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 200μm is required to minimize the threshold and optimize the surface-emitted slope efficiency. A groove-to-period duty cycle of ∼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.
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Turnbull et al. (2005) studied this question.
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