| 摘要 |
PURPOSE:To improve recording density and to prolong a reproduction time greatly by laminating plural recording surfaces and forming each recording surface of a different film which has a large reflection factor to light having specific wavelength and large transmissivity to light having other wavelength. CONSTITUTION:An optical disk 1 has the 1st recording surface 2A, the 2nd recording surface 2B, and the 3rd recording surface 2C, and the respective recording surfaces are superposed upon transparent layers 3 and 4. Further, 5 is a transparent substrate and 6 is a transparent projection layer. The recording surfaces 2A, 2B, and 2C are formed of different films 7A, 7B, and 7C. Namely, the film 7A has characteristics of light wavelength to reflection factor (a)(transmissivity(b)) shown by a graph curve I , the film 7B has characteristics shown by a graph curve II, and the film 7C has characteristics shown by a graph curve III. The 1st-the 3rd laser light sources 10A-10C emit light beams having wavelengths lambda2, lambda4, and lambda6 during reproduction to enter a selective operation state, and the recording surfaces 2A, 2B, and 2C on one side of the disk 1 are reproduced successively to increase the reproduction time by three times as long as before. |
