Backlight module with diffusion sheet having a sub-wavelength grating

• US 9,047,792 B2
• Filed: 05/14/2013
• Issued: 06/02/2015
• Est. Priority Date: 12/17/2012
• Status: Expired due to Fees

• Current Assignee: Hon Hai Precision Industry Co., Ltd.
• Original Assignee: Hon Hai Precision Industry Co., Ltd.
• Inventors: Chen, Po-Chou
• Primary Examiner(s): Alavi, Ali
• Application Number:
  US13/893,352
• Publication Number:
  US 20140168948A1
• Time in Patent Office: 749 Days
• Field of Search: 362/97.1, 362/97.3, 362/558, 359/599, 359/707
• US Class Current: 1/1
• CPC Class Codes: G02B 5/0242 by means of dispersed particles
• CPC Class Codes: G02B 5/0252 using holographic or diffractive means
• CPC Class Codes: G02B 5/1809 with pitch less than or comparable to the wavelength
• CPC Class Codes: G09F 13/04 Signs, boards or panels, illuminated from behind the insignia

Abstract

A diffusion sheet includes a light incident surface and a light emitting surface opposite to the light incident surface. The light emitting surface includes a sub-wavelength grating to diffuse lights propagated in the diffusion sheet. The sub-wavelength grating is used to avoid a total internal reflection of some of the lights. A backlight module having the diffusion sheet is also provided.

Claims

1. A diffusion sheet comprising:

a light incident surface forming no sub-wavelength grating; and

a light emitting surface opposite to the light incident surface, the light emitting surface comprising a sub-wavelength grating formed thereat, the sub-wavelength grating being configured to avoid or reduce total internal reflection of light at the light emitting surface.

2. The diffusion sheet as claimed in claim 1, wherein the diffusion sheet is made of polymethyl methacrylate.

3. The diffusion sheet as claimed in claim 1, wherein the diffusion sheet is made of polycarbonate.

4. The diffusion sheet as claimed in claim 1, wherein the sub-wavelength grating defines a plurality of parallel channels, and each of the channels has a rectangular cross-section.

5. The diffusion sheet as claimed in claim 1, wherein a grating period of the sub-wavelength grating is less than a wavelength of the light and is greater than one third of the wavelength of the light.

6. A backlight module comprising

a plurality of aligned point light sources;

and

a diffusion sheet adjacent to the light source, the diffusion sheet comprising a light incident surface for receiving light from the point light sources and a light emitting surface opposite to the light incident surface, the light incident surface forming no sub-wavelength grating, the light emitting surface comprising a sub-wavelength grating formed thereat, the sub-wavelength grating being configured to avoid or reduce total internal reflection of the light.

7. The backlight module as claimed in claim 6, wherein a grating period of the sub-wavelength grating is less than a wavelength of the light emitted by the point light sources and is greater than one third of the wavelength of the light emitted by the point light sources.

8. The backlight module as claimed in claim 6, wherein the diffusion sheet is made of polymethyl methacrylate.

9. The backlight module as claimed in claim 6, wherein the diffusion sheet is made of polycarbonate.

10. The backlight module as claimed in claim 6, wherein the sub-wavelength grating defines a plurality of parallel channels, and each of the channels has a rectangular cross-section.