| 摘要 |
PURPOSE:To reduce unerased part on a phase change type optical disk by setting laser wavelength in erasure larger than that in recording and reproduction. CONSTITUTION:The spot diameter of a laser beam in the erasure can be set larger than the diameter of a recording pit by setting the laser wavelength in the erasure larger. This is due to the fact that the spot diameter of the laser beam converged on an optical recording medium layer is proportional to a value in which the number of apertures of a lens is divided by the laser wavelength, and it is possible to increase the spot diameter of the laser beam on the optical recording medium layer by increasing the laser wavelength in the erasure under the constant number of apertures. In other words, the erasure is performed with the spot diameter larger than the recording pit. In such a way, when the reproduction is performed with the spot diameter with the same size as that of the recording pit, the unerased part can be scarsely generated in a reproducing spot diameter area. |
