OFCG Based Coherent Optical Communications In WDM-PON System

Nowadays,the traffic trends in the optical access networks are moved from simple web based services to multimedia and video services.There is a gigantic breach amongst the current traffic trends and the current network infrastructure which strongly demands the need of optical access networks.Wavelength-division multiplexing(WDM)passive optical network(PON)is a strong candidate for next generation optical access networks.WDM-PON system is well-known for its transmission capability of high bandwidth and low cost of maintenance.The optical line terminal(OLT)of a WDM-PON should be simple in design and low in cost,which makes it highly suitable for next generation optical access networks.In this thesis,optical frequency comb generation(OFCG)based OLT schemes are proposed for a WDM-PON system,and Coherent Optical Communications.Three different schemes are proposed and presented for OFC generation with minimal resources utilization.All the schemes produces almost flat OFC lines having high tone-to-noise ratio(TNR),and least amplitude difference(AD)among the comb lines.The first one is based on a continuous wave(CW)laser source and a single Mach Zehnder Modulator(MZM),the second scheme uses cascaded configuration of intensity modulators(IMs).Whereas,the last one is also based on a single MZM,however,the CW laser source is replaced with a new pulsed laser source.In the simulation results,it is observed that all the schemes produces almost flat comb lines with high TNR and least AD,thus,assuring that the proposed schemes can be deployed in optical communications.1)The first proposed scheme is deployed in WDM-PON system where 10Gbps differential phase shift keying(DPSK)modulation scheme is utilized for transmission of 33 comb lines over 25km standard single mode fiber(SSMF).Overall,330Gbps downlink transmission has been achieved with minimal power losses.2)The second OFCG scheme utilizes cascaded configuration of intensity modulators which produces surprisingly thriving results with an overall of 78 comb lines having high TNR and low AD's among the comb lines.3)The third scheme of OFCG has an increased frequency spacing with same single MZM used in the first scheme,yet,produces even better results.This scheme is deployed in WDM-PON based coherent optical communications.In this scheme,10Gbps quadrature phase shift keying(QPSK)modulation technique is utilized for the transmission of 37 comb lines over 20km SSMF.The signal is received and recovered with the help of coherent optical receiver.Overall,a total of 740Gbps downlink transmission with minimal power losses is successfully achieved with the proposed scheme.The simulation results are in great agreement with the proposed schemes.