IEC 60793-1-40:2019
(Main)Optical fibres - Part 1-40: Attenuation measurement methods
Optical fibres - Part 1-40: Attenuation measurement methods
IEC 60793-1-40:2019 establishes uniform requirements for measuring the attenuation of optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes. Four methods are described for measuring attenuation, one being that for modelling spectral attenuation:
– method A: cut-back;
– method B: insertion loss;
– method C: backscattering;
– method D: modelling spectral attenuation.
Methods A to C apply to the measurement of attenuation for all categories of the following fibres:
– class A multimode fibres;
– class B single-mode fibres.
Method C, backscattering, also covers the location, losses and characterization of point discontinuities. Method D is applicable only to class B fibres. Information common to all four methods appears in Clauses 1 to 11, and information pertaining to each individual method appears in Annexes A, B, C, and D, respectively. This second edition cancels and replaces the first edition published in 2001. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) Improvement of the description of measurement details for B6 fibre;
b) Improvement of the calibration requirements for A4 fibre;
c) Introduction of Annex E describing examples of short cable test results on A1 multimode fibres.
Keywords: measuring the attenuation of optical fibre
Fibres optiques - Partie 1-40: Méthodes de mesurage de l'affaiblissement
IEC 60793-1-40:2019 établit des exigences uniformes pour mesurer l'affaiblissement d'une fibre optique, contribuant ainsi au contrôle des fibres et des câbles dans les relations commerciales. Quatre méthodes sont décrites pour mesurer l'affaiblissement, parmi lesquelles une méthode pour modéliser l'affaiblissement spectral:
– méthode A: fibre coupée;
– méthode B: pertes d'insertion;
– méthode C: rétrodiffusion;
– méthode D: modélisation de l'affaiblissement spectral.
Les méthodes A à C s'appliquent au mesurage de l'affaiblissement pour toutes les catégories de fibres suivantes:
– fibres multimodales de classe A;
– fibres unimodales de classe B.
La méthode C, rétrodiffusion, s'applique aussi à la localisation, aux pertes et à la caractérisation des discontinuités ponctuelles. La méthode D s'applique uniquement aux fibres de classe B. Les informations communes à ces quatre méthodes sont présentées dans les Articles 1 à 11, et les informations propres à chaque méthode individuelle, sont présentées dans les Annexes A, B, C et D, respectivement. Cette deuxième édition annule et remplace la première édition parue en 2001 dont elle constitue une révision technique. La présente édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) Amélioration de la description des détails de mesurage pour les fibres B6;
b) Amélioration des exigences d'étalonnage pour les fibres A4;
c) Ajout de l'Annexe E qui décrit des exemples de résultats d'essai sur des câbles courts pour des fibres multimodales A1.
Mots-clés: mesurer l'affaiblissement d'une fibre optique
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Standards Content (Sample)
IEC 60793-1-40 ®
Edition 2.0 2019-03
REDLINE VERSION
INTERNATIONAL
STANDARD
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Optical fibres –
Part 1-40: Measurement methods and test procedures – Attenuation
measurement methods
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IEC 60793-1-40 ®
Edition 2.0 2019-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Optical fibres –
Part 1-40: Measurement methods and test procedures – Attenuation
measurement methods
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.10 ISBN 978-2-8322-6770-7
– 2 – IEC 60793-1-40:2019 RLV © IEC 2019
CONTENTS
FOREWORD . 5
INTRODUCTION .
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Calibration requirements . 10
5 Reference test method . 10
6 Apparatus . 10
7 Sampling and specimens . 10
7.1 Specimen length . 10
7.2 Specimen end face . 10
8 Procedure . 10
9 Calculations . 10
9.1 Methods A and B . 10
9.2 Method C . 11
9.3 Method D . 11
10 Results . 11
10.1 Information available with each measurement . 11
10.2 Information available upon request . 11
10.3 Method-specific additional information . 11
11 Specification information . 11
Annex A (normative) Requirements specific to method A – Cut-back . 12
A.1 General . 12
A.2 Apparatus . 12
A.2.1 General apparatus for all fibres. 12
A.2.2 Launch apparatus for all single-mode fibres . 14
A.2.3 Launch apparatus for A1 graded-index multimode fibres . 15
A.2.4 Launch apparatus for A2 to A4 step-index multimode fibres . 17
A.2.5 Calibration requirements . 18
A.3 Procedure . 19
A.4 Calculations . 19
Annex B (normative) Requirements specific to method B – Insertion loss . 20
B.1 General . 20
B.2 Apparatus . 20
B.2.1 General set-ups . 20
B.2.2 Apparatus common to method A (cut-back). 20
B.2.3 Additional apparatus specific to method B (insertion-loss) . 20
B.2.4 Calibration requirements . 20
B.3 Procedure . 20
B.4 Calculations . 21
Annex C (normative) Requirements specific to method C – Backscattering . 22
C.1 General . 22
C.2 Apparatus . 22
C.2.1 General . 22
C.2.2 Optical transmitter . 23
C.2.3 Launch conditions . 23
C.2.4 Optical splitter . 23
C.2.5 Optical receiver . 23
C.2.6 Pulse duration and repetition rate . 23
C.2.7 Signal processor . 23
C.2.8 Display . 24
C.2.9 Data interface (optional) . 24
C.2.10 Reflection controller (optional) . 24
C.2.11 Splices and connectors . 24
C.3 Sampling and specimens . 24
C.4 Procedure . 24
C.4.1 General . 24
C.4.2 Further steps for measuring attenuation. 26
C.4.3 Further steps for measuring point discontinuities . 26
C.4.4 Calibration . 28
C.5 Calculations . 28
C.6 Results . 28
Annex D (normative) Requirements specific to method D – Spectral attenuation
modelling . 30
D.1 General . 30
D.2 Apparatus . 30
D.3 Sampling and specimens . 30
D.4 Procedure . 30
D.5 Calculations . 31
D.6 Results . 31
Annex E (informative) Examples of short cable test results on A1 multimode fibres . 33
Bibliography . 35
