Laser-cooled atoms are a key quantum medium for atomic clocks, precision metrology, and atom interferometers, and they hold strong potential to advance quantum technologies for position, navigation, and timing. Realizing this potential requires moving cold-atom systems beyond laboratory environments. Integrated photonic chips provide a path forward by improving reliability and reducing size, weight, and power consumption, enabling portable and compact quantum sensors for real-world applications. This review surveys recent progress in laser-cooled atomic platforms, with a focus on the key components that enable on-chip integration of cold-atom systems. We discuss on-chip laser stabilization and linewidth-narrowing techniques, enhanced photon-atom coupling at the chip scale, miniaturized high-vacuum chambers, and the integration of on-chip magnetic coils for cold-atom sensing. Together, these developments are critical to the deployment of chip-scale cold-atom devices in both fundamental atomic physics and practical sensing applications. We conclude with an outlook on next-generation integrated cold-atom platforms and their potential impact on quantum technologies.

Vanadium dioxide (VO2) is a promising candidate for intelligent optical limiting owing to its sharp and reversible metal-insulator transition (MIT). Here, we investigate the thermal-optical synergistic phase transition dynamics of epitaxial VO2 thin films under continuous-wave 3.8 mu m laser excitation. Thermal prebias is found to significantly reduce the optical activation threshold and compress the macroscopic optical response time scale by nearly 4 orders of magnitude. By performing spatially resolved transient measurements under Gaussian-beam illumination, we further reveal that the observed millisecond-scale response does not reflect the intrinsic speed of the phase transition but instead arises from a coupled process involving rapid local nucleation at the beam center and subsequent lateral propagation of the metallic phase across the illuminated area. While submillisecond phase nucleation is achieved locally under thermal-optical synergy, the effective optical limiting response is governed by beam-scale phase-front propagation. These results clarify the physical origin of the effective response time in VO2-based optical limiters and provide practical guidance for optimizing mid-infrared optical limiting through combined thermal biasing and spatial excitation engineering.

This study focuses on the two-dimensional semiconductor alpha-In2Se3, which exhibits excellent nonlinear optical response and tunable bandgap characteristics. It systematically investigates the evolution of its nonlinear optical properties and ultrafast carrier dynamics with thickness variation. A series of nanosheets with controllable thicknesses were fabricated via mechanical exfoliation. X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy confirmed their high-quality 2Hphase crystal structure. Steady-state spectroscopic analysis revealed that the optical bandgap widens significantly from 1.57 eV to 2.13 eV as the thickness decreases, demonstrating a pronounced quantum confinement effect. Furthermore, micro-I-scan, transient absorption spectroscopy, and pump-probe techniques were employed to systematically study its third-order nonlinear optical response and ultrafast carrier relaxation behavior. The experiments revealed that the nonlinear absorption coefficient of the material exhibits a significant thickness dependence. This work reveals the thickness-tunable nonlinear optical properties and the defectdominated carrier relaxation mechanism in two-dimensional In2Se3. It also provides crucial experimental and theoretical support for designing and developing customizable nonlinear optoelectronic devices based on this material.

Low-noise, narrow-linewidth lasers are of great importance for applications demanding exceptional spectral purity, for example, laser cooling. While the cold atom systems usually use large, expensive, and sophisticated lasers to achieve certain wavelengths, photonic integrated circuits can enable portable laser frequency locking systems. This work presents a more compact 780 nm laser stabilization scheme using an on-chip silicon nitride Mach-Zehnder interferometer as a frequency reference. Through the Pound-Drever-Hall locking technique, the system reduces frequency noise by 48.5 dB and narrows the integral linewidth to 15.4 kHz. This demonstrates a compact, high-performance solution for laser stabilization, showing the potential for rubidium atom cooling and quantum manipulation.

