insertion loss (wiring) (IL)
The term insertion loss (IL) is used equally in high- frequency technology and in lightwave technology. It is a logarithmic measure, expressed in decibels( dB), of the attenuation caused by a quadripole inserted into the transmission medium or link.
Such a quadripole may be an RF connector or contact, a filter, coupler, bias tee, crossover, FO connector, splice, or any other component that attenuates the signal being transmitted. Insertion loss always refers to a specific frequency or wavelength range.
In the case of FO links, the distance between the ferrules with the two optical fibers and the FO end face are directly included in the insertion loss. To keep this as low as possible, most optical fibers are ground slightly curved at the ends and have a direct contact, the Physical Contact( PC), with the second optical fiber. Worse values are achieved by fiber ends with oblique ground coupling, which, however, do not reflect the reflected light pulses back into the fiber.