SIST EN IEC 60793-1-44:2023

Optical fibres - Part 1-44: Measurement methods and test procedures - Cut-off wavelength (IEC 60793-1-44:2023)

IEC 60793-1-44:2023 establishes uniform requirements for measuring the cut-off wavelength of single-mode optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes. This document gives methods for measuring the cut-off wavelength for uncabled or cabled single mode telecom fibre. These procedures apply to all category B and C fibre types. There are three methods of deployment for measuring the cut-off wavelength:
- method A: cable cut-off using uncabled fibre 22 m long sample, lcc;
- method B: cable cut-off using cabled fibre 22 m long sample, lcc;
- method C: fibre cut-off using uncabled fibre 2 m long sample, lc.
All methods require a reference measurement. There are two reference-scan techniques, either or both of which can be used with all methods:
- bend-reference technique;
- multimode-reference technique using category A1(OM1-OM5) multimode fibre.
This third edition cancels and replaces the second edition published in 2011. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) used the diameter of the fibre loops to describe deployment;
b) added Annex D related to cut-off curve artifacts;
c) reorganized information and added more figures to clarify concepts.

Lichtwellenleiter - Messmethoden und Prüfverfahren - Teil 1-44: Grenzwellenlänge (IEC 60793-1-44:2023)

Fibres optiques - Partie 1-44: Méthodes de mesure et procédures d'essai - Longueur d'onde de coupure (IEC 60793-1-44:2023)

IEC 60793-1-44: 2023 établit des exigences uniformes pour mesurer la longueur d’onde de coupure des fibres optiques unimodales, contribuant ainsi au contrôle des fibres et câbles dans des relations commerciales. Le présent document donne des méthodes de mesure de la longueur d’onde de coupure pour les fibres de télécommunications unimodales câblées ou non câblées. Ces procédures s’appliquent à tous les types de fibres de catégories B et C (voir Références normatives). Il existe trois méthodes de déploiement pour mesurer la longueur d’onde de coupure.
- méthode A: coupure en câble utilisant un échantillon de fibre non câblée de longueur 22 m, lcc;
- méthode B: coupure en câble utilisant un échantillon de fibre câblée de longueur 22 m, lcc;
- méthode C: coupure de fibre utilisant un échantillon de fibre non câblée de longueur 2 m, lc.
Toutes les méthodes exigent une mesure de référence. Il existe deux techniques d’exploration de référence, l’une et/ou l’autre peuvent être utilisées avec toutes les méthodes:
- technique de la fibre de référence par courbure;
- technique de la fibre de référence multimodale utilisant la fibre multimodale de catégorie A1 (OM1-OM5).
Cette troisième édition annule et remplace la deuxième édition parue en 2011. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) utilisation du diamètre des boucles de fibres pour décrire le déploiement
b) ajout de l’Annexe D, relative aux artefacts de courbe de coupure
c) réorganisation des informations et ajout de figures supplémentaires pour clarifier les concepts.

Optična vlakna - 1-44. del: Merilne metode in postopki preskušanja - Mejna valovna dolžina (IEC 60793-1-44:2023)

Standard IEC 60793-1-44:2023 določa enotne zahteve za merjenje mejne valovne dolžine enorodnih optičnih vlaken, pri čemer pomaga pri pregledu vlaken in kablov za komercialne namene. Za dokument podaja metode za merjenje mejne valovne dolžine za nekablirana ali kablirana enorodna telekomunikacijska vlakna. Ti postopki se uporabljajo za vlakna vrste B in C. Na voljo so tri metode za merjenje mejne valovne dolžine:
– metoda A: mejna valovna dolžina kabla z vzorcem nekabliranega vlakna dolžine 22 m, lcc;
– metoda B: mejna valovna dolžina kabla z vzorcem kabliranega vlakna dolžine 22 m, lcc;
– metoda C: mejna valovna dolžina vlakna z vzorcem nekabliranega vlakna dolžine 2 m, lc.
Pri vseh metodah je potrebna referenčna meritev. Obstajata dve tehniki referenčnega skeniranja, ki ju je mogoče posamično ali skupaj uporabiti z vsemi metodami:
– upogibna referenčna tehnika;
– večrodna referenčna tehnika, pri kateri se uporablja večrodno vlakno kategorije A1(OM1-OM5).
Tretja izdaja razveljavlja in nadomešča drugo izdajo, objavljeno leta 2011. Ta izdaja je tehnično popravljena izdaja. Ta izdaja v primerjavi s prejšnjo vključuje naslednje pomembne tehnične spremembe:
a) za opis uporabe je uporabljen premer optičnih zank;
b) dodan je dodatek D, povezan z artefakti mejne krivulje;
c) informacije so reorganizirane in dodanih je več slik za pojasnitev konceptov.

