Patent ID: 7999893

Claim:
A complex birefringent medium comprising: a structure in which a plurality of birefringent layers are laminated, wherein in the complex birefringent medium, a phase difference exhibits inverse wavelength dispersibility as the whole of the complex birefringent medium, wherein when a principal refractive index having the maximum absolute value of a difference from an average value of three principal refractive indexes at a wavelength λ (nm) is designated as a first principal refractive index n1(λ), for each of the birefringent layers a normal line of the birefringent layer and a principal axis corresponding to the first principal refractive index n1(550) of the birefringent layer are in the same plane; wherein at least one of the plurality of birefringent layers has a biaxial parameter η of more than 0, defined by the following equation (2), η=| n 2(550)− n 3(550)|/| n 1(550)− n 2(550)| (2) wherein n2(550) represents a principal refractive index having the second-largest absolute value of a difference from an average value of three principal refractive indices at a wavelength 550 (nm) and n3(550) represents a principal refractive index having the minimum absolute value of a difference from an average value of three principal refractive indexes at a wavelength 550 (nm).