IEC TR 60825-17:2010 pdf – Safety of laser products – Part 17: Safety aspects for use of passive optical components and opticalcables in high power optical fibre communication systems.
class of laser product
see lEG 60825-1. sections 3.18 to 3,23 for definition of ‘class of laser product’
4 Recommendations
4.1 General considerations — the background to optical fibre damage at high powers
When optical fibres are operated at high power levels (typically > 500 mW), fibres and optical connectors can be damaged. In optical communications systems the optical power is transmitted In CW mode or at high repetition rates, and therefore catastrophic damage is predominantly caused by thermal mechanisms. It has been shown that several effects can cause high optical power-induced damage of single mode fibre systems leading to fibre failures. Systems employing high optical power operation In libres, connectors, collimators and attenuators thus carry additional sat ety concerns. For example, local heating In contaminated connectors/attenuators carrying high optical power can pose a potential fire hazard to surrounding materials, depending on the flammability of those materials.
IECITR 61292-4 provides extensive guidance on the following topics (see also (71):
— fibre fuse and its propagation;
— loss-induced heating at connectors or splices;
— connector end-face damage induced by dust/contamination;
— fibre-coat burn/melt induced by tight fibre bending.
Studies 131 on tight fibre bending at high power show that coating ageing can occur slowly and catastrophic damage effects can occur after hundreds of hours. The main implication is that damage testing must be carried out for sufficiently long times; some early experiments were conducted over short times, possibly leading to incorrect conclusions. IEC/TR 62547 should be followed for the measurement of high power damage sensitivity at bends.
As discussed by Bigot-Astruc M et al 141 and in IEC/IR 62547. a fast method of testing for potential damage effects at high powers can use a thermal imaging camera. Equilibrium temperatures are established relatively quickly, allowing the consequences of high power to be rapidly assessed. The issues concerning high power at tight bends arise because of exposure of the fibre coating to high power at or near to the bend. Coating ageing occurs at a rate determined by bend loss, launch power, environmental conditions arid coating resilience. New bend insensitive fibre designs — described by the ITU G.657 specifications — are a possible solution (see Section 2.5 in L8J). However, for extreme situations more resilient coatings may also be required.
The long-term damage effects of high power in other optical components, described for example in 4.5 and 4.9, show the need to consider the implications of high power damage research, as discussed in IEC!TR 62547,
4.2 AddItional recommendations for automatic power reduction (APR)
Extra recommendations for automatic power reduction (APR) are made because APR will become more critical in systems where fire, fibre and connector damage. and other hazards are possible if fibre is mishandled. These recommendations may include additional network management and administrative controls, electrical connectivity testing for higher reliability of APR. and others. Systems employing high optical power operation in fibres may necessitate the incorporation of automatic power reduction within one section of a main optical path in the event of recovery from the loss of optical power within that particular section of the main optical path.
Automatic power reduction should be specified and shown to have a high level of reliability forsystems using high optical power operation in fibres at all installed locations.IEC 60825-2describes an ‘adequate’ level of reliability for APR systems (500 FITs).
NOTE IEC 60825-2 defines FlITs as “an indicator of reliability defined as the number of failures per 10 n.”
Automatic power reduction should take into account all optical signals present in bothdirections on the optical path,as described in the following excerpt reproduced withpermission from Recommendation ITU-T G.664 (1999),Optical safety procedures andreguirements for optical transport systemsy.