IEC 60793-1-20:2014

IEC 60793-1-20 ®
Edition 2.0 2014-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
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Optical fibres –
Part 1-20: Measurement methods and test procedures – Fibre geometry

Fibres optiques –
Partie 1-20: Méthodes de mesure et procédures d'essai – Géométrie de la fibre
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IEC 60793-1-20 ®
Edition 2.0 2014-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical fibres –
Part 1-20: Measurement methods and test procedures – Fibre geometry

Fibres optiques –
Partie 1-20: Méthodes de mesure et procédures d'essai – Géométrie de la fibre

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 33.180.10 ISBN 978-2-8322-1884-6

– 2 – IEC 60793-1-20:2014 © IEC 2014
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and symbols. 8
4 Overview of method . 10
4.1 General . 10
4.2 Scanning methods . 10
4.2.1 General . 10
4.2.2 One-dimensional scan sources of error . 11
4.2.3 Multidimensional scanning . 12
4.3 Data reduction . 13
4.3.1 Simple combination of few-angle scan sets . 13
4.3.2 Ellipse fitting of several-angle or raster data sets . 13
5 Reference test method . 13
6 Apparatus . 13
7 Sampling and specimens . 13
7.1 Specimen length . 13
7.2 Specimen end face . 13
8 Procedure . 13
9 Calculations . 14
10 Results . 14
11 Specification information . 14
Annex A (normative) Requirements specific to Method A – Refracted near-field. 15
A.1 Introductory remarks . 15
A.2 Apparatus . 15
A.2.1 Typical arrangement . 15
A.2.2 Source . 15
A.2.3 Launch optics . 15
A.2.4 XYZ positioner (scanning stage) . 16
A.2.5 Blocking disc . 16
A.2.6 Collection optics and detector . 17
A.2.7 Computer system . 17
A.2.8 Immersion cell . 17
A.3 Sampling and specimens . 17
A.4 Procedure . 17
A.4.1 Load and centre the fibre . 17
A.4.2 Line scan . 18
A.4.3 Raster scan . 18
A.4.4 Calibration . 18
A.5 Index of refraction calculation . 18
A.6 Calculations . 20
A.7 Results . 20
Annex B (normative) Requirements specific to Method B – Transmitted near-field . 21
B.1 Introductory remarks . 21

B.2 Apparatus . 21
B.2.1 Typical arrangement . 21
B.2.2 Light sources . 22
B.2.3 Fibre support and positioning apparatus . 23
B.2.4 Cladding mode stripper . 23
B.2.5 Detection . 23
B.2.6 Magnifying optics . 24
B.2.7 Video image monitor (video grey-scale technique) . 25
B.2.8 Computer. 25
B.3 Sampling and specimens . 25
B.4 Procedure . 25
B.4.1 Equipment calibration . 25
B.4.2 Measurement . 25
B.5 Calculations . 27
B.6 Results . 27
Annex C (normative) Edge detection and edge table construction . 28
C.1 Introductory remarks . 28
C.2 Boundary detection by decision level . 28
C.2.1 General approach . 28
C.2.2 Class A multimode fibre core reference level and k factor . 29
C.2.3 Class B and C single-mode fibres . 30
C.2.4 Direct geometry computation of one-dimensional data . 30
C.3 Assembling edge tables from raw data . 31
C.3.1 General . 31
C.3.2 Edge tables from raster data . 31
C.3.3 Edge tables from multi-angular one-dimensional scans . 32
Annex D (normative) Edge table ellipse fitting and filtering. 33
D.1 Introductory remarks . 33
D.2 General mathematical expressions for ellipse fitting . 33
D.3 Edge table filtering . 34
D.4 Geometric parameter extraction . 35
Annex E (informative) Fitting category A1 core near-field data to a power law model . 36
E.1 Introductory remarks . 36
E.2 Preconditioning data for fitting . 36
E.2.1 Motivation . 36
E.2.2 Transformation of a two-dimensional image to one-dimensional radial
near-field . 36
E.2.3 Pre-processing of one-dimensional near-field data . 39
E.2.4 Baseline subtraction . 41
E.3 Fitting a power-law function to an category A1 fibre near-field profile . 41
Annex F (informative) Mapping class A core diameter measurements . 43
F.1 Introductory remarks . 43
F.2 Mapping function . 43
Bibliography . 44

