Ng, Trina Tsao-Tin
Domain transformations for optical telecommunications signals.
University of Southampton, Optoelectronics Research Centre,
In this thesis, the transformation of optical telecommunication signal waveforms between the temporal and spectral domains is investigated. Temporal optical Fourier transformations (TOFTs) are presented with the primary aim of mitigating distortions in high repetition rate telecommunication signals, by transferring them from the temporal domain into the frequency domain. Development of TOFT is extended to aid their suitability for other applications also.
The TOFT is based on inducing cross-phase modulation on the signal to be transformed, using shaped parabolic pulses as the pump. To demonstrate the technique, various methods of generating parabolic pulses are investigated and considered for their suitability for TOFTs. Firstly, parabolic pulses are generated in a nonlinear fashion exploiting their natural evolution in a normally dispersive fibre. Compensation is performed on timing jitter signals using this method. In another configuration, parabolic pulses are generated with a superstructured fibre Bragg grating. The passive nature and the chirp free parabolics generated by the grating enabled greater flexibility in the experimental parameters thus improving the fidelity of the TOFT. Compensation of pulses distorted by second and third order dispersion is demonstrated.
Unexpected results in the first two TOFT experiments led to further analysis and the derivation of the conditions for a complete TOFT. Sophisticated reconfigurable filters are used to convert an optical frequency comb (OFC) into one or more simultaneous pulse sources, each with a configurable shape and phase profile. Pulses generated using the OFC and reconfigurable filter are used to experimentally verify the new theory.
The thesis also includes a presentation of a linear frequency resolved optical gating technique. The versatility of the technique was demonstrated through the characterisation of many of the pulses generated in this thesis, providing insight to their time-frequency
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