These sensors use light signals to detect physical parameters such as temperature, pressure, strain, and vibration. The performance of fiber optic sensors can be evaluated based on several key factors including sensitivity, accuracy, resolution, linearity, hysteresis . The design of the fiber sensors can take advantage of one or several optical parameters of the guided light, such as intensity, phase, polarization, and wavelength. Radiation absorption creates electronic excited states that are trapped by localized defects for extended periods of time. The black box may contain mirrors, a gas or liquid cell,a cantilevered arm or dozens of other mechanisms that may generate,modu ate or transform a light beam. It's a device that converts light rays into electronic signals. An optical fiber sensing system is basically composed of a light source, optical fiber; a sensing element or transducer and a detector (see Fig.