IEEE 802.3 1.25 GBd MMF Link Specification Development Issues Del Hanson Hewlett-Packard Company Optical Communication Division 350 W. Trimble Road San Jose, CA 95131 del_hanson@hp-sanjose-om1.om.hp.com Introduction Near the end of the 5/21-22/96 IEEE 802.3 Gb/s Ethernet Interim Meeting, there was extensive discussion attempting to reconcile the committee's desire to support a 550 m multimode fiber (MMF) building backbone link length at 1.25 GBd with the achievable limits achievable with current 850 nm laser diode (LD) proposals which are based on over-filled launch (OFL) modal bandwidth. There was a motion to specify 550 m with 50MMF and 100 m with 62MMF (to match the existing ISO 11801 building wiring system horizontal length). This motion was tabled until the 7/96 IEEE 802.3 Gb/s Ethernet meeting when additional data on link length requirements and technical capabilities were expected to be presented. LAN backbone links primarily utilize 62MMF in the U.S. and Europe. This 550 m 62MMF link length is not supported with 850 nm sources based on the only launch conditions specified for the installed base, i.e., OFL. SMF is installed today to achieve >= 2 km link lengths. Although current 1300 nm SMF transceivers have somewhat higher complexity than 850 nm VCSEL transceivers targeted for 1 Gb/s Ethernet MMF links, recent work demonstrates that 1300 nm SMF transceivers can be leveraged for use with MMF links. They can potentially support a very high modal bandwidth when launched into MMF and a modal noise penalty, associated with mode selective loss (MSL), which is equal to the 1 dB penalty of 850 nm LDs launched into 50MMF (as documented in a separate paper presented by David Cunningham of HPL Bristol Lab following this paper). This paper provides a recommendation for specifying 850 nm transceivers to their MMF link length limits and leveraging 1300 nm SMF transceivers to support SMF links and <=850 m 62MMF link length based on the OFL modal bandwidth specification of 500 Mhz*km for 62MMF at 1300 nm which exists today. This exceeds the 550 m building backbone link length for 62MMF used predominantly in building wiring systems. The paper proposes further work to confirm the extended modal bandwidth for 1300 nm SMF launch into 62MMF to extend the link specification to 2 km for 62MMF campus backbones. 1. Outline * Summary of 850 nm laser source link length limits with multimode optical fiber (MMF) and over-filled launch (OFL) * Current Fiber Optic Link Proposals for MMF and SMF * Extending 62MMF Link Length Limits With 1300 nm Laser Link Technology * Comparison of 850 nm and 1300 nm Link Technology Strengths * Recommended Link Proposals To Meet Existing and Meet Future MMF LAN requirements 2. Objectives of Presentation * Extend Gb/s Ethernet Multimode Optical Fiber (MMF) Link Length Limits To Meet Existing Building Wiring System Backbone Requirements * Provide An Integrated View Of The Gb/s Ethernet Link Application Space For 850 nm and 1300 nm Laser Sources With MMF * Explore Leveraging 1300 nm SMF Transceivers For Use With SMF and MMF Media 3. Two figures show the worst Case link length limits for 50MMF and 62MMF at 1.25 GBd with 850 nm laser sources with over-filled launch (OFL) vs. spectral width (FWHM). Source 10-90 % response time is 0.45 ns. The objective was to meet the 550 m link length target for 50MMF as defined at the Wakefield Interim Meeting by suitably restricting the source spectral parameters. These parameters can be relaxed to the values presented at the Wakefield Interim meeting if the link length is relaxed to 450 m. -----Worst Case Link Length----- Fiber Modal Bandwidth FWHM=9 nm FWHM=7 nm FWHM=5 nm 50MMF 500 MHz*km 455 m 550 m 650 m 62MMF 160 Mhz*km 250 m 260 m 270 m 4. Current 1.25 GBd Ethernet Technology Alternatives & Link Length Limits * To meet the 550 m backbone link length with 50MMF having 500 MHz*km OFL modal bandwidth, the proposed 850 nm link length limit specifications is for FWHM = 7 nm. This achieves >250 m with 62MMF and OFL. * Specify 1300 nm SMF transceivers, following the lead of Fibre Channel, to support 2 km and 10 km SMF link lengths. 5. Modal bandwidth perspective for 62MMF at 1300 nm * Worst case OFL modal bandwidth is 500 MHz*km * Recent measurement of modal bandwidth for a group of 62MMFs having lengths in the 750 to 3000 km range showed an average OFL modal bandwidth of 987 Mhz*km and > 2 GHz bandwidth (the limit of the measurement instrument) for all fibers with SMF launch. For the longest length fiber, this implies that the modal bandwidth is > 6 GHz*km. 6. This figure shows the 62MMF link length limits at 1.25 GBd with 1300 nm laser source for various modal bandwidths. Source 10-90 % response time is 0.45 ns. The 500 Mhz*km case, corresponding to the worst case OFL specification, supports 850 m. With a 1200 Mhz*km modal bandwidth, such as might be supportable with SMF launch, 2 km 62MMF campus backbone links can be achieved in worst case. 7. Meeting Gb/s Ethernet Building Link Length Requirements * 62MMF dominates installed LANs but 850 nm technology does not support the required 550 m building backbone link length with OFL. * The Question: How can the best advantages of 850 nm and 1300 nm technology be utilized to achieve current and future network requirements? * The Barrier? The two technologies are not compatible on the same link. 8. A figure shows the cross-section of 850 nm, 980 nm and 1300 nm VCSELs. Gb/s transceivers utilizing 850 nm VCSELs are being released today. It is projected that in about three years, 1300 nm VCSELs will be released to reduce the cost of supporting 62MMF building backbone links. 9. Comparative Strengths of 850 nm and 1300 nm Link Technologies * 1300 nm Source Technology Strengths - Lower fiber attenuation; longer link lengths and smaller optical power budgets - Higher modal bandwidth with installed 62MMF - Higher eye safety limits - Higher proven reliability projected from LED-based optical sources - Can leverage for use with both SMF and MMF * 850 nm Source Technology Strengths - Lower complexity; Examples: + Possible integration of optical detector/amplifier + Easier VCSEL implementation 10. Recommendations For Gb/s Ethernet Link Technologies * Avoid the incompatibility between 850 nm and 1300 nm link transceiver interfaces on the same link. * Specify 850 nm technology for conventional 100 m horizontal links and extended horizontals to <550 m with 50MMF and 250 m with 62MMF. * Utilize 1300 nm SMF transceivers for SMF media of <2 km and <10 km link lengths. * Leverage 1300 nm SMF transceivers for <550 m building backbones. Can support 850 m 62MMF backbones based on existing 1300 nm OFL modal bandwidth. Utilize 1300 nm VCSELs later. * Explore extending 1300 nm SMF transceivers to cover <2 km 62MMF backbones. 11. Proposed Link Interface Specifications * A spread sheet table shows a detailed comparison of the 1250 MBd, 550 m link interface specifications for 50MMF links utilizing 850 nm LDs and 62MMF links utilizing 1300 nm LDs. A 7 dB optical power budget and 1 dB MSL penalty is specified in both cases.