Vector Intensity-Modulation and Channel State Feedback for Multimode Fiber Optic Links

Multimode fibers (MMF) are generally used in short and medium haul optical networks owing to the availability of low cost devices and inexpensive packaging solutions. However, the performance of conventional multimode fibers is limited primarily by the presence of high modal dispersion owing to large core diameters. While electronic dispersion compensation methods improve the bandwidth-distance product of MMFs, they do not utilize the fundamental diversity present in the different modes of the multimode fiber. In this paper, we draw from developments in wireless communication theory and signal processing to motivate the use of vector intensity modulation and signal processing to enable high-data rates over MMFs. Further, we discuss the implementation of a closed-loop system with limited channel state feedback to enable the use of precoding at the transmitter, and show that this technique enhances the performance in a 10 Gb/s MMF link, consisting of 3 km of conventional multimode fiber. Experimental results indicate that vector intensity modulation and direct detection with with two modulators and detectors, along with the use of limited feedback results in a 50% increase over the single laser and detector case.