Attenuation refers to the amount of signal loss as it travels down the fiber, typically expressed in dB/km. Losses can be caused by scattering, absorption, dispersion & bending. It is strong in the ultraviolet (UV) region and in infrar. Optical fiber coupling is the process of efficiently transferring light energy from one optical component into a receiving optical fiber, or between two separate fibers. This transfer involves channeling the light, which carries data, from a source such as a laser or LED directly into the hair-thin. There are many factors that cause fiber attenuation, but the cause is nothing more than the inherent loss of the fiber or when the fiber is bent, part of the light in the fiber will be lost due to scattering, resulting in loss.
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