This article explores the different types of Fiber Optic Sensors, their working principles, and various applications. In 2023, a group from California Institute of Technology, collaborating with Google, achieved the world's first commercial submarine cable-based second-level. Fiber-optic sensing (FOS) technology has emerged as a cutting-edge research focus in the sensor field due to its miniaturized structure, high sensitivity, and remarkable electromagnetic interference immunity. Compared with conventional sensing technologies, FOS demonstrates superior capabilities in. 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.