An electro-optical device may include a substrate having opposing first and second surfaces and an opening extending therebetween. The optical device may also include an optical waveguide extending laterally along the first surface and having an end aligned with the opening, and an electro-optical component carried by the second surface and aligned with the opening. The electro-optical device may further include an elastomeric body within the opening and having a first end face adjacent the optical waveguide and having a second end face adjacent the electro-optical component. The elastomeric body and the optical waveguide may have respective gradient refraction indices within ±5% of each other.