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.
Jorrit de Vries,
Benno H. W. Hendriks,
"Nonperiodic phase structures in optical disk systems", Proc. SPIE 4342, Optical Data Storage 2001, (10 January 2002); doi: 10.1117/12.453395; https://doi.org/10.1117/12.453395