NRZ transmission systems with bit rates exceeding 20 Gbit/s

There are two ways to construct a transmission system with a capacity exceeding 20 Gbit/s: one is increasing the transmission bit rate of a single channel with time-division multiplexing (TDM), and the other is employing wavelength-division multiplexing (WDM) transmission. Superiority between TDM and WDM depends on the chromatic dispersion of the embedded optical fiber. In high-speed transmission systems, the transmission bit rate is restricted by the operating speed of electronic and optical devices when optical processing techniques are not used. Operating speeds have been recently increased up to 40 Gbit/s and several studies on the possibility of achieving an all-electrical 40 Gbit/s transmission system have been conducted. This paper evaluates by numerical simulation using the split-step Fourier method, the transmission performance of three cases with the same total capacity of 40 Gbit/s: a single-channel case, a four-channel case (10 Gbit/s each, 200-GHz channel spacing), and a 16-channel case (2.5 Gbit/s each, 100-GHz channel spacing)