Non-stoichiometric Mg2+-Si4+ co-doping in lattice site can effectively reduce the presence of residual phases at grain boundaries and enhance the optical quality of Tb3Al5O12(TAG) garnet transparent ceramics, outperforming traditional weight ratio single-component sintering aids. However, further experimental validation and a deeper analysis of the underlying mechanisms are required to fully understand this phenomenon. In this study, a systematic investigation was carried out to explore the effects of non-stoichiometric Mg2+-Si4+ co-doping on the sintering process of TAG ceramics. Through extensive experiments and analyses, the solid-solution behavior of Mg2+/Si4+ at various sintering stages was revealed, and its correlation with densification, phase evolution, and microstructure of the grain boundary was disclosed. Through analysis of lattice parameter and oxygen vacancy concentration change, it was found that Si4+ enters the lattice earlier than Mg2+, and as temperature increases, the presence of Si4+ in turn enhances the solid solubility of Mg2+. By precisely controlling the Mg2+/Si4+ atomic ratio, optimized control of the densification process was achieved. TEM analysis of the optimal sample's grain boundaries showed that under high addition amounts of MgO and TEOS, the non-stoichiometric design method significantly reduced grain boundary residual phases. This discovery highlights the importance of synergistic optimisation of aids species and content under non-stoichiometric doping for preparing higher optical quality garnet transparent ceramics.

Flexible optical limiting materials that combine high transparency, environmental stability, and strong nonlinear optical responses are highly desirable for laser protection applications. In this work, three composite films based on vanadium oxides with different valence states, namely VO2/PMMA, V2O3/PMMA, and V2O5/PMMA, were fabricated by a solution-casting method using PMMA as the polymer matrix. The morphology, phase composition, valence states, and interfacial interactions of the powders and composite films were systematically characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The results show that the three vanadium oxides retain their characteristic structural features in the PMMA matrix. Nanosecond open-aperture Z-scan measurements at 532 and 1,064nm reveal pronounced wavelength- and composition-dependent nonlinear optical responses. At 532nm, all three composite films exhibit valley-shaped transmission attenuation and optical limiting behavior, among which V2O3/PMMA shows the strongest response and the lowest optical limiting threshold of 128.28mJ/cm(2), outperforming VO2/PMMA and V2O5/PMMA. At 1,064nm, VO2/PMMA and V2O3/PMMA still display strong attenuation-type responses, whereas V2O5/PMMA exhibits a peak-shaped response characteristic of saturable absorption. These results demonstrate that the nonlinear optical behavior of VOx/PMMA films can be effectively tuned by the vanadium valence state, providing useful guidance for the design of flexible materials for optical limiting and saturable absorption applications.

Vanadium dioxide (VO2) is a promising material for mid-infrared optical modulation due to its reversible metal-insulator transition. This study presents an efficient and stable method for fabricating VO2 thin films with enhanced optical limiting performance via crystallinity control and microstructural optimization. The process combines magnetron sputtering with gradient annealing, and the effects of annealing temperature on film structure and optical properties were analyzed using X-ray diffraction, X-ray spectroscopy, and SEM. Annealing at 550 °C yielded high-quality monoclinic VO2(M1) films with excellent crystallinity, low defect density, and island-like grains (250-300 nm). The optimized film showed reduced oxygen vacancies (17.3%) and increased V4+ content. Optical measurements revealed strong thermal switching: mid-infrared transmittance dropped from 85% at 25 °C to 35% at 80 °C, achieving a 50% modulation depth-12.5-fold higher than that of unannealed films. Under 3.8 µm laser irradiation, modulation depth tripled. The annealing process effectively improved phase purity and reduced defects by encouraging grain growth and oxygen vacancy repair. This work provides key insights into the structure-defect-property relationships in VO2 and offers a scalable route for producing high-performance phase-change oxide thin films.

Mid-infrared (MIR) photonic integration is pivotal for applications including molecular fingerprinting and remote sensing. We report Cr:ZnS-Al2O3-sapphire heterostructures fabricated via surface-activated bonding. Through the introduction of atomic-level surface activation and the deposition of an Al2O3 buffer layer, the stress caused by lattice mismatch is effectively alleviated while the diffusion of constituent elements is extremely low, maintaining high optical quality of the heterogeneous structure. The heterostructure achieves a continuous-wave output power of 2.34 W, a 77 % enhancement over pristine Cr:ZnS. Thermo-optical simulations show a 12 K temperature reduction under an incident pump power of 6 W. Leveraging the intrinsic negative group delay dispersion of sapphire and chirped mirrors, the net intra-cavity dispersion is reduced to -117 fs2, enabling direct Kerr-lens mode-locking and generating sub-100 fs pulses at 2362 nm with the average output power of 550 mW. This approach offers a novel composite structure that can be used as integrated photonic platform with on-chip gain for the MIR.

