Even though many had been selling an advanced OM3 fiber equivalent since about 2005, the formal approval of OM4 fiber, by the TIA in August 2009, created some publicity surrounding this latest optical transmission media. We began to hear all about how this new fiber would meet the demands for higher bandwidth in data centers, offering an effective modal bandwidth (EMB) of more than double the IEEE requirement for 10 gigabit/sec over a 300-meter distance. This was followed by more talk of OM4’s ability to better support future 40 and 100Gb/s applications. But lately the buzz surrounding this new fiber type seems to have subsided. Is it because fiber with this bandwidth has technically been around for nearly six years, or is it because most users will be just fine with the less-expensive OM3 for 10, 40, and 100Gig applications?
Just like OM3, OM4 is a 50-micron, laser-optimized multimode fiber for use with VCSELs. The key difference is in the refractive index of the fiber, which is more precisely graded to better equalize the arrival time of the light modes traveling at various speeds along the core of the fiber. This translates to higher bandwidth and a 550-meter reach for 10Gb/s (with some vendors claiming a 600-meter reach) and a 150-meter reach for 40/100 Gig, compared to 300 and 100 meters respectively for OM3. This also translates to a higher price tag. But do you really need it?
Let’s consider that about 70% of premise fiber links are less than or equal to 100 meters, and virtually all premise backbones today run transmission speeds of 10 gigabits per second or less. With its ability to support 10Gb/s to 300 meters, OM3 is more than able to do the job. In the data center, the links are even shorter, with 85% or more data center links at less than 100 meters. Again, OM3 more than fits the bill, even for future data center speeds of 40 and 100Gig. In short, OM3 continues to be the most cost-effective option for fiber trunk cables and even fiber patchcords. But that’s not to say that OM4 doesn’t have its place.
Given the premium for single mode transceivers, OM4 fiber is the best option for the small percentage of users needing to run 10Gb/s over links between 300 and 550 meters (or the even smaller percent who anticipate running 40 or 100Gb/s between 100 and 150 meters). Some of these users may have already installed fiber cables with an advanced OM3 equivalent. That, combined with an extremely limited need, perhaps explains why OM4 isn’t getting a lot of hype. In any case, it’s still a step in the right direction—at least until single mode transceiver prices come down considerably.