IEC TR 61292-4:2023

IEC TR 61292-4 ®
Edition 4.0 2023-01
REDLINE VERSION
TECHNICAL
REPORT
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inside
Optical amplifiers –
Part 4: Maximum permissible optical power for the damage-free and safe use of
optical amplifiers, including Raman amplifiers

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IEC TR 61292-4 ®
Edition 4.0 2023-01
REDLINE VERSION
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
ICS 33.160.10; 33.180.30 ISBN 978-2-8322-6365-5

– 2 – IEC TR 61292-4:2023 RLV © IEC 2023
CONTENTS
FOREWORD . 4
INTRODUCTION . 2
1 Scope and object . 8
2 Normative references . 8
3 Terms, definitions, and abbreviated terms . 9
3.1 Terms and definitions . 9
3.2 Abbreviated terms . 8
4 Maximum transmissible optical power to keep fibres damage-free . 9
4.1 General . 9
4.2 Fibre fuse and its propagation . 10
4.3 Loss-induced heating at connectors or splices . 11
4.4 Connector endface damage induced by dust/contamination . 12
4.5 Fibre coat burn/melt induced by tight fibre bending . 15
4.6 Summary of the fibre damage . 16
5 Maximum transmissible optical power to keep eyes and skin safe . 16
5.1 Maximum transmissible 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. 17
5.2.1 General .
5.2.1 Power limit . 17
5.2.2 Need for APR . 18
5.2.3 Wavelengths . 19
5.2.4 Locations . 19
5.2.5 Nominal ocular hazard distance (NOHD). 19
5.2.6 Power reduction times . 19
5.2.7 Medical aspects of the safety of eyes and skin in existing standards . 21
6 Maximum optical power permissible for optical amplifiers from the viewpoint of
fibre damage as well as eye and skin safety . 22
7 Conclusion . 22
Annex A (informative) General information for optical fibre fuse . 23
A.1 Introductory remark . 23
A.2 Generating mechanism . 23
A.3 Void formation mechanism . 27
A.4 Propagation characteristic of a fibre fuse . 27
A.5 Prevention and termination . 29
A.5.1 General . 29
A.5.2 Prevention methods . 29
A.5.3 Termination methods . 30
A.6 Additional safety information . 32
A.7 Conclusion . 33
Bibliography . 34

Figure 1 – Experimental set-up for fibre fuse propagation . 10
Figure 2 – Connection loss versus temperature increase . 12
Figure 3 – Test set-up . 13
Figure 4 – Surface condition contaminated with metal filings, before the test . 14

Figure 5 – Variation of power attenuation during test at several power input values for
plugs contaminated with metal filings . 14
Figure 6 – Polishing surface condition contaminated with metal filing, after 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 . 16
Figure 9 – Maximum permissible power in the fibre against APR power reduction time . 21
Figure A.1 – Front part of the fibre fuse damage generated in the optical fibre . 23
Figure A.2 – SiO absorption model . 25
Figure A.3 – Calculated fibre fuse propagation behaviour simulated with the SiO
absorption model . 26
Figure A.4 – Series of optical micrographs showing damage generated by 9,0 W

1 480 nm laser light suggesting a mechanism of periodic void formation . 27
Figure A.5 – Images of fibre fuse ignition taken with an ultra-high-speed camera and
an optical micrograph of the damaged fibre. 28
Figure A.6 – Power density dependence of the fibre-fuse propagation velocity . 29
Figure A.7 – Optical micrographs showing front part of the fibre fuse damage
generated in SMF-28 fibres with various laser intensities (1 480 nm) . 29
Figure A.8 – Principle of the optical fibre fuse passive termination method and
photograph of a fibre fuse terminator using a TEC structure. 30
Figure A.9 – Photograph of hole-assistantassisted fibre and fibre fuse termination
using a hole-assistantassisted fibre . 31
Figure A.10 – Example of fibre fuse active termination scheme . 32
Figure A.11 – Transformation of electrical signal by optical fibre fuse . 32

