Current tailoring for lowering linewidth floor

A floor, the cause of which has not been identified, in the linewidth and output power relation has been observed with conventional, solitary distributed-feedback (DFB) lasers. The authors found that the intensitiy of spontaneous emission or submode increases when the floor appears or rebroadening of the linewidth occurs, and the floor can be lowered to some extent by changing the current distribution along the stripe electrode of DFB lasers to reduce residual carriers. The linewidth and intensity of the submode versus the current injection ratio under constant power operation are shown for a three-terminal DFB laser with separated 100-μm length electrodes, κL of two, and a both-cleaved structure. A curve showing the improvement of the linewidth floor by current tailoring for this laser is also given.