Xiao-Fang Jiang

Achieving nonreciprocal transmission of circularly polarized light (CPL) is critical for chiral photonics and spin‐selective optical communication, yet existing optical diodes typically operate at fixed wavelengths. Here, we report an all‐optical, photoswitchable diode‐type device for tunable nonreciprocal (asymmetric) transmission of CPL across a broad spectrum of light using molecular motor (photoswitch)‐doped cholesteric liquid crystals (CLCs) sandwiched between polyvinyl alcohol (PVA) and polydopamine (PDA)‐PVA composite layers. Under ultraviolet irradiation, the photoswitches continuously modulate the helical twisting power of the CLC, enabling reversible tuning of the photonic bandgap (PBG) and, at higher irradiation levels, helix inversion with opposite handedness. Thus, we demonstrate dynamic switching of both the operating wavelength and the isolated CPL helicity within a single device architecture. The asymmetric PDA@PVA photothermal interface enables forward photothermal activation of the cholesteric–isotropic transition while maintaining spin‐selective Bragg reflection under backward incidence. This mechanism enables wavelength‐tunable and chirality‐adaptive nonreciprocal transmission for both right‐ and left‐handed CPL. The device achieves isolation ratios exceeding 15.10 dB at all tested wavelengths, with a maximum value of 15.80 dB at 980 nm, while maintaining insertion losses below 2.89 dB, reaching as low as 1.05 dB. Furthermore, the operating thresholds and thermal tolerance can be tailored through liquid‐crystal composition.

The attainment of a large two‐photon absorption (2 PA) cross section and a high fluorescence emission quantum yield are crucial goal in molecular design of two‐photon absorbing fluorophores. However, the intrinsic modulation guidelines have rarely been revealed. Our review offers valuable insights into the photophysical properties of several organic fluorophores in the last 5 years and provides rational guidelines for the design and synthesis of organic fluorophores with both large 2 PA cross section and high fluorescence emission quantum yield.

In this work, we develop an ITO-based metasurface integrated with disordered silver nanoparticles (DSNPs). The localized plasmon resonance of the DSNPs couples and confines incident light within the ITO layer, enabling strong nonlinear responses across a broad visible-to-near-infrared spectrum with minimal polarization dependence (with a fluctuation of 2 , the ultrathin (∼35 nm) metasurfaces exhibit a nonlinear refractive index exceeding 0.1 cm ² /GW, with a maximum value reaching 1.24 cm ² /GW. This research provides a solution for low-power, high-integration-density nonlinear nanophotonic devices and all-optical control.

An efficient method of photocyclization to improve the two-photon active cross-section of a bay-substituted perylene diimide has been developed.

Optical isolators are essential devices that enable light propagation in a single direction, finding widespread applications in fields such as optical communication and optical computing. A prerequisite for these devices to achieve optical nonreciprocity (ONR) is the violation of Lorentz reciprocity. Traditional approaches to ONR rely on external magnetic fields, spatiotemporal modulation, or nonlinear optical effects. In this work, we proposed a novel, to the best of our knowledge, simple all-optical isolator base on spatial self-phase modulation (SSPM). Through both theoretical analysis and experimental validation, we demonstrate that SSPM induces a non-reciprocal spatial distribution of light beams, providing a foundation for a highly implementable and efficient optical isolator design. The proposed isolator consists of only four basic optical elements: an aperture, a nonlinear medium, and two lenses with different focal lengths. Using zinc selenide (ZnSe), a widely available nonlinear optical medium, the device exhibits remarkable ONR performance at 800 nm such as a high isolation of 25.1 dB along with a minimal insertion loss of 2.7 dB. To further showcase the versatility of this approach, we designed an on-chip optical isolator utilizing an epsilon-near-zero (ENZ) thin film with a large third-order nonlinear refractive index, highlighting the potential of our strategy for integration into photonic circuits. Our approach to optical isolation is exceptionally simple yet highly versatile, making it a promising candidate for a wide range of commercial and industrial applications.

