On August 5, 2009 the TIA Standards Committee voted and approved the addition of a new EIA/TIA 492AAAD grade multimode fiber, which is known as OM4 fiber.
This new grade had been the topic of discussion within multimode fiber industry for nearly 3 years, and approval by TIA formalized the specification and measurement methods of an enhanced bandwidth fiber similar to those already commercialized by Corning and other fiber manufacturers.
>> What is OM4?
OM4 is a laser optimized, high bandwidth 50um multimode fiber.
OM4 fiber is not a new fiber type. All major fiber manufacturers have been selling a fiber with an effective modal bandwidth (EMB) value equivalent to that specified by OM4 since 2005.
The change is that there is now a standard that is specifically targeted at this product. Prior to the standardization of OM4 these higher bandwidth fibers were sold as part of OM3.
The requirements of the OM4 standard are identical to OM3 with the sole exception of the bandwidth values. Both the 850nm EMB and the 850nm over-filled launch (OFL) bandwidth have been increased from the OM3 requirements. See table below for specifics:
The “OM-“ multimode classification originates from the Structured Cabling Standard: IEC 11801. The IEC standardization of OM4 mirrors those of TIA 492AAAD.
>> Why was the 850nm OFL bandwidth increased from 1500 MHz*km to 3500 MHz*km
There is a belief among some members of the standards community that the 850nm OFL bandwidth needs to be scaled along with the 850nm EMB bandwidth in order to ensure maximum performance reliability.
Corning has done extensive testing in this area and does not see any such correlation for fibers measured with the miniEMBc bandwidth measurement. Therefore, Corning originally specified the product with an 850nm OFL value of 1500 MHz*km and pushed to keep that value for the OM4 standard.
During the standards debate, Corning also did testing using the DMD-mask method and did see a correlation between lower 850 nm OFL bandwidths and poor system performance. As a result, Corning supported the decision to increase the 850nm OFL bandwidth from 1500 MHz*km to 3500 MHz*km in order to protect against failures for fibers measured with the DMD-mask test method.
It is for this reason, Corning is confident in stating that there is no functional difference in Corning’s eSX+ fiber and ClearCurve OM4 fiber products as a result of this change.
>> Does this mean OM3 isn’t future-proof?
No. Most system requirements will still be met with OM3 – including 40 GbE and 100 GbE. For 10 GbE, OM3 supports 300 meters and proposals for OM4 support 550 meters. The vast majority of enterprise and data center 10 GbE link lengths are less than 300 meters so OM3 address most requirements.
For 40 GbE and 100 GbE, the draft standard includes objectives for 100 meters over OM3 and 125 meters over OM4. Studies have shown that approximately 70% of in-building links are less than or equal to 100 meters. Therefore, for ~70% users, OM3 remains the future-proof solution even for 40 GbE and 100 GbE.
>> When should I consider an OM4 fiber?
For typical premises links up to 600 meters, multimode fiber remains the cost effective solution. This is due to the fact that in a typical link, the cost of transceivers is ~10x the cost of the fiber/cable/connectors.
While single mode fiber is relatively cheap, it requires the use of costly 1300nm transceivers which are roughly 2x – 3x the cost of 850nm multimode transceivers.
By investing a little bit more money in a high quality multimode fiber structured cabling system, substantial overall savings can be reaped by enabling the use of low-cost transceivers. As systems migrate to higher bit rates such as 40 GbE and 100 GbE, initial projections show that the transceiver cost savings enabled by multimode fiber will only get bigger.
In addition, Fibre Channel members recently voted to include OM4 in their specifications with OM4 supporting 400 meters at 4 Gb/s, 200 meters at 8 Gb/s and 130 meters at 16 Gb/s.