Fiber optic temperature sensors operate based on changes in light properties as it travels through the fiber. Suitable for long-range distributed temperature sensing. Fiber-optical thermometers can be used in electromagnetically strongly influenced environment, in microwave fields, power plants or explosion-proof areas and wherever measurement with electrical temperature sensors are not possible. We demonstrate, in. Fiber Bragg grating (FBG) sensors have emerged as advanced tools for monitoring a wide range of physical parameters in various fields, including structural health, aerospace, biochemical, and environmental applications. It is known that the index variation along the major axis of the fiber can induce the coupling of counter-propagating modes at the Bragg wavelength (.