| 摘要 |
PURPOSE:To decrease crosstalk from an adjacent track or to obtain excellent S/N in the time aixs direction by arranging a diffractive means so that its diffracting directoin is in parallel or vertical to a track formed on a disc. CONSTITUTION:When a prescribes signal is recorded by frequency modulation, the diffracting direction by a diffracting grating 11 is made nearly in parallel with the direction of a track 12 in a disc 4. Thus, the spread of the beam of the semiconductor laser of the multi-mode is in the direction in parallel with the track 12 so as to prevent the crosstalk from the adjacent track from being increased. When a prescribed signal is subject to a digital modulation such as EFM modulation in the disc 4, the diffracting direction by the diffracting grating 11 is made nearly vertical in the direction of the track 12. Thus, the beam of the semiconductor laser of the multi-mode is spread in a direction vertical of the track 12 and not spread in the direction of the time axis of the same track, then the deterioration of the S/N in the time axis direction is prevented. |
