IEC 61755-1:2022

IEC 61755-1
®

Edition 2.0 2022-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE


Fibre optic interconnecting devices and passive components – Connector
optical interfaces for single-mode fibres –
Part 1: Optical interfaces for dispersion unshifted fibres – General and guidance

Dispositifs d'interconnexion et composants passifs fibroniques – Interfaces
optiques avec connecteurs pour fibres unimodales –
Partie 1: Interfaces optiques pour fibres à dispersion non décalée – Généralités
et recommandations

IEC 61755-1:2022-09(en-fr)

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---------------------- Page: 2 ----------------------
IEC 61755-1

®


Edition 2.0 2022-09




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE











Fibre optic interconnecting devices and passive components – Connector

optical interfaces for single-mode fibres –

Part 1: Optical interfaces for dispersion unshifted fibres – General and guidance




Dispositifs d'interconnexion et composants passifs fibroniques – Interfaces

optiques avec connecteurs pour fibres unimodales –


Partie 1: Interfaces optiques pour fibres à dispersion non décalée – Généralités

et recommandations












INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 33.180.20 ISBN 978-2-8322-5697-8




Warning! Make sure that you obtained this publication from an authorized distributor.

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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – IEC 61755-1:2022 © IEC 2022
CONTENTS
FOREWORD . 3
0 Introduction . 5
0.1 Overview. 5
0.2 Hierarchical relationship . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Structure of the IEC 61755 series . 8
5 Optical datum target . 9
6 Test methods . 10
7 Optical interface grades . 10
8 Key parameters . 11
9 Materials . 12
Bibliography . 13

Figure 1 – Relationship between optical interface standards and interface standards. 6

Table 1 – Multi-part structure of the IEC 61755 series. 9
Table 2 – Single-mode random mate attenuation grades at 1 310 nm (dB) . 11
Table 3 – Single-mode return loss grades at 1 310 nm (dB) . 11

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IEC 61755-1:2022 © IEC 2022 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

FIBRE OPTIC INTERCONNECTING
DEVICES AND PASSIVE COMPONENTS –
CONNECTOR OPTICAL INTERFACES FOR SINGLE-MODE FIBRES –

Part 1: Optical interfaces for dispersion unshifted fibres –
General and guidance

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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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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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) 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.
IEC 61755-1 has been prepared by subcommittee 86B: Fibre optic interconnecting devices and
passive components, of IEC technical committee 86: Fibre optics. It is an International Standard.
This second edition cancels and replaces the first edition published in 2005. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) deletion of Figure 2, Figure 3 and Table 4, and consideration of the whole parts of the text;
b) addition of the test method for random mating of the multifibre connectors;
c) introduction of a nomenclature for the specified core location variants;
d) replacement of the limited MFD range, which is now in line with the complete MFD range
specified in IEC 60793-2-50;

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– 4 – IEC 61755-1:2022 © IEC 2022
e) replacement of the references to reliability standards to reliability technical reports;
f) new general title for the series.
The text of this document is based on the following documents:
Draft Report on voting
86B/4642/FDIS 86B/4663/RVD

Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts of the IEC 61755 series, under the general title Fibre optic interconnecting
devices and passive components – Connector optical interfaces for single-mode fibres, can be
found on the IEC website.
Future documents in this series will carry the new general title as cited above. Titles of existing
documents in this series will be updated at the time of the next edition.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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.

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IEC 61755-1:2022 © IEC 2022 – 5 –
0 Introduction
0.1 Overview
A connector optical interface standard is a multi-part collection of the geometric, dimensional
and material requirements necessary in order to comply with the optical functionality
specifications for a defined interface between two optical fibres. It consists of those essential
features that are functionally critical to the optical attenuation and return loss performance of
an optical interface in the mated condition.
This series of optical interface standards for single-mode connectivity provides general
information on optical connector interfaces for non-dispersion shifted single-mode fibres,
according to IEC 60793-2-50, for class B with nominal mode field diameter range of 8,6 µm to
9,2 µm. It defines the location of the fibre core in relation to the datum target and the following
key parameters: lateral and angular misalignment, fibre mode field diameter, end face
separation, end face angle and end face high index layer condition. It also defines standardized
test methods where appropriate.
The subsequent parts of the single-mode series contain those optical interfaces that have been
standardized for international use. Each interface contains the essential information to ensure
that products conforming to the standards of the IEC 61755 series will work together repeatedly
to a known level of optical performance without the need for compatibility testing or cross
checking.
It is important to emphasize that standard optical interfaces are intended to be used with IEC
standards of various categories, which already include:
– mechanical connector interface standards;
– test and measurement methods;
– performance standards;
– reliability technical reports.
Interface standards, according to the IEC 61754 series, provide all the essential information
about a given product type or family necessary to ensure that all products compliant with the
interface standard will mate/de-mate.
Test and measurement methods, according to the IEC 61300-2 and IEC 61300-3 series, give a
prescribed approach to the way in which key parameters that are assessed are evaluated.
Performance standards, according to the IEC 61753 series, use these test and measurement
methods to define a set of conditions indicative to a known system location against which a
product can be evaluated on a ‘once off’ basis to prove that its design and manufacture are
capable of satisfying the necessary criteria.
Reliability technical reports are intended to provide the user and manufacturer with a set of
guidelines for assessing the ability of the product to continue to meet the required criteria over
time.
The two basic optical transmission performance parameters that characterize the optical
interface are attenuation and return loss. Each parameter places different physical constraints
on the optical interface. Environmental conditions also affect the performance of the optical
interface, and it may require definition of physical and mechanical dimensions to ensure that
the performance specified is maintained over the environmental extremes defined in a particular
performance standard.

