IEC 60793-1-47:2017
(Main)Optical fibres - Part 1-47: Measurement methods and test procedures - Macrobending loss
Optical fibres - Part 1-47: Measurement methods and test procedures - Macrobending loss
IEC 60793-1-47:2017 establishes uniform requirements for measuring the macrobending loss of single-mode fibres (class B) at 1 550 nm or 1 625 nm, category A1 multimode fibres at 850 nm or 1 300 nm, and category A3 and A4 multimode fibres at 650 nm, 850 nm or 1 300 nm, thereby assisting in the inspection of fibres and cables for commercial purposes. This document gives two methods for measuring macrobending sensitivity:
- Method A – Fibre winding, pertains to class B single-mode fibres and category A1 multimode fibres.
- Method B – Quarter circle bends, pertains to category A3 and A4 multimode fibres.
For both of these methods, the macrobending loss can be measured utilizing general fibre attenuation techniques, for example the power monitoring technique (see Annex A) or the cut‑back technique (see Annex B). Methods A and B are expected to produce different results if they are applied to the same fibre. This is because the key difference between the two methods is the deployment, including the bend radius and length of fibre that is bent. The reason for the difference is that A3 and A4 multimode fibres are expected to be deployed in short lengths with a smaller number of bends per unit fiber length compared to single-mode and category A1 multimode fibres. In this document, the "curvature radius" is defined as the radius of the suitable circular shaped support (e.g. mandrel or guiding groove on a flat surface) on which the fibre can be bent. In addition, informative Annex E has been added to approximate bend loss for class B single-mode fibres across a broad wavelength range at various effective bends. This fourth edition cancels and replaces the third edition published in 2009. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- former Annex A has been renumbered to Annex D;
- introduction of new Annex A on the transmitted power monitoring technique;
- introduction of Annex B on the cut-back technique;
- introduction of Annex C on the requirements for the optical source characteristics of A1 multimode measurement;
- introduction of Annex E on parallel plate (2-point) macrobend loss approximation.
Keywords: macrobending loss of single-mode fibers
Fibres optiques - Partie 1-47: Méthodes de mesure et procédures d'essai - Pertes par macrocourbures
IEC 60793-1-47:2017 établit des exigences uniformes pour la mesure des pertes par macrocourbures pour les fibres optiques unimodales (classe B) à 1 550 nm ou 1 625 nm, pour les fibres multimodales de catégorie A1 à 850 nm ou 1 300 nm, et les fibres multimodales des catégories A3 et A4 à 650 nm, 850 nm ou 1 300 nm, contribuant ainsi au contrôle des fibres et câbles dans des relations commerciales. Le présent document décrit deux méthodes destinées à mesurer la sensibilité aux macrocourbures:
- Méthode A – Enroulement de fibre, se rapporte aux fibres unimodales de classe B et aux fibres multimodales de catégorie A1.
- Méthode B – Courbures d'un quart de cercle, se rapporte aux fibres multimodales de catégories A3 et A4.
Pour les deux méthodes, les pertes par macrocourbures peuvent être mesurées par des techniques générales d'affaiblissement des fibres, par exemple la technique de mesure de la puissance (voir Annexe A) ou la technique de la fibre coupée (voir Annexe B). Les méthodes A et B sont susceptibles de produire des résultats différents si elles sont appliquées à la même fibre. Ceci est dû au fait que la différence fondamentale entre les deux méthodes réside dans la façon de les déployer, comprenant à la fois le rayon de courbure et la longueur de fibre courbée. La raison de cette différence repose sur le fait que les fibres multimodales des catégories A3 et A4 sont conçues pour être installées sur de petites longueurs et avec un faible nombre de courbures par unité de longueur de fibre par rapport aux fibres unimodales et aux fibres multimodales de la catégorie A1. Dans le présent document, le "rayon de courbure" est défini comme le rayon du support adapté de forme circulaire (par exemple, un mandrin ou une rainure de guidage sur une surface plane) sur lequel la fibre peut être courbée. En outre, l'Annexe E (informative) a été ajoutée pour présenter une approximation des pertes par courbures pour des fibres unimodales de classe B sur une large plage de longueurs d'onde pour différentes courbures effectives. Cette quatrième édition annule et remplace la troisième édition publiée en 2009 dont elle constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- l'Annexe A a été renumérotée Annexe D;
- une nouvelle Annexe A portant sur la technique de la mesure de la puissance transmise a été introduite;
- l'Annexe B portant sur la technique de la fibre coupée a été introduite;
- l'Annexe C portant sur les exigences relatives aux caractéristiques des sources optiques pour une mesure des fibres multimodales de catégorie A1 a été introduite;
- l'Annexe E portant sur l'approximation des pertes par macrocourbures utilisant des plaques parallèles (deux points) a été introduite.
