All-optical modulator based on MoS
2
-PVA thin film
Yifang Wang (王奕方), Kan Wu (吴 侃)*, and Jianping Chen (陈建平)
State Key Laboratory of Advanced Optical Communication Systems and Networks, Departm ent of Electronic
Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
*Corresponding author: kanwu@sjtu.edu.cn
Received October 2, 2017; accepted November 10, 2017; posted online January 31, 2018
The all-optical approach plays an important role in ultrafast all-optical signal processing, and the all-fiber
scheme has a wide application in optical communications. In this letter, we investigate an all-optical modulator
using few-layer molybdenum disulfide (MoS
2
)-polyvinyl alcohol (PVA) thin films based on the thermo-optic
effect and obtain a long-time stable modulated output by applying polarization interference. By absorbing
the injected 980 nm pump (control light), MoS
2
generates heat, changes the refractive index of MoS
2
, and mod-
ulates the polarization of light. The obtained thermal all-optical modulator has a rise time of 526 μs.
OCIS codes: 230.1150, 160.4330, 130.4815, 060.5060.
doi: 10.3788/COL201816.020003.
Since the discovery of graphene in 2004, two-dimensional
(2D) materials have attracted widespread attention
[1–3]
.
Many researchers have investigated novel optoelectronic
devices based on graphene, including optical modula-
tors
[4,5]
, switches
[6]
, and polarizers
[7]
. In recent years, other
kinds of 2D materials, including transition metal dichalco-
genides (TMDs), topological insulators (TIs)
[8,9]
, and
black phosphorus (BP)
[10–12]
have also been investigated.
In particular, TMDs have become a research hotspot due
to their similar photonic and electronic properties
[13–15]
,
including high optical nonlinearity
[16]
and saturable
absorption
[17,18]
. Many researchers have demonstrated
the applications of these TMDs as saturable absorbers
in Q-switched fiber lasers and mode-locked fiber lasers
[17,19]
.
Meanwhile, the all-optical scheme plays an important
role in optical communications, including all-optical
modulation, routing, and sensing. There have been some
demonstrations of all-optical modulators and phase shift-
ers based on graphene
[4–6]
. Recently, an all-optical phase
shifter near 1550 nm using few-layer 2D material tungsten
disulfide (WS
2
) deposited on a tapered fiber has been
reported
[20]
.Wuet al. demonstrate an all-optical switch by
embedding the phase shifter into one arm of a fiber Mach–
Zehnder interferometer (MZI) with good control efficiency
and high extinction ratio. However, the fiber MZI struc-
ture makes the device sensitive to the environmental
perturbation.
In this work, we demonstrate a fiber all-optical modu-
lator using few-layer molybdenum disulfide (MoS
2
)-
polyvinyl alcohol (PVA) thin films. The device is based
on polarization interference in an optical fiber, and the
thermo-optic effect of MoS
2
-PVA thin film is utilized as
a control mechanism. By absorbing the pump at
980 nm, MoS
2
generates heat, changes the refractive index
of the MoS
2
-PVA thin film, and modifies the polarization
of the incident light at 1550 nm. The demonstrated all-
optical modulator has a rise time of 526 μs. Since all
the control and signal beams propagate in the same
fiber, the environmental perturbation, e.g., air flow and
temperature change, indu ces common mode disturbance
and has very weak influence on the device operation.
Thus, our device is less sensitive to the environmental per-
turbation compared to the MZI structure. The filmy MoS
2
also provides advantages in the practical applications due
to its compactness. The device based on MoS
2
-PVA thin
film proves the potential of 2D TMDs for all-optical signal
processing devices.
A high-quality MoS
2
-PVA thin film is the key compo-
nent in the all-optical modulator, which provides signifi-
cant flexibility in practical applications. By using the
liquid-phase exfoliation (LPE) method
[19]
,MoS
2
-PVA
water dispersions with sodium cholate (SC, as a surfac-
tant) are prepared. The detailed preparation of MoS
2
dis-
persions can be referred to Ref. [
19]. The transmission
electron microscope (TEM) image of MoS
2
nanosheets
is shown in Fig.
1(a).MoS
2
nanosheets with the size of
Fig. 1. (a) TEM image of MoS
2
nanosheets in the dispersions,
(b) MoS
2
-PVA film transferred onto a fiber end, inset:
MoS
2
-PVA thin film, and (c) transmission spectrum of
MoS
2
-PVA thin film.
COL 16(2), 020003(2018) CHINESE OPTICS LETTERS February 10, 2018
1671-7694/2018/020003(4) 020003-1 © 2018 Chinese Optics Letters