Patent ID: 7986604
Filing Date: 2011-07-26
Classification: G02B,G11B

Abstract:
1. An optical element having a lens and an optical multilayer film on a surface of the lens, wherein the lens has birefringence, and an astigmatism component of wave aberration caused by the lens is 10 mλ rms or larger; the optical multilayer film generates a phase difference between P-polarization and S-polarization, which cancels the birefringence, so that the astigmatism component of wave aberration caused by the optical element is reduced to 5 mλ rms or smaller, wherein the phase difference of the optical multilayer film is increasing substantially and monotonously as being close to an outer edge portion from a center of the lens; and wherein when an angle of incidence of light entering the optical multilayer film is δ (degrees), and a phase difference between P-polarization and S-polarization of light passing through the optical multilayer film is D (degrees), a relationship between δ and D satisfies the following conditions at a wavelength of 405 nm: if δ=30 degrees, D is larger than or equal to 2 degrees but smaller than or equal to 20 degrees, and if δ=60 degrees, D is larger than or equal to 4 degrees but smaller than or equal to 40 degrees; and a change of D within a range of 30 degrees≦δ≦60 degrees is a monotonous change.