Table 1 – Threshold power of fibre fuse propagation for various fibres . 10
Table 2 – Measurement conditions. 12
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 . 19

– 4 – IEC TR 61292-4:2023 RLV © IEC 2023
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
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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.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC TR 61292-4:2014. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
IEC TR 61292-4 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is a Technical Report.
This fourth edition cancels and replaces the third edition published in 2014. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition.
a) The technical information has been updated to reflect revisions of the relevant references.
b) In particular, the descriptions provided in Clause 5 and Clause 6 have been modified
significantly to reflect changes in the cited references. Unnecessary formulas and
explanations that overlap with the references have been removed to simplify the document.
c) New information has been added to Annex A on optical fibre burning when light enters an
optical fibre with a bubble train formed by a fibre fuse.
The text of this Technical Report is based on the following documents:
Draft Report on voting
86C/1821/DTR 86C/1832/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in 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 document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

– 6 – IEC TR 61292-4:2023 RLV © IEC 2023
INTRODUCTION
This document is dedicated to the subject of maximally 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 is also
stimulating the development of many new types of fibre and non-fibre based optical amplifiers.
With the introduction of new technologies, such as long-haul, over 40 beyond 100 Gb/s, WDM
transmission, digital coherent transmission and Raman amplification, some optical amplifiers
may involve employ optical pump sources with extremely high optical power – possibly up to
several Watts. For example, erbium doped fibre amplifiers that provide extremely high output
power are described in IEC TR 61292-8 [1] , and Raman amplifiers in IEC TR 61292-6 [2].
Excessively high optical power may can cause physical damage to the fibres/optical fibres,
components and equipment, in addition to presenting a medical danger hazard to the human
eye and skin.
The possibility of fibre damage caused by high optical intensity has been discussed at technical
conferences and in technical reports for many years. The use of high intensity optical amplifiers
may cause problems in the fibre such as a fibre fuse, a heating in the splice point (connection
point), and the fibre end-face damage due to dust and the fibre coat burning due to tight fibre
bending. IEC SC 86A (Fibres and cables) has published IEC TR 62547, and SC 86B (Fibre optic
interconnecting devices and passive components) has published IEC TR 62627-01. IEC TC 31
(Equipment for explosive atmospheres) is also discussing the risk of ignition of hazardous
environments by radiation from optical equipment. The use of high intensity optical amplifiers
can cause problems in optical fibres, which include fibre fuse, heating in the splice points
(connection points), fibre endface damage due to dust, and fibre coat burning due to tight fibre
bending. For example, IEC TR 62547 [3] provides guidelines for the measurement of high-
power damage sensitivity of single-mode fibre to bends, and IEC TR 62627-01 [4] describes
cleaning methods for fibre optic connectors to reduce the risk of fibre endface damage. In
addition, other standard groups are discussing the risk of ignition of hazardous environments
caused by high-power radiation from optical equipment.
Medical aspects have long been discussed at standards groups. IEC TC 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.
The medical aspects of high-power optical radiation have also been addressed by standards.
IEC 60825-2 defines the concept of hazard levels and corresponding labelling, which addresses
the safety aspects of lasers specifically in relation to tissue damage.
In addition, IEC TR 60825-17 [5] describes safety measures to protect against effects caused
exclusively by thermal, opto-mechanical and related effects in passive optical components and
optical cables used in high power optical fibre communication systems. Moreover, ITU-T
Recommendation G.664 [6] discusses the safety feature of automatic laser power reduction.
With the recently growing interest in high power fibre amplifiers and 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.
___________
Numbers in square brackets refer to the Bibliography.

This document provides a simple informative guideline on the maximum optical power
permissible for optical amplifiers for optical amplifier users and manufacturers.

