Reconfigurable terahertz switch using flexible L-shaped metamaterial

Microelectromechanical System-Based Reconfigurable Terahertz Metamaterial for Polarization Filter, Switch, and Logic Modulator Applications

The terahertz (THz) metamaterials integrated with microelectromechanical systems (MEMS) have led to the realization of dynamic control in amplitude, phase, polarization, and spin angular momentum of the THz wave. In this study, we demonstrate an MEMS-based reconfigurable THz metamaterial (RTM) composed of a split ring resonator (SRR) for real-time modulation of THz wave. By gradually increasing the polarization angle of the incident THz wave, the resonant frequency of SRR switches from 0.74 to 1.16 THz, and the maximum modulation depth is more than 70%. When the MEMS-based RTM is actuated by different DC bias voltages, the polarization-dependent transmission intensity and resonant frequency of the device can be actively tuned. MEMS-based RTM shows logical function characteristics that can be used for logic modulators by performing the driving voltages and polarization states as 2-bit input signals and quantizing the transmission response as "on" and "off" states. The logic gates of "NAND" are at 0.439 THz and "AND" is at 0.732 THz. These results offer potential applications for the proposed MEMS-based RTM in tunable and reconfigurable polarization filters, optical switches, programmable logic modulators, and so on.

Terahertz spin-selective perfect absorption enabled by quasi-bound states in the continuum

Spin-selective absorption is broadly applicable to numerous photonic devices. Here, based on a stereoscopic full metallic resonator array, a terahertz chiral metasurface with a single-layer structure is proposed and numerically demonstrated. By employing the coupled-mode theory, we demonstrate that the chiral metasurface can near-perfectly absorb one circularly polarized wave in the quasi-bound states in the continuum-induced critical coupling region but non-resonantly reflect its counterparts. Interestingly, the linewidths and handedness of the proposed chiral metasurface can be flexibly controlled by an in-plane symmetry perturbation. Our designs might offer an alternative strategy to develop chiral metasurfaces apart from conventional methods and might stimulate many potential applications for emerging terahertz technologies.

Design of Tunable Terahertz Metamaterial Sensor with Single- and Dual-Resonance Characteristic

We present two types of refractive index sensors by using tunable terahertz (THz) metamaterial (TTM) based on two concentric split-ring resonators (SRRs) with different splits. By modifying the distance between SRRs and substrate, TTM shows tunable single- and dual-resonance characteristic. The maximum tuning range of resonance is 0.432 THz from 0.958 THz to 1.390 THz. To demonstrate a great flexibility of TTM in real application, TTM device is exposed on the surrounding ambient with different refractive index (n). The sensitivity of TTM can be enhanced by increasing SRR height, which is increased from 0.18 THz/RIU to 1.12 THz/RIU under the condition of n = 1.1. These results provide a strategy to improve the sensing performance of the metamaterial-based sensing device by properly arranging the geometric position of meta-atoms. The proposed TTM device can be used for tunable filters, frequency-selective detectors, and tunable high-efficiency sensors in the THz frequency range.

Tunable Terahertz Metamaterial with Electromagnetically Induced Transparency Characteristic for Sensing Application

We present and demonstrate a MEMS-based tunable terahertz metamaterial (TTM) composed of inner triadius and outer electric split-ring resonator (eSRR) structures. With the aim to explore the electromagnetic responses of TTM device, different geometrical parameters are compared and discussed to optimize the suitable TTM design, including the length, radius, and height of TTM device. The height of triadius structure could be changed by using MEMS technique to perform active tunability. TTM shows the polarization-dependent and electromagnetic induced transparency (EIT) characteristics owing to the eSRR configuration. The electromagnetic responses of TTM exhibit tunable characteristics in resonance, polarization-dependent, and electromagnetically induced transparency (EIT). By properly tailoring the length and height of the inner triadius structure and the radius of the outer eSRR structure, the corresponding resonance tuning range reaches 0.32 THz. In addition to the above optical characteristics of TTM, we further investigate its potential application in a refraction index sensor. TTM is exposed on the surrounding ambient with different refraction indexes. The corresponding key sensing performances, such as figure of merit (FOM), sensitivity (S), and quality factor (Q-factor) values, are calculated and discussed, respectively. The calculated sensitivity of TTM is 0.379 THz/RIU, while the average values of Q-factor and FOM are 66.01 and 63.83, respectively. These characteristics indicate that the presented MEMS-based TTM device could be widely used in tunable filters, perfect absorbers, high-efficient environmental sensors, and optical switches applications for THz-wave optoelectronics.

Tunable Split-Disk Metamaterial Absorber for Sensing Application

We present four designs of tunable split-disk metamaterial (SDM) absorbers. They consist of a bottom gold (Au) mirror layer anchored on Si substrate and a suspended-top SDM nanostructure with one, two, three, and four splits named SDM-1, SDM-2, SDM-3, and SDM-4, respectively. By tailoring the geometrical configurations, the four SDMs exhibit different tunable absorption resonances spanning from 1.5 µm to 5.0 µm wavelength range. The resonances of absorption spectra can be tuned in the range of 320 nm, and the absorption intensities become lower by increasing the gaps of the air insulator layer. To increase the sensitivity of the proposed devices, SDMs exhibit high sensitivities of 3312 nm/RIU (refractive index unit, RIU), 3362 nm/RIU, 3342 nm/RIU, and 3567 nm/RIU for SDM-1, SDM-2, SDM-3, and SDM-4, respectively. The highest correlation coefficient is 0.99999. This study paves the way to the possibility of optical gas sensors and biosensors with high sensitivity.