We haven been exploring polymethylmethacrylate, PMMA, doped with conjugated luminescent polymers for applications in plastic optical fibers (POFs) showing gain. In order to control loading and dispersion of the conjugated polymers in the PMMA matrix, new polyfluorene-PMMA copolymers were synthesised. In this communication we report on the optical properties of these copolymers, both in solution and in solid state. Furthermore, the properties of POFs fabricated with such copolymers are presented and compared with the properties of POFs based on PMMA-polyfluorene blends.