Performance of maximum likelihood sequence estimation in 10 Gb/s transmission systems with polymer optical fiber

Rapid increase of data traffic in data communication applications has pushed the demand for high-capacity and low-cost optical networks for use in local area networks (LAN), such as enterprise or datacenter backbones [1,2]. The use of 10 Gigabit Ethernet (10GbE) in such cases will often require a new installation, because the commonly used CAT-5 copper cables are unsuitable for 10GbE transmission over sufficiently long distances. Although this can be solved by upgrading the cable infrastructure to CAT-6A copper cables, it may not be a future-proof solution. A promising alternative is the use of fiber optic cables, such as multimode silica fibers. However, short-reach LAN requires very cost-efficient solutions. This makes the use of most optical fibers impractical due to the associated high installation costs. In comparison to multimode silica fibers, the perfluorinated graded-index polymer optical fiber (GI-POF) with 120 μm core-diameter is a promising alternative because the large core-diameter allows large alignment and dimensional tolerances for components. Furthermore, it still allows the use of standard high-speed transmitters and detectors at wavelengths of 850 and 1300 nm. The GI-POF thus offers ease of use and installation, with clip-on connectors requiring minimal training or specialist equipment for termination. Furthermore, cables made from GI-POF are extremely flexible, offering a bending radius of 5 mm compared with 25 mm for silica fiber cables and 30 mm for CAT-6A copper cables. Due to bandwidth limitations caused by modal dispersion in large-core multimode fibers, 10 Gb/s data transmission on such 120 μm perfluorinated GI-POF is limited to distances less than 100 m [3]. Recent research advances in electrical equalization for 10 Gigabit Ethernet multimode fiber (MMF) links show the possibility to compensate for such modal dispersion, yielding significant performance improvement [4,5]. In this paper, we investigate the performance improvement for a 100 m transmission link with 120 μm perfluorinated GI-POF operating at 10.7 Gb/s, when electrical equalization in the form of maximum likelihood sequence estimation (MLSE) is used. It is well known that for all equalization schemes, MLSE achieves the best performance [6]. These results can therefore be seen as a performance bound for using electrical equalization to combat modal dispersion. Proceedings Symposium IEEE/LEOS Benelux Chapter, 2006, Eindhoven