3
3
Scanning
the
P
oincare
Sphere
This
chapter
describes
how
you
can
use
your
polarization
controller
to
measure
polarization
dependence
,
and
how
you
can
generate
quasi-depolarized
signals
.
Setting
up
the
Hardware
Note
When
you
are
setting
up
your
hardware
,
it
is
absolutely
vital
that
the
bers
are
xed,
and
remain
unmoved
for
the
whole
of
the
measurement.
Moving
the
bers
changes
the
state
of
polarization.
Typically
,
you
will
connect
the
polarization
controller
directly
after
your
source
,
and
before
your
device
under
test
(DUT).
Before
connecting
to
the
rest
of
your
measurement
setup
,
you
should
set
the
position
of
the
polarizing
lter
(this
is
described
in
\Setting
the
P
osition
of
the
P
olarizing
Filter"
in
Chapter
2).
Setting
Up
and
Executing
a
Scan
The
sphere
application
changes
the
state
of
polarization
over
time
,
by
rotating
the
/2
and
/4
plates
.
The
rotations
can
be
done
slowly
,
to
give
a
quasi-randomly
polarized
signal,
which
you
can
use
,
with
suitable
data
logging
to
measure
polarization
dependence
.
The
rotations
can
be
done
quickly
,
to
give
a
quasi-depolarized
signal,
which
you
can
use
,
with
suitable
measurement
averaging
time
to
measure
depolarized
response
.
1.
Press
4
Sphere
5
to
select
the
application.
Scanning
the
P
oincare
Sphere
3-1