IEC 60793-1-44:2011
(Main)Optical fibres - Part 1-44: Measurement methods and test procedures - Cut-off wavelength
Optical fibres - Part 1-44: Measurement methods and test procedures - Cut-off wavelength
IEC 60793-1-44:2011 establishes uniform requirements for measuring the cut-off wavelength of single-mode optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes. This standard gives the methods for measuring the cut-off wavelength of fibre and cable. This edition constitutes a technical revision. The main change with respect to the previous edition is the withdrawal of Annex D.
This publication is to be read in conjunction with IEC 60793-1-1:2008.
Fibres optiques - Partie 1-44: Méthodes de mesure et procédures d'essai - Longueur d'onde de coupure
La CEI 60793-1-44:2011 établit des exigences uniformes pour mesurer la longueur d'onde de coupure des fibres optiques unimodales, contribuant ainsi au contrôle des fibres et câbles dans des relations commerciales. La présente norme donne les méthodes de mesure de la longueur d'onde de coupure de fibre et de câble. Cette deuxième édition annule et remplace la première édition parue en 2001. Elle constitue une révision technique. La principale modification par rapport à l'édition précédente consiste en la suppression de l'Annexe D.
Cette publication doit être lue conjointement avec la CEI 60793-1-1:2008.
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Standards Content (Sample)
IEC 60793-1-44 ®
Edition 2.0 2011-04
INTERNATIONAL
STANDARD
Optical fibres –
Part 1-44: Measurement methods and test procedures – Cut-off wavelength
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
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please contact the address below or your local IEC member National Committee for further information.
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The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
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IEC 60793-1-44 ®
Edition 2.0 2011-04
INTERNATIONAL
STANDARD
Optical fibres –
Part 1-44: Measurement methods and test procedures – Cut-off wavelength
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
S
ICS 33.180.10 ISBN 978-2-88912-451-0
– 2 – 60793-1-44 ã IEC:2011(E)
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Background . 6
4 Overview of methods . 7
5 Mapping functions . 7
6 Reference test method . 8
7 Apparatus . 8
7.1 Light source . 8
7.2 Modulation . 8
7.3 Launch optics . 8
7.4 Support and positioning apparatus . 8
7.5 Cladding mode stripper . 8
7.6 Deployment mandrel . 9
7.6.1 General . 9
7.6.2 Cable cut-off wavelength, Method A . 9
7.6.3 Cable cut-off wavelength, Method B . 9
7.6.4 Fibre cut-off wavelength, Method C . 9
7.7 Detection optics . 11
7.8 Detector assembly and signal detection electronics . 11
8 Sampling and specimens . 11
8.1 Specimen length. 11
8.2 Specimen end face . 12
9 Procedure . 12
9.1 Positioning of specimen in apparatus . 12
9.1.1 General requirements for all methods . 12
9.1.2 Deployment requirements for each method . 12
9.2 Measurement of output power . 12
9.2.1 Overview . 12
9.2.2 Bend-reference technique . 13
9.2.3 Multimode-reference technique . 13
10 Calculations . 13
10.1 Bend-reference technique . 13
10.2 Multimode-reference technique . 14
10.3 Curve-fitting technique for improved precision (optional) . 14
10.3.1 General . 14
10.3.2 Step 1, define the upper-wavelength region . 15
10.3.3 Step 2, characterize the attenuation curve . 15
10.3.4 Step 3, determine the upper wavelength of the transition region . 16
10.3.5 Step 4, determine the lower wavelength of the transition region . 16
10.3.6 Step 5, characterize the transition region with the theoretical model . 16
10.3.7 Step 6, compute the cut-off wavelength, l . 17
c
11 Results . 17
11.1 Report the following information with each measurement: . 17
11.2 The following information shall be available upon request: . 17
60793-1-44 ã IEC:2011(E) – 3 –
12 Specification information . 18
Annex A (normative) Requirements specific to method A – Cable cut-off wavelength,
l , using uncabled fibre . 19
cc
Annex B (normative) Requirements specific to method B – Cable cut-off wavelength,
l , using cabled fibre . 20
cc
Annex C (normative) Requirements specific to method C – Fibre cut-off wavelength,
l . 21
c
Bibliography . 22
Figure 1 – Deployment configuration for cable cut-off wavelength, method A . 9
Figure 2 – Deployment configuration for cable cut-off wavelength, method B . 10
Figure 3 – Default configuration to measure l . 10
c
Figure 4 – Deployment configurations for fibre cut-off measurement . 11
Figure 5 – Cut-off wavelength using the bend-reference technique . 12
Figure 6 – Cut-off wavelength using the multimode-reference technique . 13
– 4 – 60793-1-44 IEC:2011(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-44: Measurement methods and test procedures –
Cut-off wavelength
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60793-1-44 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
The main change with respect to the previous edition is the withdrawal of annex D.
