What causes insertion loss in a connector?
Insertion loss in connectors typically comes from misalignment of the fibers or bent fibers in the connectors. The misalignment comes from eccentricity of the core in the fiber, eccentricity of the hole in the ferrule and most of all the eccentricity of the fiber in the hole. Bending of the fiber typically comes from the fiber being constrained at the back of the connector while the ferrule moves back during mating.
