高斯变迹FBG在非均匀介质下的数值响应特性研究

基于光波导理论和传输矩阵法,研究光纤包层被完全腐蚀后的高斯变迹光纤布拉格光栅(FBG)在非均匀外部介质环境下的反射谱特性.仿真过程中,分别考虑高折射率区(1.43～1.45)和低折射率区(1.33～1.36)两种情况,同时假设该非均匀外部介质折射率(SRI)呈不同的线性函数分布.仿真结果表明,高斯变迹FBG的谱带宽、谱强度特性与SRI沿光栅轴向的线性分布梯度密切相关.随着SRI梯度增加,反射谱的3 dB带宽也逐渐增加,此时高、低折射率区的梯度灵敏度分别为3.775×103 nm·mm/riu和3.72×103 nm·mm/riu.研究结果对高斯变迹FBG用于生化传感领域的非均匀介质测量具有一定意义.     

基于SPSS软件的取样光栅传感特性分析

基于耦合模理论,采用传输矩阵法分析了取样光栅反射谱,取样光纤光栅在受到外界环境应变和温度影响时,其反射光谱的反射率和波长会发生变化。通过测量反射光谱的反射率变化和波长漂移,就能够实现用单根的取样光纤光栅同时测量应变和温度。通过仿真实验获得了取样光纤光栅的应变和温度传感数据。利用SPSS13.0统计学软件计算出了取样光栅反射率和波长与温度、应变变化的函数关系式,得到系数矩阵中A,B,C,D分别为-0.00033/ε,-0.00011/℃,-0.00055nm/ε,0.013nm/℃。应变测量范围为0~180     

啁啾光纤光栅的传输特性与切趾变迹研究

从麦克斯韦电磁理论导出的耦合模方程出发,应用研究非均匀光纤光栅的传输矩阵法数值研究了啁啾光栅前向波的能量传输、反射谱和时延特性,进而分析比较光纤光栅切趾变迹对反射和时延的影响以及在色散管理方面的应用.通过研究找出了一种余弦切趾函数的光纤光栅,从其特性分析可知这种变迹可以应用在波分复用/解复用、多通道的色散补偿、多通道滤波器等方面.     

电极放电对光纤光栅光谱特性的影响

采用电极脉冲电弧放电激励紫外曝光刻写的光纤布拉格光栅(FBG),重点研究了电极在栅区不同位置放电对光纤光栅光谱特性的影响。实验发现,在电极放电激励时,光栅反射率下降,光谱展宽并红移,放电引起的光谱变化具有可逆性。采用传输矩阵方法,在理论上分析了光纤光栅在电极放电产生的非均匀温度场下的光谱特性,与实验结果吻合。特别地,当电极在栅区中心位置放电时,光栅反射率下降幅度达到最大,反射谱峰值比无电极放电时小12dB,表现出开关量特性。     

均匀非均匀光纤光栅反射谱透射谱特性研究

文中阐述了光纤光栅的分类以及它们的特点和应用,根据光的耦合模理论应用MATLAB仿真均匀周期布喇格光纤光栅反射率透射率特性和非均匀啁啾光纤光栅反射率透射率特性,研究得到均匀周期布喇格光纤光栅和非均匀啁啾光纤光栅的反射率、透射率与光栅长度L成正比,L＝10mm时反射率和透射率接近100％,对比得到均匀周期布喇格光纤光栅反射率透射率,啁啾光纤光栅具有较宽的反射谱透射谱。研究结论为均匀非均匀光纤光栅器件制作提供理论依据。     

切趾函数光纤布拉格光栅的光谱特性研究

均匀光纤布拉格光栅(fiber Bragg grating, FBG)的反射谱存在旁瓣干扰,对波长解调过程会产生一定干扰,从而对传感测量结果造成一定误差。在FBG中引入切趾函数能够解决这一问题,有效抑制旁瓣。通过对切趾函数FBG耦合模理论的分析,获得了光栅参数变化对切趾FBG反射谱的作用情况。仿真实验结果表明,加入切趾函数会对FBG反射谱的旁瓣数量及大小起到明显抑制作用,反射率、中心波长、半高宽度及检测精度等反射谱特性的变化情况会受到光栅参数的影响。     

