Theoretical and experimental study of inhomogeneously pumped distributed feedback lasers

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.