EFFECTS OF STRUCTURAL PARAMETERS ON THE EXTERNAL OPTICAL FEEDBACK SENSITIVITY IN DFB SEMICONDUCTOR-LASERS

External optical feedback sensitivity in distributed feedback (DFB) se miconductor lasers is analyzed with special attention to phase-shifted and complex-coupled lasers, The effects of various structural paramet ers such as coupling strength, facet reflectivity, and corrugation pha se angle on external optical feedback sensitivity are studied. The lam bda/4 phase-shifted index-coupled DFB laser exhibits low external opti cal feedback sensitivity for large index-coupling coefficient and high facet reflectivity. Pure gain-coupled DFB lasers perform better than the phase-shiftless uniform index-coupled DFB lasers but worse than la mbda/4 phase-shifted index-coupled lasers with high coupling strengths , External optical feedback sensitivity of complex-coupled lasers depe nds significantly on the index-to-gain coupling ratio, the phase betwe en the index and gain gratings, and the total coupling.