prEN IEC 60793-1-47:2026

Lichtwellenleiter - Teil 1-47: Messmethoden und Prüfverfahren - Makrobiegeverlust

Fibres optiques - Partie 1-47: Méthodes de mesure et procédures d'essai - Pertes par macrocourbures

Optična vlakna - 1-47. del: Merilne metode in postopki preskušanja - Izgube zaradi makro upogibov

General Information

• Status: Not Published
• Publication Date: 05-Sep-2027
• ICS: 33.180.10 - Fibres and cables
• Technical Committee: CLC/TC 86A - Optical fibres and optical fibre cables
• Current Stage: 4060 - Enquiry results established and sent to TC, SR, BTTF - Enquiry
• Start Date: 01-May-2026
• Completion Date: 01-May-2026
• Ref Project: oSIST prEN IEC 60793-1-47:2026 - Optical fibres - Part 1-47: Measurement methods and test procedures - Macrobending loss

Relations

• Revises: EN IEC 60793-1-47:2018 - Optical fibres - Part 1-47: Measurement methods and test procedures - Macrobending loss
• Effective Date: 13-May-2025

Overview

prEN IEC 60793-1-47:2026, titled Optical fibres - Part 1-47: Measurement methods and test procedures - Macrobending loss, is an international draft standard developed by CLC and IEC. This standard provides uniform procedures for the measurement of macrobending loss in optical fibres, ensuring consistent quality and performance in fibre optic cables used globally. Macrobending loss refers to attenuation caused when optical fibres are bent with relatively large radii, a critical performance parameter for fibre optic infrastructure.

Target applications include single-mode (class B) and multimode (categories A1, A3, and A4) optical fibres, with specific measurement wavelengths identified for each category. The standard specifies two main measurement methods, comprehensive test procedures, and the apparatus required to assess macrobending sensitivity.

Key Topics

• Measurement Approaches:
  • Method A – Fibre winding: Used for class B single-mode and category A1 multimode fibres, employing controlled winding around a specified radius.
  • Method B – Quarter circle bends: Adopts multiple stacked plates with guide grooves for A3 and A4 multimode fibres, simulating shorter fibre deployments.
• Test Procedures:
  • Specification of apparatus (mandrel, guide groove plates, light sources, detectors, mode filters).
  • Guidance on sample preparation, including sample length and end face quality.
• Loss Measurement Techniques:
  • Transmitted power monitoring: Measures increased attenuation from introducing bends.
  • Cut-back technique: Compares attenuation before and after removing a reference fibre length.
• Launch and Detection:
  • Detailed arrangements ensuring accurate optical fibre excitation and light collection.
  • Use of mode conditioning, mode strippers, and encircled flux control for repeatable results.
• Control and Calculations:
  • Tolerances for bend radii, sample handling to avoid torsion, and correction of results for intrinsic fibre attenuation.
  • Annexes describe normative and informative methodologies, including variation in bend techniques and loss approximations.

Applications

This standard is invaluable for:

• Quality Assurance & Inspection: Enables manufacturers and test laboratories to assess optical fibre performance with respect to macrobending loss, supporting reliable deployment in communications infrastructure.
• Product Development: Assists fibre and cable designers in optimizing products for access networks (requiring tight bends) versus long-haul deployments (larger bends).
• Telecommunication Networks: Provides standardized test data supporting cable specification, procurement, and installation.
• Research & Standards Compliance: Encourages harmonization of fibre optic measurement methodology across international markets by supporting IEC, CENELEC, and ISO requirements.

The uniformity in testing helps prevent signal attenuation issues in installed networks, directly impacting the longevity and service quality of broadband, metropolitan, and access fibre optic systems.

Related Standards

For comprehensive fibre optic testing, refer to these related standards:

• IEC 60793-1 (all parts): General measurement methods and test procedures for optical fibres.
• IEC 60793-1-1:2022: General guidance on optical fibre measurement procedures.
• IEC 60793-2: Product specifications for optical fibres.
• IEC 61280-4-1:2019: Attenuation measurement procedures for installed multimode fibre cable plant.
• IEC 60793-2-10/20/30/40: Product specifications for A1 through A4 fibre categories.
• IEC 60793-1-40: Attenuation measurement and monitoring of changes in attenuation.
• ITU-T G Suppl. 59:2016: Guidance on optical fibre and cable reliability.

Compliance with prEN IEC 60793-1-47:2026 and associated standards ensures robust validation of macrobending loss, contributing to the reliability and efficiency of modern fibre optic networks.

