IEC 61755-2-2:2022

Fibre optic interconnecting devices and passive components - Connector optical interfaces for single-mode fibres - Part 2-2: Connection parameters of dispersion unshifted physically contacting fibres - Angled

IEC 61755-2-2:2022 defines a set of prescribed conditions for a single-mode fibre optic connection that is maintained in order to satisfy the requirements of attenuation and return loss (RL) performance in a randomly mated pair of angled polished physically contacting (APC) fibres. The model uses a Gaussian distribution of light intensity over the specified mode field diameter (MFD) for determination of attenuation performance grades, based on MFD mismatch and the amount of lateral and angular fibre core offsets. Attenuation and RL performance grades are defined in IEC 61755-1. This second edition cancels and replaces the first edition published in 2006. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- addition of normative references and visual requirements;
- reconsideration of the whole parts of the text to avoid misuse of the standard.

Dispositifs d’interconnexion et composants passifs fibroniques - Interfaces optiques des connecteurs pour fibres unimodales - Partie 2-2: Paramètres de connexion des fibres en contact physique à dispersion non décalée - avec angle

L'IEC 61755-2-2:2022 définit un ensemble de conditions prescrites pour maintenir une connexion optique de fibres unimodales permettant de satisfaire aux exigences de performance d’affaiblissement et d’affaiblissement de réflexion (RL) dans une paire de fibres polies en contact physique avec angle (APC), accouplées sans choix préalable. Le modèle utilise une distribution gaussienne de l’intensité lumineuse sur le diamètre de champ de mode (MFD, Mode Field Diameter) spécifié, afin de déterminer les classes de performance d’affaiblissement sur la base de la discordance MFD et de la quantité de décalages latéraux et angulaires des cœurs de fibre. Les classes de performance d’affaiblissement et de RL sont définies dans l’IEC 61755-1. Cette deuxième édition annule et remplace la première édition parue en 2006. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:
a) ajout de références normatives et d’exigences visuelles;
b) réexamen de l’ensemble des parties du texte pour prévenir toute mauvaise utilisation de la norme.

General Information

• Status: Published
• Publication Date: 13-Sep-2022
• ICS: 33.180.20 - Fibre optic interconnecting devices
• Technical Committee: SC 86B - Fibre optic interconnecting devices and passive components
• Current Stage: PPUB - Publication issued
• Start Date: 14-Sep-2022
• Completion Date: 14-Oct-2022

Relations

• Revises: IEC 61755-2-2:2006 - Fibre optic connector optical interfaces - Part 2-2: Optical interface standard single mode angled physically contacting fibres
• Effective Date: 05-Sep-2023

Overview

IEC 61755-2-2:2022 is an international standard published by the International Electrotechnical Commission (IEC) focused on fibre optic interconnecting devices and passive components. Specifically, it addresses the connector optical interfaces for single-mode fibres with angled polished physically contacting (APC) fibres that are dispersion unshifted. The standard defines the connection parameters required to ensure specified performance levels in terms of attenuation and return loss (RL) for randomly mated APC fibre pairs.

This second edition, which updates the prior 2006 version, introduces normative references and visual requirements to prevent misuse and fully support consistent performance verification. It uses a Gaussian model of light distribution over the mode field diameter (MFD) to establish attenuation performance grades considering MFD mismatch and lateral/angular core offsets.

---

Key Points

• Scope: Defines conditions to achieve reliable optical connections with APC single-mode fibres, ensuring performance per attenuation and return loss standards.
• Performance Grades: Attenuation and return loss grades are classified, with attenuation grades B to D corresponding to connector performance from best to standard.
• APC Connection Focus: Applies to angled polished contacts to minimize back reflections and improve RL performance.
• Gaussian Light Model: Uses Gaussian light intensity distribution to model insertion loss based on fibre core alignment, MFD mismatch, and angular offsets.
• Visual and Measurement Criteria: Includes visual inspection and measurement procedures, referencing IEC 61300 series standards for attenuation and RL testing.
• Wavelength Range: Applicable for single-mode fibres operating between 1310 nm and 1625 nm.
• Updated Requirements: Embeds strict normative references and updated visual acceptance criteria to ensure robust connection quality.

---

Applications

IEC 61755-2-2:2022 is essential for:

• Manufacturers of fibre optic connectors and adapters specializing in single-mode APC connectors.
• Quality control and testing laboratories validating optical performance in telecommunication networks.
• Network designers and installers requiring standardized parameters for fibre optic interconnect performance.
• Data centers and high-speed communication systems where low attenuation and high return loss are critical to signal integrity.
• Optical component calibrations and certification, ensuring compliance with international quality standards.

Achieving adherence to IEC 61755-2-2 ensures:

• Consistent low insertion loss resulting in minimal signal attenuation in fibre connections.
• Superior return loss (≥ 55 dB mating return loss), essential for reducing back reflections which can degrade signal quality.
• Reliable performance in randomly mated APC connectors, optimizing interoperability across multi-vendor systems.

