Theoretical and experimental study of inhomogeneously pumped distributed feedback lasers

Abstract

We have investigated inhomogeneously pumped index-coupled distributed feedback (DFB) laser structures both theoretically and experimentally. Using a transfer matrix method, an optimized device structure was designed which drastically suppresses the longitudinal sidemodes by concentrating the injection current in the region close to the phase-shift position. In this way, a high yield of monomode lasers together with an easy fabrication technique was achieved without the necessity of end facet antireflection coating. Experimental evidence of the improvement of the single-mode stability is given first by three-section DFB lasers operated by two different injection currents. Second, the proposed three-segment laser pumped with a single drive current was implemented simply by splitting up the contact of a mushroom type 2×λ/8 phase-shifted DFB laser. We observed the theoretically predicted enhanced stability of the Bragg mode with a sidemode suppression ratio of 52 dB and a higher yield of monomode lasers compared with uniformly pumped conventional DFB laser devices.