Distributed refractive index sensing with cascaded TFBGs via derivative spectrum analysis.

Cladding modes; Derivative spectra; Grating periods; Mode spectrum; Refractive index sensing; Refractive index sensor; Single point; Spectra analysis; Tilted fiber Bragg grating; Wavelength division; Atomic and Molecular Physics, and Optics

Abstract :

[en] Tilted fiber Bragg gratings (TFBGs) are highly sensitive refractometric probes, but their broad cladding-mode spectra have long been considered incompatible with wavelength-division multiplexing. As a result, TFBG refractive-index sensors are generally restricted to single-point operation, despite their inherent advantages. Here, we demonstrate for the first time that multiple bare, uncoated TFBGs (inscribed with distinct grating periods and tilt angles) can be cascaded within a single-mode fiber and independently interrogated over an 80-nm bandwidth. Although the cladding-mode spectra strongly overlap, we show that first-order derivative spectrum analysis isolates the local slope of each cut-off mode, effectively suppressing the envelope distortions typically induced by upstream gratings. This enables reliable and decoupled multipoint refractive-index sensing, with sensitivities of 52-58 nm/RIU that are fully consistent with intrinsic TFBG performance in aqueous media and remain stable after cascading. The derivative method enhances the demodulation accuracy by up to 65% and preserves linearity (R2 = 0.94-0.98) while maintaining cross-talk below 0.03 nm. These results overturn the longstanding belief that TFBG refractometers cannot be multiplexed, paving the way for compact, low-cost, and scalable quasi-distributed chemical and biological sensing networks based on TFBG arrays.

Disciplines :

Materials science & engineering

Author, co-author :

Zheng, Jieqing ; Université de Mons - UMONS > Recherche > Service ERC Unit - Advanced Photonic

Hu, Xuehao ; Université de Mons - UMONS > Faculté Polytechnique > Service d'Electromagnétisme et Télécommunications

Chah, Karima ; Université de Mons - UMONS > Recherche > Service ERC Unit - Advanced Photonic ; WEL Research Institute, Wavre, Belgium

Caucheteur, Christophe ; Université de Mons - UMONS > Faculté Polytechnique > Service d'Electromagnétisme et Télécommunications ; WEL Research Institute, Wavre, Belgium

Language :

English

Title :

Distributed refractive index sensing with cascaded TFBGs via derivative spectrum analysis.

Publication date :

09 February 2026

Journal title :

Optics Express

eISSN :

1094-4087

Publisher :

Optica Publishing Group (formerly OSA), United States

Volume :

Issue :

Pages :

5459 - 5471

Peer reviewed :

Peer Reviewed verified by ORBi

Additional URL :

https://opg.optica.org/viewmedia.cfm?URI=oe-34-3-5459&seq=0

Research unit :

F108 - Electromagnétisme et Télécommunications

Research institute :

Research Institute for Materials Science and Engineering

Funding text :

Fund for Scientific Research (F.R.S. \u2013 FNRS). The author thanks the technical support of Mariel David.

Available on ORBi UMONS :

since 14 March 2026

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