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Difference Between OS1 And OS2 Fibre Optic Cable

The easiest points to remember are OS1 is for Indoor / Tight Buffered cable; OS2 is for Outdoor / Loose Tube cable.  I believe the confusion has arisen as OS2 grade fibre (as in 250um) has been used in the former, but once the 900um tight buffer is applied and it’s manufactured into a cable and stresses have been applied, it no longer meets the OS2 classification.

There is a great deal of confusion about the purpose and meaning of the cabled Single Mode optical fibre Categories OS1 and OS2. This confusion exists at all levels of the industry and affects, in equal measure, the suppliers of optical fibre and optical fibre cable, distributors, installers, customer and their consultants. This Application Note explains the differences between the specifications of OS1 and OS2

• OS1 and OS2 are cabled Single Mode optical fibre specifications
• Category OS1 is appropriate to Indoor and Universal tight buffered cable constructions
• Category OS2 is appropriate to Outdoor and Universal loose tube solutions (where the cabling process applies no stress to the optical fibres)
• Cables with either OS1 or OS2 performance are constructed from B1.3 optical fibres (also known as ITU specification G.652D) or B6_a fibres (a less bend sensitive singlemode optical fibre which is similar to, and compatible with, B1.3. Also known as ITU specification G.657)
• OS1 or OS2 performance is not related to Single Mode optical fibres according to ITU specification G.655 (Non Zero Dispersion Shifted fiber)

European standards and ISO/IEC
• The European Standard EN 50173-1:2007 states that both OS1 and OS2 cabled optical fibres can only be constructed from B1.3 (or ITU G.652D) and B6.a (or ITU G.657) optical fibre according to EN 60793-2-50. Unfortunately, ISO/IEC have not made this logical leap – even in the latest proposed amendment of ISO/IEC 11801 (which now features both OS1 and OS2). This is summarised in Table 1:

SM fibre


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