Optimized filtering for 40-gb/s/ch-based DWDM transmission systems over standard single-mode fiber

We show that the optimized optical filtering at the transmitter and receiver side is the key technology for the achievement of higher spectral efficiencies in 40-Gb/s-based dense wavelength-division-multiplexing (DWDM) systems. Through the improved filtering, the spectral efficiency of 0.8 b/s/Hz can be realized in DWDM systems independently on the used modulation format.