2 results
Search Results
Now showing 1 - 2 of 2
- ItemImproving the modulation bandwidth in semiconductor lasers by passive feedback(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2006) Radziunas, Mindaugas; Glitzky, Annegret; Bandelow, Uwe; Wolfrum, Matthias; Troppenz, Ute; Kreissl, Jochen; Rehbein, WolfgangWe explore the concept of passive-feedback lasers for direct signal modulation at 40 Gbit/s. Based on numerical simulation and bifurcation analysis, we explain the main mechanisms in these devices which are crucial for modulation at high speed. The predicted effects are demonstrated experimentally by means of correspondingly designed devices. In particular a significant improvement of the modulation bandwidth at low injection currents can be demonstrated.
- ItemSemiconductor laser linewidth theory revisited(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2021) Wenzel, Hans; Kantner, Markus; Radziunas, Mindaugas; Bandelow, UweMore and more applications require semiconductor lasers distinguished not only by large modulation bandwidths or high output powers, but also by small spectral linewidths. The theoretical understanding of the root causes limiting the linewidth is therefore of great practical relevance. In this paper, we derive a general expression for the calculation of the spectral linewidth step by step in a self-contained manner. We build on the linewidth theory developed in the 1980s and 1990s but look from a modern perspective, in the sense that we choose as our starting points the time-dependent coupled-wave equations for the forward and backward propagating fields and an expansion of the fields in terms of the stationary longitudinal modes of the open cavity. As a result, we obtain rather general expressions for the longitudinal excess factor of spontaneous emission (K-factor) and the effective Alpha-factor including the effects of nonlinear gain (gain compression) and refractive index (Kerr effect), gain dispersion and longitudinal spatial hole burning in multi-section cavity structures. The effect of linewidth narrowing due to feedback from an external cavity often described by the so-called chirp reduction factor is also automatically included. We propose a new analytical formula for the dependence of the spontaneous emission on the carrier density avoiding the use of the population inversion factor. The presented theoretical framework is applied to a numerical study of a two-section distributed Bragg reflector laser.