# Fluorinated Polymers for Photonics--From Optical Waveguides to Polymer-Clad Glass Optical Fibers
## 4 Conclusions  
The development of new and alternative materials for passive optical waveguides and components and claddings for optical glass fibers is of great interest within the large field of applications of thermosetting UV-curable polymers. It has been shown that for each application a modular system of resins could be compiled to tune the necessary optical, thermal and/or mechanical properties. For optical waveguide materials, it is necessary to develop thermosetting polymers with very low optical propagation losses, specific refractive indices and low thermo-optic coefficients. It has been shown that such materials can be achieved by co-polymerization of different halogenated monomers and glycolidyl-functionalized acrylates. The formation of a three-dimensional network structure proceeds via cross-linking reaction of the oxirane groups and irradiation with UV light. This was also possible by the combination of different fluorinated double bonds containing monomers and viscous oligomers, followed by photochemical radical cross-linking on the substrate. In both cases, it was possible to decrease the thermo-optic coefficient using inorganic nanoparticles of SiO\({}_{2}\) and MgF\({}_{2}\) without compromising optical propagation losses. Thus, the determined optical propagation losses of about 0.5 dB\(\cdot\)cm\({}^{-1}\) at 1547 nm were comparable to the value for the reference material, but the thermo-optic coefficient was lower. Also, the development of alternative fluoroacrylates for claddings for optical glass fibers was very successful. The thermosetting polymer containing two commercially available fluorinated oligomers provides an excellent curing behavior, especially for UV  
Figure 20: Dynamic Mechanical Analysis of two acrylate-based coating materials: storage modulus (\(E^{\prime}\)) and loss factor (\(tan\delta\)) as a function of temperature.  
LED curing. It was found that this resin cures very fast and completely by irradiation with 390 nm UV-LEDs. Furthermore, curing printable coatings under air and ambient conditions with different combinations of 300 nm LEDs and 390 nm LEDs was studied. Despite the availability of many commercial fluorinated materials, future developments are still required to reduce the cost of usually expensive materials and improve their optical and processing properties in the direction of specific applications. In the case of waveguide materials, especially for core materials, a proportion of fluorinated molecules could be changed for other halogenated molecules. This was also shown in our research.  
L.M.G.: methodology, data acquisition, writing--original draft preparation; M.K.: project administration, writing--review and editing; C.D.: funding acquisition, supervision, writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the German Federal Ministry of Education and Research (Project PolyPhotonics, Support Code 03 VKCT1C) and within the consortium Advanced UV for Life (Project InnoUV-Faser, Support Code 03 ZZ0124A).  
Data are contained within the article.  
The authors declare no conflicts of interest.