Fabrication of polymer waveguides and spot size converters by UV induced refractive index modification
Résumé
"Generalization of optical communication promotes fabrication of low cost integrated waveguide components. Polymer waveguides are attractive because they are very simple to process and are promising for low cost devices. Up to date, several methods are used to make single mode guides in polymer films. Traditionally, they require multi-step processes involving photolithography, etching and annealing. The UV induced modification of the dielectrics property of polymers is a useful technique for low cost realization of integrated optical circuits and can enable a direct writing process. This paper reports a demonstration of photo-printed waveguides in an intrinsically photosensitive polymer film. In this polymer (PVCi: PolyVinylCinnamate), local UV irradiation yields a lowering of refractive index even at telecom wavelengths (1300 and 1550 nm). We show significant achievement concerning the index contrasts up to 3x10-2 at 1550 nm. The more the refractive index contrast between the core and cladding increases, the more the guide size and curvature can be reduced, allowing the manufacture of smaller photonic devices. However miniaturization of optical planar waveguides in integrated devices increases the coupling losses from and to single-mode optical fibers. Simulations and experimental demonstrations with PVCi photosensitive waveguides also show the potential of photo-printing process to make efficient index mode converters between small planar waveguides and single-mode fibers. The process uses the post-irradiation of the guide by an UV source to gradually decrease the refractive index from the guide to the fibre.