Mode-locked fiber laser in the C-band region for
dual-wavelength ultrashort pulses emission using
a carbon nanotube saturable absorber
Kuen Yao Lau (刘坤耀)
1
, Pin Jern Ker (郭炳仁)
1
, Ahmad Fauzi Abas
2
,
Mohammed Thamer Alresheedi
2
, and Mohd Adzir Mahdi
3,
*
1
Electronics Research Group, Institute of Power Engineering, Universiti Tenaga Nasional, 43000 Kajang,
Selangor, Malaysia
2
Department of Electrical Engineering, College of Engineering, King Saud University, Riyadh 11421, Kingdom
of Saudi Arabia
3
Wireless and Photonics Networks Research Centre, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM
Serdang, Selangor, Malaysia
*Corresponding author: mam@upm.edu.my
Received December 1, 2018; accepted January 30, 2019; posted online May 8, 2019
A saturable absorber is commonly employed to generate an ultrashort laser with a mode-locking scheme. In an
erbium-doped fiber laser system, the laser regimes of either 1530 or 1550 nm wavelength are procured based on
the absorption profile of the erbium-doped fiber. The absorption of the erbium-doped fiber is designed to emit at
both wavelengths by controlling the net gain of the laser cavity. Subsequently, simultaneous erbium-doped fiber
laser emission is attained at 1533.5 and 1555.1 nm with the pulse duration of 910 and 850 fs, respectively.
Therefore, this work maximizes the output portfolios of a mode-locking fiber laser for dual-wavelength ultrashort
pulses emission.
OCIS codes: 140.3538, 190.7110, 320.7090.
doi: 10.3788/COL201917.051401.
The fast growing adaption of the fiber laser in industry has
appeared to be the alternative technology to prior art,
solid-state lasers. There are two categories of fiber lasers:
continuous wave and pulsed fiber lasers. This work focuses
on the latter category on generating ultrashort pulses,
termed as mode-locked fiber laser (MLFL). A technique
to generate MLFL is the integration of a saturable
absorber (SA) inside the fiber laser cavity. In a laser
cavity, the SA transmits light at high excitation inten-
sities with reduced optical loss when the initial states of
the absorbing transition are empty, and the final states
are fully occupied. This phenomenon is dubbed as satu-
rable absorption, which occurs in a medium with strong
absorbing dopant ions.
Numerous technologies have been proposed with
saturable absorption properties, such as a semiconductor
SA mirror (SESAM) and integrating materials with fiber
end facets or microfib ers. However, SESAM requires strin-
gent and complicated fabrication facilities that spur
researchers to investigate fiber-based SAs. The integrated
materials in a fiber-based SA include a carbon nanotube
(CNT), graphene, transition metal dichalcogenides, topo-
logical insulator, phosphorene, gold nanorods, and lately
graphene-oxide carboxylic acid
[1–6]
. Despite being an exten-
sively studied material since 2004 for the first SA demon-
stration by Set et al.
[7]
, the progress of a CNT-SA for a
dual-fiber laser at a near 1.55 μ m wavelength emission
with femtosecond pulses is limited. Most CNT-SAs
deploy the sandwiched structure in a dual-wavelength
mode-locked laser, which shows the limitation of low
thermal damage threshold. Therefore, a tapered fiber
CNT-SA was demonstrated for the generation of a dual-
wavelength MLFL with better thermal management
[8]
.
However, the pulse duration of a 1533 nm mode-locked
laser was attained at 1.06 ps in Ref. [
8]. In order to
generate dual-wavelength MLFL, net gain cross section
variation is demonstrated by changing cavity losses
[8,9]
or monitoring the pump power
[10]
. In addition, two chirped
fiber Bragg gratings with a 1 and 6 nm bandwidth, respec-
tively are used to divide the mode-locked laser into two
regions at around 1550 nm
[11]
.
In this work, we propose a solution of generating two
mode-locked laser outputs with closely spaced operating
wavelengths using a tapered fiber CNT-SA. The tapered
fiber CNT-SA possesses insertion losses of 2.46 dB at
1550 nm and a modulation depth of 2.5%, in conjunction
with our previous works in Refs. [
12,13]. The laser cavity is
designed with the implementation of a red/blue wave-
length division multiplexer (R/B-WDM), which splits
the laser propagation into two separate optical paths at
wavelengths near 1530 and 1550 nm. This work presents
the dual-MLFL with the shortest pulse duration of 910
and 850 fs, pulse repetition rate of 10.47 and
10.89 MHz using CNT-SA with C-band emission wave-
length at 1533.5 and 1555.1 nm, respectively. The dual-
mode-locked lasers contribute to practical applications,
such as asynchronous optical sampling, which operates
with fixed pulse repetition rate difference as sources of
COL 17(5), 051401(2019) CHINESE OPTICS LETTERS May 10, 2019
1671-7694/2019/051401(4) 051401-1 © 2019 Chinese Optics Letters