Abstracts Category : Other

Longitudinal effects and intensity-phase coupling indistributed feedback semiconductor lasers

by Lars Magnus Olofsson

The phenomenon of intensity-phase coupling insemiconductor lasers is investigated theoretically as well asexperimentally for distributed feedback lasers. In addition,conditions for a uniform intensity profile are identified for suchlasers. The theoretical study of intensity-phase coupling examinesthe importance of the longitudinal laser structure for thiscoupling exploiting a near threshold model. For the case of uniformgain and carrier density no effect is expected from a periodic orquasi-periodic corrugation. On the other hand, when the gain-layeris corrugated or a gain-coupling mechanism is otherwiseimplemented, the influence may be considerable. It is shown thatthe degree of gain-coupling relative to index-coupling betweenright- and left-travelling waves and the specific mechanism bywhich variations in the carrier density influence this coupling areof key importance. We find that depending on the degree and natureof the gain-coupling the strength of the intensity-phase couplingmay be considerably reduced or enhanced. </br>Aninterferometric method is used to measure the coupling betweenintensity- and phase-modulation for 1.55m distributed feedbacklasers for different bias and modulation frequency undersmall-signal modulation of the injection current. The strength ofthe measured intensity-phase coupling is quantified in terms of aneffective chirp factor. We find this factor to increasemonotonically and nearly double as the modulation frequencyincreases from below to above the resonance frequency of therelaxation oscillation. Our results contradict the commonly heldview of the chirp factor as a constant parameter for a given laserstructure.