工作波长为2.94 μm保偏空芯负曲率光纤

提出一种保偏空芯负曲率光纤,可用于传输工作波长为2.94 μm的中红外激光。首先通过调整y方向包层管的厚度和嵌套管到包层管内径的最大距离使 y方向偏振模式与包层管表面模式发生微弱耦合,再通过优化纤芯直径和包层管的外径诱导y方向偏振模式与包层管表面模式发生相位匹配,造成y方向偏振模式泄露出纤芯。包层管间的缝隙引导高阶模式泄露出纤芯,而x方向偏振模式因包层管和嵌套管的厚度具有抑制耦合的作用而保持低损耗传输。最终得到一种工作波长为2.94 μm的保偏空芯负曲率光纤,x方向偏振模式的限制损耗为2.8×10^-2 dB/m,偏振消光比大于2×10³,高阶模抑制比大于100,双折射为1.4×10^-5。当光纤y方向弯曲,且半径为25 cm时,弯曲损耗为0.62 dB/m。     

超低损耗高双折射空芯反谐振太赫兹光子晶体光纤

本文提出了一种以环烯烃共聚物（Cyclic Olefin Copolymer, COC）为基底的超低损耗高双折射空芯反谐振太赫兹光子晶体光纤,该光纤的包层由两组（共六个）无节点嵌套管组成。采用时域有限差分法（Finite Difference Time Domain method, FDTD）结合完美匹配层（Perfectly Matched Layer, PML）边界条件对其导波特性进行分析。仿真结果表明,在0.8~1.35 THz范围内,总传输损耗小于0.1 dB/m,双折射大于2.12×10^-5,色散在±0.027 ps/THz/cm。在1.12 THz处,最低总传输损耗仅为0.543×10^-2 dB/m,双折射值为2.06×10^-4。同时,分析了该光纤的弯曲性能,表明在y方向,当弯曲半径超过19 cm时,弯曲损耗小于0.1 dB/m,具有良好的弯曲性能。     

基于模式耦合的低弯曲损耗大模场带隙光纤研究

提出一种大模场带隙光纤,由排布在正方结构网 格中的高折射率介质柱形成导光机制。采用有 限元法分析了直光纤与弯曲光纤下的模式损耗与模场面积等特性。研究结果表明:这种光纤 具有较宽的带 隙,可同时支持基模和高阶模的传输,两种模式的泄漏损耗均低于1×10－3 dB/m。当光纤弯曲时,其包层会 产生具有强泄露损耗的包层模,并在一定的弯曲半径下与纤芯的高阶模发生强耦合。当弯曲 半径在15～20cm 之间时,基模弯曲损耗小于0.01dB/m,而高阶模损耗大于1dB/m, 因而光纤可以经弯曲实现大模场单模传 输。在1064nm波长处,其直光纤的基模模场面 积为1319.62μm², 而在弯曲状态下的模场仍可达到975.00μm²以上,因而可实现大 模场的低弯曲损耗传输。     

带反馈双波导耦合微环共振器光学特性的理论研究

设计了一种带反馈的双波导微环耦合结构,利用传输矩阵法得到了透过率公式和相移公式。根据透过率公式,得到了随相移变化的非对称类Fano共振曲线。详细分析了各耦合区的透射系数对透过率曲线的影响,得知在t₁=t₂=t₃=0.2条件表现出的滤波特性比不带反馈的结构要好。在该条件下,微环和直波导的损耗系数都对透过率的影响比较敏锐,当损耗从0.8变到1时,透过率峰值几乎从0变到1。除此之外,透过峰附近的延迟系数达到29.1,所以该结构还可以用作光延迟     

螺旋波纹波导回旋行波管的模式耦合机制

从波导的等效边界条件出发,结合波导的激发方程组,通过数学推导说明了螺旋波纹波导回旋行波管的模式耦合机制。TE_1,1模会在螺旋波纹波导中耦合出TE_-2,1模,并且通过计算说明TE_-2,1模主要和TE_1,1模的空间-1次谐波发生耦合。     

超大带宽高频XBAR谐振器研究

随着第五代移动通信(5G)时代的到来,高频、大带宽的谐振器成为通信行业的迫切需求。该文设计制备了一款可实现高频超大带宽的横向激发体声波谐振器(XBAR)。该谐振器A1模式的谐振频率为5.81 GHz,机电耦合系数可达39.6%,Q-3 dB为248;A3模式的谐振频率高达17.04 GHz,机电耦合系数为7.0%。该谐振器A1和A3模式的频率温度漂移系数(TCF)分别为-72.6×10^-6/℃和-38.5×10^-6/℃。此外,该文还提出了一种新型叉指电极(IDT)结构,该结构可以抑制寄生模式,提升谐振器性能。     

