Fiber array fabrication technique for 15-μm-diameter single-mode fibers

We describe a technique to package 15-μm-diam single-mode fibers on a silicon substrate that can be incorporated into an endoscopic probe tip. The single-mode fibers in the array can be used in coherent imaging applications such as optical coherence tomography. Fiber-to-substrate and fiber-to-fiber coupling effects are studied using beam propagation techniques to determine the different design characteristics and the maximum length of the reduced diameter fiber that can be packaged in the probe tip. Single-mode fibers are etched to reduce the cladding diameter from 125to15μm. A 2-μm-thick silica layer is grown in the silicon substrate to minimize the fiber-substrate coupling. Reduced diameter fibers are placed into a 5-mm by 150-μm trench etched in a silicon-silica substrate and fixed with UV curable cement. Active alignment is used to ensure the correct alignment of fibers. The fiber array is experimentally evaluated to test fiber placement accuracy, throughput, and cross talk. Optical coherence tomography images are also obtained with the array.