Figure 1 – Sampling on a chord . 11
Figure 2 – Scan of a non-circular body . 12
Figure A.1 – Refracted near-field method – Cell . 16

– 4 – IEC 60793-1-20:2014 © IEC 2014
Figure A.2 – Typical instrument arrangement . 16
Figure A.3– Typical index profile line scan of a category A1 fibre . 19
Figure A.4 – Typical raster index profile on a category A1 fibre . 19
Figure B.1 – Typical arrangement, grey scale technique . 21
Figure B.2 – Typical arrangement, mechanical scanning technique . 22
Figure B.3 – Typical 1-D near-field scan, category A1 core . 26
Figure B.4 − Typical raster near-field data, category A1 fibre . 27
Figure C.1 – Typical one-dimensional data set, cladding only . 29
Figure C.2 – Typical graded index core profile . 30
Figure C.3 – Raster data, cladding only . 31
Figure E.1 – Filtering concept . 38
Figure E.2 – Illustration of 1-D near-field preconditioning, typical video line . 40

INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
OPTICAL FIBRES –
Part 1-20: Measurement methods and test procedures –
Fibre geometry
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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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 60793-1-20 has been prepared by subcommittee SC86A: Fibre
and cables, of IEC technical committee TC86: Fibre optics.
This second edition cancels and replaces the first edition, published in 2001, and constitutes
a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• the reference test method for all fibre types is changed to the video grey scale transmitted
near field method from the refracted near field method;
• the test lengths for all fibre types are now to be specified in the fibre’s detail specification;
• the core illumination wavelength for all multimode fibre types may now to be specified in
the fibre’s detail specification although defaults are given;

– 6 – IEC 60793-1-20:2014 © IEC 2014
• the core k-factor (decision level) is now to be specified in the detail specification for all
multimode fibre types;
• this edition is substantially more specific in describing the measurement; data reduction
and transformation is fully described;
• the data reduction methodology for both refracted near-field and transmitted near-field
methods are now unified and consistent.
The text of this standard is based on the following documents:
CDV Report on voting
86A/1562/CDV 86A/1623/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts 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 publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of March 2016 have been included in this copy.

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
This standard gives two methods for measuring fibre geometry characteristics:
– Method A: Refracted near-field, described in Annex A;
– Method B: Transmitted near-field, described in Annex B.
Methods A and B apply to the geometry measurement of all class A multimode fibres, class B
single-mode fibres and class C single-mode interconnection fibres. The fibre’s applicable
product specifications, IEC 60793-2-10, IEC 60793-2-20, IEC 60793-2-30, IEC 60793-2-40,
IEC 60793-2-50 and IEC 60793-2-60, provide relevant measurement details, including sample
lengths and k factors.
The geometric parameters measurable by the methods described in this standard are as
follows:
– cladding diameter;
– cladding non-circularity;
– core diameter (class A fibre only);
– core non-circularity (class A fibre only);
– core-cladding concentricity error.
NOTE 1 The core diameter of class B and class C fibres is not specified. The equivalent parameter is mode field
diameter, determined by IEC 60793-1-45.
NOTE 2 These methods specify both one-dimensional (1-D) and two-dimensional (2-D) data collection
techniques and data analyses. The 1-D methods by themselves cannot detemine non-circularity nor concentricity
error. When non-circular bodies are measured with 1-D methods, body diameters suffer additional uncertainties.
These limitations may be overcome by scanning and analysing multiple 1-D data sets. Clause 5 provides further
information.
Information common to both methods appears in Clauses 2 through 10, and information
pertaining to each individual method appears in Annexes A and B, respectively. Annex C
describes normative methods used to find the optical boundaries of the core and the cladding,
Annex D describes normative procedures to fit ellipses to sets of detected boundaries. Annex
E provides an informative fitting procedure of power-law models to graded-index core profiles.
Annex F describes an informative methodology relating to the transformation of core diameter
measurements determined with methods other than the reference method to approximate
reference method values.
– 8 – IEC 60793-1-20:2014 © IEC 2014
OPTICAL FIBRES –
Part 1–20: Measurement methods and test procedures –
Fibre geometry
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the geometrical
characteristics of uncoated optical fibres.
The geometry of uncoated optical fibres directly affect splicing, connectorization and cabling
and so are fundamental parameters requiring careful specification, quality control, and thus
measurement.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
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 – Specification for category
A4 multimode fibres
IEC 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for
class B single-mode fibres
IEC 60793-2-60, Optical fibres – Part 2-60: Product specifications – Sectional specification for
category C single-mode intraconnection fibres
IEC 61745, End-face image analysis procedure for the calibration of optical fibre geometry
test sets
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms, definitions and symbols apply:
3.1.1
body
general term describing an entity whose geometry is measured (i.e. cladding or core)

