Fiber optic sensors can be classified according to several ways. According to the location of the sensor, fiber optic sensors can be divided into intrinsic and extrinsic sensors. In intrinsic sensors, the properties of light, namely intensity, phase, or polarity, change with a directly measured quantity such as temperature. Whereas in the extrinsic sensor, there is a light modulator that transmits information from the measured variable so that there is no direct relationship between light and these variables.1. Intensity-based The intensity / power of the input and output light on the optical fiber is measured to determine the decrease in intensity. This value can be calibrated to determine the value of the measured quantity. Generally applied to temperature sensors and load sensors. 2. Polarization-based Changes in the polarization properties of light are used to detect changes in certain parameters. For example, a stress sensor uses a polarizer and analyzer component to calculate external stress. 3. Phase-based The most responsive sensor is a phase modulation based fiber optic sensor. The phase of a light wave passing through an optical fiber depends on the physical length of the fiber, the length of the optical path, the refractive index and the index profile of light propagation. In figure 4, a phase-based optical sensor is shown with a Michelson and Mach-Zehnder Interferometer. optcal sensor