40-Gb/s Dense Wavelength Division Multiplexing Transmission System

Fujitsu Telecom Networks develops and supplies optical transmission systems for domestic telecommunications carriers. For Japanese telecommunications carriers, it has recently developed the world's first 40-Gb/s Dense Wavelength Division Multiplexing (DWDM) transmission system using the return-to-zero differential quaternary phase shift keying (RZ-DOPSK) modulation format. This system can multiplex and transmit up to forty 40-Gb/s (STM-256) signals (total: 1.6 Tb/s) over one optical fiber. This paper explains the technical problems and solutions for multiplexing 40-Gb/s optical signals on a DWDM system, discuss the characteristics of various optical modulation formats, and show the superiority of RZ-DOPSK.