3.1.2
reference point
fixed coordinate in the scan’s plane
Note 1 to entry: This point is arbitrary (say the lower left corner of a video image, or the rough centre of the fibre
after the fibre is located in a scanning apparatus).
3.1.3
centre
centre of a body in the measurement plane with respect to the reference point, expressed in
micrometres
3.1.4
diameter
average diameter, in micrometres, of a nearly circular body
3.1.5
non-circularity
difference between the maximum and minimum radial deviation from the body’s centre,
normalized to the body’s diameter, expressed as a per cent
3.1.6
concentricity error
scalar distance, in micrometres between two body centres
3.1.7
scan
term used to define the collection of data along one axis of the Cartesian coordinate plane, at
a fixed angular orientation and a fixed offset from the reference point
3.1.8
scan set or set
one or more scans used together to determine the fibre’s geometry
Note 1 to entry: The set can be one scan (see limitations below), a set of scans at different angular orientations
with respect to the fibre, or a raster scan (like a video image).
3.1.9
edge table
set of number pairs representing a set of points in the scanning plane which define a closed
curve line of delineation between the cladding and the surrounding media (the cladding edge
table) or the core and the cladding (the core edge table)
3.1.10
elliptical model
ellipse fit
best fit ellipse to an edge table
3.2 Symbols
The symbols defined below are used to indicate various aspects of a scanned data set. Scans
can be one-dimensional, or two-dimensional raster scans (where the scan axes are
orthogonal on a Cartesian plane), or a set of one-dimensional scans at a set of angles.
i The index used for the scanning axis or the ‘fast’ axis in the case of a raster scan.
j The index used for the ‘slow’ axis in a raster scan.
k The index used for the angle in a multi-angular scan set.
I The set of data from one-dimensional or two-dimensional scanning. The data can be
near-field intensity data (from Method B) or index of refraction (Method A); in this

– 10 – IEC 60793-1-20:2014 © IEC 2014
standard, no delineation is made as either type of data is intermediate and is further
analysed to extract the fibre’s geometry. A single datum from a set is indicated by
subscript in a manner consistent with the nature of the data set: I for the ith point of
i
the scan in a single scan set; I for a raster data point at the jth location on the slow
j,i
th th
axis and the ith position on the fast axis; I for the i point at the k angle.
k,I
x The positional data, in micrometres, of the set. For a single scan set, the meaning of x
is clear. For a raster scan set or a multi-angle set, x refers to the positional data of the
‘fast’ axis (raster) or scan positions (for each angle). (Raster sets whose individual
lines have different fast-axis positions or multi-angle sets where each angle uses a
different set of positions are allowed by this standard, but this complication is ignored
in the forthcoming analytical development).
y The positional data, in micrometres, of the raster lines (the slow-axis locations) in a
raster scan set.
th
φ The angles in a multi-angle set. The k angle in the set is indicated by subscript: φ .
k
nS The number of points in a single scan. In the case of raster scan sets n is the number
S
of points of the fast axis. In multi-angular scan sets, nS is the number of points in any
scan. (This standard’s nomenclature ignores cases where the number of points varies
between raster lines or angles, although such data sets are allowed.)
nR The number of raster rows (slow axis scans) in a raster set.
nφ The number of angles in a multi-angle set.
NOTE The following symbols are used to describe an edge table.
X,Y A set of locations in the X-Y scan plane of the fibre which delineate a body from its
surroundings.
n The number of edge points in an edge table.
e
4 Overview of method
4.1 General
In essence, each method (A or B) defined herein describes a way of producing an image of
the fibre in a plane normal to its axis of propagation. This resultant image is then further
analysed (as described in Annexes C, D and E) to reduce the image to an expression of the
fibre’s geometry. Methods A and B can produce images which are one-dimensional (i.e. along
only one axis in the plane of the image), or two-dimensional. It is obvious that a two-
dimensional image is more information rich, and thus these images produce more complete
geometric information; the non-circularity of a body cannot be determined from a one-
dimensional scan, nor can concentricity errors be determined with any certainty.
The analysis of the image consists of two steps. The first step is to quantify where in the
image the body of interest is delineated (see Annex C). The second step reduces the
ensemble of these points of delineation to one or more geometric parameters: diameter, non-
circularity and centre (if both, the cladding and core are measured and their centres
determined then concentricity error may also be determined). Annex D describes methods
which can be used on both the cladding and core of all fibre types and Annex E describes a
method that may be used for the core body of class A fibres.
This standard addresses a range of needs, and as such, allows for a range of for data
collection and reduction. The specific limitations and uses of these approaches are discussed
below.
4.2 Scanning methods
4.2.1 General
As noted above, sampling a two-dimensional body in only one-dimension has limitations. Ideal
fibres are perfectly circular and the core and cladding are concentric; real fibres are

