Chen Cheng

Quasi-2D organic-inorganic hybrid metal halide perovskites are promising gain media for coherent light sources. However, uncontrolled crystallization and low-fidelity pattern transfer make it difficult to ensure the quality of the resulting structures. We combine 3-phosphonopropionic acid (3-PPA), which optimizes phase distribution and passivates defects, with nanoimprint lithography (NIL) that modulates crystallization kinetics to fabricate patterned quasi-2D (PEA) ₂ Cs _n-1 Pb _n Br _{3n + 1} perovskite films. As a result, the amplified spontaneous emission (ASE) threshold decreases from 5.52 to 2.11 µJ/cm ² . Under 400 nm femtosecond-pulse excitation, the photonic crystal cavity exhibits single-mode surface-emitting lasing at 456.65 nm. As the pump fluence progressively increases from 0.23 to 0.59 µJ/cm ² , the single-mode lasing intensity exhibits a monotonic growth. This work offers a promising route for integrating crystallization control, defect passivation, and photonic engineering.

Quasi‐two‐dimensional (quasi‐2D) perovskites are promising for light‐emitting and lasing devices due to their strong excitonic properties and quantum‐well structures; however, their performance is limited by phase inhomogeneity and defect‐related nonradiative losses. Here, we incorporate 3‐phosphonopropanoic acid (3‐PPA) as an additive into the quasi‐2D (PEA) ₂ Cs _{n −1} Pb _n Br _{3 n  + 1} film to improve film quality and optical gain characteristics. The 3‐PPA‐treated films exhibit improved crystallization and significantly inhibit low‐dimensional impurity phases. The introduction of 3‐PPA extended the fluorescence lifetime to 203.63 ps and accelerated the stimulated emission process, shortening the amplified spontaneous emission (ASE) lifetime to 2.82 ps. Transient absorption and nonlinear optical measurements reveal longer gain lifetimes, enhanced two‐photon absorption, and lower saturation intensity, which collectively promote more efficient population inversion. Finally, the quasi‐2D perovskite film treated with 3‐PPA exhibited stronger emission and a reduced ASE threshold of 2.25 μJ/cm ² . This work demonstrates an effective additive engineering approach that enhances the potential of quasi‐2D perovskites for efficient low‐threshold photonic devices.

Quasi‐two‐dimensional (quasi‐2D) perovskites now are promising candidate materials for obtaining laser diodes and microlaser media, requiring phase‐purification as an effective strategy to minimize energy loss and enhance optical gain. However, the intrinsic mechanism by which purified phase purity leads to high photophysical properties remains understudied. Here, by employing phenylethylammonium trifluoroacetate (PEATFA) for phase purification, it is demonstrated that phase‐purified perovskites possess suppressed exciton‐phonon coupling, prolonged gain lifetime and enhanced nonlinear absorption property. At low temperature, photoluminescence reveals that the phase‐purified quasi‐2D perovskite film has weakened quantum confinement and suppressed exciton‐phonon coupling. During the establishment of stimulated emission, the enhanced energy transfer efficiency enables sufficient carrier accumulation in higher‐dimensional phases, prolonging the gain lifetime to 98 ps. After phase purification, perovskite films exhibit better optical properties in nonlinear regime with higher two‐photon absorption (TPA) coefficient and lower saturation absorption intensity. Finally, phase‐purified films achieve optimal amplified spontaneous emission (ASE) performance with a remarkably low threshold of 3.6 µJ cm ⁻² . This work reveals the intrinsic mechanism of phase purification regulating photophysical properties, providing a scientific basis for understanding that phase purification treatment enhances the gain characteristics of perovskite materials.

