Application Note 1206 Telecommunications Fiber Loop Converters are sometimes required to operate over multimode fiber because an existing span of installed multimode fiber may already be in place between two points requiring FLC transmission. The FLCs were designed for use over singlemode fiber, and if there is a choice, singlemode fiber should be installed. However, FLC operation over multimode fiber is possible and, in fact, is a functioning application with several custom- ers. LAN applications over short distances have been successful. The following aspects of this application require attention. A 10 meter (33') singlemode jumper with a physical finish on the connector endfaces should be installed in the FLC transmitter. This singlemode jumper can then be con- nected to the multimode fiber in the span. To prevent higher order modes from being launched directly into the multimode fiber, a minimum of 10 meters (33') of singlemode fiber is required out of the transmitter. The multimode fiber can terminate directly into the FLC’s receiver at the other end of the span. Ideally, the only connection in the span will be the junction from singlemode to multimode. If fiber joining is required anywhere else in the span, fusion splicing is recommended. Because the connectors in a multimode span are not required to be in physical contact at the fiber endfaces, Fresnel reflections and alignment mismatches can degrade perfor- mance to an unacceptable level. If connectors are in the span, they should be of singlemode quality with physically contacting, radius-polished fiber endfaces. Multimode SMA and biconic fiber connectors are unacceptable. D4, SC, FC and ST ® connectors can be used, if the endface polish and the concentricity tolerances are singlemode quality. The number of connectors should be kept to the absolute minimum. Launch Conditions Connections in the Span ® Operating Fiber Loop Converters Over Multimode Fiber 2 Operating FLCs over Multimode Fiber Application Note 1206 Multimode fiber has higher loss per distance properties than singlemode fiber. Tradi- tional calculations of optical budget for the span will not take into account the pulse spreading and interference resulting from sending a singlemode signal down a multi- mode fiber. The optical budget for the DS3 FLC is 13 dB at 1300 nm wavelength. Standard Corning 62.5 mm fiber has attenuation of 0.7 dB/km. This works out to a theoretical capability of 18.5 km (11.5 miles) based on optical budget alone. When bandwidth is considered, the theoretical distance limit decreases. Bandwidth is not a limiting factor for T1/E1 FLCs and QFLCs. Bandwidth may become the limiting factor when the bit rate increases to DS3 rates or above. The bandwidth of the fiber, which is measured in the units of MHz-kilometers, should be known. Standard Corning graded-index 62.5 micron core multimode fiber typically exhibits a bandwidth of 400 MHz/km. This means that an FLC operating at 51.84 Mbps (which translates into an analog rate of 25.92 MHz) is theoretically capable of transmit- ting over a distance of 15.43 km (9.56 miles). However, more conservative distances are recommended. See Table 1 (which lists the minimum of 200 MHz/km) and Table 2 for the theoretical limits of the FLCs. The bandwidth cells of the fibers listed in the tables are minimums. Fiber of greater bandwidth capacity is available from the manufactur- ers. QLX modules operate at the same rates as the QFLC. DS3 FLCs have been successfully implemented over a distance of 10.0 km (6.2 miles on multimode fiber). Both attenuation and bandwidth