Fibre optic interconnecting devices and passive components - Connector optical interfaces for single-mode fibres - Part 2-1: Connection parameters of dispersion unshifted physically contacting fibres - Non-angled

IEC 61755-2-1:2022 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 non-angled polished physically contacting (PC) 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 requirement tables;
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 2-1: Paramètres de connexion des fibres en contact physique à dispersion non décalée - Sans angle

IEC 61755-2-1:2022 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 (PC) sans angle, accouplées sans choix préalable. Le modèle utilise une distribution gaussienne de l’intensité lumineuse sur le diamètre de champ de mode (MFD) 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 de tableaux d’exigences visuelles; b) réexamen de l’ensemble des parties du texte pour prévenir toute mauvaise utilisation de la norme.

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Publication Date
29-Aug-2022
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IEC 61755-2-1:2022 - Fibre optic interconnecting devices and passive components - Connector optical interfaces for single-mode fibres - Part 2-1: Connection parameters of dispersion unshifted physically contacting fibres - Non-angled
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IEC 61755-2-1
Edition 2.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector
optical interfaces for single-mode fibres –
Part 2-1: Connection parameters of dispersion unshifted physically contacting
fibres – Non-angled
Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces
optiques des connecteurs pour fibres unimodales –
Partie 2-1: Paramètres de connexion des fibres en contact physique à dispersion
non décalée – Sans angle
IEC 61755-2-1:2022-08(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61755-2-1
Edition 2.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector
optical interfaces for single-mode fibres –
Part 2-1: Connection parameters of dispersion unshifted physically contacting
fibres – Non-angled
Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces
optiques des connecteurs pour fibres unimodales –
Partie 2-1: Paramètres de connexion des fibres en contact physique à dispersion
non décalée – Sans angle
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.20 ISBN 978-2-8322-5630-5

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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 61755-2-1:2022  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 ................................................ 7

5.1 General ................................................................................................................... 7

5.2 Attenuation grades and criteria ............................................................................... 7

5.3 Visual requirements for return loss grades .............................................................. 8

Annex A (informative) Effect of damaged surface layer on non-angled connections ............. 10

Bibliography .......................................................................................................................... 12

Figure 1 – Lateral offset and angular offset versus attenuation, η , for
combined

single‑mode fibre with 8,9 µm MFD at 1 310 nm ..................................................................... 8

Figure A.1 – Model of the connection of convex polished end faces under compressive load 10

Figure A.2 – High index layer refractive index and thickness versus return loss for a

typical dispersion unshifted single-mode fibre ....................................................................... 11

Table 1 – Single-mode random mate attenuation grades ......................................................... 6

Table 2 – Single-mode return loss grades ............................................................................... 6

Table 3 – MFD and fibre core nominal index of refraction ....................................................... 7

Table 4 – Visual requirements for single-mode PC polished fibres with RL grade 2

single-mode (SM) (RL ≥ 45 dB) ............................................................................................... 9

Table 5 – Visual requirements for single-mode PC polished fibres with RL grade 3

single-mode (SM) (RL ≥ 35 dB) ............................................................................................... 9

Table 6 – Visual requirements for single-mode PC polished fibres with RL grade 4

single-mode (SM) (RL ≥ 26 dB) ............................................................................................... 9

---------------------- Page: 4 ----------------------
IEC 61755-2-1:2022  IEC 2022 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC INTERCONNECTING DEVICES AND
PASSIVE COMPONENTS – CONNECTOR OPTICAL
INTERFACES FOR SINGLE-MODE FIBRES –
Part 2-1: Connection parameters of dispersion
unshifted physically contacting fibres – Non-angled
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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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.

IEC 61755-2-1 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 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 requirement tables;

b) reconsideration of the whole parts of the text to avoid misuse of the standard.

---------------------- Page: 5 ----------------------
– 4 – IEC 61755-2-1:2022  IEC 2022
The text of this International Standard is based on the following documents:
Draft Report on voting
86B/4629/FDIS 86B/4653/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

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.

