Date of Award
Open Access Dissertation
Doctor of Philosophy in Physics (PhD)
Administrative Home Department
Department of Physics
Committee Member 1
Committee Member 2
Committee Member 3
Durdu O. Guney
The rapid growth of optical communication networks requires monolithic integration of various optical components such as lasers, modulators, detectors, amplifiers. Optical feedback due to reflected light at the interfaces of several components in a photonic circuit has detrimental effects to the normal operation of laser by increasing noise, forcing laser to oscillate into different lasing modes etc. So optical isolators are crucial components to make complex optical circuits possible by preventing the feedback signal from coupling back to the lasers sources. For this purpose, an optical isolator that can reduce the feedback signal by > 30 dB and at the same time offers very low insertion loss of < 1 dB is desired. Only bulk magneto-optic Faraday rotator-based optical isolators that needs biasing magnets deliver such a performance. However they are not compatible with integrated circuits. Here we present our biasing magnet free thin film optical isolator with ≥30 dB of isolation and < 0.5 dB of insertion loss and also talk about progress towards its integration into semiconductor platforms.
In this quest for on-chip optical isolators, we also present the results of experimentation on a novel physical phenomenon of topological edge mode based optical isolation and localization of the edge mode in a single channel in a system of multiple coupled channels. The localization of the field in a single edge channel for forward propagating light and delocalization of the field for reflected light serves the purpose of an optical isolator with predicted isolation as high as 50 dB. Localization of power as high as 29 dB in single waveguide channel as compared to the power in outermost channel in a system of 7 coupled waveguides has been measured.
Moreover, the formulation of electromagnetic spin-orbit coupling in magneto-optic media as an alternative source of non-paraxial optical vortices is also presented. It shows that magnetization-induced electro- magnetic spin-orbit coupling is possible and that it leads to unequal spin to orbital angular momentum conversion in magneto-optic media evanescent waves in opposite propagation-directions. Generation of free-space helicoidal beams based on this conversion is shown to be spin-helicity and magnetization dependent. We show that transverse-spin to orbital angular momentum coupling into magneto-optic waveguide media engenders spin-helicity-dependent unidirectional propagation.
Karki, Dolendra, "MAGNETLESS AND TOPOLOGICAL EDGE MODE-BASED ON-CHIP ISOLATORS AND SPIN-ORBIT COUPLING IN MAGNETO-OPTIC MEDIA", Open Access Dissertation, Michigan Technological University, 2018.