Issue link: http://www.epageflip.net/i/1043933
November/December 2018 I 39 Review of Multimode Optical Fiber Types • OM1 Standards designate OM1 (62.5/125 µm) cable as orange. However, there is some legacy orange cable that was available before the OM1 specification. This early cable has a modal bandwidth of 160 MHz/km @ 850 nanometers (nm), as opposed to 200 MHz/km for OM1. If an orange cable is encountered that is not marked OM1, the technician may need to assume the cable is 160 MHz/km. • OM2 OM2 (50/125 µm) provides a much better modal bandwidth than OM1, 500 MHz/km @ 850 nm. The industry standard color for OM2 is gray. However, there are some early OM2 cable installed that is orange, so always check the markings to make sure. • OM3/OM4 Both laser-optimized OM3 and OM4 cable share the color aqua, since TIA and ISO have not introduced a new color for OM4. However, some manufacturers introduced the color Erika (heather) violet to designate OM4. This color designation is important to differentiate the two types, as the modal bandwidth of OM4 (4,700 MHz/km @ 850 nm) is significantly better than OM3 (2,000 MHz/km @ 850 nm). • OM5 The color lime for OM5 cable was approved by TIA and ISO in 2017. Note in Figure 2 that OM5 has the same modal bandwidth as OM4 @ 850 nm. The main difference between the two options is that OM5 is designed specifically to handle short wave division multiplexing, which transmits four channels on one duplex multimode optical fiber pair between 850 nm and 953 nm. However, for all existing IEEE applications, there is no current advantage of OM5 over OM4. While multimode optical fiber comes in either 50 micron or 62.5 micron core size, the ANSI/TIA-568.0-D standard recommends 850 nm laser-optimized 50/125 micron be installed for new structured cabling designs. This includes both OM3 and OM4 classifications to support 10 Gigabit Ethernet (10 GbE) and possibly provide a migration plan to support future 40 and 100 GbE applications. Both OM1 (62.5/125 micron) and OM2 (50/125 micron) classifications are now considered legacy fiber types. Understanding Distance Limits • 1 GbE/s The majority of enterprise optical fiber networks today still run 1000BASE-SX, delivering up to 1 GbE/s over multimode. OM1 cable supports 1000BASE-SX out to 275 meters (m) and that distance jumps to 550 m with OM2 cable. OM3, OM4 and OM5 came after the 1000BASE-SX standard was written, so the distances up to 860 m listed in Figure 2 are based on the gigabit fiber channel values. When ICT managers require distances upwards of 860 m, they will likely want to consider singlemode cable instead of multimode. • 10 GbE/s Many enterprise networks are moving beyond 1000BASE-SX and transitioning to 10 Gigabit Ethernet networks, such as 10GBASE-SR. This is where distance considerations really come into play. A network using OM1 has a maximum distance of 275 m for 1000BASE-SX, but it would see a distance limit of only 33 m for 10GBASE-SR. Similarly, OM2 fiber for 1000BASE-SX has a 550 m limit, but drops down to 82 m for 10GBASE-SR. The introduction of OM3 increased that distance to a more usable 300 m in the enterprise. Multimode optical fiber is the most common media choice for both backbone and horizontal distribution within the LAN.