This article explores the different types of Fiber Optic Sensors, their working principles, and various applications. A fiber-optic sensor is a sensor that uses optical fiber either as the sensing element ("intrinsic sensors"), or as a means of relaying signals from a remote sensor to the electronics that process the signals ("extrinsic sensors"). Fibers have many uses in remote sensing. In 2023, a group from California Institute of Technology, collaborating with Google, achieved the world's first commercial submarine cable-based second-level. Jose Miguel Lopez-Higuera: Handbook of Optical Fiber Sensing Technology, John Wiley & Sons, 2002. P 603 Radiation absorption excites an orbital electron to a higher energy level.