Synthesis of very low birefringence polymers using fluorinated macromers for polymeric waveguides

A series of highly fluorinated acrylic macromers and monomers containing perfluoroalkyl, perfluorophenyl, and perfluorocyclohexyl pendant groups were synthesized in an attempt at reducing absorption losses and birefringences. The macromers, prepared by the anionic polymerization of fluorinated acrylic monomers, were viscous liquids with number average molecular weights of 15,000-16,000 g mol^-1. Macromer and monomer mixtures that generally exhibited viscosities suitable for the ultraviolet-imprint process were photopolymerized to prepare the polymeric films. At 850 nm, the films had very low birefringences (approximately 0.0001) and their refractive indices (RIs) were linearly dependent on the mixture compositions; this allowed the RIs of films to be fine-tuned within at certain range. At 850 nm, the propagation losses of the multimode waveguides ranged from 0.12 dB cm^-1 to 0.15 dB cm^-1, demonstrating that these polymers are potentially useful as optically passive waveguide materials.