UV-induzierte Herstellung monomodiger Wellenleiter in Polymeren

Abstract

This thesis describes the development of a process for fabricating single mode polymer waveguides. By systematic analysis of process parameters using basic waveguide components, the feasibilities and limits of this approach are given. The process is based on the UV-induced modification of the dielectric properties of polymethylmethacrylate. Two approaches for the lateral structuring of waveguides are used. In the first approach the lateral structuring is achieved by conventional photolithographic technique using a Quartz/chrome mask. The second approach uses in the first step the LIGA-technique to pre-emboss the polymer substrate. The embossed ridge or a groove structure serve as masking structures for and ensuing flood exposure. For the investigation of the photochemical reactions dependant on environmental process conditions, spectroscopic methods are used. The influence of additives or copolymerisation on photochemistry are studied using different homo- and copolymers. It can be shown that the dominating photochemical reactions are independent of the material used. During photolysis in ambient air, photooxidation products can be detected, which increase the absorption of the waveguides in the third optical window at 1550 nm. The second optical window at 1310 nm remains unaffected. The oxidation products can be avoided by exposing in an inert gas atmosphere or vacuum. A new process variant is achieved with respect to smaller irradiation doses, higher index contrast and higher thermal stability of the waveguides. It can be shown that the addition of bromium leads to higher index contrasts and higher glass transition temperatures of the waveguide materials. For the development of an integrated optical sensor, which is based on immobilized living cells on the waveguide surface, first investigations for immobilization of living cells on the waveguide structures have been successfully carried out. Cell adhesion of L929 fibroblast on the photochemical modified region of test structures was demonstrated. Furthermore the structuring of waveguides by masking with pre-embossed polymer substrates and following flood exposure was demonstrated. The approach using LIGA-techniques provide the opportunity to integrate the waveguides in a micro-optical bench. For demonstration, waveguides with passive fibre alignment structures have been successfully fabricated. The approach presented here provides the opportunities to have a mass fabrication process using replication technologies of a microoptical bench with integrated singlemode waveguides.