Theses and Dissertations

Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

Hamidreza Ramezani

Second Advisor

Nikolaos Dimakis

Third Advisor

HyeongJun Kim


Periodically refractive index modulation has been known as a novel method to introduce non-reciprocity in optical lattices inspiring many works to propose on-chip optical components such as optical insulators and amplifiers. This type of modulation by coupling two waveguide propagating modes, let them exchange a population called photonic intraband transition. This modulation type also can be applied to the imaginary part of the refractive index, which perturbs the absorption in the waveguide. Non-hermitian physics is a promising field that studies physical effects in such systems without energy conservation. These systems have degeneracy points called Exceptional points in which two or more eigenvalues and their corresponding eigenvectors coalesce, in contrast with Hermitian systems which eigenvectors are always perpendicular. This thesis investigates the effects of operating a complex modulated waveguide at exceptional points to propose new on-chip optical devices theoretically. The main result of this operation is asymmetric coupling between two modes in which the population transfers only from one mode to another, not vice versa. The first device proposed in Chapter 2 is a modulated waveguide with a specific modulating function that causes robust frequency conversion in the GHz regime. This robustness refers to the sustainability of the amplitude and phase of the converted light against geometrical disorder. Also, in Chapter 3, multifrequency logic gates have been proposed, the first multifrequency logic gate in linear media. The modulating functions for those devices are set to operate the system at an exceptional point independent of geometrical parameters.


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