528 CHAPTER D. ULTIMATE SYSTEM CAPACITY
350 Tb/s assuming that the optical fiber acts as a linear channel. The highest capacity
realized for WDM systems in a 2001 experiment was 10.9 Tb/s [2]. The most limiting
factor is the spectral efficiency; it is typically limited to below 0.8 (b/s)/Hz because of
the use of the binary amplitude-shift keying (ASK) format (on–off keying). The use
of phase-shift and frequency-shift keying (PSK and FSK) formats in combination with
advanced coding techniques is likely to improve the spectral efficiency.
The impact of the nonlinear effects and the amplifier noise on the ultimate capacity
of lightwave systems has been studied in several recent publications [3]–[8]. Because
the amplifier noise builds up in long-haul systems, the maximum channel capacity
depends on the transmission distance and is generally larger for shorter distances. It
also depends on the number of channels transmitted. The most important conclusion is
that the maximum spectral efficiency is limited to 3–4 (b/s)/Hz because of the nonlinear
effects. As a result, the system capacity may remain below 150 Tb/s even under the
best operating conditions.
References
[1] C. E. Shannon,Proc. IRE 37 , 10 (1949).
[2] K. Fukuchi, T. Kasamatsu, M. Morie, R. Ohhira, T. Ito, K. Sekiya, D. Ogasahara, and
T. Ono, Paper PD24,Proc. Optical Fiber Commun. Conf., Optical Society of America,
Washington, DC, 2001.
[3] P. P. Mitra and J. B. Stark,Nature 411 , 1027 (2001).
[4] A. Mecozzi,IEEE Photon. Technol. Lett. 13 , 1029 (2001).
[5] J. Tang,J. Lightwave Technol. 19 , 1104 (2001).
[6] J. Tang,J. Lightwave Technol. 19 , 1110 (2001).
[7] J. B. Stark, P. P. Mitra, and A. Sengupta,Opt. Fiber Technol. 7 , 275 (2001).
[8] E. E. Narimanov and P. P. Mitra,J. Lightwave Technol. 20 , 530 (2002).