An optical filter includes a substrate, a filter layer on the substrate and including color filters, and a light-converting layer over the filter layer and including light-converting portions respectively corresponding to the color filters. A low refractive index layer is between the filter layer and the light-converting layer and has a refractive index less than a refractive index of the light-converting layer. A first capping layer is between the low refractive index layer and the light-converting layer and has a refractive index ranging between the refractive index of the light-converting layer and the refractive index of the low refractive index layer.