<s>
A	O
fiber	B-Device
laser	I-Device
(	O
or	O
fibre	B-Device
laser	I-Device
in	O
Commonwealth	O
English	O
)	O
is	O
a	O
laser	O
in	O
which	O
the	O
active	O
gain	O
medium	O
is	O
an	O
optical	B-Architecture
fiber	I-Architecture
doped	O
with	O
rare-earth	O
elements	O
such	O
as	O
erbium	O
,	O
ytterbium	O
,	O
neodymium	O
,	O
dysprosium	O
,	O
praseodymium	O
,	O
thulium	O
and	O
holmium	O
.	O
</s>
<s>
Fiber	O
nonlinearities	O
,	O
such	O
as	O
stimulated	B-Architecture
Raman	I-Architecture
scattering	I-Architecture
or	O
four-wave	O
mixing	O
can	O
also	O
provide	O
gain	O
and	O
thus	O
serve	O
as	O
gain	O
media	O
for	O
a	O
fiber	B-Device
laser	I-Device
.	O
</s>
<s>
An	O
advantage	O
of	O
fiber	B-Device
lasers	I-Device
over	O
other	O
types	O
of	O
lasers	O
is	O
that	O
the	O
laser	O
light	O
is	O
both	O
generated	O
and	O
delivered	O
by	O
an	O
inherently	O
flexible	O
medium	O
,	O
which	O
allows	O
easier	O
delivery	O
to	O
the	O
focusing	O
location	O
and	O
target	O
.	O
</s>
<s>
Fiber	B-Device
lasers	I-Device
can	O
have	O
active	O
regions	O
several	O
kilometers	O
long	O
,	O
and	O
so	O
can	O
provide	O
very	O
high	O
optical	O
gain	O
.	O
</s>
<s>
Fiber	B-Device
lasers	I-Device
are	O
compact	O
compared	O
to	O
solid-state	O
or	O
gas	O
lasers	O
of	O
comparable	O
power	O
,	O
because	O
the	O
fiber	O
can	O
be	O
bent	O
and	O
coiled	O
,	O
except	O
in	O
the	O
case	O
of	O
thicker	O
rod-type	O
designs	O
,	O
to	O
save	O
space	O
.	O
</s>
<s>
Fiber	B-Device
lasers	I-Device
are	O
reliable	O
and	O
exhibit	O
high	O
temperature	O
and	O
vibrational	O
stability	O
and	O
extended	O
lifetime	O
.	O
</s>
<s>
Other	O
applications	O
of	O
fiber	B-Device
lasers	I-Device
include	O
material	O
processing	O
,	O
telecommunications	O
,	O
spectroscopy	O
,	O
medicine	O
,	O
and	O
directed	O
energy	O
weapons	O
.	O
</s>
<s>
Unlike	O
most	O
other	O
types	O
of	O
lasers	O
,	O
the	O
laser	O
cavity	O
in	O
fiber	B-Device
lasers	I-Device
is	O
constructed	O
monolithically	O
by	O
fusion	O
splicing	O
different	O
types	O
of	O
fiber	O
;	O
fiber	B-Device
Bragg	I-Device
gratings	I-Device
replace	O
conventional	O
dielectric	O
mirrors	O
to	O
provide	O
optical	O
feedback	O
.	O
</s>
<s>
They	O
may	O
also	O
be	O
designed	O
for	O
single	O
longitudinal	O
mode	O
operation	O
of	O
ultra-narrow	O
distributed	O
feedback	O
lasers	O
(	O
DFB	O
)	O
where	O
a	O
phase-shifted	O
Bragg	B-Device
grating	I-Device
overlaps	O
the	O
gain	O
medium	O
.	O
</s>
<s>
Fiber	B-Device
lasers	I-Device
are	O
pumped	O
by	O
semiconductor	O
laser	O
diodes	O
or	O
by	O
other	O
fiber	B-Device
lasers	I-Device
.	O
</s>
<s>
Many	O
high-power	O
fiber	B-Device
lasers	I-Device
are	O
based	O
on	O
double-clad	B-Device
