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

A multi-beam optical pickup, comprising:

• a semiconductor laser;
• a diffraction grating for generating a plurality of beams, said diffraction grating including a plurality of gratings having an axis of symmetry perpendicular to a direction in which a beam is divided and at least two gratings with different fundamental cycles, wherein said plurality of gratings are composed of a series of straight lines that are oriented parallel to the axis of symmetry and arranged at an increased spacing from the middle of the diffraction grating toward an outward periphery of the diffraction grating;
• a hologram element for transmitting a light beam transmitted through said diffraction grating for generating a plurality of beams and reflected from a recording medium;
• and
• an internal light receiving portion for receiving the light beam transmitted through said hologram element.

A multi-beam optical pickup, comprising:

• a semiconductor laser;
• a diffraction grating for generating a plurality of beams, said diffraction grating including a plurality of gratings having an axis of symmetry perpendicular to a direction in which a beam is divided and oriented parallel to the axis of symmetry, wherein said plurality of gratings are divided into a plurality of regions and each region comprises at least two gratings, and wherein a fundamental cycle for each region changes in a non-continuous step-wise fashion;
• a hologram element for transmitting a light beam transmitted through said diffraction grating for generating a plurality of beams and reflected from a recording medium;
• and
• an internal light receiving portion for receiving the light beam transmitted through said hologram element.