Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2001-09-28
2003-12-09
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S053190, C369S053100
Reexamination Certificate
active
06661769
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical storage medium such as an optical disk or optical card, a data recording and reproducing apparatus for recording, reproducing, and deleting data on the optical storage medium, and a tilt detection apparatus for detecting the angle between the optical storage medium and a light beam converged by a convergent system in the data recording and reproducing apparatus.
2. Description of Related Art
Optical storage technologies using optical disks having a pattern of pits for recording data as a high density, high capacity storage medium have found applications ranging from recording digital audio and video to document filing systems and computer data file storage. Digital Versatile Disks (DVD) read with a 650 nm visible wavelength semiconductor laser as the light source have in particular recently become popular because of their high density storage capacity, and standards for read-only DVD-ROM media, write-once DVD-R media, and multiply rewritable DVD-RAM media have been established.
FIG. 15
shows the configuration of the optical system of a prior art optical pickup head system for reading DVD-ROM media as exemplary of an optical storage medium. The light source, a semiconductor laser
1
, emits a divergent beam
70
of linear polarized light with a wavelength &lgr;=0.65 &mgr;m. The divergent beam
70
is reflected by half mirror
7
, bending the light path so that the beam
70
passes a collimator
8
with a 20 mm focal length and is converted to parallel light. The parallel beam
70
is then converted to a convergent beam by a 3 mm focal length objective lens
9
, passes the transparent layer
40
a
and converges on the data recording surface
40
b
of the storage medium
40
. The aperture of objective lens
9
is restricted by aperture
12
to a numerical aperture NA of 0.6. The thickness of the transparent layer
40
a
is 0.6 mm.
The beam
70
reflected from the data recording surface
40
b
passes the objective lens
9
and collimator
8
, then passes the half mirror
7
and astigmatism is introduced. The beam
70
then passes a concave lens
11
with a tilted optical axis, thereby correcting the astigmatism and coma introduced when the beam
70
passed the half mirror
7
, and is received by a photodetector
31
. Axis
31
e
is parallel to the image of the recording track on data recording surface
40
b
in the beam received by the photodetector
31
.
The photodetector
31
has four receiving parts
31
a
to
31
d
, each outputting a current signal
131
a
to
131
d
according to the amount of light detected. Each of the receiving parts
31
a
to
31
d
is 50 &mgr;m×50 &mgr;m. The current signals
131
a
to
131
d
output from the receiving parts
31
a
to
31
d
are respectively input to circuit part
51
a
to
51
d
of current-voltage conversion circuit
51
, converted thereby to a voltage signal V
51
a
to V
51
d
, and output from the optical pickup head system.
A focusing error signal is calculated from the signals V
51
a
to V
51
d
output from the optical pickup head system using an astigmatism method, that is, as (V
51
a
+V
51
c
)−(V
51
b
+V
51
d
). When the medium is a DVD-ROM as in this example, a tracking error signal is obtained using a differential phase detection (DPD) method comparing the phase of V
51
a
~V
51
d
; if the medium is a DVD-RAM, the tracking error signal is calculated using a push-pull method, that is, by calculating (V
51
a
+V
51
d
)−(V
51
b
+V
51
c
). The focusing error signal and tracking error signal are amplified to a desired level and phase-compensated, then supplied to actuators
91
and
92
for focus and tracking control.
If the numerical aperture NA of the objective lens
9
is increased to 0.6, it will not be possible to faithfully read data recorded to the storage medium
40
if warping of the storage medium
40
is great. The angle between the storage medium
40
and converged beam
70
is therefore detected using a reflection photocoupler.
This reflection photocoupler consists of light source
97
and photodetector
98
. The light source
97
is a light-emitting diode. The receiving part of the photodetector
98
is divided into two parts. The signal strength of the output from the two receiving parts of the photodetector
98
varies according to the tilt of the storage medium
40
. It is therefore possible to obtain a signal corresponding to the tilt of the storage medium
40
by differentially amplifying the signals output from the photodetector
98
. Though not shown in the figure, the beam
70
is constantly controlled to a desired angle relative to the storage medium
40
regardless of how the storage medium
40
is warped by inclining the entire optical system, including the photocoupler and optical pickup head system, using this signal corresponding to the tilt.
However, when the warp of storage medium
40
is detected using a reflection photocoupler, the cost of the optical system is necessarily increased as a result of the additional parts and the additional steps needed for assembly.
Furthermore, because the track to which the beam used for tilt detection is emitted and the track to which the beam is emitted for reading data are different, it is not possible to sufficiently correct tilt of the optical storage medium if the tilt differs according to the position in the radial direction, and faithful signal reproduction may not be possible.
To resolve the problems associated with using a photocoupler for tilt detection, Japanese Patent Laid-Open Publication (kokai) H10-97753 (U.S. patent application Ser. No. 08/877363), Kokai 2000-57606, Kokai 2000-90948, Kokai 2000-123390, Kokai 2000-137923, Kokai 2000-149296 (U.S. patent application Ser. No. 09/386458), Kokai 2000-149298, and Kokai 2000-123390 (U.S. patent application Ser. No. 09/386458) teach a tilt detection apparatus using the DVD-RAM guide groove and the CAPA address area. This tilt detection apparatus does not require a photocoupler, and simplifies the optical design.
When a photocoupler is used for tilt detection, closed loop control is not possible without driving the entire optical system, including the photocoupler, and adjusting for tilt to the optical storage medium. The problem is that because the entire optical system is driven, adaptation to a thin data recording and reproducing apparatus is difficult.
Furthermore, because tilt detection using the guide groove and CAPA is effective when the pitch Gp of the guide groove formed on the optical storage medium is greater than &lgr;/NA, more data can be recorded and good tilt detection can be achieved when tracks are formed on both lands and grooves as in DVD-RAM media. However, if a data track is provided in only the land or the groove, data recording capacity drops if Gp>&lgr;/NA so that good tilt detection can be achieved, and if Gp<&lgr;/NA so that data recording capacity is increased, good tilt detection cannot be achieved.
Considering the problems of a prior art apparatus as described above, an object of the present invention is to provide an optical storage medium, a tilt detection apparatus using the optical storage medium, and a data recording and reproducing apparatus using the tilt detection apparatus such that when a tilt detection apparatus is used to detect optical storage medium tilt, stable detection of optical storage medium tilt is possible by means of a simple configuration when the guide channel pitch is decreased in order to increase data storage capacity.
SUMMARY OF THE INVENTION
To achieve the above object, an optical storage medium according to the present invention having guide grooves with a pitch of Gp1 between adjacent grooves has intermittent grooves Gn−1 and Gn+1 adjacent to opposite sides of an n-th groove Gn with non-groove spaces formed in grooves Gn−1 and Gn+1, creating an area where pitch Gp2 of groove Gn is equivalent to twice pitch Gp1 so that &lgr;/NA≧Gp1≧&lgr;/(2·NA) where &lgr; is the wavelength of a bea
Furumiya Shigeru
Ishibashi Hiromichi
Kadowaki Shin-ichi
Sano Kousei
Edun Muhammad
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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