Spatially resolved equalization and decision feedback equalization for multimode fiber links

The increased deployment of gigabit Ethernet (GbE) optical LANs will be followed by the use of 10 gigabit Ethernet (10GbE) of server farm, campus backbone, inter campus links and storage networks. While 10GbE standard includes use of single-mode fiber (SMF), numerous fiber links in such networks will demand the cost-effectiveness of multimode fiber (MMF). However, just as with SMF, dispersion in MMF can severely limit the link distance. Specifically, the different propagation velocities of the distinct optical modes in MMF lead to large differential mode delay (DMD) that typically overwhelms the chromatic dispersion. For speeds approaching 10-Gbps, MMF is limited to distances ranging up to tens of meters. Moreover, in contrast to typical dispersion in singlemode fiber, DMD can vary dramatically from fiber to fiber, and even launch condition. Consequently, to compensate for dispersion in MMF, a dynamic compensation or a technique that is independent of channel response must be used. We present results of work that implement a combination of both approaches that compensates for DMD in multimode fiber links, in an efficient and robust manner.