| 摘要 |
PURPOSE: To accurately record a large amount of information without generating any quantum error by setting the length of a diffraction grating array being a recording unit to be less than the diameter of spot beam and composing the diffraction grating array of diffraction grating bells which continuously vary in grating stripe interval. CONSTITUTION: When a part of a recording track 1 is expanded, three kind of diffraction grating arrays (a)-(c) are present in the scanning direction (x) of the spot beam. The respective grating arrays (a)-(c) have length less than the diameter 3 of the read spot beam and one of them (diffraction grating array (a)) is regarded as one recording unit 2. The direction where the diffraction gratings are arrayed and the direction meaning the length less than the beam diameter, are (x) direction. In the recording unit 2, plural kinds of diffraction grating cells which change in grating stripe interval, cell by cell, are arranged. For example, four kind of diffraction grating cells are arrayed in the recording unit 2 and the array direction of grating stripes formed on the respective cells is fixedly the (x) direction. |
