Explore the vast range of titles available.

Topological insulators are a new class of materials that exhibit robust and scatter-free transport along their edges — independently of the fine details of the system and of the edge — due to topological protection. To classify the topological character of two-dimensional systems without additional symmetries, one commonly uses Chern numbers, as their sum computed from all bands below a specific bandgap is equal to the net number of chiral edge modes traversing this gap. However, this is strictly valid only in settings with static Hamiltonians. The Chern numbers do not give a full characterization of the topological properties of periodically driven systems. In our work, we implement a system where chiral edge modes exist although the Chern numbers of all bands are zero. We employ periodically driven photonic waveguide lattices and demonstrate topologically protected scatter-free edge transport in such anomalous Floquet topological insulators. Vanishing Chern numbers usually mean that a system is topologically trivial, but this rule may be violated for periodically driven systems. Here, Maczewsky et al. report topologically protected edge modes in a periodically driven photonic lattice with all bands of zero Chern number.

Topological quantum matter can be realized by subjecting engineered systems to time-periodic modulations. In analogy with static systems, periodically driven quantum matter can be topologically classified by topological invariants, whose non-zero value guarantees the presence of robust edge modes. In the high-frequency limit of the drive, topology is described by standard topological invariants, such as Chern numbers. Away from this limit, these topological numbers become irrelevant, and novel topological invariants must be introduced to capture topological edge transport. The corresponding edge modes were coined anomalous topological edge modes, to highlight their intriguing origin. Here we demonstrate the experimental observation of these topological edge modes in a 2D photonic lattice, where these propagating edge states are shown to coexist with a quasi-localized bulk. Our work opens an exciting route for the exploration of topological physics in time-modulated systems operating away from the high-frequency regime. A periodically driven system may show a novel type of topologically protected edge modes that has no static analogue. Here, Mukherjee et al . report the observation of such anomalous chiral edge modes in an ultrafast-laser-inscribed slowly-driven photonic lattice.

Anderson’s groundbreaking discovery that the presence of stochastic imperfections in a crystal may result in a sudden breakdown of conductivity1 revolutionized our understanding of disordered media. After stimulating decades of studies2, Anderson localization has found applications in various areas of physics3–12. A fundamental assumption in Anderson’s treatment is that no energy is exchanged with the environment. Recently, a number of studies shed new light on disordered media with dissipation14–22. In particular it has been predicted that random fluctuations solely in the dissipation, introduced by the underlying potential, could exponentially localize all eigenstates (spectral localization)14, similar to the original case without dissipation that Anderson considered. We show in theory and experiment that uncorrelated disordered dissipation can simultaneously cause spectral localization and wave spreading (dynamical delocalization). This discovery implies the breakdown of the commonly known correspondence between spectral and dynamical localization known from the Hermitian Anderson model with uncorrelated disorder.Experimental and theoretical results of wave propagation in a disordered system with non-Hermitian disorder are presented, showing that wave spreading occurs in the parameter regime where all eigenstates are expected to be localized.

Photonic integrated circuits have the potential to pervade into multiple applications traditionally limited to bulk optics. Of particular interest for new applications are ferroelectrics such as Lithium Niobate, which exhibit a large Pockels effect, but are difficult to process via dry etching. Here we demonstrate that diamond-like carbon (DLC) is a superior material for the manufacturing of photonic integrated circuits based on ferroelectrics, specifically LiNbO 3 . Using DLC as a hard mask, we demonstrate the fabrication of deeply etched, tightly confining, low loss waveguides with losses as low as 4 dB/m. In contrast to widely employed ridge waveguides, this approach benefits from a more than one order of magnitude higher area integration density while maintaining efficient electro-optical modulation, low loss, and offering a route for efficient optical fiber interfaces. As a proof of concept, we demonstrate a III-V/LiNbO 3 based laser with sub-kHz intrinsic linewidth and tuning rate of 0.7 PHz/s with excellent linearity and CMOS-compatible driving voltage. We also demonstrated a MZM modulator with a 1.73 cm length and a halfwave voltage of 1.94 V. Lithium niobate (LN) is difficult to process via dry etching. Here, authors demonstrate the fabrication of deeply etched, tightly confining, low loss LN photonic integrated circuits with losses 4 dB/m using diamond like carbon as a hard mask.

