arXiv subjects

Jian-Wen Dong

Publications and source records attributed to Jian-Wen Dong.

At least 19 recordsLinked to original sources

arXiv2026

Photonic half-semimetals with dual semimetal-insulator topology

Topological wave systems have largely evolved along two distinct paradigms: gapless topological semimetals and gapped topological insulators. While topological semimetals support bulk transport, they generally lack intrinsic selectivity among propagation channels; topological insulators enable robust transport but confine it to narrow interfaces, limiting spatial utilization. Here, we theoretically demonstrate and experimentally realize time-reversal-invariant spin-valley photonic half-semimetals (HSMs), which exhibit a dual semimetal-insulator topology within a single bulk band structure. In HSMs, the bandgap closes selectively in spin-valley space: for a given spin (valley), one valley (spin) is semimetallic while the other remains insulating. This coexistence of spin- and valley-resolved gapless and gapped band structures makes HSMs fundamentally distinct from both conventional semimetals and insulators. As a defining bulk phenomenon, an HSM functions as a spin-valley-locked beam splitter, intrinsically enabling valley-selective spin routing. Moreover, when four complementary HSMs are assembled into a periodic superlattice, the same dual topology enables reciprocal spin-valley-resolved multilane helical transport with 100% spatial utilization. These results establish HSMs as a platform for selective bulk wave control and multichannel topological transport beyond conventional topological phases.

physics.optics↗

arXiv2025

Chiral Valley Edge States

Valleytronics has emerged as a promising paradigm, enabling comprehensive control of the valley degree of freedom (DoF) for energy-efficient and high-speed information processing. However, backscattering-induced valley depolarization remains a fundamental limitation, stemming from the weak topological protection of the valley Hall phase. Here, we propose and demonstrate the concept of chiral valley edge states, which integrate the robust unidirectional chiral edge states with valley DoF. By controlling the valley Dirac masses, we selectively confine the chiral edge band around a single valley, enabling back-scattering-free propagation while imparting valley polarization. Our strategy not only addresses the valley depolarization issue but also introduces a unique functionality--valley multiplexing--allowing independent and arbitrary control over waves associated with different valley polarizations. We demonstrate our concept experimentally within hybrid topological photonic crystal systems composed of Chern and valley photonic crystals. Moreover, two key components for valley multiplexing are demonstrated: a valley (de-)multiplexer and a valley-locked waveguide crossing, facilitating non-interfering signal routing. Our results establish a novel interplay between the topological quantum Hall and valley Hall phases, offering a new framework for robust valley-based information processing.

physics.optics↗

arXiv2025

Overcoming Intrinsic Dispersion Locking for Achieving Spatio-Spectral Selectivity with Misaligned Bi-metagratings

Spatio-spectral selectivity, the capability to select a single mode with a specific wavevector (angle) and wavelength, is imperative for light emission and imaging. Continuous band dispersion of a conventional periodic structure, however, sets up an intrinsic locking between wavevectors and wavelengths of photonic modes, making it difficult to single out just one mode. Here, we show that the radiation asymmetry of a photonic mode can be explored to tailor the transmission/reflection properties of a photonic structure, based on Fano interferences between the mode and the background. In particular, we find that a photonic system supporting a band dispersion with certain angle-dependent radiation-directionality can exhibit Fano-like perfect reflection at a single frequency and a single incident angle, thus overcoming the dispersion locking and enabling the desired spatio-spectral selectivity. We present a phase diagram to guide designing angle-controlled radiation-directionality and experimentally demonstrate double narrow Fano-like reflection in angular (5°) and wavelength (14 nm) bandwidths, along with high-contrast spatio-spectral selective imaging, using a misaligned bilayer metagrating with tens-of-nanometer-scale thin spacer. Our scheme promises new opportunities in applications in directional thermal emission, nonlocal beam shaping, augmented reality, precision bilayer nanofabrication, and biological spectroscopy.

physics.optics↗

arXiv2025

Realization of chiral whispering gallery mode cavities enabled by photonic Chern insulators

Recently, whispering gallery modes (WGMs) have attracted considerable attention due to their extensive applications in the development of on-chip microcavities, high-sensitivity sensors, and high-performance lasers. Conventional WGMs are achiral under the time-reversal symmetry, and show high sensitivity to defects in optical devices. Here, we introduce topological physics into photonic cavities and demonstrate the realization of chiral WGMs enabled by photonic Chern insulators. Through comprehensive numerical simulations and experimental measurements, we reveal the critical differences between chiral and achiral WGMs, highlighting the robustness of chiral WGMs even in the presence of defects within the cavities. Our research provides valuable insights into the design of robust WGM cavities and offers a novel platform for exploring light-matter interaction phenomena.

