Date of Award

3-10-2025

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

First Advisor

Prof. William Whelan Curtin

Second Advisor

Dr. Ganga Chinna Rao Devarapu

Third Advisor

Prof. Antonella D'Orazio

Abstract

This thesis introduces advanced nanophotonic integrated devices aimed at improving miniaturized, cost-effective multi-gas detection and on-chip spectroscopic systems. Traditional spectroscopic techniques often require bulky optical components and multiple detectors, limiting their scalability for multi-gas sensing. The proposed integrated duplexers and triplexers enable switching between lasers to detect multiple gases using a single system. The work focuses on the design and optimization of broadband angled multimode interference duplexers, directional coupler-based duplexers, and cascaded directional coupler-based triplexers for combining spectroscopically relevant wavelengths in the near-infrared region. The target gases include ammonia, methane, and carbon dioxide. Through comprehensive simulations and experimental investigations, the proposed on-chip designs demonstrate superior performance compared to existing solutions and have a unique advantage in terms of smaller footprint and improved coupling efficiency. DC-based duplexer has been successfully integrated with laser and GRIN lens components, resulting in a ready-to-use module for multi-gas sensing applications.

A semi-integrated photonic sensing system is presented, exploiting on-chip waveguides with Quartz Enhanced Photoacoustic spectroscopy and Light induced thermoelastic spectroscopy (LITES). Side-polished optical fibers are explored to enhance light-matter interaction path when detecting water vapor and methane gases using LITES method. To further improve integration of integrated nanophotonic devices with spectroscopic devices and to enhance lightmatter interaction, a novel wave confinement approach is introduced using high-contrast grating hollow core waveguides. These waveguides feature a reflective surface that maintains high transmission while allowing gas flow through the sidewalls, making them particularly suitable for gas spectroscopic applications. They are specifically optimized for methane sensing at a wavelength of 3.27 μm. The final goal of this thesis is to develop a complete system that integrates a multiplexer with integrated lasers and high-efficiency interaction pathways, such as hollow core waveguides, into a spectroscopic device. This compact and integration-friendly design holds great promises for enabling the development of portable, high-precision, and realtime multi-gas sensing devices for applications from industrial, agricultural to environmental monitoring.

Access Level

info:eu-repo/semantics/openAccess

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