An optical coupler having an optical core in which a small concentration of refractive microparticles has been added to a suspension material of the optical core. The result is that light from an optical source is bent slightly by the refractive effects of the microparticles and is coupled into the higher order of modes over a relatively short distance within the optical core. These microparticles are closely matched to the index of refraction of the suspension material resulting in smaller deflection angles and fewer reflections. In addition, these microparticles match the specific gravity of the suspension material such that they do not settle out of a suspension while the optical core material is being hardened from a semi-liquid state.