Metasurface plays a key role in various terahertz metadevices, while the designed terahertz metasurface still lacks flexibility and variety. On the other hand, inverse design has drawn plenty of attention due to its flexibility and robustness in the application of photonics. This provides an excellent opportunity for metasurface design as well as the development of multifunctional, high-performance terahertz devices. In this work, we demonstrate that, for the first time, a terahertz metasurface supported by the electromagnetically induced transparency (EIT) effect can be constructed by inverse design, which combines the particle swarm optimization algorithm with the finite-difference time-domain method. Incorporating germanium (Ge) film with inverse-designed metasurface, an ultrafast EIT modulation on the picosecond scale has been experimentally verified. The experimental results suggest a feasibility to build the terahertz EIT effect in the metasurface through an optimization algorithm of inverse design. Furthermore, this method can be further utilized to design multifunctional and high-performance terahertz devices, which is hard to accomplish in a traditional metamaterial structure. In a word, our method not only provides a novel way to design an ultrafast all-optical terahertz modulator based on artificial metamaterials but also shows the potential applications of inverse design on the terahertz devices.

The extraordinary proliferation of digital coding metasurfaces turns the real-time manipulation of electromagnetic (EM) waves into reality and promotes the programmable operation of multifunctional equipment. However, current studies are mainly involved in the modulation of the transmission process, and little attention has been given to the control of EM wave generation, especially in the terahertz (THz) band. Here, we conceptually propose and experimentally demonstrate coded terahertz emission, which integrates the efficient generation and control of THz waves across a wide frequency band. For validation, two types of stripe-patterned ferromagnetic heterostructures with opposite spin Hall angles were utilized as coding units. The two distinct states in each coding unit (with two polarization or phase states of 0° and 180°) can be characterized as “0” and “1” digits, which can be switched by manipulating the optical field distribution of the pump beam. Such an ability to realize simultaneous terahertz coding and terahertz emission is essential for meeting the increasingly demanding requirements of integration and miniaturization. Our work endows ferromagnetic heterostructures with controllable spatial characteristics and benefits their applications in wireless communications and holographic imaging.

The bound state in the continuum (BIC) is a unique nonradiating eigenstate that possesses rich physics and has attracted intensive attention in the field of optics and photonics. Actively tailoring BICs in a designable fashion is highly desired for diversified photonic devices. However, to date, most BIC‐assisted works have been limited to showing passive control in a fixed structure configuration without tuning the spectral responses. Here, a new scheme to construct a coupled photon cavity for spatiotemporal lineshape tailoring, in which a nonradiating BIC is embedded in the electromagnetic induced transparency (EIT) window, is proposed. This approach uses the phase transition of VO2 inclusions to induce spatial symmetry breaking, leading to the formation of a quasi‐BIC coupled EIT state. As an extra dimension for dynamic tuning, a layer with a transient photoconductivity much shorter than the photon lifetime is introduced to ultrafast switch the leaky modes for both EIT‐ and quasi‐BIC‐coupled EIT cavities. As the symmetry‐protected BIC and coupling effect are quite common in optical metasurfaces, this proposal provides a general paradigm to active steer spatiotemporal spectrum across multiple dimensions, which is thus believed to promote active metadevices for potential applications in modulators, sensors, filters, and dynamic imaging.

Spatiotemporal Lineshape Tailoring In article number 2203680, Tian Jiang and co‐workers demonstrate a novel reconfigurable metasurface supporting a symmetry‐protected bound state in the continuum in the electromagnetic induced transparency window. With active media embedded in the proposed metasurface, spatiotemporal lineshape tailoring with resonance mode conversion and ultrafast amplitude switching is successfully achieved, which is appealing for next‐generation flat photonic devices with high‐compact, functionality‐integrated, and fast‐speed properties.

The ability to actively manipulate free-space optical signals by using tunable metasurfaces is extremely appealing for many device applications. However, integrating photoactive semiconductors into terahertz metamaterials still suffers from a limited functionality. The ultrafast switching in picosecond timescale can only be operated at a single frequency channel. In the hybrid metasurface proposed here, we experimentally demonstrate a dual-optically tunable metaphotonic device for ultrafast terahertz switching at frequency-agile channels. Picosecond ultrafast photoswitching with a 100% modulation depth is realized at a controllable operational frequency of either 0.55 THz or 0.86 THz. The broadband frequency agility and ultrafast amplitude modulation are independently controlled by continuous wave light and femtosecond laser pulse, respectively. The frequency-selective, temporally tunable, and multidimensionally-driven features can empower active metamaterials in advanced multiplexing of information, dual-channel wireless communication, and several other related fields.