Flat spectral response arrayed waveguide grating (AWG) in silicon-on-insulator (SOI) via ion implantation.

This thesis proposed and demonstrated a flat-spectral response Arrayed Waveguide Grating (AWG) in Silicon-on-Insulator (SOI). The response exhibits a flat spectral of approximately 0.5nm with a crosstalk level of round -3dB. The high crosstalk is due to the phase errors as a result of fabrication tolerance and errors. Two main errors were identified. Firstly, the systematic errors of waveguide rib width and etched depth and secondly, the random variation of photomask resolution which was subjected to fabrication equipment in Southampton University. These errors have been investigated and the observations of the analysis were consistent with the experimental result. The AWG is designed to operate at a centre wavelength of 1.55mum at a grating order of 52 with path length differences of 23.62mum. The rib waveguides of the array are designed to operate as singlemode waveguides and to exhibit minimum polarisation dependence. As this thesis is to proof of principle, additional optimisation of the AWG is not carried out. The main ideology of the design method is to introduce free carriers to parts of the waveguides across the grating arms to induce absorption. This will modify the shape the field distribution across the array waveguides from a Gaussian to a SINC function. By applying Fourier optics to the free space region of the AWG, this field profile is the inverse Fourier transforms of the required output field of the AWG, which is the flat spectral response. This method gives the robustness of tailoring the optical field distribution across the AWs by the appropriate choice of net doping concentration, and hence gives room for design flexibility without increasing the physical dimension of the AWG significantly. The potential of achieving a smaller SOI AWG device with the use of higher net dosage and the realisation of achieving a uniform doping concentration through multiple implantations has been discussed. Keywords: Arrayed Waveguide Gratings (AWG), Flat-spectral response, Ion Implantation, Rib waveguides, Silicon-on-insulator (SOI), Silicon photonics