IEC TR 61292-4:2010

IEC/TR 61292-4
®
Edition 2.0 2010-03
TECHNICAL
REPORT

colour
inside
Optical amplifiers –
Part 4: Maximum permissible optical power for the damage-free and safe use of
optical amplifiers, including Raman amplifiers


IEC/TR 61292-4:2010(E)

---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2010 IEC, Geneva, Switzerland

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It also gives information on projects, withdrawn and replaced publications.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

---------------------- Page: 2 ----------------------
IEC/TR 61292-4
®
Edition 2.0 2010-03
TECHNICAL
REPORT

colour
inside
Optical amplifiers –
Part 4: Maximum permissible optical power for the damage-free and safe use of
optical amplifiers, including Raman amplifiers


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
S
ICS 33.160.10; 33.180.30 ISBN 978-2-88910-481-9
® Registered trademark of the International Electrotechnical Commission

---------------------- Page: 3 ----------------------
– 2 – TR 61292-4 © IEC:2010(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope and object.7
2 Normative references .7
3 Abbreviated terms .8
4 Maximum transmissible optical power to keep fibres damage-free .8
4.1 General .8
4.2 Fibre fuse and its propagation .9
4.2.1 Introduction .9
4.2.2 Experiment and results .9
4.2.3 Conclusion .10
4.3 Loss-induced heating at connectors or splices.10
4.3.1 Introduction .10
4.3.2 Experiment on the connector .10
4.3.3 Results and considerations.11
4.3.4 Conclusion .11
4.4 Connector end-face damage induced by dust/contamination .12
4.4.1 Introduction .12
4.4.2 Test setup .12
4.4.3 Measurements.12
4.4.4 Test on clean connectors.12
4.4.5 Test on connectors contaminated with skin grease .12
4.4.6 Test on connectors contaminated with dust .13
4.4.7 Test on connectors contaminated with metal dust.13
4.4.8 Conclusion .14
4.5 Fibre-coat burn/melt induced by tight fibre bending .14
4.6 Summary of the fibre-damage experiments.15
5 Maximum transmissible optical power to keep eyes and skin safe .16
5.1 Maximum permissible exposure (MPE) on the surface of eye and skin .16
5.2 Maximum permissible optical power in the fibre for the safety of eye and skin .16
5.2.1 Need for APR .18
5.2.2 Wavelengths.18
5.2.3 Locations.18
5.2.4 Nominal ocular hazard distance (NOHD) .18
5.2.5 Power reduction times .18
5.2.6 Medical aspects of the safety of eyes and skin in existing standards .19
6 Maximum optical power permissible for optical amplifiers from the viewpoints of
fibre damage as well as eye and skin safety.20
7 Conclusion .20
Bibliography.21

Figure 1 – Experimental setup for fibre fuse propagation .9
Figure 2 – Connection loss versus temperature increase .11
Figure 3 – Test setup.12
Figure 4 – Surface condition contaminated with metal filings, before the test .13

---------------------- Page: 4 ----------------------
TR 61292-4 © IEC:2010(E) – 3 –
Figure 5 – Variation of the power attenuation during the test at several power input
values for plugs contaminated with metal filings.13
Figure 6 – Polishing surface condition contaminated with metal filing, after the test .14
Figure 7 – Thermo-viewer image of tightly-bent SMF with optical power of 3 W at
1 480 nm .15
Figure 8 – Temperature of the coating surface of SMFs against bending with optical
power of 3 W at 1 480 nm .15
Figure 9 – Maximum permissible power in the fibre against APR power reduction time .19

Table 1 – Experimental results of the threshold power of fibre fuse propagation .9
Table 2 – Measurement conditions .11
Table 3 – Examples of power limits for optical fibre communication systems having
automatic power reduction to reduce emissions to a lower hazard level .17
Table 4 – Location types within an optical fibre communication system and their typical
installations .18

---------------------- Page: 5 ----------------------
– 4 – TR 61292-4 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

OPTICAL AMPLIFIERS –

Part 4: Maximum permissible optical power
for the damage-free and safe use of optical amplifiers,
including Raman amplifiers


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.
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 61292-4, which is a technical report, has been prepared by subcommittee 86C: Fibre
optic systems and active devices, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2004 and constitutes a
technical revision with updates reflecting new research in the subject area.

