Linewidth dependence on side-mode suppression in three-electrode DFB laser

A 1000μm-long three-electrode DFB laser with a large sidetuning and with a minimum linewidth of 4 MHz is demonstrated. The correlation between the main mode linewidth and DFB submode suppression is large. Side-modes on the opposite sides of the stop band are seen to broaden the linewidth to different extents. A Fabry-Perot mode 50 nm away has no observable effect on the linewidth.