IEC 61755-2-5:2015

IEC 61755-2-5 ®
Edition 1.0 2015-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector
optical interfaces –
Part 2-5: Connection parameters of non-dispersion shifted single-mode
physically contacting fibres – Angled for reference connection applications

Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces
optiques de connecteurs –
Partie 2-5: Paramètres de connexion de fibres unimodales à dispersion non
décalée en contact physique – Avec angle pour applications en tant que
connecteurs de référence
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IEC 61755-2-5 ®
Edition 1.0 2015-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Connector

optical interfaces –
Part 2-5: Connection parameters of non-dispersion shifted single-mode

physically contacting fibres – Angled for reference connection applications

Dispositifs d’interconnexion et composants passifs fibroniques – Interfaces

optiques de connecteurs –
Partie 2-5: Paramètres de connexion de fibres unimodales à dispersion non

décalée en contact physique – Avec angle pour applications en tant que

connecteurs de référence
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.20 ISBN 978-2-8322-7277-0

– 2 – IEC 61755-2-5:2015 © IEC 2015
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Performance grades . 6
4 Description . 6
5 Criteria for a fit within performance grades . 7
5.1 General . 7
5.2 Attenuation grades and criteria . 7
6 Use of selected fibre to assemble reference connector plugs . 9
7 Reference adaptor . 9
8 Attenuation measurement uncertainty contribution . 9
Annex A (informative) Example of determination of the attenuation measurement
uncertainty . 10

Figure 1 – Representation of fibre core position of single connector plug under the
assumption of worst case alignment with identical connector plug. 8
Figure A.1 – Attenuation measurement uncertainty contribution for Grade 1 reference
connectors . 10

Table 1 – Single-mode attenuation grades at 1 310 nm (dB) . 6
Table 2 – Mode field diameter and fibre core nominal index of refraction for fibre to be
used in reference connector plugs . 7
Table 3 – Measurement uncertainty contribution of reference connectors . 9

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

Part 2-5: Connection parameters of non-dispersion
shifted single-mode physically contacting fibres –
Angled for reference connection applications

FOREWORD
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61755-2-5 has been prepared by subcommittee 86B: Fibre optic
interconnecting devices and passive components, of IEC technical committee 86: Fibre optics.
This bilingual version (2019-08) corresponds to the monolingual English version, published in
2015-01.
The text of this standard is based on the following documents:
FDIS Report on voting
86B/3846/FDIS 86B/3867/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.

– 4 – IEC 61755-2-5:2015 © IEC 2015
The French version of this standard has not been voted upon.
This publication 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.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site 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.
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 2-5: Connection parameters of non-dispersion
shifted single-mode physically contacting fibres –
Angled for reference connection applications

1 Scope
This part of IEC 61755 defines a set of prescribed conditions that should be maintained in order
to satisfy the requirements of angled polished reference connections.
The prescribed conditions include dimensional limits and optical fibre requirements of the
optical interface to meet specific requirements for reference connection (plugs and adaptors)
used for attenuation measurements.
Two different grades for reference connections are defined in this standard. The use of each of
these grades depends on the application and on the targeted attenuation measurement
uncertainty. The model uses a Gaussian distribution of light intensity over the specified
restricted mode field diameter (MFD) range.
This standard is intended to be used for shipping and acceptance inspections.
The reference connector plug is specified for B1.1, B1.3 and B6 fibres as specified in
IEC 60793-2-50.
The use of the reference connector plug would not be recommended where classification of
fibre is difficult, for example construction and maintenance of cable plant.
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 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for
class B single-mode fibres
IEC 61300-3-4, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-4: Examinations and measurements – Attenuation
IEC 61300-3-42, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-42: Examinations and measurements – Attenuation of single
mode alignment sleeves and or adaptors with resilient alignment sleeves
IEC 61755-2-1, Fibre optic interconnecting devices and passive components –Connector optical
interfaces – Part 2-1: Connection parameters of non-dispersion shifted single-mode physically
contacting fibres – Non-angled