Figure A.1 – Arrangement of equipment to make for loss measurement at one
a specified wavelength . 12
Figure A.2 – Arrangement of equipment used to obtain loss spectrum . 13
Figure A.3 – General launch arrangement . 13
Figure A.4 – Limited phase space launch optics . 16
Figure A.5 – Two examples of optical fibre scramblers . 17
Figure A.6 – Lens system . 17
Figure A.7 – Launch fibre . 18
Figure A.8 – Mode scrambler (for A.4 fibre) . 18
Figure A.9 – A wide-spectrum source (line "b") could lead to attenuation measurement
errors due to sharp variations on spectral attenuation of polymer-core fibres (line "a") . 19
Figure B.1 – Calibration of insertion loss measurement set . 21
Figure B.2 – Measurement of insertion loss . 21
Figure C.1 – Block diagram of an OTDR . 22
Figure C.2 – Schematic OTDR trace for a "uniform" specimen preceded by a
dead-zone fibre . 25
Figure C.3 – Schematic OTDR trace for a "uniform" specimen not preceded by a dead-
zone fibre . 25
– 4 – IEC 60793-1-40:2019 RLV © IEC 2019
Figure C.4 – Schematic OTDR trace showing apparent loss due to point discontinuities,
one reflective and one non-reflective . 27
Figure C.5 – Schematic of an expanded OTDR trace showing two point discontinuities,
one with apparent gain, and another with no apparent loss or gain . 27
Figure E.1 – Example of attenuation coefficient tests on A1a.1 fibre . 33
Figure E.2 – Example of attenuation coefficient tests on A1a.3 fibre . 33
Figure E.3 – Example of attenuation coefficient tests on A1b fibre . 34
Table A.1 – Mandrel sizes Size examples . 16
Table A.2 – Launch conditions for A2 to A4 fibres . 17
INTERNATIONAL ELECTROTECHNICAL COMMISSION
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OPTICAL FIBRES –
Part 1-40: Measurement methods and test procedures –
Attenuation measurement methods
FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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This redline version of the official IEC Standard allows the user to identify the changes
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– 6 – IEC 60793-1-40:2019 RLV © IEC 2019
International Standard IEC 60793-1-40 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Improvement of the description of measurement details for B6 fibre;
b) Improvement of the calibration requirements for A4 fibre;
c) Introduction of Annex E describing examples of short cable test results on A1 multimode
fibres.
The text of this International Standard is based on the following documents:
FDIS Report on voting
86A/1909/FDIS 86A/1927/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.
A list of all parts in the 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, 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 charac-
teristics
– 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 charac-
teristics.
– 8 – IEC 60793-1-40:2019 RLV © IEC 2019
OPTICAL FIBRES –
Part 1-40: Measurement methods and test procedures –
Attenuation measurement methods
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the attenuation of
optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes.
Four methods are described for measuring attenuation, one being that for modelling spectral
attenuation:
– method A: cut-back;
– method B: insertion loss;
– method C: backscattering;
– method D: modelling spectral attenuation.
Methods A to C apply to the measurement of attenuation for all categories of the following
fibres:
– class A multimode fibres;
– class B single-mode fibres.
Method C, backscattering, also covers the location, losses and characterization of point
discontinuities.
To date, method D has been demonstrated only on class B fibres.
Method D is applicable only to class B fibres.
Information common to all three measurements, and to the modelling method four methods
appears in Clauses 1 to 8 11, and information pertaining to each individual method appears in
Annexes A, B, C, and D, respectively.
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 60793-1-1, Optical fibres – Part 1-1: Measurement methods and test procedures –
General and guidance
IEC 60793-1-22, Optical fibres – Part 1-22: Measurement methods and test procedures –
Length measurement
IEC 60793-1-43, Optical fibres – Part 1-43: Measurement methods and test procedures –
Numerical aperture measurement
IEC 61746-1, Calibration of optical time-domain reflectometers (OTDR) – Part 1: OTDR for
single mode fibres
IEC 61746-2, Calibration of optical time-domain reflectometers (OTDR) – Part 2: OTDR for
multimode fibres
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60793-1-1 and the
following 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
3.1
attenuation
attenuation of a fibre at wavelength λ between two cross-sections, 1 and 2, separated by a
distance and defined as
P ()λ
A()λ = 10log
(1)
P ()λ
where
A(λ) is the attenuation, in dB, at wavelength λ;
P (λ) is the optical power traversing cross-section 1;
P (λ) is the optical power traversing cross-section 2.
Note 1 to entry: Attenuation is a measure of the decreasing optical power in a fibre at a given wavelength. It
depends on the nature and length of the fibre and is also affected by measurement conditions.
3.2
attenuation coefficient
attenuation per unit length
attenuation per unit length for a uniform fibre under steady state conditions
Note 1 to entry: It is possible to define the attenuation per unit length or the attenuation coefficient as follows:
A()λ
(2)
αλ() =
L
which is independent of the chosen length of the fibre,
where
α(λ) is the attenuation coefficient;
A(λ) is the attenuation at wavelength λ;
L is the length, in kilometres.
Note 2 to entry: Uncontrolled launching conditions normally excite higher order lossy modes that produce
transient losses and result in attenuation that is not proportional to the length of the fibre. A controlled, steady-
state launching condition yields attenuation that is proportional to the fibre's length. Under steady-state conditions,
an attenuation coefficient of a fibre can be determined and the attenuation of concatenated fibres added linearly.
