Health Monitoring of Long-Haul Fiber Communication System Using Chaotic OTDR

A novel chaotic optical time-domain reflectometry(OTDR)-based approach was proposed for monitoring long-haul fiber communication systems with multiple fiber segments. The self-phase modulation and group velocity dispersion effects of the optical cable was considered in demonstrating the proof-of-concept experiment and simulation. In experiments, the correlation peaks are clearly obtained from the correlation trace between the reference and reflected(or scattered) light signals propagating in three optical-fiber segments. The technique affords a high spatial resolution of 2 m, and further long-haul fiber simulations indicate that the sensing distance can be more than 3300 km. Thus, the new proposed technique can be effectively applied for health monitoring of long-haul fiber communication systems.

Perovskite-transition metal dichalcogenides heterostructures: recent advances and future perspectives

Transition metal dichalcogenides(TMDs)and perovskites are among the most attractive and widely investigated semiconductors in the recent decade.They are promising materials for various applications,such as photodetection,solar energy harvesting,light emission,and many others.Combining these materials to form heterostructures can enrich the already fascinating properties and bring up new phenomena and opportunities.Work in this field is growing rapidly in both fundamental studies and device applications.Here,we review the recent findings in the perovskite-TMD heterostructures and give our perspectives on the future development of this promising field.The fundamental properties of the perovskites,TMDs,and their heterostructures are discussed first,followed by a summary of the synthesis methods of the perovskites and TMDs and the approaches to obtain high-quality interfaces.Particular attention is paid to the TMD-perovskite heterostructures that have been applied in solar cells and photodetectors with notable performance improvement.Finally through our analysis,we propose an outline on further fundamental studies and the promising applications of perovskite-TMD heterostructures.

Multidimensional optical tweezers synthetized by rigid-body emulated structured light

Structured light with more extended degrees of freedom(DoFs)and in higher dimensions is increasingly gaining traction and leading to breakthroughs such as super-resolution imaging,larger-capacity communication,and ultraprecise optical trapping or tweezers.More DoFs for manipulating an object can access more maneuvers and radically increase maneuvering precision,which is of significance in biology and related microscopic detection.However,manipulating particles beyond three-dimensional(3D)spatial manipulation by using current all-optical tweezers technology remains difficult.To overcome this limitation,we theoretically and experimentally present six-dimensional(6D)structured optical tweezers based on tailoring structured light emulating rigid-body mechanics.Our method facilitates the evaluation of the methodology of rigid-body mechanics to synthesize six independent DoFs in a structured optical trapping system,akin to six-axis rigid-body manipulation,including surge,sway,heave,roll,pitch,and yaw.In contrast to previous 3D optical tweezers,our 6D structured optical tweezers significantly improved the flexibility of the path design of complex trajectories,thereby laying the foundation for next-generation functional optical manipulation,assembly,and micromechanics.

Quantum light sources from semiconductor

Semiconductor provides a physics-rich environment to host various quantum light sources applicable for quantum information processing. These light sources are capable of deterministic generation of non-classical photon streams that demonstrate antibunching photon statistics, strong indistinguishability, and high-fidelity entanglement. Some of them have even successfully transitioned from proof-ofconcept to engineering efforts with steadily improving performance[ 1]. Here, we briefly summarize recent efforts and progress in the race towards ideal quantum light sources based on semiconductor materials. The focus of this report will be on group III–V semiconductor quantum dots, defects in wide band-gap materials, emitters in two-dimensional van der Waals layered hosts, and carbon nanotubes, as these systems are well-positioned to benefit from recent breakthroughs in nanofabrication and materials growth techniques.

Opto-valleytronics in the 2D van der Waals heterostructure

The development of information processing devices with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momentum space) to encode the information instead of charges. The valley information in some material such as monolayer transition metal dichalcogenide (TMD) can be controlled by using circularly polarized light. This opens a new field called opto-valleytronics. In this article, we first review the valley physics in monolayer TMD and two-dimensional (2D) heterostructure composed of monolayer TMD and other materials. Such 2D heterostructure has been shown to exhibit interesting phenomena such as interlayer exciton, magnetic proximity effect, and spin-orbit proximity effect, which is beneficial for opto-valleytronics application. We then review some of the optical valley control methods that have been used in the monolayer TMD and the 2D heterostructure. Finally, a summary and outlook of the 2D heterostructure opto-valleytronics are given.

