1. Field of the Invention
This invention relates to a disc-shaped recording medium and, more particularly, to a disc-shaped recording medium having a land and a groove formed alternately thereon. This invention also relates to a disc recording and/or reproducing method and apparatus for recording and/or reproducing data for the above disc-shaped recording medium and to a tilt detecting method for detecting tilt produced in recording and/or reproducing data on or from the disc-shaped recording medium.
2. Description of Related Art
An optical disc, such as a so-called CD (Compact Disc) or DVD (Digital Versatile Disc), is widely known as a recording medium having e.g., digital data optically recorded thereon.
An optical disc recording and/or reproducing apparatus for recording and/or reproducing digital data on or from the optical disc illuminates small-sized light spot, which is the converged laser light, on an optical disc run in rotation to record and/or reproduce the digital data. The optical head causes the laser light to follow a track formed on the optical disc surface in order to record digital data in stability on the optical disc or in order to reproduce digital data recorded on the optical disc.
Recently, such an optical disc has been devised in which, for raising the recording density of the optical disc, the land and the groove are alternately formed e.g., spirally to record data on the land and/or the groove.
As an example, there is known a system in which an address is afforded by a wobbled groove and is detected by a land as a recording track, as in MD-DATA2.
However, difficulties are met in address detection in case groove exhibiting superior recording characteristics is used as a recording track. Although a system is also envisaged in which both the land and the groove are designed to serve as recording tracks, difficulties are similarly met in such case in address detection.
Moreover, in the above-described optical disc, radial tilt tends to be produced due to warping of the disc caused by environmental factors, such as temperature or humidity, in use and/or on storage or as a result of handling states, or due to tilt of the optical head in an optical disc drive device. Since this tilt is responsible for aberration in the replay light spot, distortion in the playback signals, lowered MTF (modulation transfer function) or lowered recording power is produced in a known manner.
Recently, the tendency is towards increasing the numerical aperture (NA) of an objective lens in an optical head in an optical disc drive device for raising the recording density of the optical disc. For example, an objective lens with the value of NA of 0.45 and an objective lens with the value of NA of 0.60 are used for CD and DVD, respectively. As a result, the optical disc tends to be warped and, due the larger value of NA, the aberration angle dependency is also increasing.
On the other hand, in an optical disc driving device, such a system is in use in which a dedicated sensor is provided for detecting the tilt value for tilt compensation and in which an objective lens in an optical head or an actuator is inclined based on a detected signal.
However, if, in the conventional optical disc drive device, an optical disc is of a small diameter, there may not be provided a sufficient spacing in which to install a sensor used for detecting a tilt value to render the tilt value detection difficult.
It is therefore an object of the present invention to provide a disc-shaped recording medium in which addresses may be detected not only in case the land is used as a recording track but also in case the groove exhibiting higher recording properties is used as a recording track.
It is another object of the present invention to provide a disc recording and/or reproducing method and apparatus in which addresses may be detected not only in case the land is used as a recording track but also in case the groove exhibiting higher recording properties is used as a recording track.
It is yet another object of the present invention to provide a disc recording and/or reproducing apparatus and a tilt detecting method in which it is possible to detect tilt produced in a disc-shaped recording medium not only in case the land is used as a recording track but also in case the groove exhibiting higher recording properties is used as a recording track.
In one aspect, the present invention provides a disc-shaped recording medium in which a land and a groove are formed alternately and in which data is recorded on said land and/or said groove, wherein two of said grooves facing each other with a land in-between are wobbled based on respective different wobbling frequencies.
In another aspect, the present invention provides a recording and/or reproducing apparatus for a disc-shaped recording medium for recording and/or reproducing data on or from said disc-shaped recording medium having two sorts of wobbled grooves, each groove sort being of different wobbling frequencies, and lands, said grooves and lands being arranged alternately, said apparatus comprising optical head means for illuminating laser light, converged into spots, on said disc-shaped recording medium and for receiving return light reflected back and diffracted from said disc-shaped recording medium, and address information detection means for detecting the address information from the return light received by said optical head means.
In another aspect, the present invention provides a recording and/or reproducing method for recording and/or reproducing data on or from the disc-shaped recording medium having two sorts of wobbled grooves, each groove sort being of different wobbling frequencies, and lands, said grooves and lands being arranged alternately, said method comprising the steps of illuminating laser light on said disc-shaped recording medium and receiving the return light reflected back and diffracted from said disc-shaped recording medium, and detecting the address information from the received return light.
In another aspect, the present invention provides a recording and/or reproducing apparatus for a disc-shaped recording medium for recording and/or reproducing data on or from the disc-shaped recording medium having two sorts of wobbled grooves, each groove sort being of different wobbling frequencies, and lands, said grooves and lands being arranged alternately, said apparatus comprising optical head means for illuminating laser light, converged into spots, on said disc-shaped recording medium and for receiving return light reflected back and diffracted from said disc-shaped recording medium, amplitude information detection means for detecting an amplitude of a signal derived from the return light received by said optical head means, and tilt detection means for detecting a tilt value based on the signal amplitude detected by said amplitude information detection means.
In another aspect, the present invention provides A tilt detection method for detecting a tilt generated in recording and/or reproducing data on or from a disc-shaped recording medium having two sorts of wobbled grooves, each groove sort being of different wobbling frequencies, and lands, said grooves and lands being arranged alternately, said method comprising the steps of illuminating laser light, converged into spots, on said disc-shaped recording medium and for receiving the return light reflected back and diffracted from said disc-shaped recording medium, detecting an amplitude of a signal based of the received return light, and detecting a tilt value based on the detected signal amplitude.
According to the present invention, address detection becomes possible not only in case the land is used as a recording track but also in case the groove exhibiting more satisfactory recording characteristics. In addition, tilt detection becomes possible not only in case the land is used as a recording track but also in case the groove exhibiting more satisfactory recording characteristics.