IEC 61755-6-2:2018

IEC 61755-6-2 ®
Edition 1.0 2018-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector
optical interfaces –
Part 6-2: Connection of 50 μm core diameter multimode physically contacting
fibres – Non-angled for reference connector application, at wavelength of
850 nm using selected A1a fibre only

Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces
optiques de connecteurs –
Partie 6-2: Connexion de fibres multimodales en contact physique d’un diamètre
de cœur de 50 μm – Connecteurs de référence sans angle, à une longueur
d’onde de 850 nm et en utilisant uniquement les fibres A1a choisies

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IEC 61755-6-2 ®
Edition 1.0 2018-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector

optical interfaces –
Part 6-2: Connection of 50 μm core diameter multimode physically contacting

fibres – Non-angled for reference connector application, at wavelength of

850 nm using selected A1a fibre only

Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces

optiques de connecteurs –
Partie 6-2: Connexion de fibres multimodales en contact physique d’un diamètre

de cœur de 50 μm – Connecteurs de référence sans angle, à une longueur

d’onde de 850 nm et en utilisant uniquement les fibres A1a choisies

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.20 ISBN 978-2-8322-5718-0

– 2 – IEC 61755-6-2:2018 © IEC 2018
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Performance grade . 6
5 Description . 6
6 Criteria for a fit within the performance grade . 7
7 Use of selected fibre in reference-grade connectors . 8
8 Calculated attenuation of random mated grade 1 reference connectors . 8
9 Reference adapter . 9
10 Attenuation measurement uncertainty contribution . 9
Annex A (informative) Multimode attenuation measurement uncertainty contribution . 10
A.1 General . 10
A.2 Sources of variability. 10
A.2.1 Measurement condition and setup . 10
A.2.2 Geometry mismatch . 10
A.3 Overall uncertainty . 11
Bibliography . 12

Figure 1 – Geometrical requirements for fibre core location after termination relative to
the ferrule axis and the connector plug key . 8
Figure 2 – Calculated attenuation of random mated grade 1 reference connectors . 9
Figure A.1 – Attenuation measurement uncertainty contribution for grade 1 reference
connectors resulting from lateral offset, NA and CD mismatch . 10

Table 1 – Multimode attenuation grade at 850 nm . 6
Table 2 – Optical interface parameter values for 1,25 mm and 2,5 mm diameter PC
ferrules for MM reference connectors . 8
Table A.1 – Evaluation of the uncertainty contribution due to measurement conditions . 11

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC INTERCONNECTING
DEVICES AND PASSIVE COMPONENTS –
CONNECTOR OPTICAL INTERFACES –

Part 6-2: Connection of 50 μm core
diameter multimode physically contacting fibres –
Non-angled for reference connector application,
at wavelength of 850 nm using selected A1a fibre only

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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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 61755-6-2 has been prepared by subcommittee 86B: Fibre optic
interconnecting devices and passive components, of IEC technical committee 86: Fibre optics.

– 4 – IEC 61755-6-2:2018 © IEC 2018
The text of this International Standard is based on the following documents:
FDIS Report on voting
86B/4124/FDIS 86B/4128/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 61755 series, published under the general title Fibre optic
interconnecting devices and passive components – Connector optical interfaces, 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.
FIBRE OPTIC INTERCONNECTING
DEVICES AND PASSIVE COMPONENTS –
CONNECTOR OPTICAL INTERFACES –

Part 6-2: Connection of 50 μm core
diameter multimode physically contacting fibres –
Non-angled for reference connector application,
at wavelength of 850 nm using selected A1a fibre only

1 Scope
This part of the IEC 61755 defines the dimensional limits of an optical interface for reference
connectors necessary to meet specific requirements for fibre-to-fibre interconnection of non-
angled polished multimode reference connectors with cylindrical ferrules intended to be used
for attenuation measurements in the field or factory.
One grade of reference connector is defined in this document. The reference connector is
terminated to selected IEC 60793-2-10:2015 A1a fibre. The geometrical dimensions and
tolerances of the specified reference connector have been developed primarily to limit the
variation in measured attenuation between multiple sets of two reference connectors, and
therefore to limit the variation in measured attenuation between randomly chosen reference
connectors when mated with connectors in the field or factory.
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 60793-2-10:2015, Optical fibres – Part 2-10: Product specifications – Sectional
specification for category A1 multimode fibre
IEC 61300-3-4, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-4: Examinations and measurements – Attenuation
3 Terms and definitions
No terms and definitions are listed in this document.
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

– 6 – IEC 61755-6-2:2018 © IEC 2018
4 Performance grade
This document currently only specifies one performance grade. However, the construction of
the document allows inclusion for other grades in the future, if necessary. The performance
grade for physical contact (PC) non-angled polished reference connectors detailed in this
document is listed in Table 1.
The specified attenuation for the grade is obtained when the reference plug is connected with
other reference plugs in a reference adapter, and the attenuation is measured in accordance
with IEC 61300-3-4 (insertion method B).
Table 1 – Multimode attenuation grade at 850 nm
a
Reference grade Attenuation Contribution to measurement uncertainty

dB dB
1 ≤ 0,1 ±0,071
a
As described in Annex A, related to the measurement of the attenuation between any connector according to
the IEC optical interface standards and a population of reference connectors.