Annexes A, B and C form an integral part of this standard.
This standard should be read in conjunction with IEC 60793-1-1.
60793-1-44 ã IEC:2011(E) – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
86A/1369/FDIS 86A/1385/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60793-1-4x series, published under the general title Optical fibres
– measurement methods and test procedures, can be found on the IEC website
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
– 6 – 60793-1-44 ã IEC:2011(E)
OPTICAL FIBRES –
Part 1-44: Measurement methods and test procedures –
Cut-off wavelength
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the cut-off wavelength
of single-mode optical fibre, thereby assisting in the inspection of fibres and cables for
commercial purposes.
This standard gives the methods for measuring the cut-off wavelength of fibre and cable
There are two methods for measuring cable cut-off wavelength, l :
cc
· Method A: using uncabled fibre;
· Method B: using cabled fibre.
There is only one method (Method C) for measuring fibre cut-off wavelength, l .
c
The test method in this standard describes procedures for determining the cut-off wavelength
of a sample fibre in either an uncabled condition (l ) or in a cable (l ). Three default
c cc
configurations are given here: any different configuration will be given in a detail specification.
These procedures apply to all category B and C fibre types (see Normative references).
All methods require a reference measurement. There are two reference-scan techniques,
either or both of which may be used with all methods:
· bend-reference technique;
· multimode-reference technique using category A1 multimode fibre.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60793-1-1, Optical fibres – Part 1-1: Measurement methods and test procedures –
General and guidance
IEC 60793-1-40, Optical fibres – Part 1-40: Measurement methods and test procedures –
Attenuation
3 Background
Theoretical cut-off wavelength is the shortest wavelength at which only the fundamental mode
can propagate in a single-mode fibre, as computed from the refractive index profile of the
fibre.
In optical fibres, the change from multimode to single-mode behaviour does not occur at an
isolated wavelength, but rather smoothly over a range of wavelengths. For purposes of
60793-1-44 ã IEC:2011(E) – 7 –
determining fibre performance in a telecommunications network, theoretical cut-off
wavelength is less useful than the lower value actually measured when the fibre is deployed.
Measured cut-off wavelength is defined as the wavelength greater than which the ratio
between the total power, including launched higher-order modes, and the fundamental mode
power has decreased to less than 0,1 dB. According to this definition, the second-order (LP )
mode undergoes 19,3 dB more attenuation than the fundamental (LP ) mode at the cut-off
wavelength.
Because measured cut-off wavelength depends on the length and bends of the fibre, the
resulting value of cut-off wavelength depends on whether the measured fibre is configured in
a deployed, cabled condition, or it is short and uncabled. Consequently, there are two overall
types of cut-off wavelength:
· Cable cut-off wavelength, measured in an uncabled fibre deployment condition
(method A), or in a cabled condition (method B);
· Fibre cut-off wavelength, measured on a short length of uncabled, primary-coated
fibre.
Cable cut-off wavelength is the preferred attribute to be specified and measured.
4 Overview of methods
All of the methods shall use the transmitted-power technique, which measures the variation
with wavelength of the transmitted power of a fibre under test compared to a reference
transmitted-power wavelength scan. The reference scan normalizes wavelength-dependent
fluctuations in the measurement equipment so that the attenuation of the LP mode in the
specimen can be properly characterized and the cut-off wavelength precisely determined.
The reference scan uses one of the following two techniques:
· the specimen with an additional, smaller-radius fibre bend;
· a (separate) category A1 multimode fibre.
This procedure can determine the cut-off wavelength of a fibre specimen in either a cabled or
uncabled condition. Each method has its own default configurations; the detail specification
will give any different configuration required.
The fibre cut-off wavelength, (l ), measured under the standard length and bend conditions
c
described in this standard, will generally exhibit a value larger than l . For normal installed
cc
cable spans, it is common for the measured l value to exceed the system transmission
c
wavelength. Thus cable cut-off wavelength is the more useful description of system
performance and capability.
For short cables, e.g. a pigtail with a length shorter (and possibly a bending radius larger)
than described in this method, the cable may introduce modal noise near the cut-off
wavelength when lossy splices are present (>0.5 dB).
5 Mapping functions
A mapping function is a formula by which the measured results of one type of cut-off
wavelength are used to predict the results that one would obtain from another type.
An empirical mapping function is specific to a particular fibre type and design. Generate
mapping functions by doing an experiment in which samples of fibre are chosen to represent
the spectrum of cut-off wavelength values for the fibre type, then measure the values using
– 8 – 60793-1-44 ã IEC:2011(E)
the two methods to be mapped. Linear regression of the respective values will often produce
a satisfactory mapping function. When establishing criteria for fibre selection, residual errors
in the regression shall be taken into account.
The customer and the supplier shall agree to the confidence level of each mapping function
established.
