DESIGN METHOD OF DIFFRACTION ELEMENT, DIFFRACTION ELEMENT, OBJECTIVE LENS UNIT, OPTICAL PICKUP AND OPTICAL DISK DEVICE

摘要

PROBLEM TO BE SOLVED: To easily design a diffraction element having satisfactory characteristics.;SOLUTION: When a diffraction grating DG wherein a wavelength λ not to be diffracted and a wavelength λ to be diffracted are respectively determined as design targets is designed, values of refractive indices n of materials M1 and M2 to be candidates in each wavelength λ are substituted for a left side of formula (16), a right side of formula (16) is made to be a ratio of simple integers by satisfying formula (11) and the materials M1 and M2 to be the candidates are discriminated to be suitable as materials which constitute the diffraction grating DG when formula (17) is satisfied. Thus, the materials M1 and M2 capable of forming the diffraction grating DG as to be specified designed can be easily selected.;COPYRIGHT: (C)2008,JPO&INPIT