O p t i c a l F i b r e

Cost-effective bandwidth scaling in data-centre applications is being enabled by recent advances in laser-optimized multimode fibres and their characterization as Russell Ellis explainsThe overriding Trend in modern data centres is the relentless drive towards higher data rates to support bandwidth-intensive data services Another key development has been the sharp decline in the cost of optical-fibre solutions in recent years which for many network designers has made multimode fibre the automatic choice for supporting these short-distance high-data-rate applications

Those who are familiar with multimode-based solutions will already be aware of their many benefits These include cheaper electronics and easier connectorization as well as higher bandwidth longer reach and increased security compared with bulkier UTP (unshielded twisted pair) cables With bandwidth demands continuing to grow rapidly ndash and with greater restric-tions on building and cabling infrastruc-ture for safety security and environmental reasons ndash the decision on which fibre type to install has never been so important

Indeed the trend towards higher data rates has demanded continued improve-ments to the design and manufacture of the optical fibre Older multimode fibres were optimized to operate with LEDs but these OM1 and OM2 fibre types are typically limited to data rates in the Mbits range In contrast laser-optimized multimode fibres are designed specifically to work with low-cost vertical cavity surface emitting lasers (VCSELs) that operate at 850 nm and speeds of up to 10 Gbits ndash although these OM3 fibres are still compatible with LEDs

In the five years since 10 Gbits Ether-net was introduced there has also been a significant change in the way laser-op-timized multimode fibres are produced

LED-optimized OM1 and OM2 fibres suffer from dips in the refractive index along the centre line of the fibre as well as other inaccuracies in the glass core These variations are not particularly important at Mbits data rates but even today OM1 and OM2 fibres are untested and unreliable for higher-speed applications

Meanwhile new manufacturing tech-niques for laser-optimized multimode fibres based on Corningrsquos Outside Vapour Deposition process eliminate the dips in refractive index along the fibre that limit performance This means that OM3 fibres deliver more accurate core profiles which in turn makes it possible to extract much higher bandwidth from the glass (figure 1)

Measurement and bandwidthAlongside these advances in fibre tech-nology accurate measurement of fibre bandwidth is crucial for designers to push network performance to the limit The key priority for network designers is to ensure that their choice of fibre will meet

their speed and reach requirements while maintaining high reliability This in turn is dependent on the bandwidth of the mul-timode fibre ndash defined as frequency times dis-tance measured in MHzkm ndash which determines the information-carrying capacity of each fibre

If the bandwidth is known accurately the system reach can be calculated for any data rate or system application such as Ether-net Fibre Channel at 1 2 4 or 8 Gbits and so on And high-data-rate applications that are now being supported in data centres are more reliant than ever on the accuracy with which the intrinsic laser bandwidth of a multimode fibre can be measured

Multimode fibre bandwidth can only be measured accurately during manufactur-ing and not during cable making or client testing after cable installation Simula-tions and functionality testing are also crucial to determine the data rate and link distance that can be supported by a fibre since system reach also depends on factors such as the transceivers and the number

Refined multimode fibre supports high-rate data

Fine tune a pumped Tisapphire laser is tuned for parameters such as pulse width and power spectral characteristics and stability The laser output is coupled to Corningrsquos minEMBc-DMD reference system at the Center for Fiber-optic Testing the worldrsquos first fibre-testing facility

corning

copy Inst i tute of Physics and IOP Publishing Ltd Repr inted f rom the Autumn 2007 issue of FibreSystems Europe

O p t i c a l F i b r e

copy Inst i tute of Physics and IOP Publishing Ltd Repr inted f rom the Autumn 2007 issue of FibreSystems Europe

and type of connectors that are needed in the link of a real network

The latest and most accurate way to measure the intrinsic laser bandwidth properties of a multimode fibre is known as minEMBc (minimum calculated effective modal bandwidth) and is defined by the IEC 60793-1-49 standard that was estab-lished in 2006 The minEMBc technique is designed to replace the previous Differ-ential Modal Delay (DMD) mask method which was first developed to test OM3 fibres during early development work of the 10 Gbits Ethernet standard

DMD drawbackThe DMD method was originally devised as a passfail screening test to identify fibres that could support 10 Gbits over 300 m However the DMD mask method does not actually measure bandwidth but instead assumes a bandwidth value of 2000 MHzkm This means that the DMD-mask method cannot always screen out OM3 fibres that will not operate correctly with all commercially available 10 Gbits transceivers Whatrsquos more DMD-mask measured fibres are only characterized against 10 Gbits Ethernet and a target distance of 300 m but in reality there are large variations in link distances proto-cols and the data rate of the service

