宽可调谐SG-DBR激光器波长测试控制系统

采用传统设备结合虚拟仪器的方法,研制了一套宽可调谐取样光栅DBR(SampledGratingDBR,SG-DBR)激光器的波长测试控制系统。系统能自动向SG-DBR激光器提供电流扫描,同时对激光器输出的光谱数据进行采集、处理,生成SG-DBR激光器的“波长-电流”数据查询表;通过快速查找数据查询表数据,并对激光器提供相应驱动电流,准确控制SG-DBR激光器输出波长。系统数据处理采用了一种新颖的算法,利用输出光边模抑制比(SMSR)来筛选激光器模式稳定工作点,确保数据查询表中的工作点数据均不会发生模式跳变。实验证明,本系统稳定、可靠,波长控制精度高,波长控制误差不超过±0.02nm。     

Multidirectional lateral gradient films with position-dependent photonic signatures made from porous silicon

We describe here the fabrication of laterally graded porous silicon films which display gradients of photonic reflectance peaks spanning the optical spectrum. We demonstrate that up to three of these gradients can be overlayed to produce multidirectional photonic gradients with position-dependent spectral bar-codes. Each gradient is generated by asymmetric anodisation of silicon using temporal variations (sinusoidal or square-wave) in current density affording rugate and Bragg reflectors, respectively. The fabricated optical structures and the quality of the photonic resonances are characterised by optical reflectivity measurements and scanning electron microscopy. We finally remove the pSi gradient layers from the silicon substrate by applying an electropolishing current and embed the free-standing pSi membranes in polydimethylsiloxane to form flexible and foldable photonic films.     

空间用GaInP/GaAs/Ge三结太阳电池的抗辐照性能及退化机制研究

利用TFC光学膜系设计软件,设计出空间用GaInP/(In)GaAs/Ge三结太阳电池的分布式布拉格反射器(DBR)。由15对Al0.2Ga0.8As/Al0.9Ga0.1As组成的布拉格反射器在中心波长850 nm处反射率高达96%,可以使800~900 nm波段内红外光有效反射后被二次吸收,提高了Ga As子电池的抗辐照能力。通过对两种电池结构A、B地面模拟辐照试验获得1 Me V电子辐照下Ga In P/Ga As/Ge太阳电池电学参数随辐照注量退化的基本规律。在此基础上应用PC1D模拟程序分析太阳电池内部的载流子输运机理,建立1 Me V电子辐照下两种电池结构中多数载流子浓度和少数载流子扩散长度随辐照电子注量变化的基本规律。研究结果表明,多数载流子浓度和少数载流子扩散长度均随入射电子注量的增大而减小,同时原电池结构A中多数载流子去除率和少数载流子扩散长度损伤系数明显高于新电池结构B,由此表明包含布拉格反射器的新电池结构具有更强的抗辐照能力。     

An ultra-compact tunable Bragg reflector based on edge propagating plasmons in graphene nanoribbon

A mid-infrared planar Bragg reflector, which is based on the fundamental edge plasmonic mode in the nanoribbons is proposed and numerically demonstrated in this paper. The simulation results calculated with the three-dimensional (3D) finite element method reveal that it shows superb wide-band filtering characteristics in the mid-infrared frequencies, and the bandwidth of stopband in the reflector can be dynamically modulated by varying the chemical potentials of corresponding nanoribbon waveguides. In addition, its band properties on the ribbon width are also analyzed. This kind of Bragg reflector exhibits extreme compactness of lateral scales and wonderful light confinement in both the longitudinal and the lateral directions, which is expected to have significant applications in constructing 3D highly integrated optical networks for signal processing.     

An ‘electromagnetic wiggler’ originating from refraction of waves at the side edge of a Bragg reflector

Calculations are reported which predict that light incident on the side edge of a Bragg reflector can show varied and unusual refraction behaviour, including a rapid transition from positive to negative refraction. Although under certain conditions negative refraction can occur, it is concluded that perfect lensing based on it is unlikely to be realised in practice. However, it is shown that light incident obliquely on the structure can be made to propagate normal to the interface after refraction while exhibiting lateral oscillations of its Poynting vector, an effect that could possibly find application in an ‘electromagnetic wiggler’. It is also shown that negative group velocity rather than negative effective mass is required for the observation of the negative refraction, and in the case of low refractive index contrast, negative refraction occurs only when the size of the illumination spot exceeds a critical value, which is inversely proportional to the contrast of the refractive indices.     

