Design, Fabrication and Characterisation of Laser Micromachined Devices in Electro-Optic Polymer Thin Films

Abstract

The objective of this disertation was to explore the feasibility and performance of new integrated optical devices into electro-optic polymer thin films. While Mach-Zehnder modulators and ring resonator type of devices in electro-optic polymers are well explored, in this research the attempt was made to demon- strate an electro-optic tunable Bragg grating in a chromophore doped polymer waveguide. Bragg gratings are one of the key components of integrated optical circuits as narowband filters or switches. The realization of efficient Bragg gratings in polymer waveguides would considerably reduce the cost and simplify the fabrication of the tunable grat- ings. Most current tunable integrated polymer gratings utilize a thermo-optic effect in order to provide tuning of the Bragg gratings which imposes limits to the tuning speed (∼ 10−3 s due to the thermal diffusion). Novel chromophores, specially designed to exibit high molecular NLO fig- ure of merit, were used for doping a number of different polymers and then electrically poled in order to introduce a macroscopic electro-optic effect in the material. The fabrication process of the device consisted of several steps: the spin- coating of both buffer and active layers onto an ITO glass substrate, formation of the waveguides by laser micromachining, grating inscription via permanent photodegradation of the chromophore, poling of the doped polymer and finally, coupling to the fiber. While currently most of the structures in polymer films are being photo- bleached or ion-etched, laser micro-machining was explored here as an alternate method for fabricating waveguides. Permanent inscription of the gratings in doped polymers and poling of the material were researched in great detail in order to achieve the optimum performance of the device.