Date of Award

5-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical Engineering and Computer Science

First Advisor

Md Selim Habib

Second Advisor

Kanishka Perera

Third Advisor

Naveed Mahmud

Fourth Advisor

Brian A. Lail

Abstract

This thesis presents the design and simulation of an 8-tube single-ring anti-resonant hollow-core fiber for sensing applications, with particular emphasis on methane gas detection at the fundamental absorption wavelength of 3.3 µm. Conventional solid-core silica optical fibers exhibit strong multi-phonon material absorption beyond 2.5 µm, rendering them fundamentally unsuitable for efficient light guidance and direct gas sensing at mid-infrared wavelengths. Anti-resonant hollow-core fibers overcome this limitation by guiding light predominantly through an air-filled hollow core via the anti-resonant reflecting optical waveguide mechanism, in which the thin silica glass walls of the cladding tubes act as Fabry-Pérot etalons that confine the guided optical field within the hollow core at anti-resonance wavelengths. The proposed fiber geometry incorporates eight non-touching capillary tubes arranged symmetrically around a hollow core of radius 40 µm, with a cladding tube radius of 20 µm, a wall thickness of 1900 nm selected according to the ARROW formula to position the transmission window at 3.3 µm, and an inter-tube gap of 2.5 µm. Numerical simulations were performed using the finite element method implemented in COMSOL Multiphysics with the electromagnetic waves frequency domain module, employing a perfectly matched layer boundary condition to accurately model the leaky guided modes of the proposed structure. A comprehensive parametric study investigating the effects of core radius, tube radius, wall thickness, and operating wavelength on the confinement loss characteristics of the proposed design was conducted. The total propagation loss at 3.3 µm was determined to be 273.9 dB/m, with a power-in-core fraction of approximately 0.97 confirming efficient light-gas interaction. Methane sensing performance was evaluated using the Beer-Lambert law in conjunction with absorption data from the HITRAN molecular spectroscopic database, demonstrating a minimum detectable methane concentration of 1 ppm, which is well below the lower explosive limit of 50,000 ppm and confirms the viability of the proposed anti-resonant hollow-core fiber as an effective platform for sensitive mid-infrared methane gas detection.

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Available for download on Thursday, June 18, 2026

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