The difference between OS1 and OS2 optical fibre. Why it matters?

Specifying the right type of optical fibre will ensure that you have the best performing product for your application. There has been some debate and confusion in the industry as to differences between OS1 and OS2 fibre types and what the terminology actually means.

This confusion exists at all levels of the industry, including suppliers of optical fibre products, distributors, consultants, end users and installers.

Therefore, the following information is provided to assist the telecommunications industry in understanding the differences between OS1 and OS2 fibre types.

Firstly, OS1 and OS2 specifications refer to cabled single mode optical fibre.

• Single mode OS1 is indoor tight buffered fibre, i.e. a 900 micron multi-fibre cable, tightly jacketed fibre with Nylon, Hytrel or PVC. An OS1 cable could also be a Micro-core LSZH indoor cable which consists of 250 micron fibres, with the fibres being tightly enclosed in a cable with aramid strengthening yarn and a LSZH jacket. The attenuation of a OS1 fibre is slightly higher than an OS2 fibre (e.g. 0.30dB/km @1550 for OS1 vs 0.19dB/km @1550 for OS2).
• Single mode OS2 is an outdoor and loose tube optical fibre cable and is suitable for outdoor applications where the cabling process applies no stress to the optical fibres. For instance, a 250 micron coated multi-fibre, which is loose inside an enclosure or tube and/or is free to move, is classified as OS2.
• OS1 or OS2 performance cables are constructed from B1.3 optical fibres (also known as ITU specification G.652D). Furthermore, OS1 and OS2 cable types can also include cables manufactured from B6_A fibre, which is commonly referred to as bend insensitive singlemode optical fibre, or ITU specification G657A2, which is also compatible with B1.3 optical fibre.
• OS1 or OS2 single mode fibre performance, does not relate to ITU specification G.655 (Non-dispersion shifted single mode optical fibres.

In summary, in the majority of cases, OS1 cabled optical fibre is appropriate for indoor and universal tight buffered cable constructions, which are mainly deployed in internal building/campus networks, as well as internal cabling within telecom exchanges and data centres.

OS2 cabled optical fibre is appropriate for outdoor and universal loose tube solutions, which would include external plant and most backhaul networks.

Therefore, when specifying or deciding which cabled optical fibre type to specify, consider the application as well as how and where the cable will be installed.

For further information on optical fibre products, please contact Warren & Brown Technologies who are leaders in optical fibre technology.

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