Optical fiber sensor is an amplifier-separated photoelectric sensor. There are also through-beam type, retro-reflection type and diffuse reflection type in optical fiber sensor. The function of fiber optic sensors is somewhat similar to that of photoelectric sensors, which can detect the presence of objects from a long distance. The difference is that the size of the optical fiber sensor is smaller than that of the photoelectric sensor, and the spot diameter is much smaller than that of the photoelectric sensor.