Abstract: An optical recording medium in which a medium identification code is recorded as a nonvolatile mark which is formed through irreversible change of a recording film, such as magnetization characteristic change, deformation and formation of a hole, so as to prevent illegal copying of the optical recording medium, and a recording/reproducing method for the same.

Abstract: An optical recording medium in which a medium identification code is recorded by using a nonvolatile mark which is formed through irreversible change of a recording film, such as magnetization characteristic change, deformation and formation of a hole, so as to prevent illegal copy of the optical recording medium, and a recording/reproducing method for the same.

Abstract: An erasable optical disc medium on which information is recorded and read by using a laser beam, which comprises (i) a phase transition type information recording layer, (ii) an optical interference layer and (iii) an optical reflection layer, formed in this order on a transparent substrate, in such a state that a reflectance of the medium is higher before information is recorded and a reflectance of the recorded portions of the medium is lower after recording.

Abstract: A compatible optical disk in which information can be reproduced by a player normally used exclusively for reproduction, and writing, rewriting and erasure can be performed, comprises a recording film material characterized in that the reflectivity of a flat portion of the disk is lower than 50% in an erased or unrecorded state and the reflectivity of a recorded area is increased by recording by an irradiation of light, a light beam-guiding groove (12) formed on the surface of the disk substrate so that information is recorded or read out along the trough portion (12) or crest portion (17) of the guiding groove, and the reflectivity is enhanced in the crest portion (17) between the troughs or in the trough portion (12) between the crests.

Abstract: An optical recording medium using a recording layer of an alloy taking two different crystalline states exhibiting different reflectivities is preferably manufactured by depositing a plurality of layers, each of which consists essentially of an element or an intermetallic compound, i.e. a material having a lower crystallizable temperature, to form a recording layer having a desired average chemical composition, while heating a substrate on which the recording layer is being deposited.