| 摘要 |
PROBLEM TO BE SOLVED: To prevent overlapping of information recording positions between adjacent layers by reducing a defocussing amount caused by surface wobbling of an optical recording medium when first light for recording/reproducing information and second light different from the first light are applied, via a common objective lens, to the optical recording medium including a reference plane having a reflection film and an information recording layer different from the reference plane, and a focus-aligned position of the first light is adjusted by changing collimation of the first light.SOLUTION: An optical system is designed such that an absolute value of an objective lens magnification β by the first light is set to be equal to or more than a square root of D/α, where a focal depth λ/NAof the first light defined by a wavelength λ of the first light and a numerical aperture NA for the first light of the objective lens is α, and a maximum surface wobbling range of an optical recording medium is D. Thus, a defocussing amount is suppressed to be within the focal depth α. |
