High Spectral Efficient Optical Communication System Using Higher-Order QAM

In recent years,with the rapid development of the Internet industry,the explosive growth of data services such as mobile Internet,big data and cloud computing make the transmission capacity face the pressure of continuous expansion.The growing demand for optical network interconnection applications has made it increasingly difficult to increase the capacity and spectral efficiency(SE)of optical networks.The replacement of existing techniques for communication system such as intensity and on-off-keying(OOK)modulation format with advanced modulation formats and coherent technology has been at a top trend.In this thesis,high spectral efficient optical communication system using higher order QAM is proposed along with coherent detection scheme.Coherent optical communication system using higher order QAM with pulse shaping techniques,polarization multiplexing(Pol-MUX)and a coherent homodyne receiver with enhanced sensitivity of photodetectors and a DSP unit with novel equalization and compensation method have been newly developed as the utmost common source for spectral efficient optical communication.The work for this thesis is summarized in the following.1)Firstly,research on the scheme for higher order QAM signal generation with trapezoidal pulse shaping.Higher order QAM such as 128-QAM and 256-QAM with trapezoidal pulse shaping and their simulation results and advantages are discussed.After trapezoidal pulse shaping,signal is polarization multiplexed and sent over more than 80 km length of optical fiber.For the case of 128 QAM along with pulse shaping with trapezoidal optical filtering,280 Gbit/s over a single channel of more than 80 Km fiber-optic length has been transmitted with minimal power loss and lowest BER.2)Secondly,on the receiver side balanced coherent detection scheme with InGaAs waveguide layers scheme is designed.The enhanced sensitivity and achieved result such as BER and EVM which are calculated while changing OSNR and symbol rate are discussed in details.These results are also compared with all previously employed schemes.Root raised cosine filter was used and signal was homodyne-detected and processed in DSP unit in offline mode.Error vector magnitude(EVM)was 0.97%with back to back method and after transmission it was less than 1.76%.3)Thirdly,128QAM and 256QAM high-order modulation techniques are implemented utilizing an adaptive equalization DSP algorithm.In the case of 256 QAM,240 and 320 Gbit/s with 15 and 20 Symbol/s respectively transmitted and coherently detected.BER and EVM was also observed while changing OSNR and symbol rate and all the results were also compared with all previously employed schemes.