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The precise manipulation of neural activity is of great significance to reveal the function of complex neural circuits in brain, especially the mechanism of neurological disorders such as epilepsy, Parkinson's, and Alzheimer's disease. In the past decades, optogenetics has become a powerful tool to investigate the function of neural circuits due to its unique advantages of cell specificity and high spatiotemporal resolution. However, to date, most optogenetic manipulation has been conducted in an open‐loop fashion. The closed‐loop neural modulation is still an important task. Here, a closed‐loop optogenetic modulation system is developed for ultra‐fast, ‐accurate, and ‐stable manipulation of neural activities in behaving mice. Specifically, this system is mediated by a functional fiber probe with excellent low optical loss (0.052 dB cm−1 at 589 nm) and electrical impedance (5.40 MΩ µm−2 at 1 kHz). In vivo electrophysiology and behavioral experiments demonstrated that the system can be successfully applied for the identification and intervention of seizures in epilepsy mice with high efficiency. It is envision that the closed‐loop manipulation system has promising applications in brain science, neuroscience, and neuromodulation therapies. [ABSTRACT FROM AUTHOR]

In the digital era, the need for high‐density data storage techniques has become increasingly imperative. To address this, the study has demonstrated a multi‐dimensional shingled optical recording technique, utilizing femtosecond laser‐induced nanostructures in silica glass. The evolution of the bulk nanostructures is investigated on a pulse‐by‐pulse basis using multiple microscopic analysis techniques. The formation of the nanostructures is attributed to a self‐adaptive near‐field anisotropic nanostructuring process. Furthermore, it is shown that writing in a 3D shingled configuration significantly reduces the volume per data voxel to a size of 500 nm × 500 nm × 1.0 µm, surpassing the diffraction limit. This reduction is achieved even when employing an infrared laser and a relatively low numerical aperture objective lens. As a result, the approach increases the data storage capacity by at least two orders of magnitude compared to conventional techniques. The work paves the way for advanced shingled optical recording techniques offering ultra‐dense capacity, ultra‐long lifetime, and low energy consumption. [ABSTRACT FROM AUTHOR]

Glass ceramics may exhibit enhanced functionalities compared to the glass and crystal counterparts due to the synergistic effect with the "1+1 > 2" feature in a cooperative manner. Nonlinear optical property is expected to be next breakthrough in presenting synergistic effect in glass ceramics. In this article, we give a comprehensive review of the recent progress of the development in nonlinear glass ceramics with unique photonic domain structure, emphasizing their synergistic effect in nonlinear response. The applications in photonics of the nonlinear glass ceramics are also described. Finally, we also present the opportunities and challenges for further exploring synergistic effect in nonlinear response in glass ceramics. [ABSTRACT FROM AUTHOR]

With the rapid development of 5G networks, the Internet of Things, and new‐generation of AI, there are considerable demands on expanding the capacity of contemporary optical fiber communication systems. One of the most effective avenues involves the extension of the bandwidth of Er‐doped fiber amplifiers, but with limited success. Herein, an Er‐activated hybridized glass fiber are reported, which can help realize broadband telecommunication. The effect of element hybridization on the bandwidth of Er‐activated fiber is clarified and the structure‐optical response relationship is established. A two‐step deposition approach is proposed to overcome the immiscibility barrier of different hybridized elements, and Er‐activated fiber with uniform doping is constructed. The activated fiber presents excellent compatibility with commercial telecommunication systems, providing a small signal gain of >13 dB in the whole L‐band range and a maximum gain of 28 dB. Furthermore, the Er‐activated fiber amplifier device is successfully developed. It exhibits outstanding optical amplification performance with gain >24 dB in the range of 1580–1624 nm, gain fluctuation less than ±0.9 dB, and noise figure <6.5 dB. The results not only provide a new strategy for developing novel active broadband optical fibers, but a valuable solution for new‐generation large‐capacity optical fiber communication systems. [ABSTRACT FROM AUTHOR]

Bismuth (Bi)-doped glasses with broadband near-infrared (NIR) emission have been drawing increasing interest due to their potential applications in tunable fiber lasers and broadband optical amplifiers. Yet, the realization of highly efficient and ultra-broadband Bi NIR emission covering the whole telecommunication window remains a daunting challenge. Here, via rationally controlling the content of Al2O3 to control the local environment and structural defect states around the Bi NIR active centers (BACs), various luminescence centers can coexist stably in a glass matrix. Consequently, tunable ultra-broadband multi-band NIR emission with four emission bands at ∼924, ∼1154, ∼1265, and ∼1516 nm was achieved in a Bi-doped germanate glass under single wavelength excitation. More importantly, such ultra-broadband multi-band Bi NIR emission with excellent thermal stability can be well retained after the glass was drawn into an optical fiber by a rod-in-tube method. The fibers show an obvious broadband ASE spectrum spanning a range of 1000–1600 nm. This work is helpful for understanding the mechanism of Bi NIR emission and offers a simple and feasible method for developing novel photonic devices with ultra-broadband Bi NIR emission. [ABSTRACT FROM AUTHOR]

