An optical information recording medium (hereafter, abbreviated as an optical disc), which is rewritable and removable, has been widely used as a file storage for a personal computer. In order to cope with such demand, various techniques to increase a recording capacity have been developed. As a method of increasing the recording capacity, there is a method of increasing a recording density in a radial direction and a circumferential direction.
As the method of increasing the recording density in the radial direction, there is a land groove recording format in which both of a land (a flat portion) and a groove (a trench portion) are used as a recording track. This method is the method of increasing the recording density by using both of the land and the groove as the recording track, although only one of the land and the groove has been conventionally used as the recording track.
In this land groove recording method, CNR (Carrier to Noise Ratio), a jitter or a crosstalk, which indicates a single signal quality of each of the land and the groove, becomes problematic. Moreover, an influence of a crosstalk between signals recorded on tracks adjacent to each other, namely, from the groove adjacent to the land, or a crosstalk from a signal recorded on the land adjacent to the groove is induced.
Also typically, in the land groove recording, there is a difference of a crosstalk property between a land track that is concave in the sight of an incident surface of a reproducing laser and a groove track that is convex. In addition, there is a difference between a signal amount leaking to the groove from the land and a signal amount leaking to the land from the groove, thus complex designs have been carried out upon taking into account such problems.
Also, as the land and the groove are close to each other as the recording tracks, the phenomena of the CNR and the jitter become further complex.
On the other hand, as the method of increasing the recording density in the circumferential direction, there is a Magnetically Induced Super Resolution (MSR). This is the technique of reading out a recording mark, which is recorded finer than a diffractive limit of a reproduction light, through a magnetically formed opening on an upper layer (a so-called reproduction layer). This technique enables the marks adjacent to each other at the diffractive limit or less to be separated and read out.
However, if this land groove recording and the MSR are combined, the crosstalk and the jitter in both tracks of the land and the groove and the magnetic property of the MSR provide the relation of trade-off. Since there is neither a design technique that simultaneously satisfies all of them, nor an optimal design technique, this problem is difficult to be solved. Partially, for example, the crosstalk is considered to be related to an inclination angle between the land and the groove, and the jitter and the magnetic property of the MSR are considered to be caused by arithmetic average roughness on a land surface and a groove surface, and a shape of the pattern. However, the optimal combination of them or a controllable parameter has not been achieved yet.
Also, since the above-mentioned optimal combination has not been obtained, an original disc of an optical information recording medium to manufacture the optical information recording medium and a method of manufacturing the same are not obtained.
The present invention is proposed in view of the above-mentioned circumstances and, therefore, an object of the present invention is to provide an optical information recording medium which includes both a land and a groove as a recording track and has a high signal quality.