---------------------- Page: 6 ----------------------
TR 61292-4 © IEC:2010(E) – 5 –
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86C/889/DTR 86C/921/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.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61292 series, published under the general title Optical amplifiers,
can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability 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.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

---------------------- Page: 7 ----------------------
– 6 – TR 61292-4 © IEC:2010(E)
INTRODUCTION
This technical report is dedicated to the subject of maximum permissible optical power for
damage-free and safe use of optical amplifiers, including Raman amplifiers. Since the
technology is quite new and still evolving, amendments and new editions to this document can
be expected.
Many new types of optical amplifiers are entering the marketplace and research on it is also
stimulating many new types of fibre and non-fibre based optical amplifier research. With the
introduction of such technologies as long-haul, 40 Gb/s, WDM transmission and Raman
amplification, some optical amplifiers may involve optical pump sources with extremely high
optical power – up to, possibly, several watts.
Excessively high optical power may cause physical damage to the fibres/optical
components/equipment as well as present medical danger to the human eye and skin.
The possibility of fibre damage caused by high optical intensity has recently been discussed
at some technical conferences. IEC technical committee 86 (Fibres optics) and subcommittee
86A (Fibres and cables) has published IEC 62547: Guidelines for the measurement of high-
power damage sensitivity of single-mode fibres to bends – Guidance for the interpretation of
results. IEC technical committee 31 (Equipment for explosive atmospheres) is also discussing
the risk of ignition of hazardous environments by radiation from optical equipment.
The medical aspects have long been discussed at standards groups. IEC technical committee
76 (Optical radiation safety and laser equipment) precisely describes in IEC 60825-2 the
concept of hazard level and labelling and addresses the safety aspects of lasers specifically
in relation to tissue damage.
ITU-T study group 15 (Optical and other transport networks) has published Recommendation
G.664, which primarily discusses the automatic laser power reduction functionality for safety.
With the recent growth of interest in fibre Raman amplifiers, however, some difficulties have
been identified among optical amplifier users and manufacturers in fully understanding the
technical details and requirements across all such standards and agreements.
This technical report, therefore, provides a simple informative guideline on the maximum
optical power permissible for optical amplifiers.

---------------------- Page: 8 ----------------------
TR 61292-4 © IEC:2010(E) – 7 –
OPTICAL AMPLIFIERS –

Part 4: Maximum permissible optical power
for the damage-free and safe use of optical amplifiers,
including Raman amplifiers



1 Scope and object
This part of IEC 61292, which is a technical report, applies to all commercially available
optical amplifiers (OAs), including optical fibre amplifiers (OFAs) using active fibres, as well
as Raman amplifiers. Semiconductor optical amplifiers (SOAs) using semiconductor gain
media are also included.
This technical report provides a simple informative guideline on the threshold of high optical
power that causes high-temperature damage of fibre. Also discussed is optical safety for
manufacturers and users of optical amplifiers by reiterating substantial parts of existing
standards and agreements on eye and skin safety.
To identify the maximum permissible optical power in the optical amplifier from damage-free
and safety viewpoints, this technical report identifies the following values:
– the optical power limit that causes thermal damage to the fibre, such as fibre fuse and
fibre-coat burning;
– the maximum permissible exposure (MPE) to which the eyes/skin can be exposed without
consequential injury;
– the optical power limit in the fibre that causes MPE on the eyes/skin after free-space
propagation from the fibre;
– the absolute allowable damage-free and safe level of optical power of the optical amplifier
by comparing (a) and (c).
The objective of this technical report is to minimize potential confusion and misunderstanding
in the industry that might cause unnecessary alarm and hinder the progress and acceptance
of advancing optical amplifier technologies and markets.
It is important to point out that the reader should always refer to the latest international
standards and agreements because the technologies concerned are rapidly evolving. In fact,
the concept of hazard level and labelling is still evolving: more rigorous labelling requirements
are under discussion in IEC Technical Committee 76 as of October 2008.
The present technical report will be frequently reviewed and will be updated by incorporating
the results of various studies related to OAs and OA-supported optical systems in a timely
manner.
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 60825-1:2007, Safety of laser products – Part 1: Equipment classification and
requirements

