In this chapter, a temperature sensor is demonstrated based on four different techniques; intensity modulated fiber optic displacement sensor (FODS), lifetime measurements, microfiber loop resonator (MLR) and stimulated brillouin scattering. Fiber-optic high-temperature sensors are gradually replacing traditional electronic sensors due to their small size, resistance to electromagnetic interference, remote detection, multiplexing, and distributed measurement advantages. This paper reviews the sensing principle, structural design, and. This article explores the structure, working principles, advantages, and disadvantages of Fiber Optic Temperature Sensors.