| 摘要 |
<P>PROBLEM TO BE SOLVED: To unnecessitate changing an interval of a beam expander in recording and reproducing of a plurality of optical disks of which the wavelength of a light beam being adaptable is different. <P>SOLUTION: A first light beam is made incident on an objective lens unit 13 as parallel light, a second beam is made incident on it as parallel light or divergent light, also in the objective lens 13, in a range of wavelength near wavelength λ1a of the first light beam, if wavelength being longer than λ1a is assumed to λ1b, a converged point position of λ1b is approached to the objective lens 13 for a converged point position at which the light beam of λ1a is made incident on the objective lens, when refraction power for the first light beam of a spherical aberration compensation lens group of a spherical aberration compensation means 6 is assumed to P1, refraction power for the second light beam is assumed to P2, and refraction power by which the light beam is bent to the optical axis direction is assumed to positive, P1=0, P2<0, under such a condition, the first light beam is made incident as parallel light, and the second light beam is made incident as diverging light. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
