*Additive Manufacturing of Optical Waveguides DOI: http://dx.doi.org/10.5772/intechopen.105349*

used rapid prototyping technologies [33]. Compared with SLA technology, DLP technology has the characteristics of fast printing speed, high printing accuracy, and uniform mechanical strength [34]. The curing depth is the key to the success of the layer connection. The setting of the layer thickness should be appropriately smaller than the curing depth to ensure the connection between each layer while avoiding the shrinkage and deformation problems caused by excessive curing and eliminating anisotropy [35].

Polyjet technology also uses UV lamp curing. Its working principle is that the nozzle controlled by the X-/Y-axis sprays photosensitive resin on the printing platform, and each layer of material is sprayed and irradiated with UV light for photocuring. After each layer is cured, the printing platform drops along the Z-axis direction, and the previous process is repeated until the printing is finished, exhibited in **Figure 4f**. Like the FDM technology, a support structure is usually required. The support material and the structural material are sprayed at the same time to achieve stable support for complex or overhanging structures. The support materials are generally water-soluble materials, which are easy to remove later [36]. Polyjet technology has many advantages of rapid prototyping manufacturing, providing good surface finish, high precision and layer resolution, high printing efficiency, and also enabling multi-material printing.
