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Hyperbolic lattices are a new type of synthetic materials based on regular tessellations in non-Euclidean spaces with constant negative curvature. While so far, there has been several theoretical investigations of hyperbolic topological media, experimental work has been limited to time-reversal invariant systems made of coupled discrete resonances, leaving the more interesting case of robust, unidirectional edge wave transport completely unobserved. Here, we report a non-reciprocal hyperbolic network that exhibits both Chern and anomalous chiral edge modes, and implement it on a planar microwave platform. We experimentally evidence the unidirectional character of the topological edge modes by direct field mapping. We demonstrate the topological origin of these hyperbolic chiral edge modes by an explicit topological invariant measurement, performed from external probes. Our work extends the reach of topological wave physics by allowing for backscattering-immune transport in materials with synthetic non-Euclidean behavior. Here the authors experimentally demonstrate the anomalous and Chern topological phases in a hyperbolic non-reciprocal scattering network, establishing unidirectional channels to induce new and exciting wave transport properties in curved spaces.

Coherent perfect absorption (CPA), or anti-lasing, has been so far inherently restricted to continuous wave scenarios, drastically restricting its applications to standard linear steady-state systems. However, future technologies based on enhanced light-matter interactions typically require the dynamic emission and absorption of pulses, as in ultrafast optics, frequency-comb technologies, or spiking neuromorphic networks. Here, we propose to extend the reach of anti-lasing to pulsed operation. We unveil the phenomenon of fast temporal anti-lasing, in which perfect absorption of photons occurs transiently over ultrashort time scales, creating fast absorption pulses associated with broadband absorption frequency combs. This is obtained by leveraging robust topological transitions occurring in a hysteretic scattering system, which is temporally modulated to loop near a CPA singularity. Our work evidences the interplay between intrinsic memory and topology in wave scattering, unveiling the rich physics of Floquet engineering through topological switching. We envision applications in spiking photonic networks with robust emission, routing and detection of spikes, which may form the basis for future analog neuromorphic hardware. Coherent perfect absorption has been limited to continuous wave operation, restricting its use in dynamic systems. Here, authors demonstrate fast temporal anti-lasing that achieves coherent perfect absorption over ultrashort timescales by using topological transitions in hysteretic scattering systems.

Vortex singularities in acoustic and electromagnetic fields are instrumental degrees of freedom in advanced wavefront-shaping schemes and robust high-throughput communications. Laser sources that emit coherent vortices in free space have been demonstrated at optical frequencies, however their microwave counterparts, vortex masers , have remained entirely unexplored, despite their promising application potential as low-noise quantum sources and sensors. Here, we demonstrate a room-temperature maser emitting pulses of electromagnetic radiation with polarization and phase vortices, based on the physics of 3D topological vectorial singularities. Nontrivial microwave photons with polarization winding are emitted from a maser made of a subwavelength dielectric cavity filled with an organic gain medium. By topping the cavity with a chiral metasurface, the circular polarizations decouple, allowing the masing of pulses with nonzero orbital angular momentum revealed through nontrivial wavefront winding. Our work paves the way for multidimensional vortex and singularity emission from volumetric coherent microwave sources, topological photonic radiation, and novel practical applications of masers. Researchers demonstrate the first room-temperature vortex maser, a compact cubic device that emits structured microwave beams carrying topological singularities and orbital angular momentum, opening new avenues for communications and sensing.

Arbitrary polarized vortex beam induced by polarization singularity offers a new platform for both classical optics and quantum entanglement applications. Bound states in the continuum (BICs) have been demonstrated to be associated with topological charge and vortex polarization singularities in momentum space. For conventional symmetric photonic crystal slabs (PhCSs), BIC is enclosed by linearly polarized far fields with winding angle of 2 π , which is unfavorable for high-capacity and multi-functionality integration-optics applications. Here, we show that by breaking σ z -symmetry of the PhCS, asymmetry in upward and downward directions and arbitrarily polarized BIC can be realized with a bilayer-twisted PhCS. It exhibits elliptical polarization states with constant ellipticity angle at every point in momentum space within the vicinity of BIC. The topological nature of BIC reflects on the orientation angle of polarization state, with a topological charge of 1 for any value of ellipticity angle. Full coverage of Poincaré sphere (i.e., − π 4 ≤ χ ≤ π 4 and − π 2 ≤ ψ ≤ π 2 ) and higher-order Poincaré sphere can be realized by tailoring the twist angles. Our findings may open up new avenues for applications in structured light, quantum optics, and twistronics for photons. Bilayer twisted photonic crystal slabs enable arbitrarily polarized bound states in continuum (BICs) covering full Poincare sphere.

