Engineering and characterisation of chalcogenide-based photonic microstructures

Information and communication are playing a growing role in modern society. In this increasingly interconnected and networked world that we live in, it has become critically important to find a way to have faster and more efficient storage and transmission of data. As the network capacity continues to grow, so does the need for fast signal regeneration and switching devices. It seems that electronics and semiconductor technology will not be able to keep up with the growing telecommunication market. The top speed at which integrated electronic circuits can operate is starting to level out. However, by transmitting signals with light rather than electrons, it is possible to obtain a larger bandwidth in both smaller and more energy efficient devices. To achieve this goal it is necessary to control and manipulate the propagation of light through so-called photonic crystals (PhCs). These materials are highly periodic structures with the optical equivalent to the energy gap in semiconductors. PhCs have the potential to address many of the problems that currently limit the speed and capacity of optical communication networks. They represent a new tool for the microscopic engineering of light and thus have recently received great attention in a variety of fields. However, to employ the high technology potential of PhCs, it is crucially important to achieve a dynamical tunability of their properties. As such, it is necessary to turn to PhCs made of nonlinear materials, in which the optical response depends on light intensity. The nonlinearity of optical materials is essential, if we wish to create devices such as optical diodes, transistors, switches, and limiters. The combination of nanophotonics, the application of light in nanometre scale structures, and nonlinear materials promises dramatic improvements in the ability to generate, harness and confine light, and will be the route to compact, energy efficient photonic processors. Photosensitive chalcogenide glasses (ChGs) have recently been utilised as a unique building block for three-dimensional (3D) PhCs because of their high refractive index (high-n), high nonlinearity and high transparency in the near to mid-infrared (IR) region. Such properties are crucial to open 3D complete band gaps with wavelength tunability. The aim of this thesis is to use ChGs as the material platform to generate nonlinear PhCs that can find application in all-optical devices. Towards this goal a fabrication technique is required that can produce high quality 3D woodpile PhCs in ChGs and allows for the introduction of localised defects within the periodic structures, a crucial aspect for the realisation of optical devices. Although several methods have been proposed, direct laser writing (DLW), using a femtosecond laser induced multi-photon process, has proved to be the most convenient, efficient and flexible approach to generate arbitrary PhCs with functional stop gaps....The work presented in this thesis is a step towards the realisation of the photonic chip that operates with photons instead of electrons (as seen in the semiconductor devices of today). The development of nonlinear functional PhCs will find extensive applications in the new generation of all-optical integrated devices. These devices promise to be a platform for ultrahigh speed all-optical signal processing in more compact and higher performance devices.