Patent ID: 7082088

Claim:
A disc-shaped optical recording medium for recording information thereon by being irradiated with a laser beam to form recording marks on a recording layer while being rotated about the center of the disc, the optical recording medium being capable of reading the recorded information by irradiating the recording mark with a reading laser beam, wherein a plurality of virtual recording cells are set on the recording layer continuously in a concentric fashion or in a spiral fashion about the center of the disc, the virtual recording cell being defined by a unit length in a rotational direction of the disc and a unit width perpendicular thereto; the unit length of at least part of the virtual recording cell is set so as to have an arc length of the same center angle with respect to the center of the disc irrespective of positions in a radial direction of the disc; the recording layer of the virtual recording cell allows for forming thereon recording marks of different sizes in response to the laser beam with at least one of irradiation time and irradiation power of the laser beam being modulated in five stages or more; and thereby information can be recorded in multi-levels in five stages or more by modulating an optical reflectivity in accordance with at least an area ratio of the recording mark to the virtual recording cell between the area ratio and optical transmittance.