A light diffusing fiber including one or more segments, and a thermochromic coating on at least a portion of the light diffusing fiber. The thermochromic coating is opaque at a first temperature, and is transparent at a second temperature. A system for detecting the temperature of an apparatus including the apparatus, a light diffusing fiber thermally coupled to the apparatus, and a light source optically coupled to the light diffusing fiber. A method for detecting the temperature of an apparatus including thermally coupling a light diffusing fiber to the apparatus, optically coupling a light source to the light diffusing fiber, and monitoring the light diffusing fiber for transmitted light.