IEC TR 62547:2009
(Main)Guidelines for the measurement of high-power damage sensitivity of single-mode fibres to bends - Guidance for the interpretation of results
Guidelines for the measurement of high-power damage sensitivity of single-mode fibres to bends - Guidance for the interpretation of results
IEC/TR 62547:2009(E) is a technical report that describes two methods for the measurement of the sensitivity of single-mode optical fibres to high-power damage at bends.
- Method 1 - Failure time characterization as a function of the launch power and bend conditions (bend angle and bend diameter).
- Method 2 - Equilibrium temperature measurement.
General Information
Relations
Standards Content (Sample)
IEC/TR 62547 ®
Edition 1.0 2009-03
TECHNICAL
REPORT
Guidelines for the measurement of high-power damage sensitivity of single-
mode fibres to bends – Guidance for the interpretation of results
IEC/TR 62547:2009(E)
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.
Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.
IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: www.iec.ch
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00
IEC/TR 62547 ®
Edition 1.0 2009-03
TECHNICAL
REPORT
Guidelines for the measurement of high-power damage sensitivity of single-
mode fibres to bends – Guidance for the interpretation of results
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
W
ICS 33.180.10 ISBN 978-2-88910-762-9
– 2 – TR 62547 © IEC:2009(E)
CONTENTS
FOREWORD.4
1 Scope.6
2 Normative references .6
3 Background .7
4 Test procedures .8
4.1 Safety .8
4.1.1 Safety issues.8
4.1.2 Eye safe working .9
4.1.3 Risk of fire / flame .9
4.1.4 Risk of atmospheric pollution from coating by-products .9
4.1.5 Risk of fibre fuse initiation .9
4.1.6 Risk of damage to downstream components .9
4.1.7 Risk avoidance .9
4.2 General .10
4.3 Apparatus.10
4.3.1 Light source.10
4.3.2 Isolator .10
4.3.3 Bend jig .11
4.3.4 Receiver.11
4.3.5 Attenuator .11
4.3.6 Computer .11
4.3.7 Camera .11
4.3.8 Thermal imaging camera .11
4.3.9 Oven .11
4.3.10 Sample.11
4.4 Test Method 1. Failure time characterization as a function of the launch
power and bend conditions (bend angle and diameter) .12
4.4.1 Description and procedure.12
4.4.2 General comments and conclusions on test Method 1.13
4.4.3 Reported items for test Method 1.14
4.5 Test Method 2 – Equilibrium temperature measurement .14
4.5.1 General .14
4.5.2 Coating heating measurements and power lost at bend .15
4.5.3 Analysis – Test Method 2: Equilibrium temperature .16
4.5.4 Test conditions for test Method 2.18
4.5.5 Conclusions on test Method 2.18
4.5.6 Reported items for test Method 2.19
5 Conclusions.19
Annex A (informative) Robustness of fibres against damage from exposure to high-
power at bends .21
Bibliography.39
Figure 1 – An example of experimental layout.10
Figure 2 – Damage results for fibre type ‘G’.12
TR 62547 © IEC:2009(E) – 3 –
Figure 3 – Example of time evolution of loss power and maximum temperature reached
by the coating at the apex when high-power is launched (P = 3,2W, Bend diameter = 5
mm, λ = 1360 nm Reference [10]) .14
Figure 4 – Sample FLIR camera output of the fibre bent under high-power. The cross-
mark indicates the location of the maximum temperature .15
Figure 5 – Evolution of the coating equilibrium temperature as a function of launched
power (see reference [10]) .16
Figure A.1 – Clamping arrangements for high-power damage testing in 180° bends.23
Figure A.2 – Clamping arrangement for high-power damage testing in 90° bends .23
Figure A.3 – Typical R1 failure characteristics with a loss of greater than 10 dB .24
Figure A.4 – Typical R2 failure characteristics .24
Figure A.5 – A schematic illustration of the 3 regimes in the first fibres tested .24
Figure A.6 – Monitor signal changes – typical for a R1 failure .25
Figure A.7 – Monitor signal changes – typical for a R2 failure .25
