Gallium and titanium diffused optical waveguide devices in sapphire

Abstract

This thesis describes new methods to realise an integrated Ti:Sapphire laser using thermal ionic diffusion. Passive and active waveguides were fabricated by thermal diffusion of gallium and titanium ions in sapphire.Theoretical simulations were established which describe the potential of planar Ti:Sapphire waveguide lasers and intracavity wavelength selection devices. A diffusion study of gallium, titanium and gallium/titanium co-doping is presented; the diffusion coefficient of gallium ions in sapphire was calculated to be 3.3x10-17 m2s-1 at 16000 °C and the diffusion coefficient of titanium ions in sapphire at 16000 °C was found to be 1.7x10-15 m2s-1. Planar Ga:Sapphire passive waveguides were realised by thermal diffusion of gallium ions. The refractive index of sapphire at 800nm is approximately 1.766 and the index change induced by gallium doping was found to be up to 6x10-3 and the mode sizes of the waveguides were as small as 1µm at 488nm. A fabrication procedure based on SU-8 photolithography and ion beam milling was developed for micromachining the surface of sapphire. Using this fabrication technique Ga:Sapphire ridge waveguides were fabricated by diffusion of gallium and exhibited mode sizes as small as 2µm at 633nm. Using the same fabrication technique the realisation of the first Ti-diffused sapphire ridge waveguide lasers is reported. Finally, the fabrication of sapphire optical circuits using titanium and gallium co-doping is described and fluorescence characterisation of these waveguides is given