High wavelength stability fiber Bragg grating filter based on nonlinearity correction of thermal effects

Fiber Bragg grating (FBG) filters should have stable temperature sensitivity across the full range, especially near zero. However, it is hard to achieve due to overlooked nonlinearity influences of thermal effects characterized by the thermo-optic and thermal expansion coefficients. To address this, this paper introduces nonlinearity into the design of a bimetallic structure FBG filter. Theoretical analysis shows temperature sensitivity is approximately linear when considering nonlinearity, but constant if ignored. The wavelength shift varies parabolically with temperature, with optimal stability near the vertex. Adjusting the structure size controls the stable temperature region. Experiments validate the model, and this paper realizes a highly stable FBG filter with a maximum wavelength shift of 0.25 pm and sensitivity of 0.025 pm/°C in the 55-65°C range. This study provides theoretical and experimental guidance for optimizing FBG filter stability.