Forward Error Correcting Codes for 100 Gbit/s Optical Communication Systems

This PhD thesis addresses the design and application of forward error correction (FEC) in high speed optical communications at the speed of 100 Gb/s and beyond. With the ever growing internet traffic, FEC has been considered as a strong and cost-effective way to improve the quality of transmission (QoT) to meet the increasing demand on the quality of service (QoS).

The scientific content presented in this thesis tackles three major research problems. Firstly, the study of FEC codes becomes essential to get a high coding gain (CG) suited for 100 Gb/s optical fiber links. Secondly, low-complexity low-power-consumption FEC hardware implementation plays an important role in the next generation energy efficient networks.

Thirdly, a joint research is required for FEC integrated applications as the error distribution in channels relies on many factors such as non-linearity in long distance optical fiber links, cross-talks in wavelength division multiplexing (WDM) setups and so on. FEC with a product code structure has been investigated theoretically and experimentally.

The iterative decoding method applied to FEC codes in a product code structure can effectively reduce the bit error rate (BER). Proposals on beyond bound decoding (BBD) and adaptive FEC algorithms are also presented. BBD is an add-on in some cases to help with the further reduction of the BER. FEC aided transmission in a short distance data center link is presented.

With the help of FEC and a low cost vertical-cavity surfaceemitting laser (VCSEL), 100 Gb/s raw data rate is achieved, which demonstrates the possibility of building a high speed short-range link with cheap elements. FEC integration in a WDM metropolitan transmission link is also presented. The experimental performance of FEC in both linear and nonlinear regimes is demonstrated in a dual polarization (DP) 16-ary quadrature amplitude modulation (16QAM) and coherent detection based WDM transmission over 741 km at a raw data rate of 88.8 Gb/s.

FEC can compensate in both regimes, but the channel analysis does not show an additive white Gaussian noise (AWGN) channel. Besides, a denser WDM grid changes the shape of the BER curve based on the analysis of the experimental results, which requires a stronger FEC code. Furthermore, a proof-of-the-concept hardware implementation is presented.

The tradeoff between the code length, the CG and the complexity requires more consideration in the FEC code choice in a certain application. The presented adaptive FEC is one of the few published research results to enable the efficient bandwidth usage as the transmission channels can be affected by many factors.

In conclusion, the results presented in this thesis consist of proposals on FEC codes and their associated experimental demonstration and hardware implementation. The demonstrated high CG, flexibility, robustness and scalability reveal the important role of FEC techniques in the next generation high-speed, high-capacity, high performance and energy-efficient fiber-optic data transmission networks.