PhD Defence Sergio Vazquez-Cordova

Sergio Vazquez-Cordova is a PhD student in the MESA+ research group Optical Sciences. His supervisor is Jennifer Herek. 

erbium-doped channel waveguide amplifiers in amorphous aluminium oxide and crystalline potassium double tungstate 

The main motivation of this thesis is the development of erbium-doped channel waveguide amplifiers capable of offering high net gain at the telecom C-band (1525− 1565 nm) for its potential integration in optical interconnects. Two erbium-doped platforms, Al2O3 and KRE(WO4)2, are proposed, and different waveguide designs are considered and discussed. Spectroscopic parameters of materials are employed in a rate equation model to estimate the gain. Simulation figures are later compared to the experimental results. Although the application focus of these devices is driven toward the telecommunications industry, amplification of signals (λ ∼ 1.5 μm) can be employed in other areas such as the generation of microwave signals, sensors, imaging such as optical-coherence-tomography, among others.

In Chapter 2 the fundamental physical processes of the interaction of light with rare-earth ions, as well as the inter-ion interaction are described. These theories will later be implemented in the calculations and compared to experimental results presented in following chapters. Chapter 3 introduces the optical characterisation techniques and measurements performed in erbium-doped channel waveguides. The fabrication and design of the channel waveguides in both platforms are presented in Chapter 4. Experimental results and theoretical simulations on the gain of different samples with a variation in doping concentrations in Al2O3:Er3+ long spiral waveguides (> 10 cm) are provided in Chapter 5. These devices are experimentally put under test at various pumping conditions, and the outcome is presented. Furthermore, gain saturation as a result of signal-power increase is studied. Temperature effects on the gain in these devices are also studied experimentally. In Chapter 6 the spectroscopy and gain performance of erbium-doped potassium double tungstate channel waveguides are presented. A time-resolved study reveals the presence of energy-transfer up-conversion processes. Luminescence decays from the first excited state of erbium are studied at different excitation densities for a range of doping concentrations for the determination of the strength of inter-ionic processes. Additional detrimental factors on signal amplification such as pump excited-state absorption (ESA) are investigated in this type of waveguides. Finally, simulations employing the acquired spectroscopic data, suggest the optimal conditions for a high-gain amplifier. Chapter 7 presents the conclusions of this work and suggestions to further steps.