Data Center and Multimode Fibers
Multimode fiber is being widely used in data centers. You might ask why not single-mode fiber? The answer is cost. As is known to all, the price of single-mode fiber is generally more expensive than multimode fiber. In addition multimode fibers provide a significant value proposition when compared to single-mode fiber, as multimode fiber utilizes low cost 850 nm transceivers for serial and parallel transmission. If you had all money you wanted and you’d just run single-mode fiber which has all the bandwidth you need, then you can go plenty of distance. However, this perfect situation would cost a lot of money. Thus, most data center would choose multimode fiber. OM1, OM2, OM3 and OM4 are the most popular multimode fiber. But OM3 and OM4 are gradually taking place of OM1 and OM2 in data centers.
OM stands for optical multimode. OM3 and OM4 are both laser-optimized multimode fibers with 50/125 core, which are designed for use with 850nm VCSELS (vertical-cavity surface-emitting laser) and are developed to accommodate faster networks such as 10, 40 and 100 Gbps. Compared with OM1 (62.5/125 core) and OM2 (50/125 core), OM3 and OM4 can transport data at higher rate and longer distance. The following statistics (850 nm Ethernet Distance) shows the main differences between these four types multimode fibers, which can explain why OM3 and OM4 is more popular in data center now in some extent.
| Fiber Type | 1G | 10G | 40/100G |
| OM1 | 300 m | 36 m | N/A |
| OM2 | 500 m | 86 m | N/A |
| OM3 | 1 km | 300 m | 100 m |
| OM4 | 1 km | 550 m | 150 m |
Why Use OM3 and OM4 in 40/100G Migration
The Institute of Electrical and Electronics Engineers (IEEE) 802.3ba 40/100G Ethernet Standard was ratified in June 2010. The standard provides specific guidance for 40/100G transmission with multimode and single-mode fibers. OM3 and OM4 are the only multimode fibers included in the standard. The reason why OM3 and OM4 are applied in 40/100G migration is that they can meet the requirements for the migration cabling performance.
Bandwidth, total connector insertion loss and transmission distance are two three main factors should be considered when evaluation the performance needed for cabling infrastructure to meet the requirements for 40/100G. These factors can impact the cabling infrastructure’s ability to meet the standard’s distance of at least 100 meters over OM3 fiber and 150 meters over OM4 fiber. The following explains why OM3/OM4 are the chosen ones for 40/100G migration.
Get Higher Bandwidth With OM3/OM4
Bandwidth is the first reason why OM3 and OM4 are used for 40/100G migration. OM3 and OM4 are optimized for 850nm transmission and have a minimum 2000 MHz?km and 4700 MHz?km effective modal bandwidth (EMB). Comparing the OM1 and OM2 with a maximum 500 MHz?km, advantages of OM3 and OM4 are obvious. With a connectivity solution using OM3 and OM4 fibers that have been measured using the minimum Effective Modal Bandwidth calculate technique, the optical infrastructure deployed in the data center will meet the performance criteria set forth by IEEE for bandwidth.
Get Longer Transmission Distance With OM3/OM4
The transmission distance of fiber optic cables will influence the data center cabling. The manageability and flexibility will be increased with fiber optic cables with longer transmission distance. OM3 fiber and OM4 fiber can support longer transmission distance compare with other traditional multimode fibers. Generally OM3 fibers can run 40/100 Gigabit at 100 meters and OM4 fibers can run 40/100 Gigabit at 150 meters. This high data rate and longer distance cannot be achieved by other traditional multimode fiber like OM1 and OM2. Employing OM3 fiber and OM4 in 40/100G migration is required.
Get Lower Insertion Loss With OM3/OM4
Insertion loss has always been an import factor that technically should consider during the data center cabling. This is because the total connector loss within a system channel impacts the ability to operate over the maximum supportable distance for a given data rate. As total connector loss increased, the supportable distance at that data rate decreases. According to the 40/100G standard, OM3 fiber is specified to a 100m distance with a maximum channel loss of 1.9dB, which includes a 1.5dB total connector loss budget. And OM4 fiber is specified to a 150m distance with a maximum channel loss of 1.5 dB, including a total connector loss budget of 1.0 dB. With low-loss OM3 and OM4 fiber, maximum flexibility can be achieved with the ability to introduce multiple connector mating into the connectivity link and longer supportable transmission distance can be reached.
OM3 or OM4?
Choosing OM3/OM4 is a wise and required choice for data center 40/100G migration. However, OM3 and OM4, which is better? Numerous factors can affect the choice. However, the applications and the total costs are always the main factors to consider to figure out whether OM3 or OM4 is needed.
First, the connectors and the termination of the connectors for OM3 and OM4 fibers are the same. OM3 is fully compatible with OM4. The difference is just in the construction of fiber cable, which makes OM4 cable has better attenuation and can operate higher bandwidth at a longer distance than OM3. Thus, the cost for OM4 fiber is higher than OM3. As 90 percent of all data centers have their runs under 100 meters, choosing OM3 comes down to a costing issue. However, looking in the future, as the demand increases, the cost will come down. Thus, OM4 might be the most viable product at some point soon.
No matter choosing OM3 or OM4, the migration is underway. With good performance like high data rate, long transmission distance and lower inserting loss, OM3/OM4 fiber is a must in data center migration to 40/100G.
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