Passively harmonic mode-locked erbium-doped fiber
laser at a 580 MHz repetition rate based on carbon
nanotubes film
Qianqian Huang (黄千千)
1
, Tianxing Wang (王天行)
1
, Chuanhang Zou (邹传杭)
1
,
Mohammed AlAraimi
2,3,4
, Aleksey Rozhin
2,3
, and Chengbo Mou (牟成博)
1,
*
1
Key Laboratory of Specialty Fiber Optics and Optical Access Networks, Shanghai University, Shanghai 200072, China
2
Aston Institute of Photonic Technologies (AIPT), Aston University, Birmingham, B4 7ET, United Kingdom
3
Nanoscience Research Group, Aston University, Birmingham B4 7ET, United Kingdom
4
Al Musanna College of Technology, Muladdah, Al Musanna P.C.314, Sultanate of Oman
*Corresponding author: mouc1@shu.edu.cn
Received September 1, 2017; accepted October 13, 2017; posted online December 20, 2017
We propose and demonstrate a passively harmonic mode-locked erbium-doped fiber laser (EDFL) using carbon
nanotubes polyvinyl alcohol (CNTs-PVA) film. The laser allows generation of the pulses with a repetition rate of
580 MHz, which corresponds to the 22nd harmonics of a 26.3 MHz fundamental repetition rate under 323 mW
pump power. A particularly noteworthy feature of the pulses is the super-mode suppression ratio (SMSR), which
is over 40 dB, indicating a stable operation.
OCIS codes: 140.3500, 160.4236, 320.7160.
doi: 10.3788/COL201816.020019.
In recent years, a high repetition rate fiber laser was
intensively explored, which is able to pave a promising
way for the applications of optical frequency metrology
[1]
,
optical communication
[2]
, as well as high speed optical sam-
pling
[3]
. Ordinarily, the methods for realizing high repetition
pulses focus on three aspects. An impactful approach is
actively mode-locking, which is in a position to scale up
the repetition rate to a few tens of gigahertz easily, while
extra modulators incorporated in a laser will add a level
of complexity
[4,5]
. Additionally, an alternative mean is to
employ a short cavity. Unfortunately, the cavity length,
to a great extent, is restrained by the physical size of fiber
devices and limited pump power
[6–8]
. Furthermore, har-
monic mode-locking (HML) can be adopted to sidestep
the drawback of the limitation of fiber length and achieve
high repetition rate simultaneously, where multiple solitons
due to high pump power
[9,10]
organize themselves and
exhibit equal spacing between adjacent pulses under a spe-
cific condition
[11,12]
.
Thus far, a passive mode-locking (PML) fiber laser
with some unique features of compact size, superior heat
dissipation performance, and fairly easy maintenance has
motivated much interest. There are various approaches
to obtain mode-locked pulses, such as nonlinear polariza-
tion rotation (NPR)
[13,14]
, nonlinear optical loop mirror
(NOLM)
[15]
, semiconductor saturable absorber mirror
(SESEAM)
[16]
, and the carbon-based saturable absorbers
(SAs), including nanoscale graphite
[17]
, charc oal
[18]
, and
carbon nanotubes (CNTs)
[19–21]
. In fact, most of them have
also been demonstrated to achieve HML. In particular,
CNTs are intensively applied SAs that process favorable
properties of a fast recovery time, wideband wavelength
range, as well as being insensitive to environmental
perturbation
[22]
. Moreover, in order to improve the damage
threshold and emit higher energy, a CNT SA of the
evanescent-wave interaction type is proposed, which is
formed by deposition on a D-shaped fiber
[23]
, a fiber
taper
[24]
, or a microfib er
[25]
. Jun et al. first obtained a
943 MHz pulse train at the 34th harmonics with excellent
noise performance under 195 mW pump power
[26]
. Further-
more, through engineering the dispersion of the cavity,
4.9 GHz pulses, corresponding to t he 128th HML was
finally realized under 395 mW pump power with 40 dB
super-mode suppression ratio (SMSR)
[27]
. However, the
structure is considerably conditional on the special fiber
devices, which will bring additional complexity to the
system
[28]
. Another credible SA type is a CNTs film sand-
wiched between two fiber connector ferrules, exhibiting
virtues of simple construction, mature manufacturing,
easy implementation, and high flexibility
[29–31]
. Never-
theless, the CNTs film is rarely exploited to achieve a rel-
ative repetition rate pulse train. Up till now, the highest
repetition rate of 328 MHz, corresponding to the 23rd
harmonics with a larger than 30 dB SMSR, has been
examined by a passively harmonically mode-locked fiber
laser using CNTs film
[32].
In this work, we experimentally demonstrate passive
HML of an erbium-doped fiber laser (EDFL) using a
CNTs polyvinyl alcohol (PVA) film. After slightly adjust-
ing the intra-cavity birefringence, the laser is in a position
to deliver pulse trains with a 580 MHz repetition rate,
corresponding to the 22nd harmonics of the 26.3 MHz
fundamental repetition rate under 323 mW pump power.
To the best of our knowledge, this is the highest repetition
rate achieved by using a CNTs film as an SA. Espe cially,
the radio frequency (RF) spectrum indicating a 40.6 dB
COL 16(2), 020019(2018) CHINESE OPTICS LETTERS February 10, 2018
1671-7694/2018/020019(5) 020019-1 © 2018 Chinese Optics Letters