The principle of operation of a fiber sensor is that the transducer modulates some parameter of the optical system (intensity, wavelength, polarization, phase, etc. Radiation absorption excites an orbital electron to a higher energy level. Heating the material enables the trapped states to interact with phonons and decay into lower-energy. 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"). They can identify color based on the wavelength characteristics of reflected light.
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