Optical parametric processes in periodically poled silica fibres
Glass, an amorphous centrosymmetric material, does not possess any macroscopic second-order optical nonlinearity, thus preventing processes such as linear electro-optic modulation and parametric frequency conversion. This thesis describes work carried out at Southampton using poling techniques in order to induce a significant second-order nonlinearity in optical glass fibres, so as to achieve efficient quasi-phase-matched optical parametric processes. An all-fibre frequency converter presents several interesting advantages over traditional nonlinear crystals, in particular with respect to ruggedness, damage threshold and integrability with existing optical circuits. Also, parametric fluorescence is a source of twin-photon pairs, presenting peculiar correlation properties that can be exploited both for the realisation of quantum key distribution systems (Quantum Cryptography) and for the investigation of fundamental phenomena in quantum optics. Studying and better understanding of the poling processes and optimisation of the quasi-phase-matching technique in poled optical fibres led to the fabrication of novel nonlinear fibre devices. The achievement of more than 20% second-harmonic generation efficiency, the first demonstration of parametric fluorescence from an optical fibre and of periodic UV erasure of the nonlinearity in a germano-silicate fibre represent the key results described in this thesis.