The effects of geometry parameters of graded-index polymer optical fiber (GI-POF) components on the coupling efficiency and signal mixed proportion are studied in this thesis. Simulation and experimental approaches are used to investigate the effects of light sources on the coupling efficiency of misalighment, Y-couplers and V-groove couplers. Two different light sources are employed in this study: Laser diode (LD) and vertical-cavity surface-emitting laser (VCSEL). The optimum coupling angle and refractive index of filler in the Y-coupler are studied with a light-emitting diode (LED) light source. A good agreement between the simulation and the experiment results is shown in this work. Furthermore, two V-groove array arrangements, i.e. the parallel V-groove array and the skew V-groove array, are proposed in this study to mix multi-light-sources. The optimum parameters of V-groove are designed to achieve the highest coupling efficiency. The performances of different V-groove array arrangements have also been demonstrated for multi-signal mixing.