Expanded beam fibre-optic cable assemblies operate in harsh environments

October 18, 2017 // By Julien Happich
Fibre-optic cables have been used in outside broadcast installations since the 1990s but, as the industry makes the transition to 4K and UHDTV there is a greater reliance on using them outdoors.

For TV studio and internal outside-broadcast vehicle conditions, various traditional standardised butt-joint fibre-optic connection technologies are increasingly preferred to copper types, as they offer improved bandwidth signal handling over larger distances and different signal types can be multiplexed over a single fibre-optic cable. In an expanded-beam connector, the diameter of the optical beam is expanded by approximately 40 times, and this expanded beam is coupled into the opposite connector before being collimated back down to the original beam size and re-coupled into the fibre. Since the beam size is expanded by as much as 40 times, the influence of a 0.02 mm piece of dirt between a pair of ceramic ferrule-based connectors is reduced by 40 times in a pair of expanded-beam connectors.  It is this effect of collimating and greatly increasing the optical beam diameter that results in the connector being less sensitive to small particles of dust or other contamination, which could completely obscure transmission in butt-joint type connectors. 

The aluminium shell housings of these expanded-beam fibre-optic connectors have a hermaphroditic mating design which means that there is no possibility for mismating. As a result, they allow easy “daisy chaining” of end-to-end terminated cable assemblies in accordance with the allowable power budget. This means that multiple mating can be achieved, supporting repeated temporary outside-broadcast field installation conditions to an IP 68 protection degree.

Such expanded-beam FO cable assemblies can be safely applied even in the harshest of conditions. Even if the unmated open face of a lensed connector is totally immersed in mud, this will cause minimal damage to the optical faces within the insert. The open connector can be rinsed in water before drying the inner optic faces and wiping them clean with a cloth or tissue. Daisy-chain and through bulkhead I/O cable assemblies are supplied with fitted covers. 

The aluminium shell housings and covers have a shock-protected rubber boot, and the interlinking fibre-optic cable includes an