Q-switched and mode-locked Er-doped fiber laser
using PtSe
2
as a saturable absorber
KANG ZHANG,
1
MING FENG,
1,
*YANGYANG REN,
1
FANG LIU,
1
XINGSHUO CHEN,
1
JIE YANG,
1
XIAO-QING YAN,
1,2
FENG SONG,
1
AND JIANGUO TIAN
1
1
Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, School of Physics and TEDA Applied Physics School,
Nankai University, Tianjin 300071, China
2
e-mail: yanxq01@nankai.edu.cn
*Corresponding author: mingfeng@nankai.edu.cn
Received 14 June 2018; revised 25 July 2018; accepted 25 July 2018; posted 25 July 2018 (Doc. ID 335211); published 23 August 2018
We report a passively Q-switched and mode-locked erbium-doped fiber laser (EDFL) based on PtSe
2
, a new
two-dimensional material, as a saturable absorber (SA). Self-started Q-switching at 1560 nm in the EDFL was
achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 mW, the maximum
single Q-switched pulse energy is 143.2 nJ. Due to the polarization-dependent characteristics of the PtSe
2
-based
SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization
state. A mode-locked pulse train with a repetition rate of 23.3 MHz and a pulse width of 1.02 ps can be
generated when the pump power increases to about 80 mW, and the stable mode-locked state is maintained
until the pump power reaches its maximum 450 mW. The maximum single mode-locked pulse energy is
0.53 nJ. This is the first time to our knowledge that successful generation of stable Q-switched and mode-locked
pulses in an Er-doped fiber laser has been obtained by using PtSe
2
as a saturable absorber. © 2018 Chinese Laser
Press
OCIS codes: (140.3510) Lasers, fiber; (140.7090) Ultrafast lasers; (140.3380) Laser materials; (160.4670) Optical materials.
https://doi.org/10.1364/PRJ.6.000893
1. INTRODUCTION
Q-switching and mode-locking are two main ways to generate
pulses [1–4]. Among the two technologies, saturable absorbers
(SAs) play a vital role in passive Q-switching and mode-locking
[5–13]. Fiber lasers have the advantages of simple structure,
small size, low price, and high environmental stability [12–17].
Therefore, it is clear that the development of pulsed lasers
depends greatly on the development of saturable absorbing
materials. Traditional SAs, such as semiconductor saturable
absorber mirrors (SESAM), face many defects, such as narrow
working bandwidth and complex manufacturing packages,
which greatly limit the developm ent of pulsed lasers. With
the advancement of material science, new nanomaterials such
as carbon nanotubes (CNTs) [8,9], graphene [10–12], gra-
phene oxide [13], black phosphorus (BP) [17,18], and topo-
logical insulators (TI) [19–22] have emerged one after another,
and their performance has been qualitatively improved as their
prices have declined. Recently, transition-metal dichalcogenides
(TMDs) (e.g., MoS
2
[23], WS
2
[24,25], TiS
2
[26], MoTe
2
[27,28]) have attracted much attention from laser researchers
due to their thickness-dependent band gap and unique absorp-
tion property [29 ,30]. PtSe
2
also attracts our attention as a
new member of the layered TMDs family [31–35]. PtSe
2
’s
characteristic of having a widely tunable band gap allows it
to effectively respond to near-infrared light, and its photo-
responsivity is comparable with that of BP [36]. Monolayer
PtSe
2
has an indirect band gap of about 1.2 eV, while the band
gap of double-layered PtSe
2
is reduced to 0.21 eV. Three or
more layers of PtSe
2
have a zero band gap, and the macroscopic
properties are represented by semimetals [31]. Compared to
MoS
2
, a TMD material that has been widely studied in the
field of laser mode-locking, PtSe
2
has a higher carrier mobility
that is comparable to that of graphene [35–38]. Therefore, it
can produce a fast nonlinear response to incident light and can
achieve narrower pulses. In addition, the narrower energy band
gap of PtSe
2
allows it to have nonlinear effects in a wider wave-
length range. Moreover, the characteristics of the zero bandgap
of multi-layered PtSe
2
and the high carrier mobility are similar
to graphene, although there is a large difference in the band
structures. Therefore, PtSe
2
has the potential to substitute for
graphene as an excellent SA.
In this paper, we report an erbium-doped fiber laser (EDFL)
based on PtSe
2
as an SA with obvious polarization-dependent
saturable absorption, and we have obtained both passive
Q-switching and mode-locking pulses. As far as we know,
Research Article
Vol. 6, No. 9 / September 2018 / Photonics Research 893
2327-9125/18/090893-07 Journal © 2018 Chinese Laser Press