Omni-polarized Faraday isolator based on non-Hermitian Faraday system.

Non-Hermitian systems have recently attracted significant attention in photonics due to the realization that the interplay between gain and loss can lead to entirely new and unexpected features. Here, we propose and demonstrate a non-Hermitian Faraday system capable of non-reciprocal omni-polarizer action at the exceptional point. Notably, both forward and backward propagating light with arbitrary polarization converge to the same polarization state. Leveraging the robustness and non-reciprocity of the non-Hermitian Faraday system, we realize an omni-polarized Faraday isolator that can effectively isolate any polarized light without the need for a polarizer at the incident port of backward propagation. Remarkably, under the given parameter configuration, the isolator achieves a maximum isolation ratio of approximately 100 dB and a minimum isolation ratio of around 45 dB for various polarized light, accompanied by near-zero insertion loss. Furthermore, our research reveals the remarkable tolerance of the non-Hermitian Faraday isolator to nonlinear effects. This unique characteristic allows us to harness nonlinear effects to achieve various optical functions, all while maintaining excellent isolation performance. The proposed non-Hermitian Faraday system paves the way for the realization of magnetically or optically switchable non-reciprocal devices.

Transient cavity-cavity strong coupling at terahertz frequency on LiNbO3 chips.

Terahertz (THz) microcavities have garnered considerable attention for their ability to localize and confine THz waves, allowing for strong coupling to remarkably enhance the light-matter interaction. These properties hold great promise for advancing THz science and technology, particularly for high-speed integrated THz chips where transient interaction between THz waves and matter is critical. However, experimental study of these transient time-domain processes requires high temporal and spatial resolution since these processes, such as THz strong coupling, occur in several picoseconds and microns. Thus, most literature studies rarely cover temporal and spatial processes at the same time. In this work, we thoroughly investigate the transient cavity-cavity strong-coupling phenomena at THz frequency and find a Rabi-like oscillation in the microcavities, manifested by direct observation of a periodic energy exchange process via a phase-contrast time-resolved imaging system. Our explanation, based on the Jaynes-Cummings model, provides theoretical insight into this transient strong-coupling process. This work provides an opportunity to deeply understand the transient strong-coupling process between THz microcavities, which sheds light on the potential of THz microcavities for high-speed THz sensor and THz chip design.

Electro-Optical Comb Envelope Engineering Based on Mode Crossing.

Resonator-enhanced electro-optical (EO) combs could generate a series of comb lines with high coherence and stability. Recently, EO comb based on thin-film lithium niobate (TFLN) has begun to show great potential thanks to the high second-order nonlinearity coefficient of lithium niobate crystal. Here we demonstrate that EO comb envelope engineering based on mode crossing induced a quality factor reduction in the TFLN racetrack microcavity both in the numerical simulation and experiment. Our method paves the way for the generation of EO combs with an arbitrary envelope.

Collective Cell Radial Ordered Migration in Spatial Confinement.

Collective cells, a typical active matter system, exhibit complex coordinated behaviors fundamental for various developmental and physiological processes. The present work discovers a collective radial ordered migration behavior of NIH3T3 fibroblasts that depends on persistent top-down regulation with 2D spatial confinement. Remarkably, individual cells move in a weak-oriented, diffusive-like rather than strong-oriented ballistic manner. Despite this, the collective movement is spatiotemporal heterogeneous and radial ordering at supracellular scale, manifesting as a radial ordered wavefront originated from the boundary and propagated toward the center of pattern. Combining bottom-up cell-to-extracellular matrix (ECM) interaction strategy, numerical simulations based on a developed mechanical model well reproduce and explain above observations. The model further predicts the independence of geometric features on this ordering behavior, which is validated by experiments. These results together indicate such radial ordered collective migration is ascribed to the couple of top-down regulation with spatial restriction and bottom-up cellular endogenous nature.

Electrically Tunable Two-Color Cholesteric Laser.

Two-color lasing emission from an asymmetric structure, consisting of two dye-doped cholesteric liquid crystal (DD-CLC) layers separated by a transparent interlayer, is demonstrated. The DD-CLC mixtures have different reflection bands with long-wavelength band edges located at the green and red wavelengths of the visible spectrum, respectively. For the laser action, the CLC hosts provide the feedback, and the fluorescent laser dyes represent the active medium. When the stacked structure is optically pumped above the threshold, two simultaneous laser lines separated by 123 nm are observed at the long-wavelength band edges of the DD-CLC mixtures. The influence of an electric field on lasing behavior is also analyzed and discussed in terms of the reflection spectrum and laser action. The results show a reversible tuning of the reflection band, accompanied by a modification of the lasing characteristics under the application of an external field. Above a specific threshold voltage, one of the emission lines is suppressed and the other is conserved. With a further increase in the voltage, both laser emissions are entirely inhibited. The investigated structure demonstrates a simple technique to obtain an electrically tunable multi-wavelength laser, which might pave the way for a new generation of organic laser sources.