A highly distributed Bragg stack with unique geometry provides effective camouflage for Loliginid squid eyes

Cephalopods possess a sophisticated array of mechanisms to achieve camouflage in dynamic underwater environments. While active mechanisms such as chromatophore patterning and body posturing are well known, passive mechanisms such as manipulating light with highly evolved reflectors may also play an important role. To explore the contribution of passive mechanisms to cephalopod camouflage, we investigated the optical and biochemical properties of the silver layer covering the eye of the California fishery squid, Loligo opalescens. We discovered a novel nested-spindle geometry whose correlated structure effectively emulates a randomly distributed Bragg reflector (DBR), with a range of spatial frequencies resulting in broadband visible reflectance, making it a nearly ideal passive camouflage material for the depth at which these animals live. We used the transfer-matrix method of optical modelling to investigate specular reflection from the spindle structures, demonstrating that a DBR with widely distributed thickness variations of high refractive index elements is sufficient to yield broadband reflectance over visible wavelengths, and that unlike DBRs with one or a few spatial frequencies, this broadband reflectance occurs from a wide range of viewing angles. The spindle shape of the cells may facilitate self-assembly of a random DBR to achieve smooth spatial distributions in refractive indices. This design lends itself to technological imitation to achieve a DBR with wide range of smoothly varying layer thicknesses in a facile, inexpensive manner.     

具有分布式反射器的无源编码器件的研究

建立了具有多个分布式Ｂｒａｇｇ反射结构的无源器件的研究方法。该研究可用于分析光纤光栅、表面波（ＳＡＷ）编码器、具有分布式Ｂｒａｇｇ的结构的微波谐振器和金属栅周期加载漏波天线等无源器件 。     

以四面体非晶碳为布拉格反射栅高声阻抗材料的固贴式薄膜体声波谐振器性能仿真分析

为了提高固贴式薄膜体声波谐振器(SMR)的电学和声学品质,实现四面体非晶碳(ta-C)在体声波器件领域的新应用,建立了以ta-C为布拉格反射栅高声阻抗材料的SMR模型,利用MathCAD仿真研究布拉格反射栅层数对该SMR的谐振特性的影响以及ta-C中sp3杂化含量和高/低声阻抗层厚度偏差对SMR的品质因子(Q值)的影响。结果表明层数的增加提高了SMR的品质;ta-C薄膜sp3杂化含量越高,达到饱和Q值所需层数越少,当含量为80%时,至少需要6层(3对)布拉格反射层使SMR达到优异Q值;距离压电堆越近的高/低声阻抗层,其厚度偏差对Q值的影响越大,从而实现了高频率(8GHz)低损耗的SMR的设计。     

Selective response of Nitinol substrate using Bragg reflector structures

The aim of this work is to elaborate low stress dichroic filters intended for the control of shape memory alloys deformation (SMA). This deformation has been performed by the use of laser sources (658 nm and 785 nm, for this preliminary study) in order to heat different samples of SMA. The two dichroic filters have been elaborated using a Bragg reflector structure with the choice of the materials discussed considering the superelastic behaviour of the substrate. The presented structure was made up of the stack of two materials, the amorphous hydrogenated silicon (a-Si:H) and the amorphous polymethacrylic acid (a-pMAA), deposited on glass substrate with the order: (a-Si:H a-pAM)3 a-Si:H. Finally the dichroic filters have been tested with success: the deformation of shape memory alloy has been observed and the filters show a high stability towards laser irradiation.     

具有渐变层半导体DBR的MOCVD外延制备

应用金属有机化合物气相淀积(MOCVD)制备了具有渐变层的半导体布拉格反射镜(DBR),分别是抛物线性、线性和突变结构的DBR.三种反射镜结构都设计为8个周期,通过白光反射谱测量突变DBR具有最大反射率.应用原子力显微镜对所制备的DBR表面形貌进行分析.结果表明,相同周期数情况下线性渐变DBR相对于其他两种结构粗糙度最小,具有良好的表面形貌,可以应用于垂直腔面发射激光器的研制.     

Nanoscopic medicine: the next frontier

The extraordinary progress that has taken place in cell science and optical nanoscale microscopy has led recently to the concept of medical nanoscopy. Here, we lay out a concept for developing live cell nanoscopy into a comprehensive diagnostic and therapeutic scheme referred to as nanoscopic medicine, which integrates live cell nanoscopy with the structural and functional studies of nanoscopic protein machines (NPMs), the systems biology of NPMs, fluorescent labeling, nanoscopic analysis, and nanoscopic intervention, in order to advance the medical frontier toward the nanoscopic fundament of the cell. It aims at the diagnosis and therapy of diseases by directly visualizing, analyzing, and modifying NPMs and their networks in living cells and tissues.