What are OS1 and OS2 Singlemode Optical Fibers?


Standardization in fiber optic industry is one of the most confusing areas for many people involved in the business. Some times customers mention fiber optic cable standards that may not be suitable to their area of application. To add to these confusions, there are many international specifications than required for the same type of fiber optic cable and optical fiber types.

The relatively recent entry of OM and OS terminologies in fiber optic technology is new to many fiber optic cable manufacturers. This points to the lack of uniform standardization and lack of common understanding among the professionals involved in fiber optics from different parts of the world. Fiber optics might have connected the business houses around the world to help communication faster and closer. Use of common terminology that will be helpful to everybody involved in fiber optic technology is a must especially for fiber optic engineers and technicians.

There are two recent entries in Fiber optic terminology. The first one is OS1 and the second one is OS2. OS1 refers to a very old specification for single mode fiber. Performance values of these single mode fibers are traceable to ISO/IEC 11801 published in 1995. The mechanical, optical and environmental characteristics of OS1 singlemode fibers are compliant with ITU-T G.652A or ITU-T G.652B. OS1 singlemode fibers compliant with ITU-T G.652B are equivalent to IEC 60793-2-50 Type B1.1

Recent entry of new terminology of OS1 was first introduced in the year 2002. Though OS1 fiber categories are ITU-T G.652A and ITU-T G.652B compliant optical fibers, the low water peak fibers categorized in ITU-T recommendations as G.652C and G.652D also comes under OS1 fibers. Thus OS1 is a general term used to specify Single mode optical fibers that comes under the heading of ITU-T G.652.

OS2 was introduced in the year 2006. OS2 fibers are very clearly the low water peak fibers. Single mode fibers categorized in ITU-T as G.652C and G.652D comes under OS2 fibers. The difference between OS1 and OS2 optical fibers lies in the fact that OS1 covers all the singlemode fibers that complies with ITU-T G.652 characteristics. On the other hand OS2 fibers are low water peak fibers only. Low water peak fibers, ITU-T G.652C or G.652D fibers can be used for CWDM applications. Coarse wavelength Division Multiplexing, a kind of Wavelength Division multiplexing technology utilizes 20nm spacing between subsequent channels.

optical fiberITU-T G.652A or ITU-T G.652B optical fibers are not intended to be used for transmission at 1383nm wavelength due to their inherent attenuation characteristics. The attenuation at water peak region of the spectrum is quite high and are not recommended for use. ITU-T G.652C and ITU-T G.652D fibers can be used for a full spectrum transmission with lower attenuation values at 1383nm.

OS2 single mode optical fiber cables can not be connected with OS1 single mode optical fiber cables. It may lead to unpredicted signal performance at water peak region. This is one of the reasons for demand from some corners to have a new specification for Indoor fiber optic cables with ITU-T G.652C or G.652D optical fibers. OS2 specifications are included in the new IEC 60794-3 standards for Outdoor fiber optic cables. The reason is that OS2 single mode optical fibers support single mode operation for 5km and 10km at 10G. The low attenuation values of OS2 single mode optical fibers imply the cable construction to be that of a loose tube fiber optic cable. Ribbon optical fibers will have little high attenuation compared to loose tube fiber optic cables.

To support the use of OS terminology, there are published fiber optic cable standards that contain OS1 single mode optical fibers for Indoor cables. The IEC 60794-2-11; 2005 and BS EN 60794-2-11; 2005, a detailed specification for simplex and duplex cables for use in premises cabling, Detailed specification for multi fibre optical distribution cables for use in premise cabling (IEC 60794-2-21: 2006 and BS EN IEC 60794-2-21: 2006), Detailed specification for optical fibre ribbon cables for use in premises cabling (IEC 60794-2-31: 2006 and BS EN IEC 60794-2-31: 2006)

OS1 mentioned standards for outdoor optical fiber cables are the detailed specification for duct and direct buried optical telecommunication cables for use in premises cabling (IEC 60794-3-12:2006 and BS EN IEC 60794-3-12:2006) & detailed specification for optical self supporting aerial telecommunication cables for use in premises cabling (IEC 60794-3-21:2006 and BS EN IEC 60794-3-21:2006)

Also, OS2 single mode optical fibers are mentioned in the new editions of IEC-60794-3-12 (Detailed specification for duct and directly buried optical telecommunication cables for premises cabling and in IEC-60794-3-21 (Detailed specification for optical self supporting aerial telecommunication cables for use in premises cabling.

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