椭圆芯双模光纤干涉模斑中心间距的研究

通过弱波导近似的方法，讨论了椭圆芯双模光纤中沿光纤长轴的基模模斑半径Wx和短轴的基模模斑半径Wy尺寸，分析了它们的比值随入射光波长λ及纤芯半长轴与半短轴的比值a/b的变化规律。 针对基模LP01和第一高阶模LP11间的相位差变化，计算了双模干涉模斑的分布结构。计算结果表明，当基模LP01和第一高阶模LP11间的相位差为π/2时，两瓣干涉模斑有相同的结构特征。同时，两瓣模斑的中心间距S随Wx/Wy的的增加而变大。而且，当入射波长在0.65 μm和 1.31 μm之间变化时，结合两瓣模斑的中心间距S随Wx/Wy的变化规律，首次给出了S的计算公式。这对于实际应用如传感器和光纤耦合器件设计是很重要的。

一种使用双棱镜的动态小角度测量方法

提出一种基于正切关系和相位调制技术的动态小角度测量方法。使用双棱镜组成干涉测量臂引导两束平行光至分束棱镜处干涉,通过提取携带被测信息的干涉信号的相位实现动态的小角度测量。由于采用位置探测器(PSD)对测量臂中两平行光束的间距进行测量,简化了测量方程,消除了装置中双棱镜必须对称放置的要求。通过正弦地改变半导体激光器的注入电流在时域内实现对干涉信号的相位调制,形成准外差干涉测量模式,提高了光程差的测量精度。实验验证了该方法的可行性,并讨论了影响小角度测量精度的误差因素。研究结果表明,基于该方法的动态小角度的重

New doubly periodic waves of the (2+1)-dimensional double sine-Gordon equation

New exact solutions of the (2 + 1)-dimensional double sine-Gordon equation are studied by introducing the modified mapping relations between the cubic nonlinear Klein-Gordon system and double sine-Gordon equation. Two arbitrary functions are included into the Jacobi elliptic function solutions. New doubly periodic wave solutions are obtained and displayed graphically by proper selections of the arbitrary functions.

掺镱双包层光纤放大器的放大特性

从掺镱(Yb)光纤放大器的功率传输方程出发,利用有限差分法对小模场面积(SMA)和大模场面积(LMA)掺镱双包层光纤放大器的放大特性进行了分析比较。采用模场直径(MFD)6.5 μm和20 μm的双包层掺镱光纤作为放大器增益介质进行窄线宽连续信号的放大,在915 nm激光抽运下模拟计算了大、小模场面积输出功率随输入信号功率、抽运光功率和光纤长度的变化特性,特别是对于大模场面积光纤放大器,最优光纤长度的选择至关重要;讨论了模场直径不同时的最优抽运功率和光纤长度的选择,得出4 m光纤放大时的临界抽运功率为4

锥形光纤的功率分布特性

从波动理论出发,对锥形光纤的纵向传播常数进行泰勒(Taylor)级数展开,经近似得到了锥形光纤功率分布的解。基于此理论,对锥形光纤的功率分布特性进行了讨论,并分析了锥形光纤的长度、锥度和光纤折射率等参数对锥形光纤不同模式功率分布的影响。为了减小功率泄漏,当光从锥形光纤大端入射时,应当减小锥长,减小锥度,增大纤芯包层折射率差;当光从锥形光纤小端入射时,应当增加锥长,增加锥度,增大纤芯包层折射率差。在长锥长、大锥度情况下,光纤折射率分布的影响相对较小。

双程掺镱光纤放大器的增益特征及优化

比较了掺钕光纤和掺镱光纤对1064nm光放大的特点．基于速率方程和传输方程，数值分析了在915nm泵浦下双程掺镱光纤放大器的增益特征，并且和传统的单程放大进行了比较．分析了信号光和泵浦光，以及粒子数沿着光纤方向的分布特点．最后对双程掺镱光纤放大器进行了优化．

水下目标光学隐蔽深度遥感获取方法

针对用透明度盘深度(SD)估计水下目标的光学隐蔽深度(OCD)的方法缺乏科学性与准确性,提出了利用水色卫星遥感数据获取水下目标光学隐蔽深度的方法。在给出水下目标光学隐蔽深度概念的基础上,分析了水下目标对水中光传输的影响,并根据目标背景对比度传输方程建立了水下目标隐蔽深度与透明度盘深度的转换关系。建立了水下目标光学隐蔽深度的遥感获取模式,并对模式进行了实验验证。结果表明,黑色模型的理论计算和实测数据的相对误差小于30%,而白色模型的理论计算和实测数据的相对误差小于20%。

Self-adaptive optical systems for long-distance flying optics

The focusing characteristics of long-distance flying optics were studied systemically for TEMmn Gaussian beams. The results show that the ABCD law of parameter q can be extended to Gaussian modes of any order when waist radius w in the imaginary part of parameter q is replaced by Rayleigh range Z(R) of a certain resonator in the equation. The difference between the real focal length and the geometric focal length, defined as Delta f, was calculated for laser applications. A novel self-adaptive optical system was demonstrated for precisely controlling the focusing characteristics of long-distance flying optics, Theoretical analyses and experimental results were consistent. (c) 2006 Optical Society of America.

