Abstract: An optical information recording medium (1) includes on a substrate (50), a ROM layer (20), a RE layer (40), an intermediate layer (30) separating the ROM layer (20) and the RE layer (40), and a light transmitting layer (10) provided farthest from the substrate (50). The RE layer (40) is an information recording layer provided most farthest from the light transmitting layer (10), and is a recording layer of BCA recorded in a format easily determinable as compared to an information recording format used in the ROM layer (20), and antifouling property of a surface of the light transmitting layer (10) is set based on the RE layer (40). This makes it easy for the recording and reproducing apparatus to confirm a disc type, allows for sharing one recording and reproducing apparatus with other types of optical discs, and simplifies the disc production.

Abstract: In a focus optical system for optical discs or optical disc master exposure apparatuses, a relative positional relation between a cylindrical lens and a 4-division detector in an astigmatic optical system is adjust so that an interference fringe appearing in reflected light derived from an optical disc master is made to be incident on a dead zone of the 4-division detector. Thus, an astigmatic focus servo free from effects of variations in a focus error signal due to the interference fringe is realized. As a result of this, effects of the interference fringe appearing in the reflected light derived from an optical disc or optical disc master can be suppressed.

Abstract: In a focus optical system for optical discs or optical disc master exposure apparatuses, a relative positional relation between a cylindrical lens and a 4-division detector in an astigmatic optical system is adjust so that an interference fringe appearing in reflected light derived from an optical disc master is made to be incident on a dead zone of the 4-division detector. Thus, an astigmatic focus servo free from effects of variations in a focus error signal due to the interference fringe is realized. As a result of this, effects of the interference fringe appearing in the reflected light derived from an optical disc or optical disc master can be suppressed.