Polymer optical fibers (POF) are widely used for transmission in short range applications e.g. in local area networks and data links in vehicles like cars, ships or planes. Compared to glass fibers, POFs show much higher intrinsic losses, but their flexibility, robustness and easy handling make them also attractive for doping with organic laser dyes or lanthanide complexes. Large gain values can be achieved which can exploited in fiber lasers and amplifier systems. We present experimental studies on the optimization of POF~lasers using Rhodamine B (RB)~doped plymethyl methacrylate (PMMA).