8/11/2019 G0651E.doc

1/44

INTERNATIONAL TELECOMMUNICATION UNION

ITU-T G.651TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU

(02/98)

SERIES G: TRANSMISSION SYSTEMS AND MEDIA,DIGITAL SYSTEMS AND NETWORKS

Tra!"#!!#$ "%a 'ara'%r#!#'! * O+#'a -#.r% 'a.%!

Characteristics of a 50/125 m multimode

graded index otical fi!re ca!le

ITUT R%'$""%&a#$ G13

(4r%5#$6!7 CCITT R%'$""%&a#$)

8/11/2019 G0651E.doc

2/44

ITUT GSERIES RECOMMENDATIONS

T"#$%&I%%I'$ %(%T)&% #$* &)*I#+ *IGIT#, %(%T)&% #$* $)T'"%

For further details, please refer to ITU-T List of Recommendations.

INTERNATIONAL TELE4ONE CONNECTIONS AND CIRCUITS G300*G399

INTERNATIONAL ANALOGUE CARRIER SYSTEMGENERAL CARACTERISTICS COMMON TO ALL ANALOGUE CARRIERTRANSMISSION SYSTEMS

G200*G299

INDIIDUAL CARACTERISTICS OF INTERNATIONAL CARRIER TELE4ONESYSTEMS ON METALLIC LINES

G00*G99

GENERAL CARACTERISTICS OF INTERNATIONAL CARRIER TELE4ONESYSTEMS ON RADIORELAY OR SATELLITE LINKS AND INTERCONNECTIONWIT METALLIC LINES

G;00*G;;9

COORDINATION OF RADIOTELE4ONY AND LINE TELE4ONY G;0*G;99

TESTING EQUIPMENTS

TRANSMISSION MEDIA CHARACTERISTICS

G%%ra G100*G109

S7""%r#' 'a.% +a#r! G130*G139

La& '$a

8/11/2019 G0651E.doc

3/44

ITU-T RECOMMENDATION G.651

CHARACTERISTICS OF A 50/125

m MULTIMODE GRADED

INDEX OPTICAL FIBRE CABLE

Summa!

This Recommendation covers the geometrical and transmissive properties of multimode fibres having

a 50 m nominal core diameter and a 125 m nominal cladding diameter. Test methods and themeanings of the terms used are in clauses 6 and 2 respectively.

S"u#$

ITUT Recommendation !.651 "as revised by ITUT #tudy !roup 15 $1%%&2000' and "asapproved under the (T#) Resolution *o. 1 procedure on the 10thof +ebruary 1%%,.

8/11/2019 G0651E.doc

4/44

+-R(-R/

ITU $International Telecommunication Union' is the United *ations #pecialied gency in the field oftelecommunications. The ITU Telecommunication #tandardiation #ector $ITUT' is a permanent organ of theITU. The ITUT is responsible for studying technical operating and tariff 3uestions and issuingRecommendations on them "ith a vie" to standardiing telecommunications on a "orld"ide basis.

The (orld Telecommunication #tandardiation )onference $(T#)' "hich meets every four years establishesthe topics for study by the ITUT #tudy !roups "hich in their turn produce Recommendations on thesetopics.

The approval of Recommendations by the 4embers of the ITUT is covered by the procedure laid do"n in(T#) Resolution *o. 1.

In some areas of information technology "hich fall "ithin ITUTs purvie" the necessary standards areprepared on a collaborative basis "ith I#- and I).

*-T

In this Recommendation the epression 7dministration7 is used for conciseness to indicate both atelecommunication administration and a recognied operating agency.

I*T88)TU8 9R-9RT: RI!;T#

The ITU dra"s attention to the possibility that the practice or implementation of this Recommendation mayinvolve the use of a claimed Intellectual 9roperty Right. The ITU ta

8/11/2019 G0651E.doc

5/44

CONTENTS

Pa%$

1 #cope................................................................................................................................................................................................................................................................1

2 /efinitions........................................................................................................................................................................................................................................................1

> +ibre characteristics..........................................................................................................................................................................................................................................>

>.1 !eometrical characteristics of the fibre............................................................................................................................................................................................................>

>.1.1 )ore diameter.........................................................................................................................................................................................................................>

>.1.2 )ladding diameter..................................................................................................................................................................................................................>

>.1.> )oncentricity error.................................................................................................................................................................................................................?

>.1.? *oncircularity...............................................................................................

........................................................................................................................?

>.2 -ptical properties of the fibre...........................................................................................................................................................................................................................?

>.2.1 Refractive inde profile..........................................................................................................................................................................................................?

>.2.2 *umerical aperture.................................................................................................................................................................................................................

?

>.> 4aterial properties of the fibre.........................................................................................................................................................................................................................?

>.>.1 +ibre materials........................................................................................................................................................................................................................?

>.>.2 9rotective materials................................................................................................................................................................................................................?

>.>.> 9rooftest level........................................................................................................................................................................................................................5

4r#%& # S?#@%ra&

G%%5a, 3998

8/11/2019 G0651E.doc

6/44

? +actory length specifications............................................................................................................................................................................................................................5

?.1 ttenuation coefficient......................................................................................................................................................................................................................................5

?.2 =aseband response............................................................................................................................................................................................................................................5

?.2.1 4odal distortion band"idth@ amplitude response...................................................................................................................................................................5

?.2.2 4odal distortion band"idth@ phase response.........................................................................................................................................................................6

?.2.> )hromatic dispersion......................................................................................

........................................................................................................................6

5 lementary cable sections.................................................................................................................................................................................................................................6

5.1 ttenuation.......................................................................................................................................................................................................................................................6

5.2 =aseband response $overall A> d= optical band"idth'................................................

.....................................................................................................................................&

5.2.1 4odal distortion band"idth...................................................................................................................................................................................................&

6 Test methods.....................................................................................................................................................................................................................................................,

6.1 Reference test method and alternative test method for geometrical and opticalparameters measurements............................................................................................

