Backlight module and liquid crystal display using same

1. A liquid crystal display (LCD) comprising:

an LCD panel comprising a first substrate, a second substrate facing the first substrate, a liquid crystal layer sandwiched between the two substrates, and an upper polarizer film being disposed at the first substrate, the upper polarizer film having a first polarization axis;

a lower polarizer film being disposed at the second substrate, and comprising a second polarization axis substantially perpendicular to the first polarization axis of the upper polarizer film; and

a backlight module adjacent to the second substrate and facing the LCD panel to illuminate the LCD panel, the backlight module comprising:

a light guide plate comprising a light incident surface and a light emitting surface;

a light source configured to emit polarized light with a first polarization orientation, the light source positioned at a side of the light incident surface; and

a retardation layer disposed in an optical path between the light emitting surface and the second substrate,

wherein the retardation layer is configured to rotate the first polarization orientation of all the polarized light emitted from the light source and transmitted to the retardation layer to a second polarization orientation, the second polarization orientation is substantially parallel to the first polarization axis of the upper polarizer film, and the rotated polarized light emitted from the retardation layer follows the optical path to the second substrate and subsequently undergoes a single pass only through the liquid crystal layer to be emitted out from the LCD via the first substrate.

2. The LCD of claim 1 , wherein the retardation layer is made from material selected from the group consisting of polyvinyl alcohol, silicon, polycarbonate, and cyclo-olefin polymer.

3. The LCD of claim 1 , wherein a rotation angle between the first polarization orientation and the second polarization orientation is defined as θ, the polarized light with the first polarization orientation entering the retardation layer is divided by the retardation layer into O-type polarized light and E-type polarized light, the O-type polarized light is polarized perpendicular to an optical axis of the retardation layer, the E-type polarized light is polarized parallel to the optical axis of the retardation layer, an included angle between the first polarization orientation and the optical axis of the retardation layer is defined to be equal to θ/2, and a phase difference δ between the O-type polarized light and E-type polarized light after emission from the retardation layer is satisfied by the formula:

δ=(2 k+ 1)π=2π( n o −n o ) d 0 /λ

wherein n o represents an index of refraction of the O-type polarized light, n e represents an index of refraction of the E-type polarized light, d 0 represents a thickness of the retardation layer, λ represents a wavelength of the polarized light transmitted in vacuum, and k is a non-negative integer.

4. The LCD of claim 1 , further comprising a reflecting film positioned adjacent a bottom surface of the light guide plate.

5. The LCD of claim 1 , wherein the light guide plate further comprises a plurality of small reflective structures each of which comprises an inclined surface.

6. The LCD of claim 1 , wherein the retardation layer has a single layer structure.

7. The LCD of claim 1 , wherein the retardation layer has a single optical axis.