Optimal 10-Gbit/sec laser and MMF specs

BY PAUL KOLESAR

Since late 1999, the TIA FO2.2.1 Working Group has been determining the necessary performance criteria for multimode fiber (MMF) and 850-nm laser transmitters to support emerging 10-Gbit/sec applications to at least 300 m. The effort succeeded in providing a low-cost solution meeting the distance requirements of the vast majority of in-building LANs, storage-area networks (SANs), and equipment room inter connections using 850-nm vertical-cavity surface-emitting laser (VCSEL) serial transceivers and laser-optimized 50-micron MMF.

To meet the needs of the market, the FO2.2.1 Working Group aligned its schedule with the development time-line of the most aggressively scheduled 10-Gbit/sec application standard. The IEEE 802.3ae 10-Gigabit Ethernet Task Force schedule called for last technical changes beginning in May. That also aligned well with the NCITS T11.2 10-Gigabit Fibre Channel Task Group, which is tracking and adopting 10-Gigabit Ethernet physical layer technology. Coincidentally, the Optical Interconnection Forum (OIF) began defining specifications for OC-192 (10-Gigabit SONET) optical interconnections within central offices.

Many companies participated in the effort. Corning Inc. chaired the Task Group and coordinated almost weekly teleconferences. Agilent Technologies, Cielo Communications Inc., IBM, Lucent Technologies, and Picolight Inc. supplied 10-Gbit/sec sources and test facilities. Corning, Draka Fibre Technology B.V., and Lucent supplied laser-optimized 50-micron fibers. Lucent cabled and characterized the fiber using its high-resolution differential mode delay (DMD) equipment. IBM and Lucent thoroughly simulated the system using source and fiber characteristics supplied by all. Lucent authored the DMD test procedure, FOTP-220, as the standard test method for characterizing the new laser-optimized MMF. Agilent, Corning, IBM, and Lucent analyzed the measurement data and simulation results. And all participated in specification negotiations.

At its June plenary meeting, the Working Group determined an optimum set of specifications that equitably distributed the performance requirements. The transmitter launch-condition specification limits the excitation to the easiest-to-control mid-order modes of the MMF, while allowing tolerances compatible with low-cost packaging. These launch-condition specifications are now written into the applications standards. The MMF requirements allow a tradeoff between mid-order-mode DMD and low- and high-order-mode DMD, effectively loosening the tolerance on the manufacturing process. The DMD requirements are written into a new draft detail specification, to be published as TIA/EIA 492AAAC.

Paul Kolesar, a distinguished member of the technical staff at Lucent Technologies, Bell Laboratories (Holmdel, NJ), represents Lucent's Optical Fiber Systems business unit on several standards committees. He can be reached at tel: 732-949-1255; fax: 732-817-2748; e-mail: pkolesar@lucent.com.

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