Figure A.8 – Damage results for fibre type ‘D’.26
Figure A.9 – High-power damage results at 90° and 180° for fibre ‘D’ .26
Figure A.10 – Time to failure versus bend diameter at different launched powers. .27
Figure A.11 – Bend loss performance at 180° (and 90° for reference) for fibre ‘D’ (see
Clause A.7 for a full discussion).28
Figure A.12 – Power limitation for primary coated fibre .28
Figure A.13 – Comparison of power limitation for primary and secondary coated fibre D.29
Figure A.14 – Maximum optical power ensuring a 25 year lifetime and 180° bend loss
versus bend diameter (from reference [10]) .30
Figure A.15 – Maximum optical power ensuring a 25 year lifetime versus 180° bend
loss .30
Figure A.16 – 180° 2-point OSA Bend Loss for fibre ‘D’ .32
Figure A.17 – 180° 2-point bend loss at 1 480 nm for fibre ‘D’.32
Figure A.18 – 2-point bend loss for fibre ‘D’ at various angles.33
o
Figure A.19 – 180 2-point bend loss at 1 480 nm for a range of fibres .34
Figure A.20 – Time to failure versus inverse of equilibrium temperature for bend
diameters varying from 4 mm to 10mm and launched power in the range 0,8 W-3,2 W .35
Figure A.21 – The effect of baking primary coated fibre ‘C’ (reference [14]) in an oven
at constant temperature .36
Figure A.22 – Time to failure for different coatings as a function of bend radius
(upward arrow indicates a test which was survived by the fibre).38
Table A.1 – Time to failure vs coating refractive index .37
– 4 – TR 62547 © IEC:2009(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
GUIDELINES FOR THE MEASUREMENT OF HIGH-POWER
DAMAGE SENSITIVITY OF SINGLE-MODE FIBRES TO BENDS –
GUIDANCE FOR THE INTERPRETATION OF RESULTS
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.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 62547, which is a technical report, has been prepared by subcommittee 86A: Fibres
and cables, of IEC technical committee 86: Fibre optics.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86A/1224/DTR 86A/1235/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
TR 62547 © IEC:2009(E) – 5 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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.
A bilingual version of this publication may be issued at a later date.
– 6 – TR 62547 © IEC:2009(E)
GUIDELINES FOR THE MEASUREMENT OF HIGH-POWER
DAMAGE SENSITIVITY OF SINGLE-MODE FIBRES TO BENDS –
GUIDANCE FOR THE INTERPRETATION OF RESULTS
1 Scope
This technical report describes two methods for the measurement of the sensitivity of single-
mode optical fibres to high-power damage at bends.
• Method 1 – Failure time characterization as a function of the launch power and bend
conditions (bend angle and bend diameter).
• Method 2 – Equilibrium temperature measurement.
Results from the two methods can only be compared qualitatively.
The results, in this technical report, are predominantly on uncabled and unbuffered fibres.
Cabled and buffered fibres are expected to respond differently – because the outer layers can
affect the ageing process. Note also that Method 2 testing cannot be applied to buffered or
cabled fibres.
These methods do not constitute a routine test to be used in the evaluation of optical fibre.
The parameters derived from the two methods are not intended to be specified within a
detailed fibre specification.
Note that the catastrophic failure modes arising and which are described in this technical
report in general occur at bending radii much smaller than specified in the single-mode fibres
specification, IEC 60793-2-50, or than would be recommended based on mechanical reliability
considerations alone.
The technical report includes Annex A which gives a discussion on the rationale for the
approaches adopted, metrics for assessment, guidance, examples and some conclusions
from initial studies.
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.