6 Reference test method
Method A of cable cut-off wavelength, using uncabled fibre, is the reference test method
(RTM), which shall be the one used to settle disputes.
The apparatus for each method is described in Clause 7.
7 Apparatus
7.1 Light source
Provide a filtered white light source, with line width not greater than 10 nm, stable in position
and intensity. The light source should be capable of operating over the wavelength range
1 000 nm to 1 600 nm for most category B fibres. An operating range of 800 nm to 1 700 nm
may be necessary for some B4 fibres, B5 fibres or some category C fibres.
7.2 Modulation
Modulate the light source to prevent ambient light affecting the results, and to aid signal
recovery. A mechanical chopper with a reference output is a suitable arrangement.
7.3 Launch optics
Provide launch optics, such as a lens system or a multimode fibre, to overfill the test fibre
over the full range of measurement wavelengths. This launch is relatively insensitive to the
input end face position of the single-mode fibre, and is sufficient to excite the fundamental
and any higher-order modes in the specimen. If using a butt splice, provide means of avoiding
interference effects.
When using a multimode fibre, overfilling the reference fibre can produce an undesired ripple
effect in the power-transmission spectrum. Restrict the launch sufficient
...
IEC 60793-1-44 ®
Edition 2.0 2011-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Optical fibres –
Part 1-44: Measurement methods and test procedures – Cut-off wavelength
Fibres optiques –
Partie 1-44: Méthodes de mesure et procédures d'essai – Longueur d’onde de
coupure
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
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International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
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Vocabulary online.
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IEC 60793-1-44 ®
Edition 2.0 2011-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Optical fibres –
Part 1-44: Measurement methods and test procedures – Cut-off wavelength
Fibres optiques –
Partie 1-44: Méthodes de mesure et procédures d'essai – Longueur d’onde de
coupure
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 33.180.10 ISBN 978-2-88912-747-4
– 2 – 60793-1-44 IEC:2011
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Background . 6
4 Overview of methods . 7
5 Mapping functions . 7
6 Reference test method . 8
7 Apparatus . 8
7.1 Light source . 8
7.2 Modulation . 8
7.3 Launch optics . 8
7.4 Support and positioning apparatus . 8
7.5 Cladding mode stripper . 8
7.6 Deployment mandrel . 9
7.6.1 General . 9
7.6.2 Cable cut-off wavelength, Method A . 9
7.6.3 Cable cut-off wavelength, Method B . 9
7.6.4 Fibre cut-off wavelength, Method C . 9
7.7 Detection optics . 11
7.8 Detector assembly and signal detection electronics . 11
8 Sampling and specimens . 11
8.1 Specimen length. 11
8.2 Specimen end face . 12
9 Procedure . 12
9.1 Positioning of specimen in apparatus . 12
9.1.1 General requirements for all methods . 12
9.1.2 Deployment requirements for each method . 12
9.2 Measurement of output power . 12
9.2.1 Overview . 12
9.2.2 Bend-reference technique . 13
9.2.3 Multimode-reference technique . 13
10 Calculations . 13
10.1 Bend-reference technique . 13
10.2 Multimode-reference technique . 14
10.3 Curve-fitting technique for improved precision (optional) . 14
10.3.1 General . 14
10.3.2 Step 1, define the upper-wavelength region . 15
10.3.3 Step 2, characterize the attenuation curve . 15
10.3.4 Step 3, determine the upper wavelength of the transition region . 16
10.3.5 Step 4, determine the lower wavelength of the transition region . 16
10.3.6 Step 5, characterize the transition region with the theoretical model . 16
10.3.7 Step 6, compute the cut-off wavelength, λ . 17
c
11 Results . 17
11.1 Report the following information with each measurement: . 17
11.2 The following information shall be available upon request: . 17
60793-1-44 IEC:2011 – 3 –
12 Specification information . 18
Annex A (normative) Requirements specific to method A – Cable cut-off wavelength,
λ , using uncabled fibre . 19
cc
Annex B (normative) Requirements specific to method B – Cable cut-off wavelength,
λ , using cabled fibre . 20
cc
Annex C (normative) Requirements specific to method C – Fibre cut-off wavelength,
λ . 21
c
Bibliography . 22
Figure 1 – Deployment configuration for cable cut-off wavelength, method A . 9
Figure 2 – Deployment configuration for cable cut-off wavelength, method B . 10
Figure 3 – Default configuration to measure λ . 10
c
Figure 4 – Deployment configurations for fibre cut-off measurement . 11
Figure 5 – Cut-off wavelength using the bend-reference technique . 12
Figure 6 – Cut-off wavelength using the multimode-reference technique . 13
– 4 – 60793-1-44 IEC:2011
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-44: Measurement methods and test procedures –
Cut-off wavelength
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60793-1-44 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
The main change with respect to the previous edition is the withdrawal of Annex D.