– 8 – IEC TR 61292-4:2023 RLV © IEC 2023
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 document provides informative guidelines on the threshold of high optical power that
causes can cause high-temperature damage of the fibre. Also discussed is optical safety for
manufacturers and users of optical amplifiers by reiterating substantial quoting 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 document identifies the following values for maximum permissible
optical power in the optical amplifier for damage-free and safe operation:
a) the optical power limit that causes thermal damage to the fibre, such as fibre fuse and fibre-
coat burning;
b) the maximum permissible exposure (MPE) to which the eyes/skin can be exposed without
consequent injury;
c) the optical power limit in the fibre that causes MPE on the eyes/skin after free-space
propagation from the fibre;
d) the absolute allowable optical power level for damage-free and safe level of optical power
operation of the optical amplifier by comparing a) and c).
The objective of this document is to minimize potential confusion and misunderstanding in the
industry that might can cause unnecessary alarms and hinder the progress and acceptance of
advancing optical amplifier technologies in the market.
It is important to point out that the reader should always refers to the latest international
standards and agreements, because the technologies concerned are rapidly evolving.
The present document will be frequently reviewed and updated in a timely manner by
incorporating the results of various studies related to OAs and OA-supported optical systems.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60825-1:2007, Safety of laser products – Part 1: Equipment classification and requirements
IEC 60825-2:2004, Safety of laser products – Part 2: Safety of optical fibre communication
systems (OFCS)
Amendment 1 (2006)
Amendment 2 (2010)
IEC TR 60825-14:2004, Safety of laser products – Part 14: A user’s guide
IEC TR 62547, Guidelines for the measurement of high-power damage sensitivity of single-
mode fibres to bends – Guidance for the interpretation of results
IEC TR 62627-01, Fibre optic interconnecting devices and passive components – Part 01: Fibre
optic connector cleaning methods
ITU-T Recommendation G.664:2012, Optical safety procedures and requirements for optical
transport systems
IEC 61291-1:2018, Optical amplifiers – Part 1: Generic specification
3 Terms, definitions, and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61291-1:2018 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.2 Abbreviated terms
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
OFCS optical fibre communication system
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 can cause
problems in the fibre such as
a) fibre fuse and its propagation,
b) heating in splice points/connection points,

– 10 – IEC TR 61292-4:2023 RLV © IEC 2023
c) fibre endface damage due to dust and other contamination, and
d) fibre coat burning and ignition of hazardous environments due to tight fibre bending or
breakage.
Subclauses 4.2 to 4.5 introduce results concerning the above issues to give guidelines for the
damage-free use of optical amplifiers. However, it should be noted that the following results are
only valid under the conditions tested, and a higher power might could be allowed applied under
different conditions.
4.2 Fibre fuse and its propagation
The safety of optical amplifiers should be is discussed from the viewpoint of laser hazard to the
eyes and skin and from the viewpoint of fibre damage such as fibre-coat burning and fibre fusing.
Subclause 4.2 experimentally analyses the fibre fuse and its propagation caused by high optical
power and discusses the threshold power of fibre fuse propagation [7]. Fibre fuse is defined as
the phenomenon in which an intense blue-white flash occurs and runs along the fibre toward
the high-power light source while forming periodic and/or non-periodic voids.
Figure 1 shows a typical measurement set-up for measuring the threshold power of fibre fuse
propagation. The fibre fuse is initiated by heating the optical fibre from outside of the fibrewith
an independent heat source, while a light at high optical power is continuously launched into
the fibre. Once the fibre fuse begins propagating, the optical source power is continuously
reduced until the fuse propagation stopped for measuring the threshold power stops. Table 1
shows the threshold powers which were measured at various wavelengths of the high-power
optical source and for various fibres. Although the threshold power depends on the wavelength
of the high-power optical source, the power for the fuse propagation is less than 1,4 W and 1,2
W for a standard single-mode fibre (SMF) and a dispersion shifted fibre (DSF) respectively,
which are used as the optical fibre for typical optical fibre communication systems.

