Dispersion Compensated Fibers with Advanced Modulation Schemes in Optical Fiber Communication System

A comprehensive study of the various modulation techniques has been discussed which helps to increase data rate, to overcome dispersion effects and various non-linear effects in the fibre. Modulation formats such as OOK (On Off Keying), BPSK (Binary Phase Shift Keying), DPSK (Differential Phase Shift Keying), DP-QPSK (Dual Polarized Quadrature Phase Shift Keying) and duobinary are studied. The DP-QPSK, DPSK and other higher modulation formats yield to better performance. Issues related to spectral efficiency, optical bandwidth, Wavelength Division Multiplexing (WDM) have also been discussed. Duobinary modulation has also stimulated much interest, especially as a practical alternative for high-spectral efficiency 40 GB/s systems alongside the more popular differential phase-shift keying (DPSK) technique. Both duobinary and DPSK can achieve the high-spectral efficiency necessary to transmit 40 GB/s data on 50GHz channel spacing. DPSK is known to have the better optical signal-to-noise ratio (OSNR) sensitivity, while duobinary is famed for a good tolerance to chromatic dispersion, and narrow optical filtering. Comparison of pulse shapes RZ and NRZ are done for DPQPSK schemes which show that RZ has better performance. An experimental study of pulse shapes for duobinary systems is also done. The RZ versus NRZ pulse shape is compared for duobinary systems that are dominated by ASE noise, fibre chromatic dispersion, and SPM nonlinearity. Surprisingly, and in stark contrast to the case of OOK, in all cases that were considered, the NRZ pulse shape is found to be superior to RZ for duobinary transmission. An analysis of the performance limitations of SMF due to SPM effect is discussed. With the aid of OptSim simulation software a DCF has been employed with proper variation in length to tackle the nonlinear effects in the transmission system. Better performance was shown when a combination of SMF length 85 km and DCF length 15 km was chosen for total 100km fiber length. The BER and eye diagram technique have been used for evaluating the system performance.