Annexes A, B and C form an integral part of this standard.
This standard should be read in conjunction with IEC 60793-1-1.
60793-1-44 IEC:2011 – 5 –
This bilingual edition corresponds to the monolingual English version, published in 2011-04.
The text of this standard is based on the following documents:
FDIS Report on voting
86A/1369/FDIS 86A/1385/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60793-1-4x series, published under the general title Optical fibres
– Measurement methods and test procedures, can be found on the IEC website
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 60793-1-44 IEC:2011
OPTICAL FIBRES –
Part 1-44: Measurement methods and test procedures –
Cut-off wavelength
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the cut-off wavelength
of single-mode optical fibre, thereby assisting in the inspection of fibres and cables for
commercial purposes.
This standard gives the methods for measuring the cut-off wavelength of fibre and cable
There are two methods for measuring cable cut-off wavelength, λ :
cc
• Method A: using uncabled fibre;
• Method B: using cabled fibre.
There is only one method (Method C) for measuring fibre cut-off wavelength, λ .
c
The test method in this standard describes procedures for determining the cut-off wavelength
of a sample fibre in either an uncabled condition (λ ) or in a cable (λ ). Three default
c cc
configurations are given here: any different configuration will be given in a detail specification.
These procedures apply to all category B and C fibre types (see Normative references).
All methods require a reference measurement. There are two reference-scan techniques,
either or both of which may be used with all methods:
• bend-reference technique;
• multimode-reference technique using category A1 multimode fibre.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60793-1-1, Optical fibres – Part 1-1: Measurement methods and test procedures –
General and guidance
IEC 60793-1-40, Optical fibres – Part 1-40: Measurement methods and test procedures –
Attenuation
3 Background
Theoretical cut-off wavelength is the shortest wavelength at which only the fundamental mode
can propagate in a single-mode fibre, as computed from the refractive index profile of the
fibre.
In optical fibres, the change from multimode to single-mode behaviour does not occur at an
isolated wavelength, but rather smoothly over a range of wavelengths. For purposes of
60793-1-44 IEC:2011 – 7 –
determining fibre performance in a telecommunications network, theoretical cut-off
wavelength is less useful than the lower value actually measured when the fibre is deployed.
Measured cut-off wavelength is defined as the wavelength greater than which the ratio
between the total power, including launched higher-order modes, and the fundamental mode
power has decreased to less than 0,1 dB. According to this definition, the second-order (LP )
mode undergoes 19,3 dB more attenuation than the fundamental (LP ) mode at the cut-off
wavelength.
Because measured cut-off wavelength depends on the length and bends of the fibre, the
resulting value of cut-off wavelength depends on whether the measured fibre is configured in
a deployed, cabled condition, or it is short and uncabled. Consequently, there are two overall
types of cut-off wavelength:
• Cable cut-off wavelength, measured in an uncabled fibre deployment condition
(method A), or in a cabled condition (method B);
• Fibre cut-off wavelength, measured on a short length of uncabled, primary-coated
fibre.
Cable cut-off wavelength is the preferred attribute to be specified and measured.
4 Overview of methods
All of the methods shall use the transmitted-power technique, which measures the variation
with wavelength of the transmitted power of a fibre under test compared to a reference
transmitted-power wavelength scan. The reference scan normalizes wavelength-dependent
fluctuations in the measurement equipment so that the attenuation of the LP mode in the
specimen can be properly characterized and the cut-off wavelength precisely determined.
The reference scan uses one of the following two techniques:
• the specimen with an additional, smaller-radius fibre bend;
• a (separate) category A1 multimode fibre.
This procedure can determine the cut-off wavelength of a fibre specimen in either a cabled or
uncabled condition. Each method has its own default configurations; the detail specification
will give any different configuration required.
The fibre cut-off wavelength, (λ ), measured under the standard length and bend conditions
c
described in this standard, will generally exhibit a value larger than λ . For normal installed
cc
cable spans, it is common for the measured λ value to exceed the system transmission
c
wavelength. Thus cable cut-off wavelength is the more useful description of system
performance and capability.
For short cables, e.g. a pigtail with a length shorter (and possibly a bending radius larger)
than described in this method, the cable may introduce modal noise near the cut-off
wavelength when lossy splices are present (>0,5 dB).
5 Mapping functions
A mapping function is a formula by which the measured results of one type of cut-off
wavelength are used to predict the results that one would obtain from another type.
An empirical mapping function is specific to a particular fibre type and design. Generate
mapping functions by doing an experiment in which samples of fibre are chosen to represent
the spectrum of cut-off wavelength values for the fibre type, then measure the values using
the two methods to be mapped. Linear regression of the respective values will often produce
– 8 – 60793-1-44 IEC:2011
a satisfactory mapping function. When establishing criteria for fibre selection, residual errors
in the regression shall be taken into account.
