Ultralong continuous wave and ultrafast fibre lasers at telecommunication wavelengths

Résumé

The birth of lasers in 1960 had a strong impact on the development of fibre optics, and consequently on nonlinear optics. Despite the enormous amount of literature concerning fibre lasers, the topic is still actual and thriving and always looking for new solutions addressing the necessities of scientific research and industry for what regards either continuous wave or ultrafast radiation sources. This thesis develops around two research lines, Raman distributed amplifiers, in the form of ultralong Raman fibre lasers, and passive ultrafast fibre lasers, which we will try to combine for the first time. The second order Raman distributed amplifier called ultralong Raman fibre laser has proven its suitability and efficiency in both unrepeatered and long-haul optical communication links. Nevertheless relative intensity noise transfer from pump to signal, especially in the case of high power co-propagating pump necessary to achieve the lowest signal power variation in the amplifier cell, may severely hinder the transmission performances. In the first part of the thesis, a characterization of the relative intensity noise transfer in the cavity and an optimization of the architecture of the amplifier is performed in order to improve the performance in a transmission system. Ultrafast radiation sources have a widespread use and are highly demanded. Mode-locked fibre lasers attract much attention due to their many advantageous features, such as compactness, low-cost, stability and easy handling. In the second part of the thesis, we focus on ultrafast passively mode-locked fibre lasers trying to overcome one of their usual limits, that is the achievement of high peak power and pulse energies in the femtosecond range. Solutions for a simple, inexpensive, polarisation independent, high peak-power passively mode-locked femtosecond ring fibre laser are developed, relying on standard and commercial components and a novel InN-based semiconductor saturable absorber mirror, that ensures self-starting mode-locking. The developed laser system is then applied to the generation of supercontinuum and pulse compression, achieved through the addition of an external reel of single mode fibre to the resonator. Fibres with different lengths and dispersion are employed to test the applicability and tunability of this low-cost, simple system. In the last part, the developed ultrafast laser is used to implement for the first time an ultralong Raman fibre laser into a pulsed laser, with the objective of generating high power ultrashort pulses taking advantage of the virtually lossless and transparent span produced by the Raman cell.