Focal shift of silicon microlens array in mid-infrared regime

采用严格数值算法对中红外硅微透镜阵列进行了模拟,该微透镜阵列特征尺寸小于波长工作波长.研究发现该微透镜阵列存在一个显著的离焦效应,其离焦量达到0; .4左右,超出了现有的传统理论模型预测范围.对微透镜阵列进行了制作和焦距测试,发现测试结果跟数值模拟基本吻合.微纳衍射光学集成系统中透镜离焦量是; 系统集成非常重要的一个参数,该研究结果为硅微透镜阵列和中红外探测器光学集成提供有效参考.In this study rigorous numerical model was utilized to characterize the focal shift of the diffractive mid infrared (MIR) silicon microlens arrays (MLAs) with the critical size smaller than the working wavelength. We found a more pronounced focal shift in mid-infrared wavelength which is out of the range predicted by existing models. Focal properties of the MLAs were also measured experimentally. The results agrees well with the simulation results. Our results provide a reference point in understanding the focal shift in MIR regime, which is important in terms of deciding the focal length of micro-nano lens systems, especially when dealing with the integration of diffractive devices in infrared optical system.Special Project on the Integration of Industry, Education and Research; of Aviation Industry Corporation of China [CXY2011XD24

Exciton-phonon interaction in quasi-two dimensional layered (PEA)2(CsPbBr3)n-1PbBr4 perovskite.

Two-dimensional (2D) Ruddlesden-Popper perovskites with bulky organic cations have attracted extensive attention in light-emitting devices and photovoltaics due to their robust environment stability, tunable luminescent color, strong exciton binding and promising efficiency. A quantum well (QW) structure is spontaneously formed by sandwiching PbBr4 layers into bulky organic cations. However, some intrinsic excitonic mechanisms in these materials still need to be elucidated. In this study, the exciton-phonon interaction of quasi-2D (PEA)2(CsPbBr3)n-1PbBr4 with different PbBr4 layer numbers (n) was analyzed by temperature-varied photoluminescence (PL), scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD). The mechanism of bandgap shifting with temperature was found to be dominated by the thermal expansion effect in the large-n 2D and bulk perovskite, and gradually switched to exciton-phonon interaction in the n = 1 (PEA)2PbBr4 phase, indicating enhanced exciton-phonon interaction in the thinner quantum well structure. Further analysis showed that the enhanced exciton-phonon interaction originated from the longitudinal optical phonon-exciton Fröhlich interaction rather than acoustic phonon-exciton coupling. We believe that our results will benefit the further optimization of light-emitting devices based on 2D perovskites

Supplementary document for Current spreading structure for GaN-based vertical-cavity surface-emitting lasers - 6562173.pdf

Supplemental document.</p

Improvement of the Emission Intensity of GaN-Based Micro-Light Emitting Diodes by a Suspended Structure

Herein, suspended GaN-based micro-light emitting diodes (LEDs) are ingeniously proposed and fabricated, showing a substantially enhanced light emission compared to conventional micro-LEDs on the sapphire substrate. The suspended architecture is prepared by transferring epitaxial layers to micrometal pillars on the copper plate after removing the original sapphire substrate. The photoluminescence intensity of the suspended micro-LED exhibits 150% higher than that of the normal device, and the electroluminescence intensity is increased by 114% in the current injection range of 0–10 mA. The enhancement of the output intensity benefits from the partially relaxed strain of the epitaxial film and the resultant reduction of the quantum confined Stark effect in the InGaN quantum well active region, as well as the improved light extraction efficiency due to the larger light-escaping area and less optical absorption and trapping, which are unambiguously verified by Raman spectroscopy and ray-tracing simulations. This study provides a new promising route to design and fabricate highly efficient micro-LEDs for practical applications