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Abstract Topological slow light exhibits potential to achieve stopped light by virtue of its widely known robust and non-reciprocal behaviours. Conventional approach for achieving topological slow light often involves flat-band engineering without disentangling the underlying physical mechanism. Here, we unveil the presence of counter-propagating waves within valley kink states as the distinctive hallmark of the slow light topological photonic waveguides. These counter-propagating waves, supported by topological vortices along glide-symmetric interface, provide significant flexibility for controlling the slowness of light. We tune the group velocity of light by changing the spatial separation between vortices adjacent to the glide-symmetric interface. We also dynamically control the group delay by introducing a non-Hermitian defect using photoexcitation to adjust the relative strength of the counter-propagating waves. This study introduces active slow light topological photonic device on a silicon chip, opening new horizons for topological photon transport through defects, topological light-matter interactions, nonlinear topological photonics, and topological quantum photonics.

6G communication requires high-speed and advanced functionalities on-chip. Here the authors demonstrate broadband phototunable topological waveguide and demultiplexing chip with record single-channel 160 Gbit/s communication link and excellent channel isolation for 300 GHz band.

The remarkable explosion of wireless devices and bandwidth-consuming Internet applications have boosted the demand for wireless communications with ultra-high data rate [...]

Abstract Space‐time wave packets are electromagnetic waves with strong correlations between their spatial and temporal degrees of freedom. These wave packets have gained much attention for fundamental properties like propagation invariance and user‐designed group velocities, and for potential applications like optical microscopy, micromanipulation, and laser micromachining. Here, free‐electron radiation is presented as a natural and versatile source of space‐time wave packets that are ultra‐broadband and highly tunable in frequency. For instance, ab initio theory and numerical simulations show that the intensity profile of space‐time wave packets from Smith‐Purcell radiation can be directly tailored through the grating properties, as well as the velocity and shape of the electron bunches. The result of this work indicates a viable way of generating space‐time wave packets at exotic frequencies such as the terahertz and X‐ray regimes, potentially paving the way toward new methods of shaping electromagnetic wave packets through free‐electron radiation.

The forthcoming sixth generation (6G) communication network is envisioned to provide ultra-fast data transmission and ubiquitous wireless connectivity. The terahertz (THz) spectrum, with higher frequency and wider bandwidth, offers great potential for 6G wireless technologies. However, the THz links suffers from high loss and line-of-sight connectivity. To overcome these challenges, a cost-effective method to dynamically optimize the transmission path using reconfigurable intelligent surfaces (RISs) is widely proposed. RIS is constructed by embedding active elements into passive metasurfaces, which is an artificially designed periodic structure. However, the active elements (e.g., PIN diodes) used for 5G RIS are impractical for 6G RIS due to the cutoff frequency limitation and higher loss at THz frequencies. As such, various tuning elements have been explored to fill this THz gap between radio waves and infrared light. The focus of this review is on THz RISs with the potential to assist 6G communication functionalities including pixel-level amplitude modulation and dynamic beam manipulation. By reviewing a wide range of tuning mechanisms, including electronic approaches (complementary metal-oxide-semiconductor (CMOS) transistors, Schottky diodes, high electron mobility transistors (HEMTs), and graphene), optical approaches (photoactive semiconductor materials), phase-change materials (vanadium dioxide, chalcogenides, and liquid crystals), as well as microelectromechanical systems (MEMS), this review summarizes recent developments in THz RISs in support of 6G communication links and discusses future research directions in this field.

Here, the authors demonstrate excitation and active tuning of sharp Fano resonances in a MEMS reconfigurable metasurface possessing multiple-input-output states. They realize XOR, XNOR, NOT and NAND logic gate operations by using two independently controllable electrical inputs and an optical readout using terahertz beam.

Optical chirality is central to many industrial photonic technologies including enantiomer identification, ellipsometry-based tomography, and spin multiplexing in optical communications. However, a substantial chiral response requires a three-dimensional constituent, thereby making the morphology highly complex to realize structural reconfiguration. Moreover, an active reconfiguration demands intense dosage of external stimuli that pose a major limitation for on-chip integration. Here, we report a low bias, electrically programmable synthetic chiral paradigm with a remarkable reconfiguration among levorotatory, dextrorotatory, achiral, and racemic conformations. The switchable optical activity induced by the chiral conformations enables a transmission-type duplex spatial light modulator for terahertz single pixel imaging. The prototype delivers a new strategy towards reconfigurable stereoselective photonic applications and opens up avenues for on-chip programmable chiral devices with tremendous applications in biology, medicine, chemistry, and photonics.

We experimentally demonstrate a digitally reconfigurable binary coded terahertz metamaterial in the Terahertz (THz) frequency with the transmission output analogous to NOR and AND logic. An electric split-ring resonator with a released central arms is used as the switchable meta-bit. Isolation of controls in adjacent meta-bits allows for three distinct reconfiguration states of the metamaterial with the output analogous to NOR and AND at 0.26 THz and 0.36 THz, respectively. Further enhancement in controllability at the unit cell level will aid in the development of dynamically programmable metamaterial operating in the transmission mode for THz frequencies. [ABSTRACT FROM AUTHOR]

In this paper, we present a multiband flexible metamaterial in which one resonance acts as a strain sensor, while the others remain unchanged with bending strain, which might occur due to wrapping around an irregular curved surface. From both experiment and simulation, four transmission dips were observed at around 0.51, 1.34, 1.72 and 1.81 THz, respectively. The results indicated that the resonance dips in the flexible metamaterial arose from the different orders of dipole resonance mode. In the experiment, the frequency shift and amplitude modulation of the transmission at the first resonance increased linearly with the increase of the relative length change Δl/L and changed as an exponential function of the applied bending strain. In addition, the first resonance frequency of the horizontal dipole blue shifted by 6.4 GHz, or about 1.29%, while the relative intensity change of 31.95% in the transmission was achieved when the strain was 2.79‰. This study promises applications in curvature sensing and other controllable metamaterial-based devices. [ABSTRACT FROM AUTHOR]