Analysis of Propagation/Leakage transition of fiber cladding modes for processing of data from dielectric tilted fiber Bragg grating sensors

Measurement: Journal of the International Measurement Confederation. 2025. Vol. 253. Article 117479.

Chubchev E. D., Dolzhenko E. I., K.A. Tomyshev, Nechepurenko I. A., Dorofeenko A. V., O.V. Butov

Tilted fiber Bragg gratings (TFBGs) possess promising characteristics for refractometric purposes. However, their
complex spectral response containing a large number of features makes the sensor’s output relevance highly
dependent on data demodulation and interpretation. We propose a method for processing sensor data based on a
detailed analysis of the system’s behavior during the transition of cladding modes from propagation to leakage
into the environment. We regarded this transition as an exceptional point, which made it possible to obtain an
analytical expression for leakage losses of cladding modes in the proximity of the leakage condition. As a result,
we built a regression model with good performance ensuring the determination of changes in the refractive index
with an accuracy of 2.1 × 10^-5 RIU.

Ключевые слова: optical sensors, exceptional points, Machine Learning, experimental data processing