Dynamics of semiconductor laser arrays.

Abstract

This thesis presents a theoretical and experimental study of semiconductor laser arrays. A time-dependent coupled-mode model is developed for analyzing the well-confined evanescently coupled index-guided arrays. The stability conditions for twin-stripe devices is derived and interpreted physically. With this model, both twin-stripe and multi-stripe devices are simulated. From these simulations, the stable outputs with lateral in-phase and out-of-phase modes are observed. Through changing the coupling coefficient, periodic and irregular outputs could also be found. These simulation results agree the stability conditions. In order to analyze most weak-guiding structures, a continuum model developed from the the beam propagation method based on the fast Fourier transform is employed. Both gain-guided and index-guided twin-stripe arrays are simulated utilizing this model. In the case of the index-guided arrays, both unstable and stable (out-of-phase) outputs are observed. The temporal energy exchange between the two stripes were noted. For the gain-guided case, stable, synchronuous Q-switched spikings, as well as irregular spiking, are observed by varying the spacing between the two laser stripes. The spatio-temporal behavior of the outputs of twin-stripe and 8-stripe devices are measured with a streak camera under continuous wave and pulsed operations. The synchronuous spiking oscillations from each stripe are noted in both arrays. By using a spectrometer, we found that the twin-stripe gain-guided device with low pump current, was single-lateral mode and single mode, while the 8-stripe CSP array displays multiple modes laterally and longitudinally. The modulation behavior of various laser arrays are measured by using a spectrum analyzer. It is found that the laser arrays are still modulable even if their outputs can still be unstable under cw operation.