Hello, everyone!
Today, I will continue to explain data center cabling. In this article about data center cabling, I will talk about optical cables with multimode fibers.
The use of optical cables in data centers has been going on for many years. Comparing optical cables with copper cables, there are a number of advantages of optical cables: longer distance, higher data speed, immunity to interference, easier installation, etc.
The most commonly used optical fibers in data centers are multimode optical fibers. Multimode fibers can be used up to 100 Gbps, which generally meets the current needs of most data centers. There are five types of multimode fibers: OM1, OM2, OM3, OM4 and OM5. They differ in core dimensions, bandwidth and range. We can see all types of MM fibers in the next table.
Table 1. Types of MM fibers
Originally, OM1 multimode fibers were used. This type of fiber has dimensions of 62.5/125 μm, with an attenuation of 3-3.5 dB/km, bandwidth 200/500 MHz-km. This type of MM fiber is not used today. In premises networks, OM2 and OM3 (sometimes OM4) are widely used. Today, for data centers, OM3 and OM4 (sometimes OM5) are widely used.
Multimode fibers are used more than singlemode fibers due to the lower cost of lasers. MM fibers use inexpensive 850 nm VCSEL lasers. To enable 10 Gbps transmission using MM fibers, one fiber for direct and one fiber for return is required. If we want to realize 40 Gbps link, we need 4 fibers for direct and 4 fibers for the return path. Then we need a cable with 12 fibers and MPO connectors. The center four MM fibers are not used. For 100 Gbps, 10 MM fibers in the forward direction and 10 MM fibers in the reverse direction are required. For this link, we have to use a cable with 24 fibers, the center four are unused. And for this cable, MPO connectors are used.
Figure 1. Optical cable with MPO connectors
Simplex or duplex MM fiber uses LC connectors because SFP (transceivers) on the device (routers, switches, servers, etc.) has small holes. When we use cables with 12 or 24 fibers, these cables have MPO connectors.
In the next article, I will explain new types of MM fibers – OM5, MM cabling evolution and singlemode fibers >> Data center cabling (4): OM5 and SM fibers.
Thank you!
