DEPTH DIRECTION INFORMATION RECORDING MEDIUM AND INFORMATION READING OPTICAL DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a depth direction information recording medium having high security preservability and an information reading optical device which reads its recording information from the recording medium. SOLUTION: The depth direction information recording medium has a layer- like structure consisting of thin-film layer-like media 1, 2 and 3 accompanied by an increase or decrease of a light attenuation quantity. The increase or decrease of the light attenuation quantity in a depth direction perpendicular to the surfaces of medium layers by the thin-film layer-like media 1, 2 and 3 is used as the recording information.