Active Control of Electromagnetically Induced Transparency Analog in Terahertz MEMS Metamaterial

Abstract

541wileyonlinelibrary.com COMMUNICATIONand their possible applications. The ultimate form of active manipulation of EIT phenomenon will be when all three primary parameters are controlled independently. The independent control of individual resonators demands for the controllability at unit cell level, and conventional approaches such as optical pumping of photoconductive elements or thermally controlled superconductor are restricted to provide only global control.Recently, microelectromechanical systems (MEMS) based tunable metamaterials have been reported to achieve controllability at unit cell level, along with the added advantage of being electrically controlled, miniaturized size and enhanced electrooptic performance. The versatility of MEMS design has enabled active manipulation of numerous THz properties such as magnetic resonance, [19][20][21][22] electrical resonance, [23][24][25] anisotropy, [ 26 ] broadband response, [ 27 ] isotropic resonance switching [ 28 ] multiresonance switching, [29][30][31] and coupling strength between resonators. [ 32 ] The enhanced controllability and direct integration of MEMS actuators into metamaterial unit cell geometry is an ideal fi t for the realization of selective control of coupled mode resonators. In this Communication, reconfi gurable metamaterial with independently controlled bright and dark mode resonators is proposed for advanced manipulation of the classical analog of EIT and slow light effects in THz spectral region. The active control of bright mode resonator enables modulation of EIT intensity, while the tuning of dark mode resonance causes the EIT peak to tune in frequency. Furthermore, simultaneous switching of bright and dark mode resonators results in dynamic switching of the system between coupled and uncoupled states. The proposed approach of selective reconfi guration can be scaled for multiresonator systems, which can be coupled either through inductive, capacitive, or conductive means.The metamaterial consists of 80 × 80 periodic array of cut wire resonator (CWR) with closely placed split ring resonators (SRRs), as shown in Figure 1 and Figure 2 . The periodicity of unit cell is 100 µm along both axial directions. The CWR has length, l C = 60 µm and width, w C = 5 µm, respectively. The SRRs have a base length, b S = 30 µm, side length, l S = 20 µm, and split gap, g S = 4 µm. The SRRs are placed at a distance of S = 2 µm from the CWR. When the polarization of the excitation fi eld is along the CWR arm, the dipole mode resonance of the CWR will be the bright mode and the inductive-capacitive (LC) mode of SRR resonance acts as the dark mode. Thus for the incident THz polarization, the direct excitation of the bright mode induces image charges on the nearby SRRs through nearfi eld inductive coupling, thereby exciting the LC resonance of the SRRs. These bright-dark resonances have contrasting line widths with identical resonance frequencies and under a strong coupling regime they experience an EIT-type of interference that gives rise to a sharp transm...

Ultrathin tunable terahertz absorber based on MEMS-driven metamaterial

“…Although a number of THz tunable transmission filters based on MEMS-driven metamaterials have been demonstrated [19][20][21][22][23][24][25][26][27][28][29][30][31] , the realization of a high-performance MEMS-driven tunable THz absorber is still challenging, and only a limited number of demonstrations have been reported so far 32 . This low number is primarily due to the severe mismatch between the actuation range of most MEMS (on the scale of 1-10 μm) and THz wavelengths on the scales of 100-1000 μm.…”

Plasmonic metalens based on coupled resonators for focusing of surface plasmons

“…For any holographic design, it is desired to have reconfigurable hologram44. Here the proposed design possesses the promising possibility for reconfigurable focusing spot, since the EIT effect could be externally controlled by integrating tunable materials as part of the unit elements354546, or directly varying the relative geometric positions using microelectromechanical system4748.…”

All-integrated terahertz modulators

“…As these resonances are fundamentally based on the structural dimensions of the metamaterial pattern, physically changing the shape of the resonant components in these arrays has a strong effect on the resonance conditions. MEMS have been used to physically alter the resonant components of individual unit cells in metamaterials, leading to the realization of active, electronically tunable THz devices [58][59][60][61][62]. MEMS are advantageous, as unit cells can be individually addressed electronically, increasing the range of tuning parameters.…”

“…When a bias is applied, an electrostatic attractive force causes them to straighten towards the substrate due to the high surface area-to-volume ratio, allowing for the electrical tuning of the metamaterial shape. This tuning method is used by Pitchappa et al [58] to independently tune the dark mode and the bright mode of a metamaterial resonator for electromagnetically induced transparency (EIT). This device employs a cut wire resonator (CWR), supporting a bright mode with a broad resonance at around 0.55 THz, and two SRRs (dark mode) with a sharper resonance at 0.55 THz, which can be excited by the CWR.…”

“…However, even though the resonant modes supported by gratings [75] and anti-dot arrangements [76] have a tunable frequency dispersion, they typically yield limited modulation depths (<10%), making these approaches not viable for the building of an efficient modulation platform. Other elegant methods rely on the optical interplay between dark and bright modes in more complex metamaterial architectures, reminiscent of the electromagnetically induced transparency [58,78].…”