Square-root topological insulators recently discovered are intriguing topological phases. They possess topological properties inherited from the squared Hamiltonian and exhibit double-band structures. The mechanism of the square root was generalized to 2n-root topological insulators, giving rise to more band gaps. In this study, we describe the experimental realization of one-dimensional 2n-root topological insulators in photonic waveguide arrays using the archetypical Su-Schrieffer-Heeger (SSH) model. Topological edge states with tunable numbers are clearly observed under visible light. In particular, we visualized the dynamic evolutions of the light propagation by varying the sample lengths, which further proved the localization and multiple numbers of edge states in 2n-root topological systems. The experiment, which involves constructing 2n-root topological photonic lattices in various geometric arrangements, provides a stable platform for studying topological states that exhibit a remarkable degree of flexibility and control. [ABSTRACT FROM AUTHOR]

Laser‐induced periodic surface structure (LIPSS) can form structural color on the metal surfaces with high production efficiency and thermal stability, and has been used in various industrial applications such as unfaded color marking and anti‐counterfeiting. Herein, a novel fabrication scheme of multilayer LIPSS is proposed by multiple writing in situ with changing the laser polarization direction, to exhibit an effect of color superposition. To verify this approach, the color formation mechanism of LIPSS on the stainless‐steel surface is analyzed by finite‐element numerical calculation and reveals that the high‐angular dispersion of LIPSS is mainly the result of optical diffraction occurring on the surface of periodic structures. The relationship between the angular dispersion of multilayer LIPSS and laser‐processing parameters is established. Through the proposed multilayer LIPSS coloring technology, vivid full‐color patterns on the steel surface are demonstrated, and the in situ superposition of three‐layer graphs is realized, which can greatly enrich the color levels and be competitive in industrial applications. [ABSTRACT FROM AUTHOR]

Excitation polarized upconversion luminescence (EPUL) from lanthanide ions has attracted considerable attention due to its wide applications in microfluidics, single particle tracking, security inks, and cell internal viscosity testing. However, controlling the degree of excitation polarization (DOEP) of the EPUL remains a significant challenge. Here, the modulation of the DOEP (from 0 to 0.5) of the EPUL from Er3+ doped single nanorods by changing the concentration of doped Er3+, Yb3+, or Mn2+ is systematically studied. By analyzing the lifetimes and disproportionate changes in luminescence intensities, it is found that optimizing Er3+, Yb3+, or Mn2+ concentration can reduce non‐radiative transition and population density in excited states, leading to the enhancement of the DOEP under a good alignment of transition dipoles. Furthermore, the possibility of anti‐counterfeiting based on such tunable EPUL is illustrated. Three kinds of fine patterns with a small size of 10 µm are realized by assembling the single nanorods accurately via optical tweezers. The patterns and their EPUL guarantee double protection for the feasibility of anti‐counterfeiting. The findings of this study offer insights into the EPUL from lanthanide ions and provide a microscale platform via the EPUL for the application of multidimensional information encoding and reconfigurable double anti‐counterfeiting. [ABSTRACT FROM AUTHOR]

The outstanding performance of halide perovskite makes it one of the champion materials for applications in optoelectronic devices. However, the stability of perovskites limits their practical applications. Among all the factors influencing the stability of perovskites, defects are one of the key factors. Till now, many chemical methods have been proposed to passivate defects. Nevertheless, there is still a lack of in situ passivation methods without the change of the composition of perovskites. Here, it is found that the external electric field can passivate the defects in FPEA2PbI4 (FPEAI = 2‐(4‐Fluorophenyl)ethylamine Hydroiodide) film in a capacitive device at 78 K, and the PL intensity can be enhanced greatly. A "charge‐soaking effect" can be observed, that is PL intensity continues to increase for a long time after removing the electric field. Besides the emission peak from free exciton, two other peaks at the lower energy side from defect‐bound excitons are observed. They are more susceptible to the external electric field than the free exciton. This work will deepen the understanding of exciton behavior and the interaction of electric field with excitons in two–dimensional (2D) hybrid perovskites for efficient light–emitting diodes (LEDs) and electrically pumped lasers. It provides a new in situ passivation method of perovskites for practical applications. [ABSTRACT FROM AUTHOR]