*Fiber Optic Sensing - Principle, Measurement and Applications*

the extrinsic sensing is that the optical fiber just plays as the transmission media, as is shown in **Figure 1(b)**. Both of them are important and are frequently used in temperature sensing, strain sensing, or pressure sensing, depending on which parameters we want to measure. Specifically, intrinsic fiber-optic sensors provide distributed sensing over a long-distance zone [4], and extrinsic sensors can help us reach inaccessible places, for example, the measurement of temperature inside aircraft jet engines and the measurement of the high temperature inside the electrical transformer. Extrinsic fiber-optic sensors provide excellent protection of measurement signals against noise corruption, and they can be used to measure vibration, rotation, displacement, velocity, acceleration, torque, and temperature [5].
