SIST EN 60793-1-49:2007

Optical fibres -- Part 1-49: Measurement methods and test procedures - Differential mode delay

This part of IEC 60793 applies only to multimode, graded-index glass-core (category A1) fibres. The test method is commonly used in production and research facilities, but is not easily accomplished in the field. This standard describes a method for characterizing the modal structure of a graded-index multimode fibre. This information is useful for assessing the bandwidth performance of a fibre especially when the fibre is intended to support a variety of launch conditions such as those produced by standardized laser transmitters. With this method, the output from a fibre that is single-mode at the test wavelength excites the multimode fibre under test. The probe spot is scanned across the endface of the fibre under test, and the optical pulse delay is determined at specified offset positions. Two results can be produced from the same data. First, the difference in optical pulse delay time between the fastest and slowest mode groups of the fibre under test can be determined. The user specifies the upper and lower limits of radial offset positions over which the probe fibre is scanned in order to specify desired limits of modal structure. The DMD data is then compared to DMD specifications that have been determined by modeling and experimentation to correspond to a minimum EMB for a range of transmitters. Second, the optical pulse shapes can be combined using specific weights to determine a calculated effective modal bandwidth (EMBc), and by calculating a sequence of EMBc values with different sets of weights, a minimum EMBc can be calculated, corresponding to a range of transmitters. The test quantifies the effects of interactions of the fibre modal structure and the source modal characteristics excluding the source spectral interactions with fibre chromatic dispersion. Adding the effects of chromatic dispersion and source spectral width will reduce the overall transmission bandwidth, but this is a separate calculation in most transmission models. In this test, the effects of non-zero spectral width are minimized but any residual effects will tend to increase the DMD value and decrease the EMBc value.

Lichtwellenleiter -- Teil 1-49: Messmethoden und Prüfverfahren - Gruppenlaufzeitdifferenz

Fibres optiques -- Partie 1-49: Méthodes de mesure et procédures d'essai - Retard différentiel de mode

Décrit une méthode de caractérisation de la structure modale d'une fibre multimodale à gradient d'indice. Cette information est utile pour évaluer les performances de largeur de bande d'une fibre lorsqu'elle est utilisée avec des sources lasers. S'applique uniquement aux fibres multimodales à cur en verre à gradient d'indice (catégorie A1). Cette méthode d'essai est généralement utilisée dans les installations de production et de recherche et n'est pas facilement réalisée sur le terrain

Optična vlakna - 1-49. del: Merilne metode in postopki preskušanja - Diferenčna zakasnitev rodov (IEC 60793-1-49:2006)

General Information

• Status: Withdrawn
• Publication Date: 14-Oct-2007
• Withdrawal Date: 12-Oct-2021
• ICS: 33.180.10 - Fibres and cables
• Technical Committee: MOC - Mobile Communications
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 12-Oct-2021
• Due Date: 04-Nov-2021
• Completion Date: 13-Oct-2021
• Ref Project: EN 60793-1-49:2006 - Optical fibres - Part 1-49: Measurement methods and test procedures - Differential mode delay

Relations

• Replaces: SIST EN 60793-1-49:2004 - Optical fibres -- Part 1-49: Measurement methods and test procedures - Differential mode delay
• Effective Date: 01-Dec-2007
• Replaced By: SIST EN IEC 60793-1-49:2019 - Optical fibres - Part 1-49: Measurement methods and test procedures - Differential mode delay (IEC 60793-1-49:2018)
• Effective Date: 06-Nov-2018
• Replaces: SIST EN 60793-1-49:2004 - Optical fibres -- Part 1-49: Measurement methods and test procedures - Differential mode delay
• Effective Date: 28-Jan-2023
• Revised: SIST EN 60793-1-49:2004 - Optical fibres -- Part 1-49: Measurement methods and test procedures - Differential mode delay
• Effective Date: 13-May-2010

