What is a common cause for a gain splice on an OTDR trace?

A gain splice on an OTDR (Optical Time Domain Reflectometer) trace typically indicates that there is a change in the optical signal strength, often at a junction between two different types of optical fibers. A mismatch in the fibers can lead to this phenomenon, as different fiber types can have different core sizes, refractive indices, or numerical apertures. When the fibers are spliced together without proper matching, there can be a significant difference in the light transmission characteristics, causing an increase in the signal (gain) at the splice point.

Having a proper splice requires matching the fibers closely to minimize signal loss; however, if they are mismatched, it can lead to specific interactions at the splice point that may amplify the signal rather than attenuate it. Understanding this principle is crucial for ensuring optimal performance in fiber optic networks.

The other answer choices address issues that could affect fiber performance or lead to losses, but they do not specifically explain the concept of gain splice as directly connected to differences in fiber types. For instance, improper connector alignment and incorrect splice methods typically result in increased losses rather than gain, while excessive bending can create points of signal degradation rather than amplification. Understanding these nuances helps in diagnosing and resolving optical fiber performance issues effectively.