Topological Insulators are a novel state of matter where spectral bands are characterized by quantized topological invariants. This unique quantized nonlocal property commonly manifests through exotic bulk phenomena and corresponding robust boundary effects. In our work we study a system where the spectral bands are associated with non-quantized indices, but nevertheless possess robust boundary states. We present a theoretical analysis, where we show that the square of the Hamiltonian exhibits quantized indices. The findings are experimentally demonstrated by using photonic Aharonov-Bohm cages. Topological insulators are characterized by quantized topological invariants. Here, the authors report an insulator state showing spectral bands without quantized indices, yet robust boundary states in a photonic setup.

The direct optical transportation of images through multimode fibres (MMFs) is highly sought after in compact photonic systems for MMF-based optical information processing. However, MMFs are highly scattering media, thus degrading information transmitted through them. Existing approaches utilize artificial neural networks or spatial light modulators to reconstruct images scrambled after propagation through the fibre. Despite these advances, achieving direct optical image transportation through MMFs using integrated optical elements with micrometre-scale footprints remains challenging. Here we develop a miniaturized diffractive neural network (DN 2 s) integrated on the distal facet of a MMF for the direct all-optical image transportation through the fibre. The DN 2 s has a footprint of 150 μm by 150 μm and is fabricated on the facet of a 0.35-m-long MMF using three-dimensional two-photon nanolithography. The fibre-integrated DN 2 s enables single-shot optical transportation of images with flat phases in real time for a constant configuration of the MMF. The system achieves a minimum image reconstruction feature size of approximately 4.90 μm over a field of view 65 μm by 65 μm when imaging handwritten digits. Transfer learning is also demonstrated by the direct optical transportation of HeLa cell images projected by spatial light modulators, which were not part of the training dataset. The concept and implementation pave the way to the integration of miniaturized DN 2 s with MMFs for compact photonic systems with unprecedented functionalities. A miniaturized diffractive neural network is fabricated on the distal facet of a multimode fibre, allowing all-optical image transportation through the fibre. With a compact footprint of 150 μm × 150 μm, the system allows the transportation of images with a minimum feature size of 4.90 μm and shows transfer learning capabilities when transporting images of biological cells projected by spatial light modulators.

Non-magnetic non-reciprocal transparency and amplification is experimentally achieved by optomechanics using a whispering-gallery microresonator. The idea may lead to integrated all-optical isolators or non-reciprocal phase shifters. Non-reciprocal devices, such as circulators and isolators, are indispensable components in classical and quantum information processing in integrated photonic circuits 1 . Aside from these applications, the non-reciprocal phase shift is of fundamental interest for exploring exotic topological photonics 2 , such as the realization of chiral edge states and topological protection 3 , 4 . However, incorporating low-optical-loss magnetic materials into a photonic chip is technically challenging 5 . In this study we experimentally demonstrate non-magnetic non-reciprocity using optomechanical interactions in a whispering gallery microresonator, as proposed in a previous work 6 . Optomechanically induced non-reciprocal transparency and amplification are observed and a non-reciprocal phase shift of up to 40° is also demonstrated. The underlying mechanism of optomechanically induced non-reciprocity has great potential for all-optical controllable isolators and circulators, as well as non-reciprocal phase shifters in integrated photonic chips.

