Abstract: When external and internal environmental variation factors (characteristics of medium, variation in voltage, deterioration of medium and the like) occur, a reproduced signal is varied. In a learning system for reproduction of a voltage layer selection type multi-layer optical disk which making recording or reproducing by irradiation of energy, a level and/or pattern of an application voltage is adjusted in accordance with a reproduced signal at a predetermined position. Even if the reproduced signal, from the reflectivity down, is varied due to the external and internal environmental variation factors (characteristics of medium, variation in voltage, deterioration of medium and the like), the reproduced signal with the high quality can be obtained from the voltage layer selection type medium.

Abstract: In an optical disk in which a recording layer is selected by applying voltages, a different address pit is formed in each recording layer. To this end, a plurality of recording layers are formed in a way that the plurality of recording layers follow a concavo-convex shape formed in a substrate, and thus the plurality of recording layers keep the concavo-convex shape even after the formation; mutually different address marks are add-on written, as a part of the address information, respectively to recording layer so that the address and track information can be confirmed in each layer.

Abstract: An information recording medium and manufacturing method for high-speed and high density recording. An inorganic film is formed by sputtering while applying a bias voltage to shift the substrate voltage potential in the negative direction, or a laminated film is formed by applying energy after coating a substrate with an organic film, and the irregularities maintained even after the laminated film is formed, so that stable, high-capacity and high-speed recording can be attained by forming a multi-information-layer that still retains the irregularities.

Abstract: An information reproducing method using PRML technology which provides asymmetry compensation and also assures media interchangeability. To compensate for asymmetry, target levels are basically adapted to readout signals and either restriction type (1) (time reversal and level reversal symmetry) or restriction type (2) (time reversal symmetry) is imposed between target levels. As a consequence, asymmetry compensation is made regardless of a readout signal distortion such as mark shift which might deteriorate media interchangeability.