J. Eur. Opt. Society-Rapid Publ. 2026, 22, 23 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2026016 Available online at: https:// jeos. edpsciences. org
EOSAM 2025 Guest editors: Omar El Gawhary, Stefan Witte, Ignacio Moreno
Review Article
Journal of the European Optical Society-Rapid Publications Fano-like resonance in optical fiber
Vinicius Piaia, Paulo Robalinho, Susana Silva, and Orlando Frazão * INESC TEC – Institute for Systems and Computer Engineering, Technology and Science, 4169-007 Porto, Portugal
Received 24 November 2025 / Accepted 18 February 2026
Abstract. Fano resonances emerge from the coherent interference between a discrete resonant state and a continuum of propagating modes, giving rise to a characteristically asymmetric spectral line shape with heightened sensitivity to minute variations in the underlying physical parameters. This study provides a chronological perspective on the development and increasing implementation of Fano-type effects in fiber-optic technology. Their implementation in fiber Bragg gratings( FBGs) through numerical simulations of resonant Fano behavior. Specifically, a Fano-like response in an FBG can be designed by introducing a tailored phase shift into the grating structure; the magnitude of this phase discontinuity constitutes an effective control parameter for tuning the interference condition and, consequently, the resulting spectral asymmetry. The resonance produces a distinctive, asymmetrical spectral response that is attractive for a broad range of photonic functionalities. Key applications include fiber-integrated sensing – where the enhanced spectral sensitivity supports the detection of changes in refractive index, temperature, pressure, or biomolecular interactions – as well as narrowband filtering and spectral shaping for telecommunications and optical signal-processing systems.
Keywords: Fano-like resonances, Optical fibers, Gratings structures and interferometry.
1 Introduction
In the literature, Fano resonances have been extensively reported across a wide range of photonic systems, underscoring their fundamental importance in controlling light – matter interactions and enabling novel optical functionalities. Representative examples include artificial photonic molecules [ 1 ], Fano lasers [ 2 ], metamaterials [ 3 ], nanophotonic structures [ 4 ], photonic crystals [ 5 ], semiconductor nanostructures [ 6 ], plasmonic nanoantennas [ 7 ], optical switches [ 8 ], all-optical modulators [ 9 ], dielectric metasurfaces [ 10 ], and topological photonic systems [ 11 ], among others. The ubiquity of Fano-type interference across such diverse platforms highlights both the universality and tunable nature of this phenomenon, which continues to attract significant interest for applications in optical filtering, switching, nonlinear photonics, and high-resolution sensing.
Despite these remarkable advances, many existing implementations rely on intricate geometries or complex fabrication techniques, which can restrict scalability and practical deployment. In this context, fiber-based platforms offer unique advantages, combining the inherent merits of optical fibers – such as low transmission loss, compact form factor, mechanical flexibility, and compatibility with existing telecommunication infrastructures – with the enhanced
* Corresponding author: orlando. frazao @ inesctec. pt spectral sensitivity and selectivity enabled by Fano resonances.
This review traces the evolution of research on Fano resonance in fiber-optic systems, revealing a clear trajectory from the first fundamental demonstrations in the mid- 2000s to the emergence of advanced, tunable, and application-driven devices after 2020. It then presents the main structures used to induce Fano resonance in optical fiber devices, such as whispering-gallery-mode resonators, microstructured optical fibers, interferometric devices, and FBGs. To exploit FBG applications, a theoretical model of a Fano-FBG is introduced, which captures the spectral evolution as either the FBG reflectivity or the fiber-end environment reflectivity is varied. Finally, the model is demonstrated in a self-referenced refractive-index sensor as one of the possible applications.
2 Fano concept
A deeper understanding of the wave-like behavior of light has enabled the development of advanced optical technologies. Among the most significant properties exploited in these innovations is resonance, which has played a central role in many of the scientific community’ s major achievements. Resonant cavities constitute the foundation of widely used optical devices, including lasers, Fabry – Pérot
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