薄包层啁啾长周期光纤光栅的色散补偿

为了提高啁啾长周期光纤光栅(LPFG)光纤通信的色散补偿能力,提出了利用薄包层啁啾LPFG进行包散补偿的方法.首先介绍了根据传输信号确定啁啾LPFG的啁啾系数、光栅长度等参数的方法.然后利用上述方法设计了对光纤中传输的中心波长为1550 nm,带宽为0.2nm的信号进行色散补偿的薄包层啁啾LPFG.利用耦合模理论及传输矩阵法计算了约1m长的此种啁啾LPFG的色散,结果表明可以补偿该光信号通过46 km光纤所产生的色散.进一步分析了切趾函数、啁啾系数、交叉耦合系数等参数对薄包层啁啾LPFG色散的影响.     

多普勒加宽非匹配∧型能级系统的无反转增益效应

对∧型能级系统连续波无反转增益效应的研究表明,在耦合光的拉比频率小于多普勒宽度的情况下,多普勒加宽的非匹配能级系统（耦合光波长λc小于探测光波长λp）的无反转增益不仅存在,而且还强于匹配系统（λc=λp）的无反转增益,文中从与无反转增益紧密联系的电磁感应透明（EIT）的角度对这一现象作了解释。     

粘度对聚合物共混物相分离动力学的影响研究

模拟了粘度反差二元流体混合物的相分离,考察了粘度对相分离动力学的影响,发现相区域的增长主要由粘度较大的组分所控制,合理地解释了粘度效应所导致的一些实验现象.证明了即使组分间的粘度比很大,也没有出现反转相结构,说明在不施加剪切流场情况下,粘度反差不是形成反转相的原因.     

多普勒加宽非匹配Λ型能级系统的无反转增益效应

对Λ型能级系统连续波无反转增益效应的研究表明,在耦合光的拉比频率小于多普勒宽度的情况下,多普勒加宽的非匹配能级系统(耦合光波长λc小于探测光波长λp)的无反转增益不仅存在,而且还强于匹配系统(λc=λp)的无反转增益,文中从与无反转增益紧密联系的电磁感应透明(EIT)的角度对这一现象作了解释.     

通过“一题多解”培养发散思维

通过几道力学题目具体说明了“一题多解”在物理教学中的作用,“一题多解”有助于学生对课本知识深入理解;有助于培养学生的发散思维;有助于学生构建正确的物理图像.     

Spectroscopic properties of Nd—doped phosphate glass with a high emission cross section

Neodymium doped phosphate glasses have been prepared by the semi-continuous melting technique. Their absorption and emission spectra have been recorded at room temperature. The Judd－Ofelt theory has been applied to evaluate the stimulated emission cross sections of ⁴F_3/2→⁴I_11/2 transition for Nd³⁺. The higher stimulated emission cross section, 4.0×10^-20cm², is obtained. The fluorescence decays of the ⁴F_3/2→⁴I_11/2 transition of Nd³⁺ are measured for the samples doped (0.7－10) wt% of Nd₂O₃ at room temperature. The concentration quenching of Nd-doped phosphate glass is mainly attributed to cross-relaxation and energy migration. The site-dependent properties of fluorescence spectra and the fluorescence lifetime of the Nd³⁺-doped phosphate glass (with 2.2wt%Nd₂O₃) are studied using laser-induced fluorescence line narrowing techniques, and the site-to-site variations of optical properties are observed at low temperature.     

不锈钢管封装短周期光纤光栅温度传感器特性及仿真分析

采用不同内外径的304不锈钢管封装制作了I型光纤光栅温度传感器,温度灵敏度均达到20 pm/℃以上,是裸光纤光栅温度传感器的2倍以上,线性度优异,能够达到0.99957以上。内外径为0.4、0.5 mm,0.75、1 mm,2、3 mm的不锈钢管封装的传感器的响应时间分别为21.2、32.3、104.3 s,响应时间随着不锈钢管的增厚而增加。薄壁管(内外径为0.4、0.5 mm)封装的光纤光栅温度传感器虽然响应时间短,但在温差为75℃的环境下波长存在异常下降的现象,这在一些应用场景中十分不利。利用ANSYS有限元仿真软件对不同内外径不锈钢管封装的光纤光栅温度传感器进行模拟,仿真得到响应时间与z轴形变量。仿真值与实验值进行比较可知,其误差较小,并且z轴形变量的变化也能较好地解释波长异常变化的原因。     

Solitons and defects in nematic liquid crystals under a simple shear flow and in a static external magnetic field

Under a simple shear flow and in a static external magnetic field, the production of defects in the director-aligning regime of nematic liquid crystals has been investigated in terms of the Leslie-Ericksen theory. The equation of motion of the nematic director, which conforms to the driven over-damped sine-Gordon equation, has a soliton solution of the amplitude w. We show that the stationary state with the director uniformly oriented at a Leslie angle is only a metastable state and the potential, which governs the motion of the director, has a nmnber of stable stationary states. For a strong magnetic field, the higher energy barrier between the stable and unstable states leads the director to be locked along the magnetic field direction. However, at the appropriate shear rate and magnetic field the defects, which appear as a stable solitary solution, can be nucleated from a uniformly aligned nematic liquid crystal. We have calculated the stationary travelling velocity of the solitary waves and the distance between a pair of defects.     

Parameters optimization of π-phase-shifted long-period fiber grating for gas sensing

The gas-sensitive film coated π-phase-shifted long-period fiber grating(LPFG),consisting of two same long-period fiber gratings cascaded by a regular fiber with length of half of the grating period,is proposed for gas sensing.The sensitivity of the sensor is defined by the change rate of the transmission at specific wavelength with respect to the film refractive index.The qualitative and numerical analyses show that to get a high sensitivity,the optimal coupling strength of each long-period fiber grating is...     

温度对晶体中稀土离子(E)-型能级电磁感应透明的影响

运用产经典理论，在Pr^3 ：YSO晶体Pr离子E－型三级级系统中，求解了探测光吸收在不同光跃迁驰豫速率与自旋跃迁驰豫速率下的瞬态及稳态解，得到了电磁感应透明现象，分析了两种驰豫对电磁感应透明的,人而揭示了掺稀土离子晶体中电磁感应透明对温度的依赖性。