Comparison of local mode shift and cut-off wavelength shift for demodulation of tilted fibre bragg grating sensors

Authors

  • Sławomir Cięszczyk Department of Electronics and Information Technology, Lublin University of Technology, ul. Nadbystrzycka 38A, 20-618 Lublin, Poland
  • Krzysztof Skorupski Department of Electronics and Information Technology, Lublin University of Technology, ul. Nadbystrzycka 38A, 20-618 Lublin, Poland
  • Patryk Panas Department of Electronics and Information Technology, Lublin University of Technology, ul. Nadbystrzycka 38A, 20-618 Lublin, Poland
  • Martyna Wawrzyk Doctoral School, Lublin University of Technology, ul. Nadbystrzycka 38D/406, 20-618 Lublin, Poland

DOI:

https://doi.org/10.24425/mms.2025.154680

Keywords

tilted fibre Bragg grating, fibre optics sensor, refractive index

Abstract

Tilted fibre Bragg gratings (TFBGs) have a characteristic transmission spectrum in the form of a fine comb of cladding mode resonances. This spectrum changes significantly when the sensor is immersed in a substance with a specific refractive index (RI) value. Surrounding RI (SRI) values can be derived from the global shape of the entire cladding mode spectrum or the local shape of a single mode. In this article, we present comparisons of two types of TFBG spectra demodulation methods for SRI determination. The first approach to determining the SRI is based on the local wavelength shift of a single mode and a group of cladding modes. As a modification, a differential method of analysis of two modes and two groups of modes (spectral bands) was proposed. As a result, differential methods with better resolution and linearity were obtained compared to single-mode analysis. To determine the local shift, the centroid, fast phase correlation and cross-correlation methods were used. The global spectrum analysis method with cut-off wavelength determination was used as the other type of demodulation method. The cut-off wavelength shift was determined using the maximum derivative method of the smoothed absolute value of the derivative of the optical spectrum. The best resolution for SRI determination with the local method was 2.4 · 10-5 RIU, while for the global method it was 1.75 · 10-5 RIU for the SRI measurement range of 1.333 to 1.361 RIU.

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Published

2025-09-30

How to Cite

Cięszczyk, Sławomir, et al. “Comparison of Local Mode Shift and Cut-off Wavelength Shift for Demodulation of Tilted Fibre Bragg Grating Sensors”. Metrology and Measurement Systems, vol. 32, no. 3, Sept. 2025, pp. art. no. 9, 1-14, doi:10.24425/mms.2025.154680.

Issue

Vol. 32 No. 3 (2025)

Section

Articles