| 摘要 |
PURPOSE:To stabilize a track signal and to enhance a light utilizing efficiency by so setting a beam shaping optical system as to allow a magnification of the system to satisfy a specific formula. CONSTITUTION:A light emitted from a semiconductor laser 1 becomes a parallel luminous flux via a coupling lens 2 and becomes a divergent luminous flux via a concave cylindrical lens 9. It again becomes a parallel luminous flux via a convex cylindrical lens 10, and is condensed by an objective lens 5 to form a spot on an optical disk 6. In this case, a beam shaping optical system 11 is formed out the lenses 9 and 10. A magnification M of the system 11 is so set as to satisfy 0.55 [M.fc.sin (theta/2)]/[f0.NA0]<=0.8, where fc is the focal distance of the coupling lens 2, theta is the angle of divergence in the direction parallet to the semiconductor to the semiconductor laser junction surface, f0 is the focal distance. of the lens 5, and NAg is a numerical aperture of the lens 5. |
