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Optical Fibre Array Manufacture using Microengineering Techniques

Dominik Weiland, Markus Luetzelschwab, Marc Desmulliez
The work done in this project concentrates on the modelling, manufacture and characterisation of a novel method to manufacture two-dimensional bundles of single mode optical fibres of highly accurate pitch. [read more]

The work done in this project concentrates on the modelling, manufacture and characterisation of a novel method to manufacture two-dimensional bundles of single mode optical fibres of highly accurate pitch. An array of micro holes, each surrounded by four electrodes has been produced using the LIGA process. Electrostatic fields between the electrodes and a metal coated optical single mode fibre, inserted into such a hole, are used to position the fibre. By monitoring the position of the fibre it can be moved to its ideal position and fixed there by curing a cement filled into the holes prior to fibre insertion. The manufacturing processes of two generations of these devices, one using a Foturan® based process, the other a modified UV-LIGA process are fully described. In the UV-LIGA process thick-film photoresist structures with aspect ratios up to 10:1 and the electroplating of 30 µm wide vias with an aspect ratio up to 7.6:1 have been realised. The combination of electrostatic actuation with the optical monitoring of the fibre pitch provides a highly accurate and sensitive alignment system. For displacements up to 100 µm the alignment method yields a sensitivity between 0.125 µm/V and 1.1 µm/V, depending on the clamping distance. Alignment accuracies below 0.5 µm can be achieved in less than 60 seconds when using a cement with low viscosity. Using non-linear system identification methods, a simulation model representing both the static and dynamic behaviour of the fibre-electrode system is derived, which is in good agreement with the experimental results. For static fibre displacement, differences below 10 % between simulated and experimental results and for the dynamic behaviour differences below 15 % are achieved. Finally, an alignment algorithm for the active alignment of highly non-linear electrostatic multi-electrode systems is developed using the system model derived. The algorithm consist of two alignment steps, the first one allowing for a fibre alignment accuracy of 0.3 µm in less than 20 seconds, the second one an accuracy below 0.1 µm in an additional 100 seconds.