Patent ID: 8305859

Claim:
An information recording medium including an information recording layer on which information is recordable, wherein: on the information recording layer, a recording mark restricted to have a length of xT to yT is formed in accordance with a prescribed modulation rule (T is a reference cycle of the modulation, and x and y are natural numbers fulfilling x<y); and the information recording medium is evaluated using an evaluation index which is found based on a ratio of a center of an amplitude of a reproduction signal corresponding to an (x+1)T mark and an (x+1)T space, with respect to a center of an amplitude of a reproduction signal corresponding to a yT mark and a yT space; where the information recording layer has a first recording density, the information recording medium is evaluated using a first evaluation index which is found based on a ratio of a center of an amplitude of a reproduction signal corresponding to an xT mark and an xT space, with respect to the center of the amplitude of the reproduction signal corresponding to the yT mark and the yT space; where the information recording layer has a second recording density which is higher than the first recording density, the information recording medium is evaluated using a second evaluation index which is found based on a ratio of the center of the amplitude of the reproduction signal corresponding to the (x+1)T mark and the (x+1)T space, with respect to the center of the amplitude of the reproduction signal corresponding to the yT mark and the yT space; where the information recording layer has the first recording density, information is recorded using a plurality of types of marks having different lengths, and a spatial frequency, which is a frequency of a reproduction signal obtained when at least one of the plurality of types of marks is reproduced, is lower than an optical transfer function (OTF) cutoff frequency; and where the information recording layer has the second recording density, information is recorded using a plurality of types of marks having different lengths, and a spatial frequency, which is a frequency of a reproduction signal obtained when at least one of the plurality of types of marks is reproduced, is around, or exceeds, the OTF cutoff frequency.