IEC 60793-1-47, Optical fibres – Part 1-47: Measurement methods and test procedures –
Macrobending loss
IEC 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for
class B single-mode fibres
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
(OFCS)
IEC/TR 61292-4: Optical amplifiers – Part 4: Maximum permissible optical power for the
damage-free and safe use of optical amplifiers, including Raman amplifiers
TR 62547 © IEC:2009(E) – 7 –
IEC 61300-2-14, Fibre optic interconnecting devices and passive components – Basic test
and measurement procedures – Part 2-14: Tests – Optical power handling and damage
threshold characterization
3 Background
Optical network operators are considering the use of high-power lasers, for example fibre
Raman amplifiers in the central office with typical launch powers in the region of 500 mW
to ~ 2 W. For standard installation practices where optical fibre minimum bend diameters are
limited to 60 mm these powers have not constituted a problem. However, there is good
evidence that bends tighter than the recommended 50 mm minimum bend diameter mistakenly
occur in practice. It is believed that these generally arise after installation from maintenance
practices which are difficult to mitigate against as the technicians servicing such networks
often work independently and can come from different organisations. Tight bends arising at
system installation stage should generally be identified and eliminated following provisioning -
by OTDR testing or from link loss measurements. Experimental evidence shows that high-
power damage can occur relatively quickly at bends less than 15 mm diameter. Damage
occurs when the coating temperature increases at bends as the coating absorbs the light lost
at the bend. Damage can take the form of coating ageing, pyrolysis and burning and if the
temperature increases above 700 °C catastrophic softening of the glass. Burning of the
coating can result in a fire. Background references are available in the Bibliography and in
IEC/TR 61292-4.
The rationale for studying the resilience of optical fibre and coatings to high-power damage at
bends is described in Clause A.1. Telecommunications operators can adopt a range of
options to avoid the risk of damage, see Clause A.2. There is now a broad agreement from a
number of laboratories on the catastrophic failure modes of the optical fibre and on the
thresholds for damage at high-powers in bent optical fibres. Observations include:
• Research has clearly shown that high optical power at tight fibre bends can cause
catastrophic damage within a few days. Tests on a range of different fibres including both
B1 and B4 primary coated fibre types have shown that catastrophic damage can
conveniently be grouped into two regimes;
– Regime 1: Catastrophic failure of the glass (R1).
– Regime 2: Catastrophic failure to the fibre coating (R2).
– A third regime, R3, has been identified in which catastrophic damage does not occur.
Here the temperature does not reach a sufficient level to cause short-term catastrophic
damage but over the longer term coating ageing and a change in some of the physical
properties of the coating may result.
Further description of the observed regimes of damage is included in Clause A. 5.
• R1 and R2 failures have been observed in both primary and secondary coated fibres.
Some fibre and coating types are more resilient than others, see references [1] , [2], [3],
[4], [5], [6], [7], [8], [9], [10], [11].
• Coating ageing can take a considerable time (e.g. reference [2]). However, it is an
indicator of potential R1 or R2 damage. Refer to Clause A.5
• Arguably at present, the greatest risk of damage to single-mode fibre systems is due to
the use of high-power Raman pumps at 1 480 nm hence much of the testing has been
carried out at this wavelength. Whilst there are general indications that the absorption
spectra of cured coating materials are generally flat in the 1 450 nm to 1 625 nm range, in
specific coating formulations absorption features could make a coating especially sensitive
at a particular wavelength. Also, bend loss in B1 and B4 fibres generally increases with
wavelength, so damage resistance may be lowered at longer wavelengths. More testing is
___________
Figures in square brackets refer to the Bibliography.
– 8 – TR 62547 © IEC:2009(E)
needed to examine fibre bend loss characteristics and the absorption spectra of cured
coating materials to ensure that wavelength dependent effects are accounted for.
• For laboratory testing and high-power system operation there are important safety issues
to be considered including a risk of flame and fire. These issues are addressed in 4. 1
• This subject is in development and the following are areas for further work.
– As discussed above, much of the testing so far has been carried out at or near to
1 480 nm and the effect of a significant change to the test wavelength is not known.
Experimental results for damage testing at wavelengths near 1 550 nm and 1 625 nm
would be useful.
– Coating absorption. Some studies have examined the effects of changing coating
composition and the ambient environment – see references [12] and [13].
– The testing of fibres with different coloured primary coatings.
– The effect of fibre production variability and for example, testing the effect of fibres
with different MAC ( MFD [μm] / cutoff wavelength [μm] ) numbers but with the same
profile type. Similarly testing of fibres with small differences in coating uniformity,
composition or degree of coating cure needs to be considered.
– Testing diverse bend geometries; the impact of bend loss variations.
– The impact of ambient temperature.
• For the most sensitive fibre tested so far the threshold for damage (R2) for a bend
loss of 4 dB bend is ~ 200 mW, see reference [14].
