<s>
A	O
polarization	B-Device
controller	I-Device
is	O
an	O
optical	O
device	O
which	O
allows	O
one	O
to	O
modify	O
the	O
polarization	O
state	O
of	O
light	O
.	O
</s>
<s>
Polarization	B-Device
controllers	I-Device
can	O
be	O
operated	O
without	O
feedback	O
,	O
typically	O
by	O
manual	O
adjustment	O
or	O
by	O
electrical	O
signals	O
from	O
a	O
generator	O
,	O
or	O
with	O
automatic	O
feedback	O
.	O
</s>
<s>
A	O
polarization	B-Device
controller	I-Device
can	O
have	O
the	O
task	O
of	O
transforming	O
a	O
fixed	O
,	O
known	O
polarization	O
into	O
an	O
arbitrary	O
one	O
.	O
</s>
<s>
Since	O
polarization	O
states	O
are	O
defined	O
by	O
two	O
degrees	O
of	O
freedom	O
,	O
for	O
example	O
azimuth	O
angle	O
and	O
ellipticity	O
angle	O
of	O
the	O
polarization	O
state	O
,	O
such	O
a	O
polarization	B-Device
controller	I-Device
needs	O
two	O
degrees	O
of	O
freedom	O
.	O
</s>
<s>
Such	O
a	O
polarization	B-Device
controller	I-Device
can	O
for	O
example	O
be	O
obtained	O
by	O
placing	O
on	O
the	O
optical	O
path	O
three	O
rotatable	O
waveplates	O
in	O
cascade	O
:	O
a	O
first	O
quarterwave	O
plate	O
,	O
which	O
is	O
oriented	O
to	O
transform	O
the	O
incident	O
elliptical	O
polarization	O
into	O
linear	O
polarization	O
,	O
a	O
halfwave	O
plate	O
,	O
which	O
transforms	O
this	O
linear	O
polarization	O
into	O
another	O
linear	O
polarization	O
,	O
and	O
a	O
second	O
quarterwave	O
plate	O
,	O
which	O
transforms	O
the	O
other	O
linear	O
polarization	O
into	O
the	O
desired	O
elliptical	O
output	O
polarization	O
.	O
</s>
<s>
Polarization	B-Device
controllers	I-Device
can	O
be	O
implemented	O
with	O
free	O
space	O
optics	O
,	O
through	O
a	O
fiber	O
pigtailed	O
U-bench	O
,	O
for	O
example	O
.	O
</s>
<s>
Polarization	B-Device
controllers	I-Device
can	O
also	O
be	O
implemented	O
in	O
an	O
all-fiber	O
solution	O
.	O
</s>
<s>
For	O
polarization	B-Device
controllers	I-Device
with	O
automatic	O
feedback	O
,	O
integrated	O
optical	O
lithium	O
niobate	O
(	O
LiNbO3	O
)	O
devices	O
are	O
very	O
suitable	O
.	O
</s>
<s>
Polarization	B-Device
controllers	I-Device
with	O
tracking	O
speeds	O
of	O
up	O
to	O
100	O
krad/s	O
on	O
the	O
Poincaré	O
sphere	O
are	O
commercially	O
available	O
(	O
see	O
external	O
link	O
at	O
the	O
bottom	O
)	O
.	O
</s>