The customer and the supplier shall agree to the confidence level of each mapping function
established.
6 Reference test method
Method A of cable cut-off wavelength, using uncabled fibre, is the reference test method
(RTM), which shall be the one used to settle disputes.
The apparatus for each method is described in Clause 7.
7 Apparatus
7.1 Light source
Provide a filtered white light source, with line width not greater than 10 nm, stable in position
and intensity. The light source should be capable of operating over the wavelength range
1 000 nm to 1 600 nm for most category B fibres. An operating range of 800 nm to 1 700 nm
may be necessary for some B4 fibres, B5 fibres or some category C fibres.
7.2 Modulation
Modulate the light source to prevent ambient light affecting the results, and to aid signal
recovery. A mechanical chopper with a reference output is a suitable arrangement.
7.3 Launch optics
Provide launch optics, such as a lens system or a multimode fibre, to overfill the test fibre
over the full range of measurement wavelengths. This launch is relatively insensitive to the
input end face position of the single-mode fibre, and is sufficient to excite the fundamental
and any higher-order modes in the specimen. If using a butt splice, provide means of avoiding
interference effects.
When using a multimode fibre, overfilling the reference fibre can produce an undesired ripple
effect in the power-transmission spectrum. Restrict the launch sufficiently to eliminate the
ripple effect. One example of restricted launch is in method A, attenuation by cut-back of
IEC 60793-1-40. Another example of restricted launch is a mandrel-wrap mode filter with
sufficient (approximately 4 dB) insertion loss.
7.4 Support and positioning apparatus
Provide a means to stably support the input and output ends of the specimen for the duration
of the test; vacuum chucks, magnetic chucks, or connectors may be used for this purpose.
Support the fibre ends such that they can be repeatedly positioned in the launch and
detection optics. When measuring λ in method B, provide a means to suitably support the
cc
cable ends.
7.5 Cladding mode stripper
Provide a means to remove cladding-mode power from the specimen. Under some
circumstances, the fibre coating will perform this function; otherwise, provide methods or
devices that extract cladding-mode power at the input and output ends of the specimen.
60793-1-44 IEC:2011 – 9 –
7.6 Deployment mandrel
7.6.1 General
Use a means to stably support the input and output ends of the specimen for the duration of
the measurement. Support the fibre ends so that they can be repeatedly and stably positioned
with respect to the launch and detection optics without introducing microbends into the
specimen.
The deployment and length of the specimen, together with the support apparatus, are key
elements of the measurement method, and they distinguish the types of cut-off wavelength.
Additional, alternative deployments may be used if the results obtained have been
demonstrated to be empirically equivalent to the results obtained using the standard
deployment, to within 10 nm, or they are greater than those achieved with the standard
configurations.
7.6.2 Cable cut-off wavelength, Method A
Provide a means to make an 80 mm diameter loop at each end of the specimen and a loop of
diameter ≥ 280 mm in the central portion. See Figure 1.
NOTE Two loops at one end can be substituted for one loop at each end.
7.6.3 Cable cut-off wavelength, Method B
Provide a means to make an 80 mm diameter loop at each end of the specimen.
See Figure 2.
NOTE Two loops at one end can be substituted for one loop at each end.
7.6.4 Fibre cut-off wavelength, Method C
Provide a circular mandrel as the initial fibre cut-off wavelength deployment. (See Figure 4a).
A split, semicircular mandrel with a radius of 140 mm that is capable of sliding, hence able to
take up slack fibre, is an alternative deployment . (See Figures 3 and 4b).
∅ ≥ 280 mm
∅ = 80 mm ∅ = 80 mm
22 m of fibre
IEC 701/11
Figure 1 – Deployment configuration for cable cut-off wavelength, method A
– 10 – 60793-1-44 IEC:2011
∅ = 80 mm ∅ = 80 mm
1 m 1 m
20 m
IEC 702/11
Figure 2 – Deployment configuration for cable cut-off wavelength, method B
NOTE The introduction of a minimum bend of the cable sufficient to permit connection of the two ends of the
whole specimen to the measurement setup is allowed.
Launch Receive
r
rr
Lower semicircular mandrel able
to slide to take up slack fibre
IEC 703/11
Figure 3 – Default configuration to measure λ
c
L
r
IEC 704/11
Key
r = 140 mm
L = 2 m (entire fibre length)
Figure 4a) – Initial deployment configuration for fibre cut-off wavelength measurement – circular mandrel
60793-1-44 IEC:2011 – 11 –
L L
r r r
r r
IEC 705/11
Key
r = 140 mm
L = 2 m (entire fibre length)
Figure 4b) – Alternative deployment configuration for fibre cut-off wavelength measurement – split mandrel
Figure 4 – Deployment configurations for fibre cut-off measurement
7.7 Detection optics
Couple all power emitted from the specimen onto the active region of the detector. As
examples, an optical lens system, a butt splice with a multimode fibre pigtailed to a detector,
or direct coupling may be used.
