Whispering-gallery-mode (WGM) microresonators can greatly enhance light–matter interaction, making them indispensable units for frequency conversion in nonlinear optics. Efficient nonlinear wave mixing in microresonators requires stringent simultaneous optical resonance and phase-matching conditions. Thus, it is challenging to achieve efficient frequency conversion over a broad bandwidth. Here, we demonstrate broadband second-harmonic generation (SHG) in the x-cut thin-film lithium niobate (TFLN) microdisk with a quality factor above 10⁷ by applying the cyclic quasi-phase-matching (CQPM) mechanism, which is intrinsically applicable for broadband operation. Broadband SHG of continuous-wave laser with a maximum normalized conversion efficiency of ∼15%/mW is achieved with a bandwidth spanning over 100 nm in the telecommunication band. Furthermore, broadband SHG of femtosecond lasers, supercontinuum lasers, and amplified spontaneous emission in the telecommunication band is also experimentally observed. The work is beneficial for integrated nonlinear photonics devices like frequency converters and optical frequency comb generator based on second-order nonlinearity on the TFLN platform.

The large-aperture pulse compression grating (PCG) is a critical component in generating an ultra-high-intensity, ultra-short-pulse laser; however, the size of the PCG manufactured by transmission holographic exposure is limited to large-scale high-quality materials. The reflective method is a potential way for solving the size limitation, but there is still no successful precedent due to the lack of scientific specifications and advanced processing technology of exposure mirrors. In this paper, an analytical model is developed to clarify the specifications of components, and advanced processing technology is adopted to control the spatial frequency errors. Hereafter, we have successfully fabricated a multilayer dielectric grating of 200 mm × 150 mm by using an off-axis reflective exposure system with Φ300 mm. This demonstration proves that PCGs can be manufactured by using the reflection holographic exposure method and shows the potential for manufacturing the meter-level gratings used in 100 petawatt class high-power lasers.

为了研究磁性水凝胶的磁致折射率变化及其在磁致光传感领域的应用，通过共混法制备了聚乙烯醇/四氧化三铁（PVA/Fe₃O₄）磁性水凝胶，并基于光纤端面反射法测试了该磁性水凝胶在不同外加磁场下的折射率变化，测得其磁致光折射率变化规律。在此基础上设计了磁性水凝胶锥形光纤传感结构。实验表明，在环境温度22 ℃，磁粒子浓度2.1%时，6.4~22.6 mT范围内基于磁性水凝胶的光纤磁场传感元件波长偏移灵敏度为86.42 pm/mT；磁粒子浓度2.9%时，5.5~30 mT范围内该传感元件波长偏移灵敏度为51.42 pm/mT。该类磁性水凝胶在光纤磁传感测量方面具有良好的应用价值。

ICESat-2（Ice， Cloud and Land Elevation Satellite-2）是世界首颗采用光子计数模式的激光测高卫星，可快速获得高精度、大尺度地面三维数据。光子探测机制使得数据中除了地面信号外，还包含大气散射等背景信号，需要通过滤波才能获得地形等信息。为分析ICESat-2背景和信号光子的分布特点及点云滤波算法的效果和适用性，本文首先选取了六种地表覆盖类型（城市、海冰、沙漠、植被、海洋及冰盖/冰川）及不同观测条件的数据，对其背景光子率进行统计分析。分析结果表明：白天观测数据的背景光子率平均为10⁶（点/秒）数量级，远高于夜晚观测数据的背景光子率——10⁴（点/秒）数量级，弱波束的背景光子率与强波束背景光子率相当，六种地表覆盖类型中，冰盖/冰川的背景光子率最高。然后，根据统计结果筛选出21组测高数据，并选取七种具有代表性的点云滤波对其进行去噪实验，分析精度后得出结论：改进局部密度法的去噪效果最佳，算法召回率、精准度和F值均大于0.90，算法较为稳定。最后，对所选取各滤波算法的精度、特点与适用性等性质进行了总结与分析，可为后续该数据的使用和滤波算法的选择提供参考。

相对可见光和短波红外谱段来说，在红外谱段进行高光谱遥感成像具有独特优势，特别是在资源勘查、地表环境监测、大气环境监测、**侦察方面。尽管当前红外高光谱成像仪主要以机载为主，还未实现星载，然而国内外相关机构从未放弃推进红外高光谱遥感的星载化。文中首先分析了国内外典型的红外高光谱成像仪的设计、实现与技术指标，从光谱分辨率、空间分辨率、辐射分辨率三个核心指标总结了现有红外高光谱成像仪的技术特点、存在问题和解决途径。未来很长的一段时间内，红外精细分光、低暗电流焦平面探测器、低温光学与背景抑制仍然是红外高光谱成像仪研制所要解决的核心问题。在此基础上，文中重点介绍了在远距离气体探测方面的应用，并分析了其独特优势。最后，展望了红外高光谱成像技术的发展方向。

We design and fabricate an unbalanced Mach–Zehnder interferometer (MZI) via electron beam lithography and inductively coupled plasma etching on lithium niobate thin film. The single unbalanced MZI exhibits a maximum extinction ratio of 32.4 dB and a low extra loss of 1.14 dB at the telecommunication band. Furthermore, tunability of the unbalanced MZI by harnessing the thermo-optic and electro-optic effect is investigated, achieving a linear tuning efficiency of 42.8 pm/°C and 55.2 pm/V, respectively. The demonstrated structure has applications for sensing and filtering in photonic integrated circuits.

Constructions of synthetic lattices in modulated ring resonators attract growing attention to interesting physics beyond the geometric dimensionality, where complicated connectivities between resonant frequency modes are explored in many theoretical proposals. We implement experimental demonstration of generating a stub lattice along the frequency axis of light, in two coupled ring resonators of different lengths, with the longer one dynamically modulated. Such a synthetic photonic structure intrinsically exhibits the physics of flat band. We show that the time-resolved band structure read-out from the drop-port output of the excited ring is the intensity projection of the band structure onto a specific resonant mode in the synthetic momentum space, where gapped flat band, mode localization effect, and flat-to-nonflat band transition are observed in experiments and verified by simulations. This work provides evidence for constructing a synthetic stub lattice using two different rings, which, hence, makes a solid step toward experimentally constructing complicated lattices in multiple rings associated with synthetic frequency dimensions.