General Information

• Status: Published
• Public Enquiry End Date: 14-Sep-2022
• Publication Date: 11-Sep-2023
• ICS: 33.180.10 - Fibres and cables
• Technical Committee: MOC - Mobile Communications
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 06-Sep-2023
• Due Date: 11-Nov-2023
• Completion Date: 12-Sep-2023
• Ref Project: EN IEC 60793-1-44:2023 - Optical fibres - Part 1-44: Measurement methods and test procedures - Cut-off wavelength

Relations

• Revised: SIST EN 60793-1-44:2011 - Optical fibres - Part 1-44: Measurement methods and test procedures - Cut-off wavelength (IEC 60793-1-44:2011)
• Effective Date: 18-May-2021

Overview

EN IEC 60793-1-44:2023 specifies uniform measurement methods and test procedures for determining the cut-off wavelength of single‑mode optical fibre. Intended for both uncabled and cabled telecom fibres, the standard supports commercial inspection and acceptance testing by defining repeatable test deployments, reference measurements and analysis procedures. This third edition (2023) replaces the 2011 edition and introduces loop‑diameter deployment description, a new Annex D on cut‑off curve artifacts, and clearer figures and organization.

Key topics and requirements

• Scope: measurement of the cut‑off wavelength for single‑mode optical fibre, applicable to all category B and C fibre types.
• Three deployment methods:
  • Method A - cable cut‑off using uncabled fibre, 22 m sample (lcc).
  • Method B - cable cut‑off using cabled fibre, 22 m sample (lcc).
  • Method C - fibre cut‑off using uncabled fibre, 2 m sample (lc).
• Reference measurements: all methods require a reference scan using one or both techniques:
  • Bend‑reference technique (mode filtering by controlled bends)
  • Multimode‑reference technique using category A1 (OM1–OM5) multimode fibre
• Apparatus and test conditions: requirements for light source, modulation, launch and detection optics, deployment mandrels (loop diameters), cladding‑mode stripping and positioning.
• Data analysis: prescribed calculation methods, mapping functions and procedures to compute cut‑off wavelength; Annex D supplies guidance and a curve‑fitting technique to identify and mitigate cut‑off curve artifacts.

Applications

• Quality control and commercial acceptance of single‑mode fibres and finished cables.
• Manufacturers verifying fibre performance during production and final inspection.
• Independent test laboratories performing compliance testing and producing certificates.
• Telecommunications and network equipment suppliers validating fibre characteristics for design and procurement.
• Use cases include supplier acceptance testing, incoming inspection, production monitoring and failure analysis where accurate cut‑off determination is needed.

Who should use this standard

• Fibre manufacturers and cable assemblers
• Test and calibration laboratories
• Product quality and compliance engineers in telecoms
• R&D teams developing single‑mode fibre products

Related standards

• IEC/EN IEC 60793 series (general guidance and other measurement parts, e.g., IEC 60793‑1‑1)
• Other parts of the IEC 60793 family governing optical‑fibre measurement and specifications

EN IEC 60793-1-44:2023 is essential for consistent, reproducible cut‑off wavelength testing and helps ensure comparable acceptance criteria across suppliers and test labs.

