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CABLING INFRASTRUCTURE

Why choose multimode fiber?Total lifecycle costs may be lower and network flexibility grea ter than wit h single-mode fiber.

T

e use o ow-cost -nm s

in conjunction with mult imode fiber

can reduce the cost of premise

network installations.

For more information

from Corning Optical Fiber:www.corning.com/opticalfiber 

he primary factor affecting theesign o premises an oca area

networ s is t e overa cost o t ecomponents. The geometrical prop-

rties an er core construction o sing e-mo en mu timo e er i er great y, suc t at

ac er type as i erent optica -per ormancettri utes t at en t emse ves to i erent com-munications networ app ications.

 W en comparing t e re ative er core geom-tries of multimode and single-mode fiber, the

ore o mu timo ei er is more t a nive times greater inia meter t an t at

a sing e-mo e i-er. The large core ofu t imo e er asistinct a vantages:

t ena es ow oss con-ection an aci itatesimp e i er-to- i err er-to-transceiverlignment and, conse-uent y, is est suiteo premises an LANpplications. Apart rom switcectronics, t e opti-a transceivers are

t e most expensivepart o a premises net-

 wor insta ation. T eswitch electronics are

n epen ent o er type an , t ere ore, c angesn transceiver cost wi ave t e greatest e ect on

the overall network costs.T ere are our main types o optica transmit-

ters t at can e use in communications net- works. These light sources differ greatly in cost,

ptica c aracteristics an per ormance.Distri ute ee ac (DFB) an Fa ry-Perot

(FP) asers are expensive re ative to ig t-emit-ting io es (LEDs) an vertica -cavity, sur ace-

mitting asers (VCSELs), ut t e ig -powern ig y ocuse source eam a ows e cient

oupling of high power levels into the small coresing e-mo e er. LEDs an VCSELs o er an

nexpensive so ution or s ort-reac app ications,ike premises networks, but are unsuitable foring e-mo e er. VCSELs ave a ow numerica aperture, ut

an ave a arge active area (~15 µm) an avere ative y ow-source power, so t at t e coup ingciency into a 9-µm sing e-mo e er core is

ow. LEDs ave ow aunc power an , wit aarge numerical aperture, are also unsuitable foroup ing into sing e-mo e ers.To ene t rom t e cost a vantages o VCSELs

nd LEDs, multimode fiber should be used, as thearge core o mu timo e er aci itates ig y

cient coup ing o LED an VCSEL power.Recently, the use of LEDs in premises networks

as ecrease ue to t eir an wi t imitationn 850-nm VCSELs ave ecome t e c oice or

ort-reac premises app ications.T e cost o a premises networ w en insta e

using mu timo e er wit 850-nm VCSELs isower t an t e cost o a networ t at as eennstalled using either single-mode or multimode

er wit 1,300-nm asers.T e OM-3 (300-meter ata rate) mu timo e

ber-optic cable (MMF) solution features anOM-3-s tan a r i ze , 300-mete r 10 -Giga it

t ernet aser-optimize mu timo e er an10GBASE-SR 850-nm VCSEL transceivers. AnOM-3+, aser-optimize mu timo e er ena esncrease in istance over t e OM-3 stan ar ,

up to 550 meters, an a so uses 10GBASE-SR850-nm VCSELs.

OM-1 conventiona (FDDI gra e) mu timo eer requires mo e-con itioning patc cor s

nd uses 10GBASE-LX4 wideband wavelengthivision mu tip exer (WWDM) 1,300-nm DFB

aser transceivers. T e sing e-mo e so ution usesingle-mode fiber-interconnect hardware and

patc cor s, wit 10GBASE-LR 1,310-nm FPaser transceivers. A t oug t e increase manu acturing costsssociate wit mu timo e er resu t in t e

nitia cost o mu timo e er eing ig er t ant at o sing e–mo e er, wit transceivers e-

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ing a ominant cost, t e use o ow-cost850-nm VCSELs in conjunction withmu timo e i er can re uce t e costo premise networ insta ations. T e

lower-cost advantage of multimode fiberrequires t e correct se ection o er typean transceiver compati i ity, ta ingaccount o current an ong-term atarate requ rements.

C eaper egacy-gra e (OM-1) mu ti-mo e er ca ing can stretc to 10 G psbut requires more expensive 1,300-nmDFB asers an mo e-con itioning patccor s, or t e use o a itiona e ectronics(10GBASE-LX4 or 10GBASE LRM).OM-3 mu timo e er can support u-ture ig er ata rates o up to 40 G ps

an engineere so utions (using OM-3+er) can ena e exten e system reac

to 550 meters. ower-cost connectors as-

ist t e ow mu timo e er-insta ationost, with the deployment enabled by thereater o set an a ignment to erances ou timo e er.

By facilitating lower transceiver andonnection costs, t e maintenance anupgra e costs o a mu timo e i erremises networ wi e ower t an anquiva ent sing e-mo e networ . Over

t e i etime o a networ , t is wi yieperationa cost savings in a ition to t eower first-installed costs.

etwor ca e over ays are expensiven s ou e avoi e in or er to maintainow operating costs. Despite the availabil-ty o 10-G ps systems, many customersto ay require on y 10 M ps. Suc custom-

rs sti require t e exi i ity to upgra et e ata rate up to 10 G ps, i necessary,

 wit out incurring t e expense o a new

ca e over ay, an so t e system s oufacilitate a broad operating date range.

T e stan ar ize 1,310-nm FP anDFB aser transmitters, require or

transmission over single-mode fiber, arerestricte y t eir in erent compositionto a ower ata rate oun ary o 1,000M ps. By contrast, ow-cost 850-nm

 VCSELs t at are suita e on y or trans-mission over mu timo e i er ave a

roa ata-rate operating range– rom10 Mbps up to 10 Gbps. Therefore, thecom ination o mu timo e i er an850-nm VCSELs constitutes a ow-costsolution that facilitates the current needso a ow ata rate networ , w i e a so u-ture proo ng t at networ y provi ing

a c ear migration pat rom 10 M ps to10 G ps on t e same er.

Reprinted from Communications News , March 2006Copyright © 2006 by Nelson Publishing Inc. • www.comnews.com