Equilibrium Dynamics of Mutually Confined Waves with Signed Analogous Masses.

We report the first experimental realization of equilibrium dynamics of mutually confined waves with signed analogous masses in an optical fiber. Our Letter is mainly demonstrated by considering a mutual confinement between a soliton pair and a dispersive wave experiencing opposite dispersion. The resulting wave-packet complex is found robust upon random perturbation and collision with other waves. The equilibrium dynamics are also extended to scenarios of more than three waves. Our finding may trigger fundamental interest in the dynamics of many-body systems arising from the concept of negative mass, which is promising for new applications based on localized nonlinear waves.

Controllable nonlinear propagation of partially incoherent Airy beams.

The self-accelerating beams such as the Airy beam show great potentials in many applications including optical manipulation, imaging and communication. However, their superior features during linear propagation could be easily corrupted by optical nonlinearity or spatial incoherence individually. Here we investigate how the interaction of spatial incoherence and nonlinear propagation affect the beam quality of Airy beam, and find that the two destroying factors can in fact balance each other. Our results show that the influence of coherence and nonlinearity on the propagation of partially incoherent Airy beams (PIABs) can be formulated as two exponential functions that have factors of opposite signs. With appropriate spatial coherence length, the PIABs not only resist the corruption of beam profile caused by self-focusing nonlinearity, but also exhibits less anomalous diffraction caused by the self-defocusing nonlinearity. Our work provides deep insight into how to maintain the beam quality of self-accelerating Airy beams by exploiting the interaction between partially incoherence and optical nonlinearity. Our results may bring about new possibilities for optimizing partially incoherent structured field and developing related applications such as optical communication, incoherent imaging and optical manipulations.

Photonic Realization of a Generic Type of Graphene Edge States Exhibiting Topological Flat Band.

Cutting a honeycomb lattice (HCL) ends up with three types of edges (zigzag, bearded, and armchair), as is well known in the study of graphene edge states. Here, we propose and demonstrate a distinctive twig-shaped edge, thereby observing new edge states using a photonic platform. Our main findings are (i) the twig edge is a generic type of HCL edge complementary to the armchair edge, formed by choosing the right primitive cell rather than simple lattice cutting or Klein edge modification; (ii) the twig edge states form a complete flat band across the Brillouin zone with zero-energy degeneracy, characterized by nontrivial topological winding of the lattice Hamiltonian; (iii) the twig edge states can be elongated or compactly localized at the boundary, manifesting both flat band and topological features. Although realized here in a photonic graphene, such twig edge states should exist in other synthetic HCL structures. Moreover, our results may broaden the understanding of graphene edge states, as well as new avenues for realization of robust edge localization and nontrivial topological phases based on Dirac-like materials.

4D Additive-Subtractive Manufacturing of Shape Memory Ceramics.

The development of high-temperature structural materials, such as ceramics, is limited by their extremely high melting points and the difficulty in building complicated architectures. Four-dimensional (4D) printing helps enhance the geometrical flexibility of ceramics. However, ceramic 4D printing systems are limited by the separate processes for shape and material transformations, low accuracy of morphing systems, low resolution of ceramic structures, and their time-intensive nature. Here, a paradigm for a one-step shape/material transformation, high-2D/3D/4D-precision, high-efficiency, and scalable 4D additive-subtractive manufacturing of shape memory ceramics is developed. Original/reverse and global/local multimode shape memory capabilities are achieved using macroscale SiOC-based ceramic materials. The uniformly deposited Al2 O3 -rich layer on the printed SiOC-based ceramic lattice structures results in an unusually high flame ablation performance of the complex-shaped ceramics. The proposed framework is expected to broaden the applications of high-temperature structural materials in the aerospace, electronics, biomedical, and art fields.

On-chip erbium-ytterbium-co-doped lithium niobate microdisk laser with an ultralow threshold.

Erbium-ion-doped lithium niobate (LN) microcavity lasers working in the communication band have attracted extensive attention recently. However, their conversion efficiencies and laser thresholds still have significant room to improve. Here, we prepared microdisk cavities based on erbium-ytterbium-co-doped LN thin film by using ultraviolet lithography, argon ion etching, and a chemical-mechanical polishing process. Benefiting from the erbium-ytterbium co-doping-induced gain coefficient improvement, laser emission with an ultralow threshold (∼1 µW) and high conversion efficiency (1.8 × 10-3%) was observed in the fabricated microdisks under a 980-nm-band optical pump. This study provides an effective reference for improving the performance of LN thin-film lasers.

