Synthesis of fluorinated polyimides and their application to passive optical waveguides

Fluorinated and chlorofluorinated polyimides with high thermal stability and low optical absorption loss in the optical communication wavelengths of 1.3 and 1.55 μm were investigated for low-loss passive waveguide applications. These polyimides were prepared from pyromellitic dianhydride (PMDA) with 1,4-bis-[4-amino-2-(trifluoromethyl)phenoxy]tetrafluorobenzene (ATPT), 1,4-bis-[4-amino-2-(trifluoromethyl)phenoxy]benzene (ATPB), and 1,3-bis-[4-amino-2-(trifluoromethyl)phenoxy]-4,6-dichlorobenzene (ATPD). Control of the refractive indices of the polymers was achieved from 1.5397–1.5671 for TE polarization and 1.5239–1.5513 for TM polarization at 1.55 μm by copolymerization of PMDA/ATPT and PMDA/ATPB. As the amount of PMDA/ATPT was increased, the refractive indices of the polymers were decreased. Rib-type optical waveguides were fabricated using these fluorinated polyimides. These waveguides exhibited a low propagation loss of less than 0.5 dB/cm at 1.55 μm.