Return Loss Testing

Return loss represents the amount of light that does not get reflected back at a connection point. The higher this loss, then the lower the amount reflected. Therefore, the higher the return loss, the lower the reflection and the better the connection.

Air gaps between two mating fibre cores will cause reflection back towards the light source. Flat polished connectors experience high reflection because the point of contact will not be at the cores, thus causing an air-gap. This sort of connection will cause return loss values in the order of 11dB to 15dB. This type of polish is not suitable for singlemode transmission and is rarely used in multimode transmission systems.

PC connectors are spring loaded so that contact is ensured when mated. This also slightly deforms the ferrule endface to offset any minor endface defects. PC polished connectors also have a convex endface. This insures that the point of contact is at the centre where the fibre core is.

There are three variations of PC polish, each achieving different values of return loss:

PC >30dB represented by /PC
SuperPC >40dB represented by /SPC
UltraPC >50dB represented by /UPC

Fibrepulse polishes all connectors to the UltraPC finish regardless of the specification required so as not to have different quality finishes out in the field. Because Fibrepulse polishes consistently at the higher specification this means that all assemblies are of the quality required for any application even when the system is upgraded.

Fibrepulse tests and records the return loss for 100% of terminated connectors, in accordance with IEC-61300-6. Typical values achieved for return loss are in excess of 55 dB. Angle polished connectors achieve the highest return loss. Because the surface of the connector ferrule is angled (it is also PC polished) any reflections are directed away from the return path to the source. Angle polishes will achieve return losses in excess of 75dB. Angles are generally 8 but can be 9 or 10. It is very important that mating connectors be of the same angle.

Return Loss Diagram

return-loss-diagram