POLYMERIC OPTICAL WAVEGUIDES FABRICATED BY PLASMA FLUORINATION PROCESS
J.R. Bartolia, V.M. Giacona, M.I. Alayob, M.N.P. Carreñob
aDept. of Polymer Technology, Faculty of Chemical Engineering, State University of Campinas-UNICAMP, P.O.Box 6066 - CEP 13083-970 - Campinas, Brazil (bartoli@unicamp.br; http://www.feq.unicamp.br/~dtp/)
bMicroeletronic Lab., Dept. of Electronic Systems Engineering, Polytechnic School of the University of S.Paulo-USP, CEP 05508-900, S. Paulo, Brazil.
Polymeric optical devices have been studied in communication and interconnection optics due to the intrinsic versatility of polymers molecular structure, that allows advantageous refractive index modeling for core and cladding, and also to their easy fabrication process or patterning capability. PMMA, polymethylmetacrylate, shows the best optical properties among transparent polymers, being a very common core material foroptical devices. Low refractive index is a requirement for cladding material and it is usually achieved with fluorinated polymers. On the other hand, plasma of fluorocarbons are frequently used either for etching of substrates in microelectronic technologies or for deposition of plasma polymerised fluorinated monomers films.
Previous works showed the feasibility to use the plasma fluorination process to modify the surface and reduce the refractive index of PMMA optical films. XPS and FTIR-ATR analysis revealed that a thin layer of a partially fluorinated polymer was deposited on the PMMA films after plasma. In this work, planar polymeric waveguides were fabricated on silicon substrate. The cladding was a fluorinated polymer film (around 1 mm) produced by CHF3 plasma polymerisation (parallel plate reactor, 13.56 MHz) and the core was a PMMA film (8 to 15 mm) prepared by spin coating. The plasma fluorinated optical films were characterized by ellipsometry, metricon prism coupler, AFM, FTIR-ATR and contact angle measurements. The polymeric waveguides with different widths (from 10 to 100 mm) and design were patterned by UV photolitography. The optical characterization was done coupling a laser beam (l=633nm), fibre-to-fibre coupling method, using a multimode optical fibre.