Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-03-09
2004-06-29
Patel, Gautam R. (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S044410, C369S116000
Reexamination Certificate
active
06757227
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording/reproducing apparatus comprising an optical head for applying a laser beam to an optical recording medium, thereby to record data on and reproduce data from the optical recording medium. More particularly, the present invention relates to an optical recording/reproducing apparatus for use in combination with a plurality of optical recording media, each having recording tracks formed at a track pitch different from the track pitch of any one of the other optical recording media, or with an optical recording medium that have a plurality of recording regions, each having recording tracks formed at a track pitch different from the track pitch of any one of the other recording regions.
Data recording media, such as playback-only optical discs, phase-change optical discs, magneto-optical discs and optical cards, are widely used to store video data, audio data and other data such as computer programs. In recent years it has been increasingly demanded that these data recording media should record data at higher densities and in greater amounts.
In recent years, compact discs (CDs), recordable compact discs (CD-Rs) and rewritable compact discs (CD-RWs) have come into use as means for recording data in computers. Hence, CD-R/RW apparatuses for recording data signals on, and reproducing them from, these optical recording media are used in increasing numbers.
It is increasingly required that a great amount of data, such as image data, be stored. It is therefore desirable to increase the recording capacity of optical recording media such as CD-Rs and CD-RWs.
As is known in the art, tracking error signals are generated by DPP (Differential Push Pull) method or three-spot method in the optical disc recording/reproducing apparatus for use in combination with optical discs such as CD-Rs and CD-RWs.
FIG. 1
shows the positional relation between beam spots on a disc and beam spots on a photodetector, illustrating how a tracking error signal is generated in the DPP method.
A main spot SPm of the main beam is formed on an optical disc
211
, while side spots SPs
1
and SPs
2
of two side beams are formed the optical disc
211
, too. The side spots SPs
1
and SPs
2
are spaced from the main spot SPm in the opposite radial directions, respectively, by a distance of Tp/2 (180°), where Tp is the intervals (track pitch) at which grooves GR (i.e., recording tracks) are arranged.
Photodiode sections
212
M,
212
S
1
and
212
S
2
constitute a photodetector
212
. Spots SPm′, SPs
1
′ and SPs
2
′ of light beams reflected from the optical disc
211
, at the spots SPm, SPs
1
and SPs
2
, are formed on the photodiodes
212
M,
212
S
1
and
212
S
2
, respectively. The photodiode section
212
M comprises four photodiodes Da to Dd, which generate detection signals Sa to Sd. The photodiode section
212
S
1
comprises two photodiodes De and Df, which output detection signals Se and Sf. The photodiode section
212
S
2
comprises two photodiodes Dg and Dh, which output detection signals Sg and Sh.
FIG. 2
shows a circuit connection for generating a tracking error signal STE in the DPP method. A subtracter
221
M subtracts the sum of the detection signals Sb and Sc from the sum of the detection signals Sa and Sd, generating a push-pull signal Sppm that corresponds to the light reflected from the main spot SPm. A subtracter
221
S
1
subtracts the detection signal Sf from the detection signal Se, generating a push-pull signal Spps
1
that corresponds to the light reflected from the side spot SPs
1
. A subtracter
221
S
2
subtracts the detection signal Sh from the detection signal Sg, generating a push-pull signal Spps
2
that corresponds to the light reflected from the side spot SPs
2
.
An adder
222
receives the push-pull signal Spps
2
supplied via an amplitude adjuster
223
having gain G
2
. The adder
222
receives the push-pull signal Spps
1
, too. The adder
222
adds the push-pull signals Spps
1
and Spps
2
, generating a sum signal Ss. A subtracter
224
receives the sum signal Ss via a amplitude adjuster
225
having gain G
1
. The substracter
224
receives the push-pull signal Sppm. The substracter
224
subtracts the sum signal Ss from the push-pull signal Sppm, generating a tracking error signal STE. Here, G
1
=A
1
/2A
2
, and G
2
=A
2
/A
3
, where A
1
is the amplitude of the push-pull signal Sppm, A
2
is the amplitude of the push-pull signal Spps
1
, and A
3
is the amplitude of the push-pull signal Spps
2
. Thus, an offset is removed from the tracking error signal STE.
FIG. 3
depicts the positional relation between beam spots on a disc and beam spots on a photodetector, illustrating how a tracking error signal is generated in the three-spot method.
A main spot SPm of the main beam is formed on an optical disc
211
, while side spots SPs
1
and SPs
2
of two side beams are formed the optical disc
211
, too. The side spots SPs
1
and SPs
2
are spaced from the main spot SPm in the opposite radial directions, respectively, by a distance of Tp/4 (90°), where Tp is the intervals (track pitch) at which grooves GR (i.e., recording tracks) are arranged.
Photodiode sections
213
M,
213
S
1
and
213
S
2
constitute a photodetector
213
. Spots SPm′, SPs
1
′ and SPs
2
′ of light beams reflected from the optical disc
211
, at the spots SPm, SPs
1
and SPs
2
, are formed on the photodiodes
213
M,
213
S
1
and
213
S
2
, respectively. The photodiode section
213
M comprises four photodiodes Da to Dd, which generate detection signals Sa to Sd. The photodiode section
213
S
1
comprises a photodiodes Df, which outputs a detection signalsSf. The photodiode section
213
S
2
comprises a photodiode De, which outputs a detection signals Se.
FIG. 4
illustrates a circuit connection for generating a tracking error signal STE in the three-spot method. A subtracter
226
subtracts the detection signal Sf from the detection signal Se, generating the tracking error signal STE.
To increase the recording capacity of such an optical recording medium as described above, it is advisable to enhance the linear density or the track density. If the linear density of the optical recording medium is increased, the jitter in the signal reproduced from the medium will increase due to inter-code interference, unless the optical system for recording data signals on and reproducing them from the medium is modified in specification. If the track density is increased without modifying the optical system, a crosstalk will develop to make it difficult to reproduce the data signals reliably.
The problems described above can be solved by modifying the optical system, thereby reducing the diameter of the reading beam spot.
To reduce the diameter of the beam spot, various methods may be used. One method is to decrease the wavelength of the laser beam applied in the optical system. Another method is to increase the numerical aperture (NA) of the objective lens incorporated in the optical system. If the wavelength of the laser beam is changed, however, data signals will be neither recorded on, nor reproduced from, the existing CD-R. This is because the dye film, or recording layer, of the CD-R has reflectance that greatly depends on the wavelength of the laser beam. Further, if the NA of the objective lens is excessively large, coma-aberration will occur as the disc warps with respect to the axis of the laser beam or spherical aberration will develop due to the uneven thickness of the disc. The aberration, whether coma-aberration or spherical aberration, will increase the jitter in the signal reproduced from the medium.
Consider the detection of tracking error signals in the process of recording data signals on, or reproducing them from, various kinds of discs, each having recording tracks formed at a track density (track pitch) different from the track density of any one of the other discs. Then, the following problems seem to arise. To generate a tracking error signal STE in the DPP method, the side spots SP
Kumagai Eiji
Morizumi Toshio
Nagashima Kenji
Patel Gautam R.
Sony Corporation
LandOfFree
Optical drive apparatus for use with different recording... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical drive apparatus for use with different recording..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical drive apparatus for use with different recording... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3325471