Optical tolerances of an actively tilted high-numerical-aperture two-lens objective for optical recording

Analytical expressions for the primary wave-front aberrations of an actively tilted two-lens objective are derived, and expressions for the higher-order wave-front aberrations for disk tilt of this lens system are presented. This analysis is important because the two-lens objective opens the way to achieving higher-numerical-aperture systems for optical recording with acceptable tolerances that cannot be achieved with a single-lens objective. To test whether the conclusions drawn from the analytically derived results remain valid for high numerical apertures, we compare the results with those obtained by ray tracing: It is shown not only that the two-lens system is tolerant of disk-thickness variations and decentering of the lenses but that it can also be made tolerant of disk tilt when the lens facing the disk is actively tilted.