PHASE CORRECTION ELEMENT AND OPTICAL HEAD DEVICE

摘要

A phase correction element and an optical head device, capable of handling three kinds of optical disk by using a single object lens. A phase correction element (100), in which a first phase correction layer (10A), consisting of an uneven unit having a rotational symmetry with respect to the optical axis of an incident light and having its sectional shape where each serrate or sawtooth-wave-form protrusion is approximated by a step shape, is formed in an area having a numerical aperture NA2, and a first phase plate (30A) for producing a double refraction phase difference, even-number times about pi/2, with respect to linearly polarized light having a wavelength lambda1 is made an integral part, and which has the functions of keeping unchanged a transmitted wave front having a wavelength lambda1 and changing a transmitted wave front having a wavelength lambda2 or a transmitted wave front having a wavelength lambda2 and a wavelength lambda3 with respect to an incident light having three wavelengths, lambda1 = 410 nm wavelength band, lambda2 = 650 nm wavelength band and lambda3 = 780 nm wavelength band.