Hybrid mode coupling for enhanced sensing and integrated photonics

Braswell, Shaneen Fujie

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https://hdl.handle.net/2142/117881 Copy

Description

Title

Hybrid mode coupling for enhanced sensing and integrated photonics

Author(s)

Braswell, Shaneen Fujie

Issue Date

2020-11-24

Director of Research (if dissertation) or Advisor (if thesis)

Goddard, Lynford

Doctoral Committee Chair(s)

Goddard, Lynford

Committee Member(s)

• Bernhard, Jennifer
• Toussaint, Kimani
• Vlasov, Yurii

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Photonics, grating coupler, sensor

Abstract

In this dissertation, we investigate the hybrid mode-coupling approach to enhance sensing and integrated photonic applications. The coupling of photonic elements is not new; the current demand is to further explore coupling strategies within photonic systems and complementary systems to meet or exceed design metrics and functionality. These strategies include the exploitation of material and structural design to enhance integration and coupling. We studied plasmonic-photonic coupling and high index contrast to enhance resonant and diffractive coupling, respectively. Hybrid mode coupling benefits sensing for real-time quantitation, interrogation of low molecular weight, and nanoscale molecules by using a plasmonic-photonic coupling. A plasmonic-photonic coupling weds the key capabilities of highly localized fields at the metal interface with the resonant nature of high-quality-factor (Q) low-loss microcavities. This new class of hybrid sensor will advance the medical, pharmaceutical, defense, and environmental industries. Conventional biosensing methods are tedious and have a long lead time for response. Furthermore, label-free optical detection of biomolecules does not generate a significant signal for detection. To address these limitations, we engineered a microring resonator-based sensor coupled to two gold concentric rings determined computationally. We report changes in the refractive index of the bulk medium and bio-monolayer at the corresponding sensitivities: 1340 nm/RIU and 105.3 fm/RIU for ∆nbiolayer = 0.2 with a volumetric size of 1.0x103 nm3. The redshift of the resonance due to bulk sensing is a six-fold increase over the conventional micro ring resonator. Subsequently, we designed and conducted an experimental study of a plasmonic chain of gold bowtie nanostructures atop a microring resonator where the splitting of the resonant modes was observed. Likewise, hybrid mode coupling advances integrated photonics applications where there is a demand to increase the performance of interconnects and components. As a requirement of the collaborative effort to build a photonic-electronic integrated circuit for energy-efficient computing, the photonic components had to be CMOS compatible. The grating coupler, a key integration component, is coupled to a vertical-cavity microlaser to power the optical circuit. For practical realization, the coupling is at normal incidence, and the grating coupler is buried within oxide to ease flip-chip integration. To address the aforementioned constraints, we engineered an approach to design a high-efficiency grating coupler based on a high contrast overlay and apodization for fiber-to-chip that yields greater than 90% coupling efficiency over a broad bandwidth. The efficient diffractive coupling mechanism is due to the presence of a dual-layer grating and constructive interference between the grating teeth, i.e., scattering elements when mode matched with the source. Furthermore, we employed S-parameter analysis to determine the theoretical limits of this design. We then applied the approach towards a purely optical polymeric material system to enhance coupling efficiency from 7% to 62%. This work advances our understanding of the coupling mechanisms to engineer devices for enhanced performance in sensing and integrated photonics applications. This works builds upon seminal past work and may serve as a building block for enhanced sensing and integrative, highly efficient photonics systems with unprecedented performance.

Graduation Semester

2020-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2020 Shaneen Fujie Braswell

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