SIST EN IEC 61757:2026

SLOVENSKI STANDARD
01-junij-2026
Nadomešča:
SIST EN IEC 61757-1:2018
Optični senzorji - Splošna specifikacija (IEC 61757:2026)
Fibre optic sensors - Generic specification (IEC 61757:2026)
LWL-Sensoren - Fachgrundspezifikation (IEC 61757:2026)
Capteurs à fibres optiques - Spécification générique (IEC 61757:2026)
Ta slovenski standard je istoveten z: EN IEC 61757:2026
ICS:
33.180.99 Druga oprema za optična Other fibre optic equipment
vlakna
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61757

NORME EUROPÉENNE
EUROPÄISCHE NORM April 2026
ICS 33.180.99 Supersedes EN IEC 61757:2018
English Version
Fibre optic sensors - Generic specification
(IEC 61757:2026)
Capteurs fibroniques - Spécification générique LWL-Sensoren - Fachgrundspezifikation
(IEC 61757:2026) (IEC 61757:2026)
This European Standard was approved by CENELEC on 2026-04-09. 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61757:2026 E
European foreword
The text of document 86C/2008/FDIS, future edition 2 of IEC 61757, prepared by SC 86C "Fibre optic
systems, sensing and active devices" of IEC/TC 86 "Fibre optics" was submitted to the IEC-CENELEC
parallel vote and approved by CENELEC as EN IEC 61757:2026.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-04-30
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-04-30
document have to be withdrawn
This document supersedes EN IEC 61757:2018 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61757:2026 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 standard indicated:
IEC 60060-1 NOTE Approved as EN IEC 60060-1
IEC 60654-4 NOTE Approved as EN 60654-4
IEC 60068-2-1 NOTE Approved as EN IEC 60068-2-1
IEC 60068-2-2 NOTE Approved as EN IEC 60068-2-2
IEC 60068-2-5 NOTE Approved as EN IEC 60068-2-5
IEC 60068-2-6 NOTE Approved as EN 60068-2-6
IEC 60068-2-10 NOTE Approved as EN 60068-2-10
IEC 60068-2-11 NOTE Approved as EN IEC 60068-2-11
IEC 60068-2-13 NOTE Approved as EN IEC 60068-2-13
IEC 60068-2-14 NOTE Approved as EN IEC 60068-2-14
IEC 60068-2-27 NOTE Approved as EN 60068-2-27
IEC 60068-2-30 NOTE Approved as EN IEC 60068-2-30
IEC 60068-2-42 NOTE Approved as EN 60068-2-42
IEC 60068-2-43 NOTE Approved as EN 60068-2-43
IEC 60068-2-78 NOTE Approved as EN IEC 60068-2-78
IEC 60529 NOTE Approved as EN 60529
IEC 60793-1-20 NOTE Approved as EN 60793-1-20
IEC 60793-1-21 NOTE Approved as EN 60793-1-21
IEC 60793-1-31 NOTE Approved as EN IEC 60793-1-31
IEC 60793-1-32 NOTE Approved as EN IEC 60793-1-32
IEC 60793-1-47 NOTE Approved as EN IEC 60793-1-47
IEC 60793-1-54 NOTE Approved as EN IEC 60793-1-54
IEC 60794-1-21 NOTE Approved as EN 60794-1-21
IEC 60825 (series) NOTE Approved as EN IEC 60825 (series)
IEC 61000-4-2 NOTE Approved as EN IEC 61000-4-2
IEC 61000-4-3 NOTE Approved as EN IEC 61000-4-3
IEC 61000-4-4 NOTE Approved as EN 61000-4-4
IEC 61000-4-5 NOTE Approved as EN 61000-4-5
IEC 61300 (series) NOTE Approved as EN 61300 (series)
IEC 61300-2-1 NOTE Approved as EN IEC 61300-2-1
IEC 61300-2-9 NOTE Approved as EN 61300-2-9
IEC 61300-2-18 NOTE Approved as EN IEC 61300-2-18
IEC 61300-2-22 NOTE Approved as EN IEC 61300-2-22
IEC 61300-2-34 NOTE Approved as EN IEC 61300-2-34
IEC 61300-2-46 NOTE Approved as EN IEC 61300-2-46
IEC 61757 (series) NOTE Approved as EN IEC 61757 (series)
IEC 62368 (series) NOTE Approved as EN IEC 62368 (series)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where 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.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60068-1 - Environmental testing - Part 1: General EN 60068-1 -
and guidance
IEC 60079-28 - Explosive atmospheres - Part 28: EN IEC 60079-28 -
Protection of equipment and transmission
systems using optical radiation
IEC 60825-1 - Safety of laser products - Part 1: EN 60825-1 -
Equipment classification and requirements
IEC 60825-2 - Safety of laser products - Part 2: Safety of - -
optical fibre communication systems
(OFCSs)
IEC 61300-3-35 - Fibre optic interconnecting devices and EN IEC 61300-3-35 -
passive components - Basic test and
measurement procedures - Part 3-35:
Examinations and measurements - Visual
inspection of fibre optic connectors and
fibre-stub transceivers
IEC 61753 series Fibre optic interconnecting devices and EN IEC 61753 series
passive components - Performance
standard
IEC/TR 61931 - Fibre optic - Terminology - -
IEC/TR 62627-01 - Fibre optic interconnecting devices and - -
passive components - Part 01: Fibre optic
connector cleaning methods
ISO/IEC Guide 99 - International vocabulary of metrology - - -
Basic and general concepts and
associated terms (VIM)
IEC 61757 ®
Edition 2.0 2026-03
INTERNATIONAL
STANDARD
Fibre optic sensors - Generic specification