• The use of different fibre secondary coatings (buffer layers to an outer diameter (OD)
of ~ 800 μm) can lower or raise damage thresholds – See reference [14].
NOTE Catastrophic failure occurs when the bend loss and consequent coating absorption drives the fibre
temperature far above the maximum temperature for environmental tests of conventional UV curable acrylate
coatings, as specified in IEC 60793-2-50.
The purpose of this document is to define measurement techniques to characterise the
robustness of optical fibre to damage of this type. However, if new fibres are developed to
minimize the possibilities of high-power damage at bends other transmission and compatibility
issues must be considered – see Clause A.3 .
Note also that study group 6 in ITU-T (ITU-T SG6) is currently working on the optical fibre
cable maintenance and support issues associated with high-power optical systems 15.
Throughout this report, illustrative data is presented for particular B1 and B4 fibre types
identified by letter from A to G from studies documented in references [2], [3], [7] and [14].
4 Test procedures
4.1 Safety
4.1.1 Safety issues
There are a number of important issues both for testing and for operational systems use.
• Eye safe working
• Risk of fire / flame
• Risk of atmospheric pollution from coating by-products
• Risk of fibre fuse initiation
• Risk of damage to downstream components.
TR 62547 © IEC:2009(E) – 9 –
Some discussion on these issues is covered. However, an individual assessment of risk
should be carried out prior to commencing a programme of tests depending on previous
experience with high-power lasers, the local working practices and the test laboratory
configuration. Also, it is recommended for first tests that an operator monitors the experiment
continually so that the failure conditions with specific fibre and / or coating types can be
correctly determined. The use of a video camera to monitor the fibre bend at high-power can
provide a safer working environment.
4.1.2 Eye safe working
All necessary safety procedures shall be taken in accordance with IEC 60825-1, Clause 2 an d
IEC 60825-2. These test procedures involve the use of optical powers that can constitute
potential ocular and skin hazards for test personnel.
At 1 480 nm, the risk of retinal damage is much reduced compared with shorter wavelengths,
as incoming radiation will mainly be absorbed in the cornea, see reference [16]. Nevertheless,
care needs to be taken to ensure that accidental exposure cannot occur and that high-powers
are only switched on once the fibre (and test condition) has been set up. Also, the use of
optical instruments for viewing can be more hazardous than not.
Laser light blocks should also be used to trap and mask radiation leaking from the test bend.
4.1.3 Risk of fire / flame
Warning note. In the case of samples that can sustain a flame care must be taken to ensure
that sample holders are non-flammable and robust clamps are used to hold the fibres in
position during testing.
4.1.4 Risk of atmospheric pollution from coating by-products
At high-powers and elevated coating temperatures, volatile components in the fibre coating
will be driven off. As this occurs and with time, the coating volume reduces, oxidation occurs
and the coating discolours. The aged or damaged coating volumes involved are small as the
damage region at a fibre bend is generally extremely localised. To reduce the risk of local
atmospheric pollution, it is recommended that the fibre bend test zone is hooded and an
extract fan is run continuously to capture particulate and purge potentially hazardous air
borne, coating by-products.
4.1.5 Risk of fibre fuse initiation
At high optical powers and with appropriate triggering it is possible to initiate the ‘fibre fuse
effect’ [17]. Note that generally launch powers of ~ 2 W - 3 W are required to trigger this
effect and the laser supply can be protected from such a risk by incorporating an optical
isolator or a fibre taper just after the laser source.
4.1.6 Risk of damage to downstream components
With some fibre samples and with the high-power being lost from the fibre at a bend, there
may be a risk to downstream components; for example where test fibre is jointed to a different
fibre type or at a further bend. To mitigate this risk, all components used shall be rated at the
power to which they could be exposed.
4.1.7 Risk avoidance
A number of steps can be taken to reduce identified risks;
• Access to the test laboratory can be restricted to authorised users.
• Warning lights external to the laboratory can alert visitors of the high-power laser hazard.
Laser safety spectacles can be made available for lab users and visitors.
– 10 – TR 62547 © IEC:2009(E)
• A video camera can be used to monitor the test bend and reduce the need to view the test
fibre directly. This reduces the risk of exposure to high-power radiation.
• The laser control system could incorporate optical monitoring for the duration of the
experiment. This can allow the driving PC to auto-shutdown the laser when a failure event
is identified.
