Power scaling and thermal effects in microwave and photonic devices

Many industrial and research realities have to face the power scaling impact on a wide range of devices and applications. During this Ph.D. project, numerical simulations, analysis and experimental activities have been performed in order to investigate the thermal effects due to the high power demand in electromagnetic devices. In addition, study and development of proper cooling systems, aimed at limiting the detrimental heat load effects on different components, have been carried out. The present work is divided into two main sections: the first one deals with the development activities conducted in collaboration with an Italian company, leader in the production of household appliances; the second one concerns the research activity carried out in the academic context. Within the company, a new microwave generation system for domestic ovens is studied and developed. It involves the use of an inverter, instead of a transformer, for driving the magnetron, the actual microwave generator. The standard transformer works at a single power level, which is regulated by switching pulses. In contrast, the inverter technology can linearly control the microwave output power. This allows more precise cooking and a better defrosting quality. A drawback of the inverter system is its sensitiveness to high temperatures, due to the high power demand during operation and to the oven environment. The temperature distribution on the inverter components is analysed and a proper cooling system, that allows their correct operation in all conditions, is developed. In parallel, the research group of applied electromagnetics of the University of Parma is studying the effects of high power demand in fiber lasers. High power fiber laser operation is illustrated and the onset of the transverse mode instability (TMI) detrimental phenomenon is described. Different strategies to increase the TMI threshold, based on fiber geometry variations, are listed. A new class of fiber lasers, based on photonic crystal fiber (PCF), is introduced to overcome these limitations. Three different types of fibers, Symmetry-free PCFs, Fully-aperiodic PCFs and Multi-core PCFs, characterized by specific geometries and guiding properties, have been analysed. For this purpose, a modal solver based on the finite element method is used, together with a custom-developed software. The fibers are thermally simulated, both individually and as part of an optical amplifier, and their maximum thermal load is defined, considering different cooling conditions.