Patent ID: 7748859

Claim:
A backlight module comprising: a light guide plate comprising a light incident surface, a top surface adjacent to the light incident surface, and a bottom surface adjacent to the light incident surface, a light source provided adjacent to the light incident surface of the light guide plate, and a grating plate provided adjacent to the bottom surface of the light guide plate, the grating plate comprising a base plate and a plurality of sub-wavelength gratings arranged on a surface of the base plate facing the light guide plate, the sub-wavelength gratings reflecting light beams directly to the bottom surface the light guide plate and polarizing the light beams, the reflected light beams are polarized to have parallel polarized directions by the sub-wavelength gratings, are transmitted through the light guide plate, and are directly emitted out of the top surface of the light guide plate, wherein the sub-wavelength gratings are parallel to each other and arranged in a grating period Λ, and the grating period Λ of the sub-wavelength gratings is in a range from about 0.08 μm to about 0.14 μm.