We report a forward-viewing asymmetric fiber cantilever scanner with two-dimensional Lissajous trajectories. The scanner was composed of a fiber cantilever, a supporting fiber, an asymmetric fiber cantilever and a quadrupole piezoelectric tube actuator with optimized parameter by finite element analysis and experiments. The scanner provided a frequency separation and field of view of 216 Hz and 350 µm ×350 µm, respectively. The best combination of two orthogonal resonance frequencies was determined to achieve a fill factor up to 92% at a scanning speed of 10 Hz. The Lissajous fiber scanner, integrated with a gradient-index lens, was assembled into a compact forward-viewing scanning unit. This work provides a structurally simple and performance-enhanced solution for resonant scanning systems, with strong potential for future use in optical endomicroscopy platforms.

Metal halide perovskites have emerged as revolutionary optical gain media, challenging conventional semiconductor lasers with their combination of solution processability, tunable emission, and exceptional optoelectronic properties. This review systematically explores recent advances in perovskite-based amplified spontaneous emission (ASE) and lasing technologies, focusing on low-dimensional systems—nanocrystal (NC) and quasi-two-dimensional (quasi-2D) perovskites. We first elucidate the fundamental photophysical principles governing ASE in these materials, contrasting the quantum confinement-dominated gain in NCs with the exciton funneling mechanism in quasi-2D structures. This is followed by a critical analysis of materials engineering strategies, highlighting how ligand/solvent/additive engineering, phase control, and plasmon coupling work together to suppress nonradiative losses to achieve sub-μJ/cm² ASE thresholds. This paper explores breakthroughs in optically pumped lasers (e.g., room-temperature continuous-wave operation, microcavity integration), as well as ongoing challenges facing electrically pumped devices, including charge injection imbalance and thermal degradation. The review further points to emerging opportunities in scalable synthesis, hybrid-size design, and applications such as on-chip photonics and bioimaging. By correlating molecular-scale defect engineering with macroscopic photonic performance, this study provides a roadmap for developing stable and efficient perovskite coherent light sources, bridging fundamental research with practical applications.

In this study, we present the development of a Y-branch superficial waveguide splitter that was fabricated using a combination of femtosecond laser writing and ablating techniques in a z-cut lithium tantalate (LiTaO3) wafer. By strategically switching focus objectives and adjusting the pulse energy, we successfully created ridge waveguides with femtosecond laser-ablated side-walls and written bottom boundaries. This unique ridge guiding structure exhibits remarkable polarization sensitivity and superior waveguiding performance, particularly at the telecommunication wavelength of 1.55 μm. The fabrication process leverages the precision and flexibility of femtosecond laser technology to achieve high-quality waveguides with well-defined geometries. The polarization sensitivity of the waveguide splitter is a significant advantage for applications in optical communication systems, where polarization control is crucial. The excellent waveguiding performance at 1.55 μm wavelength ensures efficient transmission and minimal loss, making this Y-branch splitter a promising candidate for integration into advanced photonic devices and systems.

Integrated optoelectronic systems are widely used in optical communications and other fields. As an important unit in the system, optical waveguide is the basis of optical information processing and transmission. In the past decade, the emerging field of topological photons has shown great potential in applications. The topological edge state and backscattering suppression of photonic crystal can realize the lossless transmission of light. Therefore, in the construction of optical waveguide, photonic topological insulator provides a novel idea for the study of compact volume waveguide devices. In this paper, a simple two-dimensional photonic crystal is designed. By changing the distance between the dielectric column and the center of the unit cell, the band inversion of the double degenerate p state and d state is realized in the center of the Brillouin zone, and it is proved that the essence of the band inversion is the topological phase transition. The numerical simulation results reveal that unidirectional transmission can be realized on the interface between topological trivial and nontrivial photonic crystals. The photonic crystals in this paper are only composed of lithium niobate (LN) materials and the lattice structure is simple. When topological phase transition is realized, it is not necessary to change the filling rate and size of the dielectric column, but only to move the distance of the dielectric column. Therefore, this structure is more effective in the application of topological boundary states.