.....................................................................................................................................,

6.1.1 !eneral...................................................................................................................................................................................................................................,

6.1.2 Intrinsic 3uality factor............................................................................................................................................................................................................,

6.1.> !eometrical characteristics....................................................................................................................................................................................................

,

6.2 The reference test methods for geometrical parameters and the alternative testmethod for numerical aperture@ the refracted nearfield techni3ue..............................

4r#%& # S?#@%ra&

G%%5a, 3998

8/11/2019 G0651E.doc

7/44

.....................................................................................................................................%

6.2.1 !eneral...................................................................................................................................................................................................................................%

6.2.2 4aimum theoretical numerical aperture and refractive inde difference......

........................................................................................................................10

4r#%& # S?#@%ra&

G%%5a, 3998

8/11/2019 G0651E.doc

8/44

Pa%$

6.2.> Test apparatus........................................................................................................................................................................................................................11

6.2.? 9reparation of fibre under test........................................................................

........................................................................................................................11

6.2.5 9rocedure...............................................................................................................................................................................................................................11

6.2.6 9resentation of results............................................................................................................................................................................................................12

6.> lternative test method for geometrical parameters@ thenearfield techni3ue........ .........................................................................................................................................

1>6.>.1 !eneral...........................................................................................................

........................................................................................................................1>

6.>.2 Test apparatus........................................................................................................................................................................................................................1>

6.>.> 9rocedure...............................................................................................................................................................................................................................15

6.>.? 9resentation of the results......................................................................................................................................................................................................15

6.? Reference test method for the numerical aperture@ farfield light distribution..................................................................................................................................................16

6.?.1 -bBect.....................................................................................................................................................................................................................................16

6.?.2 #pecimen preparation.....................................................................................

........................................................................................................................16

6.?.> pparatus...............................................................................................................................................................................................................................16

6.?.? 9rocedure...............................................................................................................................................................................................................................16

6.?.5 Results....................................................................................................................................................................................................................................

1&6.?.6 9resentation of results....................................................................................

4r#%& # S?#@%ra&

G%%5a, 3998

8/11/2019 G0651E.doc

9/44

........................................................................................................................1&

6.5 Reference test method and alternative test methods for attenuation measurements.........................................................................................................................................1,

6.5.1 -bBectives.......................................................................................................

........................................................................................................................1,

6.5.2 /efinition................................................................................................................................................................................................................................1,

6.5.> /escription.............................................................................................................................................................................................................................1,

6.5.? +ield of application.................................................................................................................................................................................................................

1,

6.6 The reference test method@ the cutbac< techni3ue...........................................................................................................................................................................................1%

6.6.1 8aunching conditions.............................................................................................................................................................................................................1%

6.6.2 pparatus and procedure.......................................................................................................................................................................................................21

6.6.> 9resentation of results............................................................................................................................................................................................................22

6.& +irst alternative test method@ the insertion loss techni3ue................................................................................................................................................................................22

6.&.1 8aunching conditions.............................................................................................................................................................................................................22

6.&.2 pparatus and procedure.......................................................................................................................................................................................................22

6.&.> 9resentation of results............................................................................................................................................................................................................2?

6., #econd alternative test method@ the bac

8/11/2019 G0651E.doc

10/44

........................................................................................................................2?

6.,.> 9resentation of results............................................................................................................................................................................................................25

6.% Reference test method for baseband response measurements..........................................................................................................................................................................26

6.%.1 -bBect.....................................................................................................................................................................................................................................26

6.10 Reference test method......................................................................................................................................................................................................................................2&

6.10.1 Test apparatus................................................................................................

........................................................................................................................2&

6.10.2 9rocedure...............................................................................................................................................................................................................................2,

4r#%& # S?#@%ra&

G%%5a, 3998

8/11/2019 G0651E.doc

11/44

8/11/2019 G0651E.doc

12/44

R$#"mm$&'a()"& G.651

CHARACTERISTICS OF A 50/125 m MULTIMODE GRADED

INDEX OPTICAL FIBRE CABLE

(Malaga-Torremolinos, 19!" amended at Mel#ourne, 19, $elsin%i, 199& and 'enea, 199)

1 S#"*$

This Recommendation covers a graded inde multimode fibre "hich may be used in the region of,50 nm or in the region of 1>00 nm or alternatively may be used in both "avelength regionssimultaneously. This fibre can be used for analogue and for digital transmission. Its geometricaloptical transmission and mechanical characteristics are described belo".

2 D$+)&)()"&,

2.1 a($&a()$ ($,( m$("'@ test method in "hich a given characteristic of a specified class ofoptical fibres or optical fibre cables is measured in a manner consistent "ith the definition of thischaracteristic and gives results "hich are reproducible and relatable to the reference test method andto practical use.

2.2 a(($&ua()"& #"$++)#)$&(@ In an optical fibre it is the attenuation per unit length.

*-T A The attenuation is the rate of decrease of average optical po"er "ith respect to distance along thefibre and is defined by the e3uation@

* + *

+

$ ' $ '= 0 10 10

"here@

*$+' is the po"er at distance+along the fibreC

*$0' is the po"er at+D 0C

is the attenuation coefficient in d=E d= optical $A6 d= electrical' of the ero fre3uency value.

*-T A The band"idth is limited by several mechanisms@ mainly modal distortion and chromatic dispersion inmultimode fibres.

2. #"ma()# '),*$,)"&@ The spreading of a light pulse per unit source spectrum "idth in anoptical fibre caused by the different group velocities of the different "avelengths composing thesource spectrum.

8/11/2019 G0651E.doc

13/44

*-T A The chromatic dispersion may be due to one or more of the follo"ing@ material dispersion "aveguidedispersion profile dispersion. 9olariation dispersion does not give appreciable effects in circularlysymmetricfibres.

