Research On Modulation Formats In 40Gb/s Optical Fiber Communication Systems

At present, research on 40Gbit/s DWDM systems goes deeper. The bottleneck of further expanding system capacity is transmission impairments include accumulated noise from optical amplifiers, group-velocity dispersion (GVD), polarization mode dispersion (PMD) and fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), Stimulated Raman Scattering (SRS), Stimulated Brillouin Scattering (SBS) and four-wave mixing (FWM). Some modulation formats may to some extend overcome these transmission limitations and improve spectral efficiency. The paper deals with modulation formats and the main achievements are listed as the following(1) Domestic and foreign researches and development on advanced modulation formats are reviewed. Characteristics and generation methods of some primary modulation formats are presented.(2) A novel all-optical method is proposed out to generate Modified Duobinary RZ (MD-RZ) format by using a Polarization Maintaining Fiber Loop Mirror (PMFLM). Operation principle for all-optical format conversion is theoretically analyzed and 40Gb/s MD-RZ data format generation is experimentally demonstrated.(3) Transmission performance in 40Gb/s DWDM system of four modulation formats are simulated by Optisystem software. The four modulation formats are Non-Return to Zero (NRZ), Return to Zero (RZ), Optical Duobinary (ODB), and MD-RZ, performance of which are compared in terms of dispersion tolerance, non-linear tolerance, and transmission distance. MD-RZ has higher robust against non-linear effects and most suitable in ultra long transmission.(4) Comprehensive theoretical analysis and experiments on functions of "multi-functional fiber-based all-optical formats converter". Four major format conversions are concluded which are NRZ to Pseudo RZ (PRZ), RZ to NRZ, Differential Phase-Shift Keying (DPSK) to On-Off Keying (OOK), and DPSK to MD-RZ.