• Fibres can be carefully clamped and / or taped in position in robust clamps for the duration
of the tests.
• Fire extinguishing equipment should be on-hand.
4.2 General
A suitable experimental arrangement for high-power damage testing is illustrated in Figure 1.
The apparatus description applies to both test methods. However, in Method 1 the infra-red
(IR) camera is not necessary and can be replaced by a normal colour camera - useful for
experimental monitoring purposes. The test condition suggested is:
• Two-point bend geometry (where the fibre is fixed at two points and allowed to form a
bend in free space)
• 180° configuration.
Other test conditions are discussed in Clause A. 4.
4.3 Apparatus
4.3.1 Light source
A suitable high-power source at 1 480 nm is proposed for the nominal test wavelength
(although the performance at other, typically longer, wavelengths needs to be considered as
discussed in Clause 3). Launch powers of from 100 mW to 1 500 mW or even to 5 W (see
reference [14]) need to be considered
4.3.2 Isolator
An optical isolator or fibre taper that can act as a ‘fuse’, protecting the laser.
Straight fibre
arrangement 1
Isolator
Raman pump
source
Splice
IR
Shutdown
Two-point bend
camera
Computer
Optical Optical
power meter attenuator
Straight fibre
arrangement 2
IEC 408/09
Figure 1 – An example of experimental layout
TR 62547 © IEC:2009(E) – 11 –
4.3.3 Bend jig
The fibre is constrained according to the two-point bend method, forcing the fibre into an oval
configuration (see A.7.2 and reference [18] for a detailed discussion), of 180° although, the
performance in other bend geometries and angles needs to be considered, see A . 5. 2. D et a i l
on the clamping of fibres is described in A. 4. 2.
4.3.4 Receiver
Optical power monitoring device, which ensures stability and consistency between tests.
4.3.5 Attenuator
A 99:1 fused fibre coupler and / or a variable attenuator can be used to reduce the power
level for conventional optical detectors. Alternatively a suitable high-power detector could be
used for monitoring purposes.
4.3.6 Computer
Supervisory software on the controlling computer can be used to automatically shut down the
laser within a few seconds in the event of signal loss and / or fibre failure.
4.3.7 Camera
The use of a video camera to monitor the fibre bend at high-power can provide a safer
working environment.
4.3.8 Thermal imaging camera
The maximum fibre temperature near to the bend apex can be measured using a Forward
Looking Infra Red (FLIR) camera. Suitable cameras include the ThermacamTMPM695 from
FLIR Systems with a sensitivity of ~1 °C.
4.3.9 Oven
A temperature controlled oven can provide a high temperature ageing environment for fibre
and coatings.
4.3.10 Sample
Several tens of metres of test fibre before the test bend position to provide a supply of fibre
for testing. After the test bend position, the fibre is spliced to a further length of test fibre and
then via the attenuator to a monitoring detector.
Note that the primary coating colouring material used to identify individual fibres in a bundle
provides an additional variable when it comes to high-power assessment. So far, most
reported results have been on uncoloured fibres. Knowledge of the absorption spectra of the
pigments used to colour fibre coatings could be valuable in helping to identify potentially
sensitive colorants.
Most work has been conducted on primary coated fibres (to ~ 245 μm OD) where coating or
fibre damage can readily be observed. For buffered or secondary coated fibres (to ~ 900 μm
OD) where the outer coating may be opaque and / or inflexible, the experimental set up needs
further consideration particularly regarding fibre clamping.
– 12 – TR 62547 © IEC:2009(E)
4.4 Test Method 1. Failure time characterization as a function of the launch power
and bend conditions (bend angle and diameter)
4.4.1 Description and procedure
As illustrated in Figure 2, the evaluation of the high-power damage performance of a
particular fibre sample consists of a number of individual tests of the time to failure
determined for a range of combinations of bend diameter and input power. For the most
efficient use of experimental time, it is recommended that Method 1 testing begins at the
smallest diameters (~4 mm) and at high-powers. The power level at the test point – which
may be different from that output from the laser – can be determined using a standard
calibration technique. Alternatively, power measurements can be made just before the test
bend is set up and a splice is made to the monitoring photo-detector. The required fibre bend
is set up in a suitable holder and the optical power switched on.
