Assembly-Free Ball Lens-Enhanced Optical Fiber Sensors for Fluorescent PH Detection and Surface-Enhanced Raman Spectroscopy

Abstract

This work presents a robust, assembly-free ball lens architecture fabricated directly on the end face of multimode optical fibers (MMFs), offering advances in both fluorescence-based pH sensing and surface-enhanced Raman spectroscopy (SERS). In the first application, the ball lens focuses incident excitation light precisely on a thin, dye-coated region at the fiber tip, boosting fluorescence emission for real-time, high-sensitivity pH measurements. Compared to a standard MMF sensor, the ball-lens-enhanced probe generates nearly twice the fluorescence signal under identical conditions, demonstrating improved signal collection efficiency without complex hardware modifications. The focal condition was analyzed and optimized through COMSOL Multiphysics simulations, confirming precise light focusing on the fiber end face. Extending this platform to SERS, the ball lens is treated with a femtosecond laser to produce surface nanostructures, followed by a thin coating of silver-based composite. The resulting textured and metallic surface, combined with the ball lens' inherent focusing properties, localizes the optical field and significantly augments the Raman signal. The streamlined and repeatable fabrication method ensures consistently high sensor performance, facilitating sensitive chemical and biochemical analyses. Overall, the assembly-free ball lens approach on MMFs serves as a solution to advance both fluorescence and Raman-based sensing. The enhanced signal-to-noise ratio, rapid response, and mechanical stability underscore its potential for widespread adoption in biomedical diagnostics, environmental monitoring, and industrial process control.

Department(s)

Electrical and Computer Engineering

Comments

Missouri University of Science and Technology, Grant None

Keywords and Phrases

Composite coating layer; Femtosecond laser micromachining; Fluorescence pH detection; Lens fabrication; Optical fiber sensors; Surface-enhanced Raman spectroscopy

International Standard Book Number (ISBN)

978-151069098-1

International Standard Serial Number (ISSN)

1996-756X; 0277-786X

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 International Society for Optics and Photonics, All rights reserved.

Publication Date

16 Sep 2025

Link to Full Text

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