(1) Boundary loss
If optical fiber had some irregularity at the core/clad boundary, light is emitted out of irregular parts. This emission loss is boundary loss.
(2) Microbending loss
When unequal stress is applied to optical fiber in the radial direction, the fiber axis can be bent with a relatively small radius of curvature compared with the core diameter. This type of bending is called as microbending. The loss generated by the microbending is microbending loss.
(3) Bending loss
Bending loss is yielded when optical fiber is bent with a large curvature, since the light does not exhibit the total internal reflection at the core/clad boundary, resulting in the partial emission of light out of the fiber. This is due to the fact that the incident angle to the boundary becomes smaller than the critical angle.
(4) Splice loss
Splice loss is due to light leakage or misalignment of fiber axes at the splicing position. The cause of splice loss is mismatching of the core diameter or clad diameters between connected fibers. Recent developments in the fusion splicing technique enabled a low-loss splicing of a couple of different sorts of fibers.