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"). Fibers have many uses in remote sensing. Depending on the application, fiber may be used because of its small size, or because no
electrical power is needed at the remote location, or because many sensors can be
multiplexed along the length of a fiber by using light wavelength shift for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Time delay can be determined using a device such as an
optical time-domain reflectometer and wavelength shift can be calculated using an
instrument implementing optical frequency domain reflectometry.