What is OS2 single-mode fiber?
OS2 is the cabling standard name for a single-mode fiber with a core of about 9 microns and a cladding of 125 microns. It is cabled in a form that has low attenuation at the 1310 nm and 1550 nm windows. It corresponds to ITU-T G.652.D and to IEC 60793-2-50 type B1.3 fiber, which is why you will see all three names on data sheets.
OS2 differs from OS1. OS1 is the older grade, normally used in tight buffered indoor cable, with higher attenuation limits. OS2 is the grade normally used in loose tube outdoor and inter building cable and is the usual choice for new single-mode installations. In practice most single-mode fiber now sold for data networks meets OS2 requirements, so asking for OS2 is a safe default.
Single-mode fiber differs from multimode (OM3, OM4) in core size and light source. A small core lets a laser send a single light path, so the signal spreads very little and travels much further. Typical Ethernet optics for OS2, such as 10GBASE-LR, reach 10 km, and extended optics reach farther. The transceivers cost more than short reach multimode optics, so many buildings use both types.
How it shows up in practice
- Use OS2 for runs between buildings, for risers on large sites, and for any link that must be future proof for higher speeds.
- Specify connector type and polish, such as LC/UPC or LC/APC. APC connectors, with an angled end face, must not be mated with UPC connectors.
- Ask for loss test results, and for an OTDR trace on long or spliced links, so fusion splices and connectors can be checked individually.
- Label every strand at both ends and record the path in the as built documents.