Fabrication of two-dimensional fiber optic arrays for an optical crossbar switch

Two-dimensional fiber optic arrays are fabricated for the input and output to a prototype 16-element optical crossbar switch. The switch input comprises a 4 x 4 square array of 125-μm-diam, polarization-preserving fibers with a 5-μm core. The interfiber spacing was 200 μm. For the output array, a larger 4 x 4 square array of 140-μm-diameter, 100-μm-core, multimode fibers was constructed. Interfiber spacing for this array was 800 μm. Correct positioning of the optical fibers was achieved using location holes. These were laser machined in polyimide for the input array and chemically etched in silicon for the output array. A supporting matrix of epoxy adhesive was used to allow polishing of the arrays. Location hole positions were generated to within ±3 μm in both substrate materials, although hole tapering is observed. The effects of hole tapering on fiber orientation have been minimized by aligning two separate hole arrays. Polarization errors for the input array are typically ±10 deg. Mean errors in fiber position for the partially polished input and output arrays were 3.6 and 6.3 μm, respectively. Positional errors can be reduced to the positioning accuracy of the location holes by further polishing of the fiber-matrix structure. Methods for further reducing positional errors in the future are discussed.