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 60793-1-49:2007
01-december-2007
1DGRPHãþD
SIST EN 60793-1-49:2004
2SWLþQDYODNQD±GHO0HULOQHPHWRGHLQSRVWRSNLSUHVNXãDQMD±'LIHUHQþQD
]DNDVQLWHYURGRY,(&
Optical fibres -- Part 1-49: Measurement methods and test procedures - Differential
mode delay (IEC 60793-1-49:2006)
Optische Schnittstellen von Lichtwellenleiter-Steckverbindern -- Teil 2-1: Optische
Schnittstelle von nicht abgeschrägten Einmodenfasern mit physikalischem Kontakt (IEC
60793-1-49:2006)
Interfaces optiques de connecteurs pour fibres optiques -- Partie 2-1: Interfaces optiques
pour fibres unimodales en contact physique sans angles (IEC 60793-1-49:2006)
Ta slovenski standard je istoveten z: EN 60793-1-49:2006
ICS:
33.180.10 2SWLþQDYODNQDLQNDEOL Fibres and cables
SIST EN 60793-1-49:2007 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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

EUROPEAN STANDARD
EN 60793-1-49

NORME EUROPÉENNE
July 2006
EUROPÄISCHE NORM

ICS 33.180.10 Supersedes EN 60793-1-49:2003


English version


Optical fibres
Part 1-49: Measurement methods and test procedures -
Differential mode delay
(IEC 60793-1-49:2006)


Fibres optiques  Lichtwellenleiter
Partie 1-49: Méthodes de mesure et Teil 1-49: Messmethoden und
procédures d'essai - Prüfverfahren -
Retard différentiel de mode Gruppenlaufzeitdifferenz
(CEI 60793-1-49:2006) (IEC 60793-1-49:2006)




This European Standard was approved by CENELEC on 2006-07-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60793-1-49:2006 E

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

EN 60793-1-49:2006 - 2 -
Foreword
The text of document 86A/1061/FDIS, future edition 2 of IEC 60793-1-49, prepared by SC 86A, Fibres
and cables, of IEC TC 86, Fibre optics, was submitted to the IEC-CENELEC parallel vote and was
approved by CENELEC as EN 60793-1-49 on 2006-07-01.
This European Standard supersedes EN 60793-1-49:2003.
It adds minimum calculated effective modal bandwidth (EMBc) to the test procedures, supporting
EN 60793-2-10.
This standard is to be read in conjunction with EN 60793-1-1 and EN 60793-2-10.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-04-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-07-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60793-1-49:2006 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 60825-1 NOTE  Harmonized as EN 60825-1:1994 (not modified).
IEC 60825-2 NOTE  Harmonized as EN 60825-2:2004 (not modified).

__________

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

- 3 - EN 60793-1-49:2006
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.

Publication Year Title EN/HD Year

1) 2)
IEC 60793-1-1 - Optical fibres EN 60793-1-1 2003
Part 1-1: Measurement methods and test
procedures - General and guidance


1) 2)
IEC 60793-1-22 - Optical fibres EN 60793-1-22 2002
Part 1-22: Measurement methods and test
procedures - Length measurement


1) 2)
IEC 60793-1-41 - Optical fibres EN 60793-1-41 2003
Part 1-41: Measurement methods and test
procedures - Bandwidth


1) 2)
IEC 60793-1-42 - Optical fibres EN 60793-1-42 2002
Part 1-42: Measurement methods and test
procedures - Chromatic dispersion


1) 2)
IEC 60793-1-45 - Optical fibres EN 60793-1-45 2003
(mod)  Part 1-45: Measurement methods and test + corr. April 2004
procedures - Mode field diameter


1) 2)
IEC 60793-2-10 - Optical fibres EN 60793-2-10 2004
Part 2-10: Product specifications - Sectional
specification for category A1 multimode fibres


1) 2)
IEC 61280-1-4 - Fibre optic communication subsystem test EN 61280-1-4 2003
procedures
Part 1-4: General communication
subsystems - Collection and reduction of two-
dimensional nearfield data for multimode fibre
laser transmitters




1)
Undated reference.
2)
Valid edition at date of issue.

