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Tilted fibre Bragg gratings (TFBG) have become a significant type of sensing element,
valued for their high accuracy, resistance to interference, compact size, and relatively low
manufacturing cost. Among the measurable quantities, they can be used to determine the rota‐
tion of the light polarisation plane (LPPR) within an optical fibre. Traditional TFBG‐based
methods rely on monitoring the optical power at a specific wavelength, which limits both
the measurement range and its accuracy. Other approaches use more advanced processing
algorithms that analyse selected parts of the TFBG transmission spectrum using the fast Fourier
transform (FFT) or the discrete wavelet transform (DWT). However, these techniques do not
guarantee consistently high precision across the entire range of angles, because the FFT and
DWT coefficient functions exhibit similar variations with rotation angle.
This work demonstrates that connecting two TFBGs in a cascade and rotating them rel‐
ative to each other produces cladding‐mode minima characteristic functions (MCFs) that
are mutually shifted by the LPPR angle. This shift allows direct incorporation of the minima
values into an algorithm for estimating the LPPR angle from the measured spectrum. Addi‐
tionally, the derived MCF functions show significantly lower noise levels than previously used
FFT‐based or DWT‐based characteristics. This behaviour led to the development of a new
calculation method that operates directly on the recorded spectra. A calibration procedure
was performed using MCF values obtained at 2° intervals over rotation angles from 0° to 180°,
followed by the creation of an algorithm that selects the most suitable MCF functions for
angle estimation. The proposed approach provides consistent measurement accuracy across
the entire 0–180° range and enhances overall stability. Compared to existing techniques,
the method reduces MAE by 2.6% and MSE by 66%.
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