Due to the unique anisotropic chemical and physical properties, two-dimensional (2D) layered materials, such as IV-VI monochalcogenides with puckered honeycomb structure, have received considerable interest recently. Among the IV-VI layered MX (M = Ge, Sn; X = Se, S) compounds, germanium sulfide (GeS) stands out for its strongest anisotropic thermal conductivities and figure-of-merit values. Additionally, the layer-independent direct energy bands (E g~1 .6 eV, E 1~2 .1 eV) of GeS flake provide excellent insights into further applications as visible photodetectors. Herein, the polarization-tunable nonlinear absorption (NA) patterns of GeS flake have been systematically investigated. Specifically, both the polarization-dependent Raman spectroscopy and the linear absorption (LA) spectroscopy were employed to characterize the lattice orientation and absorption edges of the 251-nm GeS flake. Considering the low damage threshold of GeS flake, the GeS/graphene heterostructure was fabricated to increase the threshold without changing the nonlinear properties of GeS. Our NA results demonstrated that a 600-nm femtosecond laser with different polarizations would excite the saturated-absorption (SA) effect along armchair and reversesaturated-absorption (RSA) effect along zigzag in the GeS/graphene heterostructure. Moreover, the function of the polarization-based GeS/graphene heterostructure all-optical switch was experimentally verified. Notably, thanks to the polarization-dependent NA patterns (SA/RSA) of GeS, the "ON" and "OFF" states of the all-optical switch can be accomplished by high and low transmittance states of continuous-wave laser (532 nm, 80 nW), whose state can be controlled by the polarization of femtosecond switching laser (600 nm, 35 fs, 500 Hz, 12 GW cm −2). The ON/OFF ratio can achieve up to 17% by changing polarization, compared with the ratios of 3.0% by increasing the incident power of switching light in our experiment. The polarization-tunable absorption patterns introduced in this work open up real perspectives for the next-generation optoelectronic devices based on GeS/graphene heterostructure.

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.