Nanoscale
PAPER
Cite this: Nanoscale, 2016, 8, 1066
Received 9th October 2015,
Accepted 26th November 2015
DOI: 10.1039/c5nr06981e
www.rsc.o rg/nanoscale
Two-dimensional material-based saturable
absorbers: towards compact visible-wavelength
all-fiber pulsed lasers†
Zhengqian Luo,‡
a
Duanduan Wu,‡
a
Bin Xu,
a
Huiying Xu,
a
Zhiping Cai,*
a
Jian Peng,
b
Jian Weng,*
b
Shuo Xu,
c
Chunhui Zhu,
c
Fengqiu Wang,*
c
Zhipei Sun
d
and
Han Zhang
e
Passive Q-switching or mode-locking by placing a saturable absorber inside the laser cavity is one of the
most effective and popular techniques for pulse generation. However, most of the current saturable
absorbers cannot work well in the visible spectral region, which seriously impedes the progress of pas-
sively Q-switched/mode-locked visible pulsed fibre lasers. Here, we report a kind of visible saturable
absorber—two-dimensional transition-metal dichalcogenides (TMDs, e.g. WS
2
, MoS
2
, MoSe
2
), and suc-
cessfully demonstrate compact red-light Q-switched praseodymium (Pr
3+
)-doped all-fibre lasers. The
passive Q-switching operation at 635 nm generates stable laser pulses with ∼200 ns pulse duration, 28.7
nJ pulse energy and repetition rate from 232 to 512 kHz. This achievement is attributed to the ultrafast
saturable absorption of these layered TMDs in the visible region, as well as the compact and all-fibre
laser-cavity design by coating a dielectric mirror on the fibre end facet. This work may open a new route
for next-generation high-performance pulsed laser sources in the visible (even ultraviolet) range.
Introduction
Compact and efficient visible-wavelength pulsed lasers are of
great interest for various applications, including underwater
detection, laser medicine, and biomedical imaging. Although
visible-wavelength pulsed solid-state bulk laser systems (e.g. Ti:
sapphire pumped optical parametric oscillators) have been
relatively matured, limitations in terms of footprint, cost and
efficiency have called for alternative laser solutions. For some
practical applications, it is highly desired that visible-wave-
length pulsed sources are compact, user-friendly, low-cost and
maintenance-free. Fortunately, visible pulsed all-fibre lasers
could satisfy all these demands. At present, visible pulsed fibre
sources are mainly based on frequency conversion techniques
(e.g. fibre optical parametric oscillator
1
or supercontinuum
generation
2,3
in photonic crystal fibres,
4
frequency doubling of
near-infrared fibre lasers,
5
and up-conversion fibre lasers
6
).
Although these techniques, by exciting optical nonlinear pro-
cesses in fibres, can indeed convert infrared pumping light
into widely-tuneable visible light,
1,2
they often suffer from low
efficiency, instability or a complex structure. In contrast, if one
combines rare-earth-doped fibre gain with Q-switching or
mode-locking technologies, compact and efficient visible
pulsed laser oscillators without additional frequency conver-
sion methods could be expected and become more attractive.
The main challenges for the past decades are from: (1)
fabricating the low-loss visible gain fibres, (2) requiring high-
power short-wavelength (ultraviolet or blue) pump laser diodes
(LDs), and (3) obtaining a suitable visible-available Q-switch or
mode-locker. Thanks to the fast development of soft-glass fibres
(e.g. ZBLAN fibre) and high-power blue GaN LDs in recent years,
exciting progress in continuous-wave visible Pr
3+
-doped ZBLAN
fibre lasers has been made,
7
but the pulsed operation of a
visible fibre laser is very rare.
8
Although active Q-switching by
an acousto-optic modulator has been recently reported in
visible wavelengths,
8
it sacrifices the all-fibre structure and
increases the system cost. In contrast, passive Q-switching or
mode-locking could be preferred, and this is therefore stimulat-
ing research on new saturable-absorption materials for passively
Q-switched/mode-locked visible fibre lasers.
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5nr06981e
‡ These authors contributed equally to this work.
a
Department of Electronic Engineering, Xiamen University, Xiamen 361005, China.
E-mail: zpcai@xmu.edu.cn
b
Department of Biomaterials, College of Materials, Xiamen University,
Xiamen 361005, China. E-mail: jweng@xmu.edu.cn
c
School of Electronic Science and Engineering, Collaborative Innovation Center of
Advanced Microstructures, Nanjing University, Nanjing 210023, China.
E-mail: fwang@nju.edu.cn
d
Department of Micro- and Nanosciences, Aalto University, FI-02150 Espoo, Finland
e
College of Optoelectronic Engineering, Shenzhen University, 518 060, China
1066 | Nanoscale,2016,8,1066–1072 This journal is © The Royal Society of Chemistry 2016