SIST EN 61202-1:2017

Fibre optic interconnecting devices and passive components - Fibre optic isolators - Part 1: Generic specification (IEC 61202-1:2016)

This part of IEC 61202 applies to isolators used in the field of fibre optics, all exhibiting the
following features:
• they are non-reciprocal optical devices, in which each port is either an optical fibre or fibre
optic connector;
• they are passive devices containing no opto-electronic or other transducing elements;
• they have two optical ports for directionally transmitting optical power.

Lichtwellenleiter - Verbindungselemente und passive Bauteile - Lichtwellenleiter-Isolatoren - Teil 1: Fachgrundspezifikation (IEC 61202-1:2016)

Dispositifs d'interconnexion et composants passifs à fibres optiques - Isolateurs à fibres optiques - Partie 1: Spécification générique (IEC 61202-1:2016)

IEC 61202-1:2016 s’applique aux isolateurs utilisés dans le domaine fibronique, possédant tous les caractéristiques suivantes:
- ce sont des dispositifs optiques non réciproques, dans lesquels chaque port est soit une fibre optique soit un connecteur fibronique;
- ce sont des dispositifs passifs qui ne contiennent pas d’éléments optoélectroniques ou d’autres éléments transducteurs;
- ils ont deux ports optiques pour les puissances optiques à émission directionnelle.
Cette quatrième édition annule et remplace la troisième édition parue en 2009. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- les termes et les définitions ont été revus;
- le niveau d’évaluation de la qualité a été supprimé de la classification;
- les numéros d'article des Annexes A et B ont été réagencés.
Mots clés: isolateurs utilisés dans le domaine fibronique

Optični spojni elementi in pasivne komponente - Optični izolatorji - 1. del: Rodovna specifikacija (IEC 61202-1:2016)

Ta del standarda IEC 61202 se uporablja za izolatorje, ki se uporabljajo za optična vlakna in imajo naslednje lastnosti:
• so nerecipročne optične naprave, v katerih so vsaka vrata optično vlakno ali optični konektor;
• so pasivne naprave, ki ne vsebujejo optoelektronskih ali drugih prevodnih elementov;
• imajo dvojna optična vrata za usmerjen prenos optične moči.

General Information

• Status: Published
• Publication Date: 05-Apr-2017
• ICS: 33.180.20 - Fibre optic interconnecting devices
• Technical Committee: MOC - Mobile Communications
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 29-Mar-2017
• Due Date: 03-Jun-2017
• Completion Date: 06-Apr-2017
• Ref Project: EN 61202-1:2017 - Fibre optic interconnecting devices and passive components - Fibre optic isolators - Part 1: Generic specification

Relations

• Replaces: SIST EN 61202-1:2009 - Fibre optic interconnecting devices and passive components - Fibre optic isolators - Part 1: Generic specification (IEC 61202-1:2009)
• Effective Date: 28-Mar-2017

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 61202-1:2017
01-maj-2017
1DGRPHãþD
SIST EN 61202-1:2009
2SWLþQLVSRMQLHOHPHQWLLQSDVLYQHNRPSRQHQWH2SWLþQLL]RODWRUMLGHO
5RGRYQDVSHFLILNDFLMD,(&
Fibre optic interconnecting devices and passive components - Fibre optic isolators - Part
1: Generic specification (IEC 61202-1:2016)
Lichtwellenleiter - Verbindungselemente und passive Bauteile - Lichtwellenleiter-
Isolatoren - Teil 1: Fachgrundspezifikation (IEC 61202-1:2016)
Dispositifs d'interconnexion et composants passifs à fibres optiques - Isolateurs à fibres
optiques - Partie 1: Spécification générique (IEC 61202-1:2016)
Ta slovenski standard je istoveten z: EN 61202-1:2017
ICS:
33.180.20 3RYH]RYDOQHQDSUDYH]D Fibre optic interconnecting
RSWLþQDYODNQD devices
SIST EN 61202-1:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN 61202-1:2017

---------------------- Page: 2 ----------------------

SIST EN 61202-1:2017


EUROPEAN STANDARD EN 61202-1

NORME EUROPÉENNE

EUROPÄISCHE NORM
March 2017
ICS 33.180.20 Supersedes EN 61202-1:2009
English Version
Fibre optic interconnecting devices and passive components -
Fibre optic isolators - Part 1: Generic specification
(IEC 61202-1:2016)
Dispositifs d'interconnexion et composants passifs à fibres Lichtwellenleiter - Verbindungselemente und passive
optiques - Isolateurs à fibres optiques - Bauteile - Lichtwellenleiter-Isolatoren -
Partie 1: Spécification générique Teil 1: Fachgrundspezifikation
(IEC 61202-1:2016) (IEC 61202-1:2016)
This European Standard was approved by CENELEC on 2017-01-12. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.


