Abstract
Open-fiber Fabry–Pérot microcavities provide a compact and versatile platform for enhancing light–matter interaction, yet their practical deployment is often limited by fabrication complexity, alignment sensitivity, and environmental instability. This thesis presents the design, fabrication, and experimental characterization of open-fiber Fabry–Pérot microcavities based on CO₂-laser-fabricated concave mirrors formed directly on single-mode fiber end faces.
Using a pulsed CO₂ laser micromachining process, concave micro-mirrors with radii of curvature around 160 µm and sub-nanometer surface roughness were reproducibly fabricated without lithographic processing or cleanroom facilities. Gaussian-beam analysis and numerical simulations guided cavity geometry selection, established mode-confinement criteria, and evaluated diffraction loss as a function of cavity length and mirror aperture. Both asymmetric plane–concave and symmetric concave–concave configurations were analyzed, with the latter shown to support robust single-mode operation over extended cavity lengths at telecommunication wavelengths.
Open-fiber cavities were assembled and characterized using reflection-based resonance measurements. Free spectral range, resonance linewidth, finesse, and quality factor were extracted through quasi-static piezoelectric scanning. The measured finesse is found to be close to the coating-limited value set by the mirror reflectivities, demonstrating stable cavity operation and quantitatively consistent agreement with theory. These results establish a complete experimental workflow linking mirror fabrication, optical design, and cavity-level performance.
Beyond fabrication and static characterization, this work positions open-fiber microcavities as a flexible experimental platform for probing dynamic cavity phenomena. The sensitivity of cavity resonances to thermally driven fluctuations motivates future studies of Brownian motion in liquid environments, while dielectric mirror coatings are identified as a key tool for engineering cavity response and enhancing optical sensitivity. Together, these results lay the groundwork for compact, robust, and application-oriented fiber-based cavity systems for precision sensing and mesoscopic photonics.
Committee Chair
Lan Yang
Committee Members
Chuan Wang, Janet Sorrells
Degree
Master of Science (MS)
Author's Department
Electrical & Systems Engineering
Document Type
Thesis
Date of Award
Winter 12-2025
Language
English (en)
Author's ORCID
https://orcid.org/0009-0003-9741-8226
Recommended Citation
Ge, Gonghao, "Open Fiber Fabry–Pérot Microcavities Enabled by CO₂-Laser-Fabricated Concave Mirrors" (2025). McKelvey School of Engineering Theses & Dissertations. 1296.
https://openscholarship.wustl.edu/eng_etds/1296