If there is loss on all fibers in the cable, this is a good indication that the cable is damaged or kinked. Connector Contamination: Single-mode fiber optic cables can be susceptible to connector contamination, which can lead to signal degradation or even complete signal loss. The link appears to be dead and I'm hoping to fix it, but I have little to no experience with fiber. The LED light of the SFP+ ports on both switches are off (not lighting up). Good troubleshooting is a sequence, not a scattershot of tests. Or it could be caused by the quality of the connector itself, such as poor end-face geometry that doesn't pass the parameters defined by IEC PAS 61755-3 standards, including angle of the polish, fiber height, radius of curvature or apex offset.