We present a systematic simulation of ultra-broadband second-harmonic generation (SHG) via dispersion engineering in a periodically poled lithium tantalate waveguide. By optimizing the waveguide geometric parameters, we simultaneously minimize the first-and second-order dispersion mismatch, achieving a flat phase-matching condition in telecommunication band. The simulated device exhibits a 3-dB bandwidth-length product (Delta lambda & sdot;L) of 7162 mu m2 and a normalized conversion efficiency of 9099% W-1cm-2. This design demonstrates a promising route toward efficient, broadband frequency conversion in integrated photonics, beneficial for integrated nonlinear photonics devices based on second-order nonlinearity on the TFLT platform.

ABSTRACT The development of multifunctional ferroelectric platforms requires on‐chip photodetection that combines wavelength selectivity, self‐powered operation, and material compatibility. We demonstrate a lithium niobate (LN) photodetector achieving these capabilities through synergistic integration of ferroelectric domain engineering and guided‐mode resonance (GMR) metasurfaces. Using focused ion beam milling on z ‐cut thin‐film LN, we create a continuous network of conductive domain walls (CDWs) at pillar‐trench interfaces while simultaneously defining a metasurface array that localizes the optical field at these same locations. This synergy enables efficient photocarrier collection directly within the conductive pathway. The device exhibits a resistivity reduction of up to 9 orders of magnitude compared to pristine LN and achieves self‐powered photodetection across the visible to near‐infrared spectrum (473–1900 nm). By tailoring the metasurface period, the response peak can be precisely tuned from 1550 to 637 nm, with responsivities reaching 0.11 A/W at zero bias and 31.8 A/W under 3 V bias. Using detectors resonantly tuned to distinct wavelengths, we demonstrate wavelength‐selective imaging with each detector responding exclusively to its target wavelength. The design leverages intrinsic ferroelectric properties, offering a material‐based pathway toward integrated photodetection in LN and other ferroelectric platforms.

Topological lasers have emerged as a promising platform for robust photonic systems, yet current implementations relying on semiconductor microcavities and resonators suffer from fundamental constraints including low optical gain, limited output power and fixed lasing sites. To address these challenges, we present an all-solid-state, reconfigurable topological laser based on a Su-Schrieffer-Heeger waveguide array platform, fabricated in disordered laser crystal (Nd:BaLaGa3O7). Harnessing the high gain provided by solid-state lasers, we experimentally and theoretically demonstrate single-mode, continuous-wave topological lasing with output power surpassing 100 mW. In addition to conventional topological edge lasing, we observe topological lasing at trivial lattice terminations and reconfigurable interface sites at arbitrary lattice positions. This unconventional behavior arises from the non-Hermitian parity-time symmetry transition in subsystem at elevated pump power. Our work demonstrates on-demand, site-selectable topological lasing, offering both fundamental insights into topological phase transitions in non-Hermitian systems and practical opportunities to develop robust, reconfigurable topological photonic devices for advanced lasing and optical information processing. Topological lasers usually emit light from a fixed spot. Here, authors report on an all-solid-state platform where topological lasing is demonstrated at trivial lattice terminations as well as at reconfigurable arbitrary sites. The device consists of a Su-Schrieffer-Heeger waveguide array, printed in a disordered Nd:BaLaGa₃O₇ crystal.

Abstract Morphological stability of active layers is a critical factor influencing the performance and longevity of organic solar cells (OSCs). This study proposes a novel approach to assess device stability based on the fractal characteristics of the active layer morphology, focusing on self‐similarity as a key parameter. Our findings indicate that a higher degree of morphological congruence between donor and acceptor materials results in more refined fractal structures and improved self‐similarity within the blending films, which is directly correlated with the improved stability of both the film morphology and device performance. By introducing acceptor molecules exhibiting a strong congruence with the donor material as a third component, we achieved high self‐similarity in the morphology of bulk heterojunction (BHJ) films, resulting in enhanced device stability. The optimized devices simultaneously maintain a power conversion efficiencie of 20.05%, underscoring the feasibility of balancing efficiency and stability. This work establishes self‐similarity as a practical metric for guiding material design, offering a scalable strategy to improve OSC durability for applications in flexible and indoor photovoltaics.