5 Description
Optical reference connectors are connectors manufactured with restricted dimensional
tolerances on dimensions that contribute to lateral and angular offset of such optical
connections. These connectors are mainly used for attenuation measurement purposes and
shall be considered as part of the measurement setup. The goal is to strongly reduce the
measurement uncertainty. The attenuation uncertainties due to the reference connectors are
defined in this document, and are discussed in Annex A.
The performance of an optical interface is not only determined by the alignment accuracy of
the optical datum targets of two mating fibres, but also by any fibre parameter mismatches.
There are three conditions affecting the alignment of two optical datum targets: lateral offset,
angular offset and longitudinal offset.
Parameters influencing the lateral and angular offset of the optical fibre axes include the
following:
• ferrule outside diameter;
• fibre hole true position;
• fibre hole angle relative to ferrule axis;
• fibre cladding diameter to fibre hole inner diameter;
• alignment sleeve inside diameter;
• fibre core true position relative to the fibre cladding diameter.
Parameters influencing the longitudinal offset of the optical fibre axes include the following:
• end face spherical radius;
• end face spherical radius apex offset;
• fibre undercut relative to the spherical ferrule radius;
• axial force on ferrule end face;
• ferrule and fibre material physical constraints;
• alignment sleeve frictional force.

Parameters influencing the fibre to fibre intrinsic attenuation include the following:
• core diameter (CD) mismatch;
• numerical aperture (NA) mismatch;
• core non circularity;
• alpha profile mismatch;
• refractive index mismatch.
The last three parameters are not considered in this document.
Parameters that govern the connector end face deformation, and control the physical contact
of two mated connectors include the following:
• end face spherical radius;
• end face spherical radius apex offset;
• fibre undercut;
• axial force on ferrule end face;
• ferrule and fibre material physical constraints;
• alignment sleeve frictional force.
6 Criteria for a fit within the performance grade
Figure 1 and Table 2 give the criteria for meeting the performance grade as listed in Table 1.
The parameters that are selected for the criteria definition are based on their degree of
significance in affecting the performance.
Multimode reference connectors shall be terminated on multimode (MM) A1a 50 µm fibre, as
specified in IEC 60793-2-10.
– 8 – IEC 61755-6-2:2018 © IEC 2018
F
IEC
Key
F ferrule
Figure 1 – Geometrical requirements for fibre core location after termination
relative to the ferrule axis and the connector plug key
Table 2 – Optical interface parameter values for 1,25 mm and 2,5 mm
diameter PC ferrules for MM reference connectors
Reference Grade 1 Unit Remarks
Parameters
Minimum Maximum
F 0 0,5 µm Eccentricity
7 Use of selected fibre in reference-grade connectors
Selected fibre shall be used with a core diameter of 50 µm ± 0,5 µm and a numerical aperture
of 0,200 ± 0,002 to restrict the variability of attenuation measurements using reference
connectors.
8 Calculated attenuation of random mated grade 1 reference connectors
The attenuation of a MM grade 1 reference connector for 1,25 and 2,5 mm PC ferrules is
expected to be lower than 0,1 dB, when measured using a reference adapter against another
randomly chosen reference connector according to this document (see Figure 2).
The selected fibre geometry parameters numerical aperture (NA) and core diameter (CD) and
the eccentricity of the fibre core in the reference plug are assumed to be uniformly distributed.
Limiting the fibre core/cladding eccentricity may be required to achieve the required
eccentricity of the fibre core in the ferrule.

3 000
0,8
2 000
0,6
0,4
1 000
0,2
0 0
0 0,02 0,04 0,06 0,08 0,10 0,12
Attenuation (dB)
IEC
Figure 2 – Calculated attenuation of random mated
grade 1 reference connectors
9 Reference adapter
To qualify reference adapters, it is recommended to use reference connector plugs as defined
in this document and measure the attenuation of the adapter in accordance with
IEC 61300-3-42 with an attenuation variation smaller than 0,03 dB.
Although the title of IEC 61300-3-42 refers to single mode alignment sleeves, the method also
applies to MM types.
10 Attenuation measurement uncertainty contribution
Using the prescribed fibre geometry, including the tolerance parameters mentioned in
Clause 6, it is possible to achieve measurements using grade 1 reference connectors that
have an uncertainty of ± 0,071 dB, where reference connectors and adapters are randomly
varied and the target encircled flux (EF) launch is satisfied (see Annex A).

