Study of the Impact of Nonlinearities on Advanced Modulation Formats in Optical Systems and Networks

Chromatic dispersion, Kerr nonlinearity, and amplified spontaneous emission (ASE) noise are three common problems for the optical communication systems. For the systems using direct detection scheme, we detect the power of the signal. Therefore, the information is carried by the signal power, which is pulse amplitude modulation (PAM). In this system, chromatic dispersion and Kerr nonlinearity will broaden the pulse and cause intersymbol interference, while ASE noise will degrade the signal to noise ratio and increase the error rate. For the system using coherent detection, we can detect not only the power but also the phase of the signal. Thus, the information can be carried by the power and the phase of the signal, which is quadrature amplitude modulation (QAM). In this system, the signal will see a phase shift during the propagation induced by the Kerr nonlinearity, which will cause an error if the phase shift is not corrected on the receiver side. In order to optimize the performance or design the solution for the system, a careful study of the impact of these three effects on the signal is needed. In this thesis, I study the theory of the pulse broadening effect caused by chromatic dispersion and Kerr nonlinearity, and as well as the bit error rate performance with the accumulation of ASE noise. Moreover, I use split-step Fourier method to solve the nonlinear Schrödinger equation in MATLAB and simulate the propagation of 2-PAM and 4-QAM signal. The impact of these three effects and the bit error rate behavior of the coherent detection system are demonstrated and discussed