AlGaN-based light-emitting diodes (LEDs) on offcut substrates enhance radiative emission via forming carrier localization centers in multiple quantum wells (MQWs). This study introduces carrier transport barrier concept, accessing its impact on the quantum efficiency of LEDs grown on different offcut sapphire. A significantly enhanced internal quantum efficiency (IQE) of 83.1% is obtained from MQWs on the 1° offcut sapphire, almost twice that of the controlled 0.2° offcut sample. Yet, 1° offcut LEDs have higher turn-on voltage and weaker electroluminescence than 0.2° ones. Theoretical calculations demonstrate the existence of a potential barrier on the current path around the step-induced Ga-rich stripes. Ga-rich stripes reduce the turn-on voltage but restrict sufficient driving current, impacting LED performance.

Indoor organic and perovskite photovoltaics (PVs) have been attracting intense interest in recent years. Theoretical limit of indoor PVs has been calculated based on the detailed balance method brought by Shockley-Queisser (known as SQ). However, realistic losses of the organic and perovskite PVs under indoor illumination are to be understood for further efficiency improvement. In this work, the efficiency limit of indoor PVs is calculated to 55.33% under the indoor illumination (2700 K, 1000 lux) when the bandgap (Eg) of the semiconductor is 1.77 eV. The efficiency limit was obtained on the basis of assumptions of 100% photovoltaic external quantum efficiency (EQEPV) when E ≥ Eg, no nonradiative recombination, and no resistance losses. In reality, the maximum EQEPV reported in the literature is 0.80 - 0.90. The proportion of radiative recombination in realistic devices is only 10-5 - 10-2, which causes the open-circuit voltage loss (ΔVloss) of 0.12 - 0.3 V. Fill factor (FF) of the indoor PVs is sensitive to the shunt resistance (Rsh). These realistic losses of EQEPV, nonradiative recombination and resistance cause the large efficiency gap between the realistic values (excellent perovskite indoor PV: 32.4%; superior organic indoor PV: 30.2%) and theoretical limit of 55.33%. In reality, it is feasible to reach the efficiency of 47.4% at 1.77 eV for organic and perovskite photovoltaics under indoor light (1000 lux, 2700 K) with VOC = 1.299 V, JSC = 125.33 μA/cm2, and FF = 0.903, when EQEPV = 0.9, EQEEL = 10-1, Rs = 0.5 Ω cm2 and Rsh = 104 kΩ cm2.

The pandemic of respiratory diseases enlightened people that monitoring respiration has promising prospect in averting many fatalities by tracking the development of diseases. However, the response speed of current optical fiber sensors is still insufficient to meet the requirements of high-frequency respiratory detection during respiratory failure. Here, a scheme for fast and stable tachypnea monitor is proposed utilizing water-soluble C₆₀-Lys ion compound as functional material for the tracking of humidity change in the progression of breath. The polarization of C₆₀-Lys can be tuned by the ambient relative humidity change and an apparent refractive index alteration can be detected due to the small size effect. In our experiments, C₆₀-Lys is conformally and uniformly deposited on the surface of a tilted fiber Bragg grating (TFBG) to fabricate an ultra-fast response, high-sensitivity, and long-term stable optical fiber humidity sensor. A RH detecting sensitivity of 0.080 dB/% RH and the equilibrium response time and recovery time of 1.85 s and 1.58 s is observed respectively. Besides, a linear relation is detected between the resonance intensity of the TFBG and the environment RH. In practical breath monitoring experiment, the instantaneous response time and recovery time are measured as 40 ms and 41 ms respectively during a 1.5 Hz fast breath process. Furthermore, an excellent time stability and high repeatability are exhibited in experiments conducted over a range of 7 days.

In this work we compare different methods to implement a triplicator, a phase grating that generates three equi-intense diffraction orders. The design with optimal efficiency features a continuous phase profile, which cannot be easily reproduced, typically affected by quantization. We compare its performance with binary and sinusoidal phase profiles. We also analyze the effect of quantizing the phase levels. Finally, a random approach is adopted to eliminate the additional harmonic orders. In all cases a liquid-crystal on silicon spatial light modulator (LCOS-SLM) is employed to experimentally verify and compare the different approaches.