Experimental progress can be monitored using a photo-detector and PC to log the received
power as a function of time as described in Figure 1 and illustrated in the results shown in
Figure A.6 and Figure A.7. Regime 1 failures (R1) are recorded – see Clause A.5 for a
description of the various failure conditions – usually within tens of minutes for standard B1 or
B4 fibres. The power can then be reduced for a new test and the experiment repeated.
Regime 2 failures (R2) can then be identified, generally with longer times to failure. Then if
the power is further reduced in a new test(s) a point is reached at which R2 failure does not
occur – even at three or more times the exposure time seen for the latest R2 failure. When
this time is reached, the test at this bend diameter can be stopped and, if the coating
properties are found to have been changed as a result of the test, the condition defined as
sub-catastrophic damage, R3 - see Clause A.5 for additional discussion and a description of
the three failure regimes. Additional tests follow at larger bend diameters as illustrated below.
Damage results can then be plotted, as for example in Figure 2.
Fibre G 180° results
Fibre G 180° results
R1
R1
2 000
10 000
R2
R2
R3
1 500
R3
1 000
1 000
4 6 8 10 12
4 6 8 10 12
Bend diameter (mm)
Bend diameter (mm)
IEC 409/09 IEC 410/09
Figure 2 – Damage results for fibre type ‘G’
Note that in a set of tests the damage trends for R1, and R2 failure types can be observed
over a range of diameters – giving confidence that the definition of the R1-R2 and R2-R3
boundaries is consistent and reliable. All of the R3 results that are reported here are for real
experimental tests – some exceed several days.
Failure power (mW)
Failure time (min)
TR 62547 © IEC:2009(E) – 13 –
Note also that:
• The minimum time to failure seems to grow exponentially with bend diameter. For a given
bend diameter, if the optical power is increased the minimum time to failure does not seem
to decrease. This is likely to be due to increased heat transfer by radiation as the
temperature increases but the effect can also be explained by a drop of both primary and
secondary coating refractive indices as temperature increases whereas the refractive
index change of silica is negligible. Then a much smaller fraction of light is dissipated in
the coating, see reference [19].
• Not all fibre types show the same trends or damage phenomena at all bend diameters. For
example, for 180° bends in fibre ‘D’, see A. 5. 1 a n d Figure A.8.
• At smaller bend angles e.g. 90°, the failure power is higher and the failure times are
extended compared with similar diameter bend at 180°, see A . 5 . 2 and Figure A.9.
• Some failure time trend inconsistencies have been observed in at least one fibre type, see
A.5.3 and reference [10].
• Bend insensitive fibres (e.g G.657 designs) are expected to offer improved resilience and
different relationships from those results shown in Figure 2.
4.4.2 General comments and conclusions on test Method 1
• Method 1 testing can be arduous; Regime 1 and Regime 2 failures in conventional B1 and
B4 fibres have been observed after more than 3 days exposure for bend diameters in
excess of 10 mm. The complete characterization of a conventional B1 or B4 optical fibre
type can take several months. With more resilient fibres and coatings, testing will take
more time.
• The use of buffer or secondary coatings can lower or raise the threshold for high-power
damage depending on the coating type – see references [5] and [14].
• The effect of different coloured primary coatings requires research.
• The impact of ambient temperature on high-power damage thresholds requires
investigation.
• Smaller angle bends (than 180°) generally require higher powers to create the same
damage effects, A . 5 . 2 and Figure A.9.
• Method 1 testing can allow thresholds for catastrophic high-power fibre damage to be
established – see A . 6.1 an d e.g . Figure A.13. These thresholds can give a system
operator a benchmark of resilience to catastrophic damage depending on the available
system margin (which limits the allowable bend loss).
• It has been reported that consistent and repeatable failure power and failure time results
can be obtained for similar tests on the same fibre, see reference [2]. However, fibres with
different MAC numbers but of the same profile type and manufacturer are likely to have
slightly different failure powers and times to failure for similar test circumstances – as a
difference in bend loss is expected for the same test bend condition . Similarly, small
differences in manufacturing tolerances for example in coating uniformity, composition or
degree of coating cure could provide an inconsistency in results. More work is required to
determine the significance of such variations.
