Singlemode Fiber – ITU-T G.657 A.1

ITU-T The long-time leader in optical single-mode fibre and cable standardization

Recommendation ITU-T G.657: “Characteristics of a bending-loss insensitive single-mode optical fibre and cable for the Access network

Background and history:
  • The roll out of fibre-to-the-home (FTTH) networks has been of global importance since the early 2000s, requiring a dedicated single-mode fibre cable Recommendation.
  • Operators and manufacturers jointly worked on swift introduction of this Recommendation in 2006 and its updates in 2009 and 2012.
  • Since its introduction, ITU-T G.657 optical fibre cables have seen a steady increase in the total optical fibre cable market.
  • ITU-T G.657 optical fibre cable offers flexible characteristics for easier deployment in streets, buildings and homes.
  • ITU-T G.657 optical fibre cable reduces the roll-out cost for operators and the total cost of ownership (TCO) of an FTTH network.
    – Increased flexibility in optical fibre cables, allowing improved installation in tight corners of buildings.
    – Smaller cabinets, pedestals, enclosures and terminations, which are important where space is at a premium. (e.g., in apartment buildings).
    – More engineer-friendly installation leading to less re-work.
Main aspects / attributes:
  • ITU-T G.657 is split into two main parts:
    – Category A fibres for Access networks.
    – Category B fibres for short distances at the end of Access networks in bending-rich environments (e.g., buildings).
  • Each category (A and B) is divided into two sub-categories:
    – G.657.A1 and G.657.A2
    – G.657.B2 and G.657.B3
  • These sub-categories have the following minimum specified bending radii:
    – G.657.A1: 10 mm
    – G.657.A2 and G.657.B2: 7.5 mm
    – G.657.B3: 5 mm
  • ITU-T G.657.A1 and ITU-T G.657.A2 fibres are fully compliant with ITU-T G.652.D fibres.
    • Compliance here means adherence to the referenced Recommendation (ITU-T G.652, category D) meeting or exceeding the values of the specified attributes.
  • ITU-T G.657.B2 and ITU-T G.657.B3 fibres are fully compatible with ITU-T G.652.D fibres (only small differences in chromatic dispersion and polarization mode dispersion (PMD).
    • Compatibility here means that these fibres will introduce negligible system impairment or deployment issues, but may not be compliant to the referenced Recommendation (ITU-T G.652.D).

Additionally, another favoured application is in central offices where ITU-T G.657 fibres mitigate the risk of communication failure and/or high power damage under inadvertent bending. Care needs to be taken to not impact long-term reliability. Examples of the relationship between minimum bend radius and maximum power can be found in IEC TR62547.


Structure of ITU-T G.657 (2012)

For access networks G.652.D compliant all bands 1260-1625nm

  • A1 Rmin = 10 mm
  • A2 Rmin = 7.5 mm

For end of Access networks (e.g., in/near buildings) G.652.D compatible all bands 1260-1625nm

  • B2 Rmin = 7.5 mm
  • B3 Rmin = 5 mm