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

Abstract

High input intensities are usually required to efficiently excite optical nonlinear effects in ultrathin structures due to their extremely weak nature. This problem is particularly critical at low 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, as a result, can be used to realize efficient third-order nonlinear 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.

Recent Advances in Terahertz Photonic Technologies Based on Graphene and Their Applications

“…By calculating the third harmonic and four‐wave mixing (FWM) output power under different scenarios, as shown in Figure 4b,d, respectively, it was demonstrated that the THG and FWM output powers of the proposed graphene‐covered hybrid metamaterial grating are much higher compared with the cases when graphene was not present. [ 98 ] It was also found that the nonlinear response remains relatively insensitive across a broad range of incident angles in this configuration. The enhanced omnidirectional nonlinear response of these hybrid graphene–plasmonic structures can be used in several promising applications, including THz frequency generators, all‐optical signal processors, wave mixers, as well as nonlinear THz spectroscopy and noninvasive THz subwavelength imaging devices.…”

“…In this case, the third harmonic was generated in reflection, which led to even higher nonlinear conversion efficiencies. [ 98 ] This structure was composed of a conventional plasmonic grating with graphene placed on top of it. High THG conversion efficiency was obtained (≈18%) using low input intensities, benifiting from the robust localization and enhancement of the electric field within the trenches of the plasmonic grating.…”

Far‐Field Excitation of Acoustic Graphene Plasmons with a Metamaterial Absorber

“…The potential applications range from ultracompact tunable metamaterials and ultrasensitive infrared spectroscopies to single‐molecule optics, quantum plasmonics, and others. [ 56 ]…”

Review on Graphene-based Absorbers for Infrared to Ultraviolet Frequencies

“…Graphene gold grating-based THz absorber Guo et al reported a hybrid graphene gold grating-based design to obtain improved nonlinear eects in the THz frequency range [88]. The design is presented in Fig.…”