– 10 – IEC 60793-1-40:2019 RLV © IEC 2019
3.3
spectral attenuation modelling
technique that predicts the attenuation coefficients across a spectrum of wavelengths from a
small number (three to five) of discrete values measured directly at different wavelengths
3.4
point discontinuity
temporary or permanent local deviation of the continuous optical time-domain reflectometer
(OTDR) signal in the upward or downward direction
Note 1 to entry: The nature of the deviation can vary with test conditions (e.g. pulse duration, wavelength, and
direction of the OTDR signal). Although a point discontinuity can have a length greater than the corresponding
displayed pulse duration (including transmitter and receiver effects), the length is usually about equal to the pulse
duration. For a correct interpretation, the guidelines in IEC 60793-1-22 should be followed for measuring length.
4 Calibration requirements
Under consideration.
See Annexes A, B, and C for methods A, B, and C, respectively.
5 Reference test method
Method A, cut-back, is the reference test method (RTM), which shall be the one used to settle
disputes.
6 Apparatus
Annexes A, B, C, and D include layout drawings and other equipment requirements for each
of the methods, respectively.
7 Sampling and specimens
7.1 Specimen length
The specimen shall be a known length of fibre on a reel, or within a cable, as specified in the
detail specification.
7.2 Specimen end face
Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each
specimen.
8 Procedure
See Annexes A, B, C and D for methods A, B, C and D, respectively.
9 Calculations
9.1 Methods A and B
Methods A and B, cut-back and insertion loss use Equations (1) and (2) respectively, which
appear in 3.1 and 3.2.
9.2 Method C
See Annex C.
9.3 Method D
See Annex D.
10 Results
10.1 Information available with each measurement
Report the following information with each measurement:
– date and title of measurement;
– identification of specimen;
– optical source wavelength;
– specimen length;
– spectral attenuation, in dB, or attenuation coefficient, in dB/km, versus wavelength or at
specific wavelength(s), as required by the detail specification.
10.2 Information available upon request
The following information shall be available upon request:
– measurement method used: A, B, C, or D;
– type of optical source used: central centroidal wavelength(s) and spectral width(s);
– launching technique and conditions used;
– indication if a dead-zone fibre was used (for method C only);
– description of all key equipment;
– for type B fibres – dimensions and number of turns of the mode filter or mode scrambler;
– pulse duration(s), scale range(s), and signal-averaging details;
– details of computation technique (calculation method);
– any deviations to the procedure that were made;
– date of latest calibration of measurement equipment.
10.3 Method-specific additional information
For methods C and D, see the additional requirements in Clauses C.6 and D.6, respectively.
This particularly applies when using method C for measuring point discontinuities.
11 Specification information
The detail specification shall specify the following information:
– type of fibre (or cable) to be measured;
– failure or acceptance criteria at the wavelength or wavelength range;
– any deviations to the procedure that apply;
– information to be reported.
– 12 – IEC 60793-1-40:2019 RLV © IEC 2019
Annex A
(normative)
Requirements specific to method A – Cut-back
A.1 General
The cut-back technique is the only method directly derived from the definition of fibre
attenuation, in which the power levels, P (λ) and P (λ), are measured at two points of the
1 2
fibre without change of input conditions. P (λ) is the power emerging from the end of the fibre,
and P (λ) is the power emerging from a point near the input after cutting the fibre. This
explains its wide acceptance as the reference test method for attenuation.
This measurement principle does not permit information to be obtained on the attenuation
behaviour over the length of the fibre, nor is it easy to measure the change of attenuation
under changing conditions. In some situations, its destructive nature is a disadvantage.
A.2 Apparatus
A.2.1 General apparatus for all fibres
A.2.1.1 General
See Figures A.1 and A.2 for diagrams of suitable test set-ups.
Figure A.1 – Arrangement of equipment to make for loss measurement at one
a specified wavelength
Figure A.2 – Arrangement of equipment used to obtain loss spectrum
A.2.1.2 General launch arrangement
Figure A.3 shows the general launch arrangement used for all fibres. See A.2.2 to A.2.4 for
further details as they apply to specific categories of single-mode and multimode fibres.
A.2.1.3 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.
Figure A.3 – General launch arrangement
A.2.1.4 Source wavelength
Measurements may can be made at one or more wavelengths. Alternatively, a spectral
response may can be required obtained over a range of wavelengths.
– 14 – IEC 60793-1-40:2019 RLV © IEC 2019
A.2.1.5 Optical detection assembly
Means shall be provided to couple all power emitted from the specimen to the active region of
the detector. For example, an optical lens system, a butt spliced to a fibre pigtail, or a
coupling directly 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
might include a photovoltaic mode photodiode amplified by a current input amplifier, with
synchronous detection by a lock-in amplifier.
A.2.1.6 Signal processing
It is customary to modulate the light source in order to improve the signal/noise ratio 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 been fully characterized with a response
function.
A.2.1.7 Cladding mode stripper
Use suitable techniques to remove optical power propagating in the cladding where this would
significantly influence the received signal.
A.2.2 Launch apparatus for all single-mode fibres
A.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.
A.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.
A.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.
A.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. For bending loss insensitive single-mode fibres,
multiple loops with smaller radius or longer cut-back specimen length can be applied. Care
should be taken that the radius is not too small as to induce wavelength-dependent
oscillations. Increase of the cut-back specimen length should be accounted for in the
attenuation computation.
A.2.2.5 Cladding mode stripper
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.
