COM•DTU Ph.D. defence


Mon 04-12-2006
Ph.D. defence by Søren Blaaberg Jensen
Tuesday, December 12th at 13:00
Building 341, auditorium 23

Structure, stability properties, and nonlinear dynamics of lateral modes of a broad area semiconductor laser

There will be a reception in building 343, room 217 afterwards.



Abstract:

The subject of this thesis is a theoretical investigation of the nonlinear lateral modes of broad area (BA) semiconductor lasers including studies of stationary properties, of stability properties, and of the dynamics of a BA laser in an external cavity.

The most prominent characteristics of the output field of a BA laser are due to lateral properties. A detailed investigation of stationary lateral field distributions is carried out and leads to the finding of a systematic structure of several categories of lateral nonlinear modes. In addition to the known definite-parity modes, asymmetric modes are found, although the physical system under investigation is symmetric. The structure and interrelationship between different modes are also seen in their tuning curves.

A stability analysis of the above mentioned stationary solutions must be carried out in order to evaluate their physical role. By means of a Green\'s function method a small-signal analysis is carried out with emphasis on the stability properties. It is found that all regarded modes are unstable except for the case of very low pump currents. The small-signal stability analysis explains why BA lasers are generally found to have fluctuating output fields: at considerable pump currents there are no stable stationary solutions.

An existing external-cavity scheme including a spatial filter is imitated theoretically and it is found that one consequence of the external cavity is to dampen the lateral dynamics of the field, which in turn leads to an improvement of the spatial coherence of the output. The near-field reveals that the external-cavity scheme changes the lateral dynamics of the BA laser to a behavior more similar to a laser array.