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– 6 – IEC 61755-1:2022 © IEC 2022
Manufacturing materials and processes also affect the optical interface and therefore the
document has been designed to allow manufacturers to demonstrate compliance with the
document while still permitting the maximum of manufacturing differentiation. The relationship
between, and suitability of, materials specified in the IEC 61755-3 series for different
performance categories as specified in IEC 61753-1, is defined, e.g. zirconia ferrule material
can be applied in all environmental categories, while the thermoset epoxy polymer material
specified for some rectangular ferrules can only be applicable for category C.
Optical interface standards define sets of required conditions, which should be maintained in
order to satisfy the requirements for the attenuation and return loss performance in a randomly
mated pair of fibres as specified in IEC 60793-2-50.
0.2 Hierarchical relationship
The hierarchical relationship between optical interface standards and interface standards is
shown in Figure 1.

IEC 61755-1
Optical interface – Part 1 :
General and guidance

IEC 61755-2 series
Optical interface – Part 2 :
Fibre to fibre, optical connection performance
requirements, e.g. lateral and angular
misalignment, mode field diameter mismatch
excluding fibre support mechanisms

IEC 61755-3 series
Optical interface – Part 3 :
Fibre support mechanisms, optical connector
end face and material deformation properties
e.g. in the case of ferrules, effects of dome
offset, fibre undercut and fibre position
necessary to meet the performance
requirements of Part 2

Mechanical connector interface IEC 61754
series.
Connector mating dimensions, e.g. effects of
spring force, etc.

Figure 1 – Relationship between optical interface standards and interface standards

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IEC 61755-1:2022 © IEC 2022 – 7 –
FIBRE OPTIC INTERCONNECTING
DEVICES AND PASSIVE COMPONENTS –
CONNECTOR OPTICAL INTERFACES FOR SINGLE-MODE FIBRES –

Part 1: Optical interfaces for dispersion unshifted fibres –
General and guidance



1 Scope
This document covers dispersion unshifted single-mode fibre optic connection interfaces. It
includes references, document structure details, definitions, and standardised optical
connection grades. The grades are based on random mated connections between two optical
connector populations according to required characteristics including fibre mode field diameter
(MFD) mismatch.
It also defines standardized test methods where appropriate.
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 61300 (all parts), Fibre optic interconnection devices and passive components – Basic test
and measurement procedures
IEC 61300-3-6, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-6: Examinations and measurements – Return loss
IEC 61300-3-34, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-34: Examinations and measurements – Attenuation of
random mated connectors
IEC 61300-3-45, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-45: Examinations and measurements – Attenuation of
random mated multi-fibre connectors
IEC 61754 (all parts), Fibre optic interconnecting devices and passive components – Fibre optic
connector interfaces
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp

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– 8 – IEC 61755-1:2022 © IEC 2022
3.1
angular misalignment
angular displacement between the two mated fibre cores
Note 1 to entry: The rotation causes the fibre core to move to a predetermined angular position with respect to a
line, which begins at the optical datum target and passes through the keying feature.
3.2
end face boundary condition
surface condition that exists at the optical interface after all termination processes have been
completed
3.3
end face separation
axial separation between the two mated fibres
3.4
high index layer
compacted region at the fibre end face where the refractive index is often higher than that of
an unpolished cleaved fibre
3.5
lateral offset
lateral displacement between the two mated fibres
3.6
mode field diameter
Gaussian model beam waist diameter
Note 1 to entry: The mode field diameter is also sometimes referred to as the mode field spot diameter (the diameter
where the radial field amplitude of the fundamental mode decreases to 1/e of its maximum at the optical fibre axis).
3.7
mode field diameter mismatch
difference in mode field diameter between the two mated fibres
3.8
optical interface
physical plane where two fibre end faces are butt-jointed to make physical contact to minimize
disturbance of the transmitted light
3.9
optical interface standard
set of required, measurable conditions which are met in order to satisfy the requirements for
attenuation and return loss performance and environmental stability in a mated pair of fibres
3.10
optical datum target
theoretical datum point on a connector interface where the optical fibre core centre or centre of
the optical waveguide is positioned
4 Structure of the IEC 61755 series
This document has a multi-part structure as shown in Table 1.

