TSD-2000-4-1-1 OPTICAL FIBRE CABLING: INSTALLATION PRACTICE: SPLICING Issue 3.1
Current specifications for the installation of optical fibre are often needlessly stringent, bearing little relevance to the operational requirements of a cabling system or the practicalities of meeting such a specification. This document defines an approach to, and limits for, commercially viable splice loss specifications whilst ensuring the operational requirements of a cabling system are not compromised.
The approach and limits herein have been developed by analysing the key operational requirements of a typical transmission system. Any given cabling channel will have a defined optical budget – the distribution of losses within that channel being irrelevant providing that the total channel loss is sufficiently low to meet that budget. It is, therefore, not necessary (and even counterproductive) to specify maximum individual splice losses except where the level of loss indicates that there has been a fault in the splicing process (in excess of 0.3dB when splicing “same product” singlemode or multimode optical fibres).
With regard to jointing of singlemode optical fibres this document recognises that although modern fusion splicing machines have been optimised to reduce the splice loss to a minimum, mode field diameter mismatch can still be a major source of splice loss between two singlemode optical fibres. An analysis of the different IEC specifications for singlemode optical fibre shows that fibres within the same generic group can have mode field mismatches that will produce significant splice losses. Monte Carlo statistical modelling techniques used to model splice losses between “same product” fibres, “same generic type” fibres, “different type” fibres and “unknown” fibres show the effect of mode field mismatch on individual and average splice loss.
From these results and from additional data from splicing equipment manufacturers, reasonable and commercially viable average splice loss limits are defined for the various fibre types. Typical levels of rework are calculated where the FIA limits are not adopted, and the cost implications are discussed. A technical checklist of the correct splicing and fibre preparation procedures required is provided to ensure that these recommended maximum splice loss limits are achievable.