Andreas Witzig

A comprehensive VCSEL device simulator

This paper deals with the design and implementation of a self-consistent electrothermooptical device simulator for vertical-cavity surface-emitting lasers (VCSELs). The model is based on the photon rate equation approach. For the bulk electrothermal transport, a thermodynamic model is employed in a rotationally symmetric body. Heterojunctions are modeled using a thermionic emission model and quantum wells are treated as scattering centers for carriers. The optical field is expanded into modes that are eigensolutions of the vectorial electromagnetic wave equation with an arbitrary, complex dielectric function. The open nature of the VCSEL cavity is treated by employing perfectly matched layers. The optical gain and absorption model in the quantum-well active region is based on Fermis Golden Rule. The subbands in the quantum well are determined by solving the stationary Schrodinger equation and using a parabolic band approximation for the electrons, light and heavy holes. The photon rate equation is fully integrated into the Newton-Raphson scheme used to solve the system of nonlinear device equations. An efficient numerical optical mode solver is used, that is based on a Jacobi-Davidson type iterative eigensolver. The latter combines a continuation scheme with preconditioner recycling. The practical relevance of the implementation is demonstrated with the simulation of a realistic etched-mesa VCSEL device.

Teaching renewable energy systems by use of simulation software : experience at iniversities of applied sciences, in in-service training, and from international know-how transfer

Experience in using simulation software for teaching solar energy and heat pump applications are presented and discussed in this publication. The authors present suitable didactic concepts specifically developed for teaching renewable energy and energy efficiency topics. Two main advantages of applying simulation software in solar education are identified: 1. simulation can provide an understanding of data that is otherwise not accessible (e.g. cumulated operating hours and number of starts of a heat pump depending on control strategy); 2. use of simulation software in teaching have a positive influence on the motivation and attitude of the students. These benefits typically come with costs of some additional effort in lecture preparation. Finally, different international teaching programs are discussed, in which simulation software currently plays a major role. It is analyzed how education programs might have to be adjusted for different cultures and industries.