Components and Techniques for High-Speed Optical Communications
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Electroabsorption modulators (EAMs) are fundamental components in optical communication systems. Their response is governed by a set of parameters inherent to their internal structure and by the external electrical components used to drive them. The first part of this thesis discusses a new method for the extraction of values for these parameters. The use of EAMs as both optical modulators and photodetectors is exploited for the purpose of parameter extraction. The proposed method allows the estimation of the parameters which govern the internal frequency response of EAMs without any knowledge of the characteristics of the electrical interconnect used to drive them. The procedure also removes the need for an accurately calibrated optical transmitter and receiver pair normally used during the characterization of optoelectronic components. Analytic description and experimental verification are presented. In the second part of this thesis, direct demultiplexing of a 10 Gbit/s channel from a 160 Gbit/s optical time division multiplexing (OTDM) signal using a single lumped, electrically driven EAM is experimentally presented for the first time. Direct demultiplexing is made possible by using an electrical driving signal for the EAM consisting of a sum of in-phase harmonics of the base channel rate. The use of a single EAM as an optical gate is quasi-analytically compared with the common approach of cascading two EAMs when performing 160 Gbit/s to 10 Gbit/s demultiplexing. The analysis reveals that the use of a single EAM is beneficial in terms of lower penalty with respect to degradations in the extinction ratio and width of the pulses used in the OTDM signal. The last part of this thesis introduces an electrical distributed oscillator which works in a regime of oscillation similar to that of mode locked laser (MLL) systems. The oscillator offers the flexibility of producing other waveforms not found in MLLs and has the potential to generate the required electrical driving signal for a single EAM OTDM demultiplexer. Other possible applications of the oscillator include the generation of short pulses for use in radar systems and wireless personal area networks.