Standards Content (Sample)

SLOVENSKI STANDARD
01-oktober-2023
Optična vlakna - 1-44. del: Merilne metode in postopki preskušanja - Mejna
valovna dolžina (IEC 60793-1-44:2023)
Optical fibres - Part 1-44: Measurement methods and test procedures - Cut-off
wavelength (IEC 60793-1-44:2023)
Lichtwellenleiter - Messmethoden und Prüfverfahren - Teil 1-44: Grenzwellenlänge (IEC
60793-1-44:2023)
Fibres optiques - Partie 1-44: Méthodes de mesure et procédures d'essai - Longueur
d'onde de coupure (IEC 60793-1-44:2023)
Ta slovenski standard je istoveten z: EN IEC 60793-1-44:2023
ICS:
33.180.10 (Optična) vlakna in kabli Fibres and cables
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60793-1-44

NORME EUROPÉENNE
EUROPÄISCHE NORM September 2023
ICS 33.180.10 Supersedes EN 60793-1-44:2011
English Version
Optical fibres - Part 1-44: Measurement methods and test
procedures - Cut-off wavelength
(IEC 60793-1-44:2023)
Fibres optiques - Partie 1-44: Méthodes de mesure et Lichtwellenleiter - Teil 1-44: Mess- und Prüfverfahren -
procédures d'essai - Longueur d'onde de coupure Grenzwellenlänge
(IEC 60793-1-44:2023) (IEC 60793-1-44:2023)
This European Standard was approved by CENELEC on 2023-08-28. 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
© 2023 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60793-1-44:2023 E

European foreword
The text of document 86A/2314/FDIS, future edition 3 of IEC 60793-1-44, prepared by SC 86A "Fibres
and cables" of IEC/TC 86 "Fibre optics" was submitted to the IEC-CENELEC parallel vote and
approved by CENELEC as EN IEC 60793-1-44:2023.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2024-05-28
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2026-08-28
document have to be withdrawn
This document supersedes EN 60793-1-44:2011 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 60793-1-44:2023 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 60793-1-40 NOTE Approved as EN IEC 60793-1-40
IEC 60793-2-10 NOTE Approved as EN IEC 60793-2-10
IEC 60793-2-50 NOTE Approved as EN IEC 60793-2-50
IEC 60793-2-60 NOTE Approved as EN 60793-2-60
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 60793-1-1 - Optical fibres - Part 1-1: Measurement EN IEC 60793-1-1 -
methods and test procedures - General
and guidance
IEC 60793-1-44 ®
Edition 3.0 2023-07
INTERNATIONAL
STANDARD
colour
inside
Optical fibres –
Part 1-44: Measurement methods and test procedures – Cut-off wavelength

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.10  ISBN 978-2-8322-7033-2

– 2 – IEC 60793-1-44:2023 © IEC 2023
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Background . 7
5 Overview of methods . 7
6 Reference test method . 8
7 Apparatus . 8
7.1 Light source . 8
7.2 Modulation . 8
7.3 Launch optics . 8
7.4 Support and positioning apparatus . 8
7.5 Deployment mandrel . 9
7.5.1 General . 9
7.5.2 Cable cut-off wavelength deployment, method A . 9
7.5.3 Cable cut-off wavelength deployment, method B . 9
7.5.4 Fibre cut-off wavelength deployment, method C. 9
7.6 Detection optics . 10
7.7 Detector assembly and signal detection electronics . 10
7.8 Cladding mode stripper . 10
8 Sampling specimen . 10
8.1 Specimen length . 10
8.2 Specimen end face . 10
9 Procedure . 11
9.1 Positioning of specimen in apparatus . 11
9.1.1 General requirements for all methods . 11
9.1.2 Deployment requirements for each method . 11
9.2 Measurement of output power . 11
9.2.1 Overview . 11
9.2.2 Bend-reference technique . 12
9.2.3 Multimode-reference technique . 12
10 Calculations . 12
10.1 Bend-reference technique . 12
10.2 Multimode-reference technique . 13
11 Mapping functions . 14
12 Results . 14
13 Specification information . 15
Annex A (normative) Requirements specific to method A – Cable cut-off wavelength,
λ
, using uncabled fibre . 16
cc
A.1 Specimen length . 16
A.2 Procedure – Position specimen on deployment mandrel . 16
Annex B (normative) Requirements specific to method B – Cable cut-off wavelength,
λ , using cabled fibre . 17
cc
B.1 Specimen length . 17
B.2 Procedure – Position specimen on deployment mandrel . 17