physics.optics↗

arXiv2024

Experimental probe of band structures of bilayer valley photonic crystals

Research on two-dimensional van der Waals materials has demonstrated that the layer degree of freedom can significantly alter the physical properties of materials due to the substantial modification of bulk bands. Inspired by this concept, layered photonic systems have been proposed and realized, revealing novel phenomena absent in their monolayer counterparts. In this work, we experimentally investigate the band structures of bilayer valley photonic crystals. Two typical structures with different stacking configurations are experimentally imaged via the near-field scanning technology, exhibiting distinct bulk band structures. Furthermore, different topological edge modes induced by distinct topology are observed, revealing that the layer degree of freedom can be regarded as a pseudospin and offer further capabilities for controlling the flow of light. Our work not only elucidates the evolution of band structures from monolayer to bilayer topological systems but also provides an experimental platform for the further exploration of bilayer topological insulators.

physics.optics↗

arXiv2024

Realization of time-reversal invariant photonic topological Anderson insulators

Disorder, which is ubiquitous in nature, has been extensively explored in photonics for understanding the fundamental principles of light diffusion and localization, as well as for applications in functional resonators and random lasers. Recently, the investigation of disorder in topological photonics has led to the realization of topological Anderson insulators characterized by an unexpected disorder-induced phase transition. However, the observed photonic topological Anderson insulators so far are limited to the time-reversal symmetry breaking systems. Here, we propose and realize a photonic quantum spin Hall topological Anderson insulator without breaking time-reversal symmetry. The disorder-induced topological phase transition is comprehensively confirmed through the theoretical effective Dirac Hamiltonian, numerical analysis of bulk transmission, and experimental examination of bulk and edge transmissions. We present the convincing evidence for the unidirectional propagation and robust transport of helical edge modes, which are the key features of nontrivial time-reversal invariant topological Anderson insulators. Furthermore, we demonstrate disorder-induced beam steering, highlighting the potential of disorder as a new degree of freedom to manipulate light propagation in magnetic-free systems. Our work not only paves the way for observing unique topological photonic phases but also suggests potential device applications through the utilization of disorder.

physics.optics↗

arXiv2024

Broadband and fabrication-tolerant 3-dB couplers with topological valley edge modes

3-dB couplers, which are commonly used in photonic integrated circuits for on-chip information processing, precision measurement, and quantum computing, face challenges in achieving robust performance due to their limited 3-dB bandwidths and sensitivity to fabrication errors. To address this, we introduce topological physics to nanophotonics, developing a framework for topological 3-dB couplers. These couplers exhibit broad working wavelength range and robustness against fabrication dimensional errors. By leveraging valley-Hall topology and mirror symmetry, the photonic-crystal-slab couplers achieve ideal 3-dB splitting characterized by a wavelength-insensitive scattering matrix. Tolerance analysis confirms the superiority on broad bandwidth of 48 nm and robust splitting against dimensional errors of 20 nm. We further propose a topological interferometer for on-chip distance measurement, which also exhibits robustness against dimensional errors. This extension of topological principles to the fields of interferometers, may open up new possibilities for constructing robust wavelength division multiplexing, temperature-drift-insensitive sensing, and optical coherence tomography applications.

physics.optics↗

arXiv2024

Topological Nature of Radiation Asymmetry in Bilayer Metagratings

Manipulating radiation asymmetry of photonic structures is of particular interest in many photonic applications such as directional optical antenna, high efficiency on-chip lasers, and coherent light control. Here, we proposed a term of pseudo-polarization to reveal topological nature of radiation asymmetry in bilayer metagratings. Robust pseudo-polarization vortex with an integer topological charge exists in P-symmetry metagrating, allowing for tunable directionality ranging from -1 to 1 in synthetic parameter space. When P-symmetry-breaking, such vortex becomes pairs of C points due to the conservation law of charge, leading to the phase difference of radiation asymmetry from π/2 to 3π/2. Furthermore, topologically enabled coherent perfect absorption is robust with customized phase difference at will between two counter-propagating external light sources. This work can not only enrich the understanding of two particular topological photonic behavriors, i.e., bound state in the continuum and unidirectional guided resonance, but also provide a topological view on radiation asymmetry, opening an unexplored avenue for asymmetric light manipulation in on-chip laser, light-light switch and quantum emitters.

