What is a potential problem indicated by an OTDR when fibers are mismatched?

When fibers are mismatched, a gain splice is a potential issue that may be indicated by an Optical Time-Domain Reflectometer (OTDR). A gain splice occurs when there is a significant difference in the refractive index or core diameter between two joined fibers, leading to increased light loss at the splice interface. This mismatch causes the fiber to not effectively transmit all of the light from one fiber to the other, leading to degradation in performance.

An OTDR measures and analyzes the reflected light within the fiber and can detect anomalies such as gain splices, which can manifest as increased loss values in the testing results. Identification of such mismatches is crucial for maintaining optimal performance in fiber optic networks, as they can lead to inefficient signal transmission and reduced overall link quality.