Abstract:
The introduction of WDM with optical amplifiers has revolutionized the optical fiber transmission system by escalating the system capability both by the number of channels and distance. Transmission capacity can be further improved by increasing the channel bit rate. The channel bit rate is upgraded to 40 Gb/s from 10 Gb/s and it is predicting that the next generation light wave communications will be based on 100 Gb/s rate or even more. This high bit rate systems will face many problems due to fiber dispersion and nonlinearity which are interconnected with transmitting power, number of channels, channel spacing, transmission length and duty cycle. The third order dispersion (TOD) effect still may be in an acceptable limit at current bit rate of optical fiber transmission scheme but its effect increases with the escalating bit rate. The presence of the TOD causes pulse broadening and ripples as well as introduces an additional temporal shift to each pulse. As a result compensation of third order dispersion along with second order dispersion has become a concern now-a-days in dispersion-managed system. This fact has motivated us in this research.
In this work a comprehensive investigation on pulse distortions has been carried out due to the TOD on ultra-high speed long-haul single channel optical fiber communication system. The optical communication system consists of dispersion-management with a periodic Er-doped fiber amplifier (EDFA). Impact of TOD is observed at the receiving end considering the variation of different factors such as bit rate, duty cycle, pulse shape, transmission distance and fiber type. Only self-phase modulation, second and TOD effects, fiber loss, ASE noise and receiver noises are considered here. In the simulation, two different dispersion-managed models have been used. One model consists of standard single mode fiber and dispersion compensated fiber (DCF). In another model, non-zero-dispersion shifted fiber is followed by DCF. Each span consists of an optical amplifier at the end terminal of every span. The numerical simulation is done by directly solving the Nonlinear Schrodinzer equation using split-step Fourier method. The simulation has been carried out using OptiSystem. Pulse center position changes with the variation of duty cycle, pulse shape and fiber type. However, these impairments could be mitigated by properly designing DM transmission systems along with consideration of other parameters. As far as real environment is considered, performance of SSMF-FBG is satisfactory while considering both GVD and TOD for high bit rate. The result obtained from this work will be helpful for designing high-speed long-haul optical fiber communication system.
