Electromagnetic Interaction and Thermal Behavior of Optically Excited Silicon in Microwave Environments

This dissertation delineates the design, simulation, and experimental outcomes of a novel isolator technology that attenuates low power (~16 mW) Ka-band microwaves by optically modulating the electromagnetic properties of an in-waveguide semiconductor (silicon) element with a 915 nm fiber laser. Three distinct geometries were devised that facilitate microwave attenuation, either by reflecting or absorbing incident microwaves, depending on the specific geometry. The unilluminated insertion loss and input return loss of each geometry was measured using a vector network analyzer, while a heterodyne detection scheme was used to capture the transient attenuation of the illuminated devices. The experimental outcomes of each isolator was compared to a multi-physics model developed in COMSOL. Reasonable agreement was observed between the measured and simulated microwave characteristics for each device. Furthermore, a theoretical analysis of the electromagnetic and thermal behavior of a semiconductor-based isolator in a high-power microwave (1 MW) and optical (up to 10 kW) environment is presented. Utilizing COMSOL, two experimentally tested geometries were geometrically scaled to operate at S-band in simulation. The heat generated in the bulk of the semiconducting material from optical, internal, and microwave sources, along with intrinsic, thermally-driven, and excess, optically generated, free carrier populations were modeled; Additionally, dynamic phenomena such as field-dependent free carrier mobility, thermal dilation of the semiconductor bandgap, and temperature-dependent thermal conductivity of the material were accounted for. This comprehensive approach enabled a detailed assessment of heat's impact on the device's electromagnetic behavior and provided valuable insights into the viability of semiconductor devices in high-power contexts.

Embargo status: Restricted until 09/2024. To request the author grant access, click on the PDF link to the left.