IEC 60793-1-44:2023 © IEC 2023 – 3 –
Annex C (normative) Requirements specific to method C – Fibre cut-off wavelength,λ . 18
c
C.1 Specimen length . 18
C.2 Procedure – Position specimen on deployment mandrel . 18
Annex D (informative) Cut-off curve artifacts . 20
D.1 Description of curve artifacts . 20
D.2 Curve-fitting technique for artifact filtering . 20
D.2.1 Overview . 20
D.2.2 General . 21
D.2.3 Step 1: define the upper wavelength region . 22
D.2.4 Step 2: characterize the spectral transmittance . 22
D.2.5 Step 3: calculate the deviation of the spectral transmittance from the
linear fit . 22
D.2.6 Step 4: determine the end wavelength of the transition region . 23
D.2.7 Step 5: determine the start wavelength of the transition region . 23
D.2.8 Step 6: characterize the transition region with the theoretical model . 23
D.2.9 Step 7: compute the cut-off wavelength, λ . 24
c
D.3 Fibre deployment method for artifact attenuation . 25
Bibliography . 27

Figure 1 – Cut-off measurement system block diagram . 7
Figure 2 – Deployment configuration for cable cut-off wavelength λ , method A . 9
cc
Figure 3 – Deployment configuration for cable cut-off wavelength λ , method B . 9
cc
Figure 4 – Standard deployment for fibre cut-off wavelength measurement . 10
Figure 5 – Cut-off wavelength using the bend-reference technique . 11
Figure 6 – Cut-off wavelength using the multimode-reference technique . 12
Figure 7 – Cable cut-off vs fibre cut-off for a specific fibre (multimode reference) . 14
Figure A.1 – Alternative cable cut-off deployment . 16
Figure C.1 – Alternative fibre cut-off deployment – Sliding semi-circle . 18
Figure C.2 – Alternative fibre cut-off deployment – Multi-bend . 19
Figure C.3 – Alternative fibre cut-off deployment – Large curve . 19
Figure D.1 – Cut-off curve with linear fit error (multimode reference) . 20
Figure D.2 – Fibre cut-off curve fitting technique (multimode reference) . 21
Figure D.3 – Curve fitting regions . 21
Figure D.4 – Fibre cut-off curve with artifacts (multimode reference) . 25
Figure D.5 – Fibre cut-off curve with artifacts (bend reference) . 25
Figure D.6 – Fibre deployment with large diameter bends for mode filtering . 26
Figure D.7 – Fibre cut-off curve with mode attenuation (multimode reference) . 26

– 4 – IEC 60793-1-44:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-44: Measurement methods and test procedures –
Cut-off wavelength
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.
IEC 60793-1-44 has been prepared by subcommittee 86A: Fibres and cables, of IEC technical
committee 86: Fibre optics. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) used the diameter of the fibre loops to describe deployment;
b) added Annex D related to cut-off curve artifacts;
c) reorganized information and added more figures to clarify concepts.

IEC 60793-1-44:2023 © IEC 2023 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
86A/2314/FDIS 86A/2327/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.
This document is to be read in conjunction with IEC 60793-1-1.
A list of all parts of the IEC 60793-1 series, published under the general title Optical fibres –
Measurement methods and test procedures, 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,
• 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.

