We integrate a polymer light-emitting diode (PLED) and a polymer waveguide on a Si substrate. The light emitted from the PLED is coupled to the waveguide by a diffuser and a reflection layer with coupling efficiency about 1%. There is no delay nor distortion between PLED emission and the light propagation in the waveguide. Good direct modulation characteristics of the waveguide output are demonstrated up to 200 kHz. The device structure and processes are based on easy spin coating and are compatible to Si technology.