Exceptional points (EPs) can achieve intriguing asymmetric control in non-Hermitian systems due to the degeneracy of eigenstates. Here, we present a general method that extends this specific asymmetric response of EP photonic systems to address any arbitrary fully-polarized light. By rotating the meta-structures at EP, Pancharatnam-Berry (PB) phase can be exclusively encoded on one of the circular polarization-conversion channels. To address any arbitrary wavefront, we superpose the optical signals originating from two orthogonally polarized -yet degenerate- EP eigenmodes. The construction of such orthogonal EP eigenstates pairs is achieved by applying mirror-symmetry to the nanostructure geometry flipping thereby the EP eigenmode handedness from left to right circular polarization. Non-Hermitian reflective PB metasurfaces designed using such EP superposition enable arbitrary, yet unidirectional, vectorial wavefront shaping devices. Our results open new avenues for topological wave control and illustrate the capabilities of topological photonics to distinctively operate on arbitrary polarization-state with enhanced performances. The authors report the chiral inversion of exceptional points (EPs) through a structural mirror-symmetric operation, extending the application of EP to any desired polarization states, surpassing the inherent limitation of conventional EP systems.

Robust chirality is demonstrated by exploiting the merging of multiple accidental bound states in the continuum (BICs). This mechanism simultaneously sustains ultrahigh-quality factor Q resonances and strong chiroptical responses across a wide region of momentum space, achieving near-perfect circular dichroism (~0.99) and an ultrahigh- Q value (~10⁴) in a planar dielectric platform.

We propose the realization of exceptional points (EP) at bound states in the continuum (BIC), with two coupled strips, made of an electron-beam resist and patterned on the thin film photonic integrated platform, which makes possible etchless photonics integrated circuits (PIC). The loss rate of the EP can be significantly decreased through merging the BIC peaks in the dual-BIC scheme. The orthogonality of the eigenvectors is retrieved for evaluating the Hermitian orthogonal eigenvectors and the non-Hermitian EP features. We also find that engineering the dimension of the dual-BIC scheme enables a transition between the coalesced eigenvectors in the EP and the orthogonal eigenvectors in the Hermitian system. This work is of great significance for the exploration on BIC-based directional coupling with ultralow-loss phase matching conditions, special coupling conditions of EPs and BICs with coupled quasi-BIC systems, dynamical EP encircling, and EP topology, in PICs.

Integrating nonlocal metasurfaces with thermal photonics has endowed thermal emissions with temporal and spatial coherence, as well as chirality. However, the static response of current thermal emitters hinders their broader applications, especially in high-precision sensing. Here, we present an anisotropic thermal metasurface that harnesses exclusively elevated temperatures inherent in thermal photonics to achieve helicity-switchable and wavelength-tunable circularly polarized coherent thermal emissions in the mid-infrared. Through a meticulous design to achieve a pair of high-Q quasi-guided mode resonances with opposite chirality and significant emission circular dichroism, we experimentally demonstrate helicity-switchable circularly polarized thermal emissions with high temporal coherence (Q > 150) and strong emission circular dichroism (>0.8) over a ~ 100 nm wavelength range through a temperature change of 250 K. We further reveal that simple geometric design enables full polarization tailoring. Our platform offers a compact and scalable pathway toward on-chip applications including circular dichroism spectroscopy for enantiomer identification. The authors demonstrate a thermal metasurface achieving wavelength-tunable and helicity switchable coherent infrared emission through temperature control, enabling high-performance on-chip circular dichroism spectroscopy for chiral molecular sensing.

Exceptional points (EPs) are spectral singularities of non-Hermitian systems and represent the coalescence of eigenvalues and eigenstates. Traditional photonic systems typically exhibit coalesced eigenstates that correspond to circular polarizations of a specific handedness, thereby restricting their applicability to only the poles of the Poincaré sphere. Here, by judiciously combining optical anisotropy, chirality and non-Hermiticity of diffractive plasmonic metasurfaces with basis transformation, we achieve a continuum of EPs for which the corresponding coalesced eigenstates can access any point on the Poincaré sphere, greatly alleviating the strict requirement of approaching EP degeneracy. Our theoretical proposal and experimental implementation overcome the main practical limitation of EPs, extending the applicability of the topological phase to arbitrarily polarized state within the diffraction region. The emergence of these non-conventional EPs not only contributes to applications in wavefront engineering and optical multiplexing, but also brings in new fundamental properties of topological systems in general. Qin et al. realized a plasmonic exceptional point distribution that covers full Poincaré sphere based on extrinsic chirality and basis transformation, extending the application of singularity induced topological phase to arbitrary polarization states.

Metasurfaces excel at local, spatially varying control of wavefronts, whereas photonic crystals (PhCs) are admired for their nonlocal resonances such as bound states in the continuum (BICs). These two regimes—local control and nonlocal collective response—have long been viewed as difficult to integrate within a single platform. Here, we introduce local-nonlocal assisted multifunctional PhCs unifying wavefront shaping and BICs by embedding meta-notches within PhC pillars. The locally tunable notches generate spectral-zero-assisted topological phase for efficient 2π coverage, while the strongly confined BIC modes remain largely unperturbed, preserving high- Q nonlocal resonances. This constructive local-nonlocal integration synthesizes the design freedom of metasurfaces with the dispersive resonance of PhCs in a single planar device. Our approach extends the capabilities of flat optics, enabling multifunctional PhCs and opening pathways toward higher-order topologies, advanced imaging, communication, and analogue optical computing.