| 摘要 |
PURPOSE:To reduce the instability of the recording, reproducing and erasing operations of a semiconductor laser due to a wavelength shift by attaching a plano-convex lens at the light-emitting surface of excessive light of a first polarizing beam splitter and providing a quadripartite photodetector in front of it. CONSTITUTION:The luminous flux from the semiconductor laser 1 is made to be parallel light 2 and when it is made incident on a beam splitter 3, the emitting power of the laser 1 is increased at the time of recording and erasing compared with that at the reproducing time, then the oscillation wavelength of the laser 1 is shifted to a longer wavelength side. Hence the luminous flux being incident on a beam forming prism is deviated positionally in the radius direction of a diskoid recording medium 7 by the shift. The first polarizing beam splitter 4 transmits 40% of a P polarization and reflects 60% of it, so the 60% excessive light is condensed with the plano-convex lens 16 and caught with the quadripartite photodetector 17 detected with the differential output (G+1)-(H+K) on the light receiving surfaces G, H, I, K of the element 17, is fed back to a track control system and corrects the shift in the radius direction. |
