Thermal gradient estimation with fiber-optic chirped FBG sensors: Experiments in biomedical applications

The measurement of short-scale (sub-millimeter) thermal gradients within 1-5 cm range can have a significant impact on several biomedical applications, including the measurement of effectiveness of thermal ablation, the estimation of blood pressure thermal differences during angioplasty, and fractional flow reserve. In this work, we propose and experimentally validate a technique to measure a thermal gradient with a fiber-optic sensor based on a linearly chirped fiber Bragg grating (LCFBG). The LCFBG spectrum is measured with a white-light setup, and a demodulation of the grating using the coupled mode theory model is used to estimate the thermal gradient. Experiments are reported in a calibration setup for a linear gradient, achieving <;1° C error, and in a laser ablation with a Gaussian-shaped thermal gradient.