Dynamics of two laterally coupled semiconductor lasers: strong- and weak-coupling theory.

Copyright © 2008 The American Physical SocietyThe stability and nonlinear dynamics of two semiconductor lasers coupled side to side via evanescent waves are investigated by using three different models. In the composite-cavity model, the coupling between the lasers is accurately taken into account by calculating electric field profiles (composite-cavity modes) of the whole coupled-laser system. A bifurcation analysis of the composite-cavity model uncovers how different types of dynamics, including stationary phase-locking, periodic, quasiperiodic, and chaotic intensity oscillations, are organized. In the individual-laser model, the coupling between individual lasers is introduced phenomenologically with ad hoc coupling terms. Comparison with the composite-cavity model reveals drastic differences in the dynamics. To identify the causes of these differences, we derive a coupled-laser model with coupling terms which are consistent with the solution of the wave equation and the relevant boundary conditions. This coupled-laser model reproduces the dynamics of the composite-cavity model under weak-coupling conditions

Locking bandwidth of two laterally coupled semiconductor lasers subject to optical injection

We report here for the first time (to our knowledge), a new and universal mechanism by which a two-element laser array is locked to external optical injection and admits stably injection-locked states within a nontrivial trapezoidal region. The rate equations for the system are studied both analytically and numerically. We derive a simple mathematical expression for the locking conditions, which reveals that two parallel saddle-node bifurcation branches, not reported for conventional single lasers subject to optical injection, delimit the injection locking range and its width. Important parameters are the linewidth enhancement factor, the laser separation, and the frequency offset between the two laterally-coupled lasers; the influence of these parameters on locking conditions is explored comprehensively. Our analytic approximations are validated numerically by using a path continuation technique as well as direct numerical integration of the rate equations. More importantly, our results are not restricted by waveguiding structures and uncover a generic locking behavior in the lateral arrays in the presence of injection

Radiation risks and confusions

This report is divided in 3 parts: (1) the origin of the 'linear no-threshold hypothesis', (2) radiation-induced malign processes, (3) consequences of confusions. After the analysis of various Drosophila experiments (1935) the scientists Timofeeff-Ressovsky, Delbrück and Zimmer draw following conclusion: the radiation induced mutation rate is independent from the dose-rate and is directly proportional to the dose. However, for malign processes one cannot ask for the relationship between the total of primarily spontaneous defects and the total of natural radiation induced defects but only for the clearly smaller rates of critically defects for cancer induction. Confusions about radiation risks can be more dangerously than the real risk itself

Interacting frequency and relaxation oscillations in a semiconductor laser with filtered optical feedback

We study a semiconductor lasers with coherent filtered optical feedback and show that characteristic frequency and relaxation oscillations interact and lead to complicated dynamics

Dynamics of semiconductor lasers with filtered optical feedback

In the filtered optical feedback (FOF) scheme a part of the emission of the laser is spectrally filtered, for example by a Fabry-Pérot filter, and than fed back into the laser. If a semiconductor laser is subject to such delayed FOF qualitative different types of oscillations are possible: the well known relaxation oscillations and, more remarkably, frequency oscillations. We explain how the continuous wave operation of the FOF laser - the external filtered modes - lose their stability and the different types of oscillations arise due to the presence of the filter. This study is restricted to the case of a narrow filter. This means that there are only a few external filtered modes within the width of the filter, so that the influence of the feedback phase can be studied explicitly

Pure frequency oscillations of semiconductor lasers with filtered optical feedback

A semiconductor laser subject to delayed filtered optical feedback can show pure frequency oscillations with a period of the order to the delay time, while the power remains practically constant. This is remarkable in light of the strong self-phase modulation in semiconductor lasers that couples frequency and power. It turns out that the dynamics of the filter plays an essential role in this behavior, because it changes the instantaneous amount of feedback in response to the instantaneous laser frequency. By using numerical bifurcation techniques we show how frequency oscillations bifurcate in Hopf bifurcatious from the continuous wave solutions known as external filtered modes