A.2.3 Launch apparatus for A1 graded-index multimode fibres
A.2.3.1 General
The launching conditions are of paramount importance in meeting the objectives stated in
Clause 1. Launching conditions are established to avoid launching power into higher-order,
transient modes. By not launching power into these transient modes of the test fibre,
attenuations which add in an approximately linear fashion will be measured. Because these
power distributions are essentially unaltered by the fibre, they are called "steady-state
distributions".
There are two commonly used techniques to produce steady-state launch conditions for
attenuation measurements: mode filters and a geometrical optics launch. Proper care in the
use of each technique gives comparable results.
Care should be taken that mode distribution is related with specimen length. For short A1
multimode fibre cables (less than 1 km), the mode distribution may not reach a steady state.
This will induce an increase in attenuation values towards shorter fibre lengths, where the
magnitude of the length dependence depends on fibre type, launch condition, etc. In these
cases, attenuation values should be obtained from cables long enough to reach a
steady-state condition, or they can be taken from the original longer donor cable. As guidance
for sufficient cable lengths, see examples of cable test results on A1 multimode fibres in
Annex E.
See Figure A.13 for a generic example of the launching arrangement using a mode filter.
Examples of each mode filter appear below.
A.2.3.2 Examples of mode filters
A.2.3.2.1 Dummy-fibre mode filter
Select a fibre of a similar type to that of the test fibre. The fibre should be long enough
(typically equal to or greater than 1 km) so that the power distribution carried by the fibre,
when the launch source of A.2.1.2 is used, is a steady-state distribution.
A.2.3.2.2 Mandrel-wrapped mode filter
Another mode filter takes the form of a mandrel around which a few turns (typically three to
five turns) of the fibre under test are wound with low tension. Select the mandrel diameter to
ensure that the transient modes excited in the test fibre have been attenuated to steady-state.
Use a far-field measurement to compare the power distribution exiting a long length of test
fibre (greater than 1 km) that has been excited with a uniformly overfilling source, with the
power distribution exiting a short length of the fibre with the mandrel applied. Select the
mandrel diameter to produce a far-field distribution in the short length that approximates the
long length far-field power distribution.
The numerical aperture (as measured by IEC 60793-1-43) of the radiation pattern exiting the
short length shall be 94 % to 100 % of the numerical aperture of the long-length pattern.
The diameter of the mandrel may differ from fibre to fibre depending on fibre and coating type.
Common prescriptions consist of diameters in the range of 15 mm to 40 mm, with five turns of
fibre within a 20 mm length of the mandrel. While mandrels of different size and arrangement
can be selected, Table A.1 illustrates common mandrel sizes for fibres of different core
diameters.
– 16 – IEC 60793-1-40:2019 RLV © IEC 2019
Table A.1– Mandrel sizes Size examples
Core diameter Mandrel diameter
µm mm
50 25
62,5 20
100 25
A.2.3.3 Example of geometrical optics launch
A limited phase space (LPS) launch is defined as a geometrically produced launch that
uniformly fills 70 % of the test fibre's core diameter and 70 % of the test fibre's numerical
aperture. This is the maximum geometrically launched power distribution that does not launch
power into leaky, unbounded modes. For a 50/125 µm, 0,2 NA graded-index multimode fibre,
the LPS launch condition consists of a uniform 35 µm spot and 0,14 NA.
An example of the optics necessary to produce the LPS launch is given in Figure A.4. It is
important to ensure that the axis of the launch beam is coincident with the axis of the fibre so
that the spot and incident cone of light are centred on the core of the fibre. Also, set up the
optical system at the wavelengths of operation to ensure proper measurement. While
mandrels of different size and arrangement can be selected, common mandrel sizes for fibres
of different core diameters, are shown in Table A.1.
Figure A.4 – Limited phase space launch optics
A.2.3.4 Mode scrambler
An essentially uniform power distribution is launched prior to the mode filter. For a source
such as an LED or laser, which does not do so form a uniform power distribution, use a mode
scrambler. The mode scrambler shall comprise a suitable fibre arrangement (for example, a
step-graded-step index profile sequence).
A "mode scrambler" is a device which is positioned between the light source and test fibre to
control launching conditions. A particular mode scrambler design is not specified. It should be
emphasized that the performance of these scramblers depends upon the launch optics and
fibre sizes (core and NA) used in the actual construction.
EXAMPLE The two designs given in Figure A.5 are for illustration purposes only.
a)
b)
Figure A.5 – Two examples of optical fibre scramblers
A.2.4 Launch apparatus for A2 to A4 step-index multimode fibres
Some examples of generic launching arrangements for short-distance fibres are described in
Figures A.6, A.7 and A.8.
The reproducibility of the attenuation measurements of step-index multimode 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 capable of
providing for spot sizes and launch NAs as given in Table A.2.
Table A.2 – Launch conditions for A2 to A4 fibres
Fibre category
a
Attribute A2.2 fibre A3 fibre A4 fibre
Glass core/glass cladding Glass core/plastic cladding Plastic core/plastic cladding
Spot size = fibre core size = fibre core size = fibre core size with full
mode launch (or use mode
scrambler with equilibrium
mode launch)
b c
Numerical aperture = fibre max. NA = fibre max. NA = fibre max. NA, with full
c
(NA) mode launch
a
Category A2.1 fibre requires further study.
b
This launch condition can be produced by overfilling a mode filter made from 2 m of fibre identical to the
fibre under test, with appropriate cladding mode stripping and using the output from this mode filter to launch
into the fibre under test.
c
This launch condition can be produced in the same manner as described in Footnote b. However, some
types of A3 and A4 fibre will not require cladding mode stripping for the mode filter.
