A theoretical analysis of linewidth broadening in frequency tunable DBR lasers

Linewidth broadening in frequency tunable distributed-Bragg-reflector (DBR) lasers with tuning sections is analyzed. The analysis is based on a simplified two-section single-mode cavity model and quantum mechanical Langevin treatment. The origin of linewidth broadening is shown to be low frequency excess FM noise caused by carrier fluctuation in the tuning section. A scaling law, which permits optimal device parameter design, is then derived. When a decrease in the carrier lifetime is combined with an increase in the tuning current, linewidth broadening can be suppressed without frequency tuning range reduction