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Efficient M/O Read/Write Head Using Faraday Rotators

IP.com Disclosure Number: IPCOM000101033D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 105K

Publishing Venue

IBM

Related People

Sincerbox, GT: AUTHOR

Abstract

A magneto-optic storage read/write head is described using Faraday rotators to provide higher efficiency in the utilization of laser power for writing, larger signals during readback, and laser isolation for the reduction of laser feedback noise.

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Efficient M/O Read/Write Head Using Faraday Rotators

       A magneto-optic storage read/write head is described
using Faraday rotators to provide higher efficiency in the
utilization of laser power for writing, larger signals during
readback, and laser isolation for the reduction of laser feedback
noise.

      A schematic of the head is shown in the figure along with
vector diagrams denoting the direction of polarization after
transmission through each element.  In this system, p-polarized light
from the laser is incident on polarization beamsplitter 1 (PBS1) and
is fully transmitted. This light is incident on a conventional
waveplate (WP1) cut to provide 45o of rotation of the plane of
polarization (counterclockwise in the figure).  The light exiting the
waveplate is incident on Faraday rotator 1 (FR1) designed to rotate
the polarization clockwise 45o .  This light is now back in the
p-direction and passes  completely through PBS2. After exiting PBS2,
the light encounters a second Faraday rotator (FR2) designed to
impart  22.5o of rotation.  This light is now incident on the medium
and after interacting

                            (Image Omitted)

 with the domain returns at an angle of 22.5o#rK,
where rK is the Kerr rotation. Upon passing through FR2 in the
reverse direction, an additional 22.5o rotation (in the same
direction) is imparted so that the light incident on PBS2 is at
45o#rK .  The s-component of this light is reflected by PBS2 to
photodetector PD2, and the p-component of the light passes through
PBS2.  The light passing backward through PBS2 encounters  FR1 and is
rotated clockwise  by 45o .  Note that this light is now orthogonal
to the original light passing in the other direction through FR1.
Waveplate WP1 rotates this light clockwise so that it enters PBS1 as
s-polarized light.  This light is totally reflected to photodetector
PD1, and very little (-32 dB) is directed back into the laser.
Differ- ential data detection is performed by subtracting the signals
from detectors PD1 and PD2.

      In comparison to 'conventional' magneto-optic read/write heads
using leaky beamsplitters of 70% transmission to provide the bias for
subsequent data detection, this head design nominally transmits all
of the laser power to the media (subject to the same surface and
aperture losses in both cases), i.e., 30% is not lost at a leaky
beamsplitter - an effective increase of 42% in available recording
power.  In addition, all of the return light is divided between the
two detectors to provide differential detection  and signal bias and
none returns to the laser to introduce noise.

      Going through the algebra, and neglecting surface reflections
and aperture losses as these are common to both systems, it is
straightforward to show that the light amplitude incident on each
detector for the Faraday ro...