– 6 – IEC 60793-1-44:2023 © IEC 2023
OPTICAL FIBRES –
Part 1-44: Measurement methods and test procedures –
Cut-off wavelength
1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the cut-off wavelength
of single-mode optical fibre, thereby assisting in the inspection of fibres and cables for
commercial purposes.
This document gives methods for measuring the cut-off wavelength for uncabled or cabled
single mode telecom fibre. These procedures apply to all category B and C fibre types.
There are three methods of deployment for measuring the cut-off wavelength:
• method A: cable cut-off using uncabled fibre 22 m long sample, λ ;
cc
• method B: cable cut-off using cabled fibre 22 m long sample, λ ;
cc
• method C: fibre cut-off using uncabled fibre 2 m long sample, λ .
c
All methods require a reference measurement. There are two reference-scan techniques, either
or both of which can be used with all methods:
• bend-reference technique;
• multimode-reference technique using category A1(OM1-OM5) multimode fibre.
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 60793-1-1, Optical fibres – Part 1-1: Measurement methods and test procedures – General
and guidance
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology 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 60793-1-44:2023 © IEC 2023 – 7 –
4 Background
Theoretical cut-off wavelength is the shortest wavelength at which only the fundamental mode
can propagate in a single-mode fibre, as computed from the refractive index profile of the fibre.
In optical fibres, the change from multimode to single mode behaviour does not occur at an
isolated wavelength, but rather smoothly over a range of wavelengths. For purposes of
determining fibre performance in a telecommunications network, theoretical cut-off wavelength
is less useful than the lower value actually measured when the fibre is deployed.
Measured cut-off wavelength is defined as the wavelength greater than which the ratio between
the total power, including launched higher-order modes, and the fundamental mode power has
decreased to less than 0,1 dB. According to this definition, the second-order (LP ) mode
undergoes 19,3 dB more attenuation than the fundamental (LP ) mode at the cut-off
wavelength.
Because measured cut-off wavelength depends on the length and bends of the fibre, the
resulting value of cut-off wavelength depends on whether the measured fibre is configured in a
deployed, cabled condition or if it is short and uncabled. Consequently, there are two overall
types of cut-off wavelength:
• cable cut-off wavelength (λ ) measured in an uncabled fibre deployment condition
cc
(method A), or in a cabled condition (method B);
• fibre cut-off wavelength (λ ) measured on a short length of uncabled, primary-coated fibre
c
(method C).
Cable cut-off wavelength is the preferred attribute to be specified and measured.
5 Overview of methods
All of the methods shall use the transmitted-power technique. A general system block diagram
is depicted in Figure 1. A fibre specimen is scanned by a wavelength spectrum. The output
optical power is measured and stored. This stored data is then analysed against a reference
power spectrum. The reference scan normalizes any wavelength-dependent fluctuations in the
measurement equipment that is not associated with the loss of the LP mode. The resulting
attenuation will thus properly characterize the cut-off wavelength.

Figure 1 – Cut-off measurement system block diagram
The reference scan uses one of the following two techniques:
• bend reference where a small diameter bend is added to the fibre specimen;
• multimode reference where the optical power through an A1(OM1-OM5) fibre is measured.

– 8 – IEC 60793-1-44:2023 © IEC 2023
Either reference technique can determine the cut-off wavelength of a fibre specimen in a cabled
or uncabled condition.
The fibre cut-off wavelength,λ , measured under the standard length and bend conditions
c
described in this document, will generally exhibit a value larger than the cable cut-off
wavelength, λ . For normal installed cable spans, it is common for the measured λ value to
cc c
exceed the long fibre’s transmission wavelength.
Cable cut-off wavelength is more useful in describing an installed network system performance
and capability, while fibre cut-off would apply to short cables or pigtails. The two cut-off
wavelengths can be mapped to each other for a specific fibre type and cut-off measurement
method. The customer and the supplier shall agree to the confidence level of each mapping
function established (see Clause 11 for details).
6 Reference test method
Method A, cable cut-off wavelength using uncabled fibre, is the reference test method (RTM).
This method shall be used to settle any disputes.
7 Apparatus
7.1 Light source
Provide a filtered white light source, with line width not greater than 10 nm, stable in position
and intensity. The light source should be capable of operating over the wavelength range
1 000 nm to 1 600 nm for most category B fibres. An operating range of 800 nm to 1 700 nm
may be necessary for some B-655 fibres, B-656 fibres or category C fibres. A scanning
monochromator with a halogen bulb is one example of this kind of source.
7.2 Modulation
Modulate the light source to prevent ambient light affecting the results, and to aid signal
recovery. A mechanical chopper with a reference output is a suitable arrangement.
7.3 Launch optics
Provide launch optics, such as a lens system or a multimode fibre, to overfill the test fibre o
...