Electronic equalization of high-speed multi-mode fiber links

The objective of this research is to investigate low-complexity, efficient electronic equalizers to increase the data rate and possibly extend the reach of multi-mode fiber (MMF) links. Specifically, we begin by baselining the performance limits of conventional receivers. A robust, in-house mode solver was developed as part of this research and is currently being used by one of the largest fiber manufacturers in their internal R & D work.; A detailed performance assessment of the impact of decision feedback equalizers has been conducted using an extensive model of the installed fiber base. The finite-length DFE results were instrumental in influencing the IEEE 802.3aq standardization effort. In particular, we were able to achieve a reach of 220m but the original goal of 300m was unattainable on 99% of the installed fiber base using DFEs of moderate complexity.; A low-cost equalizer that has excellent performance, the bi-directional DFE, was applied to the MMF channel for the first time. The performance of the infinite-length BiDFE was characterized without any constraints on the signal-to-noise ratio and on the receiver front-end, as has been previ ously done in the literature. A new joint optimization technique that helps the finite-length BiDFE perform significantly better than the infinite-length DFE was developed. It was shown that given a finite number of filter coefficients, the BiDFE utilizes them better than the conventional DFE. Furthermore, a reach of 350-400m at a data rate of 10 Gbps was shown to be feasible with equalizers of complexity similar to that currently available.; A multiple-input, multiple-output (MIMO) characterization of the MMF channel was developed through the simultaneous use of both center and offset launch together with the two-segment photo-detector. The potential benefit of MIMO processing for MMF links was demonstrated by computing Shannon capacity bounds. It was established that the 2 x 2 MIMO channel performs about 1.4dBo better than the conventional 1 x 1 link at 10 Gbps with practical joint launch. The MIMO scheme still has a performance improvement of 1dBo at 20 Gbps thereby indicating that 20 Gbps transmission is feasible.; Performance evaluation of multi-km MMF links was conducted using a comprehensive model that accounts for mode coupling effects. It was determined that ignoring mode coupling can result in under-estimation of the optimum DFE penalty by as much as 1 dBo for 1km links.