Key methods include blackbody radiation, luminescence, fiber Bragg gratings (FBGs), and interferometers. Blackbody methods measure 500-2040°C; FBGs can measure up to 320°C under optimal conditions. Choosing the right method requires balancing measurement range, accuracy, and. Optical temperature sensors are temperature sensors which are based on optical technology — in most cases, on fiber optics. They can be based on different operation principles as explained in the following. There are alternative techniques, in particular electronic temperature sensing. The temperature-dependent change of the refractive indices of the fiber, consequently the shift of its Bragg wavelength, is used as a measure of the temperature.