Lensed Fiber-Array Assembly With Individual Fiber Fine Positioning in the Submicrometer Range

An innovative design is presented enabling fine positioning of each individual fiber in a fiber array used in multiinput- and multioutput-port photonic integrated circuits. Hence, the coupling efficiency of lensed fiber arrays can be improved by eliminating the eccentricities of the lenses deposited on the individual fibers and the inaccuracies of the supporting V-groove substrates. In preparation, four different types of commercially available lensed fibers are characterized and coupling efficiencies to InP-based waveguides are determined in order to select the best applicable fibers for the array. The final fiber-tip position accuracy is within$pm 0.25 mu$m and this design is based on metal deformation by laser-welding-induced local heat. With this technique, laser-supported adjustment is possible, allowing the opportunity of fine-tuning the fiber-tip position of already secured parts in the subassembly. Owing to the accurate fiber-tip position and the assembly of the array with selected lensed fibers, coupling efficiencies of$- 2.9$to$- 3.5$dB are simultaneously measured for four fibers to InP-based waveguides with physical dimensions of 3$mu$m$times 0.6 mu$m. To compare these results, the performance of different types of regular, commercially available fiber arrays, whereby the fibers are mounted on silicon V-groove substrates, are determined. In contrast, the measured coupling efficiencies are of the order of$- 5.2$to$- 7.8$dB using similar InP-based waveguides.