WSe
2
as a saturable absorber for multi-gigahertz
Q-switched mode-locked waveguide lasers [Invited]
Ziqi Li (李子琦)
1
, Rang Li (李 让)
1
, Chi Pang (逄 驰)
1
, Yuxia Zhang (张玉霞)
2
,
Haohai Yu (于浩海)
2
, and Feng Chen (陈 峰)
1,
*
1
School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
2
State Key Laboratory of Crystal Materials and Institute of Crystal Materials,
Shandong University, Jinan 250100, China
*Corresponding author: drfchen@sdu.edu.cn
Received October 27, 2018; accepted December 7, 2018; posted online January 29, 2019
Graphene and other extraordinary two-dimensional materials together with recent advances in optical modu-
lators have set the foundations for the widespread applications of next-generation optoelectronic devices. In this
work, we report on the high-performance fundamentally mode-locked waveguide laser modulated by chemical-
vapor-deposition-grown WSe
2
as a saturable absorber. By incorporating a WSe
2
sample into a monolithic
Nd:YVO
4
waveguide platform, 6.526 GHz picosecond pulsed laser generation has been achieved at the wave-
length of 1 μm with pulse duration of 47 ps.
OCIS codes: 160.4236, 140.4050, 140.3540, 230.7370.
doi: 10.3788/COL201917.020013.
Since the discovery of graphene, the emerging two-
dimensional (2D) materials have been the subject of in-
tense research, owing to their distinctive and intriguing
optical properties
[1–5]
. Graphene possesses excellent nonlin-
ear optical properties, e.g., ultrafast relaxation time and
ultrabroadband absorption properties. Based on these,
graphene has been recognized as one of the most effective
optical modulators in ultrafast laser generation
[6,7]
. The in-
tense research of graphene related saturable absorbers
(SAs) has led to a rise of interest in exploring the satur-
able properties, as well as their application in pulsed laser
generation based on many other extraordinary 2D
materials
[8–11]
. As new functional materials for opto-
electronic applications, transition metal dichalc ogenides
(TMDCs), denoted as MX
2
(M: Mo or W and X: S, Se,
or Te), have recently been extensively studied with superb
nonlinear optical properties, such as strong light–material
interaction, broadband optical response, ultrafast recov-
ery time, and controllable optoelectronic properties
[12]
.
With these extraordinary nonlinear optical properties,
TMDCs have been successfully demonstrated to be effi-
cient optical modulators in the regime of Q-switched or
mode-locked lasers within various laser systems, such as
a fiber laser, waveguide laser, and bulk laser
[13–19]
. Among
TMDCs, the most frequently used SAs are MoS
2
and WS
2
.
Tungsten diselenide (WSe
2
) is one of the typical TMDCs
that has been recently discovered with superb nonlinear
saturable absorption properties
[20,21]
. However, the applica-
tion of WSe
2
in laser generation is still at its early age, and
there are limited reports on a 1 μm pulsed laser as well as
waveguide lasers.
Optical waveguides are microstructures in dielectric
materials that could confine light propagation within mi-
croscale volumes
[22,23]
. Based on laser crystals, waveguide
lasers could be realized and have provided a solution to
the problem that has plagued scientists on how to fabri-
cate miniature and functional laser sources in integrated
photonics chips. Compared with conventional laser
sources, waveguide lasers have the advantages of small
size, high stability, and easy integration of other optical
devices, such as fibers. With the tight confinement of
the light field, enhanced lasing performances could be
realized in waveguide structures, such as reduced laser
threshold value and higher slope efficiency. In addition,
the intensity profiles of the emitted laser could be designed
in a controllable way
[24]
. Based on the monolithic wave-
guide configuration, 2D materials have been widely ap-
plied as SAs in both Q-switched and mode-locked lasers
operating in a wide spectral range within diverse laser
systems
[25–28]
.
Multi-gigahertz (GHz) mode-locked lasers have been
the subject of intense research from academics for a large
range of applications in a number of fields, including high-
speed optical communication, frequency comb spectros-
copy, biological imaging, and nonlinear microscopy
[29–31]
.
Particularly, fundamentally mode-locked laser systems
operating with the repetition rate value up to a GHz
are favorable according to the applications in related
fields. Based on the monolithic waveguide platform,
research on the GHz mode-locked lasers is an emerging
and fast-growing field. Based on a graphene SA and a
thulium-doped yttrium aluminum garnet (Tm:YAG)
waveguide, Ren et al. realized 2 μm Q-switched mode
locking with output power of 6.5 mW and pulse rate of
7.8 GHz
[32]
. Mary et al. report on 1.5 GHz graphene
Q-switched mode-locked waveguide lasing with slope
efficiency of 48% at 1039 nm
[33]
. Recently, Thorburn
et al. achieved a graphene-based wa veguide laser with rep-
etition rate of 5.9 GHz and up to 170 mW output power
[34]
.
Most recently, the GHz picosecond waveguide laser
COL 17(2), 020013(2019) CHINESE OPTICS LETTERS February 10, 2019
1671-7694/2019/020013(5) 020013-1 © 2019 Chinese Optics Letters