2.5 #"ma()# '),*$,)"& #"$++)#)$&(@ The chromatic dispersion per unit source spectrum "idthand unit length of fibre. It is usually epressed in psE$nm F such that@

( )n n % n n> 2 1 2= +

"here@

n2 is the refractive inde of the homogeneous claddingC

n1 is the maimum refractive indeC and

% is a constant commonly called the 7%factor7.

The refractive inde profile can be measured by profiling techni3ues such as the Refracted *ear+ieldmeasurement $R*+' or Transverse Interferometry $TI' and by measurement of the near field of afullyilluminated core such as the Transmitted *ear+ield measurement $T*+'.

It is recommended that curve fitting be used "ith both the inde profiling and the T*+ techni3ues toimprove the measurement precision of the core diameter.

*-T 1 A Typically %D 0.025 for either the fitted profiling methods or the unfitted T*+ method is e3uivalentto %D 0 for the fitted T*+ method.

*-T 2 A +or fibres "ith refractive inde profiles that have gradual transition region at their coreEcladdingboundary a value of %D 0.05 for the unfitted T*+ method is e3uivalent to %D 0 for the fitted T*+ method.

2.10 #"$ 3#a'')&%4 #$&($@ +or a crosssection of an optical fibre it is the centre of that circle"hich best fits the outer limit of the core area $cladding'.

*-T 1 A These centres may not be the same.

*-T 2 A The method of best fitting has to be specified.

2.11 #"$ 3#a'')&%4 ')am$($@ The diameter of the circle defining the core $cladding' centre.

2.12 #"$ 3#a'')&%4 ')am$($ '$)a()"&@ The difference bet"een the actual and the nominalvalues of the core $cladding' diameter.

2.1 #"$/#a'')&% #"$&()#)(! $"@ The distance bet"een the core centre and the claddingcentre divided by the core diameter.

2.1 #"$ 3#a'')&%4 ("$a$ +)$'@ +or a crosssection of an optical fibre it is the regionbet"een the circle circumscribing the core $cladding' area and the largest circle concentric "ith thefirst one that fits into the core $cladding' area. =oth circles shall have the same centre as the core$cladding'.

2.15 ma:)mum ($"$()#a &um$)#a a*$(u$@ theoretical value of numerical aperture

calculated using the values of refractive inde of the core and cladding given by@

8/11/2019 G0651E.doc

14/44

( ) n ntma = 12 22G

"here@

n1 is the maimum refractive inde of the coreC

n2 is the refractive inde of the innermost homogeneous cladding.

*-T A The relationship bet"een * $2.1%' andt mais given in 6.2.2.

2.16 m"'$ +)($@ device designed to accept or reBect a certain mode or modes.

2.1 m"'$ ,#am$; m"'$ m):$@ device for inducing transfer of po"er bet"een modes in anoptical fibre effectively scrambling the modes.

*-T A +re3uently used to provide a mode distribution that is independent of source characteristics.

2.17 #"$ 3#a'')&%4 &"&-#)#ua)(!@ The difference bet"een the diameters of the t"o circlesdefined by the core $cladding' tolerance field divided by the core $cladding' diameter.

2.18 &um$)#a a*$(u$@ The numerical aperture * is the sine of the verte halfangle of the

largest cone of rays that can enter or leave the core of an optical fibre multiplied by the refractiveinde of the medium in "hich the verte of the cone is located.

2.20 $+$$$ ,u+a#$@ The cylindrical surface of an optical fibre to "hich reference is made forBointing purposes.

*-T A The reference surface is typically the cladding or primary coating surface. In rare circumstances itcould be the core surface.

2.21 $+$$$ ($,( m$("'@ test method in "hich a given characteristic of a specified class ofoptical fibres or optical fibre cables is measured strictly according to the definition of thischaracteristic and "hich gives results "hich are accurate reproducible and relatable to practical use.

2.22 3$+a#()$4 )&'$: *"+)$@ The distribution of the refractive inde along a diameter of an

optical fibre.

F)$ #aa#($),()#,

The fibre characteristics dealt "ith in this clause are those "hich ensure the interconnection of fibres"ith acceptable lo" losses.

-nly the intrinsic fibre characteristics $not depending on the cable manufacture' are recommended inthis clause. They "ill apply e3ually to individual fibres fibres incorporated into a cable "ound on adrum and fibres in installed cables.

.1 G$"m$()#a #aa#($),()#, "+ ($ +)$

.1.1 C"$ ')am$($

The recommended nominal value of the core diameter is 50 m.

The core diameter deviation should not eceed the limits of > m.

.1.2 Ca'')&% ')am$($

The recommended nominal value of the cladding diameter is 125 m.

The cladding diameter deviation should not eceed the limits of > m.

8/11/2019 G0651E.doc

15/44

.1. C"$&()#)(! $"

The recommended concentricity error should be less than 6H.

.1. N"&-#)#ua)(!

.1..1 C"$ &"&-#)#ua)(!

The recommended core noncircularity should be less than 6H.

.1..2 Ca'')&% &"&-#)#ua)(!

The recommended cladding noncircularity should be less than 2H.

.2 O*()#a *"*$()$, "+ ($ +)$

.2.1 R$+a#()$ )&'$: *"+)$

+or fibres dealt "ith in this Recommendation the normalied inde profile is epressed as@

d . .

g

$ '= 1"here@

d .n . n

n n$ '

$ ' $ '

$ ' $ '=

1

0 1

and@ n()D refractive inde at

. r a r a= E $ ' 0

aD core radius

1 >

8/11/2019 G0651E.doc

16/44

.. P""+($,( $$

The proofstress pshall be at least 0.>5 !9a "hich corresponds to a proofstrain of approimately

0.5H. 9roofstress is often specified as 0.6% !9a.

*-T A The definitions of mechanical parameters are contained in 1.2E!.650. The test method is contained in2.6E!.650.

