The optical power splitters are one of the fundamental components in optical communication. These devices are used as lightwave distributions. This paper reports the optimisation of the S-bend based optical power using Gallium Nitride (GaN) semiconductor on sapphire. The optimisation was conducted by investigating the effect of waveguide parameters on the structure using a finite difference beam propagation method (FD-BPM). The numerical experiment result showed that the proposed optical power splitter could successfully split light into two output branches. The best geometrical values of the splitter were found to be 1500 μm long and 38 μm wide accordingly, with a coupling gap of 7 μm and an offset length of 12 μm. It could split input light into two output branches almost perfectly, with the splitting ratio of 50:50. The propagation of optical field propagation along the structure was uniform. The relative power was 93.19 % at long-wavelength optical communication of 1.55μm with an excess loss of 0.31 dB.