There are several types of detection methods with fiber optic sensors, including thrubeam, reflective, retro-reflective, and definite-reflective. Each method uses an LED or other light source for non-contact detection. This prevents damage to both the target and the sensor. Finally, in 1678. A fiber optic sensor measures a physical quantity by modulating the intensity, spectrum, phase, or polarization of light traveling through the optical fiber system. Think of it like a photoresistor, which changes its resistance based. A fiber-optic sensor is a sensor that uses optical fiber either as the sensing element ("intrinsic sensors"), or as a means of relaying signals from a remote sensor to the electronics that process the signals ("extrinsic sensors").
[pdf] Optical fibers can be used as sensors to measure, , and other quantities by modifying a fiber so that the quantity to be measured modulates the,,, or transit time of light in the fiber. Sensors that vary the intensity of light are the simplest, since only a simple source and detector are required. A particularly useful feature of intrinsic fiber-optic sensors is that they can, if required, provide distributed sensing over very large distances.
[pdf] 
