The sensor head is external to the optical fiber and is based on miniature components that are used to modulate the properties of light in response to environmental changes associated with physical perturbations of interest. Fibers have many uses in remote sensing. The light beam travels through the core by. 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. Intrinsic sensors (upper part of Figure 2) directly use an optical fiber as the sensitive material (sensor head) and also as the medium to transport the optical signal with the information measured.
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