双环、三纤互耦全光纤熔锥滤波器用正常色散的双折射光纤所作的暗孤子开关的开关条件

通过将熔锥结构中强、弱耦合段的总幅度耦合系数与滤波网络方程中的幅度耦合系数等效的方法,定量分析了双环、三纤互耦滤波器的频谱特性。实验滤波器通带特性的测试结果与理论分析基本吻合。所测滤波器的中心波长、抑制度、半功率带宽及插入损耗分别为1.27 μm,>13 dB、72 μm及3.9 dB。在正常色散的双折射光纤中传输的暗孤子对之间由于耦合周期性交换能量,一个暗孤子可把能量完全转给另一暗孤子,因此双折射光纤可作光开关。本文讨论了椭圆角为35°的双折射光纤的开关条件,发现脉冲只有以特定的极化角入射才有开关现象产生,而且建立了光纤长度与孤子对相差、初始能量差的解释关系。     

概率统计课程中拓广引申式教学法探索

概率论和数理统计研究的是随机现象,有许多本学科独有的思维方式和解题模式.学生初学时会面临全新的困难.如何让学生较快地适应本课程的学习?如何引导学生主动地发现问题和探索问题?着重介绍了作者从自己的教学实践中总结出的一套行之有效的方法——拓广引申式教学法.     

Optical Storage Media with Dye-Doped Minute Spheres on Polymer Films

We have fabricated a new optical storage media using minute spheres arranged on a surface relief grating (SRG). Using minute spheres as recording bits, we can limit recordable regions by sphere size, and can realize high resolution reproduction in the plane direction. Surface relief structures were made on a polymer thin film on which we performed diffusion arrangement and adsorptive fixation of minute spheres. The stability of the arranged spheres was confirmed for heating and washing. Furthermore, we used a dipping method for a more simple arrangement of minute spheres on a large area of the substrate and made a monolayer sample of the spheres. We were able to realize a highly sensitive reconstruction of the medium using a confocal optical system as a record and readout system.     

利用场耦合理论研究开放微波谐振腔

利用电磁场的等效原理，将一个开放微波腔等效于一个闭合边界微波腔（即封闭微波腔）和开放边界（即行波吸收边界）两部分，然后利用等效封闭微波腔的本征模式及其与开放边界的耦合，建立了关于开放微波腔模式（即模式场分布、频率、品质因子）的耦合方程组，其中开放边界为行波吸收边界.以X波段六腔渡越振荡管为例进行分析，将该振荡管等效为封闭微波腔和同轴输出结构两部分，用SUPPERFISH获得封闭腔的各个模式场分布及频率，然后根据封闭微波腔与开放边界的耦合，求得六腔渡越振荡管的工作模频率为9.25GHz，品质因子为115.2，与实验测量结果基本符合.     

一种找分光计镜面反射象的方法

本文提出一种在望远镜外寻找和粗调分光计镜面反射象的方法。     

A scalar-mode representation of stochastic, planar, electromagnetic sources

A very useful theoretical tool for investigating coherence properties of stochastic scalar sources and stochastic scalar fields is the so-called coherent-mode representation. We introduce a somewhat similar new representation for planar, secondary stochastic electromag netic sources which generate beams. It consists of three expansions for the three independent elements of the 2 × 2 electric cross-spectral density matrix of the beam. The expansion of the diagonal elements of the matrix are coherent-mode representations in the sense of the scalar theory. The third one, for each off-diagonal element, is a bi-modal expansion, expressed in terms of the coherent modes of the diagonal elements.     

Log Structures on Generalized Semi-Stable Varieties

In this paper, a class of morphisms which have a kind of singularity weaker than normal crossing is considered. We construct the obstruction such that the so-called semi-stable log structures exists if and only if the obstruction vanishes. In the case of no power, if the obstruction vanishes, then the semi-stable log structure is unique up to a unique isomorphism. So we obtain a kind of canonical structure on this family of morphisms.     

Anharmonic dynamical behaviour in bcc zirconium

We present inelastic neutron scattering measurements of the low energy and strongly damped phonons in the high temperature bcc phase of zirconium. These phonons were investigated at different scattering vectors but equivalent phonon wave vectors in different Brillouin zones or along different but equivalent paths in the same Brillouin zone. Neither the observed differences in intensity nor in line shapes can be explained by the coherent one-phonon scattering law . This leads to an apparent violation of the fundamental symmetry of lattice dynamics. Taking into account the strong anharmonicity of these phonons, interferences between one- and multi-phonon scattering are held responsible for these effects. Measurements in different scattering planes reveal that due to the symmetry of the bcc lattice, these effects can only be observed in certain directions. Received: 24 December 1997 / Received in final form: 9 March 1998 / Accepted: 19 March 1998     

Cavitation in superfluid helium-4 at low temperature

We have studied the nucleation of bubbles in pure superfluid helium-4 at temperatures down to 65 mK. We have found that the nucleation is a stochastic process, and that at temperatures below 600 mK the nucleation rate is independent of temperature. These results are consistent with the assumption that the nucleation takes place via quantum tunneling. Received: 15 November 1997 / Received in final form: 19 December 1997 / Accepted: 22 January 1998     

The study of phase matching of nonlinear waves in microdroplets

In this paper, the internal field distribution of higher order MDRs of water droplets is calculated and the result shows that the higher order MDRs should dominate the nonlinear couple process. Furthermore, the phase matching required for four-wave mixing (FWM) process in the droplet is interpreted as the concept of angular momentum conservation. The slight mismatch in angular momentum leads to significant improvement of phase matching than that in optical cell.