用于射频滤波器的LN单晶薄膜XBAR的性能研究

基于铌酸锂(LN)薄膜的横向激发体声波谐振器(XBAR)能够兼具大机电耦合系数(K²)和高谐振频率(f)特性，有望满足5G应用的频段要求。然而，常规LN薄膜单层XBAR结构的温度稳定性较差，频率温度系数(TCF)较低。该文提出一种具有SiO₂温度补偿层的SiO₂/LN双层结构XBAR，并建立了精确分析层状结构XBAR的有限元模型。理论分析表明，该双层结构XBAR上激励的主模式是一阶反对称(A1)兰姆波。通过合理优化结构参数配置，能够获得高谐振频率(f~4.75 GHz)和大机电耦合系数(K²~8%)，同时其温度稳定性也得到显著改善(TCF~-36.1×10^-6/℃)，相较于单层XBAR结构提高了近70×10^-6/℃，这为研制温补型高频、大带宽声学滤波器提供了理论基础。     

硅基波导光栅耦合器与波导传输损耗的研究

对硅(Si)基波导光栅耦合器的设计与耦合性能进 行了研究。采用本征模展开法对光栅耦合器进行设计与 优化,通过实验测量了光栅的耦合性能,并对均匀光栅、自聚焦光栅和反射光栅等3种光栅 耦合器的耦合 性能进行了比较,耦合效率分别达到了达到47.86、56. 36和48.98%,自聚焦光栅可以有效改善光纤到 光纤的传输效果,耦合效率提高了8.5%。通过实验测量了基于耦合光 栅技术的Si基条形波导和槽型波导的 传输损耗,结果显示,条形波导和槽型波导的传输损耗分别为2.34d B/cm和6.31dB/mm。     

高Q值横向激发体声波谐振器的设计与制备

随着5G移动通信时代的发展,射频前端(RF front-ends)的滤波和信号处理迫切需要高频大带宽的声学谐振器。横向激发体声波谐振器(XBAR)具有超高的工作频率和超大的机电耦合系数(k²),但其品质因数(Q)值不高,阻碍了其在射频前端中的应用。该文提出了一种基于ZY切铌酸锂(LiNbO₃)的XBAR谐振器,通过有限元(FEM)仿真对谐振器进行了优化设计,并在微机电系统(MEMS)工艺下对谐振器进行加工。该文所制备的横向激发体声波谐振器A₁模式的谐振频率为4.72 GHz,k²=26.9%,Q_{3 dB}为384,温度频率漂移系数为-60.5×10^-6/℃。A₃模式的谐振频率为13.5 GHz,k²=4.4%。     

980 nm大功率高阶光栅锥形半导体激光器

为了获得高功率、窄线宽和近衍射极限输出的半导体激光器,采用高阶光栅（high order Bragg gratings,HOBGs）和主控振荡功率放大器（Master Oscillator Power-Amplifier,MOPA）结构,成功研制出一种980 nm波段的HOBGs-MOPA半导体激光器。该激光器采用周期为11.37 μm的高阶光栅进行光模式选择,通过锥角为6°的锥形波导将单模激光功率放大,实现了输出功率2.8 W,3 dB光谱线宽31 pm,光束质量因子M ²为2.51的窄线宽激光输出。     

用遗传算法求解基于高阶累积量的盲均衡问题

将遗传算法引入盲均衡技术领域，详细分析了如何用遗传算法求解基于高阶累积量盲均衡问题，并给出了一种求解算法的具体步骤。该算法不用基于领域知识的规则，具有很强的通用性与鲁棒性。通过计算机仿真验证了该算法的有效性。     

Multiple-access channels with memory with and without framesynchronism

The capacity region of frame-synchronous and frame-asynchronous, discrete, two-user multiple-access channels with finite memory is obtained. Frame synchronism refers to the ability of the transmitters to send their code words in unison. The absence of frame synchronism in memoryless multiple-access channels is known to result in the removal of the convex hull operation from the expression of the capacity region. It is shown that when the channel has memory, frame asynchronism rules out nonstationary inputs to achieve any point in the capacity region, thereby allowing only coding strategies that involve cooperation in the frequency domain but not in the time domain. This restriction drastically reduces the capacity region of some multiple-access channels with memory, and in particular the total capacity of the channel, which is invariant to frame asynchronism for memoryless channels     

一种给批量汉字加注带有声调拼音的方法

由于汉字存在着多音字的情况,所以给汉字加注带有声调的拼音带来了困难.为了解决这一问题,设计了单字与词语相结合的加注方法.首先构建了带有声调的拼音字典和词典,拼音字典中同一个多音字的拼音按照使用频率进行排放,并且对词典中的词语按照最后一个字进行了索引;然后设计了基于整词二分的二层索引结构,实现了改进的最大逆向分词算法;最后设计了三种实验方案,进行了对比实验.实验结果表明,在没有使用该方法前它的错误率为11%,使用后错误率下降为0.09%.     

