Simulations of High-Capacity Long-Haul Optical Transmission Systems

The wider and wider bandwidth required for users stimulates the increase in the bit rate transmission for optical fiber systems (Bergano 2005), and one of the current aims for long-haul links is channel transmission at 100 Gbit/s (Cai et al. 2010). To reach such a capacity, several technological approaches are required, both in terms of advanced modulation formats (Winzer and Essiambre 2006) and also methods to mitigate impairments due to in-line degradation effects, like the ASE noise of optical amplifiers (Agrawal 2007), and dispersive (Elrefaie et al. 1988) and nonlinear fiber effects (Chraplyvy 1990). Concerning advanced transmission and detection formats (Gnauk 2005), the combination of amplitude and phase modulation allows us to use a higher bit rate reducing the signal bandwidth, and therefore, these modulation formats have shown enormous advantages with respect to conventional IM-DD systems. In particular, DQPSK is assumed as one of the most interesting formats since in a bit time, four symbols can be transmitted with a consequent enormous advantage for reduction of dispersive impairments (Fuerst et al. 2006, 2008). Concerning the mitigation of fiber impairments at the end of 1980, the soliton propagation seemed the best solution for long transmission systems (Mollenauer et al. 1991); conversely, the introduction of dispersion compensating devices such as DCF and grating showed that the regime of the periodic chromatic dispersion compensation, also known as dispersion management, was the best method since it is also able to limit the accumulation of nonlinear effects (Lichtman and Evangelides 1994).