Planar waveguides are typically made from materials such as silica, silicon, polymers, or other semiconductors. They are often fabricated in the form of a thin transparent film with increased refractive index on some substrate, or possibly embedded between two substrate layers. For. An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light guides, and liquid waveguides.