ICS 33.180.99  ISBN 978-2-8327-1072-2

IEC 61757:2026-03(en)
IEC 61757:2026 © IEC 2026
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
3.1 Fibre optic sensor principles . 9
3.2 Fibre optic sensor performance parameters . 15
3.3 Interfaces. 19
4 Abbreviated terms . 19
5 Quality assurance . 19
6 Test and measurement procedures . 20
6.1 General . 20
6.2 Standard conditions for testing . 20
6.3 Test and measurement equipment requirements . 20
6.4 Visual inspection . 21
6.5 Dimensions and weight . 21
6.6 Metrological properties . 21
6.6.1 General . 21
6.6.2 Metrological parameters . 21
6.7 Optical tests . 22
6.7.1 General . 22
6.7.2 Optical power . 22
6.7.3 Nominal wavelength and appropriate spectral characteristics . 22
6.7.4 State of polarization . 22
6.7.5 Fibre connector performance . 22
6.8 Electrical tests . 22
6.8.1 General . 22
6.8.2 Parameters and test procedures . 22
6.8.3 Voltage stress . 23
6.9 Mechanical tests . 23
6.9.1 General . 23
6.9.2 Parameters and test procedures . 23
6.10 Climatic and environmental tests . 24
6.10.1 General . 24
6.10.2 Parameters and test procedures . 24
6.11 Susceptibility to ambient light . 25
6.12 Resistance to solvents and contaminating fluids . 25
7 Classification . 25
7.1 General . 25
7.2 Measurand . 26
7.2.1 General . 26
7.2.2 Presence or absence of objects or features . 26
7.2.3 Position . 26
7.2.4 Rate of positional change . 26
7.2.5 Flow . 26
7.2.6 Temperature . 27
IEC 61757:2026 © IEC 2026
7.2.7 Force per directional vector . 27
7.2.8 Force per area . 27
7.2.9 Strain . 27
7.2.10 Electromagnetic quantities . 27
7.2.11 Ionizing and nuclear radiation . 27
7.2.12 Other physical properties of materials . 27
7.2.13 Composition and specific chemical quantities . 27
7.2.14 Particulates . 27
7.3 Transduction principle . 27
7.3.1 General . 27
7.3.2 Active generation of light . 27
7.3.3 Atom-field interaction . 28
7.3.4 Coherence modulation . 28
7.3.5 Intensity modulation. 28
7.3.6 Optical spectrum modulation. 28
7.3.7 Phase modulation . 28
7.3.8 Polarization modulation . 28
7.4 Spatial distribution . 28
7.5 Interface level . 28
8 Marking, labelling, packaging and instruction manual . 29
8.1 Marking of component . 29
8.2 Marking of sealed package and instruction manual . 29
9 IEC type designation . 29
10 Safety aspects . 29
10.1 General . 29
10.2 Personal safety . 29
10.3 Safety in explosive environment . 30
11 Ordering information . 30
12 Drawings . 30
Annex A (informative) Examples of fibre optic sensors . 31
A.1 General . 31
A.2 Presence or absence of objects or features . 31
A.2.1 Level . 31
A.2.2 Proximity . 31
A.2.3 Photo interruption . 31
A.3 Position . 31
A.3.1 End position . 31
A.3.2 Linear position . 32
A.3.3 Angular position . 32
A.3.4 Proximity . 32
A.3.5 Zone (area) . 32
A.3.6 Dimensional . 32
A.4 Rate of positional change . 32
A.4.1 Linear speed or velocity . 32
A.4.2 Rotational speed or velocity . 32
A.4.3 Gyroscope . 33
A.4.4 Linear acceleration . 33
A.4.5 Rotational acceleration . 33
IEC 61757:2026 © IEC 2026
A.5 Flow . 33
A.6 Temperature . 33
A.7 Force per directional vector . 34
A.7.1 Seismic . 34
A.7.2 Vibration . 34
A.7.3 Torque . 34
A.7.4 Weight and mass . 34
A.8 Force per area . 34
A.8.1 Acoustic . 34
A.8.2 Pressure . 34
A.9 Strain . 35
A.10 Electromagnetic quantities . 36
A.10.1 Magnetic field . 36
A.10.2 Electrical current . 36
A.10.3 Electric field. 36
A.10.4 Voltage . 37
A.10.5 Electromagnetic radiation . 37
A.11 Ionizing and nuclear radiation . 37
A.12 Other physical properties of materials . 37
A.12.1 Material refractive index . 37
A.12.2 Density . 37
A.12.3 Viscosity . 37
A.12.4 Damage . 37
A.13 Composition and specific chemical quantities . 38
A.14 Particulates . 38
A.14.1 Count . 38
A.14.2 Atomic . 38
A.14.3 Turbidity . 38
A.15 Spatial distribution . 38
A.15.1 Single point . 38
A.15.2 Multiple point . 38
A.15.3 Integrating . 38
A.15.4 Distributed . 39
Bibliography . 40