In contrast the system reach for a multi-mode fibre measured with the minEMBc method can be determined for any appli-cation This technique exploits a high-resolution measurement based on DMD techniques to obtain an initial measure-ment of the fibre but then also analyses the fibre bandwidth performance more precisely with a full range of standards-compliant transceivers to calculate the minimum effective modal bandwidth By using the characteristics of a full range of real-life transceivers to calculate the bandwidth performance with all compli-ant transceiver types is ensured

The significant advantage of the minEMBc technique is that it gives each fibre its own specific measured bandwidth value enabling link distances and data-rate performance to be determined for any application ndash not just 10 Gbits Ether-net over 300 m Consequently those fibres with bandwidth capabilities in excess of 2000 MHzkm are clearly identified so that the system designer can benefit from their full bandwidth capability

To understand the strength of the minEMBc bandwidth value imagine an analogy of a car journey with and without a fuel gauge Without a fuel gauge but an

assumed quantity of fuel the maximum total range is determined by your confi-dence level in your fuel quantity assump-tions This is in effect what DMD-mask tested OM3 fibre offers In contrast the minEMBc measured bandwidth value offers a ldquofuel gaugerdquo making it possible

to use all of the available bandwidthFigure 2 shows how OM3 fibres meas-

ured using minEMBc can determine the systemrsquos reach for a host of commonly used applications In this way minEMBc is the most rigorous performance meas-urement for multimode fibre and is more

2

OM3STOP

1

E F

100G

OM3standardized minEMBc testmethod for all LOMMFs

and beyond

1 Gb Ethernet2G Fibre Channel4G Fibre Channel

10G Ethernet

0 1000 2000 3000 4000 5000minEMBc bandwidth MHzkm

ge1000 mge550 mge310 mge400 m

standardized 10 Gbits DMD-masks test

method for OM3 only

OM3 system reach DMD (2000 EMB) vs min EMBc (with 3000 EMB MHzkm)

300 m 550 m

Fig 2 Multimode fibres measured with minEMBc can take the guesswork out of system capability

100 000

10 000

1000

100

10

11985 1995 1998 2002 ~2009

year of application standardizationfibre introduction

100 Mbits

100Base-S100Base-F

ATM

1 Gbits

10 Gbits

Ethernet1000Base-SXFibre Channel

ATM

Ethernet10GBase-SRFibre ChannelSonetSDHInfiniBand

40 Gbitsor

100 Gbits

10 MbitsFDDI

LED bandwidth limitlt600 Mbits

multimodelaser bandwidthmeasurements

ge1 Gbits

minEMBc

RML

laser-optimized OM3 fibre

LED-optimized OM1 OM2 fibres

DMD(masks)

futurehigher

multi-Gbitsapplicationsav

aila

ble

band

widt

h (M

bit

s)

Fig 1 Multimode fibre is migrating towards higher performance speeds driving the need for new fibre types and improved characterization The key drivers for this are higher bandwidth demand the use of lower-cost VCSEL devices and easier and cheaper multimode connectivity

Multimode fibre type

OM classification as per ISOIEC 11801

LED bandwidth (MHzmiddotkm) [8501300 nm]

Effective (laser) modal bandwidth (EMB MHzmiddotkm) [950 nm]

Primary application speed

625125 oM1 200500 ndash 10ndash100thinspMbits

50125oM2 500500 ndash le1thinspgbits

oM3 1500500 ge2000 ge10thinspgbits

O p t i c a l F i b r e

copy Inst i tute of Physics and IOP Publishing Ltd Repr inted f rom the Autumn 2007 issue of FibreSystems Europe

reliable to safeguard link distances for any application and any data rate

For some high-data-rate platforms such as in data centres OM1 and OM2 fibre grades are already outdated Appli-cations running at speeds of 1 or 2 Gbits often require excess bandwidth capacity to boost the speed by a factor of 2 or 4 These higher speeds may not be achieved without provision for excess bandwidth capacity in the cabling otherwise each increasing step in speed causes a corre-sponding drop in reach

