Dismiss
InnovationQ will be updated on Sunday, Jan. 21, from 9am - 11am ET. You may experience brief service interruptions during that time.
Browse Prior Art Database

Three-Beam Holographic Beamsplitter for Magneto-Optic Storage

IP.com Disclosure Number: IPCOM000122930D
Original Publication Date: 1998-Jan-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 83K

Publishing Venue

IBM

Related People

Dewey, T: AUTHOR [+3]

Abstract

A Wollaston prism is a polarization element that produces from an incident light beam two plane-polarized output beams angularly separated and with their polarization states orthogonal. A recent development, which may be used to construct a simple and compact optical data storage head, is a 3-beam Wollaston. This element produces, in addition to the two beams described above, a third beam that is undeflected, and whose polarization state is mid-way between the two orthogonally polarized (and angularly deflected beams). Moreover, it is possible to design the element such that any given percentage of the input beam power is undeflected, the remainder being divided between the two deflected beams.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Three-Beam Holographic Beamsplitter for Magneto-Optic Storage

      A Wollaston prism is a polarization element that produces from
an incident light beam two plane-polarized output beams angularly
separated and with their polarization states orthogonal.  A recent
development, which may be used to construct a simple and compact
optical data storage head, is a 3-beam Wollaston.  This element
produces, in addition to the two beams described above, a third beam
that is undeflected, and whose polarization state is mid-way between
the two orthogonally polarized (and angularly deflected beams).
Moreover, it is  possible to design the element such that any given
percentage of the input beam power is undeflected, the remainder
being divided between the two deflected beams.

      In a Magneto-Optic (M-O) data storage head, the beam reflected
from the disk is used for two purposes:  one is to provide input to
servo detectors that are used to control focusing and tracking; and
the second  is to read the M-O data.  The beam is essentially plane
polarized with  the data represented by small rotations of this
polarization state. If  the neutral state is called p-polarized, then
the data may be considered  as a small, orthogonal s-polarized state.
If the p-state is aligned at  45º to the axes of a 3-beam Wollaston,
a fraction (typically 20%) of the  beam will be transmitted
undeflected to a servo detector array, while the two deflected beams
(each with 40% of the light) will be directed to a pair of data
detectors.  The polarization splitting thus achieved  is exactly what
is needed for differential M-O detection of the data.  This technique
allows all three photodetectors to be on a common  semiconductor
substrate, with a common focusing lens, thus, providing a  means for
achieving a simple and inexpensive head.  The only detraction  over a
more complex optical arrangement in which all of the "s-polarized"
light is split between th...