The intraspecific difference of the triose phosphate isomerase ( tim) gene from Giardia lamblia

目的　探讨蓝氏贾第鞭毛虫 (Giardialamblia)磷酸丙糖异构酶基因种内差异。方法　提取虫体总DNA ,对所有虫株磷酸丙糖异构酶 (tim)基因部分片段进行PCR扩增。测定序列后 ,用简约法和NJ法构建系统树进行系统发育分析。结果　共有 12 4个位点存在变异 (占所有测定序列中的 2 3% ) ,且大多数为发生在密码子的同义突变。两种构树方法所得二树的分枝结构相似 ,均将受试的 16株蓝氏贾第虫分为明显的两组。结论　宿主及地理因素对蓝氏贾第虫群体的遗传多样性影响不大。在DNA分子进化水平上 ,自然选择的影响十分显著。可将tim基因作为蓝氏贾第虫群体遗传结构一个十分有效的遗传标记。

Response of Microcystis to copper stress - Do phenotypes of Microcystis make a difference in stress tolerance?

To elucidate the role of phenotype in stress-tolerant bloom-forming cyanobacterium Microcystis, two phenotypes of M. aeruginosa-unicellular and colonial strains were selected to investigate how they responded to copper stress. Flow cytometry (FCM) examination indicated that the percents of viable cells in unicellular and colonial Microcystis were 1.92-2.83% and 72.3-97.51%, respectively, under 0.25 mg l(-1) copper sulfate treatment for 24 h. Upon exposure to 0.25 mg l(-1) copper sulfate, the activities of antioxidative enzyme, such as superoxide dismutase (SOD) and catalase (CAT), were significantly increased in colonial Microcystis compared to unicellular Microcystis. Meanwhile, the values of the photosynthetic parameters (F-v/F-m, ETRmax and oxygen evolution rate) decreased more rapidly in unicellular Microcystis than in colonial Microcystis. The results indicate that colonial Microcystis has a higher endurance to copper than unicellular Microcystis. This suggests that the efficient treatment concentration of copper sulfate as algaecides will be dependent on the phenotypes of Microcystis. (C) 2006 Elsevier Ltd. All rights reserved.

The growth patterns of juvenile and precocious Chinese mitten crabs, Eriocheir sinensis (Decapoda, Grapsidae), stocked in freshwater lakes of China

Stocking experiments with Eriocheir sinensis were conducted in two small, shallow lakes to study its growth pattern in 1994-1997. For the initially immature crabs, carapace width (CW) increases from 21.2 +/- 0.4 mm (mean +/- s.e.) for females and 22.3 +/- 0.5 mm for males in January, to 65.4 +/- 0.5 mm for females and 66.9 +/- 0.6 mm for males in October. There is no significant difference in CW and carapace length (CL), although there is a large difference in body weight (BW) between sexes in every month from January to August when crabs are juvenile, however, there are significant differences in CW, CL. and BW between sexes after September when the crabs become sexually mature. The growth curve from January to October fits a logistic equation and may be expressed as CW = 75.7 (1 + exp (0.914 - 0.011t))(-1) for females, and CW = 77.5 (1 + exp (0.889 - 0.011t))-1 for males, where CW is in mm, t in days. For precocious crabs (reaching maturity by the first autumn, CW does not change much from January to July, which indicates that precocious crabs stop growing. Like juveniles, the precocious crabs show no differences in CW and CL, but do show a statistically significant difference in BW between sexes.

Investigation of gain recovery for InAs/GaAs quantum dot semiconductor optical amplifiers by rate equation simulation

The gain recoveries in quantum dot semiconductor optical amplifiers (QD SOAs) are numerically studied by rate equation simulation. Similar to the optical pump-probe experiment, the injection of double 150 fs optical pulses is used to simulate the gain recovery of a weak continuous signal under different injection levels, inhomogeneous broadenings, detuning wavelengths, and pulse signal energies for the QD SOAs. The obtained gain recoveries are then fitted by a response function with multiple exponential terms to determine the response times. The gain recovery can be described by three exponential terms with the time constants, which can be explained as carrier relaxation from the excited state to the ground state, carrier captured by the excited state from the wetting layer, and the supply of the wetting layer carriers. The fitted lifetimes decrease with the increase of the injection currents under gain unsaturation, slightly decrease with the decrease of inhomogeneous broadening of QDs, and increase with the increase of detuning wavelength between continuous signal and pulse signal and the increase of the pulse energy.