Figure 1 – Fibre optic sensor in transmittance configuration with a passive fibre
sensing element and separate fibre leads for optical input and output . 9
Figure 2 – Fibre optic sensor in reflectance configuration with a passive sensing
element and separate fibre leads for optical input and output . 10
Figure 3 – Fibre optic sensor with an optical radiation-generating sensing element and
separate fibre lead for optical output . 10
Figure 4 – Fibre optic sensor with an optical radiation-generating sensing fibre and
separate fibre lead for optical output . 11
Figure 5 – Fibre optic sensor in backscattering configuration with a passive fibre
sensing element and one fibre lead for optical input and output . 11
Figure 6 – Distributed fibre optic sensor in loop configuration . 12
Figure 7 – Multiple point fibre optic sensor in backscattering configuration . 13
Figure 8 – Single point fibre optic sensor in backscattering configuration . 14
IEC 61757:2026 © IEC 2026
Table 1 – Electrical test parameters and procedures . 23
Table 2 – Mechanical test parameters and procedures . 24
Table 3 – Climatic and environmental test parameters and procedures . 25

IEC 61757:2026 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Fibre optic sensors - 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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 61757 has been prepared by subcommittee 86C: Fibre optic systems, sensing and active
devices, of IEC technical committee 86: Fibre optics. It is an International Standard.
This second edition cancels and replaces the first edition published in 2018. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) expansion of the list of metrological parameters;
b) updates of the terms and definitions;
c) updates of the normative references and bibliography;
d) updates of the technical descriptions in Annex A.
IEC 61757:2026 © IEC 2026
The text of this International Standard is based on the following documents:
Draft Report on voting
86C/2008/FDIS 86C/2011/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/publications.
A list of all parts in the IEC 61757 series, published under the general title Fibre optic sensors,
can be found on the IEC website.
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, or
– revised.
IEC 61757:2026 © IEC 2026
INTRODUCTION
A fibre optic sensor comprises an optical or optically powered sensing element in which incident
light is modified by the measurand in such a way that the output light of the sensing element
carries quantifiable information on the measurand. The sensing element can be the fibre itself
or an optically powered element inserted along the optical path. In a fibre optic sensor, one or
more parameters of the guided optical waves are directly or indirectly modified by the
measurand somewhere in the optical sensing element, in contrast to a fibre optic data link where
the optical information signal is merely transmitted from the transmitter to the receiver.
This document provides generic specifications on optical fibres, components, and sub-
assemblies that pertain specifically to fibre optic sensing applications. It is intended to be used
as a common working and discussion tool by the vendors of components and subassemblies
that are integrated in fibre optic sensors, as well as by designers, manufacturers, and users of
fibre optic sensors, independent of specific applications or installations. The individual parts of
the IEC 61757 series are numbered as IEC 61757-M-T, where M denotes the measurand and T
the technology of the fibre optic sensor.
To better illustrate this classification scheme, Annex A gives examples of various fibre optic
sensors. The examples are provided for illustration only and are not intended to be limitative,
nor do they constitute a recommendation or endorsement of a particular transduction principle.