Spectrum Shaping with Alphabetic Codes with Finite Autocorrelation Sequence

In this paper we consider the problem of recoding binary data into ternary sequences for synchronous baseband data transmission systems. Our major objective is the shaping of the power spectral density of the channel process in order to combat the effects of intersymbol interference caused by the low-frequency cut-off of the channel. This motivates our interest in designing codes whose channel process has small Power in the low frequency range. Based on the MacLaurin expansion of the power density function, we use as a design heuristic the normalized second derivative Δ of the latter. To make computationally manageable the expression of Δ, we restrict ourselves to a class of codes whose autocorrelation sequence contains a finite number of nonzero terms, and present a corresponding code design algorithm. As examples, we exhibit two new codes which in many respects improve over the spectra of corresponding well-known codes.     

ID-based authentication scheme combined with identity-based encryption with fingerprint hashing

Current identity-based （ID） cryptosystem lacks the mechanisms of two-party authentication and user＇s private key distribution. Some ID-based signcryption schemes and ID-based authenticated key agreement protocols have been presented, but they cannot solve the problem completely. A novel ID-based authentication scheme based on ID-based encrypfion （IBE） and fingerprint hashing method is proposed to solve the difficulties in the IBE scheme, which includes message receiver authenticating the sender, the trusted authority （TA） authenticating the users and transmitting the private key to them. Furthermore, the scheme extends the application of fingerprint authentication from terminal to network and protects against fingerprint data fabrication. The fingerprint authentication method consists of two factors. This method combines a token key, for example, the USB key, with the user＇s fingerprint hash by mixing a pseudo-random number with the fingerprint feature. The security and experimental efficiency meet the requirements of practical applications.     

一种利用Tuxedo处理集群文件服务器协作的方法

现代大型信息系统中文件量比较大,一台服务器很难支持大量文件的存储,使用集群文件服务器,可以解决大量文件存储的问题。通过实际项目中使用的方案,描述利用Tuxedo 7.1支持对XML文件分析功能,实现文件服务器互相协作的方式。特别是通过使用文件命名散列方法计算文件服务器标示号,通过XML传递该标识号到Tuxedo服务器,从而抉择将文件放置到哪台文件服务器上。这样不用在文件数据库存储文件位置,就可以直接存储并获取文件。     

Low-power MOS integrated filter with transconductors with spoiltcurrent sources

It is shown that an MOS weak-inversion differential pair can be linearized considerably by replacing the tail current source with a MOSFET biased in the weak-inversion triode region. Calculations show that the transconductance can be kept constant to within +5%/-0% for input voltages up to 130 mV. This linearized differential pair is used in a third-order transconductance-C bandpass filter with 18 Hz and 142 Hz cutoff frequencies, which draws 4.9 nA from a 1.8-V supply. Its dynamic range is 62 dB and its active area is 0.5 mm²     

Terahertz imaging with bow-tie InGaAs-based diode with broken symmetry

A silicon-lens coupled bow-tie InGaAs-based diode with broken symmetry is demonstrated for terahertz imaging applications below 1 THz at room temperature. Transient features and the dynamic range of the bow-tie InGaAs-based sensor are explored experimentally, proving the possibility to use the device in real-time imaging systems. Response time is found to be less than 7 ns, responsivity of 0.1 mA/W, and noise equivalent power of 5.8 nW/radicHz.     

寓教于乐寓教于思

本文介绍了数字电子技术基础课程教学中,改革教学方法、激发学生学习兴趣,诱导学生积极思维,将灌输知识的结论性教育转变为启发思维的过程性教育,将纪律严明的课堂气氛转变为生动活泼、主动探索课堂气氛所做的一些探索。     

Anisotropy of composite materials with inclusion with orientation preference

In this paper, the quasicrystalline model and the differential evolution strategy are applied to analyze the effective electromagnetic properties of composite materials with aligned nonspherical inclusions. The relationship between the effective wave number, volume concentration, direction of wave propagation vector, and aspect ratio of the inclusion particle are numerically studied. It is found that composite materials with small inclusion particles behave like uniaxial material. In addition, we observed general effective anisotropy in composite materials with larger inclusion particles.