**1. Introduction**

Due to the fast development of Internet, the traffic load of data network has increased dramatically in past decades. Accordingly, optical network, as the major carrier for data transmission, needs to increase its capacity to meet the increasing data rate requirement. As stated in the white paper of Optical Internetworking Forum (OIF) (see [1]), the rapid growth of data flow demands optical network to double its capacity every 12-18 months. As a result, this critical requirement pushes various types of optical transmission systems to improve their delivered data rate at the same time.

Generally, in high-speed optical communication, the increase on data rate usually comes with the increase on signal bandwidth and sampling rate. In this case, due to the sensitiveness of optical and electronic devices, the additive transmission noise will inevitably increase as well. Therefore, how to increase the throughput of optical network without loss of robustness is an essential task when designing modern high-speed optical network.

To date, various techniques have been employed to enhance the quality of data transmission in optical network. Among those approaches, Forward error correction (FEC), or commonly called error correction coding (ECC), is viewed as the most cost-effective solution, and has been widely adopted in many industrial optical transmission systems. Many specific FEC codes, including Reed-Solomon (RS), BCH, and LDPC codes, are proposed in different industrial standards for error correction in physical layer. Among them, RS code is the earliest and most widely used FEC code in optical communication. For example, RS (255, 239) was the first generation FEC code for submarine fiber-optical transmission in [2], and its code rate is still the standard parameter for frame design. In addition, for Ethernet network such as 10GBase-LR in [3], Reed-Solomon (255, 239) code is also the standard FEC code.

© 2012 Yuan et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Yuan et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

There are several reasons for the wide application of RS code. First, modern long-distance optical network, especially long-haul network, is very high-speed system (10Gbps and beyond). For other promising FEC codes, such as LDPC or Turbo code, the corresponding decoding throughput usually can not meet such stringent requirement on data rate, or with the penalty of very high hardware complexity. Instead, RS decoder can achieve such high throughput with affordable hardware resource. Second, for local optical network, such as Ethernet network, the real-time response is an important metric for system design. Compared with its counterpart, RS code has the particular advantage on low decoding latency. Therefore, RS codes are widely employed in modern optical transmission system and are believed to play an important role in next generation optical networks.

Considering the importance of RS code, its efficient implementation is quite important for the optical transmission system. A low-complexity high-speed RS encoding/decoding system will improve the overall performance significantly. Particularly, since RS decoding is the most complex procedure in the RS-based FEC system, efficient RS decoder design should be well-studied. Therefore, targeted to different level of optical communication ranging from short-distance Ethernet network to long-haul backbone system, this chapter fully introduces efficient VLSI design of RS decoder. In addition, to meet the requirement of 100Gbps era, this chapter also discusses some new FEC schemes for ultra high-speed application (beyond 100Gbps).

The chapter is organized as follows. Section 2 reviews the RS decoding. The low-complexity high-speed RS decoders for short-distance network are discussed in Section 3. Section 4 analyzes performance-improved RS burst-error decoder for medium-distance system. Some recent FEC schemes targeted to 100Gbps long-haul network are introduced in Section 5. Section 6 draws the conclusion.
