Issue link: https://www.e-digitaleditions.com/i/1192126
January/February/March 2020 I 19 This is largely due to the design of this fiber which was optimized for lower throughputs. Contrary to the active components of the network, for which upgrades can be carried out relatively easily through a software or hard- ware upgrade, the optical fiber cabling infrastructure has a performance envelope that previously could not be increased without physically changing the cable that carries the information. THE ISSUE OF MODAL DISPERSION IN MULTIMODE OPTICAL FIBERS Optical fiber is widely used to carry information due primarily to its small size, low linear losses, and insensi- tivity to electromagnetic disturbances. However, optical fiber possesses intrinsic performance limitations which are inherent to its physical properties. For multimode opti- cal fibers installed in the 1980s and 90s, such as OM1 (62.5/125 μm) and OM2 (50/125 μm), high-speed trans- mission is limited as a result of modal dispersion. Modal dispersion is a distortion mechanism occurring in multi- mode fibers. Due to the different velocities of the modes, the signal is spread out and often deformed over time during the propagation in the fiber as shown in Figure 2. A GROWING DEMAND FOR INCREASED BANDWIDTH IN LOCAL NETWORKS Over the past several years, a lot of effort has been put into the development of optical transmission systems at 10 Gb/s in LANs. A growing number of applications FIGURE 1: The growing demand for increased bandwidth in LANs. FIGURE 2: Modal dispersion affects all multimode fiber types, thereby degrading the bandwidth capacity of the multimode optical fiber. require high bandwidth in order to ensure ongoing transfer and stream- ing of large volumes of data, audio files and videos. In addition, the multiplication of mobile terminals and online devices has contributed to the need for higher bandwidth. Therefore, bandwidth-intensive applications and latency-aware traffic types are becoming ubiqui- tous in the LAN. As a result, it is necessary to be able to transport these data streams with a high quality of service (QoS) and reliabil- ity. Nearly 75 percent of the opti- cal fibers deployed in the LAN are multimode fibers. A large major- ity of deployed multimode optical fibers do not support throughput of 10 Gb/s over campus-wide links. IP Phone Individual Heterogeneous Servers LAN Switches 1—10 Gb/s 1—100 Gb/s 100M—10 Gb/s Multimode Fiber Conventional multimode input Stimulation of different modes Propagation Degraded signal Different modal velocity Wireless Access Point 10—50 Gb/s