IMPORTANT – The "colour inside" logo on the cover page of this document 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.
---------------------- Page: 6 ----------------------
IEC 61755-2-1:2022  IEC 2022 – 5 –
FIBRE OPTIC INTERCONNECTING DEVICES AND
PASSIVE COMPONENTS – CONNECTOR OPTICAL
INTERFACES FOR SINGLE-MODE FIBRES –
Part 2-1: Connection parameters of dispersion
unshifted physically contacting fibres – Non-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 non-angled polished physically contacting (PC)

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.
---------------------- Page: 7 ----------------------
– 6 – IEC 61755-2-1:2022  IEC 2022

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
defect size
diameter of the smallest circle that can encompass the entire defect
4 Attenuation and return loss grades

Attenuation and return loss grades that shall be used for PC polished connections are given in

Table 1 and Table 2 according to IEC 61755-1. The return loss grades are for non-angled

contacting fibres only. The grade that shall be used for angled PC (APC) connections is given

separately in IEC 61755-2-2.
Table 1 – Single-mode random mate attenuation grades
Attenuation
Attenuation grade Attenuation Mean Notes
≥ 97 %
dB dB
A Reserved for future application
B ≤ 0,12 ≤ 0,25
C ≤ 0,25 ≤ 0,50
D ≤ 1,0
≤ 0,50

Attenuation shall be measured by IEC 61300-3-34 for single-fibre connectors and IEC 61300-3-45 for multi-

fibre connectors.

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
Return loss grade Notes
Return loss (mated)
dB
Grade 1 is defined as ≥ 60 dB and reserved for use
1 - with angled, physically contacting fibres as defined in
IEC 61755-2-2.
2 ≥ 45
3 ≥ 35
4 ≥ 26
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.
---------------------- Page: 8 ----------------------
IEC 61755-2-1:2022  IEC 2022 – 7 –
5 Criteria for a fit within attenuation and return loss grades
5.1 General

The following Figure 1 and Table 3, Table 4, Table 5 and Table 6 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, 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 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 randomly 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.
---------------------- Page: 9 ----------------------
– 8 – IEC 61755-2-1:2022  IEC 2022
Figure 1 – Lateral offset and angular offset versus attenuation, η , for
combined
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
( )
 2ωω 21 
( ) −2⋅ d n
21 22
η =−−10log exp 2πθsin
( ) (1)
combined 10  
2 22 2
22 ωω+ λ
ωω+
 
( 21 )
ωω+ 
( 21 )
 
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

physical contacting fibres is governed by the refractive index of the fibre core (see Annex A).

The appropriate polishing method shall be applied to obtain the return loss grades in Table 2.

The quality of the end face shall be inspected using IEC 61300-3-35. The visual requirements

for single-mode non-angled PC 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 5 and Table 6.
---------------------- Page: 10 ----------------------
IEC 61755-2-1:2022  IEC 2022 – 9 –
Table 4 – Visual requirements for single-mode PC polished
fibres with RL grade 2 single-mode (SM) (RL ≥ 45 dB)
Zone Defects Scratches
(diameter) (diameter) (width)
No limit < 2 µm
A: core No limit < 3 µm
Maximum 1 ≥ 2 µm and ≤ 3 µm
25 µm None ≥ 3 µm
None > 3 µm
B: cladding No limit ≤ 25 µm
No limit
25 µm to 110 µm None > 25 µm
Table 5 – Visual requirements for single-mode PC polished
fibres with RL grade 3 single-mode (SM) (RL ≥ 35 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 1 ≥ 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
Table 6 – Visual requirements for single-mode PC polished
fibres with RL grade 4 single-mode (SM) (RL ≥ 26 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 2 ≥ 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
---------------------- Page: 11 ----------------------
– 10 – IEC 61755-2-1:2022  IEC 2022
Annex A
(informative)
Effect of damaged surface layer on non-angled connections

Since polishing usually damages the surface layer of silica fibre, a high index layer on the fibre

surface as a result of polishing is the dominating factor for non-angled connections.