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Related Standards

IEC 61755-2-2:2022 complements and references several IEC standards critical to fibre optic connector performance, including:

• IEC 61755-1: General guidelines and optical interface requirements for dispersion unshifted fibres.
• IEC 60793-2-50: Product specifications for class B single-mode optical fibres.
• IEC 61300-3-6: Test and measurement procedures for return loss in fibre optic connections.
• IEC 61300-3-34 & 3-45: Procedures for measuring attenuation in random mated single and multi-fibre connectors.
• IEC 61300-3-35: Visual inspection protocols for connectors and fibre end faces.

These standards collectively ensure a comprehensive framework for fibre optic connector design, testing, and quality assurance.

---

Summary

IEC 61755-2-2:2022 establishes clear, technically rigorous connection parameters for angled polished single-mode optical fibres to guarantee high-performance optical interfaces. By integrating modelling based on Gaussian light distribution, it specifies attenuation and return loss grades vital for modern telecommunication infrastructure. Compliance supports improved signal integrity, reduced back reflection, and enhanced global interoperability of fibre optic systems.

For engineers, manufacturers, and quality assurance professionals, adhering to IEC 61755-2-2 ensures robust, reliable single-mode fibre optic connections in line with international best practices.

Keywords: IEC 61755-2-2, fibre optic connectors, single-mode fibre, APC connectors, attenuation grades, return loss, mode field diameter, optical interfaces, fibre optic standards, optical connector testing, IEC fibre optics.

Standards Content (Sample)

IEC 61755-2-2 ®
Edition 2.0 2022-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector
optical interfaces for single-mode fibres –
Part 2-2: Connection parameters of dispersion unshifted physically contacting
fibres – Angled
Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces
optiques des connecteurs pour fibres unimodales –
Partie 2-2: Paramètres de connexion des fibres en contact physique à dispersion
non décalée – avec angle
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IEC 61755-2-2 ®
Edition 2.0 2022-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector optical

interfaces for single-mode fibres –

Part 2-2: Connection parameters of dispersion unshifted physically contacting

fibres – Angled
Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces

optiques des connecteurs pour fibres unimodales –

Partie 2-2: Paramètres de connexion des fibres en contact physique à dispersion

non décalée – avec angle
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.20 ISBN 978-2-8322-5698-5

– 2 – IEC 61755-2-2:2022 © IEC 2022
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Attenuation and return loss grades . 6
5 Criteria for a fit within attenuation and return loss grades . 6
5.1 General . 6
5.2 Attenuation grades and criteria . 7
5.3 Visual requirements for return loss grades . 8
Annex A (informative) Return loss model on angled connections . 10
Bibliography . 11

Figure 1 – Lateral offset and angular offset versus attenuation, η , for single-
combined
mode fibre with 8,9 µm MFD at 1 310 nm . 8

Table 1 – Single-mode random mate attenuation grades . 6
Table 2 – Single-mode return loss grades for APC (8°) . 6
Table 3 – MFD and fibre core nominal index of refraction . 7
Table 4 – Visual requirements for single-mode angle polished (APC) fibres
SM APC (RL ≥ 60 dB) . 9

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

Part 2-2: Connection parameters of dispersion
unshifted physically contacting fibres – Angled

FOREWORD
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IEC 61755-2-2 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 2006. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of normative references and visual requirements;
b) reconsideration of the whole parts of the text to avoid misuse of the standard.

– 4 – IEC 61755-2-2:2022 © IEC 2022
The text of this International Standard is based on the following documents:
Draft Report on voting
86B/4640/FDIS 86B/4661/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 in the IEC 61755 series, published 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
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• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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contents. Users should therefore print this document using a colour printer.

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

Part 2-2: Connection parameters of dispersion
unshifted physically contacting fibres – Angled

1 Scope
This part of IEC 61755 defines a set of prescribed conditions for a single-mode fibre optic
connection that is maintained in order to satisfy the requirements of attenuation and return loss
(RL) performance in a randomly mated pair of angled polished physically contacting (APC)
fibres. The model uses a Gaussian distribution of light intensity over the specified mode field
diameter (MFD) for determination of attenuation performance grades, based on MFD mismatch
and the amount of lateral and angular fibre core offsets. Attenuation and RL performance grades
are defined in IEC 61755-1.
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 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for
class B single-mode fibres
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 61300-3-35, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-35: Examinations and measurements – Visual inspection of
fibre optic connectors and fibre-stub transceivers
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 61755-1, 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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61755-1 and the
following apply.
– 6 – IEC 61755-2-2:2022 © IEC 2022
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3.1
defect size
diameter of the smallest circle that can encompass the entire defect
4 Attenuation and return loss grades
Attenuation and return loss grades for APC polished connections are given in Table 1 and
Table 2 according to IEC 61755-1. The return loss grade is for angled contacting fibres only.
The grades that shall be used for non-angled polished PC connections are given separately in
IEC 61755-2-1.
Table 1 – Single-mode random mate attenuation grades
a
Attenuation
Attenuation grade Attenuation mean Notes
b
≥ 97 %
dB dB
A  Reserved for future application
B ≤ 0,12 ≤ 0,25
C ≤ 0,25 ≤ 0,50
D ≤ 0,50 ≤ 1,0
a
Attenuation shall be measured by IEC 61300-3-34 for single-fibre connectors and IEC 61300-3-45 for multi-
fibre connectors.
b
The probability of a randomly mated connection set meeting the specified attenuation requirement will be
≥ 97 %. This performance is reached by means of a statistical distribution of connection parameters (MFD
mismatch, lateral offset and angular offset) using a nominal value for wavelength of 1 310 nm.