European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN 61202-1:2017 E

---------------------- Page: 3 ----------------------

SIST EN 61202-1:2017
EN 61202-1:2017
European foreword
The text of document 86B/3989A/CDV, future edition 4 of IEC 61202-1, prepared by SC 86B ”Fibre
optic interconnecting devices and passive components” of IEC/TC 86 “Fibre optics" was submitted to
the IEC-CENELEC parallel vote and approved by CENELEC as EN 61202-1:2017.

The following dates are fixed:
(dop) 2017-10-12
• latest date by which the document has to be
implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2018-01-12
standards conflicting with the
document have to be withdrawn

This document supersedes EN 61202-1:2009.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.

Endorsement notice
The text of the International Standard IEC 61202-1:2016 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60068 Series NOTE Harmonized as EN 60068 Series.
IEC 60869-1 NOTE Harmonized as EN 60869-1.
IEC 60874-1 NOTE Harmonized as EN 60874-1.
IEC 61073-1 NOTE Harmonized as EN 61073-1.
IEC 61753 Series NOTE Harmonized as EN 61753 Series.
IEC 61754 Series NOTE Harmonized as EN 61754 Series.
IEC 62005 Series NOTE Harmonized as EN 62005 Series.
2

---------------------- Page: 4 ----------------------

SIST EN 61202-1:2017
EN 61202-1:2017
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

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.

NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu

Publication Year Title EN/HD Year

IEC 60027 Series Letter symbols to be used in electrical EN 60027 Series
technology
IEC 60050-731 -  International Electrotechnical Vocabulary - - -
Chapter 731: Optical fibre communication
IEC 60617-DB -  Graphical symbols for diagrams - -
IEC 60695 Series Fire hazard testing EN 60695-10 Series
IEC 60825-1 -  Safety of laser products - EN 60825-1 -
Part 1: Equipment classification and
requirements
IEC 61300 Series Fibre optic interconnecting devices and EN 61300 Series
passive components - Basic test and
measurement procedures
IEC/TS 62627-09 -  Fibre optic interconnecting devices and - -
passive components - Vocabulary for
passive optical devices
ISO 129-1 -  Technical drawings - Indication of - -
dimensions and tolerances -
Part 1: General principles
ISO 286-1 -  Geometrical product specifications (GPS) - EN ISO 286-1 -
ISO code system for tolerances on linear
sizes -
Part 1: Basis of tolerances, deviations and
fits
ISO 1101 -  Geometrical product specifications (GPS) - EN ISO 1101 -
Geometrical tolerancing - Tolerances of
form, orientation, location and run-out
ISO 8601 -  Data elements and interchange formats - - -
Information interchange - Representation
of dates and times

3

---------------------- Page: 5 ----------------------

SIST EN 61202-1:2017

---------------------- Page: 6 ----------------------

SIST EN 61202-1:2017




IEC 61202-1

®


Edition 4.0 2016-12




INTERNATIONAL



STANDARD








colour

inside










Fibre optic interconnecting devices and passive components – Fibre optic

isolators –

Part 1: Generic specification

























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 33.180.20 ISBN 978-2-8322-3681-9



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


® Registered trademark of the International Electrotechnical Commission

---------------------- Page: 7 ----------------------

SIST EN 61202-1:2017
– 2 – IEC 61202-1:2016 © IEC 2016
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
3.1 Basic terms and definitions . 7
3.2 Component terms and definitions . 7
3.3 Performance parameter terms and definitions . 8
4 Requirements . 10
4.1 Classification . 10
4.1.1 General . 10
4.1.2 Type . 10
4.1.3 Style . 11
4.1.4 Variant . 11
4.1.5 Normative reference extensions. 11
4.2 Documentation . 12
4.2.1 Symbols . 12
4.2.2 Specification system . 12
4.2.3 Drawings . 13
4.2.4 Tests and measurements . 13
4.2.5 Test data sheets . 14
4.2.6 Instructions for use . 14
4.3 Standardization system . 14
4.3.1 Interface standards . 14
4.3.2 Performance standards . 14
4.3.3 Reliability standards . 14
4.3.4 Interlinking . 15
4.4 Design and construction . 16
4.4.1 Materials . 16
4.4.2 Workmanship . 16
4.5 Performance requirements . 16
4.6 Identification and marking . 17
4.6.1 General . 17
4.6.2 Variant identification number . 17
4.6.3 Component marking . 17
4.6.4 Package marking . 17
4.7 Packaging . 18
4.8 Storage conditions . 18
4.9 Safety . 18
Annex A (informative) Example of technology of bulk isolator based on magneto-optic
effect . 19
A.1 General . 19
A.2 Faraday rotator . 19
A.3 Analyser . 19
A.4 Birefringent crystal . 19

