Topology-empowered membrane devices for terahertz photonics

Control of terahertz waves offers a profound platform for next-generation sensing,imaging,and information communications.However,all conventional terahertz components and systems suffer from bulky design,sensitivity to imperfections,and transmission loss.We propose and experimentally demonstrate onchip integration and miniaturization of topological devices,which may address many existing drawbacks of the terahertz technology.We design and fabricate topological devices based on valley-Hall photonic structures that can be employed for various integrated components of on-chip terahertz systems.We demonstrate valleylocked asymmetric energy flow and mode conversion with topological waveguide,multiport couplers,wave division,and whispering gallery mode resonators.Our devices are based on topological membrane metasurfaces,which are of great importance for developing on-chip photonics and bring many features into terahertz technology.

Hybrid bound states in the continuum in terahertz metasurfaces

Bound states in the continuum(BICs)have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics,biosensors,and ultrafast optical switches.The most common strategy to apply BICs in a metasurface is by breaking symmetry of resonators in the uniform array that leaks the otherwise uncoupled mode to free space and exhibits an inverse quadratic relationship between quality factor(Q)and asymmetry.Here,we propose a scheme to further reduce scattering losses and improve the robustness of symmetry-protected BICs by decreasing the radiation density with a hybrid BIC lattice.We observe a significant increase of radiative Q in the hybrid lattice compared to the uniform lattice with a factor larger than 14.6.In the hybrid BIC lattice,modes are transferred toГpoint inherited from high symmetric X,Y,and M points in the Brillouin zone that reveal as multiple Fano resonances in the far field and would find applications in hyperspectral sensing.This work initiates a novel and generalized path toward reducing scattering losses and improving the robustness of BICs in terms of lattice engineering that would release the rigid requirements of fabrication accuracy and benefit applications of photonics and optoelectronic devices.

Terahertz Band: Lighting up Next-Generation Wireless Communications

With the explosion of wireless data rates,the terahertz(THz)band(0.1–10 THz)is envisioned as a promising candidate to break the existing bandwidth bottleneck and satisfy the ever-increasing capacity demand.The THz wireless communications feature a number of attractive properties,such as potential terabit-per-second capacity and high energy efficiency.In this paper,an overview on the state-of-the-art THz communications is studied,with a special focus on key technologies of THz transceivers and THz communication systems.The recent progress on both electronic and photonic THz transmitters are presented,and then the THz receivers operating in direct-and heterodyne reception modes are individually surveyed.Based on the THz transceiver schemes,three kinds of THz wireless communication systems are reviewed,including solid-state electronic systems,photonics-assisted systems and all-photonics systems.The prospective key enabling technologies,corresponding challenges and research directions for lighting up high-speed THz communication systems are discussed as well.

Photonics 60 GBaud PDM-16QAM fiber-wireless 2×2 MIMO delivery at THz-band

The terahertz photonics technique has bright application prospects in future sixth-generation(6G)broadband communication.In this study,we have experimentally demonstrated a photonics-assisted record-breaking net bit rate of 417 Gbit/s per wavelength signals delivery in a fiber-wireless converged communication system supported by advanced digital-signalprocessing(DSP)algorithms and a polarization multiplexing-based multiple-input multiple-output(MIMO)scheme.In the experiment,up to 60 GBaud(480 Gbit/s)polarization-division-multiplexing 16-ary quadrature-amplitude-modulation(PDM16QAM)signals are transmitted over 20 km fibers and 3 m wireless 2×2 MIMO links at 318 GHz with the bit error rate(BER)under 1.56×10^(−2).It is the first demonstration to our knowledge of signals delivery exceeding 400 Gbit/s per wavelength in a photonics-assisted fiber-wireless converged 2×2 MIMO communication system.

Generation and detection of pulsed terahertz waves in gas： from elongated plasmas to microplasmas

The past two decades have seen an exponential growth of interest in one of the least explored region of the electromagnetic spectrum, the terahertz （THz） frequency band, ranging from to 0.1 to 10 THz. Once only the realm of astrophysicists studying the background radiation of the universe, THz waves have become little by little relevant in the most diverse fields, such as medical imaging, industrial inspection, remote sensing, fundamental science, and so on. Remarkably, THz wave radiation can be generated and detected by using ambient air as the source and the sensor. This is accomplished by creating plasma under the illumination of intense femtosecond laser fields. The integration of such a plasma source and sensor in THz time-domain techniques allows spectral measurements covering the whole THz gap （0.1 to 10 THz）, further increasing the impact of this scientific tool in the study of the four states of matter. In this review, the authors introduce a new paradigm for implementing THz plasma techniques. Specifically, we replaced the use of elongated plasmas, ranging from few mm to several cm, with sub-mm plasmas, which will be referred to as microplasmas, obtained by focusing ultrafast laser pulses with high numerical aperture optics （NA from 0.1 to 0.9）. The experimental study of the THz emission and detection from laser-induced plasmas of submillimeter size are presented. Regarding the microplasma source, one of the interesting phenomena is that the main direction of THz wave emission is almost orthogonal to the laser propagation direction, unlike that of elongated plasmas. Perhaps the most important achievement is the demonstra- tion that laser pulse energies lower than 1 μJ are sufficientto generate measurable THz pulses from ambient air, thus reducing the required laser energy requirement of two orders of magnitude compared to the state of art. This significant decrease in the required laser energy will make plasma-based THz techniques more accessible to the scientific community, as well as opening new potential industrial applications. Finally, experimental observations of THz radiation detection with microplasmas are also presented. As fully coherent detection was not achieved in this work, the results presented herein are to be considered a first step to understand the peculiarities involved in using the micro- plasma as a THz sensor.

Single-lane 200 Gbit/s photonic wireless transmission of multicarrier 64-QAM signals at 300 GHz over 30 m

Recently,wireless communication capacity has been witnessing unprecedented growth.Benefits from the optoelectronic components with large bandwidth,photonics-assisted terahertz(THz)communication links have been extensively developed to accommodate the upcoming wireless transmission with a high data rate.However,limited by the available signalto-noise ratio and THz component bandwidth,single-lane transmission of beyond 100 Gbit/s data rate using a single pair of THz transceivers is still very challenging.In this study,a multicarrier THz photonic wireless communication link in the 300 GHz band is proposed and experimentally demonstrated.Enabled by subcarrier multiplexing,spectrally efficient modulation format,well-tailored digital signal processing routine,and broadband THz transceivers,a line rate of 72 Gbit/s over a wireless distance of 30 m is successfully demonstrated,resulting in a total net transmission capacity of up to 202.5 Gbit/s.The single-lane transmission of beyond 200 Gbit/s overall data rate with a single pair of transceivers at 300 GHz is considered a significant step toward a viable photonics-assisted solution for the next-generation information and communication technology (ICT) infrastructure.