Mots clés : macrocourbures pour les fibres optiques unimodales
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IEC 60793-1-47 ®
Edition 4.0 2017-10
REDLINE VERSION
INTERNATIONAL
STANDARD
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Optical fibres –
Part 1-47: Measurement methods and test procedures – Macrobending loss
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IEC 60793-1-47 ®
Edition 4.0 2017-10
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Optical fibres –
Part 1-47: Measurement methods and test procedures – Macrobending loss
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.10 ISBN 978-2-8322-4960-4
– 2 – IEC 60793-1-47:2017 RLV © IEC 2017
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Apparatus . 9
4.1 Method A – Fibre winding . 9
4.2 Method B – Quarter circle bends . 9
4.3 Input system . 10
4.3.1 Optical source . 10
4.3.2 Optical launch arrangement . 10
4.4 Output system and detection . 13
4.4.1 Optical divider . 13
4.4.2 Optical detector . 13
4.4.3 Optical detection assembly . 13
4.4.4 Signal processing . 13
5 Specimen . 14
5.1 Specimen length . 14
5.1.1 Method A – Fibre winding . 14
5.1.2 Method B – Quarter circle bends. 14
5.2 Specimen end face . 14
6 Procedure . 14
6.1 Method A – Fibre winding . 14
6.1.1 General consideration . 14
6.1.2 Single-mode fibres . 14
6.1.3 Multimode (A1) fibres . 15
6.2 Method B – Quarter circle bends . 16
7 Calculations . 18
8 Results . 18
8.1 Information available with each measurement . 18
8.2 Information available upon request . 18
9 Specification information . 18
Annex A (normative) Change in transmittance by transmitted power technique . 20
A.1 Apparatus . 20
A.1.1 General . 20
A.2 Procedure . 21
A.3 Calculations . 21
Annex B (normative) Cut-back technique . 23
B.1 General . 23
B.2 Apparatus . 23
B.2.1 General apparatus for all fibres. 23
B.3 Procedure . 23
B.4 Calculations . 24
Annex C (normative) Requirements for the optical source characteristics for A1
multimode measurement . 25
C.1 Encircled flux (EF) . 25
C.2 Limits on encircled flux . 25
Annex D (informative) Small bend radius phenomena . 28
D.1 General . 28
D.2 Interference between propagating and radiating modes . 28
D.3 Polarization effects . 30
D.4 High power damage . 30
Annex E (informative) Parallel plate (2-point) macrobend loss approximation . 31
E.1 General . 31
E.2 Specimen . 31
E.3 Apparatus . 31
E.3.1 General . 31
E.3.2 Stepper motor control . 32
E.3.3 Movable plate . 32
E.3.4 Fixed plate . 32
E.4 Procedure . 33
E.5 Calculation . 33
E.6 Results . 33
E.7 Comparison of results with normative test . 34
Bibliography . 36
Figure 1 – Quarter circle guide groove in plate . 10
Figure 2 – General launch arrangement . 10
Figure 3 – Lens system . 12
Figure 4 – Launch fibre . 12
Figure 5 – Mode scrambler (for A4 fibre) . 12
Figure 6 – Multiple bends using stacked plates . 17
Figure A.1 – Measurement of change in optical transmittance using reference
specimen . 20
Figure A.2 – Measurement of change in optical transmittance using stabilized source . 21
Figure B.1 – Arrangement of equipment to perform loss measurement at one specified
wavelength . 23
Figure B.2 – Arrangement of equipment used to obtain a loss spectrum . 23
Figure C.1 – Encircled flux template example . 26
Figure D.1 – Loss curves versus curve fits . 29
Figure E.1 – Schematic of possible (two-point bend) apparatus . 32
Figure E.2 – Example of applying an exponential fit to the spectral data of a B6_a2
fibre . 34
Figure E.3 – Example of 2-point bend test data for a B6_a2 fibre . 34
Table 1 – Launch conditions for A2 to A4 fibres . 13
Table C.1 – Threshold tolerance . 26
Table C.2 – EF requirements for 50 µm core fibre cabling at 850 nm . 27
Table C.3 – EF requirements for 50 µm core fibre cabling at 1 300 nm . 27
Table C.4 – EF requirements for 62,5 µm core fibre cabling at 850 nm . 27
Table C.5 – EF requirements for 62,5 µm core fibre cabling at 1 300 nm . 27
– 4 – IEC 60793-1-47:2017 RLV © IEC 2017
Table E.1 – Comparison of parallel plate (2-point) versus method A macrobend loss
measurement for a B6_b3 fibre at 10 mm diameter (ratio of mandrel / 2-point). 35
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-47: Measurement methods and test procedures –
Macrobending loss
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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– 6 – IEC 60793-1-47:2017 RLV © IEC 2017
International Standard IEC 60793-1-47 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This fourth edition cancels and replaces the third edition published in 2009. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) former Annex A has been renumbered to Annex D;
b) introduction of new Annex A on the transmitted power monitoring technique;
c) introduction of Annex B on the cut-back technique;
d) introduction of Annex C on the requirements for the optical source characteristics of
A1 multimode measurement;
e) introduction of Annex E on parallel plate (2-point) macrobend loss approximation.
The text of this International Standard is based on the following documents:
FDIS Report on voting
86A/1823/FDIS 86A/1828/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
This standard is to be read in conjunction with IEC 60793-1-1:2017.
A list of all parts of IEC 60793 series, published under the general title Optical fibres, can be
found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
Publications in the IEC 60793-1 series concern measurement methods and test procedures as
they apply to optical fibres.
Within the same series, several different areas are grouped, but all numbers are possibly not
used, as follows:
Parts 1-10 to 1-19: General
Parts 1-20 to 1-29: Measurement methods and test procedures for dimensions
Parts 1-30 to 1-39: Measurement methods and test procedures for mechanical
characteristics
Parts 1-40 to 1-49: Measurement methods and test procedures for transmission and
optical characteristics
Parts 1-50 to 1-59: Measurement methods and test procedures for environmental
characteristics
– 8 – IEC 60793-1-47:2017 RLV © IEC 2017
OPTICAL FIBRES –
Part 1-47: Measurement methods and test procedures –
Macrobending loss
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the macrobending
loss of single-mode fibres (category class B) at 1 550 nm or 1 625 nm, category A1 multimode
fibres at 850 nm or 1 300 nm, and category A3 and A4 multimode fibres at 650 nm, 850 nm or
1 300 nm, thereby assisting in the inspection of fibres and cables for commercial purposes.
This document gives two methods for measuring macrobending sensitivity:
• Method A – Fibre winding, pertains to category class B single-mode fibres and category
A1 multimode fibres.
• Method B – Quarter circle bends, pertains to category A3 and A4 multimode fibres.
For both of these methods, the optical power is measured using either the macrobending loss
can be measured utilizing general fibre attenuation techniques, for example the power
monitoring technique (see Annex A) or the cut-back technique (see Annex B). Methods A and
B are expected to produce different results if they are applied to the same fibre. This is
because the key difference between the two methods is the deployment, including the bend
radius and amount length of fibre that is bent. The reason for the difference is that A3 and A4
multimode fibres are expected to be deployed in short lengths with relatively fewer a smaller
number of bends per unit fiber length compared to single-mode and category A1 multimode
fibres.
In this document, the "curvature radius" is defined as the radius of the suitable circular
shaped support (e.g. mandrel or guiding groove on a flat surface) on which the fibre can be
bent.
In addition, informative Annex E has been added to approximate bend loss for class B single-
mode fibres across a broad wavelength range at various effective bends.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 (all parts), Optical fibres – Measurement methods and test procedures
IEC 60793-1-1:2017, 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
IEC 60793-1-46: Optical fibres – Part 1-46: Measurement methods and test procedures –
Monitoring of changes in optical transmittance
IEC 60793-2, Optical fibres – Part 2: Product specifications – General
IEC 60793-2-10, Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 61280-1-4, Fibre optic communication subsystem test procedures – Part 1-4: General
communication subsystems – Light source encircled flux measurement method
IEC 61280-4-1, Fibre-optic communication subsystem test procedures – Part 4-1: Installed
cable plant and links – Multimode fibre-optic cable plant attenuation measurement
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60793-2,
IEC 60793-1 (all parts) and IEC 60793-1-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
NOTE General definitions for fibres are provided in IEC 60793-2, definitions of the specified attributes are
contained in the relevant test methods standard of IEC 60793-1 (all parts), and general definitions for testing are
provided in IEC 60793-1-1.
