Research On Implementation Of Robust Advanced Modulation Formats For Cost-effective High Capacity PON

The trend of deployment of optical fiber in the access network has become ultimate choice because of its evaluation as a leading candidate to compete the challenges of drastic growth of bandwidth demands in future. In this contest, Passive Optical Networks (PONs) proved itself as a front-runner technique, which started from a simple and low cost architecture of single wayelength transmission on fiber with Time Division Multiplexing (TDM) based ONUs sharing. However, there are several challenges in TDM-PON, such as high splitter loss, limited number of optical network units (ONUs), aggregated bandwidth of system, acceptable power budget and restricted transmission reach. To resolve these issues, Wavelength Division Multiplexing (WDM) based passive optical networks are proposed. But for further improvement there is a need to mitigate the more bottlenecks such as design complexities, low extinction ratio, poor receiver sensitivity, high deployment cost, less spectrally-efficient design and lack of effective bandwidth utilization and wavelength sharing in WDM-PON.This dissertation covers the comprehensive and concrete research work with theoretical and analytical analysis of challenges in WDM-PON. In which, we proposed DQPSK and IRZ as robust advanced modulation formats, single fiber bidirectional architecture for cost-effectiveness, reduced channel spacing in spectrally-efficient design and hybrid WDM/TDM-PON for effective bandwidth utilization and wavelength sharing. Hence, in the thesis "Implementation of robust advanced modulation formats for cost-effective high capacity PON", following are the key innovations and contributions:Firstly, to resolve the problems of degradation of transmission quality, limitation of high data rate and sufficient transmission reach in passive optical networks (PONs), implementation of robust advanced modulation formats have been proposed innovatively in a combination of differential quadrature phase shift keying (DQPSK) in downstream and re-modulated inverse return-to-zero (IRZ) in upstream, to achieve better extinction ratio, high data rate and improved receiver sensitivity. Transmission performance has been analyzed by the simulation in Optisystem7.0, in which good symbols instance in constellation diagrams, clear eye diagrams and low transmission power penalties ensure that proposed design has good tolerance against transmission impairments.Secondly, high cost design is a big challenge in WDM-PON deployment. Therefore, in this thesis a cost-effective intensity re-modulation based centralized light source WDM-PON technique has been proposed with implementation of robust advanced modulation formats without pulse carving, dispersion compensation fiber (DCF) and erbium doped fiber amplifier (EDFA) in both direction of transmission. The deployment cost has been further reduced by employing single fiber bidirectional transmission after carefully considering the backscattering noise-resilience. The simulation results verify that proposed cost-effective WDM-PON can successfully be transmitted over a distance of20to25km with low transmission power penalties.Thirdly, explosive growth in high bandwidth demands in past few years is a most critical issue. The high capacity can be achieved by either increasing the data rate of wavelength channels or by reducing channel spacing between adjacent wavelengths to add more wavelengths channels. Therefore, another important contribution in this dissertation is the successful research towards the spectrally-efficient WDM-PON design. In which, instead of previous100GHz channel spacing,50GHz channel spacing has been employed for16channels in both direction of proposed WDM-PON. The simulation based transmission performance has been analyzed which validates the feasibility with smaller transmission penalties and resistance against transmission noise.Fourthly, how to utilize the bandwidth efficiently? It is another very important matter of concern and this can be achieved by sharing of wavelength among ONUs via TDM technique. Therefore, an innovative work is contributed by implementation of spectrally-efficient design in hybrid WDM/TDM-PON, including the potential advantages of both the WDM and the TDM techniques. The proposed design can support256ONUs having data rate up to625Mbit/s in downstream and also up to156Mbit/s in upstream for every subscriber. Further, negligible transmission power penalties have been found in the simulation results which reflect good transmission performance.Hence, this research dissertation, about implementation of robust advanced modulation formats in cost-effective high capacity PON, provides a foundation for future research work to achieve simple, cost-effective, spectrally-efficient design for the high capacity next generation access networks.