Photo-writing process of polymer optical waveguides can offer advantages to make easier connection fiber guide, and noticeably simplifies the fabrication procedure. In order to carry out a photo-writing technique, we choose a photosensitive polymer. Under UV irradiation polyvinylcinnamate (PVCi) films undergo cross-linking between cinnamoyl groups. Consequently, electronic configuration of lateral polymer groups changes and also leads to the drop of the refractive index in the visible range. This mechanism is studied with regards to the level of the electronic absorption of cinnamate centered at 275 nm. It acts on refractive index by shifting the absorption UV band. Most of the time, this influence vanishes in the Near Infrared Region (NIR). It is due to antagonist phenomena acting at the expense of the index lowering. The causes analysis leads us to optimise the irradiation spectrum, providing higher index contrasts between irradiated and non-irradiated area. We show that strong index changes can be achieved in PVCi film, up to 0.03 even in the NIR, enabling us, for example, to perform optical photo-printing waveguides for telecommunication wavelengths (1300-1550 nm). This is one of the highest contrast value reported for a photo-printed non-birefringent waveguide. Concerning optical transmission properties, first promising results have been obtained. Optical measurements in the polymer film (0.25 dB/cm at 1550 nm) and in polymer solution (less than 0.2 dB/cm at telecommunication wavelengths) have shown the high potentiality of this material.