IEC 61757:2026 © IEC 2026
1 Scope
This document defines, classifies, and provides a framework of generic tests or measurement
methods for characterizing and specifying fibre optic sensors, including their specific
components and subassemblies. The requirements of this document apply to all related fibre
optic sensor standards that are part of the IEC 61757 series. Other parts of the IEC 61757
series contain requirements that are specific to sensors that measure particular quantities, and
to a particular style or variant of such a fibre optic sensor.
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 60068-1, Environmental testing - Part 1: General and guidance
IEC 60079-28, Explosive atmospheres - Part 28: Protection of equipment and transmission
systems using optical radiation
IEC 60825-1, Safety of laser products - Part 1: Equipment classification and requirements
IEC 60825-2, Safety of laser products - Part 2: Safety of optical fibre communication systems
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 61753 (all parts), Fibre optic interconnecting devices and passive components -
Performance standard
IEC TR 61931, Fibre optic - Terminology
IEC TR 62627-01, Fibre optic interconnecting devices and passive components - Part 01: Fibre
optic connector cleaning methods
ISO/IEC Guide 99, International vocabulary of metrology - Basic and general concepts and
associated terms (VIM)
3 Terms and definitions
For the purpose of this document, the terms and definitions given in IEC TR 61931,
ISO/IEC Guide 99 (VIM), and the following 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
IEC 61757:2026 © IEC 2026
3.1 Fibre optic sensor principles
3.1.1
fibre optic sensor
part of a measuring instrument, or measuring chain, which is directly affected by the measurand,
and which generates a change in the optical characteristics of an optical fibre related to the
value of the measurand
Note 1 to entry: The optical fibre itself can act as the sensing element, or the fibre optic sensor can include an
optical or optically powered sensing element and one or more of the following (see Figure 1, Figure 2, Figure 3,
Figure 4 and Figure 5):
– optical fibre lead;
– optical fibre termination;
– optical signal conditioning.
[SOURCE: IEC 60050-311:2001,311-05-01, modified – in the term entry, “fibre optic” has been
added. In the definition, “signal” has been replaced by “change in the optical characteristics of
an optical fibre”. Note 1 to entry has been added.]

Key
1 Light source
2 Optical fibre lead
3 Optical or optically powered fibre sensing element
4 Measurand or phenomenon that is detected
5 Optical fibre lead
6 Optical receiver
7 Optical fibre splice or connection
Figure 1 – Fibre optic sensor in transmittance configuration with a passive fibre
sensing element and separate fibre leads for optical input and output
IEC 61757:2026 © IEC 2026
Key
1 Light source
2 Optical fibre lead
3 Optical or optically powered sensing element
4 Measurand or phenomenon that is detected
5 Optical fibre lead
6 Optical receiver
7 Optical fibre splice or connection
Figure 2 – Fibre optic sensor in reflectance configuration with a passive sensing
element and separate fibre leads for optical input and output

Key
1 Measurand or phenomenon that is detected (e.g. high-energy electromagnetic radiation)
2 Optical radiation-generating sensing element (e.g. scintillator crystal)
3 Optical fibre lead
4 Optical receiver
5 Optical fibre splice or connection
Figure 3 – Fibre optic sensor with an optical radiation-generating
sensing element and separate fibre lead for optical output
IEC 61757:2026 © IEC 2026
Key
1 Fibre termination
2 Measurand or phenomenon that is detected (e.g. high-energy electromagnetic radiation)
3 Optical radiation-generating sensing fibre (e.g. scintillating fibre)
4 Optical fibre lead
5 Optical receiver
6 Optical fibre splice or connection
Figure 4 – Fibre optic sensor with an optical radiation-generating
sensing fibre and separate fibre lead for optical output

