| 摘要 |
PURPOSE:To drastically improve the security of information against leakage by providing a layer of a material whose characteristic is such that it is opaque for visible light but is transparent for a beam of light used in reading on the information recording part of the titled medium. CONSTITUTION:A recording member 2 is formed on a substrate 1, and a bit of optical information 3 is recorded on the member 2. In the part of the member 2 where the information 3 is recorded, a layer of a member which is opaque in the visible region but transparent for a beam of light used in reading, such as 'Kodak Wratten Filter(R)' manufactured by Kodak Corporation in the United States is provided. As a result, reading of the information with naked eyes or with a magnifying glass is made impossible, hence the security against the leaking of the information can be drastically improved. |
