Long distance dispersion managed soliton transmission experiments

This thesis presents results of transmission experiments using optical solitons in a dispersion managed optical fibre recirculating loop. The basic concepts of pulse propagation in optical fibre are introduced before optical solitons and their use in optically amplified fibre systems are discussed. The role of dispersion management in such systems is then considered. The design, operation and limitations of the recirculating loop and soliton sources which were used and the experimental techniques are described before the experimental work is presented. The experimental work covers a number of areas all of which used dispersion management of the transmission line. A novel ultra-long distance propagation scheme which achieved low timing jitter by suppression of the amplifier noise and by working close to the zero dispersion wavelength has been discovered. The use of fibre Bragg gratings as wavelength filters to suppress noise and reduce timing jitter has been investigated. The performance of the fibre grating cornpared favourably with that of a bulk device and was in good agreement with theoretical predictions. The upgrade of existing standard fibre systems to higher bit rates is currently an important issue. The possibility of using solitons with dispersion compensation to allow an increase in data rate of existing standard fibre systems to 10Gbit/s over 5000km has been demonstrated. The applicability of this technique to longer distances, higher bit rates or longer amplifier spans is also investigated by optimisation of the dispersion management scheme. The use of fibre Bragg gratings as the dispersion compensating elements in such standard fibre transmission experiments has been examined and the main problem that these devices currently have, high polarisation mode dispersion, is discussed. The likely future direction of optical communications and what part solitons and dispersion management will play in this development is discussed in the thesis conclusions

Mathematical and numerical modelling of dispersion-managed solitons, autosolitons and self-similar optical pulses

This thesis presents theoretical investigation of three topics concerned with nonlinear optical pulse propagation in optical fibres. The techniques used are mathematical analysis and numerical modelling. Firstly, dispersion-managed (DM) solitons in fibre lines employing a weak dispersion map are analysed by means of a perturbation approach. In the case of small dispersion map strengths the average pulse dynamics is described by a perturbation approach (NLS) equation. Applying a perturbation theory, based on the Inverse Scattering Transform method, an analytic expression for the envelope of the DM soliton is derived. This expression correctly predicts the power enhancement arising from the dispersion management.Secondly, autosoliton transmission in DM fibre systems with periodical in-line deployment of nonlinear optical loop mirrors (NOLMs) is investigated. The use of in-line NOLMs is addressed as a general technique for all-optical passive 2R regeneration of return-to-zero data in high speed transmission system with strong dispersion management. By system optimisation, the feasibility of ultra-long single-channel and wavelength-division multiplexed data transmission at bit-rates ³ 40 Gbit s-1 in standard fibre-based systems is demonstrated. The tolerance limits of the results are defined.Thirdly, solutions of the NLS equation with gain and normal dispersion, that describes optical pulse propagation in an amplifying medium, are examined. A self-similar parabolic solution in the energy-containing core of the pulse is matched through Painlevé functions to the linear low-amplitude tails. The analysis provides a full description of the features of high-power pulses generated in an amplifying medium.