Fa#("! $&%( ,*$#)+)#a()"&,

#ince the geometrical and optical characteristics of fibres are barely affected by the cabling processthis clause "ill give recommendations mainly relevant to transmission characteristics of cable factorylengths.

Transmission characteristics depend greatly on the "avelength used to convey the information.

nvironmental and test conditions are paramount and are described in the guidelines for test methods.

The transmission characteristics of fibres "ill have a statistical probability distribution "hich "ill be a

function of the design and manufacturing processes. The specification of limits for the transmissioncharacteristics must therefore ta

8/11/2019 G0651E.doc

17/44

*-T 1 A The upper values of the normalied modal distortion band"idth depend on the fabrication processfibre composition and fibre and cable designC values greater than 1000 4; F

8/11/2019 G0651E.doc

18/44

is the number of splices in elementary cable sectionC

ac is the mean loss of line connectorsC

/ is the number of line connectors in elementary cable section if provided.

*-T 1 A The losses as and ac of splices and line connectors are generally defined in e3uilibrium mode

distribution conditions. In operating conditions appreciable differences may occur.

*-T 2 A The above epression does not include the loss of e3uipment connectors.

*-T > A In the overall design of a system allo"ance must be made for a suitable cable margin for futuremodifications of cable configurations $additional splices etra cable lengths ageing effects temperaturevariations etc.'.

*-T ? A The mean loss is ta A 0chromatic the chromatic band"idth is inversely proportional to the section length and if the source

spectrum is assumed to be !aussian can be epressed as@

( ) ( )( )0 M$+ 1 Lchromatic =

10 0 ??6 1

E .

"here@

is the +(;4 source line "idth $nm'C

$' is the chromatic dispersion coefficient psE$nm F

8/11/2019 G0651E.doc

19/44

"here@

0modaltotal is the overall modal distortion band"idth of an elementary cable sectionC

0modaln is the modal distortion band"idth of nthfibre in elementary cable sectionC

is the total number of concatenated fibres in elementary cable sectionC

is the modal distortion band"idth concatenation factor.

*-T A The value of the modal distortion band"idth concatenation factor is typically in the range 0.5 to1.0 depending on the effects of mode coupling at splices alpha profile compensation "avelength of maimum

band"idth etc. Kalues belo" this range can also be obtained in certain circumstances. +or a given fibre the

appropriate value of "hich should be employed can be empirically derived and can usually be obtained fromthe fibreEcable manufacturer.

6 T$,( m$("',

=oth reference and alternative test methods are usually given in this clause for each parameter and itis the intention that both the RT4 and the T4 may be suitable for normal product acceptance

purposes. ;o"ever "hen using an T4 should any discrepancy arise it is recommended that theRT4 be employed as the techni3ue for providing the definitive measurement results.

6.1 R$+$$$ ($,( m$("' a&' a($&a()$ ($,( m$("' +" %$"m$()#a a&' "*()#a*aam$($, m$a,u$m$&(,

6.1.1 G$&$a

It is assumed that the geometrical and optical parameters "hich are the subBect of thisRecommendation "ould be measured only in the factory or in the laboratories of certaindministrations "ishing to verify these parameters for system design or other purposes. ;ence it isanticipated that the measurements "ill be conducted either on sample fibre lengths or on samples

etracted from cable factory lengths.

The core diameter and noncircularity are defined using the refractive inde profile as a basis. Theremaining parameters can be derived from the refractive inde profile. ;ence it follo"s that all thegeometrical and optical parameters that are the subBect of this Recommendation and their tolerancesas appropriate can be obtained by one single basic test.

6.1.2 I&()&,)# ua)(! +a#("

The maimum theoretical * core diameter concentricity error and core noncircularity deviatesimultaneously in "ays that can either compound or compensate one another. To properly account forthese effects a theoretical splice loss can be calculated using the values of these geometrical and

optical parameters measured by eisting test methods. ither a !aussian or steadystate distributionof po"er vs. angle may be assumed. The Intrinsic Luality +actor $IL+' can be calculated as the meanof the theoretical splice losses in the t"o directions "hen the test fibre is spliced to a nominal fibre"ith ero misalignment of the reference surfaces. value of IL+ of 0.2& d= is compatible "ith theindividual tolerances recommended in clause >. If any inconsistency appears bet"een the IL+ methodand the chec< of the individual characteristics the latter "ill constitute the reference.

6.1. G$"m$()#a #aa#($),()#,

The core diameter and the cladding diameter of the fibre under test as "ell as the core and claddingcentres can be determined from an ade3uate number of points suitably distributed on thecoreEcladding and on the cladding boundaries respectively.

8/11/2019 G0651E.doc

20/44

8/11/2019 G0651E.doc

21/44

T33;09

0.020

0.015

0.010

0.005

0

A 0.005

A 0.010

Incident light

overfilling and

focussed onthe fibre face

/isc

Refracted modes only

!uided po"er

8i3uid cell

+ibre

a4 R$+a#($' &$a-+)$' ($#&)u$ S#$ma()# ')a%am

4 T!*)#a )&'$: *"+)$ "+ a %a'$' )&'$: +)$ "(a)&$' ! ($ $+a#($' &$a-+)$' ($#&)u$

8i3uid refractive

inde value

)ladding

Inde6d

ifference

Radius)ore

F)%u$ 1/G.651 R$+a#($' &$a-+)$' ($#&)u$

6.2.2 Ma:)mum ($"$()#a &um$)#a a*$(u$ a&' $+a#()$ )&'$: ')++$$$

The maimum theoretical numerical aperture is defined as@

,- n ntma = 12

22

The inde difference is defined as@

n n n= 1 2

The relative inde difference is defined as@

( ) = n n n1 2 1E

"here@

n1 is the maimum refractive inde of the fibre core

n2 is the refractive inde of the innermost cladding.

