All-fiber design of hybrid Er-doped
laser/Yb-doped amplifier system for
high-power ultrashort pulse generation
Alexey Andrianov,* Elena Anashkina, Sergey Muravyev, and Arkady Kim
Institute of Applied Physics, Russian Academy of Sciences, 46 Ulyanov Street, 603950 Nizhny Novgorod, Russia
*Corresponding author: email@example.com
Received August 30, 2010; revised October 15, 2010; accepted October 17, 2010;
posted October 19, 2010 (Doc. ID 133848); published November 9, 2010
We propose a design of an all-fiber laser system that combines the most advanced Er:fiber laser in the telecommu-
nication range and an efficient Yb-doped amplifier for generation of high-power ultrashort pulses. The
system is based on nonlinear wavelength conversion of 1:56 μm ultrashort Er:fiber laser pulses to the 1 μm range
in a short pigtail of dispersion-shifted silica fiber with subsequent amplification in the Yb-doped fiber amplifier.
Pulses with a duration as short as 85 fs and averaged power of 200 mW are demonstrated.
060.7140, 060.4370, 060.2320, 320.7090, 320.7140, 140.3510.
© 2010 Optical Society of
Recent progress in Yb-doped fiber laser systems has pro-
ven their capability to deliver high-power ultrashort
pulses suitable for many applications , in particular,
with high peak intensity sufficient to drive strong non-
linear laser–matter interaction processes, such as high
harmonic and attosecond pulse generation . Along
with their advantages, such as compactness, ease of
use, cost efficiency, and long-term stability, fiber laser
systems have great potential for power scaling via the
technologies of cladding pumping and chirped pulse am-
plification in large-mode area fibers and rods . For lack
of conventional silica-based fibers with anomalous dis-
persion in the 1 μm range, different approaches have
been developed for ytterbium-based fiber systems to pro-
duce femtosecond pulses. Thus, subpicosecond pulses
were initially created in a fiber SESAM mode-locked
master oscillator  and then spectrally broadened in
an Yb-doped fiber amplifier and compressed to sub-
100 fs duration . Even shorter pulses with a duration
of several tens of femtoseconds were demonstrated in
Yb-doped fiber systems by compressing the parabolic
pulses , as well as by dechirping the signal directly
from a high-power all-normal dispersion fiber oscillator
[7,8]. Another interesting possibility is to use photonic
crystal fibers (PCFs) exhibiting anomalous chromatic
dispersion in spectral ranges inaccessible to conven-
tional fibers . However, we believe that a more
advanced Er-doped fiber laser based on telecommunica-
tion components and integrated with an efficient Yb-
doped amplifier may become an excellent option for
intense femtosecond pulse generation, if a suitable fre-
quency converter is found. An interesting suggestion to
use a Raman-shifted and frequency-doubled erbium
femtosecond fiber laser as a seeding source for a high-
power Yb-doped amplifier was put forward by Fermann
et al. . In this Letter we present, for the first time to
the best of our knowledge, an all-fiber hybrid laser sys-
tem consisting of an Er-doped fiber laser, a nonlinear
dispersion-shifted fiber (DSF) wavelength converter, and
an Yb-doped amplifier that produces 85 fs 4 nJ pulses
with subsequent amplification to the 100 nJ level, allow-
ing recompression to a 100–200 fs duration. At the same
time, the Er-doped source provides sub-20 fs optical
pulses in the wavelength range of 1.6 to 1:8 μm, which
are inherently synchronized to the output of the ytter-
bium amplifier. The dual-wavelength source of optically
synchronized ultrashort pulses may have a variety of ap-
plications, such as seeding and pump sources for an op-
tical parametric chirped pulse amplifier (OPCPA), sum-
and difference-frequency generation, and two-color
pump–probe experiments as well.
The experimental setup is shown in Fig. 1. It consists
of a passively mode-locked Er:fiber oscillator, a diode-
pumped Er-doped fiber amplifier, a single-mode fiber
(SMF) used as a nonlinear pulse compressor, a silica DSF
for wavelength conversion, and a diode-pumped two
stage Yb-doped high-power amplifier. Additionally, wave
plates for polarization adjustment and a free space grat-
ing pair compressor are used to shorten the output pulse
to its transform-limited duration. It should be noted that a
PCF compressor, instead of a grating pair, may be used at
the output , thus providing an all-fiber system.