On-chip ytterbium-doped lithium niobate waveguide amplifiers with high net internal gain.

Integrated optical systems based on lithium niobate on insulator (LNOI) have shown great potential in recent years. However, the LNOI platform is facing a shortage of active devices. Considering the significant progress made in rare-earth-doped LNOI lasers and amplifiers, the fabrication of on-chip ytterbium-doped LNOI waveguide amplifiers based on electron-beam lithography and inductively coupled plasma reactive ion etching was investigated. The signal amplification at lower pump power (<1 mW) was achieved by the fabricated waveguide amplifiers. A net internal gain of ∼18 dB/cm in the 1064 nm band was also achieved in the waveguide amplifiers under a pump power of 10 mW at 974 nm. This work proposes a new, to the best of our knowledge, active device for the LNOI integrated optical system. It may become an important basic component for lithium niobate thin-film integrated photonics in the future.

Mesenchymal Migration on Adhesive-Nonadhesive Alternate Surfaces in Macrophages.

Mesenchymal migration usually happens on adhesive substrates, while cells adopt amoeboid migration on low/nonadhesive surfaces. Protein-repelling reagents, e.g., poly(ethylene) glycol (PEG), are routinely employed to resist cell adhering and migrating. Contrary to these perceptions, this work discovers a unique locomotion of macrophages on adhesive-nonadhesive alternate substrates in vitro that they can overcome nonadhesive PEG gaps to reach adhesive regions in the mesenchymal mode. Adhering to extracellular matrix regions is a prerequisite for macrophages to perform further locomotion on the PEG regions. Podosomes are found highly enriched on the PEG region in macrophages and support their migration across the nonadhesive regions. Increasing podosome density through myosin IIA inhibition facilitates cell motility on adhesive-nonadhesive alternate substrates. Moreover, a developed cellular Potts model reproduces this mesenchymal migration. These findings together uncover a new migratory behavior on adhesive-nonadhesive alternate substrates in macrophages.

Electrically tuned coupling of lithium niobate microresonators.

Microresonators coupled with integrated waveguides operate stably but usually lack tunability for an optimal coupling state. In this Letter, we demonstrate a racetrack resonator with an electrically modulated coupling on an X-cut lithium niobate (LN) platform by introducing a Mach-Zehnder interferometer (MZI) with two balanced directional couplers (DCs) to realize light exchange. This device provides a wide-range coupling regulation, from under-coupling and critical coupling to deep over-coupling. Importantly, it has a fixed resonance frequency when the DC splitting ratio is 3 dB. The measured optical responses of the resonator exhibit a high extinction ratio, exceeding 23 dB, and an effective half-wave voltage length Vπ·L of 0.77 V·cm, suitable for CMOS compatibility. Microresonators with tunable coupling and a stable resonance frequency are expected to find application in nonlinear optical devices on LN-integrated optical platforms.

Second-harmonic and cascaded third-harmonic generation in generalized quasiperiodic poled lithium niobate waveguides.

Lithium niobate (LN) thin film has recently emerged as an important platform for nonlinear optical investigations for its large χ(2) nonlinear coefficients and ability of light localization. In this Letter, we report the first, to the best of our knowledge, fabrication of LN-on-insulator ridge waveguides with generalized quasiperiodic poled superlattices using the electric field polarization technique and microfabrication techniques. Benefiting from the abundant reciprocal vectors, we observed efficient second-harmonic and cascaded third-harmonic signals in the same device, with normalized conversion efficiency of 1735% W-1 cm-2 and 0.41% W-2 cm-4, respectively. This work opens a new direction for nonlinear integrated photonics based on LN thin film.

Stationary Charge Radiation in Anisotropic Photonic Time Crystals.

Time metamaterials offer a great potential for wave manipulation, drawing increasing attention in recent years. Here, we explore the exotic wave dynamics of an anisotropic photonic time crystal (APTC) formed by an anisotropic medium whose optical properties are uniformly and periodically changed in time. Based on a temporal transfer matrix formalism, we show that a stationary charge embedded in an APTC emits radiation, in contrast to the case of isotropic photonic time crystals, and its distribution in momentum space is controlled by the APTC band structure. Our approach extends the functionalities of time metamaterials, offering new opportunities for radiation generation and control, with implications for both classical and quantum applications.

Dual-Wavelength Lasing with Orthogonal Circular Polarizations Generated in a Single Layer of a Polymer-Cholesteric Liquid Crystal Superstructure.