4 Apparatus
4.1 Method A – Fibre winding
The apparatus consists of a tool (e.g. a mandrel or a guiding groove on a flat surface) able to
hold the sample bent with a radius as stated in the appropriate optical fibre sectional product
specification (e.g. 30 mm for single-mode fibres and 37,5 mm for multimode fibres) and a loss
measurement instrument. Determine the macrobending loss at the wavelength as stated in the
appropriate sectional product specification (e.g. 850 nm or 1 300 nm for multimode fibres, 1
550 nm or 1 625 nm for singlemode fibre) by using either the transmitted power monitoring
technique (method A of IEC 60793-1-46 Annex A) or the cut-back technique (method A of
IEC 60793-1-40 Annex B), taking care of the appropriate launch condition for the specific fibre
type.
4.2 Method B – Quarter circle bends
The apparatus consists of one or more plates, each containing one or more "guide grooves",
and a loss measurement instrument. The plates shall be designed to be stacked during the
test without contacting the sample fibre in a lower or higher plate; such contact will affect the
measurement results. Each guide groove shall have a quarter circle segment (i.e. 90°) as
shown in Figure 1. The bend radius r, i.e. the radius of the quarter circle segment, shall be
stated in the detail specification. The width of each guide groove shall be at least 0,4 mm
greater than the diameter of the fibre is recommended to be 40 % broader than the outer fibre
diameter.
Determine the macrobending loss at the wavelength as stated in the appropriate sectional
product specification (e.g. 650 nm, 850 nm, or 1 300 nm) by using either the transmitted
power monitoring technique (method A of IEC 60793-1-46 Annex A) or the cut-back technique
(method A of IEC 60793-1-40 Annex B), taking care of the appropriate launch condition for the
specific fibre type.
– 10 – IEC 60793-1-47:2017 RLV © IEC 2017
Guide groove
r
Bend
radius
IEC
Figure 1 – Quarter circle guide groove in plate
4.3 Input system
4.3.1 Optical source
Use a suitable radiation source, such as a lamp, laser or light emitting diode. The choice of
source depends upon the type of measurement. The source shall be stable in position,
intensity and wavelength over a time period sufficiently long to complete the measurement
procedure. Specify the spectral line width (between the 50 % optical intensity power points of
the sources used) such that the line width is narrow, for example less than 10 nm, compared
with any features of the fibre spectral attenuation. Align the fibre to the launch cone, or
connect it coaxially to a launch fibre.
4.3.2 Optical launch arrangement
4.3.2.1 General
Figure 2 shows the general launch arrangement used for all fibres. Apply the appropriate
launch arrangement to produce a full or restricted launch, depending on the parameter being
measured. See 4.3.2.3 to 4.3.2.4 for further details as they apply to specific categories of
single-mode and multimode fibres.
LED/laser
Mode Cladding mode
scrambler stripper
Lamp
Mode filter Launch
Lens
IEC
Figure 2 – General launch arrangement
4.3.2.2 Launch arrangement for single-mode fibres
4.3.2.2.1 General
An optical lens system or fibre pigtail may be employed to excite the test fibre. The power
coupled into the fibre shall be stable for the duration of the measurement (see Figure A.1 or
Figure B.1).
4.3.2.2.2 Fibre pigtail
If using a pigtail, it may be necessary to use index-matching material between the source
pigtail and test fibre to eliminate interference effects.
4.3.2.2.3 Optical lens system
If using an optical lens system, provide a means of stably supporting the input end of the
fibre, such as a vacuum chuck. Mount this support on a positioning device so that the fibre
end can be repeatedly positioned in the input beam. A method of making the positioning of the
fibre less sensitive is to overfill the fibre end spatially and angularly.
4.3.2.2.4 High-order mode filter
Use a method to remove high-order propagating modes in the wavelength range of interest.
An example of such a high-order mode filter is a single loop of radius sufficiently small to shift
the cut-off wavelength below the minimum wavelength of interest, but not so small as to
induce wavelength-dependent oscillations.
Another option commonly employed on bend insensitive single mode fibres and other single
mode fibres with little or no cut-off response to bend is the use of a standard single mode
fibre as a mode filter.
4.3.2.2.5 Cladding mode stripper
Use suitable techniques to remove optical power propagating in the cladding where this would
significantly influence the received signal. The cladding mode stripper ensures that no
radiation modes, propagating in the cladding region, will be detectable after a short distance
along the fibre. The cladding mode stripper often consists of a material having a refractive
index equal to or greater than that of the fibre cladding. This may be an index-matching fluid
applied directly to the uncoated fibre near its ends; under some circumstances, the fibre
coating itself will perform this function.
4.3.2.3 Launch arrangement for A1 multimode fibres
The required launch for measuring the macrobending loss of A1 multimode fibres shall be an
encircled flux launch. The requirements for the optical source characteristics for A1 multimode
measurement are included in Annex C.
The encircled flux emitted by the launching cord depends on the characteristic of the light
source emerging from the face of the socket, the connection of the launching cord to the
socket, the optical fibre within the launch cord, and any applied mode conditioning.
The test equipment manufacturer should provide specifications for the test cord that are
compatible with the particular source implementation used. When the specification on the cord
is met and used with the test equipment, the encircled flux (EF) requirements should be
assured.
4.3.2.4 Launch arrangements for A2 to A4 multimode fibres
Below are some examples of generic launching arrangements for short-distance fibres
described in Figure 3, Figure 4 and Figure 5.
– 12 – IEC 60793-1-47:2017 RLV © IEC 2017
Fibre under test
IEC
Lens
Figure 3 – Lens system
Launch fibre
Fibre under test
Splice
Cladding mode stripper
IEC
(if necessary)
Figure 4 – Launch fibre
Fibre under test
Mode scrambler
IEC
Figure 5 – Mode scrambler (for A4 fibre)
The reproducibility of the attenuation measurements of step-index fibres is critical. Therefore,
a well-defined launching set-up description is necessary. Such a set-up can be achieved by
using commercially available optical components and shall be able to provide spot sizes and
launch numerical apertures (NAs) as given in Table 1. In addition, the measurement
wavelength shall be calibrated to within ±10 nm.
