What is the difference between OS1 and OS2 Single-Mode fibers?

In fiber optic network infrastructures, the whole concept is capable of fulfilling the high-demand and long reach needs of the customers mainly because of the deployed transceivers and fiber optic cables. The optical transceivers are the modules that are converting the electrical signal into an optical light signal and, with the help of lasers, sending it down the optical cable. The receiving part of the connection is also an optical transceiver that converts the optical light into electrical signals so the device can read the data received. Even though optical transceivers are doing the more complex job in the fiber optic network, optical cables are the most important part of the whole network infrastructure. Without them the fiber optic connection wouldn’t be possible.

 

When it comes to fiber optic cables, they come in many shapes and sizes depending on the type of the project they are needed for. However the main two categories by which they are divided are Multi-mode and Single-mode fibers. In short, they are known as MMF and SMF.

 

As we already know, Multi-mode fibers are optical cables used in fiber optic networks for short range connections, most commonly within a particular building like a Datacenter. There are four types of Multi-mode fibers existing on the market, each different from each other in the capabilities: OM1, OM2, OM3 and OM4.

 

The key difference between Multi-mode and Single-mode fibers is their reach capability. This difference occurs mainly because of the larger core of Multi-mode fiber optic cables. Because of their large core, which is around 50-100 micrometers, they are capable of carrying a lot bigger wavelength of optical light. This bigger wavelength is bouncing around the cable and the loss in power is greater. In Single-mode fibers we can find a much smaller core which is generally around 9 micrometers. Because of this they can’t carry very big wavelength. Instead the wavelength they are carrying is much narrower compared to Multi-mode, the light is directed by the transceiver directly in the core and during its travel is not bouncing around the cable. This eventually ensures longer reach with low power loss, also known as attenuation.

 

However, just like with Multi-mode fibers, Single-mode fibers are organized in categories, OS1 and OS2. Depending on the network infrastructure, knowing the difference between these two categories is vital.

 

OS1 Single-mode fibers are compliant with the ITU-T G.652 standard and its specifications. On the other hand, OS2 Single-mode fibers are compliant with ITU-T G.652C, G.652D or G.657.A1 standards. Another big difference between these two categories is their cable construction. Because OS1 is most commonly used for indoor applications, they are tight-buffered constructed. This means that they are manufactured as a solid medium. On the other hand the OS2 type of cables are constructed as loose –tube and they are mainly designed to be used outdoors. This is the main reason why OS1 cables have greater loss per kilometer compared to OS2 fibers. Generally taken the maximum attenuation allowed for OS1 cable is 1.0 dB/km and for OS2 is 0.4 dB/km. The maximum distance that an OS1 cable can reach is 2 kilometers, while the maximum distance that OS2 can reach is 10 kilometers. This is why generally, OS2 are much more expensive to produce and purchase than OS1 cables.

 

When choosing and purchasing the correct cable for your project it’s vital to understand that, in both cases, high care must be applied. If a Single-mode cable is needed for an indoor network infrastructure then OS1 is the way to go. If a Single-mode cable is needed for an outdoor network infrastructure then OS2 is the way to go.