Key
1 Light source and optical receiver (e.g. optical time domain reflectometer (OTDR))
2 Optical fibre lead
3 Measurand or phenomenon that is detected
4 Optical or optically powered sensing element
5 Fibre termination
6 Optical fibre splice or connection
Figure 5 – Fibre optic sensor in backscattering configuration with a passive fibre
sensing element and one fibre lead for optical input and output
3.1.2
distributed fibre optic sensor
fibre optic sensor which provides a spatially resolved measurement of a measurand over an
extended region by means of a continuous sensing element
Note 1 to entry: An example of a distributed fibre optic sensor in loop configuration is shown in Figure 6.
IEC 61757:2026 © IEC 2026
Key
1 Interrogation unit (see 3.1.8)
2 Front panel output connector
3 Optical fibre lead
4 Measurand or phenomenon that is detected spatially resolved
5 Continuous optical fibre sensing element
6 Optical fibre lead
7 Front panel input connector
8 Optical fibre splice or connection
NOTE Distributed fibre optic sensor single-ended configuration is also possible (see Figure 5).
Figure 6 – Distributed fibre optic sensor in loop configuration
3.1.3
extrinsic fibre optic sensor
fibre optic sensor in which the characteristics of the light are affected externally to the optical
fibre(s) by the measurand
3.1.4
integrating fibre optic sensor
fibre optic sensor which provides a measurement result of a measurand over an extended
region by means of a continuous sensing element of a defined length
Note 1 to entry: The measurand is not spatially resolved but is integrated or summed over the length of the sensing
element.
3.1.5
intrinsic fibre optic sensor
fibre optic sensor whose sensing element consists of one or more optical fibre(s) in which one
or more characteristics like intensity, phase, polarization, spectrum, wavelength or transit time
of light depend on the measurand
Note 1 to entry: There are fibre optic sensors where the sensing principle is based on a change in coating
characteristics only (e.g. chemical or humidity sensors) or on an interaction between core and cladding (e.g. bending
sensor). They can be defined as indirect intrinsic fibre optic sensors. Direct intrinsic fibre optic sensors are based
on a direct change of the fibre core characteristics (e.g. Brillouin, Raman or Rayleigh scattering based sensors).
3.1.6
multiple point fibre optic sensor
fibre optic sensor consisting of a number of single point fibre optic sensors which enables a
spatially resolved measurement of a measurand over an extended region at discrete locations
Note 1 to entry: An example of a multiple point fibre optic sensor in backscattering configuration is shown in Figure 7.
IEC 61757:2026 © IEC 2026
Key
1 Signal processor
2 Pulse generator
3 Laser diode
4 Optical splitter
5 Optical attenuator (optional)
6 Optical fibre lead
7 Measurand or phenomenon that is detected
8 Multiple optical or optically powered single point sensing elements
9 Fibre termination
10 Optical attenuator (optional)
11 Photo diode
12 Amplifier and converter
13 Control and display
14 Optical time domain reflectometer (OTDR)
15 Optical fibre splice or connection
NOTE Multiple point fibre optic sensors in transmission configuration are also possible.
Figure 7 – Multiple point fibre optic sensor in backscattering configuration
3.1.7
single point fibre optic sensor
fibre optic sensor consisting of one discrete sensing element which generates a signal related
to the value of the measurand
Note 1 to entry: An example of a single point fibre optic sensor in backscattering configuration is shown in Figure 8.
IEC 61757:2026 © IEC 2026
Key
1 Signal processor
2 Pulse generator
3 Laser diode
4 Optical splitter
5 Optical attenuator (optional)
6 Optical fibre lead
7 Measurand or phenomenon that is detected
8 Optical or optically powered single point sensing element
9 Fibre termination
10 Optical attenuator (optional)
11 Photo diode
12 Amplifier and converter
13 Control and display
14 Optical time domain reflectometer (OTDR)
15 Optical fibre splice or connection
Figure 8 – Single point fibre optic sensor in backscattering configuration
3.1.8
interrogation unit
IU
opto-electronic instrument intended to be used to make measurements in conjunction with a
fibre optic sensor
Note 1 to entry: The interrogation unit comprises at least a light source that supplies optical energy to the sensor
(see 3.1.9) and an optical receiver (see 3.1.13) that receives the light affected by the measurand in the fibre sensor.
It often also incorporates additional elements for optical or electrical signal processing (e.g. arrayed-waveguide
gratings or high-speed data acquisition units), or both, and for data archiving. Some of these functions can be
implemented in a separate unit that is connected to the IU. The IU, either by itself or in combination with other
connected units, provides signal processing functions (standardized or customized) and possibly data archiving
(usually standardized). It also provides a user interface to control and "set" the measuring parameters, select
processing options, and define and implement the data collection options (triggered, timed, or other).
Note 2 to entry: The term “interrogation unit” is commonly used in conjunction with sensors using fibre Bragg
gratings and with distributed fibre optic sensors.
3.1.9
light source
device which supplies the optical energy required to allow the interaction between the sensing
element and the measurand
Note 1 to entry: It contains, as a minimum, a luminous source and it can contain signal conditioning. When the
optical energy is generated by the phenomenon sensed, a light source is not required.
IEC 61757:2026 © IEC 2026
3.1.10
optical sensing element
optically powered sensing element
device which accepts information in the form of a physical quantity and converts it to information
in the form of an optical quantity, according to a definite physical law
3.1.11
optical fibre
filament-shaped waveguide made of dielectric materials for gui
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