Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-12-01
2003-05-20
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S120000
Reexamination Certificate
active
06567355
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical detector, an optical pickup, and an optical information reproducing apparatus (hereinafter described as an optical disc drive) using an optical pickup, capable of reproducing an information signal recorded in an optical information recording medium (hereinafter described as an optical disc).
There are various types of optical discs having different substrate thicknesses and using different wavelengths. For example, discs such as CD and CD-R have a substrate thickness of 1.2 mm and use a 780 nm band as an optimum recording/reproducing laser wavelength, whereas recently standardized discs such as DVD-ROM and DVD-RAM have a substrate thickness of 0.6 mm and use a 650 nm band as an optimum recording/reproducing laser wavelength. Optical disc drives using a laser beam having a wavelength shorter than conventionally used wavelengths have been proposed as well. Under such circumstances, the main trend of, for example, optical pickups for DVD prevailing nowadays, is to mount semiconductor lasers having two different wavelengths in 780 nm and 650 nm bands in order to be compatible with CD optical discs already widely used.
Wide use of such optical discs is forcing optical disc drives to be compact and inexpensive. Techniques of making optical pickups compact and simple are therefore essential. Effective means for compact and simple optical pickups are to reduce the number of components of an optical system, to configure an optical pickup with inexpensive components, or the like. If an optical disc drive is to be made compatible with a plurality type of optical discs, an optical system characteristic to each type of the optical disc is required. In this case, simplifying an optical system and reducing the number of components of an optical system by using common optical elements is effective for making an optical pickup compact and inexpensive. JP-A-8-55363 and JP-A-9-54977 disclose the technique of guiding each of the laser beams of two semiconductor lasers into the same intermediate optical path to reproduce information recorded in a plurality type of optical discs with one objective lens.
Most of optical pickups each having two semiconductor lasers have an optical system whose converging optical elements such as an objective lens and a collimator lens are used in common in order to make an optical pickup compact and inexpensive. An example of the structure of such an optical system is shown in
FIGS. 1A and 1B
.
Referring to
FIG. 1A
, a light beam emitted from a semiconductor laser
11
oscillating at a wavelength of, for example, 650 nm, reaches a dichromatic half prism
12
. The dichromatic half prism
12
is an optical element made of two prisms adhered each other, and has therein a reflection film which reflects a laser beam of 650 nm in wavelength by about 50% and transmits it by about 50%, and transmits a laser beam of 780 nm in wavelength by about 100%. The light beam emitted from the semiconductor laser
11
is reflected by the reflection film of the dichromatic half mirror
12
disposed at an angle of 45° relative to the optical axis of the semiconductor laser
11
, then converted into a parallel light beam by a collimator lens
5
, and reaches an objective lens
6
. The objective lens
6
is integrally held by an actuator
7
. By energizing a drive coil
8
, the light beam can be focussed to form a light spot on a data record surface of an optical disc
1
such as DVD-ROM. A light beam reflected from the optical disc
1
propagates along a reversed optical path of the incoming optical path to reach the dichromatic half prism
12
via the objective lens
6
and collimator lens
5
. About 50% of the reflected light amount transmits through the dichromatic half prism
12
and reaches a dichromatic half mirror
13
. The dichromatic half mirror
13
is an optical element which transmits a laser beam of 650 nm by about 100%, and transmits a laser beam of 780 nm in wavelength by about 50% and reflects it by about 50%.
The light beam reached the dichromatic half mirror
13
transmits therethrough and thereafter is converged at a predetermined position of an optical detector
14
.
Referring to
FIG. 1B
, a light beam emitted from a semiconductor laser
15
oscillating at a wavelength of, for example, 780 nm, transmits through a diffraction grating
16
for generating three beams and thereafter reaches the dichromatic half mirror
13
disposed at an angle of about 45° relative to the optical axis of the semiconductor laser
15
. As described above, the dichromatic half mirror
12
has the characteristics that a laser beam having a 780 nm wavelength is reflected by about 50%, and the dichromatic half prism
12
has the characteristics that a laser beam having a 780 nm wavelength is transmitted by about 100%. Therefore, the light beam emitted from the semiconductor laser
15
is reflected by the dichromatic half mirror
13
, transmitted through the dichromatic half prism
12
, thereafter converted into a parallel light beam by the collimator lens
5
, and reaches the objective lens. The objective lens
6
can focus the light beam emitted from the semiconductor laser
15
to form a light spot on a data record surface of another optical disc
10
such as CD-ROM. A light beam reflected from the optical disc
10
propagates along a reversed optical path of the incoming optical path to reach the dichromatic half mirror
13
via the objective lens
6
, collimator lens
5
and dichromatic half prism
12
.
Since the dichromatic half mirror
13
is an optical element transmitting about 50% of the laser beam having a 780 nm wavelength as described earlier, the light beam reached the dichromatic half mirror
13
transmits through the dichromatic half mirror
13
and thereafter is converged at a predetermined position of the optical detector
14
.
In the structure of the optical system illustratively shown in
FIGS. 1A and 1B
, the converging optical system from the dichromatic half prism
12
to the collimator lens
5
and to the objective lens
6
is used in common so that the number of components is reduced. The dichromatic half prism and dichromatic half mirror having a selection function of two different wavelengths and predetermined optical characteristics are used, and the semiconductor lasers having two different wavelengths are used. These optical elements having the waveform selection function and the semiconductor lasers are much expensive than other components of the optical pickup, and hinder a further cost reduction of the optical pickup.
SUMMARY OF THE INVENTION
Under such circumstances, an object of the present invention is to provide an optical detector, an optical pickup, and an optical disc drive using an optical pickup capable of recording/reproducing an information signal in/from a plurality type of optical discs, in which the structure of an optical system simpler than that of a conventional optical system can be realized and a low cost optical system structure can be realized by using inexpensive optical elements and semiconductor lasers as small in number as possible.
In order to achieve this object of the invention, in an optical detector, an optical pickup and an optical information reproducing apparatus using the optical pickup, the optical information reproducing apparatus comprises: a semiconductor laser having a first laser source, a second laser source or both; a light separation element for separating a light beam emitted from the first laser source, a second laser source or both into at least three light beams; a converging optical system for applying a light beam including the three light beams to a first optical information recording medium or a second optical information recording medium different from the first optical information recording medium; an optical detector having a first light reception area disposed at a position where a light beam emitted from the first laser source and reflected from a first optical information recording medium is applied, and a second light reception area
Fujita Shinji
Inoue Masayuki
Izumi Katsuhiko
Ohnishi Kunikazu
Shimada Ken'ichi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Huber Paul W.
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