Propagation Characteristics Of High Speed Fiber Optic Communications Affected By Nonlinear Dispersion

In the future generation of light wave systems, high speed data rate like 40 Gb/s per channel is very manifesting demand. Moreover, to pack more channels into one single fiber, channel spacing is decreased from 200GHz to 100GHz or even smaller. The direct consequence is that nonlinear and linear (nonlinear-dispersion fiber) degrading effects that will be austere in such high-speed fiber optic communication systems. To tackle these problems an optimal modulation format which is more tolerant to linear and nonlinear impairments is required urgently. The nonlinearities in optical fibers are of two types. One is stimulated scattering (Raman and Brillouin) and optical Kerr effect due to changes in the refractive index with optical power. Phase modulation due to intensity dependent refractive index induces various nonlinear effects, namely, self-phase modulation (SPM), cross-phase modulation (XPM), and four wave mixing (FWM).In this thesis, a propagation characteristic of high-speed fiber optic communication affected by nonlinear dispersion is studied. The effects of various parameters on the received power also examined. Advanced modulation formats are proposed for the purpose of enhanced transmission system in terms of either bandwidth efficiency or signal quality. High speed fiber optic communication transmission such as 40Gb/s is enviable to allow the transportation of larger bandwidth application at high speed. Using OptiSystem simulator, this thesis compares the performance among the three advanced modulation formats. These modulation formats are non-return zero (NRZ), carrier suppressed return zero (CSRZ) and differential phased shift keying (DPSK).Each modulation formats transmitted over non-zero dispersion shifted fiber (NZDSF) that has lower dispersion (4 ps per run per km) than a regular SMF (17ps per nm per km). The assessments made on the scenarios of single channel and wavelength division multiplexing (WDM) with channel spacing 100 GHz and distance in between 100km to 500km. We found that the choice of optimal fiber is dependent on modulation formats. The simulation result shows that DPSK is the best choice for a transmission high speed data rate such as 40 Gb/s for more than 500km in 4 channels,8 channels and 16 channels system than CSRZ and NRZ with WDM systems due to an excellent tolerance to linear and nonlinear fiber optic effects for high speed communication.