OBJECTIVE LENS, OPTICAL HEAD AND OPTICAL DISC DEVICE

摘要

An objective lens, an optical head, and an optical disc device (drive) capable of attaining good recording or reproduction characteristics by compensating various aberrations including variation in wavelength for various kinds of optical discs such as a high density optical disc, a DVD, a CD, and the like, under good wavelength dispersion compensation performance. The objective lens includes a first lens and a second lens substantially adhered to have the optical axes mutually matched, and functions as a convex lens, as a whole. Each lens has a central portion including the optical axis, and a peripheral portion around the central portion. The central portion of the first lens functions as a convex lens and the central portion of the second lens functions as a concave lens. Assuming the refractive index of the first lens in d line (wavelength 587.56nm) is nd1, an Abbe number represented using the refractive index of the d line, F line (wavelength 486.13nm) and C line (wavelength 656.27nm) is ?d1, the refractive index of the second lens in d line is nd2, and an Abbe number represented using the refractive index of the d line, F line and C line is ?d2, following relation is satisfied; nd1>nd2 and ?d1>?d2.