An electromagnetically induced transparency(EIT) in metamaterial resonator with two bright modes and one dark mode at the terahertz(THz) band is numerically and experimentally demonstrated. Different from two kinds of the traditional passive modulations, our design can realize the passive modulation of EIT phenomenon by adding another bright mode resonator. Simulated and experimental results show that the transmission peak varies for incident THz waves with different polarization directions due to its asymmetric structure, which provides a novel way to realize high efficiency switch and modulation.
设计并制备了两种工作在太赫兹波段的等离子体晶体波导,利用其带隙位置随波导间空气间隙变化而连续变化的特点,实现了光开关和机械可调谐滤波器的功能。利用太赫兹时域光谱系统研究了这两种等离子体晶体波导的传输和滤波性质,利用时域有限差分法计算了其透射率,用有限元法计算了其带隙性质和场分布。结果表明应用这两种结构实现的可调谐滤波器都具有良好的性能,其中一维等离子体晶体波导的调谐范围达到了130 GHz,消光比为30 d B;二维等离子体晶体波导的调谐范围达到了110 GHz,消光比可达40 d B。
It is shown that active-tunable terahertz absorbers can be realized in a sandwich-structured system comprising an ultrathin dielectric film(polyimide) on a temperature-sensitive substrate(InSb) with a metal film on the back by utilizing the intrinsic carrier density(N) variation in InSb. When increasing the temperature from 250 to 320 K, N in InSb varied from ～5.50×1015 to ～2.98×1016 cm–3. Fixing the thickness of dielectric film with the value of 1.37 μm, the absorption peak shifted from 1.41 to 3.29 THz while keeping absorption higher than 99%. This active tunability can respond to even a slight temperature perturbation, and shows polarization insensitivity as well as high tolerance of incidence-angle(absorption peak can still exceed 90% even the incidence angle reaches 60°). Besides, the refractive index of polyimide(PI) has thermal stability at the terahertz range and the merit of good workability. These characteristics guarantee the stability of activetunable performance. The peculiarities and innovations of this proposal promise a wide range of high efficiency terahertz devices, such as thermal sensors, spatial light modulators(SLMs) and so on.
Effects of oblique incidence of terahertz waves on the response of planar split-ring resonators are investigated, both experimentally and by simulation. It is found that the incident angle dependent phase delay and coupling conditions of neighboring split-ring resonator(SRR) units play important roles and greatly change both the transmission and reflection spectra for the resonant feature of linear charge oscillations. Our results show that the SRR structure-supported magnetoelectric couplings at oblique excitation are trivial and can be ignored. A highly symmetric response is found in the cross-polarization effects, which may manifest the bianisotropic properties of the SRR system but this needs further study.
A terahertz(THz) polarizer and switch structure is proposed based on the phase transition of vanadium dioxide(VO_2). When VO_2 is in the insulation phase, the resonance frequencies of the proposed structure are 1.49 THz and 1.22 THz for the x- and y-polarization, respectively. It can perform as a THz polarizer with extinction ratios of 52.5 dB and 17 dB for the y- and x-polarization, respectively; When VO_2 transforms into metallic phase, the resonance frequency for x-polarization wave shifts from 1.49 THz to 1.22 THz, while that remains still for the y-polarization component. It means that the structure can work as a polarization-dependent THz switch with a high extinction ratio of 32 dB.
