A digital copy of my PhD thesis entitled "Wavelength Extension in Speciality Fibres," is now available to download. It is a 13.26 MB PDF file which can be found here and eventually on the Imperial College Library website.
Since the invention of the laser and its first application, there has been an almost continuous stream of new applications - many of which require specific laser sources. These applications often require a laser source with a specific power, pulse duration, energy and wavelength. In some cases these demands are easily met, whilst in others they have proven rather more difficult to achieve. Traditionally, wavelength versatility has been limited to the regions for which rare earth or gas gain media are available. These lasers themselves can be used to generate other wavelengths through the nonlinear processes of second and third harmonic generation, as well as sum frequency generation. Despite all of this, there still exists a significant section of the visible and infrared spectrum for which no convenient sources exist. This thesis is concerned with the development of sources in these regions along with broadband sources covering significant portions of the spectrum by themselves.
These new wavelengths are generated in a variety of speciality fibres using either nonlinear processes or new gain media doped into standard silica fibres. Three types of speciality fibre are used: low concentration bismuth doped fibre which provides gain in the 1.0-1.4 um region; photonic crystal fibres; and very high (75%) concentration germanium fibres to generate a laser source at 2.1 um based upon stimulated Raman scattering. Photonic crystal fibres provide high nonlinearities and controllable dispersion which enables the generation of broadband supercontinuum sources based upon the interaction of many nonlinear effects. Each source will be described in depth, with particular attention given to the underlying physics that gives rise to the source. Previous and current limitations will be examined and an outlook of the future development of such sources will be discussed.
Three media files are referenced in chapter 3 of my thesis. These are animations of CW supercontinuum formation generated via simulations. The files are available to view or download via the links below. They are simple animated gifs and should be viewable in any media viewer (such as Quicktime).