Issue link: http://www.epageflip.net/i/1043933
November/December 2018 I 23 An even more recent innovation was the introduction in 2017 of OM5, known as wideband multimode fiber. Traditionally, multimode fiber has operated at a single wavelength. When higher network speeds were needed, lasers were developed that would operate at these speeds. This approach worked very well up to 10 Gb/s and, later, 25 Gb/s. To increase speeds further, however, parallel fiber systems were introduced; first for 40 Gb/s, then for 100 Gb/s. Four fibers, or lanes, were used to support these higher speed links. OM5 fiber is the first multimode fiber designed to support multiple wavelengths. It enables duplex transmission of 100 Gb/s using either two or four wavelengths between 850 and 950 nm. This is done while taking advantage of multimode fiber's longer wavelength transmission properties. The fiber's lower chromatic dispersion at longer wavelengths means that modal bandwidth requirements could be relaxed at those longer wavelengths. Commercial transceivers are available to support either technology. In fact, several large transceiver manufacturers were key contributors to the wideband multimode fiber standard. They provided guidance on the wavelength spacing needed for the most cost-effective wavelength division multiplexing (WDM). This resulted in a transmission window that went from the current 850 nm up to 953 nm. An additional requirement was the support of all existing OM4 applications and reaches. In other words, OM5 fiber is completely backward compatible with all OM4 requirements and supports applications to the same link distances. Table 2 indicates where the OM5 specifications were tightened in order to support WDM applications. Notice that the 850 nm laser bandwidth (also called effective modal bandwidth, or EMB) remains the same at 4700 Megahertz over one kilometer (MHZ-km). Transmission reach at 850 nm matches all OM4 applications. The additional bandwidth requirement is at 953 nm, the long or "far" end of the wavelength range, where a laser bandwidth of 2470 MHz-km is specified. The window between these two wavelengths is the space designed for multimode WDM applications. TABLE 2: Specification comparison between OM4 and OM5 wideband multimode fiber. Other than some limited application in service provider central offices, 100GBASE-SR10 has been less widely deployed, in large part because newer standards requiring fewer fiber pairs have been developed. OM4 Multimode Fiber OM5 (Wideband) Multimode Fiber Zero Dispersion Wavelength 1295 ≤ λ ο ≤ 1340 nm 1297 < λ ο < 1328 nm Zero Dispersion Slope S 0 ≤ 0.105 ps/nm 2. km for 1295 ≤ λ ο ≤ 1310 nm, and ≤0.000375(1590-λ ο ) ps/nm 2. km for 1310 ≤ λ ο ≤ 1340 nm S 0 ≤ 4(-103)/ (840(1-( λ ο /840) 4 )) ps/nm 2. km 850 nm Effective Modal Bandwidth (EMB) 4700 MHz-km 4700 MHz-km 953 EMB N/A 2470 MHz-km