The Evolution of MMF

MMF (Multimode Fiber) is a type of optical fiber mostly used in LAN (Local Area Network) backbones and data centers due to its high transmission data rates and low operating costs. Typically, MMF supports the data rates and distance of 100Mbit/s for distance up to 2 km, 1 Gbit/s up to 1000 m, and 10 Gbit/s up to 550 m. MMF has evolved from OM1, OM2, OM3, OM4 to WBMMF (WideBand Multimode Fiber) since it entered into the market. With the improvement in transmission rates, MMF has been optimized from multi-megabit per second transmission utilizing LED (Light Emitting Diode) light sources to multi-gigabit transmission using LCSEL (Vertical Cavity Surface Emitting Laser) sources. Since the proposal of 100G-NG, 200G/400G and 1T Ethernet, traditional MMF becomes a bottleneck for the further development of Ethernet networks for its limits in fiber cores and transmission distance. However, WBMMF can overcome these limits by providing not only more efficient support for future applications to useful distances, but also complete compatibility with legacy applications. This paper will review the history of MMF to give a thorough understanding of WBMMF.

MMF

In the early 1980s, MMF with a light-carrying core diameter was first deployed in telecoms networks. It was a practical solution to the alignment challenges by enhancing the efficiently getting light into and out of the cabling. Later, SMF (Singlemode Fiber) began to be used in public networks, as alignments achieved micron accuracy and laser diodes became available. MMF was mainly deployed in Enterprise networks, supporting applications such as PBXs (Private Telephone Switches), data multiplexers and LANs because easier alignment was cheaper and low-cost LED sources were available.

OM1 and OM2

As Ethernet and fiber applications grew dramatically in LANs and SANs (Storage Area Networks), MMF became the primary media for backbone and other applications whose capabilities exceed copper twisted pair cabling. When data rates surpassed 100 Mb/s, 850nm VCSEL (Vertical Cavity Surface Emitting Laser) gave way to LED sources due to its high cost. This sparked a conversion of MMF core diameter from 62.5 µm (OM1 cabling) to 50 µm (OM2 cabling) because 50 µm design could provide higher bandwidth to better support transmission at hundreds of megabits per second.

OM3 and OM4

With the coming of the Gigabit era, the limitations with the bandwidth measurement techniques became clear in late 1990s. The old measurement made with overfilling launch conditions no longer provided reliable indication for the concentrated under-filling launches of VCSELs. Then the new measurement, known as LOMMF (Laser Optimized Multimode Fiber) came into being. The fist LOMMF, or OM3, provided a bandwidth of at least 2000 MHz km at 850 nm. In late 2000’s, OM4 appeared, offering at least a 4700 MHz km in anticipation of 25 Gb/s per lane applications. Today, OM3 and OM4 are the main fiber media deployed for Ethernet and Fiber Channel applications.

WBMMF

WBMMF is a new fiber under deployment to extend the capability and transmission distance of traditional OM4. With a 50 µm core and 125 µm cladding, WBMMF will be physically compatible with existing multimode fiber connectivity. It is designed for transmitting up to a range of wavelengths from 850 nm to 950 nm. This will be at least quadruple the current information carrying capacity of multimode fiber. Besides, WBMMF solution can also provide the most cost-effective platform to support higher speeds with fewer fibers at greater distances.

Conclusion

The emergence of WBMMF is a great revolution in the large data center. It breaks the bottleneck of traditional MMF which uses parallel transmission technology and has limited transmission rate. WBMMF can offer high-speed transmission rate with fewer fibers and lower cost because it uses the short wavelengths. Therefore, WBMMF will find widespread application in the coming large data centers in 100G, 400G and 1T connectivity.

This article originates from http://www.fiber-optical-networking.com/2016/05/14/the-evolution-of-mmf/.