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Title:Non-reciprocal light transmission in integrated photonic systems via acousto-optic interaction
Author(s):Sohn, Donggyu Benjamin
Director of Research:Bahl, Gaurav
Doctoral Committee Chair(s):Bahl, Gaurav
Doctoral Committee Member(s):Vlasov, Yurii; Sinha, Sanjiv; Fang, Kejie
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Integrated photonics
Abstract:Photonic integrated circuits (PICs) are a promising enabling technology for high bandwidth communications and sensors. Presently, all key optical components including lasers, waveguides, and modulators can be mass fabricated on a PIC using foundry-based manufacturing. However, essential non-reciprocal devices such as optical isolators and circulators are not yet available. Commercialized off-chip non-reciprocal systems are primarily based on Faraday rotation in magneto-optic materials. This approach is challenging to implement in integrated photonic systems due to several reasons; the required materials are not available in foundries; each operational wavelength band needs a different material; localization of magnetic field is difficult in PICs and can affect magnetically sensitive systems. One possible solution is the use of spatio-temporal modulation to produce non-reciprocal effect. For instance, a medium can be modulated by a traveling wave so that light propagating in opposite directions experience non-reciprocal frequency and momentum shifts. These "momentum biased system'' do not require special magneto-optic materials and can be produced with common dielectrics that are already present in foundries. In this thesis, we extend this idea and experimentally demonstrate non-reciprocal light transmission using acousto-optic interaction in PICs. Co-fabricated electromechanical transducers are used to launch traveling acoustic waves that modulate integrated photonic components. We also show that the direction of non-reciprocity can be dynamically controlled by changing the acoustic wave direction. Using this approach, we demonstrate a reconfigurable non-reciprocal modulator that can be arranged in a multitude of reciprocal and non-reciprocal configurations by means of an external RF input. The methodology demonstrated in this thesis may enable new avenues for direction-dependent signal processing and optical isolation. Finally, I propose an important next step in the practical evolution of these devices -- a linear optical isolator -- that exhibits ideal characteristics of ultra-low forward loss and high contrast.
Issue Date:2020-05-08
Rights Information:Copyright 2020 Donggyu Sohn
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05

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