Table 1 – Launch conditions for A2 to A4 fibres
Attribute Fibre category
A2
A3 A4
Glass core/glass cladding
Glass core/plastic Plastic core/plastic
cladding cladding
Spot size = fibre core size = fibre core size = fibre core size with full
mode launch (or use mode
scrambler with equilibrium
mode launch)
a b
Numerical aperture = fibre max NA, with full
= fibre max NA = fibre max NA
b
(NA)
mode launch
a
This launch condition can be produced by overfilling a mode filter made from 2 m of fibre identical to the fibre
under test (FUT), with appropriate cladding mode stripping and using the output from this mode filter to launch
into the FUT.
b
This launch condition can be produced in the same manner as described in Note a. However, some types of
A3 and A4 fibre will not require cladding mode stripping for the mode filter.
4.4 Output system and detection
4.4.1 Optical divider
When an optical divider is required, it shall have a splitting ratio that remains constant during
the test. The splitting ratio and temperature stability shall be as shown in the relevant detail
specification. Commercially available or custom built devices may be used.
4.4.2 Optical detector
The optical detector shall be of sufficient area to intercept all of the radiated power in the
output cone and shall be sufficiently linear over the optical powers encountered.
The optical detector shall have a sufficiently uniform response over the active area and range
of incidence angle at the measurement wavelength to ensure the movement of the output
cone in position or angle relative to the detector. This shall be within the limits determined by
the mechanical design of the measurement equipment and shall not significantly affect the
results.
Where more than one detector is used, as in the arrangement shown in Figure A.1, the
detectors shall be of the same manufacturer and model and be of comparable linearity.
4.4.3 Optical detection assembly
All power emitted from the specimen should be coupled to the active region of the detector by
an appropriate means. For example, an optical lens system, a butt spliced fibre pigtail, or
direct coupling to the detector may be used. If the detector is already pigtailed, the pigtail
fibre shall have sufficiently large core diameter and numerical aperture to capture all of the
light exiting the reference and specimen fibres.
Use an optical detector that is linear and stable over the range of intensities and
measurement times that are encountered in performing this measurement. A typical system
can include a photovoltaic mode photodiode amplified by a current input amplifier, with
synchronous detection by a lock-in amplifier.
4.4.4 Signal processing
It is customary to modulate the light source in order to improve the signal-to-noise ratio (SNR)
at the receiver. If such a procedure is adopted, link the detector to a signal processing system
synchronous with the source modulation frequency. The detecting system should be
substantially linear or have known characteristics.
When low loss is expected, more test bends may be added provided there are separate
grooves for each additional bend to improve the SNR; however, the approximation of the bend
diameter along with the bend control may be further degraded.
– 14 – IEC 60793-1-47:2017 RLV © IEC 2017
5 Specimen
5.1 Specimen length
5.1.1 Method A – Fibre winding
The specimen shall be a known length of fibre, as specified in the detail specification. In
particular, the length of the sample tested for loss is determined by the measurement set-up,
i.e. curvature radius (R) and number of turns (N); any further fibre length does not affect the
measurement results, provided that the signal to noise (S/N) ratio SNR is optimised.
5.1.2 Method B – Quarter circle bends
The specimen length shall be determined according to the details shown in 6.2.
5.2 Specimen end face
Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each test
specimen.
6 Procedure
6.1 Method A – Fibre winding
6.1.1 General consideration
Loosely wind the fibre on the tool, avoiding excessive fibre twist. The number of turns,
curvature radius and wavelength at which loss is to be measured are discussed below in 6.1.1
and in 6.1.2 and 6.1.3.
Since the actual curvature radius is critical, a maximum tolerance of ±0,1 mm (for radii lower
than or equal to 15 mm) or ± 0,5 mm to 1,0 mm (for larger radii) is accepted: a tighter
tolerance on small radii is required for higher measurement sensitivity.
Both for single-mode and for multimode fibres, two optical powers can be measured using
– the power-monitoring technique, which measures the fibre attenuation increase due to a
change from the straight condition to a bent condition, or
– the cut-back technique, which measures the total attenuation of the fibre in the bent
condition. In order to determine the induced attenuation due to macrobending, this value
should be corrected for the intrinsic attenuation of the fibre.
The fibre length outside the mandrel and the reference cut-back length shall be free of bends
that might can introduce a significant change in the measurement result. Collection of excess
fibre in a bend radius of at least 140 mm is recommended.
It is also possible to rewind the fibre from a mandrel with a large radius (introducing negligible
macrobend loss) to the mandrel with the required radius. In this case, the macrobend loss can
be determined directly by using the power-monitoring technique (without the correction for the
intrinsic attenuation of the fibre).
Care must shall be taken in order not to introduce torsion on any fibre part during the
measurements, as this would affect the result.
6.1.2 Single-mode fibres
Different applications may require different deployment conditions: fibre types have been
developed which exhibit bending performances optimised for each condition.
Two typical environments are recognised for (possibly) different fibre types, for which different
measurement set-ups should be considered when characterising fibre performances.
a) Long distance networks: far from urban areas, space occupancy is not typically an issue,
and bends imposed on the fibres can be limited to relatively large radii. Fibres designed
for this application should be tested in similar conditions, i.e. with the samples wrapped
around relatively large radius mandrels, for example in the range 25 mm to 30 mm.
This measurement set-up is mainly affected by errors related to low S/N ratio SNR and by
unwanted tension, torsions or kinks on the relatively long fibre length used for the
measurement.
b) Access networks: operating conditions require bending radii as small as possible,
compatible with lifetime expectations and acceptable bend losses. For more information
on lifetime expectations please refer to ITU-T G Suppl.59:2016. Fibres designed for this
application should be tested in similar conditions, i.e. with the samples bent at small radii,
for example in the range 7,5 mm to 15 mm (see Annex C).
The measurement can be affected by different sources, i.e. reflections, which may occur
at the coating-air or coating-glass interface, at surrounding surfaces (including, when
used, the mandrel surface), or at connectors.
The test can be carried out on samples either making complete (360º) turn(s), in open air or
around a suitable support (mandrel), or making an equivalent number of partial turns, for
example U-turns (180º) or quarter turns (90º), in open air or around suitable supports. The
length under test is different for complete and partial turns; for example, the length of a
complete turn being twice the length of a U-turn or four times the length of a quarter turn. In
this document, the term "coil" refers to one complete turn. One coil could also be made of, for
example, two consecutive U-turns or four consecutive quarter turns. This should be taken
into account while normalising the results to the length of the sample (number of coils).