of the multimode fiber should be examined and the limits calculated before installing FLCs and QLXs for use over multimode fiber. Charac- terizing the fiber plant or records indicating the exact fiber type will help to determine how well FLCs and QLXs can work over multimode fiber. Call ADC Application Engineer- ing at 1-800-366-3889 before purchasing FLCs or QLXs for use over multimode fiber. Optical Budget, Bandwidth and Fiber Properties ADC CATALOG NUMBER Multimode Fiber TABLE 1: Theoretical Span Calculation for FLCs Over Multimode Fiber CORNING 50/125 Att.: 0.80 dB/km BW: min. 400 MHz.km Theoretical Capacity: Attenuation: 16.2 km / 10.0 miles Bandwidth: 15.4 km / 9.56 miles (25.920 MHz) CORNING 62.5/125 Att.: 0.70 dB/km BW: min. 200 MHz.km Theoretical Capacity: Attenuation: 18.5 km / 11.5 miles Bandwidth: 7.71 km / 4.78 miles (25.920 MHz) CORNING 100/140 Att.: 2.00 dB/km BW: min. 100 MHz.km Theoretical Capacity: Attenuation: 6.50 km / 4.03 miles Bandwidth: 3.85 km / 2.39 miles (25.920 MHz) AT & T 62.5 Att.: 1.00 dB/km BW: min. 500 MHz.km Theoretical Capacity: Attenuation: 13.0 km / 8.05 miles Bandwidth: 19.2 km / 11.9 miles (25.920 MHz) BerkTek 62.5/125 Att.: 1.00 dB/km BW: 500 MHz.km Theoretical Capacity: Attenuation: 13.0 km / 8.05 miles Bandwidth: 19.2 km / 11.9 miles (25.920 MHz) T3/FLC DS3-B1LDFC(SC) 13 dB at 1300 nm 3 Operating FLCs over Multimode Fiber Application Note 1206 CORNING 50/125 Att.: 0.80 dB/km BW: 400 MHz/km CORNING 62.5/125 Att.: 0.70 dB/km BW: 200 MHz/km CORNING 100/140 Att.: 2.00 dB/km BW: 100 MHz/km AT&T 62.5 Att.: 1.00 dB/km BW: 500 MHz/km BerkTek 62.5/125 Att.: 1.00 dB/km BW: 500 MHz/km 28.7 km 17.7 miles 32.8 km 20.3 miles 11.5 km 7.12 miles 23.0 km 13.6 miles 23.0 km 14.3 miles T1/DFLC F1544-20XR 23 dB/1300nm 27.5 km 17.0 miles 31.4 km 19.4 miles 11.0 km 6.81 miles 22.0 km 13.6 miles 22.0 km 13.6 miles T1/QLX QLX- SPXSC(FC)A2 22 dB/1300nm 27.5 km 17.0 miles 31.4 km 19.4 miles 11.0 km 6.81 miles 22.0 km 13.6 miles 22.0 km 13.6 miles T1/QFLC QFC- D3LDSC(FC) 22 dB/1300nm ADC CATALOG NUMBER Multimode Fiber 27.5 km 17.0 miles 31.4 km 19.4 miles 11.0 km 6.81 miles 22.0 km 13.6 miles 22.0 km 13.6 miles E1/DFLC F2048- 20M(R)XR 22 dB/1300 nm TABLE 2: TheoretIcal Span Calculation for FLCs Over Multimode Fiber Contact ADC Application Engineering at 1-800-366-3889 for additional assistance. Application Note 1206 12/94 Original © 1994 ADC Telecommunications, Inc. All Rights Reserved An Equal Opportunity Employer Specifications published here are current as of the date of publication of this document. Because we are continuously improving our products, ADC reserves the right to change specifications without prior notice. At any time, you may verify product specifications by contacting our headquarters office in Minneapolis. ADC Telecommunications, Inc. 4900 West 78th Street Minneapolis, Minnesota 55435 FAX: (612) 946-3292 For U.S. Sales, Call Toll Free: 1-800-366-3891 ® Telecommunications International Sales Offices: Belgium 32-2-721-5282 • United Kingdom 44-734-441955 • Montreal, Quebec (514) 677-9166 • Vancouver, BC (604) 270-1675 • Toronto, Ont. (905) 629-3104 • Ottawa, Ont. (613) 596-9937 • Singapore 65-225-8228 • Venezuela 58-2-953-1684 • Mexico City, Mexico 525-658-4519 • Sydney, Australia 61-2-975-1499 . in the Span ® Operating Fiber Loop Converters Over Multimode Fiber 2 Operating FLCs over Multimode Fiber Application Note 1206 Multimode fiber has higher. Telecommunications Fiber Loop Converters are sometimes required to operate over multimode fiber because an existing span of installed multimode fiber may already