Layer-controlled nonlinear terahertz valleytronics in two-dimensional semimetal and semiconductor PtSe_(2)

Platinum diselenide(PtSe_(2))is a promising two-dimensional(2D)material for the terahertz(THz)range as,unlike other transition metal dichalcogenides(TMDs),its bandgap can be uniquely tuned from a semiconductor in the nearinfrared to a semimetal with the number of atomic layers.This gives the material unique THz photonic properties that can be layer-engineered.Here,we demonstrate that a controlled THz nonlinearity—tuned from monolayer to bulk PtSe_(2)—can be realized in wafer size polycrystalline PtSe_(2)through the generation of ultrafast photocurrents and the engineering of the bandstructure valleys.This is combined with the PtSe_(2)layer interaction with the substrate for a broken material centrosymmetry,permitting a second order nonlinearity.Further,we show layer dependent circular dichroism,where the sign of the ultrafast currents and hence the phase of the emitted THz pulse can be controlled through the excitation of different bandstructure valleys.In particular,we show that a semimetal has a strong dichroism that is absent in the monolayer and few layer semiconducting limit.The microscopic origins of this TMD bandstructure engineering are highlighted through detailed DFT simulations,and shows the circular dichroism can be controlled when PtSe_(2)becomes a semimetal and when the K-valleys can be excited.As well as showing that PtSe_(2)is a promising material for THz generation through layer controlled optical nonlinearities,this work opens up a new class of circular dichroism materials beyond the monolayer limit that has been the case of traditional TMDs,and impacting a range of domains from THz valleytronics,THz spintronics to harmonic generation.

All-optical active THz metasurfaces for ultrafast polarization switching and dynamic beam splitting

Miniaturized ultrafast switchable optical components with an extremely compact size and a high-speed response will be the core of next-generation all-optical devices instead of traditional integrated circuits,which are approaching the bottleneck of Moore’s Law.Metasurfaces have emerged as fascinating subwavelength flat optical components and devices for light focusing and holography applications.However,these devices exhibit a severe limitation due to their natural passive response.Here we introduce an active hybrid metasurface integrated with patterned semiconductor inclusions for all-optical active control of terahertz waves.Ultrafast modulation of polarization states and the beam splitting ratio are experimentally demonstrated on a time scale of 667 ps.This scheme of hybrid metasurfaces could also be extended to the design of various free-space all-optical active devices,such as varifocal planar lenses,switchable vector beam generators,and components for holography in ultrafast imaging,display,and high-fidelity terahertz wireless communication systems.

Two-dimensional control of light with light on metasurfaces

The ability to control the wavefront of light is fundamental to focusing and redistribution of light,enabling many applications from imaging to spectroscopy.Wave interaction on highly nonlinear photorefractive materials is essentially the only established technology allowing the dynamic control of the wavefront of a light beam with another beam of light,but it is slow and requires large optical power.Here we report a proof-of-principle demonstration of a new technology for two-dimensional(2D)control of light with light based on the coherent interaction of optical beams on highly absorbing plasmonic metasurfaces.We illustrate this by performing 2D all-optical logical operations(AND,XOR and OR)and image processing.Our approach offers diffractionlimited resolution,potentially at arbitrarily-low intensity levels and with 100 THz bandwidth,thus promising new applications in space-division multiplexing,adaptive optics,image correction,processing and recognition,2D binary optical data processing and reconfigurable optical devices.

拓扑无线能量传输的实验验证

近年来,基于磁共振和近场耦合的非辐射无线能量传输技术已被广泛应用.然而,由于传输效率和功率随着距离增加而大幅降低,基于双谐振器的无线能量传输系统仅适用于中短距离应用.基于多中继谐振器的无线能量传输系统可克服该问题,然而该复杂系统对微扰和缺陷极为敏感.针对上述问题,本文实验验证了稳健性拓扑无线能量传输.电磁能量可通过位于一维无线电波拓扑绝缘体两端的拓扑边界态之间的近场耦合高效传递.该结构可等效为具有复边界电势的宇称-时间对称的Su-Schrieffer-Heeger链.此外,所设计的线圈结构可抑制不相邻线圈之间非必要的交叉耦合.该工作理论和实验上验证了即使存在微扰的情况下,该系统仍可在拓扑边界态的奇异点附近保持极高的能量传输效率.该工作将拓扑电磁材料、非厄米物理和无线能量传输技术三者结合,为未来电子、交通运输和工业中的长距离无线传输提供稳定、高效的平台.

Photonic amorphous topological insulator

The current understanding of topological insulators and their classical wave analogs,such as photonic topological insulators,is mainly based on topological band theory.However,standard band theory does not apply to amorphous phases of matter,which are formed by non-crystalline lattices with no long-range positional order but only shortrange order,exhibiting unique phenomena such as the glass-to-liquid transition.Here,we experimentally investigate amorphous variants of a Chern number-based photonic topological insulator.By tuning the disorder strength in the lattice,we demonstrate that photonic topological edge states can persist into the amorphous regime prior to the glass-to-liquid transition.After the transition to a liquid-like lattice configuration,the signatures of topological edge states disappear.This interplay between topology and short-range order in amorphous lattices paves the way for new classes of non-crystalline topological photonic bandgap materials.

In-plane coherent control of plasmon resonances for plasmonic switching and encoding

Considerable attention has been paid recently to coherent control of plasmon resonances in metadevices for potential applications in all-optical light-with-light signal modulation and image processing.Previous reports based on out-ofplane coherent control of plasmon resonances were established by modulating the position of a metadevice in standing waves.Here we show that destructive and constructive absorption can be realized in metallic nano-antennas through in-plane coherent control of plasmon resonances,which is determined by the distribution rule of electricalfield components of nano-antennas.We provide proof-of-principle demonstrations of plasmonic switching effects in a gold nanodisk monomer and dimer,and propose a plasmonic encoding strategy in a gold nanodisk chain.In-plane coherent control of plasmon resonances may open a new avenue toward promising applications in optical spectral enhancement,imaging,nanolasing,and optical communication in nanocircuits.