Quarter-wave plate (QWP) metasurfaces provide a novel approach for generating three-dimensional (3D) hybrid-order Poincaré sphere (HyOPS) beams and enabling longitudinal polarization modulation, owing to their unique spin-decoupling properties. In this work, we designed a set of QWP meta-atom metasurfaces that generate 3D HyOPS beams with continuously varying polarization states along the propagation direction. The third-, fourth- and fifth-order HyOPS beams are generated by three metasurface devices, respectively. The HyOPS beams exhibit a focal depth of 30 μm, a stable longitudinal propagation, and a continuously evolving polarization state. Notably, complete polarization evolution along the equator of the HyOPS occurs within a depth of 20 μm. Numerical calculations in MATLAB R2022b validated the feasibility of the designed QWP metasurfaces. The finite-difference time-domain (FDTD) simulations further confirmed the stable propagation and continuous polarization evolution of the longitudinal light field. Additionally, the concentric arrangement of the QWP meta-atoms on the metasurface effectively mitigates scattering crosstalk caused by abrupt edge phase variations. This work offers new insights into the generation and control of HyOPS light fields and contributes significantly to the development of miniaturized, functionally integrated high-performance nanophotonics.

Metal halide perovskites have unique luminescent properties that make them an attractive alternative for high quality light-emitting devices. However, the poor stability of perovskites with many defects and the long cycle time for the preparation of perovskite nanocomposites have hindered their production and application. Here, we prepared the perovskite mesostructures by embedding MAPbBr₃ nanocrystals in the mesopores on the surface of silica nanospheres and mixing the nanospheres with silver nanowires and poly(methyl methacrylate) (PMMA), and further explored their optical properties. The perovskite mesostructures exhibited superfluorescence (SF) under 785 nm laser excitation and the decay time was as short as 0.59 ps using a double exponential decay fit. The optical nonlinearity of these perovskite mesostructures under two-photon excitation was investigated by the Z-scanning technique. The samples exhibited both two-photon absorption (TPA) and saturation absorption (SA) with nonlinear absorption coefficients β ranging approximately 0.15 to 0.89 cm/GW corresponding to the TPA, and a saturation intensity of about 0.026 GW/cm² was determined. In addition, the quality of the perovskite mesostructures was shown to be significantly improved, including an increase in radiative efficiency and an extension of the optical gain lifetime. The samples were excited by a two-photon femtosecond laser pump at room temperature and atmospheric pressure, and the laser peak appeared at 540.1 nm with a low amplified spontaneous emission (ASE) threshold of 0.52 mJ/cm². Moreover, the perovskite mesostructures have been added to the fiber laser system as a saturable absorber, and the Q-switched pulse is generated at the wavelength of 1.5 µm. Our work effectively demonstrates that perovskite mesostructured materials can be functionalized for photonic devices, paving the way for further exploration of complex, functional and practical perovskite.

The generation of vector beams using metasurfaces is crucial for the manipulation of light fields and has significant application potential, ranging from classical physics to quantum science. This paper introduces a novel dielectric metasurface composed of quarter‐wave plate (QWP) meta‐atoms, known as a QWP metasurface, designed to generate focused vector beams (VBs) of Bell‐like states under right circularly polarized illumination. The propagation phase imparted on both the co‐ and cross‐polarized components of the output field constructs hyperbolic and helical phase profiles with topological charge l _p , whereas the Pancharatnam–Berry (PB) phase acts only on the cross‐polarized component to construct another helical phase profile with topological charge l _g . Thus, the co‐ and cross‐polarized components form two orthogonal vector vortex (VV) modes with topological charges l _p and l _p + l _g , respectively. When the parameter conditions are satisfied by matching the incident polarization chirality σ and topological charges l _p and l _g , the focused VBs of Bell‐like states are generated by simultaneously manipulating the two VV modes, in contrast to existing QWP metasurfaces. The polarization states of the generated VBs are manipulated using the initial orientation angle θ ₀ of the meta‐atom. Overall, this research provides an innovative strategy for metasurface design, enhancing the functionality of metasurface devices for a broader range of application scenarios.