Planar ion-exchanged waveguide lasers in glass
This thesis describes the realisation of integrated optical sources in rare-earth doped glass substrates using ion-exchange planar waveguide fabrication technology. The planar configuration offers the possibility of photolithographic definition of complex multiple-cavity devices, of monolithic integration of devices such as modulators for switching and tuning, and for mass production. A process to introduce rare-earth ions into ion-exchangeable glasses was developed, and used to fabricate neodymium-doped BK-7 glass substrates. Techniques for design, fabrication and characterisation of potassium ion-exchanged waveguides for laser applications in these substrates are described. The properties of waveguides in a substrate doped with 1.5wt.% neodymium oxide are presented. A method to form laser resonators incorporating ion-exchanged waveguides is described. Single- and multiple-cavity waveguide lasers operating in single transverse mode at both pump and lasing wavelengths have been demonstrated and their characteristics are presented. The factors affecting lasing thresholds of the single-cavity lasers were investigated, and devices with thresholds low enough to be pumped by a single-stripe laser diode were realised. A theoretical model for the analysis of optical multiple-cavity resonators is developed. These resonators are shown to exhibit frequency selecting properties that may be exploited to realise multifunctional sources. The potential of the planar configuration was demonstrated by integrating Y-junction multiple-cavity waveguide lasers and monolithic thermo-optic phase modulators. These lasers have been line-narrowed, tuned in wavelength, and Q-switched by applying modulation voltages to the thermo-optic modulators.