Thermally stable multi-mode polymer optical waveguide fabricated by single-step photo-patterning of fluorinated polyimide/epoxy hybrids

Abstract

Novel polyimide (PI)/epoxy hybrid material for single-step photo-patterning of optical waveguides was prepared by blending of a semi-aromatic fluorinated poly(amic acid silylester) (PASE), a cycloaliphatic epoxy compound, and a photo-acid generator. A large refractive index change (δn, > 0.01), which is sufficient for multi-mode optical waveguides, was obtained between the polymer films prepared with and without UV irradiation. The refractive index change was generated by cationic reaction between the silylated carbonyl ester groups of PASE and epoxy rings, which was initiated by UV irradiation and promoted by successive thermal curing. The difference in molecular structures, which results in the refractive index changes, were characterized by FT-IR measurements, and it was clarified that the films with and without UV irradiation showed PASE and PI structures, respectively. These films exhibited high thermal stability higher than 230°C, which are desirable for waveguide fabrication for optical inter-connects and lightwave circuits. Using this hybrid material, channel-type optical waveguides were successfully fabricated by the single-step photo-patterning procedure without development by aqueous or organic solvents, which is more facile and economical for waveguide mass-fabrication.