Highly fluorinated and photocrosslinkable liquid prepolymers for flexible optical waveguides

Abstract

We evaluate highly fluorinated liquid prepolymers and their UV-cured films for flexible optical waveguide applications. Two liquid prepolymers, 2,3,5,6,2′,3′,5′,6′-octafluoro-4,4′-bis-[2-{2-[1,1-difluoro-2-(2,3,5,6-tetrafluoro-4-vinyl-phenoxy)-ethoxy]-1,1,2,2-tetrafluoro-ethoxy}-2,2-difluoro-ethoxy]-biphenyl (7) and 2,3,5,6,2′,3′,5′,6′-octafluoro-4,4′-bis-[2-(2-{2-[1,1-difluoro-2-(2,3,5,6-tetrafluoro-4-vinyl-phenoxy)-ethoxy]-1,1,2,2-tetrafluoro-ethoxy}-1,1,2,2-tetrafluoro-ethoxy)-2,2-difluoro-ethoxy]-biphenyl (8), are synthesized with decafluorobiphenyl, 2,3,4,5,6-pentafluoro styrene, and fluorinated triethylene glycol or fluorinated tetraethylene glycol. The prepolymers are photocurable to give flexible and transparent films. The refractive indices of the films made from the prepolymers are controlled with their blending composition, 1.417–1.437 at a wavelength of 1.31 μm. The optical losses of the films prepared from prepolymers 7 and 8 are 0.25 and 0.23 dB cm−1 at a wavelength of 1.31 μm, respectively. The films are thermostable at temperatures over 400 °C. The ultimate stress, initial modulus, and elongation of the films prepared from prepolymers 7 and 8 are 17.1 MPa, 1.25 GPa, and 1.5% and 12.3 MPa, 0.44 GPa, and 6.9%, respectively. Optical waveguides fabricated from the prepolymers are flexible without any substrate film and the optical losses at a bending radius of 1.5 mm are under 0.2 dB. We identify the liquid prepolymers as possible good candidate materials for flexible optical waveguide applications by studying the optical transmission in flexible optical waveguides fabricated from them.