Figure A.6 – Lens system
– 18 – IEC 60793-1-40:2019 RLV © IEC 2019
Figure A.7 – Launch fibre
Figure A.8 – Mode scrambler (for A.4 fibre)
A.2.5 Calibration requirements
A.2.5.1 General calibration requirements
Calibrate the optical source's centroidal wavelength to within ±10 nm.
A.2.5.2 Requirements for A4 fibres
For A4 fibres it is common to perform attenuation measurements at specific wavelengths
using an LED as optical source. Owing to characteristic strong sharp variations in attenuation
over the wavelength spectrum of some polymeric materials, additional optical characterization
measurements should be performed in order to take into account effects that could affect the
measurement when calibrating wide-spectrum sources used for attenuation measurement,
especially when the centroidal wavelength is significantly far from the intended wavelength
measurement. A full characterization will ensure repeatability of the measurements and avoid
the negative influence of the following effects:
– Distortion on the attenuation measurement
An optical source with wide spectrum, for example, an LED, will cause measurement
errors on the measurements, since parts of the optical spectrum lie in low-loss
wavelengths and other parts lie in higher-loss wavelengths. This is illustrated in Figure A.9
with the Gaussian line "b" showing the spectral response for an LED source used to
measure A4 fibres and with the expected spectral attenuation indicated by the line "a". To
take proper consideration of the potentially high attenuation variations, the source shall be
calibrated both in its centroidal wavelength and spectral width and it should be checked
that these two characteristics match the expected wavelength attenuation of the fibre
under test.
– Spectral filter effect
Light with a wide spectrum undergoes relatively little attenuation at some wavelengths
while other spectral parts suffer higher losses when propagating through A4a fibres. With
longer measured fibre lengths, the detected LED spectral maximum shifts towards the
fibre attenuation-minimum wavelength. This can be seen in Figure A.9, where the original
spectral source is illustrated with the line "b" (characterised through a 0 m fibre length)
and the same spectra detected after passing different lengths of an A4 fibre. As the
measurement-fibre length increases, a shift on the maximum of the detected Gaussian
signal occurs towards the wavelength of minimum attenuation of the fibre (lines "c" to "f" in
Figure A.9).
Figure A.9 – A wide-spectrum source (li
...
IEC 60793-1-40 ®
Edition 2.0 2019-03
INTERNATIONAL
STANDARD
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Optical fibres –
Part 1-40: Attenuation measurement methods
Fibres optiques –
Partie 1-40: Méthodes de mesurage de l'affaiblissement
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IEC 60793-1-40 ®
Edition 2.0 2019-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical fibres –
Part 1-40: Attenuation measurement methods
Fibres optiques –
Partie 1-40: Méthodes de mesurage de l'affaiblissement
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.10 ISBN 978-2-8322-6593-2
– 2 – IEC 60793-1-40:2019 © IEC 2019
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Calibration requirements . 9
5 Reference test method . 9
6 Apparatus . 9
7 Sampling and specimens . 9
7.1 Specimen length . 9
7.2 Specimen end face . 9
8 Procedure . 9
9 Calculations . 9
9.1 Methods A and B . 9
9.2 Method C . 9
9.3 Method D . 9
10 Results . 9
10.1 Information available with each measurement . 9
10.2 Information available upon request . 10
10.3 Method-specific additional information . 10
11 Specification information . 10
Annex A (normative) Requirements specific to method A – Cut-back . 11
A.1 General . 11
A.2 Apparatus . 11
A.2.1 General apparatus for all fibres. 11
A.2.2 Launch apparatus for all single-mode fibres . 13
A.2.3 Launch apparatus for A1 multimode fibres . 14
A.2.4 Launch apparatus for A2 to A4 multimode fibres . 16
A.2.5 Calibration requirements . 17
A.3 Procedure . 18
A.4 Calculations . 18
Annex B (normative) Requirements specific to method B – Insertion loss . 19
B.1 General . 19
B.2 Apparatus . 19
B.2.1 General set-ups . 19
B.2.2 Apparatus common to method A (cut-back). 19
B.2.3 Additional apparatus specific to method B (insertion-loss) . 19
B.2.4 Calibration requirements . 19
B.3 Procedure . 19
B.4 Calculations . 20
Annex C (normative) Requirements specific to method C – Backscattering . 21
C.1 General . 21
C.2 Apparatus . 21
C.2.1 General . 21
C.2.2 Optical transmitter . 22
C.2.3 Launch conditions . 22
C.2.4 Optical splitter . 22
C.2.5 Optical receiver . 22
C.2.6 Pulse duration and repetition rate . 22
C.2.7 Signal processor . 22
C.2.8 Display . 23
C.2.9 Data interface (optional) . 23
C.2.10 Reflection controller (optional) . 23
C.2.11 Splices and connectors . 23
C.3 Sampling and specimens . 23
C.4 Procedure . 23
C.4.1 General . 23
C.4.2 Further steps for measuring attenuation. 25
C.4.3 Further steps for measuring point discontinuities . 25
C.4.4 Calibration . 27
C.5 Calculations . 27
C.6 Results . 27
Annex D (normative) Requirements specific to method D – Spectral attenuation
modelling . 28
D.1 General . 28
D.2 Apparatus . 28
D.3 Sampling and specimens . 28
D.4 Procedure . 28
D.5 Calculations . 29
D.6 Results . 29
Annex E (informative) Examples of short cable test results on A1 multimode fibres . 31
Bibliography . 33
Figure A.1 – Arrangement of equipment for loss measurement at a specified
wavelength . 11
Figure A.2 – Arrangement of equipment used to obtain loss spectrum . 12
Figure A.3 – General launch arrangement . 12
Figure A.4 – Limited phase space launch optics . 15
Figure A.5 – Two examples of optical fibre scramblers . 16
Figure A.6 – Lens system . 16
Figure A.7 – Launch fibre . 17
Figure A.8 – Mode scrambler (for A.4 fibre) . 17
Figure A.9 – A wide-spectrum source (line "b") could lead to attenuation measurement
errors due to sharp variations on spectral attenuation of polymer-core fibres (line "a") . 18
Figure B.1 – Calibration of insertion loss measurement set . 20
Figure B.2 – Measurement of insertion loss . 20
