| 摘要 |
PURPOSE:To provide the optical disk device in extremely simple structure which can compensate the astigmatism of a semiconductor laser and obtain a spot stopped down to the limit of diffraction, and, therefore, provides high-density recording or reproduction with a high signal-to-noise ratio. CONSTITUTION:The optical disk device has the semiconductor laser 1 which has astigmatism of >=20mum, an optical disk 7 where information is recorded, and optical systems 3 and 6 which converge the laser light from the semiconductor laser 1 on said optical disk and returns part of the laser light converged on the optical disk 1 to said semiconductor laser 1 to read the information out. Said optical systems have lenses satisfying NA<=sq. rt. (lambda/DELTAZ). Here, NA is the numerical aperture of the lenses, DELTAZ is the astigmatism that said semiconductor device has, and lambda is the wavelength of said semiconductor device. |
