Fibre soliton lasers and their applications

Abstract

This thesis presents experimental and theoretical studies of picosecond soliton generation in passively modelocked optical fibre lasers and their transmission in optical fibre systems.

Chapter 2 describes an investigation into the timing jitter of a self-stabilized, passive harmonically modelocked fibre laser. It is demonstrated that the mechanism for self-stabilization is the resonant enhancement of acoustic waves excited by the soliton pulses within the cavity and that timing jitter as low as 600 fs can be achieved with this technique.

A new fibre laser cavity configuration incorporating a multi-quantum-well saturable absorber to achieve improved self-starting characteristics is presented in chapter 3. The presence of the multi-quantum-well also creates a self-stabilization effect through carrier induced refractive index changes. This laser generates transform limited pulses at repetition rates of up to 3 GigaHertz with very low levels of background radiation.

The development of a simple and stable source of picosecond solitons allowed studies of the properties of these pulses in long distance transmission systems which share many characteristics with fibre lasers. In chapter 4, a Raman amplifier with a pump wavelength of 1535 nm was designed to provide a distributed gain for the investigation of soliton properties over distances of 100 dispersion lengths. The pump source developed for the amplifier was a superfluorescent amplified spontaneous emission source capable of delivering up to 1300 MW of power in a 0.5 nm bandwidth.

Experiments on picosecond soliton pulse propagation using Raman amplification are described in chapter 5 and we demonstrate that the properties of individual pulses can be maintained over distances of greater than 150 dispersions lengths. This chapter also presents investigations of the behaviour of soliton pulse pairs reveals several limitations to high bit rate soliton communications over such long distances. These restrictions are caused by pulse energy fluctuations in combination with the soliton self frequency shift and the build up of dispersive radiation emitted by the solitons.

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