The following recommendations apply to test conditions in both cases (items a) and b) above):
Number of turns
– The number of turns should be in accordance with the values stated in the product
specification.
– For single-mode fibres, the attenuation increases in a linear fashion with the number of
turns.
– For each radius, the number of turns shall be chosen in such a way that:
• the induced loss is significantly higher than the detection limit of the set-up; when
necessary, for example for low bend loss fibres, tests may be carried out with more
turns than the specification requires – followed by linear normalization to the specified
number;
• the induced loss is significantly lower than the onset of the non-linear region in the set-
up; for bending radii in the range 5 mm to 10 mm, this may imply that not more than 5
to 10 turns should be used.
Bend radius
The value of bend radius shall be in accordance with the values stated in the product
2.
specification
Wavelength
The measurement wavelength shall be 1 550 nm or 1 625 nm, in accordance with the
relevant product specification; it should be considered that bending losses increase
exponentially with the wavelength.
NOTE The homogeneity of bend loss in different angular positions over the cross section needs
to be verified either by multiple angular position tests or by verifying the homogeneity of the
effective refractive index profile, establishing the guiding properties of the bent FUT.
6.1.3 Multimode (A1) fibres
Macrobending loss in A1 multimode fibres varies with bend radius and number of turns around
a mandrel, but is rather independent of the measuring wavelength, except for possible and is
___________
If there is excessive displacement between successive U-turns, the length of the sample arranged on two
U-turns can be shorter than one coil. A maximum displacement between adjacent U-turns of 0,5 mm is
therefore suggested.
Bending loss on single-mode fibre increases exponentially as wavelength increases and as radius decreases
(see Annex D).
– 16 – IEC 60793-1-47:2017 RLV © IEC 2017
less sensitive to wavelength than with single-mode fibres. Still, oscillating effects with
wavelength may occur which are related to successive mode groups passing cut-off and
having increased bend loss at these wavelengths.
The values of bend radius and number of turns shall be in accordance with the values stated
in the specification. When testing multiple turns, the attenuation that occurs over a specific
turn depends on the attenuation of the preceding turns. The incremental macrobending added
loss decreases with each added turn. Macrobending added loss produced by multiple turns
should not be expressed in the units of "dB/turn" by dividing the total added loss by the
number of turns. Instead, it must shall be reported in dB for the specified number of bends. An
extrapolation to more than the specified number of turns will result in an overestimation of the
overall loss.
For multimode fibres only, the launching characteristics of the light source at the launching
position of the fibre being tested shall be consistent with the expected fibre application.
Further details on MM multimode launching conditions can be found in IEC 61280-4-1
Annex C.
6.2 Method B – Quarter circle bends
This method applies to category A3 and A4 multimode fibres. The fibre to be tested should be
carefully set in the guide groove(s) (see Figure 1). The beginning of each controlled bend
shall be s metres apart from the beginning of the next controlled bend. The beginning of the
controlled bend closest to the launch end shall be 1 m from the launch. The end of the
controlled bend closest to the detector end shall be 1 m from the detector (see Figure 6).
The minimum specimen length shall be determined according to Equations (1) and (2).
(1)
L = (n −1)× s + 2
s = π × R + 2× R (2)
where
L is the minimum sample length, in m;
n is the number of quarter-turn bends;
s is the interval between each bend, in m;
R is th
...
IEC 60793-1-47 ®
Edition 4.0 2017-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical fibres –
Part 1-47: Measurement methods and test procedures – Macrobending loss
Fibres optiques –
Partie 1-47: Méthodes de mesure et procédures d'essai – Pertes par
macrocourbures
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IEC 60793-1-47 ®
Edition 4.0 2017-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical fibres –
Part 1-47: Measurement methods and test procedures – Macrobending loss
Fibres optiques –
Partie 1-47: Méthodes de mesure et procédures d'essai – Pertes par
macrocourbures
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.10 ISBN 978-2-8322-4865-2
– 2 – IEC 60793-1-47:2017 © IEC 2017
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Apparatus . 9
4.1 Method A – Fibre winding . 9
4.2 Method B – Quarter circle bends . 9
4.3 Input system . 10
4.3.1 Optical source . 10
4.3.2 Optical launch arrangement . 10
4.4 Output system and detection . 12
4.4.1 Optical divider . 12
4.4.2 Optical detector . 12
4.4.3 Optical detection assembly . 13
4.4.4 Signal processing . 13
5 Specimen . 13
5.1 Specimen length . 13
5.1.1 Method A – Fibre winding . 13
5.1.2 Method B – Quarter circle bends. 13
5.2 Specimen end face . 13
6 Procedure . 13
6.1 Method A – Fibre winding . 13
6.1.1 General consideration . 13
6.1.2 Single-mode fibres . 14
6.1.3 Multimode (A1) fibres . 15
6.2 Method B – Quarter circle bends . 15
7 Calculations . 17
8 Results . 17
8.1 Information available with each measurement . 17
8.2 Information available upon request . 17
9 Specification information . 17
Annex A (normative) Change in transmittance by transmitted power technique . 19
A.1 Apparatus . 19
A.1.1 General . 19
A.2 Procedure . 20
A.3 Calculations . 20
Annex B (normative) Cut-back technique . 22
B.1 General . 22
B.2 Apparatus . 22
B.2.1 General apparatus for all fibres. 22
B.3 Procedure . 22
B.4 Calculations . 23
Annex C (normative) Requirements for the optical source characteristics for A1
multimode measurement . 24
C.1 Encircled flux (EF) . 24
C.2 Limits on encircled flux . 24
Annex D (informative) Small bend radius phenomena . 27
D.1 General . 27
D.2 Interference between propagating and radiating modes . 27
D.3 Polarization effects . 29
D.4 High power damage . 29
Annex E (informative) Parallel plate (2-point) macrobend loss approximation . 30
E.1 General . 30
E.2 Specimen . 30
E.3 Apparatus . 30
E.3.1 General . 30
E.3.2 Stepper motor control . 31
E.3.3 Movable plate . 31
E.3.4 Fixed plate . 31
E.4 Procedure . 32
E.5 Calculation . 32
E.6 Results . 32
E.7 Comparison of results with normative test . 33
Bibliography . 35
Figure 1 – Quarter circle guide groove in plate . 9
Figure 2 – General launch arrangement . 10
Figure 3 – Lens system . 11
Figure 4 – Launch fibre . 11
Figure 5 – Mode scrambler (for A4 fibre) . 12
Figure 6 – Multiple bends using stacked plates . 16
Figure A.1 – Measurement of change in optical transmittance using reference
specimen . 19
Figure A.2 – Measurement of change in optical transmittance using stabilized source . 20
