We design and demonstrate a thermally switchable terahertz metamaterial absorber consisting of an array of orthogonal coupled split-ring metal resonators involving a VO2 phase transition. Numerical results indicate that the active metamaterial always absorbs the TE wave in dual-band regardless of insulating and metallic VO2, while the insulator-to-metal phase transition enables a switchable effect between dual-band and broadband absorption of the TM wave with the resonant frequency tunability of 33%. Especially under the metallic VO2 state, the absorption properties are polarization-dependent and exhibit a switching effect between dual-band and broadband absorption with the increase of the polarization angle. The tunable absorption mechanism can be explained by effective impedance theory and electric energy density distributions. The proposed dual-band to broadband metamaterial switching absorber may have broad applications in sensors, imaging and emitters.
Broadband and switchable versatile polarization metamaterial is crucial in the applications of imaging, sensing and communication, especially in the terahertz frequency. Here, we investigated versatile polarization manipulation in a hybrid terahertz metamaterial with bilayer rectangular rods and a complementary vanadium dioxide (VO2) layer. The VO2 phase transition enables a flexible switching from dual-band asymmetric transmission to dual-band reflective half-wave plate. The full width half maximum (FWHM) bandwidths of dual-band asymmetric transmission are 0.77 and 0.21 THz, respectively. The polarization conversion ratio (PCR) of the reflective metamaterial is over 0.9 in the frequency ranges of 1.01-1.17 THz and 1.47-1.95 THz. Angular dependences of multiple polarization properties are studied. The proposed switchable polarization metamaterial is important to the development of multifunctional polarization devices and multichannel polarization detection.
In this work, we numerically demonstrate tunable chiroptical responses in a transmissive asymmetrically split ring metamaterial composed of metal/phase change material Ge 2 Sb 2 Te 5 (GST)/metal multilayer stack. The pronounced optical contrast between the amorphous and crystalline GSTs results in a large frequency tuning range of both resonant asymmetric transmission and circular dichroism up to 38.7%. Additionally, the hybrid metamaterial can be employed to explore phase transition process between amorphous and crystalline GSTs via detecting polarization conversion or circular dichroism with low background noise since the resonant signal is quite sensitive to proportions of amorphous and crystalline GSTs. The polarization conversion efficiencies and resonant frequencies can be tuned via parameter study. This work pays a way towards the realization of GST-enabled dynamic polarization control in the optical region.
Exceptional points (EPs), the critical phase transition points of non-Hermitian parity-time (PT) systems, exhibit many novel physical properties and associated applications, such as ultra-sensitive detection of perturbations. Here, a bilayer metasurface with two orthogonally oriented split-ring resonators (SRRs) is proposed and a phase transition of the eigenpolarization states is introduced via changing the conductivity of vanadium dioxide (VO2) patch integrated into the gap of one SRR. The metasurface possesses a passive PT symmetry and an EP in polarization space is observed at a certain conductivity of the VO2. Two sensing schemes with the metasurface are proposed to achieve high-sensitivity sensing of temperature and refractive index in the terahertz (THz) range. The metasurface is promising for applications in THz biosensing and polarization manipulation.
Ultra-high-quality perfect optical absorption structures based on quasi-bound states in the continuum (quasi-BICs) are investigated and numerically demonstrated. When the radiation rate of the magnetic dipole quasi-BICs resonance is equal to the dissipate loss rate of the system, the critical coupling condition is satisfied and the perfect absorption (nearly 100%) is obtained. The ultra-high-quality factor (1.7 × 105) perfect absorption in the proposed design is mainly attributed to the extremely low external leakage loss rate of quasi-BIC and relatively small intrinsic absorption loss rate in the constituent materials. The structure exhibits excellent sensing properties with a sensitivity of 108 nm/RIU and ultra-high FOM of ∼12013. The proposed scheme is of importance in potential biosensing applications.
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