physics.optics↗

arXiv2023

Observation of gapless corner modes in synthetic translation dimensions

The introduction of synthetic dimensions in topological photonic systems enriches the exploration of topological phase of light in higher-dimensional space beyond three-dimensional real-space. Recently, the gapless corner modes of topological photonic crystals under translational deformation have been proposed, but their experimental observation is still absent. Here, we observe the gapless corner modes in a photonic crystal slab under translational deformation. The corner mode exhibits a frequency dependence that can be tuned through the translation of the slab. Importantly, we find that the existence of gapless corner modes is independent of the specific corner configuration. The gapless corner modes are experimentally imaged via the near-field scanning measurement, and validated numerically by full-wave simulations. Our work contributes to the advancement of topological photonics and provides valuable insights into the exploration of gapless corner modes in synthetic dimensions.

physics.app-ph↗

arXiv2023

Classification of Topological Phase in 2D Photonic Continuous Media Using Electromagnetic Parameters

Refractive index is a fundamental electromagnetic (EM) parameter that can describe photonic continuous media (PCM) traditionally as either transparency or opacity. Recently, topological theory offers a new set of phases to characterize PCM as either trivial or nontrivial, by using topological invariant which are not direct to EM parameters. As all of optical properties in PCM should be related to EM parameters, we formulate a topological index based on EM parameters and establish its phase map in this work. The map can analytically describe the deterministic condition for a topologically nontrivial phase. Our findings indicate that the topology of 2D bi-anisotropic PCM is determined by the sign of the topological index. Another EM parameter of pseudo surface impedance is also introduced for the opaque regions of PCM, showing that the topological opacity has a full range of impedance values ranging from negative to positive, while the trivial case only has either negative or positive impedance. The simulation results show that an interface between two opacities with differing index signs can support robustly optical propagation of topological edge states. As the index only depends on EM parameters, it will pave an insightful way to further understand the intrinsic properties of photonic topology.

physics.optics↗

arXiv2022

High-efficiency grating couplers for pixel-level flat-top beam generation

We demonstrate a kind of grating coupler that generates high quality flat-top beam with a small beamwidth from photonic integrated circuits into free-space. The grating coupler is designed on a silicon-on-insulator wafer with a 220 nm-thick silicon layer and consists of a dual-etch grating (DG) and a distributed Bragg reflector (DBR). By adjusting the structural parameters of DG and DBR, a pixel-level (6.6 um) flat-top beam with the vertical radiation of -0.5 dB and the mode match of 97% at 1550 nm is realized. Furthermore, a series of high-efficiency grating couplers are designed to create flat-top beam with different scales.

physics.optics↗

arXiv2022

Topological photonic crystals: physics, designs and applications

The recent research of topological photonics has not only proposed and realized novel topological phenomena such as one-way broadband propagation and robust transport of light, but also designed and fabricated photonic devices with high-performance indexes which are immune to fabrication errors such as defects or disorders. Photonic crystals, which are periodic optical structures with the advantages of good light field confinement and multiple adjusting degrees of freedom, provide a powerful platform to control the flow of light. With the topology defined in the reciprocal space, photonic crystals have been widely used to reveal different topological phases of light and demonstrate topological photonic functionalities. In this review, we present the physics of topological photonic crystals with different dimensions, models and topological phases. The design methods of topological photonic crystals are introduced. Furthermore, we review the applications of topological photonic crystals in passive and active photonics. These researches pave the way of applying topological photonic crystals in practical photonic devices.

physics.optics↗

arXiv2021

Second Chern crystals in four-dimensional synthetic translation space with inherently nontrivial topology

Topological states, first known as quantum Hall effect or Chern insulating crystal, have been generalized to many classical wave systems where potential applications such as robust waveguiding, quantum computing and high-performance lasers are expected. However, a crystal can be either topologically trivial or nontrivial, depending on its detailed configuration, and one needs to carefully design the structure and calculate its topological invariant before the actual applications. Here, we theoretically study and experimentally demonstrate the second Chern crystal in a four-dimensional space by introducing two extra synthetic translation dimensions. Due to the inherently nontrivial topology of the synthetic translation space, this abstract four-dimensional crystal is guaranteed to be topologically nontrivial regardless of the detailed configuration. The dimensional hierarchy of gapless boundary modes can be deduced by dimension reduction. Remarkably, one-dimensional gapless dislocation modes are observed and their robustness is confirmed in our experiments. This ubiquitous phenomenon in synthetic translation space provides perspectives on the findings of topologically nontrivial crystals and inspires the designs of classical wave devices.