• An alternative evaluation criterion could be established using this technique as a method
for assessment of fibre resilience to failure under bending and high-power for a particular
test geometry and duration if agreed between supplier and customer. Then, if the fibre
survives the test duration, the fibre performance is acceptable. However, such a criterion
does not give a complete picture as the test geometry (bend diameter and angle) only
gives a snapshot of performance and it is known that extrapolation may be difficult – see
references [10] and [13]. Also, the test duration is likely to be much less than the normal
lifetime of a fibre and damage effects are known to be non-linear and cumulative.
• The preferred test procedure is a full characterisation.
o
• Users should be aware that time to failure tests for 2-point, 180 bends with a diameter
of less than ~6mm may not allow differentiation between the high-power damage
sensitivity of different fibre and coating types, see references [10] and [23].
– 14 – TR 62547 © IEC:2009(E)
NOTE The thresholds determined by Test Method 1 generally occur at smaller bending radii and higher coating
temperatures than described in the single-mode fibre specification IEC 60793-2-50.
4.4.3 Reported items for test Method 1
The items reported are
– launch power and wavelength;
– bend diameter;
– macrobend loss with time;
– failure condition, R1 R2, or R3;
– time to failure.
4.5 Test Method 2 – Equilibrium temperature measurement
4.5.1 General
The experimental arrangement for Method 2 testing is as described in Figure 1. It has been
observed that as soon as the power is launched into the fibre the coating temperature at the
bend quickly reaches a plateau – see Clause A.8 and reference [10] for a complete
discussion. The maximum coating temperature near to the bend apex has been observed to
remain relatively stable during the major part of the test, but a change of coating colour can
be seen over time. The temperature during this stage is called the “equilibrium temperature”.
This stage can last several days. Note that in reference [23], the use of a forward looking infra
red (FLIR) camera (see Figure 4) to measure equilibrium temperature is described. A software
feature in this camera allows the maximum temperature in a section of the camera field of
view to be monitored straightforwardly.
Near failure, when the coating is discoloured, the coating temperature can rapidly increase
above 500 °C; smoke released from the coating can warn of imminent failure. The coating can
then burn off over several centimetres commencing near to the bend apex and if heating is
sufficiently rapid, the silica can reach softening point. An example of such a time evolution is
shown in Figure 3.
600 18
400 12
Equilibrium temperature
0 0
0 100 200 300 400 500 600 700 800 900
Time (s) IEC 411/09
Figure 3 – Example of time evolution of loss power and maximum temperature reached
by the coating at the apex when high-power is launched (P = 3,2 W, bend diameter =
5mm, λ = 1 360 nm, see reference [10])
Temperature (°C)
Loss power (dB)
TR 62547 © IEC:2009(E) – 15 –
4.5.2 Coating heating measurements and power lost at bend
As with Method 1 testing – see 4.4.1 – the evaluation of the performance of a particular fibre
sample consists of a series of individual tests at a range of combinations of bend diameter
and input power for which the maximum fibre temperature near to the bend apex can be
measured using a FLIR camera (see Figure 4).
D=5mm
D = 5 mm
140 D=6mm
D = 6 mm
D = 7 mm
D=7mm
D = 9 mm
D=9mm
D = 10 mm
D = 11 mm
D = 13 mm
0,0 1,0 2,0 3,0 4,0
Power (W)
IEC 413/09
The analysis in
Figure 5 points out that both power level and bending diameter impact the coating
temperature – see reference [10]. For bend diameters below 10 mm, it has been reported that
the temperature was not a linear function of the power: it first increased linearly with launch
power but begins to stabilise from ~ 1 W.
IEC 412/09
Figure 4 – Sample FLIR camera output of the fibre bent under high-power. The cross-
mark indicates the location of the maximum temperature
Temperature (°C)
– 16 – TR 62547 © IEC:2009(E)
D=5D = 5 mmmm
140 D=6D = 6 mmmm
D = 7 mm
D=7mm
D = 9 mm
D=9mm
D = 10 mm
D = 11 mm
D = 13 mm
0,0 1,0 2,0 3,0 4,0
Power (W)
IEC 413/09
Figure 5 – Evoluti
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...