Fig. 1.(Color online) Schematic of the experimental setup.
November 15, 2010 / Vol. 35, No. 22 / OPTICS LETTERS3805
0146-9592/10/223805-03$15.00/0© 2010 Optical Society of America
The Er:fiber oscillator operates in a stretched-pulse
mode-locking regime via nonlinear polarization rotation
and delivers highly chirped femtosecond pulses with
30 nm spectral bandwidth centered at 1:56 μm at a
49 MHz repetition rate. To ensure single pulse per
round-trip generation and a high quality of output femto-
second pulses, the laser pump power is set to its mini-
fundamental frequency of 49 MHz. Because the laser
does not start pulsing at this pump level, a simple elec-
tronic circuit is used to increase pump power after
switching the system to initiate mode locking. The laser
pulses are then transmitted through 2:5 m of SMF-28 fi-
ber, amplified to an average power of 200 mW in a for-
ward and backward diode-pumped Er:fiber amplifier and
subsequently compressed in ashort piece of SMF-28 fiber
inside a 1480/1560 WDM coupler that serves for back-
ward pumping of the active fiber. Fiber lengths are cho-
sen so that the positively chirped pulse from the output of
the master oscillator is compressed inside the first SMF
to its minimum duration and then stretched again before
entering the active erbium-doped fiber with normal dis-
persion. Further, the amplified 2:5 nJ pulse, having small
positive chirp, is finally compressed, mostly owing to the
solitonic effects, to the duration of about 70 fs in a short
piece of SMF-28 fiber in the output WDM coupler. This
dispersion-managed amplification scheme was chosen
so as to reduce nonlinear distortions of a high-energy
pulse at the final compression stage and was supported
Next, the key element of the proposed scheme is a DSF
wavelength converter spliced directly after the SMF
compression fiber. A proper choice of DSF parameters
permits producing seed pulses exactly in the Yb amplifi-
cation spectral range. With the use of such DSFs, extre-
mely short pulses with a duration as short as 13 fs were
generated in . In our work we use a 10 cm silica fiber
with a zero-dispersion wavelength located near 1:4 μm.
The nonlinearity of this fiber is about twice that of the
standard fiber because of a smaller mode diameter.
Additionally, due to reduced anomalous dispersion coef-
ficient at 1:6 μm, the input pulse effectively corresponds
to a high-order soliton with soliton number N ≈ 3. The
mode lockingat the
measured spectrum at the output of the DSF is shown
in Fig. 2 along with its dispersion curve, where we also
present the detailed spectrum distribution of the high-
frequency components in the 1 μm region [Fig. 2(b)]
and its autocorrelation trace [Fig. 2(d)], which corre-
sponds to a slightly chirped pulse of 55 fs duration.
We model pulse propagation by using a modified non-
linear Schrödinger equation . The sech-shaped input
pulse with 70 fs duration and 2:5 nJ energy is launched
into the fiber with dispersion, as in Fig. 2(b), and nonli-
nearity γ ¼ 2:2 W−1km−1(the estimates are based on the
measured refractive index profile of the fiber preform).
The spectral and temporal dynamics depicted in Fig. 3
show that at the beginning of propagation, the pulse un-
dergoes high-order soliton compression with corre-
sponding spectral broadening. Prior to soliton fission,
the spectrum broadens so much that a substantial part
of its blue wing falls into the normal dispersion region
and acts as a source of phase-matched radiation ,
which is clearly seen as an isolated spectral peak near
1 μm. The phenomenon of the emission of phase-
matched linear dispersive waves by perturbed solitons,
also referred to as Cherenkov radiation as well, was stu-
died both in the context of supercontinuum generation in
photonic crystal and bulk silica fibers  and was also
used for development of visible and near-IR femtosecond
sources . The wavelength of the emitted radiation is
governed by the appropriate phase-matching condition
and can be tuned by varying the input pulse power. A
phase-matched wavelength region can be shifted as a
whole by choosing a fiber with different dispersion,
namely, with a different zero-dispersion wavelength. Ba-
sically, our simulation resembles those done in PCFs
pumped at 0:8 μm . But in our work, we concentrate
on efficient dispersive wave generation in silica fibers
pumped by an Er-doped laser and its use as a seed for
an Yb-doped amplifier. It is also worthy of notice that
the main part of the initial pulse experiences dramatic
DSF and (c) its second-order dispersion coefficient β2versus
wavelength. (b) Detailed spectrum in the 1 μm region and
(d) its autocorrelation trace.
