Study On Modulation Techniques In High-speed Optical Transmission System

Along with the developing of optical fiber communication, large-capacity and long-haul fiber transmission system is developing rapidly. 40Gbit/s system, which has higher transmission rate and better flexibility, is the ideal choice to satisfy the requirement of increasing information transmission quantity. However, high transmission rate would cause damage on the quality of the signal, such as dispersion, non-linear effects and so on. Advanced modulation format is one of the key technologies of 40Gbit/s system because of its capability in mitigating transmission impairments. This paper studies on three new modulation formats: Firstly, it presents the modulation and demodulation principles of these new modulation formats. Secondly, it compares the dispersion and non-linear tolerance of multilevel phase modulation format. Results show that D8PSK modulation format have the strong capability against chromatic dispersion but less tolerance of non-linear effects. Finally, this paper focuses on the optimal extinction ratio of phase-amplitude-shift keying modulation format, analyzes in detail ODPASK modulation format's performance in optical transmission system. It is shown that RZ-ODPASK format can tolerate more dispersion than the other two formats; CSRZ-ODPASK format performs better in crosstalk in WDM system, phase-amplitude-shift keying modulation is one of the dominant candidate modulation formats in 40Gbit/s high-speed optical transmission system.