面向近红外成像超透镜的设计与仿真北大核心CSCD

由亚波长单元结构组成的超表面是近年来平面光学透镜的重点研究对象,而由超表面组成的平面超透镜与传统透镜相比,在相位调控、偏振操控、全息成像、负折射率隐身等领域有显著优势。鉴于平面超透镜的微型化、轻量化和易集成化等方面的优势,而传输型相位调控原理更加适于近红外波段的应用,且对入射光偏振态无特殊要求,本文采用时域有限差分方法(FDTD)设计并优化了一种硅基的近红外波段的超透镜。所设计的超透镜焦距为15μm,直径为20μm,所达到的数值孔径(NA)为0.56,聚焦效率为68.3%,适用于所有入射偏振且在目标波长为700 nm范围内聚焦性能优良。本文研究结果为实现近红外超透镜轻薄化和平整化提供了新思路,有望优化红外探测器镜头的设计,提高红外探测的效率。     

聚焦强度可调的高数值孔径的双焦点超透镜

基于超表面对光波的振幅、相位和偏振进行调控来实现聚焦与成像的超透镜受到广泛关注。设计了一种聚焦强度可调的高数值孔径的双焦点超透镜，并进行了理论分析和仿真验证。仿真结果表明，该超透镜能有效地将圆偏振入射光聚焦到半高宽为0.44λ的光斑上，对应的数值孔径高达0.95。此外，通过改变入射光的偏振态，可以灵活地调制两个焦点的相对强度，而不同于以往的双焦点超透镜需要对光强进行重新组合。更重要的是，当圆偏振光入射时，它的聚焦效率可达65%，可适用在0.8~1.2 THz的较宽频率范围和0°~20°的入射角内，同时该工作为多焦点超透镜的设计提供了重要思路，也将在多成像系统、光学层析成像技术等许多领域具有较高的应用价值。     

自旋依赖强度可调谐的相变超构透镜

超表面是一种基于亚波长各向异性单元结构的超薄平面光学器件,能够在微观尺度下调制电磁波相位、偏振和振幅等,从而实现波前的任意调控。超构透镜作为超表面走向实用化的重要代表,凭借其超强的光波操控能力、超紧凑结构、多功能性及与半导体工艺兼容等突出优点,引起了研究学者的极大兴趣。然而,已报道的超构透镜受限于相位分布设计,难以同时实现偏振复用及强度可调谐聚焦功能;且结构一旦确定,其电磁性能就被锁定,在灵活调制电磁波方面受到很大限制。为此,文中从各向异性单元结构的设计和优化入手,协同PB相位和传输相位,设计了两种能够在不同空间取向（横向和纵向）上实现自旋分裂的Ge₂Sb₂Se₄Te₁ (GSST) 相变超构透镜。通过改变入射圆偏振光的椭偏度,两超构透镜均可实现强度可调谐聚焦性能;通过调控相变材料Ge₂Sb₂Se₄Te₁从非晶态逐渐转变为结晶态,两超构透镜均可实现聚焦性能的连续调谐并最终达到“ON”和“OFF”的动态切换。所设计的自旋依赖强度可调谐相变超构透镜有望在多成像系统、机器视觉和显微成像等领域发挥重要作用。     

宽带消色差红外光学超构透镜研究进展（特邀）

超构透镜是由亚波长散射单元结构排列而成的具有聚焦功能的平面二维超构表面。超构表面能够在亚波长尺度上操控光场的振幅、相位、色散和偏振态,是近年来迅速发展起来的新型光场调控载体。亚波长共振纳米结构使得高阶衍射被抑制,入射光场可以完美地被调制到设计的衍射级次上,从而确保了超构表面器件具有高的光子调控效率。同时,超构单元在设计上的灵活性及其特定的电磁响应使得超构表面可以实现对光场多个维度的定制化操控。不同于传统光学透镜依赖光传播的相位累积效应,宽带消色差超构透镜通过对光场相位和相位色散的同时独立调控解决了传统通过级联多个透镜修正色差造成的光学系统复杂和体积庞大限制,为发展小型化片上集成光学提供了全新的思路。文中围绕超构透镜的相关研究,首先介绍了超构表面调控光场振幅、相位和偏振态的基本原理,在此基础上,重点回顾了近年来关于超透镜的研究发展,包括通过单一参量调控的单波长超透镜的实现,以及通过对光场偏振、相位及相位色散的多参量联合调控的多功能宽带消色差超构透镜的发展现状,最后讨论其进一步发展的可能挑战与应用前景。     