Many owners of data-centre networks are already installing OM3-based solu-tions to meet their short- to medium-term requirements for increased data rates which also avoids disruption to serv-

ices and reliability Higher bandwidth cabling is the most cost-effective solution to upgrade the network since the cost of the passive cabling element of a network is typically the lowest element accounting for less than 3 of the total In contrast switch electronics and application-based hardware typically account for more than 75 of the total investment

Figure 3 shows comparative component costs for OM1 OM2 and OM3 fibre solu-tions comprising cabling patching hard-ware and optical transceiver interfaces for a 24-port 1 Gbits Ethernet riser or Fibre Channel link Also included is the estimated incremental cost of upgrad-ing from 1 to 10 Gbits based on current 10 Gbits interface costs ndash which continue

to decline As can be seen the optical cable cost is small compared to the cost of the 1 Gbits transceivers and even smaller next to the 10 Gbits transceivers Indeed an all-OM3 850 nm link solution with 10 Gbits transceivers is typically more than 30 cheaper than an equivalent OM2 link which requires singlemode-based transceiver upgrades to support 10 Gbits

In fact the cost premium to install OM3 in the first instance for a 1ndash2 Gbits system is typically only about 1ndash2 higher than that of OM2 fibre types when one also includes electronics and installation This is because non-laser-optimized fibre types require more expensive 1300 nm single-mode-based transceivers and the use of mode-conditioning patchcords to achieve uncertified link distances at 10 Gbits which may be less than the 300 m achiev-able with OM3 fibre The lower bandwidth of OM1 and OM2 is reflected in the lim-ited 10 Gbits system reach at 850 nm ndash the lowest cost operating wavelength ndash which is also shown in figure 3

OM3 meets future data needsAs with all multimode fibre the per-formance is dependent on the bandwidth provided relative to current needs The relentless pace of increase in data speeds and demands for higher security and reli-ability means that all networks need a robust and cost-effective upgrade path which makes OM3 multimode fibre the logical choice when the multi-gigabit performance of OM1 and OM2 fibres is questionable or unspecified

Many operators may have already tran-sitioned their OM1 and OM2 cabling to Gigabit-Ethernet or 1ndash2 Gbits Fibre Chan-nel but only over shorter link distances For the next increase on the data-speed ladder such as 4ndash10 Gbits data applica-tions the limited capability of OM1OM2 grades will cause many systems to fall short of the reach requirements

With a minEMBc bandwidth certifica-tion a link can be effectively designed to maximize but at the same time safeguard system reach Today OM3 fibre accounts for more than 10 of multimode sales in EU and clearly the market is acknowledg-ing its advantages These advantages when coupled with minEMBc technology will ensure that multimode fibre will continue to deliver robust high-speed connectivity when the inevitable step up to 100 Gbits Ethernet systems arrives

Russell Ellis is senior applications engineer for Corning Optical Fiber

ErnstthinspampthinspYoungthinsponethinspofthinspgermanyrsquosthinsplargestthinspauditingthinspandthinspconsultingthinspfirmsthinspwiththinsp6500thinspemployeesthinspinthinsp22thinsplocationsthinsprecentlythinspmergedthinspitsthinspthreethinspdatathinspcentresthinspwhichthinspwerethinsplocatedthinspinthinspStuttgartthinsprotterdamthinspandthinspEschbornthinspnearthinspFrankfurtthinspldquoThethinspconsolidationthinspofthinsp

ourthinspthreethinspdatathinspcentresthinspinthinspTelecityredbusthinspallowsthinspusthinspconsiderablethinspcostthinspsavingsrdquothinspsaidthinspWolfgangthinspFroumlhlichthinspsitethinspmanagerthinspresponsiblethinspforthinspErnstthinspampthinspYoungrsquosthinsplocal-areathinspnetworkthinspandthinspdatathinsp

centrethinspinthinspEschbornthinspldquoWethinspreliedthinsponthinspthethinspnetworkingthinspspecialistthinspcorningthinspforthinspourthinspdatathinspcentrersquosthinspfibre-opticthinspnetworkrdquocorningthinspwasthinspresponsiblethinsp

forthinspthethinspplanningthinspandthinspinstallationthinspofthinspthethinspdatathinspcentrersquosthinspentirethinspfibre-opticthinspsystemthinspThisthinspfeaturedthinspthethinspcompanyrsquosthinspinfinicorthinspSX+thinsplaser-optimizedthinspmultimodethinsp(oM3)thinspfibrethinspwhichthinsphasthinspbeenthinspcertifiedthinspusingthinspminEMBcthinspinfinicorthinspSX+thinspfibrethinspisthinspdesignedthinsptothinspmeetthinspthethinspdemandsthinspofthinspthethinsp10thinspgbitsthinsp