Frequency of occurrence
Cumulative distribution function

– 10 – IEC 61755-6-2:2018 © IEC 2018
Annex A
(informative)
Multimode attenuation measurement uncertainty contribution
A.1 General
The attenuation of a multimode connectorised component (or connector) is measured against
a reference connector in a reference adapter. Since reference connector parts vary within the
tolerances allowed in this document, the variability has to be considered as a contribution to
the attenuation measurement uncertainty of the setup.
A.2 Sources of variability
A.2.1 Measurement condition and setup
This is the variability caused by factors such as power meter calibration, finite display
resolution, linearity and connector/detector coupling repeatability, source stability and launch
conditions. IEC TR 62627-04 gives a more detailed explanation of how to determine this
uncertainty for single mode fibres.
A.2.2 Geometry mismatch
Another factor causing variability is the mismatch between the fibre geometry parameters of
the reference connector and the DUT connector, such as the core diameter (CD), the
numerical aperture (NA), and the lateral offset. For the calculation, worst case mismatch is
used assuming that the DUT fibre has a CD of 47,5 µm and a NA of 0,185. The calculated
uncertainty also depends on the offset between the fibre cores of reference and DUT plugs.
See Figure A.1.
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5
Eccentricity of receiving fibre (µm)
IEC
Figure A.1 – Attenuation measurement uncertainty contribution for grade 1
reference connectors resulting from lateral offset, NA and CD mismatch
The red line presents the averaged result of a Monte Carlo simulation (MCS) of the calculated
attenuation of a DUT plug with a worst case minimal CD and NA (47,5 µm and 0,185 NA)
mated to 6 000 grade 1 reference connectors.
Attenuation (dB)
The red bars show the calculated range of values for the different lateral offsets; the black
bars are 95 % of the calculated variation representing the range for uncertainty.
The blue line presents the averaged result of the MCS of the calculated attenuation of a DUT
plug with nominal CD and NA (50 µm and 0,200 NA) mated to 6 000 grade 1 reference
connectors.
It can be seen that the calculated average attenuation for the DUT plug with nominal fibre is
much lower (approx. 0,5 dB) than for the DUT plug with minimal fibre. The calculated variation
(bars) is also much smaller.
The uncertainty U is 0,17 dB/ 2 = 0,085 dB.
Geo
A.3 Overall uncertainty
The overall measurement uncertainty is calculated from Table A.1 that is an adaptation for
multimode fibre of the tables provided in IEC TR 62627-04.
Table A.1 – Evaluation of the uncertainty contribution
due to measurement conditions
b c
Error Uncertainty Probability Divisor Standard Sensitivity Uncertainty

a b c d e f
source distribution uncertainty coefficient contribution
i X u u u(x ) c u (y)
i i i i
dB % % %
u
1 0,005 0,12 % rect 1,732 1 0,07 % 0,10 %
TypeA
√2
u
2 0,08 1,84 % rect 1,732 1 1,06 % 1 1,06 %
MMLC
u
3 0,005 0,12 % rect 1,732 1 0,07 % 0,10 %
Displ
√2
u
4 0,005 0,12 % normal 1 0,12 % 1 0,12 %
Lin
5 u 0,02 0,46 % rect 1,732 1 0,27 % 1 0,27 %
Unif
u
6 0,01 0,23 % rect 1,732 1 0,13 % 0,19 %
Pstab
√2
u
7 0,05 1,16 % rect 1,732 1 0,67 % 1 0,67 %
mating
8 U 0,085 1,96 % normal 2 0,98 % 1 0,98 %
Geo
1,63 %
u = u =
i
∑
0,071 dB
i=1
a
The uncertainty values listed in this table are, when applicable, values of IEC TR 62627-04. Refer to
IEC 62614 for uncertainty value due to multimode launch conditions.
b
Definition of the error sources is, when applicable, the same as in IEC TR 62627-04:2012, 4.2. Definition of
error due to multimode launch conditions, , is the same as IEC TR 61282-14:2016, 5.2.5.3. is
u U
MMLC Geo
defined in A.2.2. The errors have been estimated in dB and were then transformed into a percentage for all
further calculations.
c
Probability distributions are estimated for single measurements to be rectangular. For rectangular probability
distributions the uncertainty has to be divided by
√3 = 1,7321.
d
Standard uncertainty is obtained by dividing the uncertainty by the divisor.
e
Sensitivity coefficient is obtained directly from IEC TR 62627-04:2012, Formula 2, and
IEC TR 61282-14:2016, Table 5.
f
The values have been rounded up to get conservative results.

Therefore, the expanded uncertainty at 95 % confidence level is: U = 2 u = 0,142 dB.

– 12 – IEC 61755-6-2:2018 © IEC 2018
Bibliography
...