基于超表面波带片的远场偏振全息加密

超表面是一种具有灵活的偏振操纵功能的新型材料。为了获得远场偏振全息图像，通常需要添加透镜等光学元件。笔者利用超表面波带片的灵活偏振操纵及聚焦功能实现了一种新颖的远场偏振全息加密技术。在该技术中，两个自旋复用的超表面波带片被集成到单个介质超表面器件中，其中超表面的振幅（右旋圆偏振转化率）用来编码奇数和偶数环形区域的波带片，而其相位调制则用来编码透射右旋圆偏振光和左旋圆偏振光的两个全息图。此外，二维码（QR码）和振幅型/相位型全息图用于进一步隐藏加密信息，以提高信息的安全性。所提加密技术有望进一步提升数据安全性和隐私保护水平，推动光学信息加密和高密度数据存储等领域的技术发展。     

太赫兹波前调制超表面器件研究进展

超表面是一种由人工微结构组成的超薄平面器件,能够实现对电磁波振幅、相位以及偏振态的调控,具有体积小、重量轻、集成度高、可灵活操控电磁波等优势,在电磁波谱、波前调制中发挥着巨大的作用。综述了近年来基于超表面的太赫兹波前调制器件的研究进展。总结了基于Pancharatnam-Berry相位、基于局域表面等离子体共振(LSPR)、基于Mie共振的三种超表面单元结构对电磁波的振幅、相位调控机理,并讨论了实现高效率超表面的方法。之后,介绍了用于设计波前调制超表面器件的纯相位调制方法和复振幅调制方法。综述了在太赫兹波段典型的超表面波前调制器,包括单一功能、复合功能以及可调谐功能的超表面波前调制器件。在早期的研究工作中,设计的超表面可实现波束偏转、波束聚焦、全息成像、以及涡旋光束、自聚焦光束、洛伦兹光束等特殊光束产生等功能。为提高太赫兹器件的利用率,波分复用、偏振复用等功能复用的太赫兹超表面器件被提出。随着对太赫兹波前动态调控需求的增长, 一些主动的太赫兹超表面器件被提出并在实验上被验证。共有两种主动的超表面器件。其中一种主动超表面是通过将超表面结构与半导体材料或相变材料结合形成的,另一种是通过光泵浦硅片形成的全光器件。全光超表面在不用重新加工的前提下能够被重复使用。通过调整投影在硅片上的超表面图像即可动态操控太赫兹波前。全光超表面具有动态控制波束扫描和波束聚焦的能力,将来可应用于太赫兹通信、太赫兹雷达等领域。最后,对太赫兹波前调制超表面器件的发展趋势与应用前景进行了展望。     

融合计算全息术与纳米印刷术的多功能超表面研究进展

计算全息术与纳米印刷术是超表面材料的两种典型应用。近年来,融合全息术与纳米印刷术的多功能超表面成为新兴研究热点,有望在多重光学防伪、信息编码与复用、多通道图像显示、VR/AR等领域得到重要应用。文中在介绍超表面纳米印刷术和计算全息术特点的基础上,将实现两者融合的研究进展进行了详细的归类和特点分析,具体包括:正交偏振复用法、平面合成法、空间堆叠法、光谱+相位调控法、复振幅法、转角简并性法等。最后,对多功能超表面的研究前景进行了展望。     

双通道偏振复用可擦除介质型全息超表面

为进一步增强加密或存储器件的实用性与安全性，设计并实现了一种多通道偏振复用的相变全息超表面，通过在多通道全息超表面设计中引入相变介质，实现了动态的可擦除功能。当耦合相变介质层处于非晶态时，所构造的编码超表面可以产生两个独立成像的全息通道。当相变介质变为晶态时，决定相位调控的交叉偏振被关闭，对应的相位编码“被擦除”。     

圆极化复用型多功能超构表面研究进展

文中回顾并总结了课题组近期关于圆极化复用型多功能超构表面的研究进展. 从几何相位在正交圆极化波作用下的共轭对称响应出发,基于超构表面的等效琼斯矩阵提出了交叉极化双通道复用的独立调控方法,突破了几何相位的交叉极化耦合限制. 进一步,基于同极化与交叉极化分量间的幅相关系,提出了三通道复用的多元波前集成方法,实现了对透射圆极化电磁能量的全场调控. 在此基础上,通过引入手性诱导相位提出了圆极化四（全）通道复用的波前调控方法,有效提高了对圆极化电磁能量的利用效率,为提高现代通信系统信道容量及信息传输速率打下理论基础.     

基于电介质超表面的双频带双偏振通道波前调控

随着微纳加工技术的发展,超表面在亚波长尺度对电磁波的多维度调控展现出传统光学器件难以比拟的优势。基于电介质硅纳米柱结构构建了具有双频带响应的超表面,利用微结构对不同偏振入射光反射系数的差异,通过构建梯度几何相位实现了双波长下的异常反射;同时设计了超表面灰度成像阵列,在近红外波段实现了对正交偏振态和双波长入射具有不同响应的正负灰度图像。文中提出的超表面设计为基于超表面的多功能集成技术的发展奠定了基础。     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.