High focal depth with a pure-phase apodizer

High-density optical data storage requires high-numerical-aperture (NA) len ses and short wavelengths, But, with increasing NA and decreasing wavelengt h, the depth of focus (DOF) decreases rapidly. We propose to use pure-phase superresolution apodizers to optimize the axial intensity distribution and extend the DOF of an optical pickup. With this kind of apodizer, the expec ted DOF can be 2-4.88 times greater than that of the original system, and t he spot size will be smaller than that of the original system. (C) 2001 Opt ical Society of America.