Gap Loss

The power loss that occurs when an optical signal is transferred from one fiber to another that is axially aligned with it, but longitudinally separated from it. The gap allows light from the transmitting fiber to spread out as it leaves the fiber endface. When it strikes the receiving fiber, some of the light will enter the cladding, where it is quickly lost. As a result of signal strength and cohesion being lost (due to the scattering of the light), a fiber optic signal suffering from gap loss is degraded in both quality and throughput. The three basic types of gap loss are angular misalignment loss, lateral offset loss, and longitudinal displacement loss. The losses tend to be proportional to the ratio of the core radius to the size of the gap or displacement.
Gap loss can be reduced by filling the gap with a gel that matches the index of refraction of the fiber as closely as possible.