physics.optics↗

arXiv2021

Ideal Nodal Rings of One-Dimensional Photonic Crystals in the Visible Region

Three-dimensional (3D) artificial metacrystals host rich topological phases, such as Weyl points, nodal rings and 3D photonic topological insulators. These topological states enable a wide range of applications, including 3D robust waveguide, one-way fiber and negative refraction of surface wave. However, these carefully designed metacrystals are usually very complex, hindering their extension to nanoscale photonic systems. Here, we theoretically proposed and experimentally realized an ideal nodal ring in visible region using a simple 1D photonic crystal. The pi Berry phase around the ring is manifested by a 2pi reflection phase's winding and the resultant drumhead surface states. By breaking the inversion symmetry, the nodal ring can be gapped and the pi-Berry phase would diffuse into a toroidal shaped Berry flux, resulting in photonic ridge states (the 3D extension of quantum valley Hall states). Our results provide a simple and feasible platform for exploring 3D topological physics and their potential applications in nanophotonics.

physics.optics↗

arXiv2021

Topologically protected valley-dependent quantum photonic circuits

Topological photonics has been introduced as a powerful platform for integrated optics, since it can deal with robust light transport, and be further extended to the quantum world. Strikingly, valley-contrasting physics in topological photonic structures contributes to valley-related edge states, their unidirectional coupling, and even valley-dependent wave-division in topological junctions. Here, we design and fabricate nanophotonic topological harpoon-shaped beam splitters (HSBSs) based on $120$-deg-bending interfaces and demonstrate the first on-chip valley-dependent quantum information process. Two-photon quantum interference, namely, HongOu-Mandel (HOM) interference with a high visibility of $0.956 \pm 0.006$, is realized with our 50/50 HSBS, which is constructed by two topologically distinct domain walls. Cascading this kind of HSBS together, we also demonstrate a simple quantum photonic circuit and generation of a path-entangled state. Our work shows that the photonic valley state can be used in quantum information processing, and it is possible to realize more complex quantum circuits with valley-dependent photonic topological insulators, which provides a novel method for on-chip quantum information processing.

quant-ph↗

arXiv2021

Distortionless pulse transmission in valley photonic crystal slab waveguide

Valley photonic crystal is one type of photonic topological insulator, whose realization only needs P-symmetry breaking. The domain wall between two valley-contrasting photonic crystals support robust edge states which can wrap around sharp corners without backscattering. Using the robust edge states, one can achieve the pulse transmission. Here, using time-domain measurement in the microwave regime, we show distortionless pulse transmission in a sharply bended waveguide. An Omega-shaped waveguide with four 120-degree bends is constructed with the domain wall between two valley photonic crystal slabs. Experimental results show the progress of Gaussian pulse transmission without distortion, and the full width at half maximum of the output signal was changed slightly in the Omega-shaped waveguide. By measuring steady state electric field distribution, we also confirmed the confined edge states without out-of-plane radiation which benefits from the dispersion below the light line. Our work provides a way for high-fidelity optical pulse signal transmission and develop high-performance optical elements such as photonic circuits or optical delay lines.

physics.app-ph↗

arXiv2020

Frequency-dependent topological phases and photonic detouring in valley photonic crystals

Here, the frequency degree of freedom is introduced into valley photonic crystals with dual band gaps. Based on the high-order plane wave expansion model, we derive an effective Hamiltonian which characterizes dual band gaps. Metallic valley photonic crystals are demonstrated as examples in which all four topological phases are found. At the domain walls between topologically distinct valley photonic crystals, frequency-dependent edge states are demonstrated and a broadband photonic detouring is proposed. Our findings provide the guidance for designing the frequency-dependent property of topological structures and show its potential applications in wavelength division multiplexers.

physics.optics↗

arXiv2020

Transmissive Metagrating for Arbitrary Wavefront Shaping Over the Full Visible Spectrum

Metagratings have been shown to form an agile and efficient platform for extreme wavefront manipulation, going beyond the limitations of gradient metasurfaces. Previous approaches for transmissive metagratings have resorted on compound asymmetric inclusions to achieve single-channel near-perfect diffraction. However, such complex inclusions are sensitive to geometric parameters and lack the flexibility for arbitrary phase modulation, restricting applications to beam deflection. Here, we show perfect unitary diffraction in all-dielectric transmissive metagratings using rectangular inclusions by tailoring their multipole interferences. Using this principle, we experimentally demonstrate analog phase profile encoding of a hologram through displacement modulation of CMOS-compatible silicon nitride nanobars, manifesting broadband and wide-angle high diffraction efficiencies for both polarizations and across the entire visible range. Featured with extreme angle/wavelength/polarization tolerance and alleviated structural complexity for both design and fabrication, our demonstration unlocks the full potential of metagrating-based wavefront manipulation for a variety of practical applications.

physics.optics↗