Multi-layer information recording medium and information recording and reproducing apparatus

摘要

A multi-layer-information-recording medium is applied to an information recording and reproducing apparatus capable of recording or reproducing information on and from either of a single-layer-information-recording medium having a single recording layer on one side, and a multi-layer-information-recording layer having a plurality of recording layers layered on a spacer layer on one side as a change in reflectivity by irradiating a light beam. The multi-layer-information-recording medium is compatible in terms of at least reproducing and recording with a single-layer-information-recording medium having a cover layer having a predetermined refractive index "n" and a thickness "t" disposed on a recording layer on a light incident side surface. The multi-layer-information-recording medium includes a deepest recording layer deepest from the light incident side surface. The deepest recording layer is formed at an optical distance d 1 from the light incident side surface satisfying an equation d 1 =nt. The multi-layer-information-recording medium also includes at least one shallow recording layer formed at an optical distance d 2 satisfying an inequality d 2 <nt from the light incident side surface.