Holey optical fibres for high nonlinearity devices

Abstract

This thesis describes the development of a novel type of optical fibre, namely holey optical fibre (HF), for its specific incorporation in optical devices based on fibre nonlinearity. The development of the fabrication technique to produce such a fibre is discussed, and the fibres produced are characterized and used in device applications, proving the advantages of HF technology in the implementation of highly nonlinear optical devices, as well as showing its limitations. The initial fabrication problems that hindered the production of HFs with a high nonlinearity are identified and several strategies are adopted for its solution, including an experimental study of the HF drawing parameters, the invention of a novel holey fibre fabrication design based on an air clad HF jacket, the introduction of HF preform pressurization by means of a sealing technique and the use of a HF silica jacket. Thus long and robust HFs with a high nonlinearity can be reliably fabricated. In parallel with the development of the HF fabrication technique, the first applications of HF technology to high nonlinearity devices are investigated, ranging from a 2R data regenerator, based on only 3.3 m of a HF, to a Raman amplifier and a Brillouin laser based on long and robust HFs with low confinement losses, high birefringence and high anomalous dispersion at the operating wavelength. The negative impact of anomalous dispersion on the BER performances of a wavelength converter, and the limitations in terms of wavelength tuning range and phase matching of a high dispersion HF, directs our research towards the development of a HF with a relatively low normal dispersion (about -30 ps/nm . km) and an extremely high effective nonlinearity (gamma) = 70 W-1km-1). 15 meters of this HF were used to provide a demonstration of the first wavelength converter based on FWM, which allows error free-penalty free wavelength conversion of 10 Gbit/s data signals over a 10 nm bandwidth. As shown by these experiments one major issue of our HFs is the high polarization mode dispersion. We suggest a possible route to the solution of this problem, by systematically investigating the feasibility of a spun HF. We first use some hollow tubes to study the effects of preform spinning on the spin pitch, on a central hole and on an off-centre hole. Those preliminary results lead us towards the successful fabrication of the first spun HF, which demonstrates the applicability of the preform spinning technique to HF technology<br/