Jumper insertion loss analysis

Patch cable insertion loss is a relative measure of power reduction when additional passive components are added to an optical path. Therefore, measuring insertion loss is a two-part process - measuring the power through the reference source, and then measuring the power after insertion into the DUT. The difference is IL.

The loss of an unmated fiber optic connector can be estimated mathematically but cannot be measured, only the connection of a pair of mated connectors.

In a real measurement setup, a test fiber is used to transmit (and sometimes collect) light to (from) the device under test. Therefore, the quality of these test fibers is directly related to the IL reported by the DUT, since the test fiber is always part of the connection under test. Unfortunately, it is not possible to divide the measured test connector/DUT connector loss in any meaningful way and assign part of the loss to the test fiber and the rest to the DUT. If the test connector were perfect in every detail, all losses would be due to the DUT, but no fiber optic cable would be perfect, and all fiber optic connectors would introduce some loss, albeit small, including the test fiber.

A significant portion of connection loss is due to a mismatch in one or more geometric parameters of the fiber optic connector. Consider "transverse core offset", where the core and sleeve are not perfectly concentric. If the mating connectors have a different offset or are offset in a different direction, some light will be directed into the cladding and lost. This shift can be due to a misaligned fiber, a bad ferrule with the fiber hole off-center, or debris from poor assembly pushing the fiber to one side of the ferrule hole. For a single mode connection, an offset of 0.3 microns will result in a loss of approximately 0.4 dB

An important aspect of the skew loss of a pair of connectors is that it is not a simple scalar quantity, but depends on the direction of skew. If the offsets are of the same magnitude and direction, the cores will match and the losses may be small, but the opposite direction will produce high losses.