---------------------- Page: 8 ----------------------

SIST EN 61202-1:2017
IEC 61202-1:2016 © IEC 2016 – 3 –
Annex B (informative) Example of technology of optical waveguide isolator . 22
B.1 General . 22
B.2 TE mode . 22
B.3 TM mode . 22
Bibliography . 24

Figure 1 – Configuration A – Device containing integral fibre optic pigtails without
connector . 11
Figure 2 – Configuration B – Device containing integral fibre optic pigtails, with a
connector on each pigtail . 11
Figure 3 – Configuration C – Device containing connectors as an integral part of the
device housing . 11
Figure 4 – Configuration D – Device containing some combination of the interfacing
features of the preceding configurations . 11
Figure 5 – Standards currently under preparation . 16
Figure A.1 – Polarization dependent optical isolator . 20
Figure A.2 – Polarization independent optical isolator . 21
Figure B.1 – Mode conversion type of the optical waveguide isolator . 22
Figure B.2 – Phase shifter type of the optical waveguide isolator . 23
Figure B.3 – TE mode and TM mode for optical waveguide isolator . 23

Table 1 – Two-level IEC specification structure . 12
Table 2 – Standards interlink matrix . 16

---------------------- Page: 9 ----------------------

SIST EN 61202-1:2017
– 4 – IEC 61202-1:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

FIBRE OPTIC INTERCONNECTING DEVICES
AND PASSIVE COMPONENTS –
FIBRE OPTIC ISOLATORS –

Part 1: Generic specification

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
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
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.
International Standard IEC 61202-1 has been prepared by subcommittee 86B: Fibre optic
interconnecting devices and passive components, of IEC technical committee 86: Fibre optics.
This fourth edition cancels and replaces the third edition published in 2009. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the terms and definitions were reconsidered;
b) quality assessment level was deleted from classification;
c) the clause numbers of Annexes A and B have been rearranged.

---------------------- Page: 10 ----------------------

SIST EN 61202-1:2017
IEC 61202-1:2016 © IEC 2016 – 5 –
The text of this International Standard is based on the following documents:
CDV Report on voting
86B/3989A/CDV 86B/4033RVC

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 61202 series, published under the general title Fibre optic
interconnecting devices and passive components – Fibre optic isolators, can be found on the
IEC website.
A bilingual version of this publication may be issued at a later date.
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.

---------------------- Page: 11 ----------------------

SIST EN 61202-1:2017
– 6 – IEC 61202-1:2016 © IEC 2016
FIBRE OPTIC INTERCONNECTING DEVICES
AND PASSIVE COMPONENTS –
FIBRE OPTIC ISOLATORS –

Part 1: Generic specification



1 Scope
This part of IEC 61202 applies to isolators used in the field of fibre optics, all exhibiting the
following features:
• they are non-reciprocal optical devices, in which each port is either an optical fibre or fibre
optic connector;
• they are passive devices containing no opto-electronic or other transducing elements;
• they have two optical ports for directionally transmitting optical power.
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 60027 (all parts), Letter symbols to be used in electrical technology
IEC 60050-731, International Electrotechnical Vocabulary – Chapter 731: Optical fibre
communication
IEC 60617 (all parts), Graphical symbols for diagrams (available at http://std.iec.ch/iec60617)
IEC 60695 (all parts), Fire hazard testing
IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 61300 (all parts), Fibre optic interconnecting devices and passive components – Basic
test and measurement procedures
IEC TS 62627-09, Fibre optic interconnecting devices and passive components – Vocabulary
for passive optical devices
ISO 129-1, Technical drawings – Indication of dimensions and tolerances – Part 1: General
principles
ISO 286-1, Geometrical product specification (GPS) – ISO code system for tolerances on
linear sizes – Part 1: Bases of tolerances, deviations and fits
ISO 1101, Geometrical product specifications (GPS) – Geometrical tolerancing – Tolerances
of form, orientation, location and run-out
ISO 8601, Data elements and interchange formats – Information interchange –
Representation of dates and times

---------------------- Page: 12 ----------------------

SIST EN 61202-1:2017
IEC 61202-1:2016 © IEC 2016 – 7 –
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-731,
IEC TS 62627-09 and the following apply.
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 Basic terms and definitions
3.1.1
port
optical fibre or fibre optic connector attached to a passive component for the entry and/or exit
of the optical power
3.1.2
input port
port for the entry of optical power
Note 1 to entry: An isolator is a directional device. The input port should be clearly marked.
3.1.3
output port
port for the exit of optical power
Note 1 to entry: An isolator is a directional device. The output port should be clearly marked.
3.1.4
backward direction
operational direction in which the power of the optical source launches into
the output port of an isolator
Note 1 to entry: This is the direction of optical power isolation.
3.1.5
forward direction
operational direction in which the power of the optical source launches into
the input port of an isolator
Note 1 to entry: This is the intentional direction of optical power transmission.
3.2 Component terms and definitions
3.2.1
fibre optic isolator
non-reciprocal optical device intended to suppress backward reflections along an optical fibre
transmission line while having minimum insertion loss in the forward direction
Note 1 to entry: Fibre optic isolators are commonly used to avoid reflections back into laser diodes and optical
amplifiers, which can make the laser and amplifiers oscillations unstable, and cause noise in the fibre optic
transmission system.
3.2.2
bulk isolator based on magneto-optic effect
type of isolator with discrete components including a suitable magneto-optic crystal (ferro-
magnetic crystal or paramagnetic glass, diamagnetic glass, etc.), of which the fundamental
principle is based on magneto-optic effect

