All‐Optical and Ultrafast Tuning of Terahertz Plasmonic Metasurfaces

Abstract

controlling, [3] metalens, [4] and so on. Among these metasurfaces, noble metals such as gold and silver are the most common candidates for electromagnetic resonance, such as split-ring resonators, [5,6] cut wire antennas, [7] and fishnet structures. [8] Nevertheless, the metallic structures suffer from not only intrinsic absorption losses that severely limit their efficiency, but also their permanent optical properties which are difficult to be tuned by external stimuli. A feasible way to solve these problems is to employ tunable metasurfaces consisting of active media. Many kinds of active metasurfaces have been reported, including graphene, [9][10][11] transparent conducting oxides, [12] as well as various semiconductors like Si, [13,14] InAs, [15] and GaAs. [16,17] With the rapid development of active metasurfaces, numerous studies have been focused on the modulation of terahertz (THz) waves. Considerable research efforts have been devoted to the dynamic tuning of THz waves using different stimuli, such as thermal heating, [18] electrical triggering, [19] and optical excitation. [20] While intensive amplitude, phase, and polarization control of the terahertz waves have been investigated by plenty of research, achieving ultrafast and efficient modulation remains an open challenge in the THz regime. Graphene has been widely used to form plasmonic metasurfaces, as it is capable of tuning THz waves by optical pumping and electrostatic gating. [21,22] Nonetheless, the electronic doping of graphene reduces the modulation speed, and the low absorption of light due to its monolayer feature limits the modulation depth. GaAs and Si have been demonstrated to control THz waves using all-optical-induced free carrier (FC) dynamics in the semiconductors, respectively. [16,23] But the delay of photoexcited FCs is relatively long (≈1 ns) in these intrinsic semiconductors, which is an essential limitation for ultrafast modulation. More recently, hybrid metasurfaces, by integrating an ultrathin layer of spin-coated solution-processed perovskite with metallic resonators, achieved ultrafast all-optical switching with a time constant of 500 ps. [24,25] However, the photoactivity of the solution-processed perovskite is weak as the differential transmission under femtosecond pulse excitation is only about 5%. A detailed analysis of the previous THz tunable metasurfaces can be found in Table S1 in the Supporting Information.As the backbone of modern technology, Si not only plays a dominant role in electronics, but also emerges as an excellent Metasurfaces have been widely used to manipulate terahertz waves due to their great potential for achieving unique electromagnetic responses. However, to realize ultrafast and efficient control of the light in active metasurfaces is still a critical challenge. Here, an ultrafast tunable metasurface which consists of ion-implanted and annealed silicon disk array is experimentally demonstrated in the terahertz range. By utilizing the optical-pump terahertz-probe spectroscopy, the absolute transmis...

Terahertz Biochemical Molecule‐Specific Sensors

“…[4,61] Slot type antennas are more advantageous for THz sensing than rod type dipole antennas, especially with regard to the empty volume in the middle of the slot that can be filled with molecular samples such as particles or solvents. [67,68] An active metamaterial is one that changes its performance by means of optical, thermal stimulation, or applied voltage/current. [62] On the one hand, structures much smaller than wavelengths have been known to have difficulty interacting with light due to the diffraction limit.…”

A Review of THz Modulators with Dynamic Tunable Metasurfaces

“…To avoid inevitable absorption losses caused by metallic structures, the metasurfaces of the semiconductors have been heavily investigated. Noble semiconductors, such as GaAs [45,46], Si [47,48,49] and InAs [50], are the most common candidates among the dielectric metasurfaces. Yang et al proposed a transient GaAs metasurface that can achieve a wide modulation band of the dipole resonance from 0.5 to 2 THz by controlling the carrier density of GaAs [45].…”

Ultrafast and Broadband Terahertz Modulator With Polarization Selectivity

“…where ε ∞ is the high frequency dielectric constant and ε Si , ∞ = 11.7, τ d = 80 fs is the Drude model carrier scattering rate [20], the plasma frequency of Si is expressed as:…”

“…To date, some ultrafast THz modulators have been demonstrated based on the hybrid semiconductor/metasurface or semiconductor plasmonic metasurfaces, like incorporating the organicinorganic hybrid lead halide perovskites MAPbI 3 into the split-ring resonators (SRRs) [14], combining the ErAs/GaAs superlattices [15] or the radiation-damaged Si [16] with the SRRs, utilizing photonic crystal based on GaAs [17], integrating asymmetric SRRs with Ge [18] or MoS 2 [19], and employing Si [20] or GaAs [21] plasmonic structures. Ultrafast switch on of modulation is triggered by photo-doping the under lying semiconductor film or structure using a femtosecond laser pulse.…”