Quantum super-oscillation of a single photon

Super-oscillation is a counterintuitive phenomenon describing localized fast variations of functions and fields that happen at frequencies higher than the highest Fourier component of their spectra.The physical implications of this effect have been studied in information theory and optics of classical fields,and have been used in super-resolution imaging.As a general phenomenon of wave dynamics,super-oscillations have also been predicted to exist in quantum wavefunctions.Here we report the experimental demonstration of super-oscillatory behavior of a single-quantum object,a photon.The super-oscillatory behavior is demonstrated by tight localization of the photon wavefunction after focusing with an appropriately designed slit mask to create an interference pattern with a sub-diffraction hotspot(~0.45λ).Such quantum super-oscillation can be used for low-intensity far-field super-resolution imaging techniques even down to single-photon counting regime,which would be of interest to quantum physics and non-invasive and label-free biological studies.

All-optical dynamic focusing of light via coherent absorption in a plasmonic metasurface

Vision,microscopy,imaging,optical data projection and storage all depend on focusing of light.Dynamic focusing is conventionally achieved with mechanically reconfigurable lenses,spatial light modulators or microfluidics.Here we demonstrate that dynamic control of focusing can be achieved through coherent interaction of optical waves on a thin beam splitter.We use a nanostructured plasmonic metasurface of subwavelength thickness as the beam splitter,allowing operation in the regimes of coherent absorption and coherent transparency.Focusing of light resulting from illumination of the plasmonic metasurface with a Fresnel zone pattern is controlled by another patterned beam projected on the same metasurface.By altering the control pattern,its phase,or its intensity,we switch the lens function on and off,and alter the focal spot’s depth,diameter and intensity.Switching occurs as fast as the control beam is modulated and therefore tens of gigahertz modulation bandwidth is possible with electro-optical modulators,which is orders of magnitude faster than conventional dynamic focusing technologies.

Plasmonic evolution maps for planar metamaterials

Understanding the mode’s origin in planar metamaterials is fundamental for related applications in nanophotonics and plasmonics.For complex planar metamaterials,conventional analysis that directly obtains the final charge/current distribution of a mode is usually difficult in helping to understand the mode’s origin.In this paper,we propose a mode evolution method(MEM)with a core analysis tool,i.e.,plasmonic evolution maps(PEMs),to describe the mode evolution in several complementary planar metamaterials with designed plasmonic atoms/molecules.The PEMs could not only clearly explain a mode’s origin,but also reveal the role of a structure’s symmetry in the mode formation process.The MEM with PEMs can work as a simple,efficient,and universal approach for the mode analysis in different kinds of planar metamaterials.

Negative refraction of ultra-squeezed in-plane hyperbolic designer polaritons

The in-plane negative refraction of high-momentum(i.e.,high-k)photonic modes could enable many applications such as imaging,focusing,and waveguiding in a planar platform at deep-subwavelength scales.However,its practical implementation in experiments remains elusive so far.Here we propose a class of hyperbolic metasurfaces,which is characterized by an anisotropic magnetic sheet conductivity and can support the in-plane ultrahigh-k magnetic designer polaritons.Based on such metasurfaces,we report the experimental observation of the all-angle negative refraction of designer polaritons at extremely deep-subwavelength scales.Moreover,we directly visualize the designer polaritons with hyperbolic dispersions.Importantly,for these hyperbolic polaritons,we find that their squeezing factor is ultra-large.To be specific,it can be up to 129 in the experiments,an ultra-high value exceeding those in naturally hyperbolic materials.This work may pave a way toward exploring the extremely high confinement and unusual propagation of magnetic designer polaritons over monolayer or twisted bilayer hyperbolic metasurfaces.

All-optical control of exciton flow in a colloidal quantum well complex

Excitonics,an alternative to romising for processing information since semiconductor electronics is rapidly approaching the end of Moore’s law.Currently,the development of excitonic devices,where exciton flow is controlled,is mainly focused on electric-field modulation or exciton polaritons in high-Q cavities.Here,we show an alloptical strategy to manipulate the exciton flow in a binary colloidal quantum well complex through mediation of the Förster resonance energy transfer(FRET)by stimulated emission.In the spontaneous emission regime,FRET naturally occurs between a donor and an acceptor.In contrast,upon stronger excitation,the ultrafast consumption of excitons by stimulated emission effectively engineers the excitonic flow from the donors to the acceptors.Specifically,the acceptors’stimulated emission significantly accelerates the exciton flow,while the donors’stimulated emission almost stops this process.On this basis,a FRET-coupled rate equation model is derived to understand the controllable exciton flow using the density of the excited donors and the unexcited acceptors.The results will provide an effective alloptical route for realizing excitonic devices under room temperature operation.