We propose and experimentally demonstrate a lithium niobate (LN) metasurface that generates significant optical chirality simply by rotating achiral nanorods, thereby breaking mirror symmetry without the need for other complex 3D geometric structures. The chiral response originates from the non-orthogonal coupling between electric and magnetic dipole moments, which is further enhanced through strong hybridization of transverse electric (TE) and transverse magnetic (TM) modes at specific rotation angles. Theoretical simulations reveal that a rotation angle of 30 degrees leads to a near-unity circular dichroism (CD) due to robust TE-TM coupling. Experimentally, we observe a maximum linear CD of -0.37 and a strong nonlinear CD of -0.42 in second-harmonic generation (SHG). This work presents the first experimental demonstration of intrinsic nonlinear chiroptical effects from an LN metasurface platform. The simple yet effective design, easy to fabricate and extend to other nonlinear optical crystals, establishes LN metasurfaces as a promising candidate for advanced applications in chiral sensing, polarization-sensitive photonics, and quantum optics.

An archive system that encodes information in modified optical properties of glass could be a fast, efficient way to store huge quantities of data. An archive system that encodes information in modified optical properties of glass could be a fast, efficient way to store huge quantities of data.

We report on laser-written depressed-cladding waveguides with specially tailored elliptical cross-sections in LiNbO3 crystals. The experimental results reveal that both polarization characteristics and propagation losses of waveguides can be effectively modulated through precise cross-section tailoring. Second harmonic generation (SHG) performance at 1030 nm demonstrates that the SHG conversion efficiency of an elliptical cross-section waveguide is higher than that of a round one. The mu-Raman spectroscopy shows that a stress field in a waveguide core may increase with the decrease in cross-section. This work provides a practical method for realizing polarization modulation and nonlinear optical improvement of depressed-cladding waveguides, having potential applications in constructing advanced integrated photonic devices.

Rare-earth-doped materials constitute the foundation of conventional solid-state lasers, but their bulk-crystal form is inherently incompatible with photonic integration, making it challenging to realize compact, high performance nanoscale laser sources. Lithium niobate on insulator (LNOI), with its exceptional electro-optic and nonlinear optical properties, has emerged as one of the most promising platforms for integrated photonics. Combining Nd3+ doping with LNOI offers the unique possibility of uniting the efficient gain provided by Nd3+ ions with the excellent characteristics of LNOI. However, on-chip laser emission from Nd:LNOI has not been demonstrated previously. In this work, we report the first realization of an integrated Nd:LNOI microdisk laser, demonstrating lasing at 1094.17 nm under 785.10 nm pumping with a low threshold of 146 uW and a slope efficiency of 1.962*10^(-5). Beyond continuous-wave operation, we further observe self-induced laser pulsing on the hundred-microsecond scale, with a laser-pulse duration down to 500 us and an oscillation period of 6.45 ms, arising from nonlinear thermo-optic-photorefractive dynamics. We demonstrate stable continuous wave lasing and self-induced pulsed emission within a monolithically integrated Nd:LNOI cavity. Our results expand the operational degrees of freedom for LNOI-based lasers and open a new direction toward deeply integrated gain with intrinsic nonlinear dynamical processes.

As laser processing technology continues to expand into fields like medicine and information communication, there is a growing urgency for miniaturizing pulsed laser sources and integrating them into chip-scale light sources. Currently, the miniaturization of pulsed lasers mainly relies on optical waveguide structures, achieved by integrating traditional Fabry-Perot (F-P) cavities with nonlinear modulation elements. Although this design can reduce the cross-sectional area of the optical mode to a few square micrometers, the F-P cavity-based architecture requires optical waveguide lengths of several millimeters to centimeters, offering both theoretical possibilities and practical requirements for further device size reduction. Here, this work presents a passively Q-switched picosecond pulsed laser based on whispering gallery mode (WGM) microcavities, with a diameter of only 28 mu m. This WGM laser employs Cr,Nd:YAG as a self-Q-switched gain medium, generating 820-picosecond pulses at 0.75 MHz with a 3.5 mW threshold. The study explores Q-switched dynamics in a WGM resonator, showing how cavity size and Cr,Nd:YAG absorption affect pulse stability. The findings indicate that WGM cavities exhibit higher stability compared to Fabry-Perot resonators, providing strong support for the development of more compact and efficient pulsed laser systems and suggesting promising applications in future miniaturized laser technologies.