Table 2 – Single-mode return loss grades for APC (8°)
a
Return loss grade Return loss (unmated)
Return loss (mated)
dB dB
1 ≥ 60 ≥ 55
a
The test shall be carried out according to IEC 61300-3-6.

Single-mode attenuation and return loss grades are applicable for the wavelengths from
1 310 nm to 1 625 nm.
5 Criteria for a fit within attenuation and return loss grades
5.1 General
Figure 1, Table 3 and Table 4 give the criteria for meeting the attenuation and return loss
grades listed in Table 1 and Table 2. The parameters chosen for the criteria definition are based
on the degree of significance by which they affect the performance under test. The criteria
selected are based on the theoretical model in 5.2 and 5.3 as well as experimental results.

5.2 Attenuation grades and criteria
Using a Gaussian distribution for the incident light, the attenuation of the joint between two
dispersion unshifted single-mode optical fibres defined by IEC 60793-2-50 category B is given
by Formula (1). Attenuation is also referred to as insertion loss (IL), or coupling efficiency of
the fibres.
The range of the nominal MFD and index of refraction (n ) of the fibre cores are given in Table 3.
Table 3 – MFD and fibre core nominal index of refraction
Fibre sub-category Nominal wavelength Nominal MFD n (core)
nm µm
IEC 60793-2-50 fibres 1 310 8,6 to 9,2 1,452 0

These attenuation grades are based on a statistical approach defining parameter values of
connection populations to reach the attenuation to be less than or equal to the given value in
97 % of the connections. This performance is assumed at the nominal wavelength with fibre
MFD in the range defined in IEC 60793-2-50 family specification for single-mode dispersion
unshifted fibres category B.
Populations of lateral and angular offset of the random mated connections are assumed to be
statistically distributed within the specific ranges of parameter values d and θ in Formula (1).
Each curve given in Figure 1 represents maximum allowable combinations of lateral offset and
angular offset so as not to exceed the specified attenuation of any single connection, without
the contribution from fibre MFD mismatch. Additional attenuation due to mismatch of the MFD
from the randomly selected fibres is included in Formula (1).
Formula (1) is applicable to wavelengths from the range between 1 310 nm and 1 625 nm, using
the parameters for these wavelengths. The curves in Figure 1 are only shown at 1 310 nm
wavelength.
– 8 – IEC 61755-2-2:2022 © IEC 2022

Figure 1 – Lateral offset and angular offset versus attenuation, η ,
combined
for single-mode fibre with 8,9 µm MFD at 1 310 nm
Attenuation η is expressed in Formula (1) below:
combined
 

2 2
ω ω
( 21 )
 (2ωω ) 
−2⋅d n
220
η =−−10log exp 2πθsin
( ) (1)
 
combined 10
2 22 2
ωω+ λ
ωω+
 21 
( 21 )
ωω+

( )

 
where
d is the total lateral offset between two fibres;
θ is the angular offset between fibre core axes;
λ is the wavelength of transmitted light in vacuum;
n is the index of refraction of the fibre core;
ω is the transmit fibre mode field radius;
ω is the receive fibre mode field radius.
5.3 Visual requirements for return loss grades
Without considering any contamination or defect on the end face, the intrinsic return loss for
angled polished physical contacting fibres is primarily governed by the polishing angle (see
Annex A). The appropriate polishing method shall be applied to obtain the return loss grade in
Table 2. The quality of the end face shall be inspected using IEC 61300-3-35. The visual
requirements for single-mode APC polished end faces in fibre core zone (zone A), and fibre
cladding zone (zone B) based on defect size, scratch width, and their respective quantities are
shown in Table 4.
Table 4 – Visual requirements for single-mode angle
polished (APC) fibres SM APC (RL ≥ 60 dB)
Zone Defects Scratches
(diameter) (diameter) (width)
No limit < 2 µm No limit < 3 µm
A: core
Maximum 1 ≥ 2 µm and ≤ 3 µm Maximum 4 ≥ 3 µm and ≤ 4 µm
25 µm
None > 3 µm None > 4 µm
B: cladding No limit ≤ 25 µm
No limit
25 µm to 110 µm None > 25 µm
– 10 – IEC 61755-2-2:2022 © IEC 2022
Annex A
(informative)
Return loss model on angled connections
For connections with angled polished end faces, the intrinsic return loss can be calculated as
...