---------------------- Page: 9 ----------------------
– 8 – TR 61292-4 © IEC:2010(E)
IEC 60825-2:2006, Safety of laser products – Part 2: Safety of optical fibre communication
systems (OFCS)
Amendment 1(2006)
IEC/TR 60825-14:2004, Safety of laser products – Part 14: A user’s guide
ITU-T Recommendation G. 664, Optical safety procedures and requirements for optical
transport systems
3 Abbreviated terms
For the purposes of this document, the following abbreviated terms apply.
ALS automatic laser shutdown
APR automatic power reduction
DSF dispersion shifted fibre
LOS  loss of signal
MFD mode field diameter
MPE maximum permissible exposure
MPI-R single channel receive main path Interface reference point
MPI-S single channel source main path interface reference point
NOHD nominal ocular hazard distance
NZ-DSF non-zero dispersion shifted single-mode optical fibre
OA optical amplifier
OFA optical fibre amplifier
SMF single mode fibre
SOA semiconductor optical amplifier
4 Maximum transmissible optical power to keep fibres damage-free
4.1 General
The use and reasonably foreseeable misuse of high intensity optical amplifiers may cause
problems in the fibre such as:
a) fibre fuse and its propagation;
b) heating in the splice point/connection point;
c) fibre end-face damage due to dust and other contamination;
d) fibre coat burning and ignition of hazardous environments due to tight fibre bending or
breakage.
This clause introduces the experiments and their results concerning the above issues to give
guidelines for the damage-free use of optical amplifiers. However, it must be noted that the
following results are only valid under the conditions tested and that a higher power might be
allowed under different conditions.
NOTE The test method for the failure time (the time until the catastrophic failure of the glass, or the catastrophic
failure to the fibre coating happens) characteristics as a function of the launch power and bend conditions (bend
angle and diameter) is described in IEC 62547.

---------------------- Page: 10 ----------------------
TR 61292-4 © IEC:2010(E) – 9 –
4.2 Fibre fuse and its propagation
4.2.1 Introduction
The safety of optical amplifiers should be discussed from the viewpoint of laser hazard to the
eyes and skin as well as fibre damage such as fibre-coat burning and fibre fusing. This
technical report experimentally analyzes the fibre fuse and its propagation caused by high
optical power and discusses the threshold of optical power.
4.2.2 Experiment and results
The experimental setup is shown in Figure 1, in which the fibre fuse was initiated by heating
the optical fibre from outside of the fibre by using an independent heat source, while a high
optical power was continuously launched into the fibre. The wavelength of the high-power
optical source was 1 467nm, which is a typical pump wavelength for distributed Raman
amplification.

Sample 10 m - 20 m
SMF SMF
1 467 nm
Optical power
Max. 6 W meter
SMF/DSF
Splicing
Heating
(initiation for fibre fuse)
IEC  146/10

Figure 1 – Experimental setup for fibre fuse propagation
It was confirmed that the temperature of the fibre portion heated when the fuse initiated was
greater than 1 000 °C. Once the fibre fuse began propagating, the optical source power was
continuously reduced until the fuse propagation stopped. The threshold power for the fuse
propagation was 1,4 W and 1,2 W for standard single mode fibre (SMF) and dispersion shifted
fibre (DSF) respectively as shown in Table 1. The results for three trials are shown.
Table 1 – Experimental results of the threshold power
of fibre fuse propagation
Standard single mode fibre 1,41 W, 1,45 W, 1,51 W
Dispersion shifter fibre 1,19 W, 1,19 W, 1,20 W

The difference in the fibre mode-field diameter might have been the major reason for the
1
difference in the threshold powers because the fibre fuse depends on the power density [1] .
The threshold power for the fibre fuse propagation was quite reproducible.
On the other hand, it was difficult to identify the threshold power for the fibre fuse initiation
based on the above experiments because it varied significantly.
Although the mechanism of fibre fuse initiation is not yet well understood, the threshold
seems to depend on the conditions, i.e., clean or dirty, of the fibre end faces where the very
first fibre fuse takes place.
It was confirmed through repeated experiments, however, that the initiation threshold well
exceeded 1,2 W and 1,4 W for various fibre end-face conditions.
___________
1
 Figures in square brackets refer to the Bibliography.