Figure 1 – Experimental set-up for fibre fuse propagation
Table 1 – Threshold power of fibre fuse propagation for various fibres
Measurement Threshold power of
Fibre type
wavelength fibre fuse propagation
μm W
Standard single-mode fibre 1,064 1 [8]
1,467 1,4 [8]
1,48 ∼1,2 [9]
1,55 1,39 [10]
Dispersion shifted fibre 1,064 1,2 [8]
1,467 0,65 [8]
1,55 ~1,1 [11]
Dispersion compensation fibre 1,55 ~0,7 [11]

The difference in fibre mode-field diameter has been identified as the major reason for the
difference in the threshold powers because the fibre fuse depends on the power density [7], [8].
On the other hand, it is difficult to identify the threshold powers for the fibre fuse self-initiation
(without any external cause) because it varied significantly, although they well exceeded 1,4 W
and 1,2 W for standard singlemode fibre (SMF) and dispersion shifted fibre (DSF) respectively.
On the other hand, it is difficult to identify the threshold power for self-initiated fibre fuse (without
any external cause) because it varies significantly. The threshold powers for self-initiated fibre
fuse significantly exceed 1,4 W and 1,2 W for standard single-mode fibre (SMF) and dispersion
shifted fibre (DSF) respectively.
Further information on the generating mechanism, the characteristics of fibre fuse and the
prevention and termination of the fibre fuse are described in Annex A.
4.3 Loss-induced heating at connectors or splices
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. Subclause 4.2
provides experimental data and considerations for the information of the thermal effects induced
by connector and splice losses in high-power amplifiers [12].
Figure 2 shows temperature increase versus connection loss when measured by the conditions
shown in Table 2. MU type optical connectors (IEC 61754-6 series [13]) for standard
single-mode fibre (SMF) and dispersion shifted fibre (DSF) were used for this measurement.
The connector 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 [14].
Larger increases in temperature are observed in DSF rather than in SMF due to higher power
density. The result suggests that the temperature increase could be within 10 °C under practical
conditions of loss and power. A commercial dry-type connector cleaner was used in every test
for cleaning the endface of the connectors.
During repeated connection-disconnection of the connectors, neither damage nor fibre fuse was
observed. The experiments in which a cleaner was used 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, and accordingly the danger of fibre fuse, will be worse for non-zero
dispersion shifted single-mode fibre (NZ-DSF) connectors than for SMF connectors but better
than for DSF connectors, because the effective areas are SMF>NZDSF>DSF of SMFs is
typically larger than that of NZ-DSFs, and the effective area of NZ-DSFs is larger than those of
DSFs. Further quantitative studies are needed. Other types of physical contact (PC) connectors,
like SC connectors (see IEC 61754-4 [15]), show similar temperature responses, because only
their ferrule radii differ from MU type connectors.
In conclusion, it is shown that the thermal effects induced by connector and splice losses in
high-power amplifiers could be acceptable under any practical conditions foreseeable at this
moment. However, special care should be taken it is advisable to eliminate dust and
contamination from the connector endfaces and splice points that could locally induce high
temperature increases according to the power density absorbed.

– 12 – IEC TR 61292-4:2023 RLV © IEC 2023
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

Figure 2 – Connection loss versus temperature increase
4.4 Connector endface damage induced by dust/contamination
The purpose of 4.4 is to show the increase in attenuation of the connector under test when the
light power into the fibre is extremely high [16].
Figure 3 shows the scheme of the measurement set-up used in the test. The pump laser of a
Raman amplifier is used with a maximum nominal power of 2 W, at a wavelength of 1 455 nm.

