Structures within Structures As the 3D printing process is
performed additively layer by layer, geometric structures can
be fabricated inside other structures to create optical elements. For example, areas of transparent material can be
surrounded by a material with a different refractive index,
to transmit light from point to point using total internal reflection (TIR) through the inside of a model. Opaque materials printed within or around a transparent material can be used to block the transmittance of light from one section of
the model to another. This can be used to seal internal compartments and avoid optical cross talk, or to minimize light
leakage from the model that may be distracting to the user.