Synthesis and optical properties of poly(BPDA-ODA)/silica hybrid thin films

Poly(BPDA-ODA)/silica hybrid optical thin films were synthesized using a sol-gel reaction combined with spin coating and multi-step baking. The hybrid thin films were prepared by the precursors of aminoalkoxysilane capped poly(BPDA-ODA) amic acid and tetramethoxysilane (TMOS). Highly transparent hybrid thin films were obtained at a silica content of 0-51.9 wt%. The prepared hybrid thin films showed homogeneous structures and excellent surface planarity. The refractive index of the prepared hybrid thin films decreased linearly with increasing the silica content while the Abbe number showed the opposite trend. The prepared hybrid films also exhibited a much smaller optical birefringence than the parent poly(BPDA-ODA) because of the reduction of the rigid backbone by incorporating the silica moiety. Optical planar waveguides were prepared from the prepared hybrid thin films. The optical losses of the planar waveguides at 1310 nm were in the range of 0.5-1.3 dB/cm, which were reduced significantly by increasing the silica moiety. The reduction of the C-H bonding density and excellent surface planarity by incorporating the silica moiety explain the trend of optical loss. These results suggest that the prepared polyimide-silica hybrid thin films have potential applications for optical devices.