Figure B.1 – Arrangement of equipment to perform loss measurement at one specified
wavelength . 22
Figure B.2 – Arrangement of equipment used to obtain a loss spectrum . 22
Figure C.1 – Encircled flux template example . 25
Figure D.1 – Loss curves versus curve fits . 28
Figure E.1 – Schematic of possible (two-point bend) apparatus . 31
Figure E.2 – Example of applying an exponential fit to the spectral data of a B6_a2
fibre . 33
Figure E.3 – Example of 2-point bend test data for a B6_a2 fibre . 33
Table 1 – Launch conditions for A2 to A4 fibres . 12
Table C.1 – Threshold tolerance . 25
Table C.2 – EF requirements for 50 µm core fibre cabling at 850 nm . 26
Table C.3 – EF requirements for 50 µm core fibre cabling at 1 300 nm . 26
Table C.4 – EF requirements for 62,5 µm core fibre cabling at 850 nm . 26
Table C.5 – EF requirements for 62,5 µm core fibre cabling at 1 300 nm . 26
– 4 – IEC 60793-1-47:2017 © IEC 2017
Table E.1 – Comparison of parallel plate (2-point) versus method A macrobend loss
measurement for a B6_b3 fibre at 10 mm diameter (ratio of mandrel / 2-point). 34
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-47: Measurement methods and test procedures –
Macrobending loss
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
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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
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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 60793-1-47 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This fourth edition cancels and replaces the third edition published in 2009. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) former Annex A has been renumbered to Annex D;
b) introduction of new Annex A on the transmitted power monitoring technique;
c) introduction of Annex B on the cut-back technique;
d) introduction of Annex C on the requirements for the optical source characteristics of
A1 multimode measurement;
e) introduction of Annex E on parallel plate (2-point) macrobend loss approximation.
The text of this International Standard is based on the following documents:
– 6 – IEC 60793-1-47:2017 © IEC 2017
FDIS Report on voting
86A/1823/FDIS 86A/1828/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
This standard is to be read in conjunction with IEC 60793-1-1:2017.
A list of all parts of IEC 60793 series, published under the general title Optical fibres, can be
found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
Publications in the IEC 60793-1 series concern measurement methods and test procedures as
they apply to optical fibres.
Within the same series, several different areas are grouped, but all numbers are possibly not
used, as follows:
Parts 1-10 to 1-19: General
Parts 1-20 to 1-29: Measurement methods and test procedures for dimensions
Parts 1-30 to 1-39: Measurement methods and test procedures for mechanical
characteristics
Parts 1-40 to 1-49: Measurement methods and test procedures for transmission and
optical characteristics
Parts 1-50 to 1-59: Measurement methods and test procedures for environmental
characteristics
– 8 – IEC 60793-1-47:2017 © IEC 2017
OPTICAL FIBRES –
Part 1-47: Measurement methods and test procedures –
Macrobending loss
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the macrobending
loss of single-mode fibres (class B) at 1 550 nm or 1 625 nm, category A1 multimode fibres at
850 nm or 1 300 nm, and category A3 and A4 multimode fibres at 650 nm, 850 nm or
1 300 nm, thereby assisting in the inspection of fibres and cables for commercial purposes.
This document gives two methods for measuring macrobending sensitivity:
• Method A – Fibre winding, pertains to class B single-mode fibres and category A1
multimode fibres.
• Method B – Quarter circle bends, pertains to category A3 and A4 multimode fibres.
For both of these methods, the macrobending loss can be measured utilizing general fibre
attenuation techniques, for example the power monitoring technique (see Annex A) or the
cut-back technique (see Annex B). Methods A and B are expected to produce different results
if they are applied to the same fibre. This is because the key difference between the two
methods is the deployment, including the bend radius and length of fibre that is bent. The
reason for the difference is that A3 and A4 multimode fibres are expected to be deployed in
short lengths with a smaller number of bends per unit fiber length compared to single-mode
and category A1 multimode fibres.
In this document, the "curvature radius" is defined as the radius of the suitable circular
shaped support (e.g. mandrel or guiding groove on a flat surface) on which the fibre can be
bent.
In addition, informative Annex E has been added to approximate bend loss for class B single-
mode fibres across a broad wavelength range at various effective bends.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 (all parts), Optical fibres – Measurement methods and test procedures
IEC 60793-1-1:2017, Optical fibres – Part 1-1: Measurement methods and test procedures –
General and guidance
IEC 60793-2, Optical fibres – Part 2: Product specifications – General
IEC 60793-2-10, Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 61280-1-4, Fibre optic communication subsystem test procedures – Part 1-4: General
communication subsystems – Light source encircled flux measurement method
IEC 61280-4-1, Fibre-optic communication subsystem test procedures – Part 4-1: Installed
cable plant– Multimode attenuation measurement
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60793-2,
IEC 60793-1 (all parts) and IEC 60793-1-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
NOTE General definitions for fibres are provided in IEC 60793-2, definitions of the specified attributes are
contained in the relevant test methods standard of IEC 60793-1 (all parts), and general definitions for testing are
provided in IEC 60793-1-1.
4 Apparatus
4.1 Method A – Fibre winding
The apparatus consists of a tool (e.g. a mandrel or a guiding groove on a flat surface) able to
hold the sample bent with a radius as stated in the appropriate optical fibre sectional product
specification and a loss measurement instrument. Determine the macrobending loss at the
wavelength as stated in the appropriate sectional product specification by using either the
transmitted power monitoring technique (Annex A) or the cut-back technique (Annex B),
taking care of the appropriate launch condition for the specific fibre type.
4.2 Method B – Quarter circle bends
The apparatus consists of one or more plates, each containing one or more "guide grooves",
and a loss measurement instrument. The plates shall be designed to be stacked during the
test without contacting the sample fibre in a lower or higher plate; such contact will affect the
measurement results. Each guide groove shall have a quarter circle segment (i.e. 90°) as
shown in Figure 1. The bend radius r, i.e. the radius of the quarter circle segment, shall be
stated in the detail specification. The width of each guide groove is recommended to be 40 %
broader than the outer fibre diameter.
