Investigation of the patterning efficiency in a new azo-dye copolymer under UV irradiation towards photonic applications

摘要

Azo-polymers have been the subject of a growing interest since the first demonstration of reversible birefringence anddichroism effects induced optically at room temperature in such materials. It is well established that the mechanismsinvolved are related to a molecular reorientation following photo induced trans-cis-trans isomerization of thechromophores.The interest for such materials has been strengthened with the more recent demonstration that the photo-isomerizationmechanisms can be employed to induce controlled topographic modifications. A simple example is the induction of asinusoidal modulation of the film surface by the irradiation with an interference pattern between two laser beams. Such asimple step technique appears thus as a simple tool towards realisation of photonic devices.However, if the realisation of gratings with periods in the visible wavelength scale is widely investigated, a strongdecrease of the patterning efficiency is observed in the case of periods below 400nm, limiting then the potential of thetechnique.In order to circumvent this problem we have developed a new azo-polymer presenting an absorption band shifted to theUltra Violet (UV) region of the spectrum. The possibility to induce gratings with periods down to 200nm with UVirradiation is evidenced. Optical geometries of excitation have been implemented to optimise the modulation efficiencies.As a potential application of the material investigated, the realisation of a polymer micro laser based on a distributedfeedback scheme is demonstrated.