从光学工程应用的角度对全国云量情况进行了研究，重点分析了全国陆地主要地区云量总体平均情况、冷暖半年、昼夜变化等三个方面云量历史数据，研究结果表明：全国陆地主要地区总云量和低云量分布区域基本呈北少南多的情况；冷暖半年云量分布有较明显的差别，暖半年云量高于冷半年的站点区域占全国较大面积；昼夜云量分布区别主要体现在西部地区白天低云低值区会有中高云存在。在云量总体平均情况、冷暖半年、昼夜变化的分析基础上进而讨论了全国云量区域的分级情况，结果表明适合光学工程应用的1级区主要分在北方。结果有助于了解全国适于开展光学工程应用的区域，并可为进一步研究云量对光学工程应用产生的定量影响提供参考。

光学元件的健康状态是激光系统稳定运行的关键，如何在激光系统工作状态下实现光学元件的实时监测和故障诊断定位是该专业领域亟需解决的问题。针对该问题，提出了一种基于红外和可见光视频信息的光学元件故障诊断方法。首先，使用长波红外相机和可见光相机采集光学元件工作过程中的视频信息；然后，对采集的视频信息使用异常点检测算法进行处理；最后，结合光学元件温升特性对光学元件进行故障诊断及定位。试验结果表明：相同算法情况下，该方法相较于单独使用红外视频进行故障诊断的方法在故障诊断准确率、虚警率和漏警率3个指标上分别提升9.70%、3.60%和6.10%；该方法相较于单独使用可见光视频进行故障诊断的方法在故障诊断准确率、虚警率和漏警率3个指标上分别提升18.00%、16.00%和2.00%。

Active devices have drawn considerable attention owing to their powerful capabilities to manipulate electromagnetic waves. Fast and periodic modulation of material properties is one of the key obstacles to the practical implementation of active metamaterials and metasurfaces. In this study, to circumvent this limitation, we employ a cascaded phase-matching mechanism to amplify signals through spatiotemporal modulation of permittivity. Our results show that the energy of the amplified fundamental mode can be efficiently transferred to that of the high harmonic components if the spatiotemporal modulation travels at the same speed as the signals. This outstanding benefit enables a low-frequency pump to excite parametric amplification. The realization of cascaded parametric amplification is demonstrated by finite-difference time-domain (FDTD) simulations and analytical calculations based on the Bloch–Floquet theory. We find that the same lasing state can always be excited by an incidence at different harmonic frequencies. The spectral and temporal responses of the space-time modulated slab strongly depend on the modulation length, modulation strength, and modulation velocity. Furthermore, the cascaded parametric oscillators composed of a cavity formed by photonic crystals are presented. The lasing threshold is significantly reduced by the cavity resonance. Finally, the excitation of cascaded parametric amplification relying on the Si-waveguide platform is demonstrated. We believed that the proposed mechanism provides a promising opportunity for the practical implementation of intense amplification and coherent radiation based on active metamaterials.

An optical phased array (OPA), the most promising non-mechanical beam steering technique, has great potential for solid-state light detection and ranging systems, holographic imaging, and free-space optical communications. A high quality beam with low sidelobes is crucial for long-distance free-space transmission and detection. However, most previously reported OPAs suffer from high sidelobe levels, and few efforts are devoted to reducing sidelobe levels in both azimuthal (φ) and polar (θ) directions. To solve this issue, we propose a Y-splitter-assisted cascaded coupling scheme to realize Gaussian power distribution in the azimuthal direction, which overcomes the bottleneck in the conventional cascaded coupling scheme and significantly increases the sidelobe suppression ratio (SLSR) in the φ direction from 20 to 66 dB in theory for a 120-channel OPA. Moreover, we designed an apodized grating emitter to realize Gaussian power distribution in the polar direction to increase the SLSR. Based on both designs, we experimentally demonstrated a 120-channel OPA with dual-Gaussian power distribution in both φ and θ directions. The SLSRs in φ and θ directions are measured to be 15.1dB and 25dB, respectively. Furthermore, we steer the beam to the maximum field of view of 25°×13.2° with a periodic 2λ pitch (3.1 μm). The maximum total power consumption is only 0.332 W with a thermo-optic efficiency of 2.7mW/π.