Keywords: optical fibre, macrobending loss, measurement methods, test procedures, fibre attenuation, fibre optic standard, IEC 60793-1-47, fibre winding, quarter circle bends, telecommunications, quality assurance, cable testing

Standards Content (Sample)

SLOVENSKI STANDARD
01-april-2026
Optična vlakna - 1-47. del: Merilne metode in postopki preskušanja - Izgube zaradi
makro upogibov
Optical fibres - Part 1-47: Measurement methods and test procedures - Macrobending
loss
Lichtwellenleiter - Teil 1-47: Messmethoden und Prüfverfahren - Makrobiegeverlust
Fibres optiques - Partie 1-47: Méthodes de mesure et procédures d'essai - Pertes par
macrocourbures
Ta slovenski standard je istoveten z: prEN IEC 60793-1-47:2026
ICS:
33.180.10 (Optična) vlakna in kabli Fibres and cables
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

86A/2654/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 60793-1-47 ED5
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2026-02-06 2026-05-01
SUPERSEDES DOCUMENTS:
86A/2584/CD, 86A/2651/CC
IEC SC 86A : FIBRES AND CABLES
SECRETARIAT: SECRETARY:
France Mr Laurent Gasca
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

ASPECTS CONCERNED:
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
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submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Optical fibres - Part 1-47: Measurement methods and test procedures - Macrobending loss

PROPOSED STABILITY DATE: 2030
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IEC CDV 60793-1-47 © IEC 2026
CONTENTS
Contact . 2
CONTENTS . 3
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 Sample . 13
5.1 Sample length . 13
5.1.1 Method A - Fibre winding . 13
5.1.2 Method B - Quarter circle bends . 13
5.2 Sample 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 . 20
A.3 Calculations . 21
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 . 23
B.4 Calculations . 23
IEC CDV 60793-1-47 © IEC 2026
Annex C (informative) Small bend radius phenomena . 24
C.1 General . 24
C.2 Interference between propagating and radiating modes . 24
C.3 Polarization effects . 26
C.4 High power damage . 26
Annex D (informative) Parallel plate (2-point) macrobending loss approximation . 27
D.1 General . 27
D.2 Sample . 27
D.3 Apparatus . 27
D.3.1 General . 27
D.3.2 Stepper motor control . 28
D.3.3 Movable plate . 28
D.3.4 Fixed plate. 29
D.4 Procedure . 29
D.5 Calculation . 29
D.6 Results . 29
D.7 Comparison of results with normative test . 30
Bibliography . 32

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 source monitor . 20
Figure A.2 – Measurement of change in optical transmittance using stabilized optical
source . 20
Figure B.1 – Example of an arrangement of equipment to perform loss measurement at
one specified wavelength . 22
Figure B.2 – Example of an arrangement of equipment used to obtain a loss spectrum . 22
Figure C.1 – Loss curves versus curve fits . 25
Figure D.1 – Schematic of possible (two-point bend) apparatus . 28
Figure D.2 – Example of applying an exponential fit to the spectral data of a B6_a2
fibre 30
Figure D.3 – Example of 2-point bend test data for a B6_a2 fibre. 30

Table 1 – Launch conditions for A2 to A4 fibres . 12
Table D.1 – Comparison of parallel plate (2-point) versus method A macrobending loss
measurement for a B6_b3 fibre at 10 mm diameter (ratio of mandrel / 2-point) . 31

