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The expande beam connectors transmit the light beam out of the polished fibre head into the lens which expand the standard, small diameter beam into the much larger, parallel beam with the diameter of 0.4 – 1.2 mm. After being transmitted through the air, the expanded beam reaches another lens of the other part of the connector, that focuses the expanded beam into the standard, small diameter beam. There are some types of expanded beam connectors (as CTOS, AXOS) that uses glass flat windows to protect the lenses and keep the transmission line clean.
Thanks to the specific design of the connector, it is possible to reach the following features:


  • No physical contact between the optical parts, whch makes the connector extremely durable against the dust, dirt and sand which can get inside the connector.
  • Larger diameter of the light beam makes the whole system less sensitive to the particles and elemnt within the transmission beam (the same particles which at the normal diameter (50 or 62.5 µm) could stop or dramatically attenuate the signal, have no impact on the beam of the diameted up to 1.2mm.
  • Higher tolerance to the distance between the polished heads of the fibres, so critica parameter in the physical contact connectors. Expanded beam connectors are able to carry transmission even if not fully tight and locked.

The idea of expanded beam connector   Panel side of the CTOS connector as the example of the expanded beam connector, protected with the window.


  • high resistance to dirt, dust and sand
  • water tight
  • easy cleaning
  • no mechanical contact between optical parts, no risk of mechanical impact
  • long life-cycle (large number of mating cycles)
  • hermaphroditic features
  FibreCast connector as example of expanded beam connector without the lens protective window.


  • high insertion loss (0,5 … 2,5dB)
  • lower back reflectance (ok. -30 … -40dB)
  • low number of channels (max. 8)
  • relatively high cost

Radiotechnika Marketing offers the following types and series of expanded beam connectors:

  • AXOS
  • HMAtwo
  • PRLC
  • FibreCast, REBC


Jacek Rzeźnicki