Highly Sensitive and Tunable Intensity-Modulated Chirped FBG Sensor With Extended Measurement Range

A highly sensitive intensity modulated Fiber Bragg Grating (FBG) interrogation scheme is proposed that integrates compact design with elevated sensitivity and expanded measurement range. The method employs a chirped FBG(CFBG) whose spectral characteristics are tailored through the application of positive and negative temperature gradients. The influence of both positive and negative temperature gradients on the designed CFBG has been systematically investigated. By applying a suitable temperature gradient, the same CFBG structure yields multiple sensitivity levels without altering grating parameters or interrogation methodology. Sensitivity is further boosted by differential interrogation at opposing edges of the FBG reflection spectrum. The proposed approach enables tunable sensitivity spanning from 0.18 dB/με to 1.4 dB/με, while maintaining the same grating structure and interrogation methodology. The proposed technique provides ninefold improvement in sensitivity compared to standard single edge interrogation technique, achieving a high sensitivity of 1.4 dB/με with strain resolution of 0.007 με. The measurement range is expanded by aligning the interrogation wavelengths such that the effective operating regions of the CFBG overlap, enabling continuous strain tracking. The proposed scheme also offers inherent temperature compensation. Owing to its simplicity, tunability, and high sensitivity, the technique is well suited for microstrain and small-amplitude dynamic monitoring applications.