Asahi Kogaku Kogyo Kabushiki Kaisha

Pentax Corporation

Hisashi Konno

Koichi Maruyama

Suguru Takishima

Masahiro Oono

Hiroshi Nishikawa

Toshiyuki Kase

Hiroshi Yamamoto

Masato Noguchi

Takashi Morita

Makoto Iki

Wataru Kubo

Katsuki Hayashi

An optical disc apparatus includes a fixed portion having a light source portion and a movable portion that holds an objective lens and moves along a radial direction of an optical disc. The fixed portion includes the light source portion for selectively emitting short and long wavelength laser beams, and a collimator lens for collimating the laser beams. The objective lens includes a positive refractive lens and a diffractive lens structure formed on a surface of the refractive lens. The diffractive lens structure has wavelength dependence such that spherical aberration varies in the undercorrected direction as wavelength of incident light increases. The objective lens converges the short wavelength laser beam of a predetermined diffraction order onto an informatlon layer of a thin cover type optical disc, and converges the long wavelength laser beam of the identical diffraction order onto an information layer of a thick cover type optical disc.

Optical disc apparatus

A detecting apparatus which detects an inclination of an objective lens relative to a reference surface is provided. The objective lens is part of an optical data recording and reproducing apparatus in which data is optically recorded on and reproduced from a recording medium which is placed parallel to the reference surface. The apparatus includes a transparent parallel plate which is opposite the objective lens, parallel to the reference surface, and made of a material that is substantially optically equivalent to a transparent material of the recording medium. The apparatus further includes a reflecting mechanism for reflecting coherent light which has passed through the objective lens and the transparent parallel plate back towards the transparent parallel plate and the objective lens, and a beam splitting mechanism for splitting the coherent light into a first beam and a second beam. The apparatus further includes a wavefront rotating mechanism for rotating the first beam and the second beam about an optical axis in a manner such that the first beam and the second beam are rotated through 180 degrees with respect to one another, and a mechanism for superposing the first beam and the second beam to produce an optical interference.

Inclination of an objective lens in an optical information system

The optical disk apparatus of this invention is provided with a memory for memorizing a track offset signal corresponding to an angle of a galvanic mirror, or a photodetector having two pairs of photodetecting regions to detect different tracking error signals to each other, or two galvanic mirrors which are adjusted so as to prevent the track offset signal.

Optical disk apparatus

Growing community of inventors

Tokyo, Japan

Hisashi Konno