Multiport optical concentrator for multimode fibers and high-speed detector interfacing

Abstract

A single input to multiple output optical concentrator is presented that can split a millimeter-scale input area into multiple sections and concentrate each section into a separate output. The outputs are designed to have a high coupling efficiency into a multimode fiber array or high-speed photodetector array, with individual output diameters in the range of 50μm to 250μm. The concentrator uses nonimaging tapers that can provide more ideal concentration than a lens. Ray trace simulations are used to evaluate the incidence angle tolerance for linear taper designs with a 3mm length and geometric concentrations up to 64x. The taper simulation results are as good or better than the performance of a ball lens, widely used for coupling to small-area photodetectors. We present simulations for a 1x7 taper design and the first fabrication results using fused silica as the cladding and Norland Optical Adhesive with n=1.51 as the core material. The optical throughput measurements indicate excellent splitting uniformity with a standard deviation of 0.26dB. The multiport concentrator provides an advantageous form factor for splitting, concentrating, and coupling to an output array and is scalable to larger areas and outputs. As such, it is a unique optical device with applications in high-speed optical wireless communication systems as a stand-alone concentrator or secondary concentrator to a primary concentrating lens or mirror.