Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-08-28
2001-01-30
Edun, Muhammad (Department: 2753)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S109010, C369S103000, C369S094000, C369S044120
Reexamination Certificate
active
06181668
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical pickup device, and more specifically, to an optical pickup device for recording and/or reproducing digital video disc (DVD) and compact disc (CD).
BACKGROUND ART
An optical device for reading information recorded on an optical disc having a transparent substrate of about of 1.2 mm in thickness, such as a CD, by using a semiconductor laser has been provided. In such an optical pickup device, focus servo and tracking servo control for an objective lens of the pickup device is performed, a pit string on the recording surface is irradiated with laser beam, whereby audio, video and data signals are reproduced.
Referring to
FIG. 91
, in a recordable compact disc (CD-R)
150
which is one type of CDs, cyanine dye
152
is provided on a recording surface side of transparent substrate
151
, and gold
153
is further provided. CD-R has the same track pitch, recording density and pit length as those of a general CD for music, and the CD-R is different from the CD for music only in that it allows one recording. Recording is done by irradiating cyanine dye
152
with laser beam through transparent substrate
151
. When cyanine dye
152
is irradiated with laser beam, optical characteristic of the irradiated portion becomes uneven. Accordingly, at a portion not irradiated with laser beam at the time of recording, most laser beam is reflected by gold
153
at the time of reproduction, while at portions irradiated with laser beam at the time of recording, laser beam is hardly reflected at the time of reproduction.
Recently, density has been increased in order to record a motion picture for a long period of time on such an optical disc. For example, a DVD allowing recording of information of about 5 G byte on one side having the same diameter of 12 cm as the CD has been proposed. Thickness of the transparent substrate of the DVD is about 0.6 mm. One DVD formed by adhering two transparent substrates back to back allows recording of information of about 10 G byte.
However, the aforementioned pickup objective lens is designed taking into consideration the thickness of the transparent substrate of the optical disc of interest and wavelength of semiconductor laser used. Therefore, when an optical disc having a thickness different from the design is to be reproduced, laser beam is not focused on the recording surface of the optical disc, and hence reproduction is not possible. For example, an objective lens designed for a CD having transparent substrate of 1.2 mm in thickness is not capable of focusing laser beam on the recording surface of a DVD having a transparent substrate 0.6 mm in thickness.
In CD-R
150
employing cyanine dye
152
mentioned above, maximum reflectance is attained when the laser beam has the wavelength of 800 nm, while reflectance is not higher than 10% when the laser beam has the wavelength of 635 nm, as shown in FIG.
92
. Accordingly, reproduction of a CD-R is not possible by the laser beam having the wavelength of 635 nm which is used for reproduction of a DVD. In order to reproduce the CD-R with the laser beam having the wavelength of 635 nm, it may be possible to use dye having higher reflectance to the laser beam having the wavelength of 635 nm in place of cyanine dye
152
. However, it is not practical to change CD-R standard to be in line with the DVD.
The present invention was made to solve the above described problem, and its object is to provide an optical pickup device capable of recording and/or reproducing two different types of optical discs having transparent substrate of different thicknesses.
DISCLOSURE OF THE INVENTION
According to an aspect of the present invention, the optical pickup device is for recording and/or reproduction of a first optical disc having a transparent substrate of a first thickness and a second optical disc having a transparent substrate of a second thickness different from the first thickness, and the optical pickup device includes an objective lens opposing to the first or second optical disc, a numerical aperture changing element for changing numerical aperture of the objective lens in accordance with the thickness of the transparent substrate of the first or the second optical disc, a laser beam generating element for selectively generating a first laser beam having a first wavelength and a second laser beam having a second wavelength different from the first wavelength, and an optical unit for guiding the first laser beam to a first direction, guiding the second laser beam to a second direction different from the first direction, and guiding the first or the second laser beam to the objective lens.
Preferably, the optical unit includes a hologram which does not diffract the first laser beam but diffracts the second laser beam.
More preferably, the optical unit further includes a collimator lens receiving the first or the second laser beam from the laser beam generating element and guiding the received laser beam to the objective lens.
More preferably, the hologram is provided on a surface of the collimator lens.
Preferably, the optical pickup device further includes a diffiaction grating plate having a main surface on which three beam type diffraction grating for dividing the first or the second laser beam into three is formed. The hologram is provided on a surface opposite to a main surface of diffraction grating plate.
Preferably, the laser beam generating element includes a semiconductor laser and an activating circuit. The semiconductor laser includes a substrate, a first laser element provided on the substrate for generating the first laser beam, and a second laser element provided adjacent to the first laser element on the substrate for generating the second laser beam. The activating circuit selectively activates the first and the second laser elements. The optical pickup device further includes a photodetector formed spaced apart from the first and second laser elements on the substrate of the semiconductor laser, for detecting beam diffracted by the hologram, of the beams reflected from the first or the second optical disc.
Preferably, the optical unit includes a bifocal collimator lens having two points of focus.
More preferably, the bifocal collimator lens includes a first lens, a second lens provided opposing to the first lens, and a member of which diffractive index changes in accordance with the first or the second wavelength sandwiched between the first and second lenses.
More preferably, the member is cyanine dye.
More preferably, the member includes a first transparent electrode, a second transparent electrode provided opposing to the first transparent electrode, and liquid crystal sandwiched between the first and second transparent electrodes. The optical pickup device further includes an application circuit for applying a prescribed voltage between the first and second transparent electrodes in accordance with the first or the second wavelength.
More preferably, the first and second transparent electrodes are formed in stripes.
More preferably, the optical pickup device further includes a photodetector for detecting a beam reflected from the first or the second optical disc, and a beam splitter receiving the first or the second laser beam from the laser beam generating element and the reflected beam, for guiding part of the received laser beam to the objective lens and part of the received reflective beam to the photodetector. The application circuit includes an optical filter receiving the remaining part of the laser beam received by the beam splitter, for selectively transmitting either one of the first and second laser beams, a converting circuit for converting optical energy of the laser beam transmitted through the optical filter to electric energy, and a driving circuit for driving liquid crystal based on the electric energy from the converting circuit.
Preferably, the laser beam generating element includes a semiconductor laser and an activating circuit. The semiconductor laser includes a substrate, a first laser element provided on the substr
Ichiura Shuichi
Kajiyama Seiji
Kanou Yasuyuki
Tsuchiya Yoichi
Yamada Masato
Armstrong, Westerman Hattori, McLeland & Naughton
Edun Muhammad
Sanyo Electric Co,. Ltd.
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