IAN LANG ELECTRONICS

Optoelectronics

Splicing Cables.

 

The term splicing refers to joining together, and in this case we are joining two lengths of cable. Where two runs of cable need to be joined we have a choice of methods of splicing. We can either use mechanical couplers or weld the cable together. In either case we must first cleave and polish the core of the cable, and the angle of the cleave is important for if the adjacent ends are too imperfectly matched then we change the intermittent refractive index causing loss of power or transmission. We have to be careful of Fresnel reflection, which will send light back down the way it has come, and not overpolish the ends; and the two cores (though not necessarily the cladding) must be aligned correctly. In welding together  two lengths of cable, it is necessary to align the core(s) together correctly. In general cables are welded by electro-mechanical means, and the cleave, polish alignment and spark processes are either fully or semi-automated. The process costs a great deal of money, but for trunks of many cables it can be a great deal cheaper than using mechanical couplers. A mechanical couple is usually known as a couple rather than a splice but it really does not matter if the term is misused.

A popular method of coupling mechanically is to use an expanded beam connector, as shown below.

This system uses a pair of plano-concave lenses as they are quite simple and less costly. As can be seen, the light from the input, regardless of the direction it takes on leaving the end of the fibre, is guided to the end of the output fibre. Using expanded beam connection to splice together two lengths of cable means that slight positional variations can be tolerated without suffering a loss of efficiency in the transmission.  You cannot do this with a welded joint; such a splice must be a butt joint where the cables are connected directly to each other.

 

In summary for small systems a mechanical coupling is to be recommended, for large trunks a welded splice.

 

 

 

This is the end of the OTX Aspects Section. Written by Ian Lang, Oct 2010: Last update 2010

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