Due to the serious impact of hydrogen sulfide (H₂S) on the environment and human health, a series of sensors have been increasingly used in industrial production and daily life. In this work, we introduce a novel, to the best of our knowledge, detection method for trace H₂S in the liquid and gaseous phases based on the dual-quenching mechanism (DQE) of silver ion-doped nitrogen-sulfur co-doped carbon dots (N, S-CDs@Ag⁺). Ag⁺ could significantly enhance the fluorescence intensity and detection sensitivity. In the linear detection range of 10–120 nM H₂S solution, the N, S-CDs@Ag⁺ sensor has a limit of detection (LoD) of 0.83 nM and a response time of 1 min. An enhanced fluorescent sensing film is prepared by assembling N, S-CDs@Ag⁺ on a silica microsphere (SM) microstructured substrate (N, S-CDs@Ag⁺/SM@PVA) using the layer-by-layer method. In the linear detection range of 1–50 ppm, the film sensor has the advantages of low detection limit (0.41 ppm), fast response time (5 min), stable performance, electromagnetic interference resistance, ease of integration, and in-field detection. It is expected to develop into a compact portable on-site H₂S trace sensor.

传统焦深测量方法大多需要直接捕捉光斑尺寸，但超快脉冲激光系统焦点处高峰值光强容易使仪器损坏，而利用自相关和平移探测器等方法光路复杂，容易引入误差.考虑到现有方法的局限，本文提出了一种基于Z扫描技术的超快脉冲激光焦深测量新方法.从非线性光学理论出发，推导出利用开孔Z扫描技术测量具有双光子吸收特性的材料时，透射率曲线符合洛伦兹分布，拟合后可以快速确定焦点位置及焦深大小.通过仿真不同因素下的测量结果，验证了利用Z扫描技术测量光学系统焦深的可行性.通过实验测量不同样品厚度、入射光强、样品类型及不同透镜超快光学系统的透射率曲线，表明开孔Z扫描曲线的半高全宽与理论焦深值具有显著一致性.该方法将焦深大小与透射率曲线的束腰半径相关联，利用Z扫描曲线的洛伦兹分布特性排除了不同因素对测量结果的影响，能够准确测量超快脉冲激光聚焦系统的焦深.

Chiral microlasers hold great promise for optoelectronics from integrated photonic devices to high-density quantum information processing. Despite significant progress in lead-halide perovskite emitters, chiral lasing with high dissymmetry factors (g_lum) has not yet been realized. Here, we demonstrate chiral single-mode microlasers with exceptional stability and tunable emission across the visible range by combining CsPbCl_xBr_3-x perovskite microrods (MRs) with a cholesteric liquid crystal (CLC) layer. The MRs lase via a whispering gallery mode (WGM) microcavity and confer chirality through the encapsulated CLC layer, thus exhibiting circularly polarized lasing with dissymmetry factors reaching 1.62. Importantly, we demonstrate wavelength-tunable high dissymmetry chiral lasers in a broad spectral range by tuning the halide composition and using CLC layers with the desired photonic bandgap (PBG). This facile approach to generate chiral lasing not only is applicable to semiconductor nano- and microcrystals but also paves the way for potential integration into nanoscale photonic devices.

Mixed‐halide perovskites (MHPs) have emerged as important semiconductor materials for optoelectronic devices due to the bandgap tunability by halide composition. However, their device applications are hampered by light‐induced ion migration and halide segregation, leading to the formation of lower bandgap domains with red‐shifted photoluminescence. Previous studies of phase segregation in MHPs have predominantly focused on their linear optical properties. Herein, nonlinear absorption (NLA) properties of MAPbBr₂I films before and after femtosecond laser irradiation are investigated using the Micro‐I‐scan technique. An unusual NLA switching from reverse‐saturable absorption (RSA) to saturable absorption (SA) under intense laser illumination is found. It is unveiled that the initial RSA originates from two‐photon absorption in uniform bromide‐rich regions of as‐prepared film whereas the SA occurs due to state filling effect in the newly generated low bandgap I‐rich phases under laser irradiation. The switching threshold and effective NLA coefficient are highly dependent on the distribution of halide ions, which is controllable through the laser illumination time. Furthermore, an all‐optical logic gate scheme is demonstrated based on the unusual NLA switching. The results not only unveil that halide segregation results in NLA switching in MHPs but also pave the way for the realization of MHPs‐based nonlinear photonic devices.