8/11/2019 G0651E.doc

22/44

8/11/2019 G0651E.doc

23/44

The maimum theoretical numerical aperturet ma determined in this "ay can be higher than the

numerical aperture * obtained at ,50 nm using the Reference Test 4ethod. This may be related tothe maimum theoretical numerical aperturetma obtained at 5?0 or 6>> nm using the lternative

Test 4ethod "ith the follo"ing epression@

,- 2 ,-t= ma6

"here %D 0.%5 "hen the profile measurement is made at 5?0 nm and %D 0.%6 "hen the measurementis made at 6>> nm.

6.2. T$,( a**aa(u,

schematic diagram of the test apparatus is sho"n in +igure 2.

6.2..1 S"u#$

stable laser giving a fe" milli"atts of po"er in the T4 00mode is re3uired.

;e*e laser "hich has a "avelength of 6>> nm may be used but a correction factor must beapplied to the results for etrapolation at different "avelengths. It shall be noted that measurement at

6>> nm may not give complete information at longer "avelengths in particular nonuniform fibredoping can affect the correction.

3uarter"ave plate is introduced to change the beam from linear to circular polariation because thereflectivity of light at an airglass interface is strongly angle and polariationdependent.

pinhole placed at the focus of lens 1 acts as a spatial filter.

6.2..2 Lau #"&')()"&,

The launch optics "hich are arranged to overfill the * of the fibre bring a beam of light to a focus

on the flat end of the fibre. The optical ais of the beam of light should be "ithin 1of the ais of thefibre. The resolution of the e3uipment is determined by the sie of the focussed spot "hich should be

as small as possible in order to maimie the resolution e.g. less than 1.5 m. The e3uipment enablesthe focussed spot to be scanned across the fibre diameter.

6.2.. L)u)' #$

The li3uid in the li3uid cell should have a refractive inde slightly higher than that of the fibrecladding.

6.2.. S$&,)&%

The refracted light is collected and brought to the detector in any convenient manner provided that allthe refracted light is collected. =y calculation the re3uired sie of disc and its position along the

central ais can be determined.

6.2. P$*aa()"& "+ +)$ u&'$ ($,(

length of fibre of about 1 metre is re3uired.

9rimary fibre coating shall be removed from the section of fibre immersed in the li3uid cell.

The fibre ends shall be clean smooth and perpendicular to the fibre ais.

6.2.5 P"#$'u$

Refer to the schematic diagram of the test apparatus $+igure 2'.

8/11/2019 G0651E.doc

24/44

m

4

1

2

>

?

5

6

T3309

8aser

Luarter "ave plate

8enses

8i3uid cell

/isc

8enses

9hotodiode

mplifier

M: recorder

lectronic

micrometer

8amp

8ens

50 m pinhole

4otor

+ibre

F)%u$ 2/G.651 T!*)#a aa&%$m$&( "+ ($ $+a#($' m$a-+)$' ($,( ,$(-u*

6.2.5.1 F)$ *"+)$ *"(

The launch end of the fibre to be measured is immersed in a li3uid cell "hose refractive inde isslightly higher than that of the fibre cladding. The fibre is bac< illuminated by light from a tungstenlamp. 8enses 2 and > produce a focussed image of the fibre.

The position of lens > is adBusted to centre and focus the fibre image the laser beam is simultaneouslycentred and focussed on the fibre.

The disc is centred on the output cone. +or multimode fibre the disc is positioned on the optic ais toBust bloc< the lea

8/11/2019 G0651E.doc

25/44

b' +ibre identification.

c' /epending on specification re3uirements@

i' profiles through core cladding centres calibrated for the operating "avelengthC

ii' profiles along the core maBor and minor aes calibrated for the operating "avelengthC

iii' profiles along the cladding maBor and minor aes calibrated for the operating

"avelengthCiv' raster scan across the entire fibre if adoptedC

v' core diameter 1C

vi' cladding diameter 1C

vii' coreEcladding concentricity errorC

viii'core noncircularityC

i' cladding noncircularityC

' maimum theoretical numerical aperture@t maC

i' inde difference@ nC

ii' relative inde difference@ .

d' Indication of accuracy and repeatability.

e' Temperature of the sample and environmental conditions $if necessary'.

6. A($&a()$ ($,( m$("' +" %$"m$()#a *aam$($,9 ($&$a-+)$' ($#&)u$

6..1 G$&$a

The nearfield techni3ue can be used for the measurement of geometrical characteristics and of therefractive inde profile of multimode optical fibres. #uch measurements are performed in a manner

consistent "ith the definition and the results are reproducible and relatable to the reference testmethod and to practical use.

The measurement is based on the scanning of a magnified image of the output and of the fibre undertest over a crosssection "here the detector is placed.

(hen measuring the geometrical characteristics of the fibre the four concentric circle nearfieldtemplate can be applied to an enlarged image of the fibre detected "ith obBective evaluation methodssuitable to obtain a high degree of accuracy and reproducibility. In particular the core diameter shall

be measured ta

8/11/2019 G0651E.doc

26/44

T33109

#ource8aunch

optics

)ladding

mode

stripper

4agnifying

optics/etector mplifier

/ata

storage

+ibre

F)%u$ /G.651 T!*)#a aa&%$m$&( "+ ($ &$a-+)$' ($,( ,$(-u*

6..2.1 L)%( ,"u#$

The light source shall be incoherent adBustable in intensity and stable in position intensity and"avelength over a time period sufficiently long to complete the measurement procedure. The +ull(idth ;alf 4aimum $+(;4' spectral line"idth shall be recorded. second light source can beused if necessary for illuminating the cladding.

6..2.2 Lau)&% #"&')()"&,The launch optics "hich "ill be arranged to overfill the fibre "ill bring a beam of light to a focus onthe flat input end of the fibre.

