Fiber optic sensors in the ATLAS Inner Detector

A prototype system of Fiber Optic Sensors (FOS) for the accurate measurement of temperature and relative humidity, has been installed inside the Inner Detector volume of the ATLAS experiment at the LHC. The goal is to evaluate the behavior of the technology against radiation effects, and possibly to assess its suitability for future collider experiments, starting from HL-LHC. It follows the description of the work that has led to the choice of the sensors, their testing and calibration in the laboratory, their successive installation and operation in ATLAS, and the development of the data acquisition chain. The first results on performance are reported.