Theory on Distributed Feedback (DFB) Lasers with Strong Periodic Modulations

Abstract

DFB (Distributed Feedback) lasers do not use conventional resonator mirrors, but provide feedback via backward Bragg scattering from periodic modulations of refractive index and/or gain of the iaser medium. An important feature is the high spectral selectivity which originates in the Bragg effect and allows selection of longitudinal modes |l|. Hitherto, DFB theories were restricted to small modulations |2,3,4,5|. In this paper, we study the effects of strong DFB modulations on the basis of a complex Hill equation which can be solved analytically. This procedure provides for the first time a direct access to the complex characteristics of future DFB lasers with strong modulations.