New configurations for high-efficiency prism couplers with application to GeO2 optical waveguides

A new prism coupler configuration is described which is very simple and reproducible. This device has been used to couple an Ar laser beam into a TEO single-mode GeO2 thin film waveguide with efficiencies exceeding 92%. Two specific air gap profiles using only one ball bearing and two sets of aluminum films have been examined.The theoretical description and experimental performance of this new type of prism coupler are presented; in both cases the air gap profiles are very close to the theoretically optimum shape, especially for a gap which does not have a mechanical contact point near the input optical beam incidence point on the waveguide. This approach is particularly advantageous for use with a fragile or soft thin film waveguide, since surface damage can more easily be avoided. Theoretical coupling efficiencies of 96.4 and 98.8% are predicted for the particular experimental samples investigated, and measured values of 90 and 92% have been achieved.