Determine the macrobending loss at the wavelength as stated in the appropriate sectional
product specification by using either the transmitted power monitoring technique (Annex A) or
the cut-back technique (Annex B), taking care of the appropriate launch condition for the
specific fibre type.
Guide groove
r
Bend
radius
IEC
Figure 1 – Quarter circle guide groove in plate
– 10 – IEC 60793-1-47:2017 © IEC 2017
4.3 Input system
4.3.1 Optical source
Use a suitable radiation source, such as a lamp, laser or light emitting diode. The choice of
source depends upon the type of measurement. The source shall be stable in position,
intensity and wavelength over a time period sufficiently long to complete the measurement
procedure. Specify the spectral line width (between the 50 % optical intensity power points of
the sources used) such that the line width is narrow, for example less than 10 nm, compared
with any features of the fibre spectral attenuation. Align the fibre to the launch cone, or
connect it coaxially to a launch fibre.
4.3.2 Optical launch arrangement
4.3.2.1 General
Figure 2 shows the general launch arrangement used for all fibres. Apply the appropriate
launch arrangement to produce a full or restricted launch, depending on the parameter being
measured. See 4.3.2.3 to 4.3.2.4 for further details as they apply to specific categories of
single-mode and multimode fibres.
LED/laser
Mode Cladding mode
scrambler stripper
Lamp
Mode filter Launch
Lens
IEC
Figure 2 – General launch arrangement
4.3.2.2 Launch arrangement for single-mode fibres
4.3.2.2.1 General
An optical lens system or fibre pigtail may be employed to excite the test fibre. The power
coupled into the fibre shall be stable for the duration of the measurement (see Figure A.1 or
Figure B.1).
4.3.2.2.2 Fibre pigtail
If using a pigtail, it may be necessary to use index-matching material between the source
pigtail and test fibre to eliminate interference effects.
4.3.2.2.3 Optical lens system
If using an optical lens system, provide a means of stably supporting the input end of the
fibre, such as a vacuum chuck. Mount this support on a positioning device so that the fibre
end can be repeatedly positioned in the input beam. A method of making the positioning of the
fibre less sensitive is to overfill the fibre end spatially and angularly.
4.3.2.2.4 High-order mode filter
Use a method to remove high-order propagating modes in the wavelength range of interest.
An example of such a high-order mode filter is a single loop of radius sufficiently small to shift
the cut-off wavelength below the minimum wavelength of interest, but not so small as to
induce wavelength-dependent oscillations.
Another option commonly employed on bend insensitive single mode fibres and other single
mode fibres with little or no cut-off response to bend is the use of a standard single mode
fibre as a mode filter.
4.3.2.2.5 Cladding mode stripper
Use suitable techniques to remove optical power propagating in the cladding where this would
significantly influence the received signal. The cladding mode stripper ensures that no
radiation modes, propagating in the cladding region, will be detectable after a short distance
along the fibre. The cladding mode stripper often consists of a material having a refractive
index equal to or greater than that of the fibre cladding. This may be an index-matching fluid
applied directly to the uncoated fibre near its ends; under some circumstances, the fibre
coating itself will perform this function.
4.3.2.3 Launch arrangement for A1 multimode fibres
The required launch for measuring the macrobending loss of A1 multimode fibres shall be an
encircled flux launch. The requirements for the optical source characteristics for A1 multimode
measurement are included in Annex C.
The encircled flux emitted by the launching cord depends on the characteristic of the light
source emerging from the face of the socket, the connection of the launching cord to the
socket, the optical fibre within the launch cord, and any applied mode conditioning.
The test equipment manufacturer should provide specifications for the test cord that are
compatible with the particular source implementation used. When the specification on the cord
is met and used with the test equipment, the encircled flux (EF) requirements should be
assured.
4.3.2.4 Launch arrangements for A2 to A4 multimode fibres
Below are some examples of generic launching arrangements for short-distance fibres
described in Figure 3, Figure 4 and Figure 5.
Fibre under test
IEC
Lens
Figure 3 – Lens system
Launch fibre
Fibre under test
Splice
Cladding mode stripper
IEC
(if necessary)
Figure 4 – Launch fibre
– 12 – IEC 60793-1-47:2017 © IEC 2017
Fibre under test
Mode scrambler
IEC
Figure 5 – Mode scrambler (for A4 fibre)
The reproducibility of the attenuation measurements of step-index fibres is critical. Therefore,
a well-defined launching set-up description is necessary. Such a set-up can be achieved by
using commercially available optical components and shall be able to provide spot sizes and
launch numerical apertures (NAs) as given in Table 1. In addition, the measurement
wavelength shall be calibrated to within ±10 nm.
Table 1 – Launch conditions for A2 to A4 fibres
Attribute Fibre category
A2 A3 A4
Glass core/glass cladding
Glass core/plastic Plastic core/plastic
cladding cladding
Spot size = fibre core size = fibre core size = fibre core size with full
mode launch (or use mode
scrambler with equilibrium
mode launch)
a b
Numerical aperture = fibre max NA, with full
= fibre max NA = fibre max NA
b
(NA)
mode launch
a
This launch condition can be produced by overfilling a mode filter made from 2 m of fibre identical to the fibre
under test (FUT), with appropriate cladding mode stripping and using the output from this mode filter to launch
into the FUT.
b
This launch condition can be produced in the same manner as described in Note a. However, some types of
A3 and A4 fibre will not require cladding mode stripping for the mode filter.
4.4 Output system and detection
4.4.1 Optical divider
When an optical divider is required, it shall have a splitting ratio that remains constant during
the test. The splitting ratio and temperature stability shall be as shown in the relevant detail
specification. Commercially available or custom built devices may be used.
4.4.2 Optical detector
The optical detector shall be of sufficient area to intercept all of the radiated power in the
output cone and shall be sufficiently linear over the optical powers encountered.
The optical detector shall have a sufficiently uniform response over the active area and range
of incidence angle at the measurement wavelength to ensure the movement of the output
cone in position or angle relative to the detector. This shall be within the limits determined by
the mechanical design of the measurement equipment and shall not significantly affect the
results.
Where more than one detector is used, as in the arrangement shown in Figure A.1, the
detectors shall be of the same manufacturer and model and be of comparable linearity.
