<s>
A	O
tapered	B-Device
double-clad	I-Device
fiber	I-Device
(	O
T-DCF	O
)	O
is	O
a	O
double-clad	B-Device
optical	I-Device
fiber	I-Device
which	O
is	O
formed	O
using	O
a	O
specialised	O
fiber	O
drawing	O
process	O
,	O
in	O
which	O
temperature	O
and	O
pulling	O
forces	O
are	O
controlled	O
to	O
form	O
a	O
taper	O
along	O
the	O
length	O
of	O
the	O
fiber	O
.	O
</s>
<s>
This	O
tapering	O
of	O
the	O
fiber	O
enables	O
the	O
combination	O
of	O
the	O
characteristics	O
of	O
conventional	O
8	O
–	O
10µm	O
diameter	O
double-clad	B-Device
single-mode	B-Device
fibers	I-Device
to	O
propagate	O
light	O
in	O
fundamental	O
mode	O
with	O
those	O
of	O
larger	O
diameter	O
(	O
50	O
–	O
100µm	O
)	O
double-clad	B-Device
multi-mode	B-Device
fibers	I-Device
used	O
for	O
optical	O
amplification	O
and	O
lasing	O
.	O
</s>
<s>
The	O
technology	O
was	O
granted	O
a	O
patent	O
in	O
2013	O
as	O
a	O
means	O
to	O
overcome	O
the	O
nonlinear	O
optical	O
effects	O
which	O
previously	O
limited	O
the	O
power-scaling	O
of	O
fiber	B-Device
lasers	I-Device
and	O
fiber	O
amplifiers	O
.	O
</s>
<s>
The	O
result	O
of	O
forming	O
a	O
tapered	O
geometry	O
double-clad	B-Device
fiber	I-Device
is	O
that	O
the	O
light	O
introduced	O
into	O
the	O
thin	O
end	O
propagates	O
in	O
a	O
wide	O
core	O
without	O
changing	O
the	O
mode	O
content	O
.	O
</s>
<s>
Consequently	O
,	O
the	O
use	O
of	O
T-DCF	O
for	O
optical	O
amplification	O
in	O
a	O
multi-mode	B-Device
fiber	I-Device
maintains	O
good	O
beam	O
quality	O
by	O
elevating	O
the	O
thresholds	O
of	O
stimulation	O
of	O
non-linear	O
effects	O
including	O
Brillouin	O
and	O
Raman	B-Architecture
scattering	I-Architecture
and	O
spontaneous	O
emission	O
.	O
</s>
<s>
The	O
double-clad	B-Device
structure	O
of	O
the	O
fiber	O
means	O
the	O
core	O
can	O
be	O
pumped	O
with	O
higher-power	O
than	O
could	O
be	O
propagated	O
in	O
the	O
fiber	O
.	O
</s>
