This work presents the Polydimethylsiloxane (PDMS)/Metal oxide-based flexible polymeric film casting by altering the composition of additive metal oxides to achieve refractive index engineering. Determining the changes in refractive index values with composition enables the design of the best operating polymeric optical waveguide. In addition, each composite was optically characterized and obtained a percentage Transmittance in the 400-1100 nm wavelength range. In addition, Atomic Force Microscopy (AFM) analysis was performed to investigate the surface roughness of the samples. Considering the obtained knowledge on refractive index values, we fabricated the waveguide system having core and cladding formed by composite PDMS.