PURPOSE: To form bump-like information bits in a recording layer in such a manner that the longitudinal dimension of the information bit differs along the direction of information tracks by forming a specified double layer of a synthetic resin for the recording layer.
CONSTITUTION: The substrate 1 has a recording double layer 4 of a synthetic resin on one surface. The first synthetic resin layer 2 of the recording double layer 4 adjacent to the substrate 4 has a rather high coefft. of expansion and lower glass transition temp. than room temp., and the second synthetic resin layer 3 bonded to the first layer 2 has a rather low coefft. of expansion and higher glass transition temp. than room temp. The both synthetic resin layers 2, 3 contain a dye which absorbs laser beam 5 used, and when the layers are irradiated with the beam 5, bump-like information bits are formed in the recording layer 4 in such a manner that the longitudinal dimension of the information bit differs along the direction of information tracks and that the width of the bits perpendicular to the information tracks is same or almost same. thereby producing bumps having almost same width and different longitudinal dimension which is accurately formed without causing local changes in the size of bumps.
YOSEFUASU MARINUSU UIEIN
JIYOOJI HAWAADO JIYONSON
HAWAADO ENSAIN SHIMONZU
PHILIPS & DU PONT OPTICAL