Ethernetthinspstandardthinspandthinspisthinspideallythinspsuitedthinsptothinspdata-centrethinspapplicationsthinspThethinspinstallationthinspalsothinsp

usedthinsppre-terminatedthinspcablingthinspsolutionsthinsptothinspenablethinspthethinsp600thinspm2thinspfacilitythinspwiththinspathinspcapacitythinspofthinspupthinsptothinsp500thinspserversthinsptothinspbethinspcompletedthinspinthinsponlythinspsixthinspweeksinfinicorthinspmultimodethinsp

fibrethinspsolutionsthinspensurethinsplaserthinsptransceiverthinspcompatibilitythinspandthinspsystemthinspperformancethinspforthinspathinspwidethinsprangethinspofthinsppremisesthinspnetworkthinspapplications

case study ernst amp yOung data centre Fr ankFur t

140

120

100

080

060

040

020

000 0

100

200

300

optical cable patching HW 1 Gbit TxRx

10 Gbit TxRxmode-conditioning patch cords

24-port 20m link constructed usingOM1 solution based on 1000Base-SX and 10GBase-LX4 + MCPSOM2 solution based on 1000Base-SX and 10GBase-LX4 + MCPSOM3 solution based on 1000Base-SX and 10GBase-SR

OM1 OM2 OM3

300m

~82m

~33m

rela

tive

aver

age

selli

ng p

rice

10G

reac

h (m

) [at

850

nm]

Fig 3 Average price differences of 1 Gbits multimode links comprising OM1 OM2 and OM3 fibres for an upgrade to 10 Gbits costs Plus the difference in system reach for a 10 Gbits link

O p t i c a l F i b r e

copy Inst i tute of Physics and IOP Publishing Ltd Repr inted f rom the Autumn 2007 issue of FibreSystems Europe

and type of connectors that are needed in the link of a real network

The latest and most accurate way to measure the intrinsic laser bandwidth properties of a multimode fibre is known as minEMBc (minimum calculated effective modal bandwidth) and is defined by the IEC 60793-1-49 standard that was estab-lished in 2006 The minEMBc technique is designed to replace the previous Differ-ential Modal Delay (DMD) mask method which was first developed to test OM3 fibres during early development work of the 10 Gbits Ethernet standard

DMD drawbackThe DMD method was originally devised as a passfail screening test to identify fibres that could support 10 Gbits over 300 m However the DMD mask method does not actually measure bandwidth but instead assumes a bandwidth value of 2000 MHzkm This means that the DMD-mask method cannot always screen out OM3 fibres that will not operate correctly with all commercially available 10 Gbits transceivers Whatrsquos more DMD-mask measured fibres are only characterized against 10 Gbits Ethernet and a target distance of 300 m but in reality there are large variations in link distances proto-cols and the data rate of the service

In contrast the system reach for a multi-mode fibre measured with the minEMBc method can be determined for any appli-cation This technique exploits a high-resolution measurement based on DMD techniques to obtain an initial measure-ment of the fibre but then also analyses the fibre bandwidth performance more precisely with a full range of standards-compliant transceivers to calculate the minimum effective modal bandwidth By using the characteristics of a full range of real-life transceivers to calculate the bandwidth performance with all compli-ant transceiver types is ensured

The significant advantage of the minEMBc technique is that it gives each fibre its own specific measured bandwidth value enabling link distances and data-rate performance to be determined for any application ndash not just 10 Gbits Ether-net over 300 m Consequently those fibres with bandwidth capabilities in excess of 2000 MHzkm are clearly identified so that the system designer can benefit from their full bandwidth capability

To understand the strength of the minEMBc bandwidth value imagine an analogy of a car journey with and without a fuel gauge Without a fuel gauge but an

assumed quantity of fuel the maximum total range is determined by your confi-dence level in your fuel quantity assump-tions This is in effect what DMD-mask tested OM3 fibre offers In contrast the minEMBc measured bandwidth value offers a ldquofuel gaugerdquo making it possible

to use all of the available bandwidthFigure 2 shows how OM3 fibres meas-

ured using minEMBc can determine the systemrsquos reach for a host of commonly used applications In this way minEMBc is the most rigorous performance meas-urement for multimode fibre and is more

