Browse Prior Art Database

Selective Aperture Illumination for Increased Depth of Focus

IP.com Disclosure Number: IPCOM000115659D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Bargerhuff, R: AUTHOR [+4]

Abstract

Large Numerical Aperture (NA) lenses are required in optical storage systems to provide very small optical spots for reading and writing high density data on optical storage disks. Such lenses have very shallow depths of focus. The depth of focus of a high NA lens can be increased and the Full Width at Half Maximum spot width decreased by illumination of the lens with an annular beam formed using an axicon lens pair. The axicon lens pair can also be made as one element which we refer to as a "halo beam expander". By redistributing the energy in this way a significant advantage is achieved over obscuration techniques in that no light is lost due to obscuration.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 85% of the total text.

Selective Aperture Illumination for Increased Depth of Focus

      Large Numerical Aperture (NA) lenses are required in optical
storage systems to provide very small optical spots for reading and
writing high density data on optical storage disks.  Such lenses have
very shallow depths of focus.  The depth of focus of a high NA lens
can be increased and the Full Width at Half Maximum spot width
decreased by illumination of the lens with an annular beam formed
using an axicon lens pair.  The axicon lens pair can also be made as
one element which we refer to as a "halo beam expander".  By
redistributing the energy in this way a significant advantage is
achieved over obscuration techniques in that no light is lost due to
obscuration.

      When a collimated, Gaussian beam is incident on the halo beam
expander as shown in the Figure with the beam centered along the axis
of symmetry of the expander, the beam leaving the exit surface of the
expander will be an annular beam with the peak intensity at the inner
annular radius and the minimum intensity at the outer annular radius.
The radii of the annular regions is established by the radius of the
incident beam and the design of the halo expander.

      The halo beam expander can be a single glass or plastic optical
element.  The simple geometrical structure lends itself to molding
techniques and the lens could be made as a single cavity mold.  If
necessary for ease of manufacturing it could also be two separate
...