Different distributed feedback (DFB) configurations in optically pumped polymer lasers, including the active Bragg grating structures, the dielectric grating structures spin-coated with polymeric semiconductors, and the actively waveguide dielectric grating structures (AWGS), are studied systematically. In the experiment, the F8BT polymer poly [(9,9- dioctylfluorenyl-2,7-diyl)-alt-co- (1,4-benzo-{2,1’,3} -thiadiazole)] is employed as the active medium in the three laser configuration. And all grating structures are fabricated though interference lithography or interference ablation. It is found that the AWGS design has advantages over the other two. The continuous and high-quality active waveguide in the AWGS enables low-threshold (115 \mu J/cm2) laser emission with narrow linewidth (~0.4 nm at full-width at half-maximum). The experimental verifications are in good agreement with the theoretical analysis. These results reveal some interesting mechanisms in optically pumped DFB polymer lasers, and it may be enlightening to the construction of electrically driven organic lasers.