2

OM3STOP

1

E F

100G

OM3standardized minEMBc testmethod for all LOMMFs

and beyond

1 Gb Ethernet2G Fibre Channel4G Fibre Channel

10G Ethernet

0 1000 2000 3000 4000 5000minEMBc bandwidth MHzkm

ge1000 mge550 mge310 mge400 m

standardized 10 Gbits DMD-masks test

method for OM3 only

OM3 system reach DMD (2000 EMB) vs min EMBc (with 3000 EMB MHzkm)

300 m 550 m

Fig 2 Multimode fibres measured with minEMBc can take the guesswork out of system capability

100 000

10 000

1000

100

10

11985 1995 1998 2002 ~2009

year of application standardizationfibre introduction

100 Mbits

100Base-S100Base-F

ATM

1 Gbits

10 Gbits

Ethernet1000Base-SXFibre Channel

ATM

Ethernet10GBase-SRFibre ChannelSonetSDHInfiniBand

40 Gbitsor

100 Gbits

10 MbitsFDDI

LED bandwidth limitlt600 Mbits

multimodelaser bandwidthmeasurements

ge1 Gbits

minEMBc

RML

laser-optimized OM3 fibre

LED-optimized OM1 OM2 fibres

DMD(masks)

futurehigher

multi-Gbitsapplicationsav

aila

ble

band

widt

h (M

bit

s)

Fig 1 Multimode fibre is migrating towards higher performance speeds driving the need for new fibre types and improved characterization The key drivers for this are higher bandwidth demand the use of lower-cost VCSEL devices and easier and cheaper multimode connectivity

Multimode fibre type

OM classification as per ISOIEC 11801

LED bandwidth (MHzmiddotkm) [8501300 nm]

Effective (laser) modal bandwidth (EMB MHzmiddotkm) [950 nm]

Primary application speed

625125 oM1 200500 ndash 10ndash100thinspMbits

50125oM2 500500 ndash le1thinspgbits

oM3 1500500 ge2000 ge10thinspgbits

O p t i c a l F i b r e

copy Inst i tute of Physics and IOP Publishing Ltd Repr inted f rom the Autumn 2007 issue of FibreSystems Europe

reliable to safeguard link distances for any application and any data rate

For some high-data-rate platforms such as in data centres OM1 and OM2 fibre grades are already outdated Appli-cations running at speeds of 1 or 2 Gbits often require excess bandwidth capacity to boost the speed by a factor of 2 or 4 These higher speeds may not be achieved without provision for excess bandwidth capacity in the cabling otherwise each increasing step in speed causes a corre-sponding drop in reach

Many owners of data-centre networks are already installing OM3-based solu-tions to meet their short- to medium-term requirements for increased data rates which also avoids disruption to serv-

ices and reliability Higher bandwidth cabling is the most cost-effective solution to upgrade the network since the cost of the passive cabling element of a network is typically the lowest element accounting for less than 3 of the total In contrast switch electronics and application-based hardware typically account for more than 75 of the total investment

Figure 3 shows comparative component costs for OM1 OM2 and OM3 fibre solu-tions comprising cabling patching hard-ware and optical transceiver interfaces for a 24-port 1 Gbits Ethernet riser or Fibre Channel link Also included is the estimated incremental cost of upgrad-ing from 1 to 10 Gbits based on current 10 Gbits interface costs ndash which continue

to decline As can be seen the optical cable cost is small compared to the cost of the 1 Gbits transceivers and even smaller next to the 10 Gbits transceivers Indeed an all-OM3 850 nm link solution with 10 Gbits transceivers is typically more than 30 cheaper than an equivalent OM2 link which requires singlemode-based transceiver upgrades to support 10 Gbits

In fact the cost premium to install OM3 in the first instance for a 1ndash2 Gbits system is typically only about 1ndash2 higher than that of OM2 fibre types when one also includes electronics and installation This is because non-laser-optimized fibre types require more expensive 1300 nm single-mode-based transceivers and the use of mode-conditioning patchcords to achieve uncertified link distances at 10 Gbits which may be less than the 300 m achiev-able with OM3 fibre The lower bandwidth of OM1 and OM2 is reflected in the lim-ited 10 Gbits system reach at 850 nm ndash the lowest cost operating wavelength ndash which is also shown in figure 3

