Patent ID: 7688700
Filing Date: 2010-03-30
Classification: G02B,G11B

Abstract:
1. A phase correction element for transmitting three kinds of light beams having wavelengths λ 1 , λ 2 and λ 3 respectively (λ 1 <λ 2 <λ 3 ), which has an area of numerical aperture NA 2 and an area of numerical aperture NA 1 including the area of numerical aperture NA 2 (NA 1 >NA 2 ) in an element plane in which the light is incident, of the phase correction element; wherein in the area of numerical aperture NA 2 , a first phase correction layer comprising a concavo-convex portion of a saw-tooth-form or an approximated saw-tooth-form having a cross-sectional shape of a saw-tooth-form or a saw-tooth-form, each of whose tooth is approximated by a step form, and having a rotational symmetry with respect to the optical axis of an incident light, is formed, and the first phase correction layer and a phase plate which transforms linearly polarized incident light having a wavelength of λ 1 into circularly polarized light by generating an odd number times of π/2 of birefringent phase difference, are integrally formed, whereby a transmitted wavefront of light having a wavelength of λ 2 , or light having a wavelength of λ 2 and light having a wavelength of λ 3 incident in the region of numerical aperture NA 2 are changed while a transmitted wavefront of light having a wavelength of λ 1 incident in the region of numerical aperture NA 1 is maintained regardless of the polarization state, said phase correction element further comprises a first transparent material and a second transparent material having different refractive index wavelength dispersions from each other, wherein the difference Δn of their refractive indexes is 0 at the wavelength λ