Figure 3 – Test set-up
The optical connectors used are SC-PC type with a perfectly clean surface and with skin grease
(from the human operator), dust (from the floor of the lab), and metal filings (from a metallic
sleeve) applied.
a) Test result on clean connectors
Two plugs without defects on the polished fibre surface were used. The laser power was
increased in steps to 1,2 W after a thorough cleaning. The test was conducted at ambient
temperature and in a chamber at 70 °C. During the entire test, the variation of the
attenuation was less than 0,02 dB and the visual examination of the fibre surface at the
microscope did not show any damage.
b) Test result on connectors contaminated with skin grease
A layer of grease was put down on two plugs without any defect, by simply touching the
polished surface with the hands. When increasing the power from 100 mW to 1 200 mW at
ambient temperature, the attenuation varied within a few hundredths of a dB. The visual
inspection with a microscope after the test showed a cleaning effect, probably due to high
temperature near the fibre. After the surface cleaning, no damage was observed.
c) Test result on connectors contaminated with dust
In this case, dust from the laboratory floor was put on the polished surface of the plugs.
After the initial increase of the attenuation from a normalized value of 0 dB to 0,06 dB with
200 mW input power, the attenuation started to decrease with the increase in the power until
–0,15 dB with 1,2 W input power. This effect of improvement in power transmission could
be due to a cleaning action of the high temperature on the finest particles. Also, in this case,
after the cleaning at the end of the test, the surfaces did not show any damage.
d) Test result on connectors contaminated with metal dust
In this test, metal dust obtained by filing a metallic sleeve of an adapter was put down on
the plug surfaces. This condition simulates the presence of metallic particles produced by
the friction of the ferule during the insertion into a metallic sleeve.
A first test was performed by heavily contaminating the surfaces, as Figure 4 shows. This
The heavy contamination is clear evident from the initial attenuation value, which was 3 dB
to 4 dB higher than the ones obtained for the other conditions.
During the test, already at 200 mW, the attenuation increased by about 0,3 dB. At the
400 mW step, the damage became evident as the attenuation increased to 1,1 dB (see
Figure 5). As failure occurred, the test was stopped to visually inspect the surfaces.
Obvious signs of burning were observed on the core of both fibres that could not be
eliminated by cleaning the surface. The visual inspection of polished surface through a
microscope (Figure 6) shows fused metal glued embedded on the fibre cores. These clots
contaminations are not removable by cleaning the surfaces.

– 14 – IEC TR 61292-4:2023 RLV © IEC 2023

Figure 4 – Surface condition contaminated with metal filings, before the test

Figure 5 – Variation of power attenuation during test at several
power input values for plugs contaminated with metal filings

Figure 6 – Polishing surface condition contaminated with metal filing, after test
In conclusion, it was confirmed that there is no damage risk to the connectors due to high optical
power under the conditions tested, if the connectors are correctly used and handled. In
particular, it is recommended never not advisable to ever open connectors while high optical
power is passing through them. However, a correct cleaning procedure and visual analysis of

the polished connector surface is fundamental for a good and reliable network, particularly when
metallic sleeves are used.
4.5 Fibre coat burn/melt induced by tight fibre bending
Subclause 4.5 provides some examples of the fibre coat burn/ or melt induced by tight fibre
bending [8]. The fibre coatings used were
a) UV curable resin: white, blue, green, and uncoloured, and
b) nylon white.
The fibre used was single-mode (SMF).
By using a thermo viewer image of the bent fibre, the highest temperature at the surface of
each fibre coating was measured. Figure 7 shows an image of the tightly bent fibre with an
optical power of 3 W at 1 480 nm. Shown in Figure 8 is the temperature at the coating surface
versus bending diameter for 3 W at 1 480 nm. The temperature of the nylon coat surface
reached 150 °C or higher; the nylon coating melted or even burned. The nylon coat burned in
the test after the fibre break at the point where the fibre coat melted.
By considering the test results together with the long-term reliability degradation of coated SMF,
it is suggested that the coated fibre bend diameter should be kept at more than 20 mm and
more than 30 mm for optical powers of 1 W and 3 W, respectively, under the conditions tested.
Another test revealed that transparent UV resin was more durable than coloured UV resin
against tight bending.
Figure 7 – Thermo viewer image of tightly bent SMF
with optical power of 3 W at 1 480 nm