---------------------- Page: 13 ----------------------

SIST EN 61202-1:2017
– 8 – IEC 61202-1:2016 © IEC 2016
Note 1 to entry: The technology of a bulk isolator based on magneto-optic effect is described in Annex A.
3.2.3
in-line isolator
type of isolator with optical fibre for the entry input and output of the light
3.2.4
optical waveguide isolator
type of isolator with planer epitaxial magneto-optic crystal layers on a suitable substrate
Note 1 to entry: The technology of an optical waveguide isolator is described in Annex B.
3.2.5
polarization-dependent optical isolator
type of isolator not designed to have performance independent of the state of the polarization
of the incident light
3.2.6
polarization-independent optical isolator
type of isolator in which the optical performance characteristics are independent of the
polarization state of the incident light
3.2.7
polarization maintaining optical isolator
type of isolator with a polarization maintaining optical fibre for input and output, designed to
maintain polarization of the light, and which is adjusted to the optical axis of the polarization
maintaining optical fibre
3.2.8
single-stage isolator
type of isolator composed of a basic isolator unit such as a set of polarizer, faraday rotator
and analyser
3.2.9
dual-stage isolator
double-stage isolator
type of isolator composed of two basic isolator units connected in tandem for the purpose of
obtaining more backward loss
3.2.10
PMD compensated optical isolator
type of isolator designed to compensate the polarization mode dispersion which is intrinsic to
the birefringent crystal
3.3 Performance parameter terms and definitions
3.3.1
operating wavelength
wavelength at which a passive optical component is designed to operate with the specified
performance
3.3.2
operating wavelength range
specified range of wavelengths including all operating wavelengths
Note 1 to entry: In the case of an optical isolator as nominally a wavelength independent and wavelength non-
selective device, passband is nominally same as operating wavelength range.

---------------------- Page: 14 ----------------------

SIST EN 61202-1:2017
IEC 61202-1:2016 © IEC 2016 – 9 –
3.3.3
insertion loss
maximum value of logarithmic transmission coefficient, a (where i ≠ j) within the passband for

ij
conducting port pair
Note 1 to entry: It is the optical attenuation from a given port to a port which is another port of conducting port
pair of the given port of a passive device. Insertion loss is a positive value in decibels. It is calculated as:
 
P
out
 
IL=−10log
10
 
P
 in

where
P is the optical power launched into the port;
in
P is the optical power received from the other port of the conducting port pair.
out
Note 2 to entry: In the case of an optical isolator as a non-reciprocal device, IL is defined as the maximum value
of attenuation from the input port to the output port.
Note 3 to entry: In the case of an optical isolator as nominally a wavelength independent and wavelength non-
selective device, passband is nominally same as operating wavelength range.
Note 4 to entry: In the case of a polarization-independent isolator, IL is defined as the maximum value for any
state of polarization of P .
in
Note 5 to entry: In the case of a polarization-dependent isolator, IL is defined as the linearly polarized light which
coincides with the polarizing direction of the polarizer in the isolator of P .
in
3.3.4
isolation
minimum value of a (where i ≠ j) for isolated port pair
ij
Note 1 to entry: In case of an optical isolator, isolation is the minimum attenuation value of backward direction.
Note 2 to entry: Isolation is a positive value expressed in dB.
3.3.5
polarization dependent loss
PDL
for polarization independent isolators, maximum variation of insertion loss caused by a
variation in the state of polarization (SOP) over all the SOPs.
3.3.6
polarization mode dispersion
PMD
for polarization-independent isolators, average delay of the travelling time between the two
principal states of polarization (PSP), when an optical signal passes through an optical
isolator
3.3.7
return loss
(where i = j) of the logarithmic transfer matrix
value of a
ij
Note 1 to entry: It is the fraction of input power that is returned from a port of a passive component and is defined
as follows:
 
P
refl
 
RL=−10log
i 10
 
P
i
 

where
P is the optical power launched into a port;
i
P is the optical power received back from the same port.
refl
Note 2 to entry: For an optical isolator, return loss is defined for the input port and the output port.

---------------------- Page: 15 ----------------------

SIST EN 61202-1:2017
– 10 – IEC
...