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Low Profile and High Numerical Aperture Optical System for Storage Head

IP.com Disclosure Number: IPCOM000107587D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Lean, EG: AUTHOR

Abstract

Disclosed is a high-capacity optical storage system. In order to obtain a smaller spot and, hence, higher areal density, the numerical aperture (NA) of the final focusing lens must be increased. It is also desirable to minimize the profile height of the head so that more optical disks can be squeezed in a given form factor. The conventional optical head design consists of a 45-degree mirror to direct the collimated incident beam with a diameter of D to the final focusing lens with a NA of 0.6, for example. The total height of the head profile must include the incident beam diameter, the focal length and the physical thickness of the focusing lens. The minimal height of the head profile will be much more than twice that of the beam diameter, 2 D.

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Low Profile and High Numerical Aperture Optical System for Storage Head

       Disclosed is a high-capacity optical storage system.  In
order to obtain a smaller spot and, hence, higher areal density, the
numerical aperture (NA) of the final focusing lens must be increased.
It is also desirable to minimize the profile height of the head so
that more optical disks can be squeezed in a given form factor.  The
conventional optical head design consists of a 45-degree mirror to
direct the collimated incident beam with a diameter of D to the final
focusing lens with a NA of 0.6, for example.  The total height of the
head profile must include the incident beam diameter, the focal
length and the physical thickness of the focusing lens.  The minimal
height of the head profile will be much more than twice that of the
beam diameter, 2 D.

      A high NA (>0.7) and low profile (1.2 D) optical head based on
parabolic mirror design may be utilized.  As shown in  Fig. 1, the
collimated incident beam (with a diameter D) is focused into a
diffraction limited spot by a parabolic mirror.  The equation for the
parabolic curve in the xy plane is given by y(2) = 4p(x+p), where p
is the distance from the vertex to the focus in the parabolic
equation.  It can be shown that for a NA = 0.7 system with a design
of p =D/4, the height of the head profile will be 1.207 D.  The
working distance from the incident beam is 0.207 D.

      The height of the head can be further reduced...