fiber	I-Device
.	O
</s>
<s>
The	O
lasing	O
mode	O
propagates	O
in	O
the	O
core	O
,	O
while	O
a	O
multimode	B-Device
pump	O
beam	O
propagates	O
in	O
the	O
inner	O
cladding	O
layer	O
.	O
</s>
<s>
This	O
arrangement	O
allows	O
the	O
core	O
to	O
be	O
pumped	O
with	O
a	O
much	O
higher-power	O
beam	O
than	O
could	O
otherwise	O
be	O
made	O
to	O
propagate	O
in	O
it	O
,	O
and	O
allows	O
the	O
conversion	O
of	O
pump	O
light	O
with	O
relatively	O
low	O
brightness	B-Application
into	O
a	O
much	O
higher-brightness	O
signal	O
.	O
</s>
<s>
There	O
is	O
an	O
important	O
question	O
about	O
the	O
shape	O
of	O
the	O
double-clad	B-Device
fiber	I-Device
;	O
a	O
fiber	O
with	O
circular	O
symmetry	O
seems	O
to	O
be	O
the	O
worst	O
possible	O
design	O
.	O
</s>
<s>
Tapered	B-Device
double-clad	I-Device
fiber	I-Device
(	O
T-DCF	O
)	O
has	O
tapered	O
core	O
and	O
cladding	O
which	O
enables	O
power	O
scaling	O
of	O
amplifiers	O
and	O
lasers	O
without	O
thermal	O
lensing	O
mode	O
instability	O
.	O
</s>
<s>
Recent	O
developments	O
in	O
fiber	B-Device
laser	I-Device
technology	O
have	O
led	O
to	O
a	O
rapid	O
and	O
large	O
rise	O
in	O
achieved	O
diffraction-limited	O
beam	O
powers	O
from	O
diode-pumped	O
solid-state	O
lasers	O
.	O
</s>
<s>
Due	O
to	O
the	O
introduction	O
of	O
large	O
mode	O
area	O
(	O
LMA	O
)	O
fibers	O
as	O
well	O
as	O
continuing	O
advances	O
in	O
high	O
power	O
and	O
high	O
brightness	B-Application
diodes	O
,	O
continuous-wave	O
single-transverse-mode	O
powers	O
from	O
Yb-doped	O
fiber	B-Device
lasers	I-Device
have	O
increased	O
from	O
100W	O
in	O
2001	O
to	O
over	O
20kW	O
.	O
</s>
<s>
In	O
2014	O
a	O
combined	O
beam	O
fiber	B-Device
laser	I-Device
demonstrated	O
power	O
of	O
30kW	O
.	O
</s>
<s>
High	O
average	O
power	O
fiber	B-Device
lasers	I-Device
generally	O
consist	O
of	O
a	O
relatively	O
low-power	O
master	O
oscillator	O
,	O
or	O
seed	O
laser	O
,	O
and	O
power	O
amplifier	O
(	O
MOPA	O
)	O
scheme	O
.	O
</s>
<s>
State	O
of	O
the	O
art	O
high-power	O
fiber	B-Device
laser	I-Device
technologies	O
using	O
rod-type	O
amplifiers	O
have	O
reached	O
1kW	O
with	O
260fs	O
pulses	O
and	O
made	O
outstanding	O
progress	O
and	O
delivered	O
practical	O
solutions	O
for	O
the	O
most	O
of	O
these	O
problems	O
.	O
</s>
<s>
However	O
,	O
despite	O
the	O
attractive	O
characteristics	O
of	O
fiber	B-Device
lasers	I-Device
,	O
several	O
problems	O
arise	O
when	O
power	O
scaling	O
.	O
</s>
<s>
The	O
most	O
significant	O
are	O
thermal	O
lensing	O
and	O
material	O
resistance	O
,	O
nonlinear	O
effects	O
such	O
as	O
stimulated	B-Architecture
Raman	I-Architecture
scattering	I-Architecture
(	O
SRS	O
)	O
,	O
stimulated	B-Algorithm