Abstract Recent advancements in integrated two-dimensional (2D) nonlinear optical (NLO) materials open new avenues for photonic technologies. This structure of 2D materials leads to strong light–matter interaction, high carrier density, quantum confinement effect and tunable bandgap, which contribute to their high NLO coefficients, ease tuning of their NLO properties, and ease of integration with micro-optoelectronic devices. This review focuses on recent advances in 2D NLO materials for integrated optical platforms. We first discuss the various strategies for integrating 2D NLO materials with photonic structures such as waveguides, optical fibers, microcavities, and metasurfaces. Next, we highlight the NLO phenomena exhibited by these integrated systems, including harmonic generation, multiphoton processes, and nonlinear refraction and absorption. Finally, we highlight emerging applications in areas such as nonlinear light sources, ultrafast pulse generation, optical frequency combs, photodetectors, terahertz generation, and optical computing. By highlighting recent breakthroughs, this review aims to provide a roadmap for advancing integrated 2D materials toward high-performance photonic technologies.

Explosive vapor bubble formation around laser-heated nanoparticles underpins the performance of key optical materials and devices, including optical limiters and random lasers. However, modeling this complex, multi-physics phenomenon in a way that captures both the material's behavior and its optical response remains a challenge. Here, we present a simple thermodynamic model describing the response of a carbon-nanoparticle-based optical material to a nanosecond laser pulse. The model reveals a sequence of successive, nearly periodic explosive boiling events at the expanding vapor-liquid interface-a "hopping" bubble dynamics driven by intrinsic thermodynamic feedback. This material-specific behavior persists as long as the nanoparticle temperature rises. Crucially, the predicted bubble dynamics correlate strongly with our experimental time-resolved transmittance data, directly linking the material's nanoscale thermal response to its macroscopic optical properties. Our approach not only explains the high optical limiting performance observed in carbon-based suspensions but also provides a computationally efficient framework for understanding and predicting the behavior of nanoparticlebased optical materials under intense laser radiation, with implications for cavitation, shock-wave generation, and even hypersonic wave emission. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

The development of synaptic devices capable of integrating optical sensing and long-term information storage remains a critical challenge in bio-inspired neuromorphic computing. To address the rapid decay of information in photoelectric synapses following cessation of illumination, we fabricated an artificial photoelectric synaptic device based on a small-angle (similar to 1.9 degrees) twisted bilayer MoS2 moir & eacute; superlattice structure and ReS2. By exploiting the cooperative effects of moir & eacute; potential wells and heterointerface charge trapping, our device achieves prolonged optical information retention (similar to 4.8 & times; 10(3) s) and demonstrates a "1 + 1 >> 2" synergistic enhancement effect. Based on techniques including Kelvin probe force microscopy (KPFM), scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and transient absorption, we elucidate the roles of moir & eacute; potentials and interfacial charge trapping in governing synaptic performance. The device successfully emulates essential neurobiological behaviors, including excitatory postsynaptic current, long/short-term memory transition, paired-pulse facilitation, Pavlovian conditioning, and handwritten digit recognition in neural network simulation. This work not only advances the understanding of moir & eacute;-regulated charge storage mechanisms but also establishes a promising platform for high-fidelity, high-performance neuromorphic hardware.

Irregular-shaped perfect vector vortex beams (IPVVBs), as a novel form of structured light for optical field manipulation, have attracted significant attention due to their combined properties of spatial vectorization, orbital angular momentum control, and polygonal symmetry. Compared with traditional circularly symmetric vortex beams, IPVVBs offer notable advantages in mode control and freedom expansion, providing new possibilities for high-dimensional optical field encoding, optical manipulation, and information transmission. In this paper, using an all-dielectric metasurface designed with pure geometric phases, we achieve the generation and spatial polarization control of integer and fractional order irregular-shaped perfect vector vortex beams on the hybrid Poincaré sphere by introducing a cross-phase distribution. The proposed IPVVBs exhibit unique topological properties and stable propagation characteristics. Moreover, the designed metasurface exhibits excellent broadband performance, enabling efficient generation of IPVVBs across multiple wavelengths. Furthermore, we experimentally demonstrate the edge imaging capability of IPVVBs, achieving a resolution of up to 3.1 μm. This work opens up new research directions in cutting-edge fields such as modern optical imaging, microscopic manipulation, and quantum communication.