Figure C.1 – Block diagram of an OTDR . 21
Figure C.2 – Schematic OTDR trace for a "uniform" specimen preceded by a dead-
zone fibre . 24
Figure C.3 – Schematic OTDR trace for a "uniform" specimen not preceded by a dead-
zone fibre . 24
Figure C.4 – Schematic OTDR trace showing apparent loss due to point discontinuities,
one reflective and one non-reflective . 26
– 4 – IEC 60793-1-40:2019 © IEC 2019
Figure C.5 – Schematic of an expanded OTDR trace showing two point discontinuities,
one with apparent gain, and another with no apparent loss or gain . 26
Figure E.1 – Example of attenuation coefficient tests on A1a.1 fibre . 31
Figure E.2 – Example of attenuation coefficient tests on A1a.3 fibre . 31
Figure E.3 – Example of attenuation coefficient tests on A1b fibre . 32
Table A.1 – Size examples . 15
Table A.2 – Launch conditions for A2 to A4 fibres . 16
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-40: Attenuation measurement methods
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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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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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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Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60793-1-40 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Improvement of the description of measurement details for B6 fibre;
b) Improvement of the calibration requirements for A4 fibre;
c) Introduction of Annex E describing examples of short cable test results on A1 multimode
fibres.
– 6 – IEC 60793-1-40:2019 © IEC 2019
The text of this International Standard is based on the following documents:
FDIS Report on voting
86A/1909/FDIS 86A/1927/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.
A list of all parts in the 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.
OPTICAL FIBRES –
Part 1-40: Attenuation measurement methods
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the attenuation of
optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes.
Four methods are described for measuring attenuation, one being that for modelling spectral
attenuation:
– method A: cut-back;
– method B: insertion loss;
– method C: backscattering;
– method D: modelling spectral attenuation.
Methods A to C apply to the measurement of attenuation for all categories of the following
fibres:
– class A multimode fibres;
– class B single-mode fibres.
Method C, backscattering, also covers the location, losses and characterization of point
discontinuities.
Method D is applicable only to class B fibres.
Information common to all four methods appears in Clauses 1 to 11, and information
pertaining to each individual method appears in Annexes A, B, C, and D, respectively.
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 60793-1-1, Optical fibres – Part 1-1: Measurement methods and test procedures –
General and guidance
IEC 60793-1-22, Optical fibres – Part 1-22: Measurement methods and test procedures –
Length measurement
IEC 60793-1-43, Optical fibres – Part 1-43: Measurement methods and test procedures –
Numerical aperture measurement
IEC 61746-1, Calibration of optical time-domain reflectometers (OTDR) – Part 1: OTDR for
single mode fibres
IEC 61746-2, Calibration of optical time-domain reflectometers (OTDR) – Part 2: OTDR for
multimode fibres
– 8 – IEC 60793-1-40:2019 © IEC 2019
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60793-1-1 and the
following 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
3.1
attenuation
attenuation of a fibre at wavelength λ between two cross-sections, 1 and 2, separated by a
distance and defined as
P ()λ
A()λ = 10log
(1)
P ()λ
where
A(λ) is the attenuation, in dB, at wavelength λ;
P (λ) is the optical power traversing cross-section 1;
P (λ) is the optical power traversing cross-section 2.
Note 1 to entry: Attenuation is a measure of the decreasing optical power in a fibre at a given wavelength. It
depends on the nature and length of the fibre and is also affected by measurement conditions.
3.2
attenuation coefficient
attenuation per unit length for a uniform fibre under steady-state conditions
Note 1 to entry: It is possible to define the attenuation per unit length or the attenuation coefficient as follows:
A()λ
αλ()= (2)
L
which is independent of the chosen length of the fibre,
where
α(λ) is the attenuation coefficient;
A(λ) is the attenuation at wavelength λ;
L is the length, in kilometres.
Note 2 to entry: Uncontrolled launching conditions normally excite higher order lossy modes that produce
transient losses and result in attenuation that is not proportional to the length of the fibre. A controlled, steady-
state launching condition yields attenuation that is proportional to the fibre's length. Under steady-state conditions,
an attenuation coefficient of a fibre can be determined and the attenuation of concatenated fibres added linearly.
3.3
spectral attenuation modelling
technique that predicts the attenuation coefficients across a spectrum of wavelengths from a
small number (three to five) of discrete values measured directly at different wavelengths
3.4
point discontinuity
temporary or permanent local deviation of the continuous optical time-domain reflectometer
(OTDR) signal in the upward or downward direction
Note 1 to entry: The nature of the deviation can vary with test conditions (e.g. pulse duration, wavelength, and
direction of the OTDR signal). Although a point discontinuity can have a length greater than the corresponding
displayed pulse duration (including transmitter and receiver effects), the length is usually about equal to the pulse
duration. For a correct interpretation, the guidelines in IEC 60793-1-22 should be followed for measuring length.
4 Calibration requirements
See Annexes A, B, and C for methods A, B, and C, respectively.
5 Reference test method
Method A, cut-back, is the reference test method (RTM), which shall be the one used to settle
disputes.
6 Apparatus
Annexes A, B, C, and D include layout drawings and other equipment requirements for each
of the methods, respectively.
