Optical regulation strategy with the aid of hybrid materials can significantly optimize the performance of terahertz devices. Gold nanobipyramids (AuNBPs) with synthetical tunability to the near-infrared band show strong local field enhancement, which improves optical coupling at the interface and benefits the modulation performance. We design AuNBPs-integrated terahertz modulators with multiple structured surfaces and demonstrate that introducing AuNBPs can effectively enhance their modulation depths. In particular, an ultrahigh modulation enhancement of 1 order of magnitude can be achieved in the AuNBPs hybrid metamaterials accompanied by the multifunctional modulation characteristics. By application of the coupled Lorentz oscillator model, the theoretical calculation suggests that the optical regulation with AuNBPs originates from increased damping rate and higher coupling coefficient under pump excitation. Additionally, a terahertz spatial light modulator is constructed to demonstrate multiple imaging display and consume extremely low power, which is promising for the potential application in spatial and frequency selective imaging.

We have demonstrated the active manipulation of metamaterial-induced transparency (MIT) in a terahertz hybrid metamaterial with graphene overlayer under photoexcitation. It is found that the introduction of graphene can greatly modify the resonant dips and transparency window through the formed depolarization field around unequal-length double bars to weaken dipole resonances and their destructive interference. Transient control of MIT behaviors is determined by the photogenerated carrier dynamics, which influences the distributions of currents and electric fields in the resonant region to hinder the near-field coupling of two bright modes. Optical modulation depth is sensitive to bar spacing due to an anomalous increased double-bar coupling involving intracell and intercell interaction. Heterointerface formed by the added graphene with substrate could further enhance terahertz response via effective separation of the photoexcited carriers. Theoretical calculation based on the coupled Lorentz oscillator model reveals that the photoinduced terahertz response mainly originates from the coupling and damping in hybrid structures. Our findings could facilitate the development of graphene-based dynamical terahertz modulators and optoelectronic devices.

A terahertz hybrid metamaterial incorporated with active media VO2 holds great promise for the realization of a new generation of reconfigurable and multifunctional devices. However, for the electrical control, many efforts on reducing high working threshold are usually based on the utilization of patterned VO2 patches or additional insulation layers, which will increase the complexity of the fabrication procedure. Here, we have proposed an effective strategy only by combining the surface microstructure and the unpatterned VO2 film to realize the tunability of working current and uncover its highly dependent correlation with the structural resonance responses. It is shown the fully modulated current in our hybrid metastructures can be reduced with the prominently separated hysteresis loops. Further developed binary encoders can perform not only the information transformation of the fixed code symbols but also the arbitrary encoding with the programmable current pulse. Additionally, the dynamic color display can be accomplished to illustrate the intriguing function of the information encryption and multi-image reappearance with the current as the decryption key. Our work provides an approach to reduce the operating current and paves a pathway for the development of photonic memory information processors.

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Combined with experimental and simulated results, the resonances and metamaterial-induced transparency have been theoretically investigated using the Lorentz oscillator model for terahertz metamaterials with unequal-length bar structures. The bar spacing has an impact on the spectral evolution, implying that the coupling between metal bars varies correspondingly in one unit cell and the adjacent cells. Different from the evidence that the strongest coupling occurs in double bar structures when the bar spacing is uniform in the entire sample, the coupling in 3 bar structures is more complicated due to the weakened coupling with the middle bar and increased coupling between the other 2 bars by further increasing the bar spacing. The dependence of calculated transmission spectra on the damping rate and coupling coefficient is demonstrated, showing that the fitting parameters could control and tune the resonant dips, the transparency peaks, and even the quality factors of the spectra regularly. Furthermore, the sensing properties have been investigated by simulating the spectral evolution with the overlayers of different refractive indices to optimize the sensing parameters. Our obtained results could advance the understanding of resonance coupling and offer the possibility to further study the modulation and biosensing in the coupled terahertz devices.