Jorrit Ernst De Vries

Application of nonperiodic phase structures in optical systems.

Wide, nonperiodic stepped phase structures are studied to correct various parameter-dependent wave-front aberrations in optical systems. The wide nature of these phase structures makes them easy to manufacture with sufficient compensation of the wave-front aberrations. Wave-front aberration correction for both continuous and discrete parameter variations are studied. An analytical method is derived for the discrete parameter variations to find the optimal phase structure. Both theoretical and experimental results show that these nonperiodic phase structures can be used to make (1) lenses athermal (defocus and spherical aberration compensated), (2) lenses achromatic, (3) lenses with a large field of view, (4) lenses with a reduced field curvature, and (5) digital versatile disk objective lenses for optical recording that are compatible with compact disk readout.

Nonperiodic phase structures in optical disk systems

For DVD/CD compatibility, a non-periodic phase structure (NPS) has been developed, consistent of a limited number of wide zones. Sufficient correction of the spherical aberration due to the combination of a DVD objective lens and a CD cover layer thickness is achieved. Two options have been worked out for better definition of the numerical aperture for CD. Tests of these options with a separate phase plate in combination with a standard DVD lens showed good performance, with slightly larger tilt margins than for the conventional solution. The NPS has been implemented in a glass/2P objective lens, to obtain a lens compatible for DVD + RW and CD - RW. With this lens, read and write tests of both DVD and CD were successful.