Influence of grating characteristics on the operation of circular-grating distributed-feedback polymer lasers

We explore the influence of grating characteristics on the lasing performance of polymer circular-grating distributed-feedback lasers. A range of circular-grating sizes and profiles were fabricated on a single silica substrate, which was coated with a thin film of the conjugated polymer poly[2-methoxy-5-(2'ethylhexyloxy)-1,4-phenylene vinylene]. Variations in lasing threshold and surface-emitted slope efficiency were determined as a function of grating outer diameter and duty cycle. The experimental lasing results are compared with predictions from a theoretical analysis based on an adaptation of the transfer matrix method. We find that an outer diameter of at least 200 mu m is required to minimize the threshold and optimize the surface-emitted slope efficiency. A groove-to-period duty cycle of similar to 25% gives the lowest lasing thresholds by optimizing the in-plane feedback. We also find that the structure of the polymer-air surface varies substantially with substrate duty cycle, which has implications for optimum device design. (c) 2005 American Institute of Physics.