We present a miniaturized laser frequency-stabilization module based on the 87Rb 5S1/2 -> 5D5/2 two-photon transition. A 778 nm external-cavity diode laser excites the atoms in a small vapor cell, and the generated 420 nm fluorescence provides the stabilization for closed-loop feedback. The optical system-including micro-optics, a vapor cell, and a heater-is fully integrated on a 3D-printed nylon substrate with a total volume of 20 cm3 and a weight of 10.4 g. By optimizing the structure and stabilization scheme, we obtain a high-signal-to-noise ratio (SNR) fluorescence signal and an error signal. The stabilized laser reaches fractional frequency stability of 1.1 & times; 10-11 @ 1 s and 2.89 & times; 10-13 @ 100 s.

Combined with modern microfabrication techniques, thinning laser crystals into laser gain films with a thickness of several hundred nanometers provides a promising approach for high-power on-chip amplifiers and lasers. However, the fabrication of such films still faces challenges in precise thickness control, scalability, and optical loss control. Here, we report a method for preparing submicron-thick laser gain films using Nd:YAG ceramics. By optimizing the ion implantation and annealing processes, we developed an optimal stepwise annealing strategy from 400 degrees C to 900 degrees C. This enabled the successful transfer of an Nd:YAG ceramic film with lateral dimensions of several hundred micrometers onto a sapphire substrate. The transferred film was characterized by transmission electron microscopy (TEM), photoluminescence imaging, and spectroscopy, confirming its structural integrity and favorable luminescent properties. Based on the newly constructed Nd:YAG-on-sapphire (NYOS) platform, we designed a Si3N4 waveguide amplifier operating at 1064 nm. Simulations indicate that this device can achieve a peak gain of approximately 25 dB at 1064 nm over a waveguide length of 12 cm. This work demonstrates the feasibility of preparing ceramic films via ion slicing and provides a promising strategy for developing siliconintegrated Nd:YAG optical amplifiers.

The miniaturization, intense integration, and high-density power of modern electronic and energy devices necessitate extensive management of thermal energy and electromagnetic waves. Creating lightweight, stable, and multifunctional materials to meet these demands remains a challenge. Here, we describe preparing graphene aerogel through the condensation dehydration of hydrophilic polymers and further forming scenario-adaptive multifunctional films through 2500 degrees C heat treatment and paraffin hybridization. The graphene materials exhibit extensive thermal management with high performances covering high thermal conductivity (up to 76.4 W center dot m-1 center dot K-1), superior heat dissipation, tunable electro-thermal conversion, cycling heat storage, and flame retardancy. Additionally, they provide tunable and effective electromagnetic interference shielding performances with high specific shielding effectiveness (up to an average of 91.6 dB, maximum of 123 dB) in a wide frequency range, featuring anti-corrosive absorption-dominant shielding across the X-band, Ku-band, and K-band. Surface engineering of graphene including tuning surface chemical groups and interface couplings contributes to flexible thermal management and electromagnetic shielding. This work might offer a green strategic approach to developing extensive thermal and electromagnetic wave managements of graphene materials.

In recent years, the perfect vortex beam with independent wavefront spiral correlation has attracted extensive attention since its beam diameter is independent of topological charge. Perfect vortex beams are expected to make significant progress in optical fiber communications, particle manipulation, quantum information, and other areas. Traditional optical devices are difficult to integrate into the system due to their large size. In this paper, we design and realize a perfect vortex beam with a high reflection efficiency of 90.17% by an all-dielectric metasurface through a Pancharatnam-Berry (PB) phase modulation structure. The cross-polarization conversion efficiency measured by experiment is 89.81%. By modulating the parameter r(0) in the phase function, we can achieve flexible manipulation of topological charges and ring diameters. In addition, we also demonstrate the generation of a four-channel perfect vortex beam array based on the Dammann grating, with a beam uniformity of 40%. Our research will be of great significance for the realization of compact and multifunctional on-chip integrated photonic devices.

Low-noise stable lasers have broad applications in metrology, spectroscopy, communication, and quantum physics. Here we demonstrate locking a semiconductor laser to an on-chip silicon nitride Mach-Zehnder interferometer (MZI) using the Pound-Drever-Hall (PDH) stabilization technology. After locking, the frequency noise of the laser is suppressed by up to 37 dB, and the relative stability reaches 3 x 10(-10) at a gate time of 1 ms, showing an order of magnitude improvement compared to a free-running operation. In addition, the linewidth of the stabilized laser is 420 kHz at an integration time of 10 ms, narrowed by eight times. (c) 2025 Optica Publishing Group. All rights, including for text and data nologies, are reserved.