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

NORME CEI
INTERNATIONALE
IEC



60793-1-49
INTERNATIONAL


Deuxième édition
STANDARD

Second edition

2006-06


Fibres optiques –
Partie 1-49:
Méthodes de mesure et procédures d'essai –
Retard différentiel de mode

Optical fibres –
Part 1-49:
Measurement methods and test procedures –
Differential mode delay
 IEC 2006 Droits de reproduction réservés  Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any
utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including
électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: [phone] Telefax: [phone] E-mail: [e-mail] Web: www.iec.ch
CODE PRIX
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PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue

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

60793-1-49  IEC:2006 – 3 –
CONTENTS
FOREWORD.5
1 Scope.9
2 Normative references .9
3 Terms and definitions .11
4 Apparatus.13
4.1 Optical source .13
4.2 Stability .13
4.3 Launch system .13
4.4 Detection system.15
4.5 Computational equipment.17
5 Sampling and specimens.17
5.1 Test sample .17
5.2 Specimen endfaces .17
5.3 Specimen length.17
5.4 Specimen packaging .17
5.5 Specimen positioning .17
6 Procedure .17
6.1 Adjust and measure system response .17
6.2 Adjust detection system.19
6.3 Measure the test sample .19
7 Calculations and interpretation of results.21
7.1 Differential mode delay (DMD) .21
7.2 Minimum calculated effective modal bandwidth .21
7.3 Length normalization .25
8 Documentation .25
8.1 Report the following information for each test:.25
8.2 The following information shall be available upon request: .25
9 Specification information .25

Annex A (normative) Source spectral width limitation.29
Annex B (informative) Discussion of measurement details .35
Annex C (informative) Determining DMD weights for EMBc calculation .43
Annex D (informative)  EMBc calculation information .49
Annex E (informative)  Comparison between this standard and ITU recommendations .55

Bibliography.57

Figure B.1 – Idealized DMD data .35

Table A.1 –Highest expected dispersion for any of the commercially available
Category A1 fibres .33
Table D.1 – DMD weightings – Example set 1.49
Table D.2 – DMD weightings – Example set 2.51

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

60793-1-49  IEC:2006 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

OPTICAL FIBRES –

Part 1-49: Measurement methods and test procedures –
Differential mode delay


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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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 60793-1-49 has been prepared by subcommittee 86A Fibres and
cables, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2003, of which it
constitutes a technical revision. This edition adds minimum calculated effective modal
bandwidth (EMBc) to the test procedures, supporting IEC 60793-2-10.
The text of this standard is based on the following documents:
FDIS Report on voting
86A/1061/FDIS 86A/1077/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.

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

60793-1-49  IEC:2006 – 7 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This standard is to be read in conjunction with IEC 60793-1-1 and IEC 60793-2-10.
IEC 60793-1-4X consists of the following parts, under the general title Optical fibres:
Part 1-40: Measurement methods and test procedures − Attenuation
Part 1-41: Measurement methods and test procedures − Bandwidth
Part 1-42: Measurement methods and test procedures − Chromatic dispersion
Part 1-43: Measurement methods and test procedures − Numerical aperture
Part 1-44: Measurement methods and test procedures − Cut-off wavelength
Part 1-45: Measurement methods and test procedures − Mode field diameter
Part 1-46: Measurement methods and test procedures − Monitoring of changes in optical
transmittance
Part 1-47: Measurement methods and test procedures − Macrobending loss
Part 1-48: Measurement methods and test procedures − Polarization mode dispersion
Part 1-49: Measurement methods and test procedures − Differential mode delay
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.

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

60793-1-49  IEC:2006 – 9 –
OPTICAL FIBRES –

Part 1-49: Measurement methods and test procedures –
Differential mode delay



1 Scope
This part of IEC 60793 applies only to multimode, graded-index glass-core (category A1)
fibres. The test method is commonly used in production and research facilities, but is not
easily accomplished in the field.
This standard describes a method for characterizing the modal structure of a graded-index
multimode fibre. This information is useful for assessing the bandwidth performance of a fibre
especially when the fibre is intended to support a variety of launch conditions such as those
produced by standardized laser transmitters.
With this method, the output from a fibre that is single-mode at the test wavelength excites
the multimode fibre under test. The probe spot is scanned across the endface of the fibre
under test, and the optical pulse delay is determined at specified offset positions.
Two results can be produced from the same data. First, the difference in optical pulse delay
time between the fastest and slowest mode groups of the fibre under test can be determined.
The user specifies the upper and lower limits of radial offset positions over which the probe
fibre is scanned in order to specify desired limits of modal structure. The DMD data is then
compared to DMD specifications that have been determined by modeling and experimentation
to correspond to a minimum EMB for a range of transmitters. Second, the optical pulse
shapes can be combined using specific weights to determine a calculated effective modal
bandwidth (EMBc), and by calculating a sequence of EMBc values with different sets of
weights, a minimum EMBc can be calculated, corresponding to a range of transmitters.
The test quantifies the effects of interactions of the fibre modal structure and the source
modal characteristics excluding the source spectral interactions with fibre chromatic
dispersion. Adding the effects of chromatic dispersion and source spectral width will reduce
the overall transmission bandwidth, but this is a separate calculation in most transmission
models. In this test, the effects of non-zero spectral width are minimized but any residual
effects will tend to increase the DMD value and decrease the EMBc value.
2 Normative references
The following referenced documents are indispensable for the application 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.