一种低成本FBG高温传感器的研究

采用相位掩模法,利用紫外光在载氢普通掺锗单模石英光纤中制作出光纤布拉格光栅(FBG)。同时,将反射率为17dB的光栅FBG1和反射率为41dB的光栅FBG2置于30～1000℃的高温炉内进行温度特性比较实验。在30～870℃范围内FBG1和FBG2两者中心波长随温度的变化趋势一致,且两个光栅反射波长都在870℃时消失,当温度继续升高到900℃时,仅有FBG2再次出现反射率为1dB的反射峰。对经过高温处理后的FBG2再次进行30～1000℃温度测量实验,温度灵敏度为0.02nm/℃,线性度为0.999。实验结果表明,对于具有高反射率的FBG进行高温热处理后,其可以在30～1000℃的温度范围内进行传感测量,且中心波长随温度变化呈良好的线性关系。利用该方法可以制作出低成本的可用于高温环境测量的FBG温度传感器。     

基于莫尔效应的光纤光栅变迹的研究

从理论上分析了利用莫尔效应进行变迹所引起的光纤光栅反射谱和色散特性的变化 ,指出由于莫尔条纹状的折射率调制使平均有效折射率在光栅区维持不变 ,所以可以实现纯变迹。与此成为对照的是 ,常用的升余弦函数变迹由于存在F P腔效应 ,因此在短波边的边模抑制效果不够满意。利用拉伸和二次曝光法产生的莫尔效应 ,实现了对光纤光栅的纯变迹 ,边模抑制比比相同工艺条件下的未变迹提高了约 6dB。     

FBG-FP的应变与温度解耦方法研究

光纤光栅(Fiber Bragg Grating, FBG)的温度与应变交叉敏感问题在实际工程应用中至关重要。本文提出了一种采用级联FBG的法布里-珀罗(FBG-Fabry-Perot, FBG-FP)传感器进行温度与应变同时测量的方法。级联FBG阵列由氩离子紫外激光器基于相位掩模板方法制作,其形成的FP干涉峰和光栅反射谱包络可以实现温度与应变的解耦。在不同的温度条件下,由FBG-FP反射谱包络10 dB带宽所对应中心波长值可得FBG-FP的温度灵敏度系数为9.5 pm/℃。分别在无应力、有应力且恒温条件下,通过解读FP干涉峰的波长变化得到该级联FBG-FP的温度和应变灵敏度系数分别为9.1 pm/℃和1.03 pm/με。实测的温度与应变值可由干涉峰波长、反射谱包络与温度、应变的函数关系求得。结果表明该FBG-FP可以实现温度与应变的同时测量。     

应变和温度变化对超结构光纤光栅光谱的影响北大核心

对由FBG(布拉格光纤光栅)和LPFG(长周期光纤光栅)构成的SFG(超结构光纤光栅),采用耦合模方程的相似变换解法,研究了应变梯度和温度梯度对SFG的透射谱和反射谱的影响。模拟结果表明,SFG在应变梯度或温度梯度的作用下,其反射光谱和ν阶包层模的透射光谱按确定规则独立漂移,据此可以同时求出光栅所在位置的应变和应变梯度,或温度和温度梯度。     

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.     

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.     

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.     

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.     

A rigorous proof of MIMO channel capacity’s increase with antenna number

It is well known that adding more antennas at the transmitter or at the receiver may offer larger channel capacity in the multiple-input multiple-output（MIMO） communication systems. In this letter, a simple proof is presented for the fact that the channel capacity increases with an increase in the number of receiving antennas. The proof is based on the famous capacity formula of Foschini and Gans with matrix theory.     

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.