Abstract-Hybrid Graphene-Plasmonic Gratings to Achieve Enhanced Nonlinear Effects at Terahertz Frequencies

Tianjing Guo, Boyuan Jin, and Christos Argyropoulos

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.11.024050

High input intensities are usually required to efficiently produce nonlinear optical effects in ultrathin structures due to their extremely weak nature. This problem is particularly critical at low terahertz frequencies because high-input-power terahertz sources are not available. The demonstration of enhanced nonlinear effects at terahertz frequencies is particularly important since these nonlinear mechanisms promise to play a significant role in the development and design of new reconfigurable planar terahertz nonlinear devices. In this work, we present an alternative class of ultrathin nonlinear hybrid planar terahertz devices based on graphene-covered plasmonic gratings exhibiting very large nonlinear response. The robust localization and enhancement of the electric field along the graphene monolayer, combined with the large nonlinear conductivity of graphene, can lead to boosted third-harmonic-generation and four-wave-mixing nonlinear processes at terahertz frequencies. These interesting nonlinear effects exhibit very high nonlinear conversion efficiencies and are triggered by realistic input intensities with relatively low values. In addition, the third-harmonic-generation and four-wave-mixing processes can be significantly tuned by the dimensions of the proposed hybrid structures, the doping level of graphene, or the input intensity, whereas the nonlinear radiated power remains relatively insensitive to the incident angle of the excitation source. The nonlinear hybrid graphene-covered plasmonic gratings presented have a relative simple geometry and, as a result, can be used to realize efficient third-order nonlinear terahertz effects with a limited fabrication complexity. Several new nonlinear terahertz devices are envisioned on the basis of the proposed hybrid nonlinear structures, such as frequency generators, all-optical signal processors, and wave mixers. These devices are expected to be useful for nonlinear terahertz spectroscopy, noninvasive terahertz subwavelength imaging, and terahertz communication applications.

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Abstract-Hybrid Graphene-Plasmonic Gratings to Achieve Enhanced Nonlinear Effects at Terahertz Frequencies

Tianjing Guo, Boyuan Jin, Christos Argyropoulos

https://arxiv.org/abs/1809.08194

High input intensities are usually required to efficiently excite optical nonlinear effects in ultrathin structures. This problem is particularly critical at terahertz (THz) frequencies because high input power THz sources are not available. The demonstration of enhanced nonlinear effects at THz frequencies is particularly important since these nonlinear mechanisms promise to play a significant role in the development and design of new reconfigurable planar THz nonlinear devices. In this work, we present a novel class of ultrathin nonlinear hybrid planar THz devices based on graphene-covered plasmonic gratings exhibiting very large nonlinear response. The robust localization and enhancement of the electric field along the graphene monolayer, combined with the large nonlinear conductivity of graphene, can lead to boosted third harmonic generation (THG) and four-wave mixing (FWM) nonlinear processes at THz frequencies. These interesting nonlinear effects exhibit very high nonlinear conversion efficiencies and are triggered by realistic input intensities with relative low values. In addition, the THG and FWM processes can be significantly tuned by the dimensions of the proposed hybrid structures, the doping level of graphene, or the input intensity values, whereas the nonlinear radiated power remains relatively insensitive to the incident angle of the excitation source. The presented nonlinear hybrid graphene-covered plasmonic gratings have a relative simple geometry and can be used to realize efficient third-order THz effects with a limited fabrication complexity. Several new nonlinear THz devices are envisioned based on the proposed hybrid nonlinear structures, such as frequency generators, all-optical signal processors, and wave mixers. These devices are expected to be useful for nonlinear THz spectroscopy, noninvasive THz subwavelength imaging, and THz communication applications.

Abstract-Nonlinear graphene metasurfaces with advanced electromagnetic functionalities

Boyuan Jin; Christos Argyropoulos,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10722/107221R/Nonlinear-graphene-metasurfaces-with-advanced-electromagnetic-functionalities/10.1117/12.2319878.short?SSO=1


The optical nonlinear effects can provide different advanced electromagnetic functionalities, such as wave mixing and phase conjugation, which can be applied in a variety of new applications. However, these effects usually suffer from extremely weak nature and require high input intensity values in order to be excited. Interestingly, the large third order nonlinearity of graphene, along with the strong field confinement stemming from its plasmonic behavior, can be utilized to enhance several relative weak nonlinear effects at infrared (IR) and terahertz (THz) frequencies. Towards this goal, various nonlinear graphene metasurfaces are presented in this work to effectively increase the efficiency of different optical nonlinear effects and, as a result, decrease the required input intensity needed to be excited. In particular, we will show that the efficiency of four-wave mixing (FWM) can be improved by several orders of magnitude by using a nonlinear metasurface composed of patterned graphene ribbons, a dielectric interlayer, and a metallic reflector acting as substrate. We also demonstrate that the self-phase modulation (SPM) nonlinear process can be enhanced by using an alternative graphene nonlinear metasurface, operating as coherent perfect absorber, leading to a pronounced shift in the resonant frequency of the coherent perfect absorption (CPA) effect of this structure as the input intensity of the impinging incident waves is increased. This property will provide a robust mechanism to dynamically tune and switch the CPA process. Furthermore, it will be presented that strong negative reflection and refraction can be achieved by a single graphene monolayer film due to the enhancement of another nonlinear process, known as phase conjugation. This nonlinear process is envisioned to be used in the construction of a perfect imaging device with subwavelength resolution.