noncircular and have concentricity errors. Non-circularity and concentricity cannot be
measured by a one-dimensional scan and one-dimensional scanning may under- or over-
estimate the average diameter of a noncircular body. One-dimensional scanning may be
useful for fibres whose non-circularity and concentricity errors are known to be small and one-
dimensional scans are commonly used to determine the core diameter of class A fibres.
4.2.2 One-dimensional scan sources of error
4.2.2.1 Scanning a chord
Actual diameter
Measured diameter
IEC
Figure 1 – Sampling on a chord
Figure 1 illustrates the error that occurs when the sampling axis is not co-linear with the
centre of the body. When the sampling axis misses the body’s centre, the body’s diameter is
underestimated. This is a second order error.
4.2.2.2 Scanning non-circular bodies
If a body is non-circular, a one-dimensional scan will not fully describe the body’s shape.
Sampling a body in one dimension will generally under-estimate or over-estimate the average
diameter of the body. It may be assumed that this problem can be rectified by sampling the
body in two orthogonal axes (i.e. X and Y), but in general, this is not sufficient. Consider
Figure 2:
– 12 – IEC 60793-1-20:2014 © IEC 2014

IEC
IEC
Figre 2a – Major diameter Figure 2b – Average diameter
Figure 2 – Scan of a non-circular body
Figure 2 illustrates errors that occur when an elliptical body is sampled on one or two axes. In
the major diameter example (Figure 2a), the ellipse’s major diameter is aligned with the X
axis. In this case, sampling only in X will over-estimate the body’s average diameter; the fact
that the body is non-circular will be missed (likewise, sampling the body only in Y will
underestimate the body’s diameter). In this orientation, if the body is sampled on both axes
the body will be completely characterized: both its average diameter and non-circularity are
discovered. However, in the ‘average diameter’ case, sampling on either axes gives the same,
approximately correct diameter for both axes; if both axes are sampled it would appear that
the body is perfectly circular. Analysing ±45 ° scans will give the correct non-circularity and
diameter, but there is no way to know the proper angular scan angles beforehand. At
orientations other than –45 ° and +45 °, the body’s average diameter will be measured
correctly, but the body’s circularity will be underestimated.
4.2.2.3 Concentricity indeterminacy
If a single axis is scanned, the core’s centre relative to the cladding centre cannot be known.
Scanning two orthogonal axes can provide a reasonable estimate of the core’s centre. This
estimate will degrade if the core is scanned on a chord far from the core’s centre. If the core
is substantially smaller than the cladding and is significantly non-concentric, then one or more
scans may miss the core entirely.
4.2.3 Multidimensional scanning
4.2.3.1 Multi-angle scanning
As suggested in 5.2.2.2 and 5.2.2.3, the estimation of the geometry of the fibre can be
improved by scanning on two orthogonal axes. Combining scans over more than two angles
(for example at 0 °, 45 °, 90 ° and 135 °) will improve these estimates further. Acquiring data
at multiple angles can be accomplished by rotating the fibre in its holding chuck, or, if the
scanner is so designed, by the mechanics of the scanner itself. Note that all angular scans
shall share a single frame of reference (a common origin) or errors will be introduced.
4.2.3.2 Raster scanning
If the scanner is capable of motion on two orthogonal axes, then it is possible that a two-
dimensional image of the fibre may be constructed by performing a raster scan.
Measurement of the transmitted near-field using grey-scale video is inherently a raster scan.

