Fluorene-based rib waveguides with optimized geometry for long-term amplified spontaneous emission stability

ABSTRACT Amongst the different optoelectronic applications of conjugated polymers, waveguide amplifiers and optically pumped lasers are those requiring larger photochemical stability, owing to the large irradiation conditions under operation. In this context, suitable waveguide optimization enabling the reduction of amplified spontaneous emission (ASE) threshold values appears as important as synthetic chemistry protocols to promote polymer robustness against photo‐oxidation. In this work, we develop rib waveguides with different geometries based on four different fluorene‐based compounds and assess the influence of rib confinement on ASE properties. We observe ASE threshold values as low as 8.9 × 10−4 mJ cm−2, being among the lowest threshold values reported so far on blue emitting polymer/oligomer waveguides. We demonstrate that the enhanced ASE efficiency on some of these rib waveguides leads to a fivefold increase in operation lifetime respect to spin‐coated slab waveguides, thus confirming the impact of waveguide geometry on ASE operation stability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1040–1045 Long‐term operation of blue emitting polyfluorene‐based optical amplifiers is compromised by their relatively low photostability. In this work, rib waveguides based on different fluorene‐based compounds with different side‐chain substituents are developed. A nine‐fold reduction in energy fluence threshold for amplified spontaneous emission (ASE) is observed with respect to thin films, which is associated to confinement and enhanced waveguiding properties. Appropriate rib width optimization allows for a significant enhancement in ASE stability.