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Abstract
Manipulating optical signals in the mid-infrared (mid-IR) range is a highly desired task for applications in chemical sensing, thermal imaging, and subwavelength optical waveguiding. To guide highly confined mid-IR light in photonic chips, graphene-based plasmonics capable of breaking the optical diffraction limit offer a promising solution. However, the propagation lengths of these materials are, to date, limited to approximately 10 µm at the working frequency f = 20 THz. In this study, we proposed a waveguide structure consisting of multilayer graphene metamaterials (MLGMTs). The MLGMTs support the fundamental volume plasmon polariton mode by coupling plasmon polaritons at individual graphene sheets over a silicon nano-rib structure. Benefiting from the high conductivity of the MLGMTs, the guided mode shows ultralow loss compared with that of conventional graphene-based plasmonic waveguides at comparable mode sizes. The proposed design demonstrated propagation lengths of approximately 20 µm (four times the current limitations) at an extremely tight mode area of 10−6 A0, where A0 is the diffraction-limited mode area. The dependence of modal characteristics on geometry and material parameters are investigated in detail to identify optimal device performance. Moreover, fabrication imperfections are also addressed to evaluate the robustness of the proposed structure. Moreover, the crosstalk between two adjacent present waveguides is also investigated to demonstrate the high mode confinement to realize high-density on-chip devices. The present design offers a potential waveguiding approach for building tunable and large-area photonic integrated circuits.
Highlights
Significant enhancements achieved in light–matter interactions, nonlinear optical effects, chemical and biological sensing sensitivities, and resolution in imaging and spectroscopy can further benefit from the localization of light waves in deep subwavelength sizes
We propose a high-performance graphene plasmonic waveguides (GPWs) based on multilayer graphene metamaterials (MLGMTs) [43,44] on a Si nano-rib waveguide partially covered by a lowindex porous SiO2 film
The structure consists of a porous layer sandwiched by MLGMTs, which are formed by alternating graphene–dielectric layers, and a Si nano-rib which are formed alternating graphene–dielectric layers,Here, and a the
Summary
Significant enhancements achieved in light–matter interactions, nonlinear optical effects, chemical and biological sensing sensitivities, and resolution in imaging and spectroscopy can further benefit from the localization of light waves in deep subwavelength sizes. The most promising approach to achieve this goal is to excite surface plasmon polaritons (SPPs) [1] by coupling photons and free electrons at metal–dielectric interfaces. Alternative metallic materials are necessary because of the weak confinement of SPP modes in conventional noble metals for mid-IR and terahertz (THz) bands [6,7]. Graphene is considered a promising candidate for SPP waveguiding in the mid-IR [6,7,9,11,12] and THz [9,12] ranges because of its nearly pure imaginary surface conductivity and extreme light confinement. The real and imaginary parts of the surface conductivity of graphene characterize the ohmic loss and magnitude of the wavevector, respectively. At the spectral bands of mid-IR and THz, the real part of Nanomaterials 2021, 11, 2981.
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