4.3 Data reduction
4.3.1 Simple combination of few-angle scan sets
When reducing data sets where only a few angular orientations are measured, it is generally
sufficient to employ simple data reduction. For each body, the diameter can be determined by
averaging the diameters of each angular scan; the non-circularity by using the maximum and
minimum diameters from the set of angles. When both cladding and core are measured, the
concentricity error can be determined simply from the angle showing the worst-case
centration error. See Annex D for more information.
4.3.2 Ellipse fitting of several-angle or raster data sets
When many data points may be extracted from the scan set, as is the case when many angles
are scanned or when raster scanning is employed, the edge tables may be fit to elliptical
models. Annex E describes the methodology to fit a body’s edge table (determined as
described in Annex D).
For both the cladding and the core for all fibre categories, ellipse fitting is the reference
method.
5 Reference test method
The reference test method (RTM) is the video grey-scale transmitted near-field method
described in Annex B for all fibre categories. Data analysis shall employ boundary detection
as described in Annex C, and ellipse fitting to reduce the edge tables to geometry, as
described in Annex D. See Annexes A and B for a discussion of reference sample lengths for
all fibre classes, and refer to Annex C for a discussion of the decision threshold factor k for
class A fibres.
6 Apparatus
Annexes A and B include layout drawings and other equipment requirements for each of the
Methods A and B, respectively.
7 Sampling and specimens
7.1 Specimen length
Annexes A and B specify the required sample lengths for their respective methods.
7.2 Specimen end face
Prepare a clean, flat end face, perpendicular to the fibre axis, at the input and output ends of
each specimen. The accuracy of measurements is affected by a non-perpendicular end face.
End angles less than 1 ° are recommended.
See Clause B.2 for the tighter requirements on end faces when using Method B.
8 Procedure
Use the procedures given in IEC 61745 for calibration. Annexes A and B document the
procedures for Methods A and B, respectively.

– 14 – IEC 60793-1-20:2014 © IEC 2014
9 Calculations
Refer to Annexes C, D and E for details regarding the calculations.
10 Results
The following information shall be provided with each measurement:
– date and title of measurement;
– identification and description of specimen;
– measurement results for each parameter specified (see the applicable annex).
The following information shall be available upon request:
– measurement method used: Method A or B;
– specimen length;
– arrangement of measurement set-up;
– details of measurement apparatus (see applicable annex);
– relative humidity and ambient temperature at the time of the measurement;
– most recent calibration information.
11 Specification information
The detail specification shall specify the following information:
– type of fibre to be measured;
– failure or acceptance criteria;
– information to be reported;
– any deviations to the procedure that apply.

Annex A
(normative)
Requirements specific to Method A – Refracted near-field
A.1 Introductory remarks
The refracted near-field measurement directly measures the refractive index variation across
the fibre (core and cladding). The method can be calibrated to give absolute values of
refractive indices. It can be used to obtain profiles of both single-mode and multimode fibres.
A refracted near-field measurement determines the radial dependence of relative index
variations of a fibre by scanning a spot of light across its end-face. If a theoretical ray of light
could be generated, then changes in index could be detected by injecting the ray into the fibre
at an angle greater than the maximum numerical aperture of the fibre and measuring its exit
angle. Since an ideal ray cannot be generated and since the fibre’s physical dimensions are
of the order of 100 optical wavelengths, an integral approach using an angular bundle of rays
is taken. A small spot of light with a numerical aperture greater than the fibre’s is scanned
across the end-face of a fibre at a normal angle of incidence. The light cone which exits the
fibre is then sampled at a small range of high angles (i.e. greater than the numerical
aperture). The total power in this sampled region is then determined as a function of the radial
location of the launch spot. As the light traverses the local index differences in the fibre, it
refracts, changing its exit angle. Light that passes through the core and then the cladding will
exit the fibre at shallower angles than light that passes solely through the cladding. Since only
high angle light is sampled, the core region’s total detected power will be lower than the
cladding. The relative power at a given scan position is thus directly proportional to the fibre’s
index at that position.
A.2 Apparatus
A.2.1 Typical arrangement
See Figures A.1 and A.2 for schematic diagrams of the test apparatus.
A.2.2 Source
Provide a stable laser giving a few milliwatts of power in the TEM mode.
A HeNe laser, which has a wav
...