Assuming there are no endface scratches and defects, the intrinsic return loss for convex

polished end faces is expressed as R in Formula (A.1):
ORL
 2 
2 2
 
  
 
nn n n
 
12 00
− nE +  − n G +− n  H 
 
0 21
 
  
nn n n
 
 21  2 1
  
   
R = −10 log
(A.1)
ORL 10
 2 
 
  
 
 nn nn 
12 00
 
2nF −+ nE +  + n G + + n  H
 
0  0 21
 
  
 nn n n 
 
 2 1  2 1
 
  
 
 
where
E = sinδ sinδ ;
1 2
F = cosδ cosδ ;
1 2
G = cosδ sinδ ;
1 2
H = sinδ cosδ ;
1 2
δ = 2πn d /λ;
1 1 1
δ = 2πn d /λ;
2 2 2

n and d are the refractive index and thickness of the high index layer of fibre 1;

1 1

n and d are the refractive index and thickness of the high index layer of fibre 2;

2 2
n is the refractive index of glass fibre core.
As for n , n , n , d and d , refer to Figure A.1.
1 2 0 1 2
Figure A.1 – Model of the connection of convex polished
end faces under compressive load

By mating two fibres with the same high index layer (n = n and d = d ), such intrinsic return

1 2 1 2

loss can be calculated from the refractive index and thickness of the high index layer as shown

in Figure A.2.
---------------------- Page: 12 ----------------------
IEC 61755-2-1:2022  IEC 2022 – 11 –
Figure A.2 – High index layer refractive index and thickness versus
return loss for a typical dispersion unshifted single-mode fibre
---------------------- Page: 13 ----------------------
– 12 – IEC 61755-2-1:2022  IEC 2022
Bibliography

IEC 61755-2-2, 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 61755-3-1, Fibre optic interconnecting devices and passive components – Connector

optical interfaces for single-mode fibres – Part 3-1: Connector parameters of dispersion

unshifted physically contacting fibres – Non-angled 2,5 mm and 1,25 mm diameter cylindrical

full zirconia ferrules
___________
---------------------- Page: 14 ----------------------
– 14 – IEC 61755-2-1:2022  IEC 2022
SOMMAIRE

SOMMAIRE .......................................................................................................................... 14

AVANT-PROPOS .................................................................................................................. 15

1 Domaine d’application ................................................................................................... 17

2 Références normatives .................................................................................................. 17

3 Termes et définitions ..................................................................................................... 17

4 Classes d’affaiblissement et d’affaiblissement de réflexion ............................................ 18

5 Critères d’ajustement dans les classes d’affaiblissement et d’affaiblissement de

réflexion ........................................................................................................................ 19

5.1 Généralités ........................................................................................................... 19

5.2 Classes d’affaiblissement et critères ..................................................................... 19

5.3 Exigences visuelles pour les classes d’affaiblissement de réflexion ...................... 20

Annexe A (informative) Effet d’une couche de surface endommagée sur les

connexions sans angle .................................................................................................. 22

Bibliographie ......................................................................................................................... 24

Figure 1 – Décalage latéral et décalage angulaire en fonction de l’affaiblissement,

ηcombiné, pour les fibres unimodales de MFD 8,9 µm à 1 310 nm ............................................ 20

Figure A.1 – Modèle de connexion des faces d’extrémité polies convexes sous charge

de compression .................................................................................................................... 22

Figure A.2 – Indice de réfraction et épaisseur de la couche d’indice élevé en fonction

de l’affaiblissement de réflexion pour une fibre unimodale typique à dispersion non

décalée ................................................................................................................................. 23

Tableau 1 – Classes d’affaiblissement en unimodal et accouplement sans choix

préalable .............................................................................................................................. 18

Tableau 2 – Classes d’affaiblissem
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