Optical connectors: Common plug types and trends
Megahh expanded beam technology: Multi-fibre connectors as key components in passive fibre optic infrastructure
Knowledge of the technology surrounding fibre optic connectors
Adequate fibre optic connectors are critical to the performance and reliability of optical transmission lines. Widely used connector types are: LC connector, SC connector, MTP/MPO connector, E-2000 connector. LC connectors are currently the foremost used on the market and have gradually replaced the SC type in recent years(Megahh expanded beam technology). MTP/MPO as multi-fibre connectors are mainly utilized in data centre infrastructures. The E-2000 finds its home primarily in typical telecommunication network environments. additionally, new designs like very small form factor connectors and innovative concepts such as “expanded beam optical” are coming to market.
Optical connectors with “physical contact”
Unlike the above common optical connectors – LC connector, SC connector, MTP®/MPO connector, E-2000® connector – look, they need a common contact principle as the basis. This principle is named physical contact. fairly often appreciated as a PC contact.
Contact principle and characteristics of PC and APC connectors
The optical fibres are fixed during a small precision ceramic pin, called a ferrule, and therefore the end face is subsequently polished during a specially defined process. Inside the connector adapter, these sleeves are cantered on one another and a precisely defined pressing force creates direct physical contact between the optical fibres. additionally, to ferrule tolerances, the polishing process is extremely important to fibre connector quality. This principle exists in two versions: the so-called PC and APC connectors. For PC connectors, the top faces are aligned directly against each other, while for the APC variant, they’re at an 8-degree angle to each other. APC connectors are characterized by high and stable return loss. this is often an increasingly important parameter, especially for high-speed applications.
Cleanliness factor and proper handling of fibre optic connectors
However, one challenge remains: potential contamination of the connector face! Possible effects are higher insertion loss – especially for single mode fibres – also as reduced return loss, which within the worst case can lead to complete link failure. additionally, there’s a risk of permanent damage to the polished face if they are inserted dirty. Then the whole connector needs to be replaced. For of these reasons, there are comprehensive guidelines for handling fibre optic connectors.
The most important thing is: The PC and APC connectors can only be inserted if they are absolutely clean. Therefore, all fibre optic connectors must be checked for cleanliness employing a special microscope before connection. If they’re soiled in any way, they need to be carefully cleaned. then, their cleanliness is checked again. only the front sides of the connectors are completely clean can they be inserted. In some cases, this process is often quite laborious and time-consuming.
Optical connectors supported the principle of expanded beam technology
For this reason, another concept of fibre optic connectors was developed a while ago. which uses the principle of an expanded bundle. that’s why they are called expanded couplings. Here collimating lenses are attached ahead of the sleeve or directly in front of the fibre. which on one side expands and parallelizes the sunshine beam and on the opposite side focuses it back into the fibre (see figure). What does this achieve? The expansion of the beam significantly reduces the effect of dirt particles. additionally, there’s no physical contact of the end surfaces, which reduces the danger of damage to the end surfaces by dirt.