Diffraction grating having multiple gratings with different cycles for generating multiple beams and optical pickup using such diffraction grating

摘要

A diffraction grating (8) for generating a plurality of beams includes a plurality of gratings (12). The plurality of gratings (12) are formed to have an axis of symmetry perpendicular to the direction in which a beam is divided on a surface of diffraction grating (8) and include at least two gratings having different fundamental cycles. Diffraction grating (8) for generating a plurality of gratings have the plurality of gratings (12) formed such that the gratings have an axis of symmetry perpendicular to the direction in which a beam is divided on a surface of the diffraction grating (8) for generating a plurality of beams and that the fundamental cycle increases as a function of the distance from the axis of symmetry, and therefore aberration in the periphery of scattering light can be reduced.