ

_G, and λ

_B, respectively, and W_R, W_G and W_B denote statistical weight factors for wavelengths of λ

_R, λ

_G, and λ

_B, respectively.

9. The backlight module as define in claim 6, wherein a plurality of microstructures is formed on the reflective surface of the light guide plate.

10. The backlight module as defined in claim 9, wherein at least one microstructure is in the shape of a V-shaped groove.

11. The backlight module as defined in claim 6, wherein the backlight module further comprises a diffusion sheet, a prism sheet, and a reflective polarizing beam splitter, the prism sheet being located over the light output surface of the light guide plate, the reflective polarizing beam splitter being arranged one of between the light output surface and the diffusion sheet, between the diffusion sheet and the prism sheet, and over the prism sheet.