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We report the results of a study of the optical gain properties of binary blend films of regioregular poly(3-hexylthiophene) (RR-P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Efficient optical gain is observed in the 10-20 wt. % RR-P3HT composition range and can be tuned to the ∼650 nm window utilised for polymer optical fibre data-communications, with maximum gain ∼50 cm-1. At higher P3HT fractions, gain thresholds increase substantially, consistent with the observed concomitant improvement in photocharge generation. Distributed feed back lasers with one-dimensional gratings exhibit pump pulse thresholds as low as 8 nJ (26 μJ cm-2, 2.17 kW cm-2), lower than many other polymer-based gain media in this wavelength range. They also provide relatively high slope efficiencies >2%. The confluence of efficient optical gain with electronic properties that are conducive to charge carrier injection and transport is relatively novel and is expected to be a necessary requirement for the achievement of electrically pumped lasing. [ABSTRACT FROM AUTHOR]