| 摘要 |
PURPOSE:To reduce the crosstalk between a light beam for reproduction and a light beam for recording and to reduce the cost by separating the light beam for reproduction and light beam for recording without using any special optical system and setting the position of a photodetector according to the beam spot diameter of the light beam for reproduction. CONSTITUTION:The numerical aperture of a light converging means 14 is denot ed as NA, the magnification (m) of an optical system provided between a record ing medium 16 and the detecting means 20 is as (m), and the interval on the recording medium 16 between 1st and 2nd light beams Lr and Lw converged on the recording medium 16 is denoted as d1. Then the photodetecting means 45 is provided in a position where the distance Z between the virtual light convergence point of the 1st light beam Lw converged by separative light con verging means 27 and the position where the photodetecting means 45 is pro vided is less than (m<2> d1)/(2.NA). Therefore, any special optical system for separating and detecting the light beam Lr for reproduction and light beam Lw for recording is not required and the crosstalk between the light beam Lr for reproduction and light beam Lw for recording is reduced. Consequently, a low-cost, high-accuracy multi-beam optical head is obtained. |
