Patent ID: 7806537

Claim:
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 or strains existing in the light guide plate, an angle in the range more than about 0 and less than about 90 degrees between one of the two orthogonal stresses or strains and the light input surface of the light guide plate, a stress or strain difference existing between the two orthogonal stresses or strains; a phase retardation due to the stress or strain difference, the phase retardation being defined by the equations: δ = 2 ⁢ π ⁢ C ⁢ Δσ ⁢ ⁢ L / λ = 2 ⁢ k ⁢ ⁢ π + π k = 0 , 1 , 2 , 3 , 4 , … δ represents the phase retardation value of light passing through the light guide plate twice, L represents twice the thickness of the light guide plate, C represents the stress-optical or strain-optical coefficient, Δσ represents the stress difference or strain difference, and λ represents wavelength of an incident light.