The refractive index change of polariton propagation in a GaAs quantum-well waveguide was measured as a function of the electric field. Its temperature dependence was also measured. The experimental results showed that the refractive index change of the polariton propagation was at least three times as large as that of the conventional light propagation. This effect remains up to 40 K, and coincides with the temperature dependence of the rate of polariton scattering by phonons. We also Fabricated directional-coupler-type switching devices to apply this large refractive index change, and were able to demonstrate the operation in a single quantum-well waveguide. Our results indicate that extremely small and low driving voltage switching devices may be feasible.