Investigation of linewidth and side-mode suppression for a DBR laser with integrated passive waveguide

A semiconductor laser device consisting of an active part monolithically integrated with a passive waveguide and a DBR grating is theoretically investigated. It is shown that for a 2 mm-long device a linewidth below 4 MHz can be achieved. The linewidth does not exceed this value even if the lasing frequency is tuned by several gigahertz. The side-mode suppression remains larger than 30 dB.