Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Patent
1997-08-15
1999-08-31
Dinh, Tan
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
3692751, G11B 724
Patent
active
059462876
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to an optical disc including guide grooves and pits, and more particularly to improvements for obtaining reasonable push-pull signals.
Optical discs using the so-called ISO standard have spiral guide grooves, wherein emboss shaped pits are molded (formed) in advance between respective grooves at the inner circumferential portion or the header portion.
In such optical discs, the optical pick-up is subjected to seek operation in the radial direction of the disc to move it to the target track on the basis of tracking error signal (so called push-pull signal) from the groove. In that regard, a threshold is set in the vicinity of center value of the push-pull signal to detect how many times the push-pull signal crosses (traverses) this threshold to thereby count the number of tracks to detect the target track. At the same time, the target address is detected on the basis of an address signal from the emboss shaped pit to carry out recording or reproduction of information.
Meanwhile, in these optical discs where pits in emboss form are molded in advance between respective as described above, a phenomenon occurs in that the signal amplitude of the tracking error signal (the so called push-pull signal) in the area including pits is reduced to one half (1/2).about.one third (1/3) as compared to the signal amplitude in the area comprised of only grooves.
This is because an approach has been conventionally preferentially employed to take the information signal amplitude from the area comprised of only grooves as a large value, so the tracking error signal from the area including pits is sacrificed.
Accordingly, when the tracking error signal is greatly reduced in the area including pits by the phenomenon described above, inconveniences occur such that tracking cannot be precisely under taken and/or any error takes place in the tracking count operation.
SUMMARY OF THE INVENTION
An object of this invention is to provide an optical disc capable of suppressing a decrease of the signal amplitude of the push-pull signal in the area where grooves and pits are mixed.
To attain the above-described object, an optical disc of this invention is directed to an optical disc in which concentrical or spiral guide grooves are formed on a base (substrate), and pits in emboss form are molded between these respective guide grooves, the depth of the pits being set so that a push-pull signal by the pits is caused to exhibit reverse polarity with respect to a push-pull signal by the guide grooves.
In a more practical sense, when the wavelength of reproduction laser beams is .lambda. and refractive index of the base is n, the depth Dp of the pit is caused to fall within the range expressed as 0.32 .lambda.
.ltoreq.Dp.ltoreq.0.51 .lambda.
.
Preferably, that when the track pitch is t, the width Wp of the pit is 0.27 t.ltoreq.Wp.ltoreq.0.36 t.
Further, the depth Dg and the width Wg of the guide groove preferably are respectively expressed as 0.0875 .lambda.
.ltoreq.Dg.ltoreq.0.1625 .lambda.
and 0.27 t.ltoreq.Wg.ltoreq.0.36 t.
In this invention, since the depth of the pit is set so that it falls within the reasonable range, there is no possibility that a bad influence is exerted on the push-pull signal. As a result, e.g., the possibility that any erroneous counting may take place at the time of tracking count operation is lessened. In addition, an adequate information signal amplitude from the area including pits is ensured.
In accordance with this invention, in the area comprised of only grooves and the area where pits exist between respective grooves, an approach can be made such that the polarities and the magnitudes of push-pull signals (from the respective areas), which are the most important for the purpose of tracking of the laser beam spot, are not caused to be changed.
Since the previously described effect can be obtained also in the case where the laser beam spot crosses (traverses) the header area (area from which address signal is obtained) of the optical disc, erroneous co
REFERENCES:
patent: 4949331 (1990-08-01), Maeda et al.
Kagawa Masaki
Nakayama Hiroshi
Dinh Tan
Sony Corporation
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