| 摘要 |
PURPOSE:To eliminate the crosstalk in a read mode and to improve the recording density by dividing a recording track into two parts to record bit trains of different depths to each divided track and reading these bit trains by the beams of different wavelengths. CONSTITUTION:The laser beams given from light sources 21 and 22 have different wavelengths lambda1 and lambda2 (lambda2=lambda1) and are put into a beam splitter 24 with a minute angle difference between their optical axes. Then both beams irradiate a medium 28 with a slight shift secured between positions of irradiation of both beams in the radius direction of the medium 28. In other words, the beams lambda1 and lambda2 irradiate bits 31 and 32 respectively. The depths d1 and d2 of these bits are proportional to the values of beams lambda1 and lambda2 respectively. At the same time the diameters of spots 33 and 34 are also proportional to beams lambda1 and lambda2 respectively. The beam lambda1 reads the bit 31 and a part of this beam also irradiates the bit 32. However the reflected light given from the bottom part of the bit 32 has a difference of phase by 2 radians owing to the relation between (d) and lambda and has no difference of optical intensity to receive no modulation of the bit 32. So is with the effect obtained by the bit 31 of the beam lambda2. |
