Professional Manufacturer of Fiber Optic Products

Difference Between OS1 and OS2 Fiber

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.

OS1 fiber’s attenuation should be less than 1,0 dB/km while OS2 fiber’s attenuation should be less than 0.4dB/Km. Please note this requirements are for cabled optic fiber.

At the beginning OS1 fiber was stated to be constructed with G652A/B fiber(B1.1), OS2 fiber is constructed with G652C/D(B1.3) fiber. But later, 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. However, 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)


  • 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)



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