Fiber optic cable has a small bend angle
The light stays in the core because of total internal reflection: the cladding around the core has a lower refractive index, so light bounces back inward at shallow angles. Bending of a fiber optic cable can damage the cable if the curvature of the bend is too small. Damage may not always be obvious, like a kink in the cable, but may include broken fibers, fibers with higher loss due to stress and cable structural damage that may lead to reliability problems. Proper bend radius control ensures the integrity of optical performance and protects the glass. As the bending becomes more acute, more light leaks out (shown in the picture below).
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