Patent ID: 7370999

Claim:
A light guide plate comprising: a light incident portion for receiving light, the light incident portion including at least one first diffractive optical element located thereat; a light reflecting portion for reflecting at least a portion of the light input through the light incident portion; and a light emitting portion opposite to the light reflecting portion for outputting the input light including the reflected light, wherein the at least one first diffractive optical element comprises a plurality of protrusions each having a curved surface, at least two of the protrusions are arranged symmetrically opposite to each other across a central axis of symmetry of the at least one first diffractive optical element, and the at least one first diffractive optical element has a phase retardation represented by φ(x), which satisfies the following equation: φ( x )= k 0 n 2 ( f −√{square root over ( f 2 +x 2 )}), wherein f represents a focal length of the at least one first diffractive optical element, n 2 represents an index of refraction of a material located at a focus of the at least one first diffractive optical element, x represents a distance from any point on a curved surface of the at least one first diffractive optical element to the central axis of symmetry, k 0 represents a quantity of waves of the light input through the at least one first diffractive optical element, and is calculated by the following equation: k 0 =2π/λ, and λ represents a wavelength of the light input through the at least one first diffractive optical element if such light travels in a vacuum.