Multilevel Manchester (2 bits/symbol) coding with optical equaliser for increasing the transmission distance of high-speed fibre optic links

This study accessed the performance of the four-level Manchester coding (4-MC) and four-level modified Manchester (4-MM) technique at the bit rates of 20 and 40 Gb/s for the first-order and second-order optical equalisers. The performances were evaluated with respect to bit error rate (BER), power penalty, eye diagrams, and dispersion tolerance. Based on the results by utilising the second-order optical equaliser, at 20 Gb/s, the transmission distance of 4-MC and 4-MM was extended by 25 and 27 km of standard single-mode fibre (SSMF), respectively, while at the bit rate of 40 Gb/s, the 4-MC and 4-MM transmission distance was extended by 6.5 and 7.5 km of SSMF, respectively. Hence, the second-order optical equaliser can adequately compensate for the fibre dispersion and consequently the overall BER performance. Therefore, the proposed system could serve as an alternative to the next-generation high-speed optical transmission links.