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To reduce the coupling loss of a fiber-to-ridge waveguide connection, a planar silica spot-size converter is implemented in the form of a nonperiodic segmented waveguide structure with irregular tapering. A simple single-step lithography process is sufficient for the fabrication of the planar structures. An evolutionary algorithm has been successfully applied for the optimization. The simulated results obtained with a 3D FD-BPM program are compared with measurements of implemented couplers, showing very good agreement. A waveguide-to-fiber coupling efficiency improvement exceeding 2 dB per converter is shown. Structures obtained with this approach are very short (~140 mm) and simple to integrate on the same wafer with other planar structures such as phased arrays or ring resonator structures.
By: M.M. Spühler, D. Erni, B.J. Offrein, G.-L. Bona, R. Germann, and I. Massarek
Published in: Journal of Lightwave Technology, volume 16, (no 9), pages 1680-5 in 1998
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