Optical reproducing method for optical medium with aligned prepit portion

#The present invention relates to an optical recording medium and more particularly to a high-density optical recording medium having a track width smaller than an optical spot diameter.

#An example of a medium for performing high-density (narrow track) recording is disclosed in, for example, JP-A-6-176404. According to this example, in an optical recording medium having grooves and lands which are formed on a substrate and information recording areas which are formed in association with both the groove and the land, prepits are disposed on a virtual extension line of the boundary between a groove and a land. In particular, the prepits are located on only one side of any specific position of the center line of each groove.

#With this construction, recording information is formed on both the groove and the land, the prepits have charge of address data representative of the recording areas and one prepit is used in common to a pair of adjacent groove and land to provide address data therefor. When the technique as above is applied to, for example, a phase change recording medium or a magneto-optical recording medium, interference of information (crosstalk) between adjacent lands or grooves due to the optical interference effect within an optical spot can be prevented, thereby permitting narrowing of track.

#FIG. 1 is an enlarged fragmentary plan view of a first embodiment of an optical recording medium according to the present invention.

#FIG. 2 is a waveform diagram of reproduced signals from the medium of FIG. 1.

#FIG. 3 is a block diagram of an apparatus for recording and reproduction of the optical recording medium used in the present invention.

#Embodiment 1 (Optical Recording Medium)

#Referring now to FIG. 1, there is illustrated, in enlarged fragmentary plan view form, an optical recording medium of the present invention. Grooves 84 each having a width of 0.6 μm and a depth of 50 nm and lands 85 each having a width of 0.6 μm are arranged alternately in the radial direction of the medium and recorded marks 81 are formed on the two kinds of areas. In other words, each of the groove 84 and land 85 serves as a recording area. In a prepit area 83, any groove is not formed but pits 82 are disposed on an extension of the boundary between a land and a groove. Each of the pits has a width of 0.35 μm and a depth of 50 nm. The prepit area is divided into a first prepit area 831 and a second prepit area 832. In the first prepit region 831, pits 82 are disposed on the upper side, as viewed in the drawing, of the center line of the land 85 and in the second prepit area 832, pits 82 are disposed on the lower side, as viewed in the drawing, of the center line of the land 85. Accordingly, when an optical spot 21 scans, for example, the land 85, pits on only either one of the sides are always reproduced and there is no fear that crosstalk will occur between adjacent tracks. Therefore, address data recorded in the form of the prepits can duly be reproduced without crosstalk.

#Since the pits 82 do not adjoin to each other in the radial direction, they can be formed with ease Also, pits 82 are uniformly disposed on both sides of a track (a land or a groove) and hence the influence on a tracking servo signal, which is caused by the pits 82, can be canceled. Accordingly, the tracking offset can be suppressed to a sufficiently small level.