Patent ID: 7990817

Claim:
An optical disk medium comprising: a plurality of information tracks on which data is formed as a mark and a space in an area of the optical disk medium without grooves at both sides of the information tracks; and a thin film material, which is formed in the mark, and which has an optical constant varying between in a high temperature state and in a low temperature state, wherein in the low temperature state, an optical phase of the mark is substantially equal to an optical phase of the space, wherein in the high temperature state, at least the optical phase of the mark is set to be different from the optical phase of the space, and wherein the mark is responsive to irradiation of a condensed optical beam so as to be heated to the high temperature state in which at least the optical phase of the mark is different from the optical phase of the space so as to enable detection of a push-pull signal from the different optical phases of the mark and the space of the information tracks independent of grooves of the optical disk medium.