7 Sampling and specimens
7.1 Specimen length
The specimen shall be a known length of fibre on a reel, or within a cable, as specified in the
detail specification.
7.2 Specimen end face
Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each
specimen.
8 Procedure
See Annexes A, B, C and D for methods A, B, C and D, respectively.
9 Calculations
9.1 Methods A and B
Methods A and B, cut-back and insertion loss use Equations (1) and (2) respectively, which
appear in 3.1 and 3.2.
9.2 Method C
See Annex C.
9.3 Method D
See Annex D.
10 Results
10.1 Information available with each measurement
Report the following information with each measurement:
– 10 – IEC 60793-1-40:2019 © IEC 2019
– date and title of measurement;
– identification of specimen;
– optical source wavelength;
– specimen length;
– spectral attenuation, in dB, or attenuation coefficient, in dB/km, versus wavelength or at
specific wavelength(s), as required by the detail specification.
10.2 Information available upon request
The following information shall be available upon request:
– measurement method used: A, B, C, or D;
– type of optical source used: centroidal wavelength(s) and spectral width(s);
– launching technique and conditions used;
– indication if a dead-zone fibre was used (for method C only);
– description of all key equipment;
– for type B fibres – dimensions and number of turns of the mode filter or mode scrambler;
– pulse duration(s), scale range(s), and signal-averaging details;
– details of computation technique (calculation method);
– any deviations to the procedure that were made;
– date of latest calibration of measurement equipment.
10.3 Method-specific additional information
For methods C and D, see the additional requirements in Clauses C.6 and D.6, respectively.
This particularly applies when using method C for measuring point discontinuities.
11 Specification information
The detail specification shall specify the following information:
– type of fibre (or cable) to be measured;
– failure or acceptance criteria at the wavelength or wavelength range;
– any deviations to the procedure that apply;
– information to be reported.
Annex A
(normative)
Requirements specific to method A – Cut-back
A.1 General
The cut-back technique is the only method directly derived from the definition of fibre
attenuation, in which the power levels, P (λ) and P (λ), are measured at two points of the
1 2
fibre without change of input conditions. P (λ) is the power emerging from the end of the fibre,
and P (λ) is the power emerging from a point near the input after cutting the fibre. This
explains its wide acceptance as the reference test method for attenuation.
This measurement principle does not permit information to be obtained on the attenuation
behaviour over the length of the fibre, nor is it easy to measure the change of attenuation
under changing conditions. In some situations, its destructive nature is a disadvantage.
A.2 Apparatus
A.2.1 General apparatus for all fibres
A.2.1.1 General
See Figures A.1 and A.2 for diagrams of suitable test set-ups.
Figure A.1 – Arrangement of equipment for loss measurement at
a specified wavelength
– 12 – IEC 60793-1-40:2019 © IEC 2019
Figure A.2 – Arrangement of equipment used to obtain loss spectrum
A.2.1.2 General launch arrangement
Figure A.3 shows the general launch arrangement used for all fibres. See A.2.2 to A.2.4 for
further details as they apply to specific categories of single-mode and multimode fibres.
A.2.1.3 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 to a launch fibre.
Figure A.3 – General launch arrangement
A.2.1.4 Source wavelength
Measurements can be made at one or more wavelengths. Alternatively, a spectral response
can be obtained over a range of wavelengths.
A.2.1.5 Optical detection assembly
Means shall be provided to couple all power emitted from the specimen to the active region of
the detector. For example, an optical lens system, a butt spliced to a fibre pigtail, or a
coupling directly 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
might include a photovoltaic mode photodiode amplified by a current input amplifier, with
synchronous detection by a lock-in amplifier.
A.2.1.6 Signal processing
It is customary to modulate the light source in order to improve the signal/noise ratio 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 been fully characterized with a response function.
A.2.1.7 Cladding mode stripper
Use suitable techniques to remove optical power propagating in the cladding where this would
significantly influence the received signal.
A.2.2 Launch apparatus for all single-mode fibres
A.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.
A.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.
A.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.
A.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. For bending loss insensitive
single-mode fibres, multiple loops with smaller radius or longer cut-back specimen length can
be applied. Care should be taken that the radius is not too small as to induce
wavelength-dependent oscillations. Increase of the cut-back specimen length should be
accounted for in the attenuation computation.
A.2.2.5 Cladding mode stripper
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
– 14 – IEC 60793-1-40:2019 © IEC 2019
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.
A.2.3 Launch apparatus for A1 multimode fibres
A.2.3.1 General
The launching conditions are of paramount importance in meeting the objectives stated in
Clause 1. Launching conditions are established to avoid launching power into higher-order,
transient modes. By not launching power into these transient modes of the test fibre,
attenuations which add in an approximately linear fashion will be measured. Because these
power distributions are essentially unaltered by the fibre, they are called "steady-state
distributions".
There are two commonly used techniques to produce steady-state launch conditions for
attenuation measurements: mode filters and a geometrical optics launch. Proper care in the
use of each technique gives comparable results.
Care should be taken that mode distribution is related with specimen length. For short A1
multimode fibre cables (less than 1 km), the mode distribution may not reach a steady state.
This will induce an increase in attenuation values towards shorter fibre lengths, where the
magnitude of the length dependence depends on fibre type, launch condition, etc. In these
cases, attenuation values should be obtained from cables long enough to reach a
steady-state condition, or they can be taken from the original longer donor cable. As guidance
for sufficient cable lengths, see examples of cable test results on A1 multimode fibres in
Annex E.
See Figure A.3 for a generic example of the launching arrangement using a mode filter.
Examples of each mode filter appear below.