OM3 meets future data needsAs with all multimode fibre the per-formance is dependent on the bandwidth provided relative to current needs The relentless pace of increase in data speeds and demands for higher security and reli-ability means that all networks need a robust and cost-effective upgrade path which makes OM3 multimode fibre the logical choice when the multi-gigabit performance of OM1 and OM2 fibres is questionable or unspecified

Many operators may have already tran-sitioned their OM1 and OM2 cabling to Gigabit-Ethernet or 1ndash2 Gbits Fibre Chan-nel but only over shorter link distances For the next increase on the data-speed ladder such as 4ndash10 Gbits data applica-tions the limited capability of OM1OM2 grades will cause many systems to fall short of the reach requirements

With a minEMBc bandwidth certifica-tion a link can be effectively designed to maximize but at the same time safeguard system reach Today OM3 fibre accounts for more than 10 of multimode sales in EU and clearly the market is acknowledg-ing its advantages These advantages when coupled with minEMBc technology will ensure that multimode fibre will continue to deliver robust high-speed connectivity when the inevitable step up to 100 Gbits Ethernet systems arrives

Russell Ellis is senior applications engineer for Corning Optical Fiber

ErnstthinspampthinspYoungthinsponethinspofthinspgermanyrsquosthinsplargestthinspauditingthinspandthinspconsultingthinspfirmsthinspwiththinsp6500thinspemployeesthinspinthinsp22thinsplocationsthinsprecentlythinspmergedthinspitsthinspthreethinspdatathinspcentresthinspwhichthinspwerethinsplocatedthinspinthinspStuttgartthinsprotterdamthinspandthinspEschbornthinspnearthinspFrankfurtthinspldquoThethinspconsolidationthinspofthinsp

ourthinspthreethinspdatathinspcentresthinspinthinspTelecityredbusthinspallowsthinspusthinspconsiderablethinspcostthinspsavingsrdquothinspsaidthinspWolfgangthinspFroumlhlichthinspsitethinspmanagerthinspresponsiblethinspforthinspErnstthinspampthinspYoungrsquosthinsplocal-areathinspnetworkthinspandthinspdatathinsp

centrethinspinthinspEschbornthinspldquoWethinspreliedthinsponthinspthethinspnetworkingthinspspecialistthinspcorningthinspforthinspourthinspdatathinspcentrersquosthinspfibre-opticthinspnetworkrdquocorningthinspwasthinspresponsiblethinsp

forthinspthethinspplanningthinspandthinspinstallationthinspofthinspthethinspdatathinspcentrersquosthinspentirethinspfibre-opticthinspsystemthinspThisthinspfeaturedthinspthethinspcompanyrsquosthinspinfinicorthinspSX+thinsplaser-optimizedthinspmultimodethinsp(oM3)thinspfibrethinspwhichthinsphasthinspbeenthinspcertifiedthinspusingthinspminEMBcthinspinfinicorthinspSX+thinspfibrethinspisthinspdesignedthinsptothinspmeetthinspthethinspdemandsthinspofthinspthethinsp10thinspgbitsthinsp

Ethernetthinspstandardthinspandthinspisthinspideallythinspsuitedthinsptothinspdata-centrethinspapplicationsthinspThethinspinstallationthinspalsothinsp

usedthinsppre-terminatedthinspcablingthinspsolutionsthinsptothinspenablethinspthethinsp600thinspm2thinspfacilitythinspwiththinspathinspcapacitythinspofthinspupthinsptothinsp500thinspserversthinsptothinspbethinspcompletedthinspinthinsponlythinspsixthinspweeksinfinicorthinspmultimodethinsp

fibrethinspsolutionsthinspensurethinsplaserthinsptransceiverthinspcompatibilitythinspandthinspsystemthinspperformancethinspforthinspathinspwidethinsprangethinspofthinsppremisesthinspnetworkthinspapplications

case study ernst amp yOung data centre Fr ankFur t

140

120

100

080

060

040

020

000 0

100

200

300

optical cable patching HW 1 Gbit TxRx

10 Gbit TxRxmode-conditioning patch cords

24-port 20m link constructed usingOM1 solution based on 1000Base-SX and 10GBase-LX4 + MCPSOM2 solution based on 1000Base-SX and 10GBase-LX4 + MCPSOM3 solution based on 1000Base-SX and 10GBase-SR

