Modelling of self-aligned total internal reflection waveguide mirrors: an interlaboratory comparison

Results of modelling of light propagation in 45° self-aligned total internal reflection rib waveguide mirrors on InP substrate are compared. Six laboratories participated in the comparison with the following six modelling methods: the standard fast-Fouriertransform beam propagation method (BPM), the standard finite-difference (FD) BPM using the Crank-Nicholson scheme (two laboratories), the FD-BPM with the correction for the slowly varying envelope approximation, the method of lines, the eigenmode expansion and propagation method, and a simple method based on the field overlap. All the laboratories used the effective-index method to reduce the three-dimensional problem to two dimensions. The differences among the results obtained by different methods are briefly discussed and qualitatively compared to measured values.     

Limit theorems for Markov chains of finite rank

We consider a Markov chain with a general state space, but whose behavior is governed by finite matrices. After a brief exposition of the basic properties of this chain, its convenience as a model is illustrated by three limit theorems. The ergodic theorem, the central limit theorem, and an extreme-value theorem are expressed in terms of dominant eigenvalues of finite matrices and proved by simple matrix theory.     

Informal Networks and Absenteeism Within an Organization

This article discusses the relationship between the informal ties of the employees within an organization and their absentee rates.~To explain this relationship, the assumption is made that within a department, a more or less stable norm concerning illegal absenteeism exits, and that the strength of this norm is related to the tightness of the informal relationships between the employees: the more consensus on the absentee norm, irrespective of the degree of tolerance, the more cohesive this department. Furthermore, according to the fairness theory of Adams (1965), a relationship between the tightness of the informal relations, the norm concerning illegal absenteeism and the absentee rate is expected: the more cohesive, the higher the effect of the group norm on the short-term absentee rate. Network data of 62 employees of eight comparable teams within a housing corporation were collected by means of a questionnaire, and combined with data on the absentee rates of the employees. The data supported the hypotheses concerning the relationship between the group norm, the tightness of the informal relations and the short-term absentee rates of the employees within a department.     

Design of 1480-nm diode-pumped Er3+-doped integrated optical amplifiers

Abstact Erbium-doped Y₂O₃ integrated optical amplifiers are designed for low-threshold operation and 3 dB amplification. The most important design parameter for minimal threshold, the erbium concentration, is found to have an optimum value of 0.35 at% for a given waveguide structure with 1.0 dB cm^-1 background loss. The corresponding threshold power is 7 mW. The pump power to obtain 3 dB gain is found to be 22 mW for an amplifier with an optimum erbium concentration of 0.6 at% and 2.8 cm length. At 30 mW pump power the maximum gain is shown to be 5 dB.Designing is done using a comprehensive numerical model of an erbium-doped integrated optical amplifier. In the model two-dimensional intensity-dependent overlap integrals are used, which allow arbitrary erbium dopant profiles and waveguide crosssections. Concentration-dependent effects such as quenching and upconversion are also included in the model.Input parameters for the model are determined from measurements on an unoptimized Er: Y₂O₃ optical waveguide amplifier. Amplification simulations and gain measurements of the unoptimized waveguides are found to be in close agreement, providing a sound basis for the design calculations.     

Slow Light Excitation in Tapered 1D Photonic Crystals: Theory

Slow light (SL) states corresponding to wavelength regions near the bandgap edge of grated structures are known to show strong field enhancement. Such states may be excited efficiently by well-optimized adiabatic transitions in grated structures, e.g., by slowly turning on the modulation depth. To study adiabatic excitations, a detailed research in 1D is performed to obtain insight into the relation between the device parameters and properties like enhancement and modal reflection. The results enable the design of an adiabatic device for efficient excitation of SL states in 1D. The effect of small wavelength variations as well as small fluctuations in the modulation depth of the grating has been investigated.     

Charge driven fragmentation of nucleobases

We studied multiple ionization of single nucleobases by means of slow highly charged ions (Xe(q+), q=5-25). The products of the subsequent fragmentation were studied using high resolution coincidence time-of-flight spectrometry. We observed a strong dependence of the fragment kinetic energies on the initial charge state of the intermediate parent ions as well as on the initial chemical environment of the respective fragment ions within the parent molecule. The data allow us to shed light on the charge distribution within the molecule as well as on the fragmentation dynamics of these intermediate size systems.     

Z oscillations in ion-induced fullerene fragmentation

Multiply charged ion-induced fragmentation and ionization of C60 is governed by electronic and nuclear stopping of the projectile as well as charge exchange. We have studied the collision dynamics as a function of the projectile atomic number Z ( 2相似文献   

最小熵产生定理与光学被动腔

基于文献[5]中我们所获得的本征型光学双稳系统的熵产生表达式,本文证明该系统(光学被动腔)能够很好地满足最小熵产生定理。 关键词：