What do diameter differences between spliced fibers indicate on an OTDR?

The diameter differences between spliced fibers can indicate a gain in one direction and a high loss in the opposite direction. When splicing fibers of different diameters, the varying core sizes can lead to misalignment of light traveling through the fibers. This misalignment often results in light being partially lost at the splice, which can cause higher loss in one direction. The OTDR (Optical Time-Domain Reflectometer) is used to measure these losses by sending a pulse of light down the fiber and analyzing the returning signal. In essence, if the fibers have different diameters, the splice loss may manifest differently based on the propagation of the light, leading to the conclusion of uneven gain or loss in opposite directions.

When evaluating the other choices, uniform loss across all splices would not be expected if there are size discrepancies, as that generally indicates efficient coupling at the splice. No significant changes in fiber quality might suggest similar diameters or proper splicing techniques, which would not apply if diameters differ. Improved signal strength in both directions would not accurately describe the behavior of spliced fibers with diameter differences, as that typically presses toward the idea of uniform fibers that exhibit low splice loss.