During maintenance, bending patch cords into sharp angles, forming overly tight loops in cable managers, or overtightening cable ties can all induce micro-bending loss. Unlike backbone cables, patch cords are frequently connected, disconnected, bent, and handled by technicians, making them the most vulnerable. While this was only a minor issue, it greatly affected both the optical alignment and, as indicated by test results in the field, return loss, which ideally should be approximately -65 dB, increased to 20 dB or more because of light reflecting into transceiver modules. The result of feedback at the. Insertion loss (IL) and return loss (RL) are key performance indicators of fiber optic patch cords. Consequently, the optical power budget is quickly consumed, leading to unstable transmission. Whenever a Patch Cord transitions from clean glass to an air gap. Minor end-face contamination or micro-bending loss may not be evident under low load conditions, but as link budgets tighten, ports are replaced, or cleaning procedures are improperly executed, these issues can be amplified-often leading to misdiagnosis as transceiver or port failures. Common. 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.