Characteristics of Plasmonic Bragg Reflectors with Graphene-Based Silicon Grating
Song et al. Nanoscale Research Letters
Characteristics of Plasmonic Bragg Reflectors with Graphene-Based Silicon Grating
Ci Song 1
Xiushan Xia 1
Zheng-Da Hu 1
Youjian Liang 1
Jicheng Wang 0 1
0 Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences , 912, Beijing 100083 , China
1 School of Science, Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, Jiangnan University , Wuxi 214122 , China
We propose a plasmonic Bragg reflector (PBR) composed of a single-layer graphene-based silicon grating and numerically study its performance. An external voltage gating has been applied to graphene to tune its optical conductivity. It is demonstrated that SPP modes on graphene exhibit a stopband around the Bragg wavelengths. By introducing a nano-cavity into the PBR, a defect resonance mode is formed inside the stopband. We further design multi-defect PBR to adjust the characteristics of transmission spectrum. In addition, through patterning the PBR unit into multi-step structure, we lower the insertion loss and suppress the rippling in transmission spectra. The finite element method (FEM) has been utilized to perform the simulation work.
Plasmonics; Bragg reflectors; Graphene-based; FEM
-
Background
Surface plasmon polaritons (SPPs) are surface waves that
propagate along the boundary surface between dielectric
and metallic materials with fields decaying exponentially in
both sides, thereby creating the subwavelength confinement
of electromagnetic waves [1]. These are mainly
electromagnetic modes resulting from the resonant interaction
between light waves and the collective electron oscillations,
which leads to its unique properties [2]. Plasmonic
nanostructures offer the potential to overcome diffraction limits
in dielectric structures, enabling us to miniaturize optical
devices [3]. For example, plasmonic has been widely
researched in integrated photonic circuits [4], photonic
crystals [5], optical antennas [6, 7], nano-laser [8], data
recording [9], filters [10], refractive index sensor [11],
biological sensors [12], metalens [13], plasmonic lens [14], and
so forth. Among the structures based on SPPs, the
metalinsulator-metal (MIM) structure has been investigated
extensively in designing plasmonic Bragg reflector. For
example, periodic changes in the dielectric materials of the
MIM waveguides have been proposed to design effective
filtering around the Bragg frequency [15]; the
thickmodulated and index-modulated Bragg reflectors have been
reported to widen bandgap [16]; metal-embedded MIM
structure also has been studied to improve the performance
of conventional step profile MIM plasmonic Bragg
reflectors (PBRs) [17]. However, plasmonic materials, usually
noble metals, are hardly tunable and have great ohmic
losses at the wavelength regimes of interest, therefore
limiting their potential for some specific applications.
Graphene, a single layer of carbon atoms densely
arranged into a honeycomb pattern, has been widely explored
as a newly alternative to plasmonic material [18, 19].
Graphene plasmonics, similar to metal plasmonics at the visible
region, can be easily induced in the near-infrared to
terahertz (THz) regime. In particular, the surface charge
density, namely chemical potential, can be actively modified by
chemical doping or external gate voltage, thus giving rise to
dramatic changes in the optical properties [20].
Additionally, SPPs bound to graphene display a strong field
confinement, already verified by experiments [21, 22]. These
remarkable and outstanding properties in turn enable a
utility optical material in optoelectronic applications. In
recent years, great attention has been focused on
graphenebased plasmonic waveguides [23–27]. de Abajo et al. have
researched the propagation properties of graphene
plasmonic waveguide constituted by individual and paired
© 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.
nanoribbons [28]. The tunable nano-modulators based on
graphene plasmonic waveguide modulators have been
proposed and numerically demonstrated [29]. Lu et al. have
designed a slow-light waveguide based on graphene and
silicon-graded grating [30]. Wang et al. have utilized a
graphene waveguide achieving a tunable plasmonic Bragg
reflector [31].
In this paper, we propose a PBR structure consisting of a
single-layer graphene and silicon grating and numerically
study its performance. We employ a silica spacer layer to
separate the monolayer graphene and silicon grating and
an external voltage gating to tune the surface conductivit (...truncated)