+or 50E125 m gradedinde fibres the overfill launching conditions are obtained "ith a light cone

"hose +(;4 intensity measured from the nearfield is greater than &0 m and "hose +(;4 in the*umerical perture $*' measured from the farfield is greater than an * of 0.>.

6..2. Ca'')&% m"'$ ,()**$

suitable cladding mode stripper shall be used to remove the optical po"er propagating in thecladding and to ensure that all the lea. The magnification shall be selected to be compatible "ith thedesired spatial resolution and shall be recorded.

6..2.6 D$($#("

suitable detector shall be employed "hich provides the pointtopoint intensity of the magnifiednearfield pattern. +or eample any of the follo"ing techni3ues can be used@

a' scanning photodetector "ith pinhole apertureC

b' scanning mirror "ith fied pinhole aperture and photodetectorC

c' scanning vidicon charge coupled devices or other patternEintensity recognition devices.

8/11/2019 G0651E.doc

27/44

The detector shall be linear in behaviour $or shall be linearied' over the range of intensitiesencountered. The sensitive area of the detector shall be small "ith respect to the enlarged image of theoutput end of the fibre and shall be recorded.

6..2. Am*)+)$

n amplifier shall be employed in order to increase the signal level. The band"idth of the amplifier

shall be chosen according to the type of scanning used. (hen scanning the output end of the fibre"ith mechanical or optical systems it is customary to modulate the optical source. If such a

procedure is adopted the amplifier should be lin

8/11/2019 G0651E.doc

28/44

v' resulting dimensional parameters li.2.>.

6...5 D),*a!

+or eample M:recorder screen.

6.. P"#$'u$

6...1 P))*$ "+ m$a,u$m$&( 3F)%u$ 4

The radiant intensity $light po"er per solid angle element' is determined as a function of the polar

angle of one plane of the fibre ais $radiation pattern'. The distance dbet"een the end of the sampleand the detector must be large compared to the core diameter of the optical fibre.

9ossible solutions are@

A sample fied largearea detector fiedC

A sample fied smallarea detector linear displaceableC

A sample linear displaceable smallarea detector fiedC

A sample fied smallarea detector angular displaceableC

A sample and rotatable smallarea detector fied.

1 #ee ppendi I.

8/11/2019 G0651E.doc

29/44

T33>09

8 d

#ource

8aunching

device

)ladding

mode

stripper

+ibre

/etector

F)%u$ /G.651 P))*$ "+ m$a,u$m$&( +" +a-+)$' '),()u()"&

6...2 P$*aa()"&

The sample is fied in the sample holder and the light is launched in accordance "ith 6.?.>.>.

6... M$a,u$m$&(

The radiant intensity is determined as a function of the polar angle in one plane of the fibre ais.

6..5 R$,u(,

+ibres covered by this Recommendation have a near parabolic refractive inde profile. Therefore forthe launching conditions recommended in 6.?.>.> $uniform mode distribution' the farfield radiantintensity curve can be approimated in the region above 10H of the maimum intensity by thefollo"ing parabola@

( ) ( ) ( )[ ]* * ,- = 0 1 2sin E

The angle is then determined by the point of intersection of this parabola "ith the abscissa. In

general it is sufficient to determine the angle by the 5H value of the maimum radiant intensity out

of the full radiant intensity curve.The numerical aperture is@

,-=sin

6..6 P$,$&(a()"& "+ $,u(,

The follo"ing details shall be presented@

a' Test setup arrangement "ith indication of the scanning techni3ue used.

b' 8aunching characteristics $dimension and * of the launching cone'.

c' (avelength and +(;4 spectral "idth of the source.

d' Type of cladding mode stripper $if used'.e' #canning conditions.

f' +ibre identification and length.

g' Temperature of the sample and environmental conditions if necessary.

h' Indication of the accuracy and repeatability.

i' Resulting numerical aperture.

8/11/2019 G0651E.doc

30/44

6.5 R$+$$$ ($,( m$("' a&' a($&a()$ ($,( m$("', +" a(($&ua()"& m$a,u$m$&(,

6.5.1 O$#()$,

The attenuation tests are intended to provide a means "hereby a certain attenuation value may beassigned to a fibre length such that individual attenuation values may be added together to determine

the total attenuation of a concatenated length.

6.5.2 D$+)&)()"&

The a(($&ua()"& A 34at "avelength bet"een t"o crosssections 1 and 2 separated by distanceL

of a fibre is defined as@

( ) ( )

( ) ( )-

*

*

= 10

1

2

log d=

"here *1 $' is the optical po"er traversing the crosssection 1 and *2 $' is the optical po"er

traversing the crosssection 2 at the "avelength . +or a uniform fibre under e3uilibrium condition it

is possible to calculate the attenuation per unit length or the attenuation coefficient.

( ) ( )

=

-

L

d=

unit length

"hich is independent of the chosen length of the fibre.

*-T A ttenuation values specified for factory lengths should be measured at room temperature $i.e. a single

value in the range N10) to N>5)'.

6.5. D$,#)*()"&

Three methods have been suggested for attenuation measurements.

1' The cutbac< techni3ue is a direct application of the definition in "hich the po"er levels*1and*2are measured at t"o points of the fibre "ithout change of input conditions. *2is the

po"er emerging from the end of the guide and*1is the po"er emerging from a point near theinput after cutting the fibre.

2' The insertion loss techni3ue is in principle similar to the cutbac< techni3ue but *1 is thepo"er emerging from the output of the launching system. The measured attenuation is thesum of the attenuation of the inserted length of fibre and the attenuation caused by theconnection bet"een launching system and the fibre under test. It is necessary to correct theresult for connection losses.

>' The bac

8/11/2019 G0651E.doc

31/44

6.6 T$ $+$$$ ($,( m$("'9 ($ #u(a#? ($#&)u$

6.6.1 Lau)&% #"&')()"&,

6.6.1.1 D$+)&)()"& "+ au)&% #"&')()"&,

The launching conditions are of paramount importance in meeting the stated obBectives. 8aunchingconditions should be such as to approimate 3uilibrium 4ode /istribution $4/' "hich isunderstood to eist "hen the po"er distribution of field patterns at the output of the fibre issubstantially independent of the length of the fibre.

