| Popis: |
This thesis explores all-optical regeneration techniques for advanced modulation formats with the overall aim of increasing the transmission reach of optical data links. In order to carry out this work, a number of tools were developed for the generation of advanced optical modulation formats. They included a combination of techniques involving the use of a delay line interferometer (DLI), time gating and coherent temporal superposition. A BPSK seed signal was used to generate QPSK (with a single DLI) and 16-QAM (with two concatenated DLIs) signals. The all-optical regeneration schemes studied in this thesis take several forms: phase preserving amplitude regeneration; phase only regeneration; and phase and amplitude regeneration, many of them including PSA configurations as building blocks. Firstly, phase preserving amplitude regenerators were numerically and/or experimentally investigated. A multilevel amplitude regenerator in a PSA configuration, which was based on parametric pump-saturation, was analysed. A highly nonlinear fibre based dual-pump degenerate scheme was used to effect amplitude regeneration on a 4-level amplitude shift keying signal. Another amplitude regeneration scheme, this time based on optical injection locking, was also experimentally analysed, transmitting a BPSK signal over a 600-km long dark bre link. Secondly, a wavelength converting PSA-based phase regenerator for an M-PSK signal was developed by coherently summing the conjugated signal with the (M - 1)th phase harmonic, where M is the number of modulated symbols in the signal. This regenerator offers flexibility of operating power and harmonic mixing coefficient. Both numerical and experimental studies prove the feasibility of the proposed scheme. Another proposed regenerator, operating at the gain minima in a PSA configuration and working by coherently summing the signal to the π phase shifted (M+1)th harmonic, offers squeezing in both the amplitude and phase of the input signal. The latter work of this thesis introduces a phase regenerator which is designed to target higher-order M-PSK signals using a (simpler) M/2-PSK PSA-based regenerator. |