7.8 Detector assembly and signal detection electronics
Use a detector that is sensitive to the output radiation over the range of wavelengths to be
measured and that is linear over the range of intensities encountered. A typical system might
include a germanium or InGaAs photodiode, operating in the photo-voltaic mode, and a
current-sensitive preamplifier, with synchronous detection by a lock-in amplifier. Generally, a
computer is required to analyse the data.
8 Sampling and specimens
8.1 Specimen length
Choose the specimen length according to which parameter is being measured and, if the
parameter is cable cut-off wavelength, the method to be used. See the appropriate annex:
Annex A or B for the cable cut-off wavelength measurement or Annex C for fibre cut-off
wavelength.
– 12 – 60793-1-44 IEC:2011
8.2 Specimen end face
Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each
specimen.
9 Procedure
9.1 Positioning of specimen in apparatus
9.1.1 General requirements for all methods
Align the input and output ends of the specimen to the launch and detection optics. Do not
change the launch and detection conditions during the course of the measurement.
Unless otherwise specified, when installing the specimen in the apparatus, and when using a
cladding-mode stripper, take care to avoid imposing any additional fibre bends smaller
than those specified in the configuration for the particular measurement being made.
9.1.2 Deployment requirements for each method
Deploy the specimen using the information in Clause 7:
• Cable cut-off wavelength, method A (see Annex A)
• Cable cut-off wavelength, method B (see Annex B)
• Fibre cut-off wavelength, method C (see Annex C)
9.2 Measurement of output power
9.2.1 Overview
Record the output power, P (λ), along the wavelength range, in increments of 10 nm or less.
s
The range shall be broad enough to encompass the expected cut-off wavelength and, as
outlined below, ultimately result in a curve similar to that in Figure 5 (using the bend-
reference technique) or Figure 6 (using the multimode-reference technique).
A (λ) dB
b
∆A ≥ 2 dB
b
0,1
Wavelength λ
Cable cut-off wavelength λ
cc
IEC 706/11
Figure 5 – Cut-off wavelength using the bend-reference technique
60793-1-44 IEC:2011 – 13 –
Wavelength λ
Cable cut-off wavelength λ
cc
0,1 dB
∆A ≥ 2 dB
m
A (λ) dB
m
IEC 707/11
Key
A (λ) = The spectral transmittance referenced to the multimode fibre (dB)
m
Figure 6 – Cut-off wavelength using the multimode-reference technique
9.2.2 Bend-reference technique
With input and output conditions unchanged, introduce a smaller-diameter bend between input
and the output. The exact value of the smaller diameter may be determined prior to
measurement; it should be small enough to attenuate the second-order mode, but not too
small in order to avoid macrobending effects at higher wavelengths. A radius between 10 and
30 mm is typical for most B1.1 to B5 fibres. For some B6 fibres, the radius shall be much
smaller, and this measurement technique may not be adequate for these fibres. See Note to
10.1.
Record the transmitted spectral power, P (λ), over the same wavelength range and with the
b
same spectral increments as in making the original measurement on the specimen.
9.2.3 Multimode-reference technique
Replace the specimen with a short (< 10 m) length of category A1 multimode fibre as a
reference. Record the transmitted signal power, P (λ), over the same wavelength range and
m
with the same spectral increments as in making the original measurement on the specimen.
NOTE The power using the multimode-reference technique, P (λ), may be stored in a computer for use in
m
repetitive measurements on different specimens.
10 Calculations
10.1 Bend-reference technique
Calculate the spectral transmittance of the specimen without the smaller-radius bend,
referenced to the condition where the smaller-radius bend is introduced:
P (λ)
s
A (λ) = 10 log in dB (1)
b 10
P (λ)
b
where
A (λ) is the spectral transmittance referenced to the smaller-radius bend (dB);
b
P (λ) is the output power;
s
P (λ) is the transmitted spectral power through the sample with the smaller-radius bend
b
introduced.
– 14 – 60793-1-44 IEC:2011
Figure 5 shows a schematic result. The short and long wavelength edges are determined by
the specimen deployed with and without the smaller-radius bend, respectively. Determine the
longest wavelength at which A (λ) = 0,1 dB from Figure 5. This is the cut-off wavelength,
b
provided that ∆A is equal to or greater than 2 dB.
b
If ∆A < 2 dB, or if it is unobservable, broaden the wavelength scan and enlarge the single-
b
mode launch conditions, or decrease the smaller-bend radius. Repeat these adjustments and
the measurement procedure until ∆A > 2 dB.
b
NOTE For certain implementations of bend-insensitive fibres (category B6) ∆A will not reach 2 dB loss, because
b
of the very
nature of these fibres. It is recommended to use the multimode-reference technique as reference scan
for these fibres.
