All-optical signal processing using cascaded quadratic interactions in periodically poled lithium niobate waveguides.
University of Southampton, Faculty of Physical and Applied Sciences,
This thesis investigates all-optical signal processing using cascaded quadratic nonlinearities in periodically poled lithium niobate (PPLN) waveguides for telecommunication applications. PPLN waveguides which possess high second-order nonlinearity are attractive due to their suitable properties with respect to high compactness, high operating speed and resistance to parasitic effects. They allow the implementation of various advanced signal processing functionalities which will be required in future ultrahigh speed fibre-optic communication systems. Several novel all-optical signal processing techniques relying on two types of cascaded quadratic processes in PPLN waveguides, namely cascaded second harmonic generation and difference frequency generation (cSHG/DFG) and cascaded sum frequency generation and difference frequency generation (cSFG/DFG), are demonstrated. These two processes are conventionally employed for wavelength conversion in the telecommunication band. To facilitate the use of these wavelength converters, a systematic study of the acceptance bandwidths of cSHG/DFG and cSFG/DFG in PPLN waveguides is presented. Following this study, an optical time- divisionmultiplexing to wavelength-division multiplexing format conversion scheme, which relies on the generation of linearly chirped pulses which are then optically switched with data pulses using cSHG/DFG in a PPLN waveguide, is demonstrated. Signal regeneration techniques exploiting cascaded quadratic nonlinearities in PPLN waveguides are also investigated. An all-optical signal retiming system for on-off keying signals relying on pulse shaping and cSHG/DFG-based switching in a PPLN waveguide is demonstrated. Subsequently, two novel configurations of PPLN-based phase sensitive amplifiers (PSA) which have the potential as regenerators for phase-shift keying signals are demonstrated. Finally, a novel method for the elimination of arbitrary frequency chirp from short optical pulses is presented. In addition, the thesis contains a study on the use of OFCGs as telecommunication sub-picosecond pulse sources. Both a theoretical and experimental study of the intensity and phase properties of the pulses generated by an OFCG is presented. Furthermore, two approaches are proposed to compensate for the intrinsic chirp of the OFCGs
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