COL 10(4), 041405(2012) CHINESE OPTICS LETTERS April 10, 2012
Graphene-based Q-switched pulsed fiber laser in a linear
configuration
Y. K. Yap
1
, Richard M. De La Rue
1
, C. H. Pua
1
, S. W. Harun
2
, and H. Ahmad
1
1
Photonics Research Centre, Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia
2
Department of Electrical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia
∗
Corresp onding author: yapyuenkiat@yahoo.com
Received August 30, 2011; accepted October 25, 2011; posted online January 6, 2012
A pulsed laser system is realized with graphene employed as a Q-switch. The graphene is exfoliated from
its solution using an optical deposition and the optical tweezer effect. A fiber ferrule that already has
the graphene deposited on it is inserted into an erbium-ytterbium laser (EYL) system with linear cavity
configuration. We successfully demonstrate a pulsed EYL with a pulse duration of approximately 5.9 µs
and a repetition rate of 20.0 kHz.
OCIS codes: 140.3540, 140.3538.
doi: 10.3788/COL201210.041405.
Graphene, an allotrope of carbon whose structure is one-
atom-thick planar sheets of sp
2
-bonded carbon atoms
densely packed in a honeycomb crystal lattice (i.e., con-
sisting of a hexagonal array of sp
2
-bonded carbon atoms
similar to those found in bulk graphite) is currently a
major research topic of interest due to its uniqueness
as a two-dimensional (2D) material. Bonaccorso et al.
presented a detailed description on various aspects of
graphene as well as its many possible applications in
photonics and optoelectronics, where the combination of
its unique optical and electronic properties could be fully
exploited in the absence of a bandgap
[1]
. The linear dis-
persion of the Dirac electrons in graphene allows for ultra
wideband tunability
[1]
. Its thin dimension and electronic
properties make it suitable for electronic devices such
as transistors and gas sensors. Graphene’s resistivity to
acids and alkalines provides an opportunity for its use
in inert coatings as well. In optoelectronics, its special
optical properties enable graphene to have an ultrashort
recovery time in saturation absorption. In addition, it
displays smaller non-saturable loss and a higher damage
threshold. The unique absorption of light by graphene
can become saturated when the input optical intensity is
above a specific threshold value. Graphene can be read-
ily saturated under strong excitation over the visible to
near-infrared region due to the universal optical absorp-
tion resulting from the zero band-gap structure. This be-
havior is relevant for the mode-locking and Q-switching
of fiber lasers, where short pulses have been achieved by
using graphene-based saturable absorb ers
[2−6]
. The first
mode-locked laser in a ring configuration was reported
by Hasan et al.
[7]
, whose research observed saturation
absorption over at least a 20-nm range with a pulse
duration of ∼800 fs. Using graphene as a saturable ab-
sorber, Sun et al. successfully produced a mode-locked
pulse train at a repetition rate of 19.9 MHz from a ring
erbium-doped fiber laser (EDFL)
[8]
. Graphene has also
been used to mitigate the mode competition in EDFLs
as well as stabilize the multi-wavelength oscillation
[9]
.
In this letter, we describe the successful production of a Q-
switched pulsed laser using graphene inserted into a laser
oscillation system within a linear cavity configuration.
Thus far, as optical pulse generation by graphene has
been reported primarily in a ring laser configuration,
this device is, to the best of our present knowledge, the
first ever Q-switched pulsed fiber laser using graphene
achieved in a linear laser cavity configuration. One mo-
tivation of the present work is to propose a simple and
efficient setup for short pulse generation (i.e., mode-
locked operation) in a linear configuration.
The graphene flakes (in a solution) used in this research
were supplied by Graphene Research. The graphene had
to be deposited onto a fiber ferrule; we employed the
optical tweezer effect for this purpose. The setup for de-
positing graphene onto the fiber ferrule is shown in Fig.
1. The fiber was prepared by removing the PVC coating,
cleaving, and then placing it into the solution. Optical
radiation from a 980-nm laser diode (LD) at 10 dBm was
then propagated through the fiber; the laser was left on
for 30 min. The laser beam has a very high intensity;
therefore, at the end face of the fiber ferrule, it produces a
very strong electric field gradient, resulting in the attrac-
tion of the graphene flakes along the field-gradient into
the region of the strongest electric field. The laser beam
exerts a force on the flakes that are in the beam, along
the direction of beam propagation. The LD was then
turned off, and the fiber was removed from the solution.
Fig. 1. (a) Experimental setup for deposition of graphene onto
the end face of the fiber ferrule; (b) graphene flakes could be
clearly seen in the solution. The flakes were deposited onto
the ferrule by an attractive force caused by the gradient of
the strong electric field near the end of the ferrule.
1671-7694/2012/041405(4) 041405-1
c
° 2012 Chinese Optics Letters