Brillouin	I-Algorithm
scattering	I-Algorithm
(	O
SBS	O
)	O
,	O
mode	O
instabilities	O
,	O
and	O
poor	O
output	O
beam	O
quality	O
.	O
</s>
<s>
Moreover	O
,	O
specially	O
developed	O
double	O
cladding	O
structures	O
have	O
been	O
used	O
to	O
reduce	O
the	O
brightness	B-Application
requirements	O
of	O
the	O
high-power	O
pump	O
diodes	O
by	O
controlling	O
pump	O
propagation	O
and	O
absorption	O
between	O
the	O
inner	O
cladding	O
and	O
the	O
core	O
.	O
</s>
<s>
Several	O
types	O
of	O
active	O
fibers	O
with	O
a	O
large	O
effective	O
mode	O
area	O
(	O
LMA	O
)	O
have	O
been	O
developed	O
for	O
high	O
power	O
scaling	O
including	O
LMA	O
fibers	O
with	O
a	O
low-aperture	O
core	O
,	O
micro-structured	O
rod-type	O
fiber	O
helical	O
core	O
or	O
chirally-coupled	O
fibers	O
,	O
and	O
tapered	B-Device
double-clad	I-Device
fibers	I-Device
(	O
T-DCF	O
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
types	O
of	O
mode	O
locking	O
used	O
with	O
other	O
lasers	O
,	O
fiber	B-Device
lasers	I-Device
can	O
be	O
passively	O
mode	O
locked	O
by	O
using	O
the	O
birefringence	O
of	O
the	O
fiber	O
itself	O
.	O
</s>
<s>
Semiconductor	O
saturable-absorber	O
mirrors	O
(	O
SESAMs	O
)	O
can	O
also	O
be	O
used	O
to	O
mode	O
lock	O
fiber	B-Device
lasers	I-Device
.	O
</s>
<s>
This	O
freedom	O
of	O
design	O
has	O
further	O
extended	O
the	O
application	O
of	O
SESAMs	O
into	O
modelocking	O
of	O
fiber	B-Device
lasers	I-Device
where	O
a	O
relatively	O
high	O
modulation	O
depth	O
is	O
needed	O
to	O
ensure	O
self-starting	O
and	O
operation	O
stability	O
.	O
</s>
<s>
Fiber	B-Device
lasers	I-Device
working	O
at	O
1µm	O
and	O
1.5µm	O
were	O
successfully	O
demonstrated	O
.	O
</s>
<s>
Graphene	O
saturable	O
absorbers	O
have	O
also	O
been	O
used	O
for	O
mode	O
locking	O
fiber	B-Device
lasers	I-Device
.	O
</s>
<s>
In	O
the	O
non-mode	O
locking	O
regime	O
,	O
a	O
dark	O
soliton	O
fiber	B-Device
laser	I-Device
was	O
successfully	O
created	O
using	O
an	O
all-normal	O
dispersion	O
erbium-doped	O
fiber	B-Device
laser	I-Device
with	O
a	O
polarizer	O
in-cavity	O
.	O
</s>
<s>
Experimental	O
findings	O
indicate	O
that	O
apart	O
from	O
the	O
bright	O
pulse	O
emission	O
,	O
under	O
appropriate	O
conditions	O
the	O
fiber	B-Device
laser	I-Device
could	O
also	O
emit	O
single	O
or	O
multiple	O
dark	O
pulses	O
.	O
</s>
<s>
Multi-wavelength	O
emission	O
in	O
a	O
fiber	B-Device
laser	I-Device
demonstrated	O
simultaneous	O
blue	O
and	O
green	O
coherent	O
light	O
using	O
ZBLAN	O
optical	B-Architecture
fiber	I-Architecture
.	O
</s>
<s>
Another	O
type	O
of	O
fiber	B-Device
laser	I-Device
is	O
the	O
fiber	B-Device
disk	I-Device
laser	I-Device
.	O
</s>
