Lens, optical head, optical information writing/reading apparatus and optical information recording medium writing/reading method

摘要

Conventional lenses for DVD/CD compatible writing/reading are liable to CD jitter deterioration due to phase shifts in a central area. Setting a corresponding base material thickness of an intermediate area to greater than 1.2 mm which is the base material thickness of the CD makes it possible to reduce jitter deterioration due to phase shifts and eliminate level differences between the central area and peripheral area, facilitate manufacturing of processing metal molds, allow extension of a life, which in turn makes it possible to use glass as a lens material, realize cost reduction or provide a system with higher precision and higher reliability. IMAGE