We investigate the laser emission from a polymer-cholesteric liquid crystal superstructure with coexisting opposite chiralities fabricated by refilling a right-handed polymeric scaffold with a left-handed cholesteric liquid crystalline material. The superstructure exhibits two photonic band gaps corresponding to the right- and left-circularly polarized light. By adding a suitable dye, dual-wavelength lasing with orthogonal circular polarizations is realized in this single-layer structure. The wavelength of the left-circularly polarized laser emission is thermally tunable, while the wavelength of the right-circularly polarized emission is relatively stable. Due to its relative simplicity and tunability characteristics, our design might have broad application prospects in various fields of photonics and display technology.

Topological super-modes engineering with acoustic graphene plasmons.

Acoustic graphene plasmons (AGPs) in a graphene-dielectric-metal structure possess extreme field localization and low loss, which have promising applications in strong photon-matter interaction and integrated photonic devices. Here, we propose two kinds of one-dimensional crystals supporting propagating AGPs with different topological properties, which is confirmed by the Zak phase calculations and the electric field symmetry analysis. Moreover, by combining these two plasmonic crystals to form a superlattice system, the super-modes exist because of the coupling between isolated topological interface states. A flat-like dispersion of super-modes is observed by designing the superlattice. These results should find applications in optical sensing and integrating photonic devices with plasmonic crystals.

Hybrid Machine Learning Approach for Evapotranspiration Estimation of Fruit Tree in Agricultural Cyber-Physical Systems.

The flourish of the Internet of Things (IoT) and data-driven techniques provide new ideas for enhancing agricultural production, where evapotranspiration estimation is a crucial issue in crop irrigation systems. However, tremendous and unsynchronized data from agricultural cyber-physical systems bring large computational costs as well as complicate performing conventional machine learning methods. To precisely estimate evapotranspiration with acceptable computational costs under the background of IoT, we combine time granulation computing techniques and gradient boosting decision tree (GBDT) with Bayesian optimization (BO) to propose a hybrid machine learning approach. In the combination, a fuzzy granulation method and a time calibration technique are introduced to break voluminous and unsynchronized data into small-scale and synchronized granules with high representativeness. Subsequently, GBDT is implemented to predict evapotranspiration, and BO is utilized to find the optimal hyperparameter values from the reduced granules. IoT data from Xi'an Fruit Technology Promotion Center in Shaanxi Province, China, verify that the proposed granular-GBDT-BO is effective for cherry tree evapotranspiration estimation with reduced computational time, and acceptable and robust predictive accuracy. Consequently, the precise estimation of crop evapotranspiration could provide operational guidance for plant irrigation, plant conservations, and pest control in the agricultural greenhouse.

Molecular Resolution Mapping of Erythrocyte Cytoskeleton by Ultrastructure Expansion Single-Molecule Localization Microscopy.

The combination of expansion microscopy and single-molecule localization microscopy has the potential to approach the molecular resolution. However, this combination meets challenges due to the hydrogel shrinkage in the presence of imaging buffer. Here, a method of ultrastructure expansion single-molecule localization microscopy (U-ExSMLM) based on skillfully adhering the gel onto poly-l-lysine (pLL)-coated coverslip is developed to prevent lateral shrinkage of the hydrogel. U-ExSMLM is then applied to dissect the membrane cytoskeleton organization of human erythrocytes at molecular resolution. The resolved nanoscale spatial distributions of cytoskeleton proteins, including the N/C-termini of ß-spectrin, protein 4.1, and tropomodulin, show good agreement with the acknowledged model of erythrocyte cytoskeleton structure, demonstrating the reliability of U-ExSMLM. Furthermore, the concentration of pLL is adjusted to preserve the physiological biconcave morphology of erythrocytes, and it is found that the spectrin cytoskeleton in the dimple regions has lower density and larger length than that in the rim regions, which provides the direct evidence for cytoskeleton asymmetry in human erythrocytes. Therefore, the integrated method offers future opportunities to study the ultrastructure of membrane cytoskeleton at molecular resolution.

Frequency modulation of terahertz microcavity via strong coupling with plasmonic resonators.

Tunable terahertz (THz) microcavities are crucial for the compact on-chip THz devices, aiming to future cloud-based computing, and artificial-intelligence technologies. However, the solutions to effectively modulate THz microcavities remain elusive. Strong coupling has been widely demonstrated in many configurations at different ambient conditions to date and may serve as a promising tool to modulate THz microcavities. Here, we schematically design a microcavity-plasmon hybrid system, and propose an effective approach to modulating the resonant frequencies of THz microcavities by the microcavity-resonator strong coupling. In this case, we observed the strongly coupling states, where the resultant two-polariton branches exhibit an anti-crossing splitting in the frequency domain, experimentally exhibiting a ∼6.2% frequency modulation to the microcavity compared to the uncoupled case. This work provides an efficient approach to modulating chip-scale THz microcavities, thereby facilitating the development and application of compact THz integrated devices, further empowering the evolution of future information processing and intelligent computing system.