Investigation of a UV-laser generated planar polymeric waveguide directly and after five years of preparation using an interferometric method

• Preparation of polymeric optical waveguides using UV-laser lithographic methods.
• Refractive indices in two cases, directly and five years later of preparation.
• A crucial change of refractive indices detected after five years of preparation.
• The photochemical reactions for the two times are explained.
• The impact on mode field distribution and the effective mode indices defined.

Polymeric integrated-optical waveguides were prepared in a planar chip using UV-laser lithographic method. Five waveguide samples were irradiated by an excimer laser of wavelength 248 nm with different irradiation parameters (fluence and irradiation doses). Using Mach–Zehnder interferometer, the refractive index depth profiles of these samples are determined in two cases, directly and five years later of preparation. A crucial change of refractive indices profiles has been recorded after five years of preparation. In the first case we got double region waveguides fitted a Gaussian shape, while in the second one we observe a single region waveguide which has exponential shape. The photochemical reactions responsible for these changes in the two cases are demonstrated. This is quite important when such waveguides are used in the applications. Also it was interesting to investigate the aging impact on mode field distributions and the effective mode indices. The mode parameters are determined based on a theoretical model and the experimentally obtained data. The results show a notable change in the mode field distributions and the propagation coefficients as influence of aging.