DIFFRACTION ELEMENT, OBJECTIVE LENS UNIT, OPTICAL PICKUP AND OPTICAL DISC APPARATUS

摘要

A diffraction element for diffracting a particular wavelength of incident optical beam includes: a base section made from a first resin and provided with a predetermined diffraction pattern; and a cover section made from a second resin and covering the diffraction pattern, wherein a rate of change of refraction index of the first resin is substantially the same as a rate of change of refraction index of the second resin in a temperature range between a first temperature and a second temperature.