OPTICAL INFORMATION CARRIER DISK

摘要

PURPOSE:To avoid defective recording/reproduction owing to abnormal diffraction by forming a chamber of a prescribed size at a corner of an outer peripheral edge part of a face of a transparent substrate covered with a hardened film which contains no information medium layer. CONSTITUTION:An information track 4 and an information medium layer 2 capable of recording/reproduction are formed at one side of a discoid transparent substrare 1. Then a chamfer having an angle alpha of 30 deg. and width (a) of 0.5mm. to the substrate 1 is formed at a corner of the outer peripheral end part of a face having no information medium layer 2. Then a hardened film having the thickness (t) of 15mum is formed on both sides of the substrate 1. In this case, the swell height (h) is set at about 30mum at the outer peripheral end of the substrate. This height is equal to 1/5 conventional value together at the sloping angle theta reduced down to 1/3-1/4 conventional value. It is desirable to set the angle of the chamfer at 20-50 deg. with the width (a) set 20-50 times as much as the thickness of the film 3.