Optical Properties of Perfluorocyclobutane Aryl Ether Polymers for Polymer Photonic Devices

Abstract

New thermoplastic PFCB aryl ether monomers, 1,5-bis(trifluorovinyloxy)naphthalene (TFVON) and 1,4-bis(trifluorovinyloxy)benzene (TFVOB), were synthesized, and homopolymers, PTFVON and PTFVOB, and a copolymer, TFVON-co-TFVOB, were successfully prepared from them by 2π + 2π cyclopolymerization. The C−H vibrational absorption of the monomer was investigated by IR and near-IR spectrum analysis. The optical properties of the polymers in the form of plastic optical fibers and thin films were examined. The absorptions corresponding to fundamental and overtones of C−H vibrations in PFCB monomers were greatly reduced due to the presence of the fluorine substituents, which could lead to low attenuation loss of the resulting polymers in the near-IR region. Polymerization conditions such as temperature and time significantly affected the optical loss values of the polymers as well as their molecular weights and thermal properties. We prepared plastic optical fibers of the PFCB polymers, and optical windows were observed at 820, 910, 1025, 1260, and 1530 nm. The attenuation loss of PTFVON was typically 0.083 dB/cm at 910 nm, the lowest optical window, 0.190 dB/cm at 1300 nm, and 0.227 dB/cm at 1550 nm. Copolymerization further reduced optical loss, and optical loss of the copolymer was about 0.03−0.1 dB/cm lower than that of the homopolymer. A birefringence of the spin-coated films of the PFCB polymers was also investigated and found to be exceptionally low. A birefringence of less than 0.001 was found in all the polymers. The lowest birefringence of 0.0005 was measured for PTFVON films.