Fabrication and application of a graphene polarizer
with strong saturable absorption
Weixiong Li,
1
Lilin Yi,
1,
* Ran Zheng,
1
Zhenghua Ni,
2
and Weisheng Hu
1
1
The State Key Lab of Advanced Optical Communication Systems and Networks, Shanghai Jiao Tong University,
Shanghai 200240, China
2
Department of Physics, Southeast University, Nanjing, China
*Corresponding author: lilinyi@sjtu.edu.cn
Received October 20, 2015; revised December 8, 2015; accepted December 21, 2015;
posted December 23, 2015 (Doc. ID 252307); published February 26, 2016
By transferring 100 nm gold-coated CVD monolayer graphene onto the well-polished surface of D-shaped fiber, we
achieve a graphene in-line polarizer with a high polarization extinction ratio of ∼27 dB and low insertion loss
of 5 dB at 1550 nm, meanwhile achieving a strong saturable absorption effect of 14%. The manufacture of this
graphene in-line polarizer also simplifies the graphene transfer process. To explore the potential applications of
the new device, we also demonstrate noise-like pulse generation and supercontinuum spectrum generation. By
launching the designed graphene device into a fiber ring laser cavity, 51 nm bandwidth noise-like pulse is
obtained. Then, launching the high-power noise-like pulse into high nonlinear fiber, a 1000 nm wide supercon-
tinuum spectrum is obtained, which is favorable for sensing and nonlinearities scientific fields. © 2016 Chinese
Laser Press
OCIS codes: (060.3510) Lasers, fiber; (140.4050) Mode-locked lasers.
http://dx.doi.org/10.1364/PRJ.4.000041
1. INTRODUCTION
Graphene has shown its outstanding performance as a satu-
rable absorber (SA) in mode-locked fiber lasers, which is
attributed to its wavelength-independent saturable absorp-
tion, easy combination with fiber, and low cost fabrication.
Soliton [1–4], stretched pulse [5], and dissipative soliton [6],
which are three main types of pulse in mode-locked fiber
lasers, have been generated using a graphene-based SA.
Besides, a graphene-based in-line fiber polarizer is also an
attractive research interest [7]. A graphene in-line polarizer
based on side-polished D-shaped fiber with a 27 dB polariza-
tion extinction ratio in the telecommunication band has been
demonstrated by the strong s-polarization effect of graphene.
However, the saturable absorption effect of the sample is not
characterized. Thus, we reach a conclusion that a fine de-
signed graphene fiber device can act as an SA and an in-line
polarizer.
We propose to transfer a gold-coated chemical vapor dep-
osition (CVD) monolayer graphene onto a moderate-polished
D-shaped fiber to achieve a graphene based in-line polarizer
and SA. First, by decreasing the polish depth to 6 um to the
core center, the insertion loss (IL) of the D-shaped fiber itself
is reduced to about 8 dB; meanwhile, the polarization depen-
dent loss (PDL) is only 1 dB. Then, by transferring a 100 nm
thick gold-coated graphene layer onto the polished surface of
the D-shaped fiber, the IL is reduced to 5 dB and the PDL is
increased to ∼27 dB; meanwhile, the saturable absorption
depth is measured to be 14%. The benefits of the solution
are summarized as follows: (1) the IL of the graphene device
is greatly decreased; (2) the PDL of the component is in-
creased; (3) the in-line graphene polarizer shows strong
saturable absorption effect due to the confinement of the
optical field by metal cover; (4) the graphene transfer process
is simplified, and the reliability of the component is also
improved because no polymethyl methacrylate (PMMA) or
resolvable stamp is used as in the traditional graphene trans-
fer process.
For seeking the potential application in optical systems,
we demonstrate the noise-like pulse generation using the
graphene-based polarizer and SA as a multifunctional mode-
locker. Besides, a demonstration of 1000 nm wide supercon-
tinuum (SC) generation is shown by the noise-like pulse we
have achieved. We hope that the new polarizing graphene
SA could play versatile roles in optics fields.
2. FABRICATION OF THE DEVICE
A. Graphene Mode-Locker Fabrication and
Characterization
D-shape fiber fabrication: We bent the single-mode fiber
(SMF) and embedded it into a glass substrate; then, we pol-
ished the glass substrate with a resolution of 1 μm. This proc-
ess ensures the polished surface is ultraflat. We monitor the IL
of the D-shaped fiber to ensure a value less than 10 dB during
the polishing process. The fabricated D-shaped fiber is with a
polished depth of 6 μm to the core center and polished length
of about 1 cm, corresponding to the IL of ∼8 dB. The radius of
curvature is long enough to not achieve the cut-off boundary
of TE
0
mode near 1550 nm wavelength, and the disclosing part
is called the evanescent field. With the graphene layer coated,
the evanescent field is enhanced because of the graphene ab-
sorption. With the graphene/gold layer coated, the evanescent
field becomes moderate because no C L band light beam
will propagate in a gold layer, the mode distribution is sup-
pressed in the fiber and the graphene layer; thus, the loss de-
creases. The side-view and cross-section of the D-shaped fiber
are showed in Figs. 1(a) and 1(b), respectively. Figure 2(a)
Li et al. Vol. 4, No. 2 / April 2016 / Photon. Res. 41
2327-9125/16/020041-04$15.00/0 © 2016 Chinese Laser Press