The design, fabrication, and testing of a highly multimode polymeric 88 star coupler is described. The design process allowed a comparison to be made of ray tracing and beam propagation methods for the design of such highly multimode waveguide devices. The results obtained with either of these two different methods agree well with actual measurements on a fabricated 88 multimode-input star coupler with a refractive index difference of Δn=0.0274 and a device length of L=4.25 cm. The reduction in the rms power fluctuation in the output guides with the choice of a higher refractive index difference is demonstrated.