---------------------- Page: 11 ----------------------
– 10 – TR 61292-4 © IEC:2010(E)
The above information was made available from Furukawa Electric (Japan in Oct. 2002) and
was reported [1] at the 2003 International Laser Safety Conference in Jacksonville, FL, USA.
This issue was also discussed in other literature [2] [3] as follows.
The main physical mechanism responsible for the fibre fuse phenomenon and its propagation
is optical discharge propagation due to thermal conductivity. It can be initiated in most fibre
types by launching a CW laser into a fibre and ensuring contact of the fibre output end face
with some absorbing surface or by heating a section of the fibre.
The temperature of the optical discharge plasma is about 5 000 °K to 10 000 °K. The speed of
its propagation is about 1m/s in typical single mode fibres at a laser power of approximately
1 W. Examination of the fibre core after such discharge reveals extensive damage in the form
of voids which have the form of bubbles (sometimes periodic) or long non-periodic filaments.
Because the most probable reason for optical discharge is a contaminated end face, fusion
splicing is the most reliable way to reduce the risk of high-power damage. Optical isolators
used in some schemes can also be damaged. Unfortunately, their survivability at high power
is an open question.
The literature [3] includes a figure reporting the measured dependencies of threshold intensity
for the propagation of optical discharge through the fibre (the power at which such
propagation is terminated) on the mode field diameter of single-mode fibres of different core
compositions.
The figure includes 21 data points among which, however, just one experimental point using
1,48 micrometer wavelength for silica-based single-mode fibre is applicable [2] to typical
optical transmission systems.
2
The threshold intensity I for this experimental point was 1,0 (MW/cm ) for MFD (mode field
th
diameter) Dm = 12,6 micrometer. The threshold power is calculated as 1,3 W.
4.2.3 Conclusion
The threshold optical powers of fibre fuse propagation reported in Figure 1 and Table 1 were
found to be 1,4 W and 1,2 W for SMF and DSF respectively under the conditions tested. On
the other hand, the fuse-initiation threshold varied significantly, although they well exceeded
1,4 W and 1,2 W. Another report identified that 1,3 W could be allowed for SMF, although the
information available on the fibre was limited.
4.3 Loss-induced heating at connectors or splices
4.3.1 Introduction
In extremely high power optical amplifiers, the loss-induced heating at fibres and connectors
or splices could lead to damage, including fibre-coat burning, fibre fuse, etc. This subclause
provides experimental data [4] and considerations for information.
4.3.2 Experiment on the connector
Table 2 summarizes the measurement conditions. The experiment used MU type optical
connectors for standard single mode fibre (SMF) and dispersion-shifted fibre (DSF), where
loss was increased by optical fibre misalignment. The optical source used was a 2-W Raman
pump at 1 480 nm. The connector temperature was measured by a thermocouple placed on
the sleeve. Since the MU ferrule diameter was only 1,25 mm, the sleeve temperature was
almost the same as that of the ferrule; ferrule temperature is the most important factor
determining the long-term reliability of optical connectors [5].

---------------------- Page: 12 ----------------------
TR 61292-4 © IEC:2010(E) – 11 –
Table 2 – Measurement conditions
Parameter Conditions
Fibre SMF, DSF
Connectors MU type
Ferrule Zirconia
Connector/splice loss Imperfect alignment
Wavelength Raman pump – 1 480 nm
Power 2 W
Temperature measurement Thermocouple on the sleeve

4.3.3 Results and considerations
Figure 2 shows temperature increase versus connection loss. More temperature increase was
observed in DSF than in SMF due to higher power density.


25
SMF
DSF
20

15

10

5

0
0,4 0,6 0,8 1,0 1,2
0 0,2
Connection loss  (dB)
IEC  147/10

Figure 2 – Connection loss versus temperature increase
The data suggest that the temperature increase could be within 10 °C under realistic
conditions of loss and power. A commercial dry-type connector cleaner was used each time.
During repeated connection-disconnection of the connectors, neither damage nor fibre fuse
was observed. The experiments with the use of the cleaner identified no problems in terms of
fibre/connector damage and reliability. Without the cleaner, however, the experiment with the
DSF connector indicated that fibre fuse could occur after repeated connection-disconnection
of more than 200 times.
Such temperature increase,
...