When an optical fiber is subjected to a large bend with a bend radius comparable to its core diameter, its transmission characteristics change. A large number of conduction mode is converted into radiation mode, no longer continue to transmit, but into the cladding is absorbed by the coating layer or cladding, thus causing additional loss of the fiber. There are two types of bending losses in optical fibers as follows.
1. macrobending loss
2. Micro-bending loss
If the radius of curvature of the fiber bend is too small, it will cause a change in the propagation path of light, so that light penetrates from the core to the cladding, and may even leak outward through the cladding. Under normal conditions, light propagation in the fiber along the axial direction of the constant Lu should meet: n2ko < β < nko. When the fiber is bent, the light is transmitted in the bent part, to keep the same phase of the electric and magnetic fields in a plane, the closer to the outside, the greater its speed will be. When it reaches a certain position, its phase velocity will exceed the speed of light, which means that the conduction mode will become the radiation mode, so that part of the eastern power of the light will be lost, which means that the attenuation will increase
