Abstract

In optical recording there is a strong drive towards higher densities and higher data rates [1]. In these optical recording systems the read out spot is diffraction-limited. The spot diameter is approximately λ/NA with λ the wavelength in vacuum and NA (=n₅ sin θ (see figure 1)) the numerical aperture of the objective lens. To increase the data density the spot size must be decreased. This can be achieved by using a laser with a smaller wavelength or by increasing the NA of the objective lens. In either case this reduction in spot size leads to tighter tolerances for the optical system. A way to relax the tolerances of the optical system is by using a two-element lens system in which both lenses are actuated independently [2]. It has been shown that such a system is able to compensate for the spherical aberration arising due to disk thickness variations [2]. A problem is however the small tolerance for disk tilt. Here we present a way to compensate for disk tilt in a two-element objective lens system.

© 1998 Optical Society of America