Abstract-Modulators for mid-infrared and terahertz light

 

Journal of Applied Physics

Eric Herrmann,  Hua Gao, Zhixiang Huang, Sai Rahul Sitaram, Ke Ma,  Xi Wang, 

(a) Schematic drawing of a hybrid silicon split-ring resonator metasurface pumped by near-infrared femtosecond pulses. (b) Co-polarized transmission efficiency when pumping is ON (red) and OFF (blue). (a) and (b) Reproduced with permission from Cong et al., Light Sci. Appl. 7, 28 (2018). Copyright 2018 Springer Nature. (c) Schematic drawing of germanium-coated aluminum split-ring resonator metasurface on Kapton film, pumped by an 800 nm pulse. (d) THz transmission amplitude through the metasurface for various pump-probe delay times. (c) and (d) Reproduced with permission from Lim et al., Adv. Mater. 30, 1705331 (2018). Copyright 2018 John Wiley and Sons.

https://aip.scitation.org/doi/abs/10.1063/5.0025032

The rise of mid-infrared and terahertz wave technology over the past two decades has led to incredible insights and potential applications for next-generation optoelectronics. Modulators, which control amplitude, phase, and/or polarization of incident light, are widely used in communications, imaging, and sensing and are crucial for further development of technology functioning in the mid-infrared and terahertz frequency regimes. The lack of natural materials with optical responses in these frequency regimes has led to a surge in engineering efforts to create novel devices and architectures for achieving control over the properties of mid-infrared and terahertz radiation. Major efforts in the field have been devoted to studying carrier concentration modulation, liquid crystals, phase-change materials, and micro-electromechanical systems for controlling the light–matter interaction. Although there has been considerable progress in realizing mid-infrared and terahertz modulators, novel approaches are seeking higher modulation speed, more functionality, and miniaturized size. In this perspective, we review the recent advancements of modulators for mid-infrared and terahertz wavelengths. We discuss various modulation mechanisms, along with their relative performance, and consider future architectures to improve upon the current technology for mid-infrared and terahertz modulation.

Abstract-Nonlinearity in the Dark: Broadband Terahertz Generation with Extremely High Efficiency

Ming Fang, Nian-Hai Shen, Wei E. I. Sha, Zhixiang Huang, Thomas Koschny, and Costas M. Soukoulis

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.027401

Plasmonic metamaterials and metasurfaces offer new opportunities in developing high performance terahertz emitters and detectors beyond the limitations of conventional nonlinear materials. However, simple meta-atoms for second-order nonlinear applications encounter fundamental trade-offs in the necessary symmetry breaking and local-field enhancement due to radiation damping that is inherent to the operating resonant mode and cannot be controlled separately. Here we present a novel concept that eliminates this restriction obstructing the improvement of terahertz generation efficiency in nonlinear metasurfaces based on metallic nanoresonators. This is achieved by combining a resonant dark-state metasurface, which locally drives nonlinear nanoresonators in the near field, with a specific spatial symmetry that enables destructive interference of the radiating linear moments of the nanoresonators, and perfect absorption via simultaneous electric and magnetic critical coupling of the pump radiation to the dark mode. Our proposal allows eliminating linear radiation damping, while maintaining constructive interference and effective radiation of the nonlinear components. We numerically demonstrate a giant second-order nonlinear susceptibility $\sim {10}^{-11}m/V$, a one order improvement compared with the previously reported split-ring-resonator metasurface, and correspondingly, a 2 orders of magnitude enhanced terahertz energy extraction should be expected with our configuration under the same conditions. Our study offers a paradigm of high efficiency tunable nonlinear metadevices and paves the way to revolutionary terahertz technologies and optoelectronic nanocircuitry.

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Abstract-Maxwell-Hydrodynamic Model for Simulating Nonlinear Terahertz Generation from Plasmonic Metasurfaces

Ming Fang, Zhixiang Huang, Wei E. I. Sha, Xianliang Wu

(Submitted on 18 Sep 2017)

https://uk.arxiv.org/abs/1709.05735

The interaction between the electromagnetic field and plasmonic nanostructures leads to both the strong linear response and inherent nonlinear behavior. In this paper, a time-domain hydrodynamic model for describing the motion of electrons in plasmonic nanostructures is presented, in which both surface and bulk contributions of nonlinearity are considered. A coupled Maxwell-hydrodynamic system capturing full-wave physics and free electron dynamics is numerically solved with the parallel finite-difference time-domain (FDTD) method. The validation of the proposed method is presented to simulate linear and nonlinear responses from a plasmonic metasurface. The linear response is compared with the Drude dispersion model and the nonlinear terahertz emission from a difference-frequency generation process is validated with theoretical analyses. The proposed scheme is fundamentally important to design nonlinear plasmonic nanodevices, especially for efficient and broadband THz emitters