4.4.3 Optical detection assembly
All power emitted from the specimen should be coupled to the active region of the detector by
an appropriate means. For example, an optical lens system, a butt spliced fibre pigtail, or
direct coupling to the detector may be used. If the detector is already pigtailed, the pigtail
fibre shall have sufficiently large core diameter and numerical aperture to capture all of the
light exiting the reference and specimen fibres.
Use an optical detector that is linear and stable over the range of intensities and
measurement times that are encountered in performing this measurement. A typical system
can include a photovoltaic mode photodiode amplified by a current input amplifier, with
synchronous detection by a lock-in amplifier.
4.4.4 Signal processing
It is customary to modulate the light source in order to improve the signal-to-noise ratio (SNR)
at the receiver. If such a procedure is adopted, link the detector to a signal processing system
synchronous with the source modulation frequency. The detecting system should be
substantially linear or have known characteristics.
When low loss is expected, more test bends may be added provided there are separate
grooves for each additional bend to improve the SNR; however, the approximation of the bend
diameter along with the bend control may be further degraded.
5 Specimen
5.1 Specimen length
5.1.1 Method A – Fibre winding
The specimen shall be a known length of fibre, as specified in the detail specification. In
particular, the length of the sample tested for loss is determined by the measurement set-up,
i.e. curvature radius (R) and number of turns (N); any further fibre length does not affect the
measurement results, provided that the SNR is optimised.
5.1.2 Method B – Quarter circle bends
The specimen length shall be determined according to the details shown in 6.2.
5.2 Specimen end face
Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each test
specimen.
6 Procedure
6.1 Method A – Fibre winding
6.1.1 General consideration
Loosely wind the fibre on the tool, avoiding excessive fibre twist. The number of turns,
curvature radius and wavelength at which loss is to be measured are discussed below in 6.1.1
and in 6.1.2 and 6.1.3.
Since the actual curvature radius is critical, a maximum tolerance of ±0,1 mm (for radii lower
than or equal to 15 mm) or ±1,0 mm (for larger radii) is accepted: a tighter tolerance on small
radii is required for higher measurement sensitivity.
Both for single-mode and for multimode fibres, two optical powers can be measured using
– the power-monitoring technique, which measures the fibre attenuation increase due to a
change from the straight condition to a bent condition, or
– the cut-back technique, which measures the total attenuation of the fibre in the bent
condition. In order to determine the induced attenuation due to macrobending, this value
should be corrected for the intrinsic attenuation of the fibre.
The fibre length outside the mandrel and the reference cut-back length shall be free of bends
that can introduce a significant change in the measurement result. It is also possible to rewind
– 14 – IEC 60793-1-47:2017 © IEC 2017
the fibre from a mandrel with a large radius (introducing negligible macrobend loss) to the
mandrel with the required radius. In this case, the macrobend loss can be determined directly
by using the power-monitoring technique (without the correction for the intrinsic attenuation of
the fibre).
Care shall be taken in order not to introduce torsion on any fibre part during the
measurements, as this would affect the result.
6.1.2 Single-mode fibres
Different applications may require different deployment conditions: fibre types have been
developed which exhibit bending performances optimised for each condition.
Two typical environments are recognised for (possibly) different fibre types, for which different
measurement set-ups should be considered when characterising fibre performances.
a) Long distance networks: far from urban areas, space occupancy is not typically an issue,
and bends imposed on the fibres can be limited to relatively large radii. Fibres designed
for this application should be tested in similar conditions, i.e. with the samples wrapped
around relatively large radius mandrels, for example in the range 25 mm to 30 mm.
This measurement set-up is mainly affected by errors related to low SNR and by unwanted
tension, torsions or kinks on the relatively long fibre length used for the measurement.
b) Access networks: operating conditions require bending radii as small as possible,
compatible with lifetime expectations and acceptable bend losses. For more information
on lifetime expectations please refer to ITU-T G Suppl.59:2016. Fibres designed for this
application should be tested in similar conditions, i.e. with the samples bent at small radii,
for example in the range 7,5 mm to 15 mm (see Annex C).
The measurement can be affected by different sources, i.e. reflections, which may occur
at the coating-air or coating-glass interface, at surrounding surfaces (including, when
used, the mandrel surface), or at connectors.
The test can be carried out on samples either making complete (360º) turn(s), in open air or
around a suitable support (mandrel), or making an equivalent number of partial turns, for
example U-turns (180º) or quarter turns (90º), in open air or around suitable supports. The
length under test is different for complete and partial turns; for example, the length of a
complete turn being twice the length of a U-turn or four times the length of a quarter turn. In
this document, the term "coil" refers to one complete turn. One coil could also be made of, for
example, two consecutive U-turns or four consecutive quarter turns. This should be taken
into account while normalising the results to the length of the sample (number of coils).
The following recommendations apply to test conditions in both cases (items a) and b) above):
Number of turns
– The number of turns should be in accordance with the values stated in the product
specification.
– For single-mode fibres, the attenuation increases in a linear fashion with the number of
turns.
– For each radius, the number of turns shall be chosen in such a way that:
• the induced loss is significantly higher than the detection limit of the set-up; when
necessary, for example for low bend loss fibres, tests may be carried out with more
turns than the specification requires – followed by linear normalization to the specified
number;
• the induced loss is significantly lower than the onset of the non-linear region in the set-
up; for bending radii in the range 5 mm to 10 mm, this may imply that not more than 5
to 10 turns should be used.
___________
If there is excessive displacement between successive U-turns, the length of the sample arranged on two
U-turns can be shorter than one coil. A maximum displacement between adjacent U-turns of 0,5 mm is
therefore suggested.
Bend radius
The value of bend radius shall be in accordance with the values stated in the product
2.
specification
Wavelength
The measurement wavelength shall be 1 550 nm or 1 625 nm, in accordance with the
relevant product specification; it should be considered that bending losses increase
exponentially with the wavelength.
The homogeneity of bend loss in different angular positions over the cross section needs to
be verified either by multiple angular position tests or by verifying the homogeneity of the
effective refractive index profile, establishing the guiding properties of the bent FUT.
6.1.3 Multimode (A1) fibres
Macrobending loss in A1 multimode fibres varies with bend radius and number of turns around
a mandrel and is less sensitive to wavelength than with single-mode fibres. Still, oscillating
effects with wavelength may occur which are related to successive mode groups passing cut-
off and having increased bend loss at these wavelengths.
The values of bend radius and number of turns shall be in accordance with the values stated
in the specification. When testing multiple turns, the attenuation th
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