In the past decade, polymer materials have been intensively studied for optical waveguide devices including digital optical switches, Mach-Zehnder interferometer (MZI) switches, directional coupler switches, and total-internal-reflection switches. The devices show fantastic characteristics1–5 such as wide bandwidth,6 high extinction ratio,7 small cubage, and easy integration. The key requirements for optical waveguide materials include low intrinsic absorption loss in the infrared communication region, high thermal and environmental stability, and flexible refractive index controllability. Compared with inorganic materials, polymer materials show attractive properties such as high thermal stability and easily controlled refractive index.8–10 A wide variety of polymers have been applied as optical waveguide materials, including poly(arylence ether)s,11,12 polyimides (PI),13 poly(methyl methacrylate) (PMMA),14 polystyrene (PS),15 etc. PI, an important high-performance polymer material, represents many prominent properties such as excellent thermal stability, good mechanical properties, and low coefficient of thermal expansion.16–20 To reduce the optical loss at infrared communication region caused by the carbon-hydrogen (CH) bond vibrational absorption, we substitute hydrogen with heavy atoms in CH bond, such as fluorine, deuterium, and chlorine. Because the wavelength of the vibrational modes obtained from carbon–fluorine, carbon–deuterium, and carbon–chlorine bonds are longer than that of the vibrational mode obtained from the CH bond,21–23 the absorption in optical communication region would obviously decrease. Recently, hyperbranched polymers have attracted considerable attention for their excellent properties such as low viscosity, good solubility in organic solvents, and facile fictionalization. Besides the structure researches of hyperbranched polymer, more and more studies are focused on their new applications, such as optical and electronic materials,24 polymer electrolytes,25 nanotechnology,26 and other high-tech areas.27–29
In this article, we synthesize crosslinkable fluorinated hyperbranched polyimides (FHBPIs) by condensation of a triamine monomer, 1,3,5-tris(2-trifluoromethyl-4-minopheoxy) benzene (TFAPOB), and series of aromatic ether dianhydride monomers with different flexible linear length, respectively. These FHBPIs show high optical clarity at the communication wavelength region of 1310 and 1550 nm, sufficient thermal stability, good solubility, and low birefringence, and based on these materials, high performance classic MZI thermo-optic (TO) waveguide switches are successfully fabricated, which proves that the FHBPIs could be used as suitable candidates for optical communication devices.