Browse Prior Art Database

Increased Circulation Ratio in an Optical-Storage Head

IP.com Disclosure Number: IPCOM000111754D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Dewey, AG: AUTHOR

Abstract

Semiconductor lasers used in optical-storage heads have a divergent output beam that is elliptical in cross section. The ratio M between the two divergence angles (parallel and perpendicular to the laser junction) is typically between 2 and 3. In future lasers it is possible that this ratio M will be as high as 6 or more if other parameters of the laser are optimized. This disclosure shows how to incorporate such a laser in an existing head design by simply changing a prism assembly.

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Increased Circulation Ratio in an Optical-Storage Head

      Semiconductor lasers used in optical-storage heads have a
divergent output beam that is elliptical in cross section.  The ratio
M between the two divergence angles (parallel and perpendicular to
the laser junction) is typically between 2 and 3.  In future lasers
it is possible that this ratio M will be as high as 6 or more if
other parameters of the laser are optimized.  This disclosure shows
how to incorporate such a laser in an existing head design by simply
changing a prism assembly.

      Fig. 1 shows a prism assembly used in an optical-storage head.
It has two functions: one is to bend the incoming elliptical laser
beam 1º  through 90º, and the second is to expand the
beam in the plane of the Figure by a factor of M, thus creating a
circular output beam 2.  The magnification M is determined by the
angle of incidence of 75º, M = 3.  Higher magnification would
require a larger angle of incidence which is not practical.

      Fig. 2 shows a new prism assembly which could be a direct
replacement for the old assembly, and provide a magnification M as
high as 7.4 by appropriate choice of the prism angles.  In Fig. 2,
the incidence angle on both surfaces 4 and 6 is 75º  and the
magnification at surface 5 is 1.2x, giving an overall magnification
of 3 x 3/1.2 = 7.4.