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ICT Today October/November/December 2020

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Page 46 of 79

October/November/December 2020 I 47 PART 1 — MMF TECHNOLOGY, MARKET, AND INDUSTRY TRENDS VCSEL Light Sources Drive MMF's Growth Vertical cavity surface emitting lasers (VCSELs) are the light source of choice for today's MMF transmission over advanced optical multimode OM3, OM4, and OM5 optical fiber. The VCSELs offer several advantages 1 over light-emitting diode (LED) and edge-emitting laser (EEL) technology typically used in singlemode links, including: • Low power • Cost • Power efficiency • Manufacturability • Integration • Reliability • Testability • Custom packaging Multimode optical fiber, with its larger core size compared to SMF, can more easily capture light from a transceiver, thereby decreasing alignment costs. While the cost of SMF optical sources have declined recently due to advances in silicon photonics, the less stringent alignment costs for MMF relative to SMF extend to multi- mode connectors. A small 8µm SMF core is also much more susceptible to dust and contamination than a 50µm MMF core, making MMF links more robust in enterprise and data center networks. For distances of less than 150 m and up to 550 m in some applications, the lower cost of connectivity, installation and ongoing maintenance, along with lower cost of 850 to 940 nanometer (nm) transceiver modules, make the combination of laser-optimized MMF and VCSEL-based transceivers the most cost-effective optical short-reach solution for enterprise and data center applications. Ethernet Market and Fibre Channel Market Trends The Ethernet market continues to grow and move to higher speeds. For traditional on-premises enterprise data center and LAN applications, OM3/4/5 fiber and VCSEL-based optics dominate structured cabling and point-to-point optical short-reach links. The vast majority of traditional enterprise links are less than 100 m, while virtually all traditional enterprise optical data center links are less than 300 m. In applications with speeds less than or equal to 10 gigabits per second (Gb/s), twisted-pair copper solutions have had remarkable success. However, at speeds greater than and equal to 10 Gb/s, optical solutions including traditional fiber cable/transceiver links and active optical cables (AOCs) are typically used. For distances less than 100 to 150 m, MMF is the solution of choice, while SMF is typically used for longer links. Direct-attach copper (DAC) cables are often used for reaches less than 5 m. In 2018, IEEE 802.3 completed IEEE Std 802.3cd TM -2018, which defined standards for 50GBASE-SR, 100GBASE-SR2 and 200GBASE-SR4 on 50 Gbaud lanes over OM3/OM4/OM5 operating at 850 nm. In January 2020, IEEE 802.3 completed IEEE Std 802.3cm™-2020, defining two new standards for 400 Gb/s Ethernet over OM3/OM4/OM5 MMF. Moreover, 400GBASE-SR4.2 is notable, as it is the first multimode solution that uses wavelength division multiplexing (WDM) to increase the data rate traveling over a pair of fibers. Proprietary and multisource agreement (MSA) solutions often fill in the gaps for specific appli- cations. Extended reach (up to 400 m for 40 Gb speeds) of standards-based solutions are often available for customers who may have the need to support longer distances. In 2017, the short wavelength division multi- plexing (SWDM) MSA released specifications for 40 Gb SWDM4 and 100 Gb SWDM4; commercial products became available at the end of that year. The 100 Gb BiDi solutions were introduced in the same time frame, adding another 100 Gb/s MMF/VSCSEL solution for duplex links. On the Road to 400 Gb/s Ethernet Currently, 100 Gb/s speeds are being used primarily by cloud data centers and leading-edge enterprise data centers. A significant portion of these adopters are utilizing the 100GBASE-SR4 solution, underscoring the continued cost/power/overall value proposition of MMF-VCSEL solutions with increasing data rates.

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