Advanced Modulation Formats and Multiplexing Techniques for Optical Telecommunication Systems

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Since ancient times, one of the principal needs of people has been to communicate. This need created interest in devising communication systems for sending messages from one place to another. The advent of high performance computer processors brought many advantages for digital communications over that of analog. These benefits include more features, easy storage and faster processing. These caused huge amount of information, which is increasing exponentially every year, to be carried over communication networks. Various types of communication system appeared over the years. Among the basic motivations behind each type are to improve the transmission fidelity, increase the data rate, and increase the transmission distance between stations. All these facilities are achievable utilizing optical fiber communications. Optical fiber offers several advantages over the traditional media (e.g., twisted wire pair and coaxial cable). Its decisive advantages are huge bandwidth and very low attenuation and noise (Arumugam, 2001). The first, results in higher bit rate, and the second, results in longer transmission distance. These potentials can be further pushed by utilizing multiplexing techniques and/or advanced modulation formats. The invention of wavelength division multiplexing (WDM) (G. E. Keiser, 1999) contributes great benefit to the optical fiber communication systems especially after the introduction of Erbium-doped fiber amplifier (EDFA). Using WDM, about forty channels can be accommodated in the C-band at 100 GHz (0.8 nm) channel spacing. Based on this condition, up to 1.6 Tb/s transmission capacity has been reported (Zhu et al., 2001). More channels can be transmitted using ultra-dense WDM technique by considering channel spacing of as close as 12.5 GHz (Ciaramella, 2002; Sang-Yuep, Sang-Hoon, Sang-Soo, & Jae-Seung, 2004). Using such channel spacing, up to 2.5 Tb/s transmission is reported (Gyo-Sun et al., 2007) by multiplexing 256 12.5 Gb/s channels, and transmitted over 2000 km standard single mode fiber (SSMF). Larger transmission capacity can be achieved by utilizing the Sand L-bands (Freund et al., 2005; Seo, Chung, & Ahn, 2005). Using triple bands (S + C + L), 10.92 Tb/s transmission is experimentally reported (Fukuchi et al., 2001) by using 273 WDM channels and 50 GHz spacing. 2