| 摘要 |
PROBLEM TO BE SOLVED: To downsize the device by improving the light utilization efficiency on a CD side of a system having a recording and reproducing optical system for, for example DVDs and CDs, to increase a recording speed, increasing the NA on the CD side to improve recording characteristics and simplifying the optical layout over the entire part. SOLUTION: In recording and reproducing of the CD, the divergent luminous flux from a second hologram unit 29 mounted with a semiconductor laser chip is coupled by a finite system anamorphic lens 3' and an intensity distribution is shaped from an elliptic shape to a circular shape. The luminous flux transmitted through the anamorphic lens 3' is divergent light. Since the beam shape of the semiconductor laser may be shaped from the ellipse to the circle in a divergent light path, the light utilization efficiency is improved and even when the optical disk of a substrate thickness different from the design value of the objective lens 27 is subjected to recording and reproducing, the spherical aberration (of the objective lens 27 is corrected by making the incident luminous flux to the lens to the divergent light and therefore a large numerical aperture(NA) is possible and the disk surface spot of the diffraction threshold may be formed. |