红外双视场镜头在投入使用之前需进行冲击、振动以及高低温试验，试验中有时会出现各种问题，例如，镜头被破坏、镜头成像不稳定、镜头运动卡顿等。针对上述问题，本文对一款焦距为25-75mm、F1.0-1.2的红外双视场镜头进行了冲击、振动分析。在前人工作的基础上，建立了相应的冲击振动模型，基于建立的冲击振动模型对该红外双视场镜头进行了相应的仿真分析。其次，针对镜头的传动件进行了受力分析，提出一种设计凸轮曲线的方法，以减小运动受力，降低凸轮筒在低温下卡死的概率。结合以上工作，对该镜头进行了相应的冲击振动以及高低温试验，试验结果比较令人满意。由上述为红外双视场镜头的仿真分析以及结构设计提供参考，避免因设计阶段中的缺陷，造成的经济以及时间上的损失。

本文针对水下海洋生物检测任务存在的目标间相互遮挡、细长型目标检测精度低以及小目标众多等问题，提出了一种基于YOLOv5的水下目标检测算法。该算法通过引入可变形卷积、空洞卷积和注意力机制来重新设计主干网络，增强特征提取能力，解决目标间相互遮挡以及细长型目标检测精度低的问题；同时，提出加权显示视觉中心特征金字塔模块，解决特征融合不充分问题，降低小目标漏检率；并调整YOLOv5算法的网络结构，增加融合注意力机制的小目标检测层，提升对小目标物体的检测能力。实验结果表明，改进后的YOLOv5算法在URPC数据集上平均精度达到87.8％，较原有的YOLOv5算法提高了5.3个百分点、同时检测速度保持在34FPS，在水下目标检测任务中能够有效提高精确度，降低漏检、错检率。

本文提出并制备了一种基于法布里-珀罗干涉仪游标效应的高灵敏度光纤应变传感器。该传感器包含两个并联的法布里-珀罗干涉仪，其中传感干涉仪由单模光纤和一小截毛细石英管熔接构成，参考干涉仪通过单模光纤放置在光纤熔接机中对齐构成。当两个干涉仪具有相近的自由光谱范围时，利用干涉仪游标效应进一步放大了传感干涉仪的应变敏感性。在此基础上，通过简单地调节熔接机改变参考干涉仪腔长，并联结构可以选择不同放大倍数以获得不同灵敏度。实验结果表明，在熔接机的辅助下，在0~250με的应变范围内并联结构的应变灵敏度分别达到22.16pm/με和32.88pm/με，比单一结构的灵敏度（5.76pm/με）分别提高了3.84、5.70倍。该传感器具备制作简单、灵敏度高、重复性好、操作方便以及成本低等优点，为应变检测提供了新的思路。

作为下一代HDR显示器的有力竞争者，Mini-LED背光的液晶显示是新型显示技术发展的重要方向。Mini-LED背光的液晶显示由于背光分区和液晶漏光等结构特点，不可避免地引入了光晕效应。为探究环境光对Mini-LED背光LCD光晕感知的影响，本研究建立了基本的Mini-LED背光LCD光学成像模型，并基于该模型设计了系统的视觉感知实验。实验研究了不同环境光照度、不同局部调光区大小以及不同LCD对比度下，人眼对光晕的感知效果，并基于实际光测量，探究了环境光对光晕感知的影响机制。结果表明，环境光对Mini-LED背光的液晶显示的光晕感知具有显著性影响，环境光会显著影响图像对比度，其照度与光晕感知强度基本呈负相关。本研究可为不同环境光场景下Mini-LED背光液晶显示系统的设计与优化提供参考。

铁路线轨道道床上异物的准确监测对列车安全行驶具有重要意义。利用深度学习基于重构的无监督异常检测算法可以解决异常数据不足对检测的影响，但编码器“泛化”能力过于强大，能够很好地重建异常样本，影响其检测精度。针对此问题，本文提出了一种基于图像修复的无砟轨道道床的异常检测算法。首先，利用Inpainting思想对图像进行掩码，通过不完整的非异常图像训练来对图像进行修复重建，以此来提高模型对其上下文的语义理解，增强模型的重建能力；其次，在测试时，采用测试图像与重建图像在多尺度下的平均异常图最大值作为重构误差来计算异常分数，扩大异常图像与正常图像的重构误差的界限；最后，实验表明，所提出的算法在公开数据集MNIST、CIFAR-10及无砟轨道道床数据集上均优于其他方法。

Recently, there has been increased attention towards 3D imaging using single-pixel single-photon detection (also known as temporal data) due to its potential advantages in terms of cost and power efficiency. However, to eliminate the symmetry blur in the reconstructed images, a fixed background is required. This paper proposes a fusion-data-based 3D imaging method that utilizes a single-pixel single-photon detector and a millimeter-wave radar to capture temporal histograms of a scene from multiple perspectives. Subsequently, the 3D information can be reconstructed from the one-dimensional fusion temporal data by using Artificial Neural Network (ANN). Both the simulation and experimental results demonstrate that our fusion method effectively eliminates symmetry blur and improves the quality of the reconstructed images.