– 6 – IEC 61755-2-5:2015 © IEC 2015
IEC 61755-2-2, Fibre optic interconnecting devices and passive components –Connector
optical interfaces – Part 2-2: Connection parameters of non-dispersion shifted single-mode
physically contacting fibres – Angled
IEC 61755-3 (all parts), Fibre optic interconnecting devices and passive components –
Connector optical interfaces – Part 3-x: Connector parameters of non-dispersion shifted single-
mode physically contacting fibres
IEC TR 62627-04, Fibre optic interconnecting devices and passive components – Technical
report – Part 04: Example of uncertainty calculation: Measurement of the attenuation of an
optical connector.
3 Performance grades
Performance grades for APC polished reference connectors are given in Table 1. The specified
attenuation for each grade is obtained when the reference plugs are connected to each other
with the reference adaptor.
Table 1 – Single-mode attenuation grades at 1 310 nm (dB)
a a b
Reference grade Attenuation Contribution to measurement uncertainty
dB dB
R1
≤0,1 ±0,1
R2 ≤0,2 ±0,2
a
Under the assumption of worst case alignment with identical connector plug. Expected attenuation measured
when connecting two plugs of the same grade may be higher due to significant measurement uncertainty
b
As described in Clause 8.
4 Description
Optical reference connector plugs are connector plugs manufactured with restricted tolerances
for dimensions relevant to lateral and angular offset. These connector plugs are used for
attenuation measurement purposes according to IEC 61300-3-4, and shall be considered as
part of the measurement set-up since they strongly contribute to its measurement uncertainty
(for example see IEC TR 62627-04). The attenuation measurement uncertainty contributions
for both grades of reference connectors are listed in Table 3.
The principal performance of a reference connector plug is given by its contribution to
measurement uncertainty (estimated based on the reproducibility of an attenuation
measurement of the same device performed using multiple different reference connector plugs
of the same grade) which is determined by the accuracy with which the core of the optical fibre
is aligned to the optical datum target and determines the random attenuation performance of a
reference connector population.
The main parameters influencing the performance of the reference connector plugs are fibre
core location, fibre core axis angle and mode field diameter variability. Figure 1 represents the
fibre alignment tolerances for the two different reference grades described in this standard,
under the assumption of using selected reference fibre, described in Table 2.
The design curves given in Figure 1 each represent maximum allowable combinations of a given
specific fibre core location and an associated fibre core axis angle to not exceed the specified
attenuation of any single considered connection. The design curves shown represent the
determination of the parameters under a worst case mismatch of the mode field diameter of the
selected fibres as given in Table 3, i.e. 9,1/9,3 µm and a wavelength of 1 310 nm. These mode
field diameter ranges are selected within the IEC 60793-2-50 family specification for single-
mode, non-dispersion shifted fibres as given in Table 2.

5 Criteria for a fit within performance grades
5.1 General
Figure 1 and Table 2 give the criteria for meeting the performance grades listed above in Table
1. The parameters chosen for the criteria definition are based on the degree of significance in
affecting the performance under test.
5.2 Attenuation grades and criteria
Considering a beam with a Gaussian distribution, the coupling efficiency, η, of two single mode
fibres is given by Equation (1).
Table 2 – Mode field diameter and fibre core nominal index of refraction
for fibre to be used in reference connector plugs
a
MFD
Nominal
n
µm 0
Fibre type wavelength
(core)
nm
Min. Max.
Dispersion unshifted fibre 1 310 9,1 9,3 1,452 0
a
MFD as specified here has a narrow tolerance compared to tolerance field in IEC 60793-2-50.

The attenuation (also referred to as insertion loss, IL, or coupling efficiency) of the fibres equals
η Attenuation η is expressed as in Equation (1) below:
combined. combined .
 