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

60793-1-49  IEC:2006 – 11 –
IEC 60793-1-1: Optical fibres − Part 1: Measurement methods and test procedures –- General
and guidance
IEC 60793-1-22: Optical fibres − Part 1-22: Measurement methods and test procedures –
Length measurement
IEC 60793-1-41: Optical fibres – Part 1-41: Measurement methods and test procedures –
Bandwidth.
IEC 60793-1-42: Optical fibres − Part 1-42: Measurement methods and test procedures −
Chromatic dispersion
IEC 60793-1-45: Optical fibres − Part 1-45: Measurement methods and test procedures -
Mode field diameter
IEC 60793-2-10: Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 61280-1-4: Fibre optic communication subsystem test procedures – Part 1-4: General
communication subsystems – Collection and reduction of two-dimensional nearfield data for
multimode fibre laser transmitters
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE The user of this standard specifies either the maximum DMD for the outer (R ) and inner (R )
OUTER INNER
limits of radial offset position over which the probe spot is scanned, or the minimum EMBc among the EMBc values
calculated from a sequence of DMD weightings.
3.1
differential mode delay
DMD
the estimated difference in optical pulse delay time between the fastest and slowest modes
excited for all radial offset positions between and including R and R
INNER OUTER
3.2
effective modal bandwith
bandwidth associated with the transfer function, H(f), of a particular laser/fibre combination
3.3
inner limit
R
INNER
outer limit
R
OUTER
limits of radial offset positions on the endface of the fibre under test over which the probe spot
is scanned

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

60793-1-49  IEC:2006 – 13 –
4 Apparatus
4.1 Optical source
Use an optical source that introduces short duration, narrow spectral width pulses into the
probe fibre.
The temporal duration of the optical pulse shall be short enough to measure the intended
differential delay time. The maximum duration allowed for the optical pulse, characterized as
full width at 25 % of maximum amplitude, will depend both on the value of DMD to be
determined and the sample length. For example, if the desired length-normalized DMD limit is
0,20 ps/m over a sample of length 500 m, the DMD to be measured is 100 ps, and a pulse of
duration less than ~110 ps is needed. Testing to the same DMD limit in a 10 000 m length of
fibre requires measuring a DMD of 2 000 ps, and a pulse a wide as ~2 200 ps may be used.
Detailed limits are given in 6.1, and may depend on the source spectral width.
Chromatic dispersion induced broadening resulting from source spectral width shall be within
the limits indicated in Annex A. The requirement on spectral width may be met either by using
a spectrally narrow source, or alternatively by the use of appropriate optical filtering at either
the source or detection end.
The centre wavelength shall be within ±10 nm of the nominal specified wavelength.
A mode locked titanium-sapphire laser is an example of a source usable for this application.
4.2 Stability
Devices shall be available to position the input and output ends of the test specimen with
sufficient stability and reproducibility to meet the conditions of 4.3 and 4.4.
4.3 Launch system
The probe fibre between the light source and test sample shall propagate only a single mode
at the measurement wavelength. The mode field diameter of the probe fibre at λ shall be
(8,7λ – 2,39) ± 0,5 µm, where λ is the measurement wavelength in micrometers, and the
mode field diameter is determined using IEC 60793-1-45. This equation produces a mode
field diameter of 5 µm at 850 nm and 9 µm at 1 310 nm, which corresponds to commercially
available single-mode fibres.
Ensure that the output of the probe fibre is single-mode. One method to do this is to strip
higher order modes by wrapping the probe fibre three turns around a 25-mm diameter
mandrel.
The output spot of the probe fibre shall be scanned across the endface of the test sample with
a positional accuracy less than or equal to ±0,5 µm.
The output beam from the probe fibre shall be perpendicular to the endface of the test sample
to within an angular tolerance of less than or equal to 1,0 degree.
The launch system shall be capable of reproducibly centring the output spot of the probe fibre
to within ±1,0 µm.