A.2.3.2 Examples of mode filters
A.2.3.2.1 Dummy-fibre mode filter
Select a fibre of a similar type to that of the test fibre. The fibre should be long enough
(typically equal to or greater than 1 km) so that the power distribution carried by the fibre,
when the launch source of A.2.1.2 is used, is a steady-state distribution.
A.2.3.2.2 Mandrel-wrapped mode filter
Another mode filter takes the form of a mandrel around which a few turns (typically three to
five turns) of the fibre under test are wound with low tension. Select the mandrel diameter to
ensure that the transient modes excited in the test fibre have been attenuated to steady-state.
Use a far-field measurement to compare the power distribution exiting a long length of test
fibre (greater than 1 km) that has been excited with a uniformly overfilling source, with the
power distribution exiting a short length of the fibre with the mandrel applied. Select the
mandrel diameter to produce a far-field distribution in the short length that approximates the
long length far-field power distribution.
The numerical aperture (as measured by IEC 60793-1-43) of the radiation pattern exiting the
short length shall be 94 % to 100 % of the numerical aperture of the long-length pattern.
The diameter of the mandrel may differ from fibre to fibre depending on fibre and coating type.
Common prescriptions consist of diameters in the range of 15 mm to 40 mm, with five turns of
fibre within a 20 mm length of the mandrel. While mandrels of different size and arrangement
can be selected, Table A.1 illustrates common mandrel sizes for fibres of different core
diameters.
Table A.1 – Size examples
Core diameter Mandrel diameter
µm mm
50 25
62,5 20
100 25
A.2.3.3 Example of geometrical optics launch
A limited phase space (LPS) launch is defined as a geometrically produced launch that
uniformly fills 70 % of the test fibre's core diameter and 70 % of the test fibre's numerical
aperture. This is the maximum geometrically launched power distribution that does not launch
power into leaky, unbounded modes. For a 50/125 µm, 0,2 NA graded-index multimode fibre,
the LPS launch condition consists of a uniform 35 µm spot and 0,14 NA.
An example of the optics necessary to produce the LPS launch is given in Figure A.4. It is
important to ensure that the axis of the launch beam is coincident with the axis of the fibre so
that the spot and incident cone of light are centred on the core of the fibre. Also, set up the
optical system at the wavelengths of operation to ensure proper measurement. While
mandrels of different size and arrangement can be selected, common mandrel sizes for fibres
of different core diameters, are shown in Table A.1.
Figure A.4 – Limited phase space launch optics
A.2.3.4 Mode scrambler
An essentially uniform power distribution is launched prior to the mode filter. For a source
such as an LED or laser, which does not form a uniform power distribution, use a mode
scrambler. The mode scrambler shall comprise a suitable fibre arrangement (for example, a
step-graded-step index profile sequence).
A "mode scrambler" is a device which is positioned between the light source and test fibre to
control launching conditions. A particular mode scrambler design is not specified. It should be
emphasized that the performance of these scramblers depends upon the launch optics and
fibre sizes (core and NA) used in the actual construction.
EXAMPLE The two designs given in Figure A.5 are for illustration purposes only.
– 16 – IEC 60793-1-40:2019 © IEC 2019
a)
b)
Figure A.5 – Two examples of optical fibre scramblers
A.2.4 Launch apparatus for A2 to A4 multimode fibres
Some examples of generic launching arrangements for short-distance fibres are described in
Figures A.6, A.7 and A.8.
The reproducibility of the attenuation measurements of multimode 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 capable of providing for spot
sizes and launch NAs as given in Table A.2.
Table A.2 – Launch conditions for A2 to A4 fibres
Fibre category
a
Attribute A2.2 fibre A3 fibre A4 fibre
Glass core/glass cladding Glass core/plastic cladding Plastic core/plastic cladding
Spot size = fibre core size = fibre core size = fibre core size with full
mode launch (or use mode
scrambler with equilibrium
mode launch)
b c
Numerical aperture = fibre max. NA = fibre max. NA = fibre max. NA, with full
c
(NA) mode launch
a
Category A2.1 fibre requires further study.
b
This launch condition can be produced by overfilling a mode filter made from 2 m of fibre identical to the
fibre under test, with appropriate cladding mode stripping and using the output from this mode filter to launch
into the fibre under test.
c
This launch condition can be produced in the same manner as described in Footnote b. However, some
types of A3 and A4 fibre will not require cladding mode stripping for the mode filter.
Figure A.6 – Lens system
Figure A.7 – Launch fibre
Figure A.8 – Mode scrambler (for A.4 fibre)
A.2.5 Calibration requirements
A.2.5.1 General calibration requirements
Calibrate the optical source's centroidal wavelength to within ±10 nm.
A.2.5.2 Requirements for A4 fibres
For A4 fibres it is common to perform attenuation measurements at specific wavelengths
using an LED as optical source. Owing to characteristic strong sharp variations in attenuation
over the wavelength spectrum of some polymeric materials, additional optical characterization
measurements should be performed in order to take into account effects that could affect the
measurement when calibrating wide-spectrum sources used for attenuation measurement,
especially when the centroidal wavelength is significantly far from the intended wavelength
measurement. A full characterization will ensure repeatability of the measurements and avoid
the negative influence of the following effects:
– Distortion on the attenuation measurement
An optical source with wide spectrum, for example, an LED, will cause measurement
errors on the measurements, since parts of the optical spectrum lie in low-loss
wavelengths and other parts lie in higher-loss wavelengths. This is illustrated in Figure A.9
with the Gaussian line "b" showing the spectral response for an LED source used to
measure A4 fibres and with the expected spectral attenuation indicated by the line "a". To
take proper consideration of the potentially high attenuation variations, the source shall be
calibrated both in its centroidal wavelengt
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