IEC TR 61292-4:2004

TECHNICAL IEC
REPORT TR 61292-4
First edition
2004-08
Optical amplifiers –
Part 4:
Maximum permissible optical power
for the damage-free and safe use
of optical amplifiers, including
Raman amplifiers
Reference number
IEC/TR 61292-4:2004(E)
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TECHNICAL IEC
REPORT TR 61292-4
First edition
2004-08
Optical amplifiers –
Part 4:
Maximum permissible optical power
for the damage-free and safe use
of optical amplifiers, including
Raman amplifiers
” IEC 2004  Copyright - all rights reserved
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– 2 – TR 61292-4 ” IEC:2004(E)

CONTENTS
FOREWORD.3

INTRODUCTION.5

1 Scope and object.6

2 Maximum transmissible optical power to keep fibres damage-free .6

2.1 Fibre fuse and its propagation.7

2.2 Loss-induced heating at connectors or splices.8

2.3 Connector end-face damage induced by dust/contamination .10
2.4 Fibre-coat burn/melt induced by tight fibre bending.13
2.5 Summary of the fibre-damage experiments.14
3 Maximum transmissible optical power to keep eyes and skin safe.14
3.1 Maximum permissible exposure (MPE) on the surface of eye and skin .14
3.2 Maximum permissible optical power in the fibre for the safety of eye and skin .15
4 Maximum optical power permissible for optical amplifiers from the viewpoints of
fibre damage as well as eye and skin safety.18
5 Conclusion.18
Bibliography .19
Figure 1 – Experimental setup for fibre fuse propagation .7
Figure 2 – Connection loss versus temperature increase .9
Figure 3 – Test setup.10
Figure 4 – Surface condition contaminated with metal filings, before the test.11
Figure 5 – Variation of the power attenuation during the test at several power input
values for plugs contaminated with metal filings .12
Figure 6 – Polishing surface condition contaminated with metal filing, after the test.12
Figure 7 – Thermo-viewer image of tightly-bent SMF with optical power of 3 W at 1 480 nm .13
Figure 8 – Temperature of the coating surface of SMFs against bending with optical
power of 3 W at 1 480 nm .14
Figure 9 – Maximum permissible power in the fibre against APR power reduction time .17
Table 1 – Experimental results of the threshold power of fibre fuse propagation .7
Table 2 – Measurement conditions .9
Table 3 – Examples of the maximum permissible optical power in the fibre for OAs
determined by the MPE limit for the eyes and skin.16

TR 61292-4 ” IEC:2004(E) – 3 –

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,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86C/593/DTR 86C/629/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.

– 4 – TR 61292-4 ” IEC:2004(E)

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

IEC 61292 consists of the following parts, under the new general title Optical amplifiers:

Part 1: Parameters of amplifier components

Part 2: Theoretical background for noise figure evaluation using the electrical spectrum

analyzer
Part 3: Classification, characteristics and applications

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

amplifiers, including Raman amplifiers

Part 5: Polarization mode dispersion parameter – General parameter
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
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.
㩷
TR 61292-4 ” IEC:2004(E) – 5 –

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 this

subject is also stimulating many new types of fibre and non-fibre based optical amplifier

research. With the introduction of such technologies as long-haul, 40Gb/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 31 (Electrical apparatus 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. To the best of our knowledge, this is the first
international guideline on the maximum optical power permissible in optical fibre devices that
takes both physical and medical viewpoints into consideration.

– 6 – TR 61292-4 ” IEC:2004(E)

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 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 2003.

The 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 Maximum transmissible optical power to keep fibres damage-free
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.
TR 61292-4 ” IEC:2004(E) – 7 –

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.

2.1 Fibre fuse and its propagation

2.1.1 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

document experimentally analyzes the fibre fuse and its propagation caused by high optical

power and discusses the threshold of optical power.
2.1.2 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 1 467 nm, which is a typical pump wavelength for distributed Raman
amplification.
Sample 10 m - 20 m
SMF SMF
1 467 nm
Optical power
6 W Max.
meter
SMF/DSF
Splicing
Heating
(initiation for fibre fuse)
IEC 1218/04
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.
___________
1)
Figures in square brackets refer to the Bibliography.

– 8 – TR 61292-4 ” IEC:2004(E)

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.

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 [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° 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 for the mode field diameter (MFD) between 2 Pm and
14 Pm and identifies that the mean values of the threshold intensity I were 3,6 MW/cm ,
th
2 2
2,5 MW/cm and 1,2 MW/cm for the MFD of 4 Pm, 6ҏPm and 8 Pm , respectively. I was
th
constant at 1,2 MW/cm for MFD over 8 Pm.
2 2
The I varied between +0,3 MW/cm and –0,6 MW/cm , depending on the core compositions
th
under the conditions tested, except in one extraordinary case. Here, the mean thresholds for
the MFD of 8 Pm and 10 Pm respectively corresponded to 2,5 W and 1,6 W, if the entire
intensity is assumed to be within the mode field

2.1.3 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 a little more power than the above experiment
could be allowed, although the information available on the fibre was limited.
2.2 Loss-induced heating at connectors or splices
2.2.1 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 [1] and considerations for information.

TR 61292-4 ” IEC:2004(E) – 9 –

2.2.2 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 [2].

Table 2 – Measurement conditions

Parameter Conditions
Fibre SMF, DSF
Connec
...