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IEC 61755-1:2022 © IEC 2022 – 9 –
Table 1 – Multi-part structure of the IEC 61755 series
Example of parameters
Standard part and number Applicable to
to be included
Part 1 – General and guidance Document structure, definitions, definitions
preferred grades and rules under
grades
(IEC 61755-1)
which optical interfaces are created
key parameters
Part 2 Fibre to fibre interface end face separation
(IEC 61755-2 series) end face angle
lateral offset
angular misalignment
mode field diameter mismatch
end face high index layer
Part 3 Ferrule or other fibre support For cylindrical ferrules the
mechanisms if applicable following parameters apply:
(IEC 61755-3 series)
dome offset
fibre undercut
fibre core eccentricity
materials (ferrule, alignment sleeve
etc.)
For rectangular ferrules the
following parameters apply:
fibre protrusion
fibre array minus coplanarity
adjacent fibre height differential
end face angle in the x axis
end face in the y axis
end face radius in the x axis
end face radius in the y axis
fibre tip spherical radii
axial force on ferrule end face
ferrule and fibre material constants
frictional force of alignment pins in
ferrule guide holes

5 Optical datum target
The optical datum target defined in a fibre optic connector mechanical interface standard (see
IEC 61754 series) is the point at which the optical fibre core centre shall be positioned after all
termination processes have been completed. Each part of the optical interface defines the
tolerance limits for the applicable parameters that can exist around the true position for defined
performance characteristics, for example:
– IEC 61755-2 (all parts) is concerned with physically contacting fibre to fibre connections and
defines the tolerance limits for lateral offset, angular misalignment, mode field diameter
mismatch, end face angle and end face high index layer in relation to the specified
performance.
– IEC 61755-3 (all parts) is concerned with fibre optic connectors and defines the tolerance
limits for fibre core eccentricity (radial and azimuth) and tilt angle and end face geometry
parameters to ensure physical contact of the fibre cores.

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– 10 – IEC 61755-1:2022 © IEC 2022
– the mechanical connector interface standard IEC 61754 series defines keying accuracy and
contact force, etc.
6 Test methods
A standard test method shall be clearly specified for each test. Wherever possible, the test
method shall be selected from IEC 61300 series; where this is not possible, other test methods
can be specified. If a non-standard test method is used, the test method and details to be
specified shall be included in the appropriate annex of the optical interface standard.
7 Optical interface grades
Both attenuation grade and return loss grade, each of which can be selected separately, define
optical performance characteristics.
Single-mode attenuation grades are designated by a capital letter of the alphabet, i.e. A, B, etc.,
and relate to the performance expected in a random mated situation.
Return loss grades are designated by a numeral, i.e. 1, 2, etc., and relate to the performance
expected in a random mated situation.
The combination of these two grades, separated with a forward slash, i.e. A/1, B/3 etc., serves
to define the expected performance of a particular optical interface.
All performance grades specified in IEC 61755 (all parts) are based on physical contact of the
fibre cores.
In all cases, the meaning and values of A/1, B/3, etc. remain the same, so the user can easily
identify the type of interface and the performance that can be expected. While the optical
interface grade always remains the same, the connector or fibre support mechanism (e.g.
ferrule) necessary to achieve these values can change for different fibre types and end face
conditions.
All ferrule materials specified in the IEC 61755-3 series for the same connector family (e.g. PC,
APC cylindrical ferrule, rectangular ferrule) are intended to be intermateable in the lowest
specified performance category.
For example the zirconia ferrule material and titanium ferrule material can be both applied in all
environmental categories.
The applicability for each ferrule material for environmental categories according to
IEC 61753-1 is proved by the responsible IEC subcommittee for fibre optic interconnecting
devices.
Standardized optical interfaces are given in IEC 61755-2 (all parts) and IEC 61755-3 (all parts).
Within the standardized optical interface there are different technologies to achieve a specified
attenuation grade. The variants are intended to be intermateable to the lowest grade.
For example, the connection of a grade B titanium ferrule (IEC 61755-3-7) mated to a grade C
zirconia ferrule (IEC 61755-3-1) is a grade C connection.

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IEC 61755-1:2022 © IEC 2022 – 11 –
The variants for cylindrical ferrules are as follows:
Variant 1: Oriented, fibre core axis oriented towards the guide key;
Variant 2: Non-oriented, fibre core axis not oriented towards the guide key;
Variant 3: Centred, fibre core location actively centred toward ferrule axis.
Optical interface performance grades for single-mode are given in Table 2 and Table 3.
Table 2 – Single-mode random mate attenuation grades at 1 310 nm (dB)
Attenuation grade Attenuation [dB] Attenuation [dB] Notes
a
97 % mean
 Reserved for future
A
application
B ≤ 0,25 ≤ 0,12
C ≤ 0,50 ≤ 0,25
D ≤ 1,0 ≤ 0,50
a
The probability of a random mated connector set of meeting or exceeding the specified level of attenuation
will be ≥ 97 %. This performance is reached considering a statistical distribution
...