Patent ID: 7782738

Claim:
A phase plate, comprising a birefringent medium, to cause a phase difference in linearly polarized light incident on the phase plate between a polarization component having a polarization direction parallel to an optic axis of the birefringent medium and a polarization component having a polarization direction perpendicular to the optic axis, wherein the birefringent medium comprises a plurality of types of phase areas; two types of adjacent phase areas among the plurality of types of phase areas are different from each other in at least one of a phase difference and an optic axis; and each of the plurality of types of phase areas is disposed so as to have two-fold rotational symmetry with respect to an optical axis of the phase plate; and wherein phase differences produced when light having at least one of a plurality of different wavelengths is transmitted through the plurality of types of phase areas are each (90×m+360×k+α) degrees, wherein m indicates an integer of −1 or +1, k indicates an integer, and α indicates a real number of at least −20 and at most +20, and wherein differences between the phase differences produced when light having at least one of the plurality of different wavelengths is transmitted through the plurality of types of phase areas are each (360×j+β) degrees wherein j indicates an integer, and β indicates a real number of at least −40 and at most +40.