Characteristics of Plasmonic Bragg Reflectors with Graphene-Based Silicon Grating

Nanoscale Research Letters, Sep 2016

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.

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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)


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Ci Song, Xiushan Xia, Zheng-Da Hu, Youjian Liang, Jicheng Wang. Characteristics of Plasmonic Bragg Reflectors with Graphene-Based Silicon Grating, Nanoscale Research Letters, 2016, pp. 419, Volume 11, Issue 1, DOI: 10.1186/s11671-016-1633-0