Bound states in the continuums (BICs) are localized states whose eigenvalues lie within the continuum spectrum of extended states. Here, we report the experimental observation of distinct BICs in the strained type-Ⅱ Dirac photonic lattices. Using direct femtosecond laser writing, we fabricate two such lattices with tailored geometries and boundary conditions, enabling the direct observation of corner states with unique phase profiles. These states remain embedded within—yet decoupled from—the bulk continuum, exhibiting strong localization analogous to BICs. Our work establishes a new platform for studying higher-order BICs in photonic systems and opens further opportunities in Dirac photonics.

We have fabricated two categories of three-dimensional (3D) 1 × 3 waveguide beam splitters by femtosecond laser in lithium triborate (LBO) crystals. Both splitters are composed of laser-written depressed-cladding waveguides with circular cross-sections, and can realize efficient second-harmonic generation (SHG) when excited with a 1031-nm fundamental wavelength. With our beam splitter, a record SHG conversion efficiency of 9.22% has been achieved. By using laser-writing technique to tailor the cross-section of each output port of the splitter, which has three identical output ports, we have achieved the mode evolution of both fundamental and SHG waves from multi-mode to single-mode at three engineered output ports. This work successfully integrates 3D beam splitting with frequency conversion in a nonlinear crystal for the first time, to the best of our knowledge, paving a way to fabricate high-efficiency, and energy-saving photonic integrated circuits (PICs).

Femtosecond laser direct writing enables rapid and flexible fabrication of optical waveguides for integrated photonics. We systematically examined the effects of laser energy, repetition rate, scanning speed, and slit insertion on the structural and optical properties of lithium niobate waveguides fabricated with 1031 nm, 420 fs pulses. End-face coupling was employed to characterize the near-field mode profiles, polarization-dependent behaviors, and propagation losses. The results show that Type I waveguides are preferentially formed at high repetition rates or with slit insertion, while Type II waveguides are favored at low repetition rates. These findings provide quantitative design rules for LiNbO 3 waveguides in specific photonic applications.

Charge transport is an important property that influences the stability of organic solar cells (OSCs). While decreased average charge mobility during degradation is recognized as an essential factor reducing device stability, the dispersion property of charge transport is often overlooked. The dispersion parameter characterizes the dispersion of transit times in charge transport. A high dispersion parameter typically indicates a significant population of slow charge carriers in OSCs, which could introduce more charge recombination and ultimately compromise device stability. In this work, we demonstrate that the combined effect of dispersion parameter and charge mobility serves as a key indicator of degradation pathways, underscoring the critical role of the initial morphology of the active layer in device stability. This work not only establishes a morphology-transport stability framework for enhancing the charge transport stability but also discovers the significance of sustaining a balanced mobility-dispersion property for ensuring the long-term stability of OSCs.

