There are different categories of graded-index multimode fiber optic cable. The ISO/IEC 11801 Ed 2.1:2009 standard specifies categories OM1, OM2, and OM3. The TIA/EIA recognizes OM1, OM2, OM3, and OM4. The TIA/EIA ratified OM4 in August 2009 (TIA/EIA 492-AAAD). The IEEE ratified OM4 (802.ba) in June 2010. It is now updating the distance for OM4 from 300 to 400 meters for 10-GbE. This will be known as 802.3-2012.
OM1 specifies 62.5-micron cable and OM2 specifies 50-micron cable. These are commonly used in premises applications supporting Ethernet rates of 10 Mbps to 1 Gbps. They are also typically used with LED transmitters. OM1 and OM2 cable are not suitable though for today’s higher-speed networks.
OM3 and OM4 are both laser-optimized multimode fiber (LOMMF) and were developed to accommodate faster networks such as 10, 40, and 100 Gbps. Both are designed for use with 850-nm VCSELS (vertical-cavity surface-emitting lasers) and have aqua sheaths.
OM3 specifies an 850-nm laser-optimized 50-micron cable with an effective modal bandwidth (EMB) of 2000 MHz/km. It can support 10-Gbps link distances up to 300 meters. OM4 specifies a high-bandwidth 850-nm laser-optimized 50-micron cable an effective modal bandwidth of 4700 MHz/km. It can support 10-Gbps link distances of 500 meters (unofficially). 100-Gbps distances are 100 meters and 150 meters, respectively. Both rival single-mode fiber in performance while being significantly less expensive to implement.
OM1 and 2 are made with a different process than OM3 and 4. Non-laser-optimized fiber cable is made with a small defect in the core, called an index depression. LED light sources are commonly used with these cables.
OM3 and 4 are manufactured without the center defect. As networks migrated to higher speeds, VCSELS became more commonly used rather than LEDs, which have a maximum modulation rate of 622 Mbps. Because of that, LEDs can’t be turned on and off fast enough to support higher-speed applications. VCSELS provided the speed, but unfortunately when used with older OM1 and 2 cables, required mode-conditioning launch cables. Thus manufacturers changed the production process to eliminate the center defect and enable OM3 and OM4 cables to be used directly with the VCSELS.
850 nm High Performance EMB (MHz/km)
850-nm Ethernet Distance
OM3: 1000 m
OM4: 1000 m
OM3: 300 m
OM4: 550 m
OM3: 100 m
OM4: 150 m
OM3: 100 m
OM4: 150 m