Optical pickup unit and optical disk apparatus having a phase-differing periodic structure

An optical pickup unit comprising a diffraction grating that divides light into at least three luminous fluxes, the optical pickup unit condensing the three luminous fluxes to apply at least three focusing spots, independent of each other, onto a signal side of a medium, the diffraction grating being divided into at least four regions, a first region, a second region, a third region, and a fourth region, wherein

• the second region and the third region are disposed between the first region and the fourth region, and wherein
• a periodic structure of the second region is a periodic structure having a phase differing by about 75 degrees from that of a periodic structure of the first region;
• a periodic structure of the third region is a periodic structure having a phase differing by about 30 degrees from that of the periodic structure of the second region;
• and
• a periodic structure of the fourth region is a periodic structure having a phase differing by about 75 degrees from that of the periodic structure of the third region.

An optical pickup unit comprising a diffraction grating that divides light into at least three luminous fluxes, the optical pickup unit condensing the three luminous fluxes to apply at least three focusing spots, independent of each other, onto a signal side of a medium, the diffraction grating being divided into at least four regions, a first region, a second region, a third region, and a fourth region, wherein

• the second region and the third region are disposed between the first region and the fourth region, and wherein
• a periodic structure of the second region is a periodic structure having a phase differing by about 60 degrees from that of a periodic structure of the first region;
• a periodic structure of the third region is a periodic structure having a phase differing by about 60 degrees from that of the periodic structure of the second region;
• and
• a periodic structure of the fourth region is a periodic structure having a phase differing by about 60 degrees from that of the periodic structure of the third region.

An optical pickup unit comprising a diffraction grating that divides light into at least three luminous fluxes, the optical pickup unit condensing the three luminous fluxes to apply at least three focusing spots, independent of each other, onto a signal side of a medium, the diffraction grating being divided into at least four regions, a first region, a second region, a third region, and a fourth region, wherein

• the second region and the third region are disposed between the first region and the fourth region, and wherein
• a periodic structure of the second region is a periodic structure having a phase differing by about 105 degrees from that of a periodic structure of the first region;
• a periodic structure of the third region is a periodic structure having a phase differing by about 30 degrees from that of the periodic structure of the second region;
• and
• a periodic structure of the fourth region is a periodic structure having a phase differing by about 105 degrees from that of the periodic structure of the third region.

An optical pickup unit comprising a diffraction grating that divides light into at least three luminous fluxes, the optical pickup unit condensing the three luminous fluxes to apply at least three focusing spots, independent of each other, onto a signal side of a medium, the diffraction grating being divided into at least four regions, a first region, a second region, a third region, and a fourth region, wherein

• the second region and the third region are disposed between the first region and the fourth region, and wherein
• a periodic structure of the second region is a periodic structure having a phase differing by about 120 degrees from that of a periodic structure of the first region,
• a periodic structure of the third region is a periodic structure having a phase differing by about 60 degrees from that of the periodic structure of the second region;
• and
• a periodic structure of the fourth region is a periodic structure having a phase differing by about 120 degrees from that of the periodic structure of the third region.

An optical pickup unit comprising:

• a diffraction grating configured to diffract laser light to generate at least three beams including a main beam of zero order, a sub-beam of +1 order diffraction, and a sub-beam of −1 order diffraction;
• and
• an objective lens configured to condense at least the three beams, to be applied to a signal face of an optical disk,
• the diffraction grating including a first region, a second region disposed adjacently to the first region in a width direction across a direction in which a periodic structure is repeated, a third region disposed adjacently to the second region in the width direction, and a fourth region disposed adjacently to the third region in the width direction,
• a periodic structure of the first region being different in phase by less than 180 degrees from a periodic structure of the second region,
• the periodic structure of the second region being different in phase by less than or equal to 180 degrees from a periodic structure of the third region,
• the periodic structure of the third region being different in phase by less than 180 degrees from a periodic structure of the fourth region,
• the periodic structure of the fourth region being different in phase by less than 180 degrees from the periodic structure of the first region,
• the second region being smaller in width than each of the first region and the fourth region,
• the third region being smaller in width than each of the first region and the fourth region,
• the diffraction grating divided into two equal parts in the width direction by a border between the second region and the third region.