Hyperbranched fluorinated polyimides with tunable refractive indices for optical waveguide applications

A series of halogenated hyperbranched polyimides (HBPIs) with tunable refractive indices (RIs) has been designed and prepared for use as novel optical waveguide materials. The hyperbranched structure of these polymers leads to multifarious and controllable chemical structures. The degree of branching in these HBPIs was estimated using 1H NMR spectroscopy. The halogen-terminated HBPIs were found to exhibit high glass transition temperature, good thermal stability, excellent transparency, low birefringence and low optical loss in the wavelength windows for telecommunication. Due to the high polarizability of the C–Cl bond at the terminal groups, RIs were precisely controlled by adjusting the C–Cl bond content without additional optical losses. Finally, several waveguide devices were fabricated by the reactive ion etching (RIE) technique and were found to exhibit good optical propagation at a wavelength of 1.55 μm.