– 16 – IEC TR 61292-4:2023 RLV © IEC 2023

Figure 8 – Temperature of the coating surface of SMFs against bending
with optical power of 3 W at 1 480 nm
4.6 Summary of the fibre damage
In 4.2, it was found that fibre fuse, once it was initiated for any reason, propagated if the input
signal power was higher than 1,4 W and 1,2 W for SMF and DSF, respectively, under the
conditions tested. However, care should be taken it is not advisable to even momentarily push
the fibre across a sharp edge that may could induce a tight bend and trigger fibre fuse even at
a lower power than the above.
In 4.3, it was shown that the thermal effects induced by the connector and splice losses in high-
power amplifiers could be acceptable under any practical conditions.
In 4.4, the connectors were tested with the input powers up to 1,2 W. It was found that only
case discovered that the only case that caused permanent damage to the fibre core was when
surfaces were contaminated with metal particles.
In 4.5, fibre coat burning induced by fibre tight bending was addressed. It is suggested that the
bend diameter of coated fibre should be kept over 20 mm and 30 mm for optical powers of 1 W
and 3 W, respectively, under the conditions tested.
Based on 4.2 to 4.5, it is concluded that power levels up to at least 1,2 W can be used without
damaging OAs. The actual upper limit of the power is under study by considering, for example,
the types of fibre and cleanliness of the fibre endfaces.
In addition, IEC TR 62627-01 [4] describes methods to prevent damage to the connector, and
IEC TR 62547 [3] describes methods to measure the damage of fibre tight bending.
5 Maximum transmissible optical power to keep eyes and skin safe
5.1 Maximum transmissible exposure (MPE) on the surface of eye and skin
In IEC 60825-1:2014, MPE is defined as the "level of laser radiation to which, under normal
circumstances, persons may be exposed without suffering adverse effects" [17]. The MPE
values used by IEC have been specified in the ANSI-Z136 series [18] and are based on animal
non-human experiments. IEC TR 60825-14:2004 gives more details on MPE [19].
IEC 60825-2:2004 includes the following normative text in which it is requested that optical fibre
communication systems (OFCSs) be designed not to exceed the MPE, including the time period
before an automatic power reduction (APR) system completes its function [20]:
"Where the OFCS uses an APR feature to meet the limits of a hazard level that is lower than
that which would have to be assigned if no APR feature would be present, the irradiance or
radiation radiant exposure during the maximum time to reach the lower hazard level […] (not

greater than 1 s for unrestricted, 3 s for restricted or controlled locations) shall not exceed the
irradiance or radiant exposure limits for either the eye or skin (equivalent to MPEs for the eye
and skin), corresponding to the shut-down period of the APR. For unrestricted/restricted
locations and controlled locations the measurement distances is are 100 mm and 250 mm,
respectively, for this subclause [i.e., IEC 60825-2:2021, 4.7.4] only."
NOTE In the text described in IEC 60825-2, there is a sentence with a clause number, but in the above text, that
number is deleted.
In IEC 60825-2 [20], the hazard levels of laser products, including OAs, are determined based
on the classification rule of IEC 60825-1 [17]. In the existing standards, automatic laser
shutdown (ALS) could have the same meaning as APR.
5.2 Maximum permissible optical power in the fibre for the safety of eye and skin
5.2.1 General
Informative Annex D of IEC 60825-2:2004 and IEC 60825-2:2004/AM2:2010 gives the following
formula that calculates the maximum permissible optical power P in the fibre by using the
maximum permissible exposure (MPE) to the eyes/skin after free-space propagation.
πd MPE 1
P =
4t
 
 πω d 
 
1 − exp − 0,125 
 
 λNOHD  (1)
 
 
where
P is the total power in fibre, in W;
–2
MPE is the maximum permissible exposure, Jm ;
ω is the mode field diameter (1/e power density), in m;
d is the limiting aperture diameter, in m;
t is the shut down time, in s;
NOHD is the nominal ocular hazard distance, in m;
λ is the wavelength, in m.
Based on Formula (1), Table D.14 of IEC 60825-2:2004 and IEC 60285-2:2004/AMD2:2010
shows examples of power limits for optical fibre communication systems that have the APR to
reduce the power to a lower hazard level. MPEs used in the calculation are shown in Tables 5,
6 and 7 of IEC 60825-14:2004.
Table 3 reiterates Table D.14 of IEC 60825-2:2004 and IEC 60285-2:2004/AMD2:2010. It shall
be noted that the maximum permissible optical power in such OAs can be increased by reducing
the power reduction time of the APR (the shut down time).
5.2.1 Power limit
Table 3 shows examples of power limits for unrestricte
...