The response of a ternary, parity–time-symmetric system that exhibits a third-order exceptional point increases as a function of the cube-root of induced perturbations. Exceptional points, exceptional optics Recent insights into open (non-Hermitian) physical systems have led to a new range of optical systems in which, counter-intuitively, loss is introduced. By careful tuning of loss and gain, certain degeneracies called 'exceptional points' emerge, which have intriguing properties that can be harnessed, for example, in new types of lasers, one-way optical waveguides and topological effects. Two papers in this issue demonstrate the high sensitivity of such non-Hermitian degeneracies to external perturbations, which can be used for precision sensing and detection. Weijian Chen et al . report sensing of nanoparticles with exceptional points generated in a silicon dioxide micro-toroid resonator. Hossein Hodaei et al . generated a higher-order exceptional point by coupling three micro-rings made from a semiconductor laser material. This third-order exceptional point has an even higher, cube-root (rather than square-root) dependence on perturbations. The two papers together provide a new route to ultraprecise chip-based sensing systems. Non-Hermitian degeneracies, also known as exceptional points, have recently emerged as a new way to engineer the response of open physical systems, that is, those that interact with the environment. They correspond to points in parameter space at which the eigenvalues of the underlying system and the corresponding eigenvectors simultaneously coalesce 1 , 2 , 3 . In optics, the abrupt nature of the phase transitions that are encountered around exceptional points has been shown to lead to many intriguing phenomena, such as loss-induced transparency 4 , unidirectional invisibility 5 , 6 , band merging 7 , 8 , topological chirality 9 , 10 and laser mode selectivity 11 , 12 . Recently, it has been shown that the bifurcation properties of second-order non-Hermitian degeneracies can provide a means of enhancing the sensitivity (frequency shifts) of resonant optical structures to external perturbations 13 . Of particular interest is the use of even higher-order exceptional points (greater than second order), which in principle could further amplify the effect of perturbations, leading to even greater sensitivity. Although a growing number of theoretical studies have been devoted to such higher-order degeneracies 14 , 15 , 16 , their experimental demonstration in the optical domain has so far remained elusive. Here we report the observation of higher-order exceptional points in a coupled cavity arrangement—specifically, a ternary, parity–time-symmetric photonic laser molecule—with a carefully tailored gain–loss distribution. We study the system in the spectral domain and find that the frequency response associated with this system follows a cube-root dependence on induced perturbations in the refractive index. Our work paves the way for utilizing non-Hermitian degeneracies in fields including photonics, optomechanics 10 , microwaves 9 and atomic physics 17 , 18 .

Laser displays, which exploit characteristic advantages of lasers, represent a promising next-generation display technology based on the ultimate visual experience they provide. However, the inability to obtain pixelated laser arrays as self-emissive full-color panels hinders the application of laser displays in the flat-panel sector. Due to their excellent optoelectronic properties and processability, organic materials have great potential for the production of periodically patterned multi-color microlaser arrays. Here, we demonstrate for the first time full-color laser displays on precisely patterned organic red-green-blue (RGB) microlaser matrices through inkjet printing. Individual RGB laser pixels are realized by doping respective luminescent dyes into the ink materials, resulting in a wide achievable color gamut 45% larger than the standard RGB space. Using as-prepared microlaser arrays as full-color panels, we achieve dynamic laser displays for video playing through consecutive beam scanning. These results represent a major step towards full-color laser displays with outstanding color expression. In the next generation of display technology for portable devices, lasers could replace LEDs to achieve more vibrant colours. Here, Zhao et al. demonstrate a dynamic full-color display in which each pixel is made up of three printed organic microlasers to cover the RGB space.

While optical fibers display excellent performances in the infrared, visible and ultraviolet ranges remain poorly addressed by them. Obtaining better fibers for the short-wavelength range has been restricted, in all fiber optics, by scattering processes. In hollow-core fibers, the scattering loss arises from the core roughness and represents the limiting factor for loss reduction regardless of the cladding confinement power. Here, we report on the reduction of the core surface roughness of hollow-core fibers by modifying their fabrication technique. The effect of the modified process has been quantified and the results showed a root-mean-square surface roughness reduction from 0.40 to 0.15 nm. The improvement in the core surface entailed fibers with ultralow loss at short wavelengths. The results reveal this approach as a promising path for the development of hollow-core fibers with loss that can potentially be orders of magnitude lower than the ones achievable with silica-core counterparts. In all fiber optics, loss in the visible and UV is restricted by scattering. By improving the core roughness of hollow-core fibers, record attenuation values at short-wavelengths were achieved, opening exciting prospects in visible and UV-photonics.