External optical feedback sensitivity is analyzed for a quarter-wave-shifted, index-coupled, distributed-feedback semiconductor laser with asymmetries m reflectivity of facets and in the position of a X/4 phase shift. Proper asymmetric structures can withstand higher levels of external optical feedback compared with symmetric structures. However, the mode discrimination and yield are reduced for asymmetric lasers because of statistical variation of the corrugation phases at the reflecting facets. # 1997 Optical Society of America
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