Abstract
Femtosecond (fs) laser inscription enables fiber Bragg gratings (FBGs) to be positioned beyond the fiber core, including within the cladding, thereby expanding control over modal interactions and directional sensing. These cladding fiber Bragg gratings (CLFBGs) extend FBG functionality through interactions with core, cladding, and evanescent fields. Their operation does not involve fundamentally different grating physics; rather, core-mode, cladding-mode, and coupled-mode responses depend on power distribution, modal overlap with the laser-inscribed refractive-index modulation (RIM), grating position, fiber geometry, modal excitation, and interrogation configuration. This Perspective reviews advances in CLFBG fabrication, optical characteristics, sensing mechanisms, and applications. Cladding-waveguide-assisted, evanescent-field-coupled, and direct cladding-mode-excitation architectures are compared in terms of mechanisms, design trade-offs, and performance, and distinguished from conventional core FBGs and tilted FBGs (TFBGs) regarding directional sensitivity, spectral complexity, environmental interaction, multiplexing, and application suitability. Capabilities in vectorial and multiparameter sensing, including curvature, bending direction, torsion, acceleration, temperature, and environmental monitoring, are discussed. Challenges including limited reflectivity, birefringence-induced distortion, multiplexing constraints, fabrication repeatability, and long-term stability are assessed alongside mitigation strategies involving plane-by-plane inscription, mode-field-engineered fibers, hybrid distributed interrogation, and data-driven demodulation. This Perspective outlines pathways toward reliable, multifunctional, multiplexed, and distributed sensing in harsh environments.
Recommended Citation
K. Dey et al., "Femtosecond-Laser-Inscribed Cladding Fiber Bragg Gratings: Architectures, Design Trade-Offs And Future Sensing Opportunities," Laser and Photonics Reviews, Wiley-VCH Verlag; Wiley, Jan 2026.
The definitive version is available at https://doi.org/10.1002/lpor.71860
Department(s)
Electrical and Computer Engineering
Publication Status
Open Access
Keywords and Phrases
cladding fiber Bragg gratings (CLFBGs); dense multiplexing; evanescent-wave coupling; femtosecond (fs) laser micromachining; fiber-optic sensing; vector sensing
International Standard Serial Number (ISSN)
1863-8899; 1863-8880
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2026 Wiley-VCH Verlag; Wiley, All rights reserved.
Creative Commons Licensing
This work is licensed under a Creative Commons Attribution 4.0 License.
Publication Date
01 Jan 2026