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

60793-1-49  IEC:2006 – 15 –
If directly coupled to the test sample, the gap between the output end of the probe fibre and
the endface of the test sample shall be no more than 10 µm.
A free space optics system of lenses or mirrors may be used to image the output spot of the
probe fibre onto the endface of the test sample. When using this type of launch system, care
should be taken to ensure that substantially the same modes are excited in the test fibre as
would be if the beam were coupled directly from the output of the single-mode probe fibre. For
example, a system of lenses or mirrors may be used to image the output of a single-mode
fibre onto the end face of the test sample.
Provide means to remove cladding light from the test sample. Often the fibre coating is
sufficient to perform this function. Otherwise, use cladding mode strippers near both ends of
the test sample. If the fibre is retained on the cladding mode stripper(s) with small weights,
care shall be taken to avoid microbending at these sites.
4.4 Detection system
Use an optical detection apparatus suitable for the test wavelength. The detection apparatus
shall couple all of the guided modes from the test sample onto the detector's active area, such
that the detection sensitivity is not significantly mode dependent. The detector, along with any
signal preamplifier, shall respond linearly (within ±5 %) over the range of power detected.
The temporal response of the detector system, including any optional optical attenuator, shall
not be significantly mode dependent.
A specific test for mode dependence is given in 6.1. Alternatively, the detector’s temporal
response may be a function of offset as long as it is stable over the course of the
measurement (i.e. ΔT (r) shall fulfil the ±5 % requirement of 6.1).
PULSE
Ringing of the detector system shall be limited such that maximum overshoot or undershoot
shall be less than 5 % of the peak amplitude of the detected optical signal as measured on
the reference.
The waveform of the detected optical signal shall be recorded and displayed on a suitable
instrument, such as a high-speed sampling oscilloscope with calibrated time sweep. The
recording system should be capable of averaging the detected waveform for multiple optical
pulses.
Use a delay device, such as a digital delay generator, to provide a means of triggering the
detection electronics at the correct time. The delay device may trigger the optical source, or
be triggered by it. The delay device may be internal or external to the recording instrument.
The combined effect of timing jitter and noise in the detection system shall be small enough
that the difference between successive measurements of optical delay times for any fixed
launch used in the measurement shall be less than 5 % of the measured value of DMD.
Averaging the detected waveform for multiple optical pulses may be used to reduce the
effects of timing jitter and noise. If averaging is used, each waveform shall be recorded using
at least the number of averages used when determining ΔT in 6.1 The system shall
PULSE
maintain this level of stability over the course of the measurement.

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

60793-1-49  IEC:2006 – 17 –
4.5 Computational equipment
This test method generally requires a computer to store the intermediate data and calculate
the test results.
5 Sampling and specimens
5.1 Test sample
The test sample shall be graded-index glass-core (category A1) multimode fibre.
5.2 Specimen endfaces
Prepare flat endfaces at the input and output ends of the specimen.
5.3 Specimen length
The length of the fibre shall be measured using a suitably accurate method such as that of
IEC 60793-1-22.
5.4 Specimen packaging
Support the test fibre in a manner that relieves tension and minimizes microbending.
5.5 Specimen positioning
Position the input end of the test sample such that it is aligned to the output end of the launch
system as described in 4.3.
Position the output end of the test sample such that it is aligned with the detection system, as
described in 4.4.
6 Procedure
6.1 Adjust and measure system response
Couple the output of the probe fibre into the detection apparatus. This may be accomplished
by mounting the probe fibre in the detection apparatus, or by using a short (<10 m) length of
fibre mounted between the launch system and the detection system, or by directly coupling
the probe output to the detector via a system of lenses and mirrors. If using a short fibre, it
shall be of the same type fibre as the test fibre.
Adjust the amplitude of the optical pulse to match the smallest peak amplitude expected from
the test fibre during the measurement. The smallest peak amplitude from the test fibre will
usually occur for the largest
...