10.2 Multimode-reference technique
Calculate the spectral transmittance of the specimen, referenced to that of the multimode
fibre:
P (λ)
s
A (λ) = 10log (2)
m 10
P (λ)
m
where
A (λ) is the spectral transmittance referenced to the multimode fibre (dB);
m
P (λ) is the output power;
s
P (λ) is the transmitted signal power through the multimode reference fibre .
m
Figure 6 shows a schematic result.
Fit a straight line to the long-wavelength portion of A (λ), displacing it upward by 0,1 dB, as
m
shown by the dashed line in Figure 6. Determine the longest wavelength at which this
displaced line intersects with A (λ). This is the cut-off wavelength, provided that ∆A is equal
m m
to or greater than 2 dB. Between measured data points, A (λ) is defined by linear
m
interpolation.
If ∆A < 2 dB, or if it is unobservable, broaden the wavelength scan and enlarge the single-
m
mode launch conditions. Repeat these adjustments and the measurement procedure until
∆A > 2 dB, and until the long-wavelength tail is of adequate length to be fitted by a straight
m
line.
NOTE 1 When using the multimode-reference technique, fibres with high cut-off wavelengths, when combined
with reference fibres with high water peaks, can have erroneous values reported as cut-off wavelength.
NOTE 2 For certain implementations of bend-insensitive fibres (category B6) the bend-reference technique is not
the optimal technique as reference scan. For these fibres the multimode-reference technique is recommended.
10.3 Curve-fitting technique for improved precision (optional)
10.3.1 General
In the absence of spurious humps or excessive noise in the upper-wavelength region,
accurate values for cut-off wavelength can be determined without curve fitting.
If curve fitting is considered necessary for improving precision, there are six steps. The first
two steps define the LP region, or upper-wavelength region. The next two steps define the
transition region, where LP attenuation begins to increase. The fifth step characterizes this
region according to a theoretical model. The last step computes the cut-off wavelength from
the characterization parameters.
60793-1-44 IEC:2011 – 15 –
This analysis is applicable for λ and λ measured by all methods, using either the bend-
c cc
reference technique or the multimode-reference technique.
The term α(λ) represents either A (λ) or A (λ).
b m
10.3.2 Step 1, define the upper-wavelength region
10.3.2.1 Using the bend-reference technique
One method to identify the lower wavelength of the upper wavelength region is to find the
maximum attenuation wavelength. For wavelengths greater than the maximum attenuation
wavelength, the lower wavelength of the region is the wavelength at which the following
function is a minimum: α(λ) – 8 + 8λ, with λ in μm.
The upper wavelength of the upper wavelength region is the lowest wavelength value of the
upper wavelength region plus 150 nm.
10.3.2.2 Using the multimode-reference technique
One method to identify the lower wavelength of the upper wavelength region is to find the
maximum slope wavelength, the wavelength at which the first difference, α(λ) - α (λ + 10 nm),
is largest. For wavelengths greater than the maximum slope wavelength, the lower
wavelength of the region is the wavelength at which the attenuation is a minimum.
10.3.3 Step 2, characterize the attenuation curve
Characterize the attenuation curve, α(λ), of the upper wavelength region as a linear equation
in wavelength, λ :
α(λ) = A + B (λ in µm) (3)
u u
where
α(λ) is the attenuation curve;
A and B are median attenuation values (dB).
u u
a) Using the bend-reference technique
Set B to 0 and A to the median attenuation values in the upper wavelength region. Then
u u
define a function, a(λ), to represent the difference between the attenuation and the line fit to
the upper wavelength region:
a(λ) = α(λ) – A – B λ (λ in µm) (4)
u u
where
a(λ) is the function representing the difference between attenuation and line fit (dB);
A and B are as defined for Equation (3).
u u
b) Using the multimode-reference technique
Fit the attenuation values using a special technique to avoid the effects of positive humps:
a) Find A and B by simplex regression so that the sum of the absolute values of error is
u u
minimum, and such that all errors are non-negative.
b) Determine the median of the errors and add the value to A .
u
– 16 – 60793-1-44 IEC:2011
Then define a function, a(λ), to represent the difference between the attenuation and the line
fit to the upper wavelength region, using Equation (4).
10.3.4 Step 3, determine the upper wavelength of the transition region
One method to identify the lower wavelength of the upper wavelength region is by starting at
the upper wavelength of the upper wavelength region, from step 1, the upper wavelength of
the transition region is: 10 nm plus the maximum wavelength at which a(λ) is greater than
0,1 dB.
