What might diameter differences between spliced fibers show on an optical time domain reflectometer (OTDR)?

Diameter differences between spliced fibers can indeed show distinct characteristics on an optical time domain reflectometer (OTDR), particularly indicating gain in one direction and high loss in the opposite direction. When fibers with different diameters are joined, this mismatch can lead to an increase in light reflection or scattering at the splice point.

When light travels from a fiber with a larger core diameter to a fiber with a smaller core diameter, some of the light may be reflected back into the original fiber due to the abrupt change in the refractive index profile. This reflects as gain when viewed from the direction of the larger diameter fiber. Conversely, when the light travels in the opposite direction, the transition can cause excessive light loss because the smaller core fiber cannot effectively transmit all the light coming from the larger core fiber. Hence, the OTDR will display high loss in that direction.

Understanding this behavior is crucial for diagnosing issues in the fiber optic network and optimizing performance by ensuring proper splicing techniques that take into account fiber diameter compatibility.