When characterizing “connector” loss it must be realized that a measurable connector “insertion loss” value can only occur when two connectors are inserted into a fiber optic adapter (also known as a “sleeve” or “bulkhead”) forming a connection or connector pair. To be able to judge whether a fiber optic cable plant is good, one does a insertion loss test with a light source and power meter and compares that to an estimate of what is a reasonable loss for that cable plant. These test kits are designed to allow testing of all parameters of fibre optic networks, including output power levels from the fibre, coupled source power and. To measure the insertion loss of a single-mode fiber optical device, follow these steps to ensure accuracy and reliability: 1.