10.3.5 Step 4, determine the lower wavelength of the transition region
There are various ways to determine the lower wavelength of the transition region. Here are
two examples:
a) Starting with the upper wavelength of the transition region from step 3, find the
wavelength at which a(λ) has a local maximum, and the difference between this maximum
and the next local minimum (at larger λ) is maximum.
b) Find the largest wavelength, below the upper wavelength of the transition region, such
that a(λ) is greater than 2 dB and:
• There is a local maximum for a(λ), or
• There is a local maximum for a(λ) – a(λ + 10 nm).
10.3.6 Step 5, characterize the transition region with the theoretical model
The model is a linear regression of a transformation:
a(λ )
10 10 − 1
Y (λ) = 10 log − log (5)
10 10
C ρ
where
Y(λ) is the linear regression of transformation;
a(λ) is from equation (4);
ρ
(6)
C = 10 log
10 0,01
(10 − 1)
and, unless otherwise specified, ρ = 2.
Fit the transform, Y(λ), to the following linear model, using data from the transition region:
A + B λ = – Y(λ) (7)
t t
In order to limit the effect of positive humps, the regression may be done with constraints on
errors so that negative errors in the attenuation curve will not exceed the negative errors
found in the characterization of the upper wavelength region. This fitting technique may be
accomplished with simplex methods.
Then let E = min[a(λ)], for λ in the upper wavelength region.
For the transition region, find the values of A and B from equation (7) so that the sum of the
t t
absolute values of error is minimized, and so that no error is less than – v(λ), with v(λ)derived
from w(λ) and z(λ) and defined as:
60793-1-44 IEC:2011 – 17 –
a(λ ) − E
(8)
w(λ)=10
10 w(λ)−1
z(λ)=10log − log
(9)
10 10
C ρ
where v(λ), w(λ), and z(λ) represent intermediate calculations used to simplify the overall
expression.
Then v(λ) = Y(λ) – z(λ). (10)
10.3.7 Step 6, compute the cut-off wavelength, λ
c
Evaluate the slope of the transition region and compute the cut-off wavelength.
If B is greater than a small negative value (for example, –1 to –0,1), reduce the upper
t
wavelength of the transition region by 10 nm and repeat step 5. Otherwise, compute λ as:
c
A
t
λ = − (11)
c
B
t
where
λ is the fibre cut-off wavelength (µm);
c
A and B are from equation (7).
t t
NOTE Calculate cable cut-off wavelength, λ , in the same manner as for fibre cut-off wavelength, λ , in step 6
cc c
above. Simply replace λ with λ in Equation (11), as appropriate.
c cc
11 Results
11.1 Report the following information with each measurement:
• date and title of measurement;
• identification of specimen;
• measurement results.
11.2 The following information shall be available upon request:
• if measuring cable cut-off wavelength, the method used: A or B;
• length of specimen;
• reference technique used (bend or multimode);
• type of multimode fibre used (if using multimode-reference technique);
• description of all key equipment used: light source, launch optics, cladding-mode
stripper, specimen-support mechanisms, and detection optics;
• description of monochromator (spectral scanning range, spectral width, and
incremental steps);
• description of detection and recording techniques;
• description of deployment configuration used;
• typical plot of the spectral curve, A (λ) or A (λ);
b m
• date of latest calibration of measurement equipment.
– 18 – 60793-1-44 IEC:2011
12 Specification information
The detail specification shall specify the following information:
• type of fibre or cable to be measured.
• failure or acceptance criteria.
• information to be reported.
• any deviations to the procedure that apply.
60793-1-44 IEC:2011 – 19 –
Annex A
(normative)
Requirements specific to method A –
Cable cut-off wavelength, λ , using uncabled fibre
cc
A.1 Specimen length
Use a 22 m total length of (uncabled) optical fibre.
A.2 Procedure - position specimen on deployment mandrel
As shown in Figure 1, coil the middle 20 m of the fibre specimen into a loop with a minimum
radius of 140 mm in order to conservatively simulate cabling effects. To simulate the effects
of splice organizers, apply one loop of 80 mm diameter to each 1 m end of the fibre length or
two loops of 80 mm diameter to one end. Since λ is specified as a maximum value, this
cc
configuration is sufficient to ensure specification compliance, because any further effects of
cabling, installation, and deployment can only reduce further the cable cut-off wavelength
value.
– 20 – 60793-1-44 IEC:2011
Annex B
(normative)
Requirements specific to method B –
Cable cut-off wavelength, λ , using cabled fibre
cc
B.1 Specimen length
Use a 22 m total length of optical cable, with a 1 m length of decabled fibre at each end.
B.2 Procedure - position specimen on deployment mandrel
Expose 1 m of cabled fibre from each end, and deploy the specimen as shown in Figure 2.
The middle 20 m of the jacketed cable shall be substantially straight so that the deployment
does not have a significant effect on the subsequent measurement results. To simulate the
effects of splice organizers, apply one loop of 80 mm diameter to each 1 m end of the
decabled fibre length o
...
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