Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-02-09
2003-06-24
Korzuch, William (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
Reexamination Certificate
active
06584059
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
[The invention I]
The present invention I relates to an information recording and reproducing apparatus with a new system that can be used in an optical disk for recording or for reproducing information and suppresses the generation of light quantity fluctuations.
[The invention II]
The present invention II relates to an information recording and reproducing apparatus having high efficiency in which, in an optical disk for recording or reproducing information, the information is reproduced with a plurality of light beams to increase the transfer speed of a reproducing signal, and the information is recorded with one light beam to increase recording efficiency.
In addition, the present invention II relates to an information recording and reproducing apparatus having high efficiency in which, the information is reproduced by dividing a light beam for use in a stable tracking servo signal such as a three-beam tracking or a DPP (Differential Push-pull) tracking, and the information is recorded with one light beam to increase recording efficiency.
2. Description of the Prior Art
[The invention I]
Conventional optical disks have recorded or reproduced information by using a light beam polarization-branching member, that is located between a radiation light source and a light beam convergence member and separates an outward light beam and a return light beam by polarization of light, in order to increase light efficiency.
In the following, a conventional example that has been used frequently is explained with reference to FIG.
6
.
A light beam
602
emitted from a radiation light source
601
passes through a polarization-branching member
603
and a ¼ wavelength plate
604
. The polarization-branching member
603
transmits only a linearly polarized light (P polarized light). The light beam passing through the ¼ wavelength plate
604
is converted into circularly polarized light and reaches a light beam convergence member
605
. The light beam converged by the light beam convergence member
605
reaches a record information carrier
606
. The light beam is reflected by the record information carrier
606
, passes through the light beam convergence member
605
again and then reaches the ¼ wavelength plate
604
. The light beam becomes a linearly polarized light (S polarized light) perpendicular to the incident light in the ¼ wavelength plate
604
, and is reflected by the polarization-branching member
603
. The light beam becomes a transmitted light and a partially diffracted light by a hologram
607
for detection, and reaches a photo detector
608
for reproducing a servo signal or an information signal. Since the effects of the hologram
607
for detection and the photo detector
608
are not directly related to the present invention, an explanation here is omitted.
Since this optical system uses the polarization, when there is an optical element that disturbs the polarization state of a light beam, a light quantity of the light beam returning to the photo detector
608
may decrease. For example, in a record information carrier such as an optical disk made of plastic materials, the molecular structure of the plastics changes due to later stress such as a residual stress from molding and a temperature change, generating larger birefringence. When the record information carrier
606
is birefringent, the polarization state may be disturbed as is mentioned above. In other words, light that is circularly polarized may become elliptically polarized, linearly polarized or leading to a reverse circular polarization, in an extreme case. Accordingly, the light beam that is reflected by the information carrier and transmitted by the ¼ wavelength plate
604
may be the same polarized light (P polarized light) as the incident beam, in the worst case, and not reflected by the polarization-branching member
603
because the polarization-branching member
603
only transmits P polarized lights. As a result, the light does not reach the photo detector
608
at all. Usually, when a light quantity of a light beam shining into the photo detector
608
decreases, it is designed that an automatic gain control (AGC) circuit is activated to compensate for the decrease of the light quantity. However, when the light quantity is too small, the circuit is, of course, not activated.
As is described above, in reproducing a highly birefringent optical disk, a considerable decrease of a received light quantity has been a problem when separating the outward and return beams by using polarization. Therefore, the conventional detection system poses a problem in that disturbed polarization generates a fluctuation of received light quantity, thereby affecting the detection of a servo signal and an information signal.
[The invention II]
Conventional optical disks have used a light beam emitted from a radiation light source as a single light beam, instead of dividing the light beam into a plurality of light beams, in order to increase a light efficiency in recording. On the other hand, in reproducing optical disks, a plurality of light beams are used in order to stabilize a tracking servo for tracking the disk.
Also, a reproducing method using a plurality of light beams in order to increase the transfer rate of a reproducing signal has already come into an actual use.
In the following, a conventional example of the reproducing system that has been used frequently is explained with reference to
FIGS. 14 and 15
.
FIG. 14
shows an information recording and reproducing apparatus provided with a system of generating three light beams, reproducing a signal with the light beam in the center and stabilizing a tracking with the light beams on both sides.
A light beam
1702
emitted from a radiation light source (a semiconductor laser)
1701
is divided into three light beams, that is, a zeroth-order light beam, + first order light beam and − first order light beam, by a diffraction grating
1703
, reflected by a beam splitter
1704
and reaches a light beam convergence member (an objective lens)
1705
. The light beams converged by the light beam convergence member
1705
reaches a record information carrier
1706
. The light beams reflected by the record information carrier
1706
pass through the light beam convergence member
1705
and the beam splitter
1704
again, and then reaches a photo detector
1708
for reproducing a servo signal or an information signal. The three light beams divided by the diffraction grating
1703
, which are a zeroth-order light beam, + first order light beam and − first order light beam, reach corresponding photo detectors
1708
,
1709
and
1710
. The information signal is obtained from the photo detector
1708
, and the signal for tracking servo is obtained from a difference signal of the photo detectors
1709
and
1710
. This system is called a three-beam system and widely known in general. Therefore, a detailed explanation is omitted here.
A so-called DPP (Differential Push-pull) system can be included in this three-beam system. A DPP (Differential Push-pull) system is a system in which the photo detectors
1709
and
1710
are divided in half respectively, light spots of the light beams shining into the respective photo detector are located between signal tracks to obtain a far field signal so that a difference between the far field signal and the other far field signal obtained by dividing the photo detector
1708
is used for correcting a tracking signal. This system is also widely known, so a detailed explanation is omitted here.
FIG. 15
shows the diffraction grating
1703
in detail. The diffraction grating is formed by providing a phase step with a constant period on one surface of a glass substrate
1801
. Numeral
1802
denotes the zeroth-order light beam, numeral
1803
denotes the + first order light beam, and numeral
1804
denotes the − first order light beam. The light quantity of this zeroth-order light beam
Matsuzaki Keiichi
Nishino Seiji
Saimi Tetsuo
Shiono Teruhiro
Wada Hidenori
Korzuch William
Le Kimlien
Merchant & Gould P.C.
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