6.6.1.2 Lau)&% ($#&)u$,

There are t"o commonlyused techni3ues to produce steady state launch conditions for attenuationmeasurements@

a' mode filtersC

b' geometrical optics launch.

=y proper care in the use of each comparable results can be achieved. generic eample of thelaunching arrangement using a mode filter is given in +igure 5.

T32>1809>

8/ or laser4ode scrambler

8amp

8ens

4ode filter)ladding mode

stripper

8aunch

F)%u$ 5/G.651 G$&$a au aa&%$m$&(

6.6.1.2.1 Ca'')&% m"'$ ,()**$

The cladding mode stripper ensures that no radiation modes propagating in the cladding region "illbe detectable after a short distance along the fibre. The cladding mode stripper often consists of amaterial having a refractive inde e3ual to or greater than that of the fibre cladding. This may be aninde matching fluid applied directly to the uncoated fibre near its ends@ under some circumstancesthe fibre coating itself "ill perform this function.

6.6.1.2.2 M"'$ ,#am$

n essentially uniform po"er distribution should be launched prior to the mode filter. +or a sourcesuch as a 8/ or laser "hich does not do so a mode scrambler should be used. The mode scramblershall comprise a suitable fibre arrangement $for eample a stepgradedstep inde profile se3uence'.

8/11/2019 G0651E.doc

32/44

6.6.1. E:am*$, "+ au)&% #"&')()"&,

6.6.1..1 M"'$ +)($,

T"o types of mode filters are commonly used@

3 umm/ fi#re mode filter

fibre of a similar type to that of the test fibre is selected. The fibre should be long enough$typically e3ual to or greater than 1 1909>

8amp

Intermediate lens

#pot defining

aperture

8ens

* defining

aperture

Infrared

vie"er

8ens8aunch

F)%u$ 6/G.651 L)m)($' *a,$ ,*a#$ au "*()#,

8/11/2019 G0651E.doc

33/44

6.6.2 A**aa(u, a&' *"#$'u$

6.6.2.1 T!*$, "+ m$a,u$m$&(

4easurements may be made at one or more spot "avelengths alternatively a spectral response maybe re3uired over a range of "avelengths. /iagrams of suitable test e3uipments are sho"n as eamplesin +igures & and ,.

T33909

=ias circuit

8ight

source

)ladding

mode

stripper

8aunching

system

+ibre

on test

/etector

mplifier

8evel

measurement

)ladding

mode

stripper

F)%u$ /G.651 Aa&%$m$&( "+ ($,( $u)*m$&( (" ma?$ ,*"( ",, m$a,u$m$&(

T331009

4ono

chromator

;alogen

lamp

)ladding

mode

stripper8aunching

system

+ibre

on test

/etector

8oc

8/11/2019 G0651E.doc

34/44

The fibre shall be aligned to the launch cone or connected coaially to a launch fibre.

6.6.2. O*()#a '$($#("

large area detector shall be used so that all of the radiation in the output cone$s' is intercepted. Thespectral response should be compatible "ith the spectral characteristics of the source. The detectionmust be uniform and the detection must have linear characteristics.

It is customary to modulate the light source in order to improve the signalEnoise ratio at the receiver.If such a procedure is adopted the detector should be lin' The attenuation of the fibre bet"een the points "here*1and*2have been measured can becalculated from the definition using*1and*2.

6.6. P$,$&(a()"& "+ $,u(,

The follo"ing details shall be presented@

a' 4easurement type and characteristics.

b' 8aunching techni3ue.

c' Test setup arrangement.

d' Temperature of the sample and environmental conditions $if necessary'.

e' +ibre identification.

f' 8ength of sample and the cutbac< length.

g' ttenuation measured $for the sample' at the selected "avelength.

h' ttenuation 3uoted in d=. In some cases it is possible to convert it into attenuationcoefficient in d=E

8/11/2019 G0651E.doc

35/44

T32>3098

1 2

1 2

=ias circuit

8aunching

system /etector

mplifier

8evel

measurement

/etector

mplifier

8evel

measurement

8ight

source

=ias circuit

8aunching

system

+ibre

on test

a4 Ca)a()"&

4 M$a,u$m$&(

Reference fibre

F)%u$ 8/G.651 T$ )&,$()"& ",, ($#&)u$

6..2.2 O*()#a ,"u#$

#ee 6.6.2.2.

6..2. O*()#a '$($#("

#ee 6.6.2.>.

6..2. Lau)&% ,$(-u*

#ee 6.6.1.6..2.5 C"u*)&% '$)#$

The insertion loss techni3ue re3uires the use of a very precise fibre to fibre coupling device tominimie the coupling losses and to ensure reliable results.

This coupling device can be a mechanical adBustment visually inspected or a connector "ith a coretocore positioning.

6..2.6 P"#$'u$

1' The measurement setup is initially calibrated in order to obtain an input reference level*1.

2' The fibre under test is set in the measurement setup and the coupling adBusted to give amaimum level on the optical detector. The output po"er*2is recorded.

8/11/2019 G0651E.doc

36/44

>' n attenuation is calculated according to 6.5.2. This attenuation is the sum of the attenuationof the inserted length of fibre and the attenuation caused by the connection bet"een thecoupling device and the fibre under test.

6.. P$,$&(a()"& "+ $,u(,

The follo"ing details shall be presented@

a' 4easurement type and characteristics.

b' 8aunching techni3ue.

c' Test setup arrangement.

d' Temperature of the sample and environmental conditions $if necessary'.

e' +ibre identification.

f' 8ength of sample.

g' ttenuation measured $for the sample' at the selected "avelength.

h' )onnector loss "ith its tolerance.

i' ttenuation 3uoted in d=. In some cases it is possible to convert it into an attenuationcoefficient in d=E

8/11/2019 G0651E.doc

37/44

6.7.2. O*()#a '$($#()"&

detector shall be used so that the maimum possible bac

8/11/2019 G0651E.doc

38/44

>' /iscontinuity due to local defect splice or coupling.

