Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2002-05-20
2004-05-18
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044230, C369S112080, C369S112230
Reexamination Certificate
active
06738324
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording and/or reproduction apparatus (information disc apparatus) for recording information to an optical disc having a plurality of recording layers or reproducing information from such an optical disc. In particular, the present invention relates to a tracking control technology and a focusing control technology usable for such a recording and/or reproduction apparatus.
2. Description of the Related Art
Conventional optical discs include a recording layer formed of a phase change material, a magneto-optical material, or a colorant, which is used for recording or reproduction of information. Usually, conventional optical discs include a single recording layer. In order to increase the recording capacity, three-dimensional recording or provision of multiple recording layers have been proposed.
With reference to
FIG. 8
, a conventional representative recording system will be described. An information disc apparatus
700
for recording information to or reproducing information from an optical disc
727
includes a light source
725
and an objective lens
726
. The optical disc
727
includes a substrate
728
. The substrate
728
has concaves portions
722
and convex portions
723
formed alternately. The optical disc
727
further includes a recording layer
720
provided in close contact with the concave portions
722
and the convex portions
723
.
The light source
725
emits a light beam
724
. The objective lens
726
converges the light beam
724
to one of the concave portions
722
or one of the convex portions
723
(in the example shown in
FIG. 8
, one of the concave portions
722
). The information disc apparatus
700
detects a servo signal based on the light beam
724
reflected by the concave portion
722
or the convex portion
723
, and performs focusing control and tracking control of the light beam
724
based on the servo signal.
With the combination of the information disc apparatus
700
and the optical disc
727
, information can be recorded or reproduced with one light beam
724
, but the information can be recorded only to one recording layer
720
. Three-dimensional recording is impossible.
Referring to
FIG. 9
, Japanese Laid-Open Publication No. 61-248231 discloses a method for converging two different light beams emitted by two light sources to a guide track of an optical disc and a recording layer, respectively.
An information disc apparatus
800
, described in Japanese Laid-Open Publication No. 61-248231, for recording information to or reproducing information from an optical disc
830
includes two light sources
827
and
828
, and an objective lens
831
. The optical disc
830
includes a substrate
832
. The substrate
832
has concaves portions
822
and convex portions
823
formed alternately. The optical disc
830
further includes an intermediate layer
833
provided on the substrate
832
and a recording layer
834
provided on the intermediate layer
833
.
The light source
828
emits a light beam
825
. The objective lens
831
converges the light beam
825
to the recording layer
834
. On the recording layer
834
which is away from the concave portions
822
and the convex portions
823
by a prescribed distance, information is recorded by the light beam
825
.
The light source
827
also emits a light beam
824
having a different wavelength from that of the light beam
825
. The objective lens
831
converges the light beam
824
to one of the concave portions
822
or one of the convex portions
823
(in the example shown in
FIG. 9
, one of the convex portions
823
). Based on the light beam
824
converged to and reflected by the concave portion
822
or the convex portion
823
, the focusing control and tracking control of the light beam
825
are performed.
The information disc apparatus
800
generates a servo signal based on the light beam
824
reflected by the convex portion
823
and performs focusing control and tracking control of the light beam
825
based on the servo signal.
Japanese Laid-Open Publication No. 61-248231 discloses that the range of selection of the material of the recording layer
834
is widened by the method shown in FIG.
9
. However, information can be recorded only to one recording layer
834
. Japanese Laid-Open Publication No. 61-248231 does not disclose an optical disc having a plurality of recording layers or describe recording of information to the plurality of recording layers.
The information disc apparatus
800
requires two types of light sources in order to emit two light beams having different wavelengths, and thus needs a complicated structure. In addition, it is difficult to maintain the offset amount of the two light beams
824
and
825
at a prescribed value. Therefore, a change in the relative positions of the light paths of the light beams
824
and
825
causes off-tracking or defocusing.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a recording and/or reproduction apparatus for an information medium including a substrate having concave and convex portions and a plurality of recording layers is provided. The recording and/or reproduction apparatus includes a light source for emitting a light beam; an optical system for diffracting the light beam emitted by the light source so as to output a first diffracted light beam and a plurality of second diffracted light beams; and a driving section for driving the optical system. The optical system outputs the first diffracted light beam and the plurality of second diffracted light beams, such that when one of the plurality of second diffracted light beams is converged to and reflected by one of the concave and convex portions, the first diffracted light beam is converged to one of the plurality of recording layers. The driving section drives the optical system, such that the one of the plurality of second diffracted light beams is converged to the one of the concave and convex portions.
In one embodiment of the invention, the number of the plurality of second diffracted light beams and the number of the plurality of recording layers are each M, where M is an integer equal to or greater than 2. The first diffracted light beam is converged to an N'th recording layer, among the M recording layers, by the driving section driving the optical system such that an N'th second diffracted light beam, among the M second diffracted light beams, is converged to the one of concave and convex portions, where N is an integer equal to or greater than 1 but equal to or less than M.
In one embodiment of the invention, M is an integer equal to or less than 10.
In one embodiment of the invention, the number of the plurality of second diffracted light beams is equal to the number of the plurality of recording layers.
In one embodiment of the invention, information is recorded to the one of the plurality of recording layers by the first diffracted light beam being converged to the one of the plurality of recording layers.
In one embodiment of the invention, the information medium further includes at least one intermediately layer provided between the plurality of recording layers.
In one embodiment of the invention, a straight line connecting a convergence point of the first diffracted light beam and a convergence point of each of the plurality of second diffracted light beams is substantially vertical to a surface of the plurality of recording layers.
In one embodiment of the invention, the first diffracted light beam has a light amount which is larger than a light amount of each of the plurality of second diffracted light beams.
In one embodiment of the invention, the optical system includes a collimator lens for converting the light beam emitted by the light source to a parallel light beam, an optical element for diffracting the parallel light beam so as to output the first diffracted light beam and the plurality of second diffracted light beams, and an objective lens for converging the first diffracted light beam and the plurality
Saimi Tatsuo
Shiono Teruhiro
Yamamoto Hiroaki
Edun Muhammad
Matsushita Electric Industrial Co.
Renner , Otto, Boisselle & Sklar, LLP
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