In General, fiber coating consists of primary coating, secondary or buffer coating, fiber identification, removability of coating.
1 Primary coating
Silica fiber itself has an intrinsically high strength, however surface flaws reduce its strength. A primary coating must therefore be applied immediately after drawing the fiber to size.
The optical fiber should be proof-tested. In order to guarantee long-term reliability under service conditions, the proof-test strain may be specified, taking into account the permissible strain and required lifetime.
In order to prepare the fiber for splicing, it should be possible to remove the primary coating without damage to the fiber, and without the use of materials or methods considered to be hazardous or dangerous.
The composition of the primary coating, colored if required, should be considered in relation to any requirements of local light-injection and detection equipment used in conjunction with fiber jointing methods.
Primary-coated fibres shall comply with relevant optical fibre specifications in [IEC 60793-2-10] and [IEC 60793-2-50].
NOTE – The optical fibers should be proof tested with a strain equivalent to 1 per cent. For certain applications, a larger proof-test strain may be necessary.
2 Secondary or buffer coating
If using a tight secondary coating for the fiber, it, should comply with the requirements given in [IEC 60794-3].
NOTE 1 – When a tight secondary coating is used, it may be difficult to use local light-injection and detection equipment associated with fiber jointing methods.
NOTE 2 – Mechanical coupling between fiber and cable should be carefully designed; a low coupling maycause fiber movement during installation process; a high coupling may cause high fiber stress when cable is bent.
3 Fibre identification
Fibre should be easily identified by colour/tracer/marker or position within the cable core. If a colouring method is used, the colours should be clearly distinguishable and have good colour permanence properties, also in the presence of other materials, during the lifetime of the cable.
4 Removability of coating
The primary and secondary protections should be easy to remove and should not hinder the splicing, or the fitting of fibre to optical connectors