IEC CDV 60793-1-47 © IEC 2026
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 this end and in addition to other
activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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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 corres ponding 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) IEC draws attention to the possibility that the implementation of this document may involve
the use of (a) patent(s). IEC takes no position concerning the evidence, validity or applicability
of any claimed patent rights in respect thereof. As of the date of publication of this document,
IEC [had/had not] received notice of (a) patent(s), which may be required to implement this
IEC CDV 60793-1-47 © IEC 2026
document. However, implementers are cautioned that this may not represent the latest
information, which may be obtained from the patent database available at https://patents.iec.ch.
IEC shall not be held responsible for identifying any or all such patent r ights.
IEC 60793-1-47 has been prepared by subcommittee 86A: Fibres and cables, of IEC technical
committee 86: Fibre optics. It is an International Standard.
This fifth edition cancels and replaces the fourth edition published in 2017. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) remove calculation formula in Clause 7 and reference to Clause A.3 and Clause B.4 for
transmitted power technique and cut-back technique respectively;
b) revision of Annex A on the transmitted power monitoring technique and Annex B on the cut-
back technique by directly describing how to carry out macrobending loss test and
corresponding calculations.
c) remove Annex C (see IEC 60793-1-47:2017, Annex C ed 4) and reference the requirement
of optical source characteristics for A1 multimode fibres measurement to IEC 61280-4-
1:2019, Annex F.
The text of this International Standard is based on the following documents:
Draft Report on voting
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English [change
language if necessary].
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at https://www.iec.ch/members_experts/refdocs. The main document types developed by IEC
are described in greater detail at https://www.iec.ch/publications.
This standard is to be read in conjunction with IEC 60793-1-1:2022.
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 https://webstore.iec.ch in the data related to
the specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC CDV 60793-1-47 © IEC 2026
INTRODUCTION
Publications in the IEC 60793-1 (all parts) 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
The following items were listed in the bibliography but not cited in the text. Please find a suitable
place to cite them to justify their inclusion in the bibliography:
IEC 60793-1-40, Optical fibres - Part 1-40: Attenuation measurement methods6: Measurement
methods and test procedures - Monitoring of changes in attenuationIEC 60793-1-46 [1]
IEC 60793-1-46, Optical fibres - Part 1-4
IEC 60793-2-50, Optical fibres - Part 2-50: Product specifications - Sectional specification for
class B single-mode fibresIEC 60793-2-50 [2]
ITU-T G Suppl. 59:2016, Guidance on optical fibre and cable reliability [3]
IEC CDV 60793-1-47 © IEC 2026
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 D 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 60793-1-1:2022, 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 60793-2-20, Optical fibres - Part 2-20: Product specifications - Sectional specification for
category A2 multimode fibres
IEC 60793-2-30, Optical fibres - Part 2-30: Product specifications - Sectional specification for
category A3 multimode fibres
IEC 60793-2-40, Optical fibres - Part 2-40: Product specifications - Sectional specification for
category A4 multimode fibres
IEC 61280-4-1:2019, Fibre-optic communication subsystem test procedures - Part 4-1: Installed
cable plant - Multimode attenuation measurement
IEC CDV 60793-1-47 © IEC 2026
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 60793-1-1:2022 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://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 60793-1-1:2022.
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.
IEC CDV 60793-1-47 © IEC 2026
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.
Figure 2 – General launch arrangement
IEC CDV 60793-1-47 © IEC 2026
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 set
through the measured encircled flux launch. The requirements for the optical source
characteristics for A1 multimode measurement are defined in IEC 61280-4-1:2019, Annex F.
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.
IEC CDV 60793-1-47 © IEC 2026
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.

Figure 3 – Lens system
Figure 4 – Launch fibre
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 Glass A3 Glass A4 Plastic core/plastic cladding
core/glass 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)
Numerical a b b
= fibre max NA = fibre max NA = fibre max NA, with full mode launch
aperture
(NA)
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.
IEC CDV 60793-1-47 © IEC 2026
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 sample 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 sample 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 Sample
5.1 Sample length
5.1.1 Method A - Fibre winding
The sample 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 sample length shall be determined according to the details shown in 6.2.
IEC CDV 60793-1-47 © IEC 2026
5.2 Sample end face
Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each test
sample.
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
the fibre from a mandrel with a large radius (introducing negligible macrobending loss) to the
mandrel with the required radius. In this case, the macrobending 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.59:2018. 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).
IEC CDV 60793-1-47 © IEC 2026
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
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 mod e groups passing cut-
off and having increased bend loss at these wavelengths.
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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 C).
IEC CDV 60793-1-47 © IEC 2026
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 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 multimode launching conditions can be found in IEC 61280-4-1:2019, Annex F.
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 sample length shall be determined according to Formula (1) and Formula (2).
𝐿=(𝑛−1)×𝑠+2 (1)
(2)
𝑠= 𝜋×𝑅+2×𝑅
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 the slack bend radius, in m.
IEC CDV 60793-1-47 © IEC 2026
Figure 6 – Multiple bends using stacked plates
Macrobending loss caused by multiple bends of various radii can be measured simultaneously
by stacking plates cut with grooves of various specified bend radii (see Figure 6).
Unless otherwise specified in the detail specification, the default values for the test are as
follows:
– macrobend radius: r = 25 mm;
– number of macrobends: n = 10;
– slack bend radius, R≥ 150 mm;
– wavelengths: 650 nm, 850 nm or 1 300 nm.
These parameters correspond to the interval between each macrobend being s ≥ 1 m, and a
sample length L ≥ 11 m.
The added fibre loss caused by bending shall be measured using either the transmitted power
monitoring technique (Annex A) or the cut-back technique (Annex B). Use cladding mode
strippers at the source and detector ends of the sample. A suitable cl
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