Patent ID: 6965556

Claim:
An optical information medium comprising an information bearing surface having projections and depressions and/or is capable of forming recorded marks, and a functional layer, wherein the information borne on said information bearing surface is readable by using reading light of a wavelength longer than 4NA·P L wherein P L is the minimum size of said projections and depressions or said recorded marks and NA is the numerical aperture of a reading optical system, setting the power of the reading light within such a range that the intensity of reflected light from said functional layer changes in linear proportion to a change in the readout power, and irradiating the reading light to said information bearing surface constructed by the functional layer or to said information bearing surface through the functional layer or to the functional layer through said information bearing surface; and wherein said functional layer has a thickness between 5 nm and 100 nm and is made of at least one element of Nb, Mo, W, Mn, Pt, C, Si and Ge; and wherein an information on readout power is previously recorded to said information bearing surface.