OM1 OM2 OM3

300m

~82m

~33m

rela

tive

aver

age

selli

ng p

rice

10G

reac

h (m

) [at

850

nm]

Fig 3 Average price differences of 1 Gbits multimode links comprising OM1 OM2 and OM3 fibres for an upgrade to 10 Gbits costs Plus the difference in system reach for a 10 Gbits link

O p t i c a l F i b r e

copy Inst i tute of Physics and IOP Publishing Ltd Repr inted f rom the Autumn 2007 issue of FibreSystems Europe

reliable to safeguard link distances for any application and any data rate

For some high-data-rate platforms such as in data centres OM1 and OM2 fibre grades are already outdated Appli-cations running at speeds of 1 or 2 Gbits often require excess bandwidth capacity to boost the speed by a factor of 2 or 4 These higher speeds may not be achieved without provision for excess bandwidth capacity in the cabling otherwise each increasing step in speed causes a corre-sponding drop in reach

Many owners of data-centre networks are already installing OM3-based solu-tions to meet their short- to medium-term requirements for increased data rates which also avoids disruption to serv-

ices and reliability Higher bandwidth cabling is the most cost-effective solution to upgrade the network since the cost of the passive cabling element of a network is typically the lowest element accounting for less than 3 of the total In contrast switch electronics and application-based hardware typically account for more than 75 of the total investment

Figure 3 shows comparative component costs for OM1 OM2 and OM3 fibre solu-tions comprising cabling patching hard-ware and optical transceiver interfaces for a 24-port 1 Gbits Ethernet riser or Fibre Channel link Also included is the estimated incremental cost of upgrad-ing from 1 to 10 Gbits based on current 10 Gbits interface costs ndash which continue

to decline As can be seen the optical cable cost is small compared to the cost of the 1 Gbits transceivers and even smaller next to the 10 Gbits transceivers Indeed an all-OM3 850 nm link solution with 10 Gbits transceivers is typically more than 30 cheaper than an equivalent OM2 link which requires singlemode-based transceiver upgrades to support 10 Gbits

In fact the cost premium to install OM3 in the first instance for a 1ndash2 Gbits system is typically only about 1ndash2 higher than that of OM2 fibre types when one also includes electronics and installation This is because non-laser-optimized fibre types require more expensive 1300 nm single-mode-based transceivers and the use of mode-conditioning patchcords to achieve uncertified link distances at 10 Gbits which may be less than the 300 m achiev-able with OM3 fibre The lower bandwidth of OM1 and OM2 is reflected in the lim-ited 10 Gbits system reach at 850 nm ndash the lowest cost operating wavelength ndash which is also shown in figure 3

OM3 meets future data needsAs with all multimode fibre the per-formance is dependent on the bandwidth provided relative to current needs The relentless pace of increase in data speeds and demands for higher security and reli-ability means that all networks need a robust and cost-effective upgrade path which makes OM3 multimode fibre the logical choice when the multi-gigabit performance of OM1 and OM2 fibres is questionable or unspecified

Many operators may have already tran-sitioned their OM1 and OM2 cabling to Gigabit-Ethernet or 1ndash2 Gbits Fibre Chan-nel but only over shorter link distances For the next increase on the data-speed ladder such as 4ndash10 Gbits data applica-tions the limited capability of OM1OM2 grades will cause many systems to fall short of the reach requirements

With a minEMBc bandwidth certifica-tion a link can be effectively designed to maximize but at the same time safeguard system reach Today OM3 fibre accounts for more than 10 of multimode sales in EU and clearly the market is acknowledg-ing its advantages These advantages when coupled with minEMBc technology will ensure that multimode fibre will continue to deliver robust high-speed connectivity when the inevitable step up to 100 Gbits Ethernet systems arrives

Russell Ellis is senior applications engineer for Corning Optical Fiber

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optical cable patching HW 1 Gbit TxRx

10 Gbit TxRxmode-conditioning patch cords

24-port 20m link constructed usingOM1 solution based on 1000Base-SX and 10GBase-LX4 + MCPSOM2 solution based on 1000Base-SX and 10GBase-LX4 + MCPSOM3 solution based on 1000Base-SX and 10GBase-SR

OM1 OM2 OM3

300m

~82m

~33m

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10G

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Fig 3 Average price differences of 1 Gbits multimode links comprising OM1 OM2 and OM3 fibres for an upgrade to 10 Gbits costs Plus the difference in system reach for a 10 Gbits link