?' Reflection due to dielectric defect.

5' Reflection at the end of the fibre.

T331209

d=$1'

$2'

$>'$?'

$5'

5

50

=

a4 S#$m$ "+ a**aa(u,

4 E:am*$ "+ a a#?,#a(($$' *"$ #u$

-ptical

system

)oupling

device

-ptical detector

mplifier

-scilloscope

/ata

ac3uisition

system

+ibre under test#ource

#ignalprocessor

8ength

-ptical

system

-ptical

system

F)%u$ 10/G.651 T$ a#?,#a(($)&% ($#&)u$

6.8 R$+$$$ ($,( m$("' +" a,$a&' $,*"&,$ m$a,u$m$&(,

6.8.1 O$#(

The fibre baseband response may be described in either the time domain by means of its impulseresponseg$t' or in the fre3uency domain by means of its fre3uency response '(f). The functiong$t'may be described as that function "hich "hen convolved "ith the optical po"er input pulse to the

8/11/2019 G0651E.doc

39/44

fibre gives the optical po"er output pulse from the fibre. '(f)is the ratio at any fre3uency bet"eenthe sinusoidal modulation of the optical po"er input to the fibre and the sinusoidal modulation of theoptical po"er output from the fibre.

The baseband responses in the fre3uency and time domain in a linear system are related by@

( ) ( ) ( )' f g t 6 ft t =

+

ep 2 d

The baseband response is presented in the fre3uency domain.

Those "ishing a representation in the time domain "ill still be able to obtain it by means ofmathematical operations. +or this purpose the amplitude and phase response "ould both be needed.

The amplitude response is specified in the form of the A> d= optical $A6 d= electrical' band"idth ofthe amplitudeEfre3uency curve. more complete curve should also be given.

To minimie measurement variations associated "ith irregular shaped baseband responses a !aussianfunction may be fitted to the baseband response'(f).

*o recommended values of phase response are given phase response is only re3uired in special cases.

6.10 R$+$$$ ($,( m$("'

6.10.1 T$,( a**aa(u,

schematic diagram of the test arrangement is sho"n in +igure 11.

T33109

4odulated

laser

source

8aunching

system

including

mode scrambler4andrel"rap

modefilter +ibre

under test

)ladding

mode stripper

detector and

recording system

-utput conesie &0 m* 0.>

Trigger signal $"here re3uired'

)utbac

8/11/2019 G0651E.doc

40/44

Ta$ 1/G.651 S"u#$ )&$ )'(

3&m4 3&m4

,00%00 5

12001>50 10

The means "hereby the laser is modulated $pulse or sinusoidal' shall be capable of operating atfre3uencies beyond the fre3uency at "hich the response of the fibre under test has fallen to the A> d=optical level.

The maimum emission shall substantially eceed spontaneous emission and the depth of modulationshall be as great as the etinction ratio permits in order to secure maimum signaltonoise ratio. )areshall be ta

8/11/2019 G0651E.doc

41/44

method the specific response of the instrument should be stored at this stage for subse3uent use inthe form of either an impulse A or a fre3uency A response as appropriate.

The fibre to be tested is then inserted bet"een the transmitter and receiver and the output measuredand recorded. +or use as a reference test method for single fibres the fibre is then cut bac< to a pointa convenient distance from the transmit and cladding mode stripper $if used' or from the mode filterand ta

8/11/2019 G0651E.doc

42/44

99*/IM I

A%")(m +" %$"m$()#a *aam$($,

possible "ay to obtain the positions of core and cladding centres as "ell as the diameters is given in

this ppendi.

I.1 C"$ #$&($ a&' ')am$($

The core centre and diameter are determined from an ade3uate number of scans across a fibre section"ith the appropriate %value. T"o points on the coreEcladding interface are obtained at each scan. The

points should be uniformly distributed on the perimeter of the core at least approimately.

8et@

i/i be the )artesian coordinates of the ith point of the interfaceC

ac #c be the )artesian coordinates of the core centreC

Rc be the core radiusC

+ mi be the intermediate variables +D ac2N #c

2ARc2andmiDi

2N/i2.

The un

8/11/2019 G0651E.doc

43/44

2 2

2 2

2 2

2

2

. . / .

. / / /

. / ,

a

#

+

m .

m /

m

ii

i i iii

i i ii

iii

i

i

i

i

c

c

i ii

i ii

i

i

=

The sums are performed from iD 1 to iD *being the total number of measured points.

/igital inversion of this system gives the values of ac #cand+ from "hich the value ofRcis deduced.

The core centre is the point of coordinates acand #cand its diameter is the 3uantitycD 2Rc.

I.2 Ca'')&% #$&($ a&' ')am$($

The same calculation process and definitions as for the core apply to finding@

A the coordinates of the cladding centre agand #gC

A the cladding radiusRg.

The cladding centre is the point of coordinates agand #gand its diameter is the 3uantitygD 2Rg.

8/11/2019 G0651E.doc

44/44

ITU-T RECOMMENDATIONS SERIES

#eries -rganiation of the "or< of the ITUT

#eries = 4eans of epression@ definitions symbols classification

#eries ) !eneral telecommunication statistics

#eries / !eneral tariff principles

#eries -verall net"or< operation telephone service service operation and human factors

#eries + *ontelephone telecommunication services

S$)$, G Ta&,m),,)"& ,!,($m, a&' m$')a ')%)(a ,!,($m, a&' &$("?,

#eries ; udiovisual and multimedia systems#eries I Integrated services digital net"or