Two-dimensional (2D) materials, with excellent optoelectronic properties and ultrathin structural features, have emerged as promising candidates for constructing optoelectronic synapse devices (OSDs). However, these 2D OSDs rely on van der Waals heterostructures formed by stacking multiple 2D materials or hybrid stacks of 2D and organic materials, a process that significantly complicates device fabrication. In this work, we simplify the structure of 2D OSDs to a monolayer molybdenum disulfide (MoS2) with a Fe:LiNbO3 crystal as the substrate. A monolayer MoS2 was transferred onto the surface of Fe:LiNbO3 with a pair of electrodes. Under the illumination of a 632.8 nm optical signal, a spatial electric field distribution was generated on the Fe:LiNbO3 surface due to the photovoltaic effect, which modulates the band structure of MoS2, thereby realizing the optical signal perception and storage. This MoS2/Fe:LiNbO3 structure exhibits remarkable optical synapse-like properties, including both long-term and short-term synaptic plasticity, with a paired-pulse facilitation index of 1.32. Based on this, the flicker fusion visual characteristics in biology were simulated, and the critical fusion frequency was measured to be 0.5 mHz. The result indicates the device has advantages in perceiving low-frequency signals below 0.5 mHz in multifrequency environments. Meanwhile, the MoS2/Fe:LiNbO3 structure, serving as a visual neural synapse, exhibited excellent noise filtering ability for input signals. After a noisy data set was processed by the device for 1546 s, the accuracy of image recognition training increased significantly from the original 88.7% to 99.5%. This work simplifies the structure of 2D OSDs, benefiting the construction of visual optoelectronic synapse devices.

Objective The optical stability of properties in one-dimensional all-dielectric photonic crystals (PCs) by Cion irradiation is investigated experimentally. After the PCs are irradiated over two years, the transmission and reflection spectra of both periodic and defect-typed PCs subjected to C(5+ )ion irradiation are re-measured. The old and new spectra overlap well, which demonstrates the long-term stability of the optical properties in the PCs after ion irradiation. Furthermore, changes in both transmission and reflection spectra are correlated with the Cion irradiation fluences. Both transmittance and reflectance progressively decrease with increasing irradiation fluence, and this phenomenon is attributed to the enhanced optical absorption in the photonic crystals induced by C5+ ion irradiation. The manipulation of optical properties with the photonic crystals by controlled ion irradiation is significant to engineer important optical devices. Methods In this study, the transfer matrix method (TMM) were used to simulate the optical spectra of the PCs. The PCs were composed of different dielectric materials which were deposited on the flat surface of the BK7 substrate using ion-assisted electron-beam evaporation under high vacuum conditions. The vacuum chamber was maintained at 2. 0 x 10(-2) (- z) Pa during the deposition, the temperature was set to 150 degrees C, and the thicknesses of the dielectric layers were monitored using quartz crystal sensors. After the fabrication of the PCs, ion irradiation experiments were performed at room temperature using a serial accelerator at Helmholtz-Zentrum Dresden (HZDR), Germany. After the ion irradiation, the optical spectra of the PC samples were measured using a Lambda 1050WB UV-Vis-NIR spectrophotometer (PerkinElmer). Results and Discussions This study mainly investigated the differences in optical spectra of periodic and defect-typed all-dielectric PCs irradiated by C ion with different fluences when they were placed over two years. The transmission and reflection spectra of all-dielectric periodic and defective PCs under C ion irradiation with different fluences were measured again on May 6, 2024. It was found that their spectra were nearly the same as those on February 15, 2022 (Figs. 2-7), where multiple incident angles under TE and TM polarizations were considered. The defect in the PC included two types: SiO, defect layer and Tio, defect layer. These comparison results for two types of PCs over two years showed the long-term stability of their optical spectra. Moreover, these research results indicate that the irradiated all-dielectric periodic and defective PCs are suitable for engineering optical devices with stable performance. Conclusions This study discusses the stability of optical properties of all-dielectric PCs irradiated by C ions. Two years later, the transmission and reflection spectra of irradiated PCs are measured again. The old and new optical spectra of periodic and defective PCs overlap well, which indicates the long-term stability of optical properties in the PCs after ion irradiation with different fluences. The transmittance and reflectance of the PCs gradually decrease by increasing Cion irradiation fluences, which is attributed to the enhanced optical absorption, Correspondingly, both the photonic hand gap and the defect modes of the PCs exhibit a significant blue shift which mainly comes from the reduction of the optical thickness of the PC after C ion irradiation. Otherwise, the width of the photonie band gap reduces gradually with the increase of the C irradiation fluences which is mainly due to the reduction in the optical thickness of the basic unit in the PC and the decrease of the refractive index ratio. These experimental results show that ion-irradiated all-dielectric PCs have good long-term optical stability which provides an important theoretical and experimental hasis for their practical applications.

Neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal is an excellent gain medium for optical amplification at 1.06 μm. However, its stable physical and chemical properties have long hindered the microfabrication of Nd:YAG bulk crystals with optical precision, limiting their application in photonic integrated circuits. In this work, we demonstrate a free-standing Nd:YAG waveguide amplifier with high gain. Using a corrosion-assisted patterned stripping method, a spiral Nd:YAG waveguide with a total length of 1.3 mm was directly exfoliated from a bulk crystal. Under 808 nm laser pumping, the waveguide amplifier exhibits an internal net gain of 15 dB, corresponding to a gain per unit length of 115 dB/cm. Furthermore, this Nd:YAG optical amplifier not only exhibits high gain but also possesses a compact footprint of 240 μm × 140 μm, offering expanded material options for the development of high-gain, small-scale integrated photonic devices.

Two-dimensional materials have demonstrated revolutionary potential in optoelectronic devices due to their atomic-scale thickness, high carrier mobility, and broad bandgap coverage. Among them, tungsten diselenide (WSe2) and molybdenum ditelluride (MoTe2), as representative members of the transition metal dichalcogenide (TMD) family, can be vertically stacked to form a type-I van der Waals heterojunction, offering a strategy for designing high-performance avalanche phototransistors (APTs). The core operating principle of an APT relies on carrier avalanche multiplication under a high electric field. When the device enters the avalanche breakdown regime, a strong electric field accelerates hot carriers, inducing impact ionization via collisions with the lattice and thereby generating a large number of electron-hole pairs. Unlike conventional type-II heterojunctions, in a type-I configuration, the wide-bandgap component (e.g., WSe2) functions as a barrier layer that effectively suppresses carrier recombination, while photo-generated carriers in the narrow-bandgap material (e.g., MoTe2) can cross the interface through tunneling, markedly improving carrier collection efficiency and response speed. This property allows the type-I heterojunction to significantly suppress thermal noise in the APT before reaching the critical voltage. Combined with the inherently low dielectric constant and atomic-scale thickness of 2D materials, avalanche breakdown can be achieved at substantially lower bias voltages, greatly reducing power consumption and the risk of thermal damage.

The development of flexible photonics is fundamentally limited by the scarcity of functional, flexible optical materials. While conventional materials such as rare-earth-doped yttrium aluminum garnet (YAG) crystals offer superior optical properties, their inherent rigidity precludes their use in flexible devices. Here, a corrosion-assisted patterned stripping (CAPS) technique is reported to directly fabricate flexible, microscale bi-spiral Er:YAG filaments from bulk crystals, significantly expanding the material options for flexible photonics. These filaments exhibit remarkable mechanical compliance, enduring the degree of stretching up to 300% with full recovery after thousands of stretching cycles. Integrated onto elastomeric substrates, the filaments act as low-loss optical waveguides exhibiting stable light transmission during deformation. As a proof of concept, a flexible optical waveguide amplifier operating in the telecommunication band is demonstrated, achieving a net gain of 10 dB, comparable to devices on rigid substrates. This direct conversion of rigid optical crystals into compliant components provides new design paradigms for flexible optoelectronic systems, addressing a critical materials challenge in the field.

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.

Prism-coupled layered structures, including surface plasmon resonance (SPR) sensors and resonant mirror (RM) sensors, have been widely used in refractive index sensing. However, the interference-based signal detection of RM is sophisticated, and the low quality factor of the SPR mode limits sensing performance. In this work, an absorptive RM with independently tunable radiative and absorptive losses is proposed and theoretically investigated. By controlling the buffer layer thickness and waveguide extinction coefficient separately, the radiative quality factor (Qr) and absorptive quality factor (Qa) can be adjusted without crosstalk. When Qr and Qa are matched at the critical coupling condition, perfect absorption with ultra-narrow bandwidth is achieved. With a simple layer stack and compatibility with existing prism-coupled schemes, the proposed absorptive RM may offer a promising platform for label-free sensing.