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US 6,333,908 B2Granted
Optical head having two semiconductor lasers of different wavelength, an objective lens focusing laser beams on different thickness substrates, and an annular phase shifter decreasing focused laser beam spot aberration
AssigneeHitachi, Ltd.
InventorsTakeshi Shimano, Akira Arimoto
Life of this patent
Estimating the term…
Abstract
An objective lens and an optical head including the objective lens for reading information contained on substrates having different thicknesses using laser beams having different wavelengths. The objective lens includes an annular phase shifter for decreasing an aberration of a focused spot of each of the laser beams. The annular phase shifter can be optimally combined with the objective lens having inner and outer regions each having a different substrate thicknesses.
Claims2
An optical head comprising:
- a first semiconductor laser for generating a first laser beam having a first wavelength;
- a second semiconductor laser for generating a second laser beam having a second wavelength different from the first wavelength;
- an objective lens for focusing the first and the second laser beams, having a rectangular groove, which transmits incident light of the first and the second laser beams, for shifting phase of the incident light to decrease aberration of one of focused spots of the first and the second laser beams without increasing the aberration of the other focused spot compared with an objection lens not having the rectangular groove, the incident light of the first and the second laser beam being parallel light.
Dependencies are inferred from the claim text.