Index paste is used to prevent reflections between FO conductors in FO connectors
. The index paste is a transparent gel that has the same refractive properties as the core glass
and is inserted between the connector transitions. The indexpaste creates a reflection-free transition between the core glass, the gel and the core glass.
The index paste is also used when calibrating optical fib res to avoid incorrect measurements caused by an unwanted air gap between two fibre optic ends in fibre optic connectors, which leads to attenuation.