(Color online) (a) Measured spectrum at the output of
generation in the DSF: (a) spectra and (b) pulse shape (black
curves) at different propagation distances. Fourier-filtered [(b),
red dotted curves] and dechirped [(b), blue filled curves] short-
wavelength pulses (intensity multiplied by 30 for convenience).
(Color online) Numerical modeling of dispersive wave
3806OPTICS LETTERS / Vol. 35, No. 22 / November 15, 2010
shortening because of high-order soliton compression
occurring when its relevant spectrum lies in the anoma-
lous region. The pulse duration obtained in the simula-
tion is as short as 11 fs. Our experiments verified that
after careful optimization of the fiber length, the shortest
measured pulse duration was about 12 fs . As the
pulse further propagates in the DSF, it splits into sev-
eral solitonic pulses and residual dispersive radiation
[Fig. 3(b) shows only the first soliton]. Because the fis-
sion process can also contribute to the signal content
at 1 μm, resulting in undesirable spectral fringes, the
cleanest frequency upshifted wave packet should be ex-
tracted at an earlier stage. To examine the temporal
structure of the dispersive wave packet, we plotted in
Fig. 3(b) Fourier-filtered results of the simulation in
the spectral region near 1 μm. A smooth and bell-shaped
signal experiences slight temporal broadening as it pro-
pagates in the normal dispersion region, but a dechirped
signal with a flattened spectral phase [shown in Fig. 3(b)
(red curve)] has almost a constant duration of about
46 fs. The spectra obtained in the experiment agree well
with the results of modeling. The spectral peak at
1:06 μm containing about 6% of total energy is well
approximated by a Gaussian shape with an FWHM band-
width of 38 nm [Fig. 2(b) (blue dashed curve)] corre-
sponding to a 45 fs transform-limited pulse duration.
Thus, both the experiment and modeling show the feasi-
bility of efficient frequency upconversion of high-quality
femtosecond pulses from the Er:fiber laser into the Yb
amplifier region by using dispersion-shifted silica fibers.
It is worth noting that dispersive radiation generated in a
PCF pumped by an Yb:KGW laser has been used as
a seeding source for OPCPA and demonstrated high-
quality recompressed femtosecond pulses .
The pulse is then amplified in a two-stage Yb-doped
fiber amplifier. To avoid nonlinear distortions, the pulse
is stretched to the duration of about 2 ps in a SMF and
then amplified to the average power up to 290 mW in a
short Yb-doped fiber preamplifier diode-pumped at
975 nm and further recompressed in a gold grating pair
giving 200 mW at the output. The estimated pulse dura-
tion is about 85 fs, which agrees with the bandwidth of
the amplified spectrum shown along with the autocorre-
lation in Fig. 4. For demonstrating the power scaling cap-
abilities of the proposed system, we also employed a
high-power diode-pumped (up to 20 W at 962 nm) ampli-
fier based on 4.5-m-long large-mode-area (14 μm in diam-
eter) Yb-doped fiber. At maximum pump power, the
output is 5 W of average power, which corresponds to
the pulse energy of 100 nJ after the grating compressor.
However, the amplified pulse spectrum exhibits moder-
ate gain narrowing, and nonlinear distortions are more
pronounced at such high powers, thus limiting the mini-
mum pulse duration within 135–185 fs, depending on
pulse energy. This can be easily overcome by using a
larger mode-area gain fiber or chirping the pulse further
In conclusion, we have presented a design of an all-
fiber laser system that combines an Er-doped laser
and an Yb-doped amplifier for generation of ultrashort
pulses. The key element of the system is the nonlinear
DSF wavelength converter transforming 1:58 μm ultra-
short Er:laser pulses to the 1 μm range for subsequent
ytterbium-based amplification. Pulses with a duration
as short as 85 fs and averaged 200 mW power have been
generated. We believe that the results obtained show
an appealing alternative for producing a dual-band all-
fiber optically synchronized hybrid Er/Yb femtosecond
This study was partly funded by the Russian Foun-
dation for Basic Research (RFBR) under project 10-02-
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(a) Spectrum and (b) autocorrelation trace at the out-
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