Ultra-High speed signal generation combining OTDM and high-order modulation formats

This thesis is focused on high-order modulation formats as a means to increase spectral efficiency and in turn reduce the cost per bit of an optical transmission system. Special attention is devoted to DQPSK and 16QAM, together with optical time-division multiplexing, with the aim of maximizing the exploitation of a single wavelength on a single fiber. A numerical model for simulating an optical communication system is described, and most of the effort is spent on transmitter and fiber link. By means of the mentioned model, we develop a study of the IQ modulator non-idealities, amongst which the limitedness of the phase modulators bandwidth. On top of this, we analyze the behavior and the applicability of a pulse source based on the phase modulation of a CW source and on the following propagation of the light through a dispersive element. The simulation and comparison of NRZ-DQPSK, NRZ-16QAM, 4-channel OTDM DQPSK, and 4-channel OTDM 16QAM are carried out basing on a number of typical impairments like laser linewidth, chromatic dispersion, and fiber nonlinearities. Minor attention is also devoted to different techniques to numerically simulate light propagation over nonlinear fiber. The results of an extensive laboratory experience are reported. An 8-channel OTDM QPSK system with clock recovery, coherent receiver and DSP is realized at a symbol rate of 10 GBd/s, corresponding to 160 Gb/s on a single wavelength and on a single fiber. The demodulation is shown successful and paths for improvement are depicted