Optik
144
(2017)
163–171
Contents
lists
available
at
ScienceDirect
Optik
j
ourna
l
ho
me
pa
ge:
www.elsevier.de/ijleo
Original
research
article
Raman-noise
enhanced
stimulated
Raman
scattering
in
high-power
continuous-wave
fiber
amplifier
Hanyuan
Ying
a,b,c
,
Jianqiu
Cao
a,b,c,∗
,
Yu
Yu
a,b,c
,
Meng
Wang
a,b,c
,
Zefeng
Wang
a
,b,c
,
Jinbao
Chen
a
,b,c,∗
a
College
of
Optoelectronic
Science
and
Engineering,
National
University
of
Defense
Technology,
Changsha,
Hunan,
410073,
China
b
Hunan
Provincial
Key
Laboratory
of
High
Energy
Laser
Technology,
Changsha,
Hunan,
410073,
China
c
Hunan
Provincial
Collaborative
Innovation
Center
of
High
Power
Fiber
Laser,
Changsha,
Hunan,
410073,
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
19
March
2017
Received
in
revised
form
23
June
2017
Accepted
23
June
2017
Keywords:
Fiber
amplifiers
Stimulated
Raman
scattering
Pumping
a
b
s
t
r
a
c
t
The
stimulated
Raman
scattering
(SRS)
in
high-power
continuous-wave
(CW)
fiber
ampli-
fier
is
investigated
with
the
seeded
Raman
noise
taken
into
account.
It
is
revealed
that
the
seeded
Raman
noise,
as
a
portion
of
seed
light,
should
enhance
SRS
in
high-power
CW
fiber
amplifier
even
when
it
is
much
weaker
than
the
seeded
signal
light.
The
analytic
formula
for
predicting
the
Raman
threshold
of
bi-directional
pumping
fiber
amplifier
is
given
with
the
seeded
Raman
noise
taken
into
account,
and
the
predictions
agree
well
with
the
numer-
ical
results.
It
is
also
revealed
that
the
co-pumping
amplifier
suffer
from
the
lowest
Raman
threshold,
and
the
counter-pumping
one
is
more
beneficial
to
the
SRS
suppression
than
the
bi-directional
pumping
one
when
the
pump
absorption
of
active
fiber
is
larger
than
8.7
dB.
These
results
will
provide
guidance
for
the
design
of
high-power
CW
fiber
amplifier.
©
2017
Elsevier
GmbH.
All
rights
reserved.
1.
Introduction
High-power
fiber
lasers
have
attracted
much
attention
because
of
their
advantages
such
as
compactness,
reliability,
high
efficiency,
good
beam
quality,
etc.
Particularly
with
the
rapidly
power
up-scaling
in
recent
years,
they
can
meet
various
requirements
of
academic
and
industrial
applications
[1–3].
In
2009,
a
10-kW
single-mode
fiber
laser
was
demonstrated
with
the
master
oscillator
power
amplification
(MOPA)
configuration
[4].
Nowadays,
the
MOPA
configuration
consisting
of
a
seed
fiber
oscillator
and
a
fiber
amplifier
is
most-widely
used
in
high-power
fiber
laser
system,
where
the
fiber
amplifier
plays
the
most
important
role
for
the
power
scalability
of
MOPA
fiber
laser
system.
One
fundamental
issue
limiting
the
power
scalability
of
MOPA
fiber
laser
system
is
the
stimulated
Raman
scattering
(SRS)
in
the
high-power
fiber
amplifier
[2,5,6].
It
has
been
revealed
that
when
the
signal
power
is
beyond
some
threshold
(generally
named
as
the
Raman
threshold),
SRS
should
be
present
and
preventing
the
further
increment
of
signal
power.
A
number
of
studies
were
carried
out
with
the
purpose
of
estimating
the
threshold.
At
present,
two
typical
formulas
given
by
J.
R.
Smith
[7]
and
C.
Jauregui
et
al.
[8]
are
most
widely
used,
which
are
induced
with
the
case
of
passive
fiber
and
show
that
the
threshold
is
mainly
determined
by
the
mode
area,
effective
fiber
length
and
Raman
gain.
The
Raman
threshold
of
fiber
amplifier
(also
defined
as
the
pump
power
threshold
corresponding
to
the
presence
of
SRS
effect
[9])
was
also
investigated
∗
Corresponding
authors
at:
College
of
Optoelectronic
Science
and
Engineering,
National
University
of
Defense
Technology,
Changsha,
Hunan,
410073,
China.
E-mail
addresses:
jq
cao@126.com
(J.
Cao),
kdchenjinbao@aliyun.com
(J.
Chen).
http://dx.doi.org/10.1016/j.ijleo.2017.06.098
0030-4026/©
2017
Elsevier
GmbH.
All
rights
reserved.
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