We propose an active meta-lens that can dynamically switch the coaxial focus on three statuses with the external optical pump. The meta-lens composes of two concentric sets of complementary split-ring resonator (CSRR) arrays, which function at different focal lengths, atop the silicon on sapphire substrate. With specifically structured phase distribution, the meta-lens can form completely separated double foci simultaneously. Through illuminating the internal or external CSRR arrays individually with patterned optical pump, the meta-lens switches to single focus at different points. The proposed design provides a new avenue for developing terahertz multifunctional devices applied in microscope imaging and tomography.

The beam splitter is an important functional device due to its ability to steer the propagation of electromagnetic waves. The split-ratio-variable splitter is of significance for optical, terahertz and microwave systems. Here, we are the first (to our knowledge) to propose an optically controlled dynamic beam splitter with adjustable split ratio in the terahertz region. Based on the metasurface containing two sets of reversed phase-gradient supercells, we split the terahertz wave into two symmetrical beams. Associated with the reconfigurable pump laser pattern programmed with the spatial light modulator, dynamic modulation of the split ratio varying from 1:1 to 15:1 is achieved. Meanwhile, the beam splitter works at a split angle of 36° for each beam. Additionally, we obtain an exponential relationship between the split ratio and the illumination proportion, which can be used as theoretical guidance for beam splitting with an arbitrary split ratio. Our novel beam splitter shows an outstanding level of performance in terms of the adjustable split ratio and stable split angles and can be used as an advanced method to develop active functional devices applied to terahertz systems and communications.

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In this paper, we observe the distinguishable modulation of the different eigenmodes by lattice mode in terahertz U-shaped metasurfaces, and a remarkable lattice induced suppression of the high order eigenmode resonance is demonstrated. With the quantitative analysis of Q factor and loss of the resonances, we clarify that the peculiar phenomenon of suppression is originated from the phase mismatch of the metasurfaces via introducing the phase difference between the neighboring structures. These results provide new insights into the phase mismatch mediated transmission amplitude of eigenmode resonance in metasurfaces and open a new path to developing terahertz multifunctional devices.

The amplitude shift keying (ASK) is a significant technique in communications. We propose a terahertz encoder based on the 2-dimensional electron gas (2DEG) metamaterial, which can complete ASK in the 0.43 THz and 0.81 THz independently. The ON/OFF ratio of the encoder in each band is more than 86%. The research is helpful in promoting terahertz technology and next-generation communications.