2 2 2 2 2
 
(2ω ω ) − 2 ×d n (ω ω )
2 1 2 0 2 1 2
 
η = −10log exp − 2π sin (θ ) (1)
combined
2 2 2 2 2 2
 
2 2
 ω + ω λ (ω + ω ) 
(ω + ω )  2 1 2 1 
 2 1 
where
d is the total lateral offset;
θ is the angular misalignment between fibre cores;
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.
The definition of reference connector grades is based on worst case calculation (unlike the
other level 2 optical interface standards, IEC 61755-2-1 and IEC 61755-2-2, where the
definition of performance grades is based on a statistical approach defining parameter values
to reach the given random attenuation in 97 % of the connections).
Equation (2), which has been used to calculate the curves displayed in Figure 1, is derived from
Equation (1) where the total lateral offset (d) has been replaced by the double of the fibre core
location ( ) and the angular misalignment by the double of the fibre core axis angle ( ),
2 ×F 2 ×E
the input fibre has maximum fibre mode field radius (4,65 µm) and the output fibre the minimum
fibre mode field radius (4,55 µm) specified in Table 2. That way, Equation (2) calculated the
attenuation in the case of worst case alignment of identical plugs. It shall be noted that Figure
1 can be used as a design graph for reference connector plugs, from where fibre core location
and angular misalignment can be directly read. For the definition of fibre core location and fibre
core axis angle refer to the relevant level 3 optical inferface standards (see the IEC 61755-3
series).
– 8 – IEC 61755-2-5:2015 © IEC 2015
 
2 2 2 2
 
(2ω ω ) − 2 × (2 ×F) n (ω ω )
2 1 2 0 2 1 2
 
η = −10log exp − 2π sin (2 ×E)
 
combined
(2)
2 2 2 2 2 2
 
2 2
 ω + ω λ (ω + ω ) 
2 1 2 1
(ω + ω )  
 2 1 
where
F is the fibre core location (µm);
E is the fibre core axis angle (rad);
λ is the wavelength of transmitted light in vacuum (here 1,310 µm);
n is the index of refraction of the fibre core (here 1,452 0);
ω is the transmit fibre mode field radius (here 4,55 µm);
ω is the receive fibre mode field radius (here 4,65 µm).
The shown design curves represent the determination of the parameters under a worst case
mismatch of the mode field diameter of the selected fibres as given in Table 2, i.e. 9,1/9,3 µm
and a wavelength of 1 310 nm. These mode field diameter ranges are selected within the
IEC 60793-2-50 product specification for single-mode non-dispersion shifted fibres as given in
Table 2. The equation is also applicable to 1 550 nm and 1 625 nm, but the design curves are
not shown in Figure 1.
0,2 dB
0,3
0,1 dB
0,2
0,1
0,0
0,0 0,1 0,2 0,3 0,4
Dimension F: Fibre core position  (µm)
IEC
Figure 1 – Representation of fibre core position of single connector plug under the
assumption of worst case alignment with identical connector plug
For cylindrical ferrule connectors, the performance presented in Figure 1 can only be achieved
when limiting the ferrule diameter tolerance to
• 1,249 0 to 1,249 5 mm for 1,25 mm ferrules, and
• 2,499 0 to 2,499 5 mm for 2,5 mm ferrules.
For terminated APC connectors, the measurement of core position and angular misalignment
are “for further study”.
Dimension E: Fibre core axis angle  (°)

6 Use of selected fibre to assemble reference connector plugs
In order to limit the variability of attenuation measurement using reference connectors, it is
mandatory to use selected fibre with restricted tolerances on mode field diameter (MFD) to 9,2
µm ± 0,1 µm, measured at 1 310 nm. Using this type of fibre and the tolerance parameters
published in this standard it is possible to reach measurement values that are repeatable within
± ,1 dB when randomly varying the reference connector plug (valid for reference Grade 1).
7 Reference adaptor
In case of a cylindrical ferrule connector, selected reference adaptors shall be used. It is
recommended to use reference connector plugs and measure them according to
IEC 61300-3-42 with an attenuation variation smaller than 0,03 dB.
8 Attenuation measurement uncertainty contribution
When performing an attenuation measurement using a reference connector plug and adaptor,
these shall be considered as part of the measurement set-up. The goal of a reference
measurement is to qualify a device under test (DUT, which may be an optical connector or
another optical component that has an input connector) by measuring the attenuation of the
DUT connected to the reference connector plug and adaptor. Since the reference connector
plug and adaptor properties vary as a function of measurement situation, this variability has to
be considered as a contribution to the attenuation measurement uncertainty of such a set-up.
The following contributions, as shown in Table 3 and in Figure A.1 have been determined as a
function of reference connector grade.
Table 3 – Measurement un
...