Fabrication of polymer waveguides and spot size converters by UV induced refractive index modification

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 met hods 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 inde x 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 betw een small planar waveguides and single-mode fibers. The process uses the pos t-irradiation of the guide by an UV source to gradually decrease the refractive index from the guide to the fibre. KEYWORDS: Integrated optics, Polymer wa veguides, UV photo-printing, Mode size converter. 1. INTRODUCTION Polymer materials with their flexibility and ability to use, present a great interest for integrated optics and photonic integrated circuits. Beside fabrication of polymer waveguides by photolithography process, the photo-inscription method takes advantage to suppress the etching step. Furthermore, the ability to vary by UV irradiation the refractive index of a photosensitive polymer opens the way to new and low cost processes avoiding difficult steps of usual methods. Thus, for example, it enables to make easier all main functionalities of waveguides : pre-connecting, wa velength filtering, m ode coupling, wave length multiplexing and switching.