| 摘要 |
PROBLEM TO BE SOLVED: To provide the optical system of the optical disk drive which is adaptive to multiple kinds of optical disk differing in protection layer thickness without moving an objective. SOLUTION: The optical system is composed of a light source part 10, a collimator lens 20, an objective 30, and a signal detection system 40. The 1st laser light (wavelength λ1) emitted by a 1st semiconductor laser 11 is made incident as parallel light on the objective 30 and converted on the recording surface of a high-recording-density disk D1. The 2nd laser light (wavelength λ2>λ1) emitted by a 2nd semiconductor laser 12 is made incident as divergent light on the objective 30 and converged on the recording surface of a low- recording-density disk D2. On a 1st surface 30a of the objective 30, a diffraction lens structure is formed which has fine ring-shaped steps at the center part. The diffraction lens structure has spherical surface aberration characteristics varying so that the spherical aberration comes to excess as the wavelength of the incident light varies to the long-wavelength side. |
