IEC TR 61292-4:2014

IEC TR 61292-4 ®
Edition 3.0 2014-10
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

61292-4
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IEC TR 61292-4 ®
Edition 3.0 2014-10
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
V
ICS 33.160.10 33.180.30 ISBN 978-2-8322-1907-2

– 2 – IEC TR 61292-4:2014 © IEC 2014

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
4.3 Loss-induced heating at connectors or splices . 10
4.4 Connector end-face damage induced by dust/contamination . 11
4.5 Fibre-coat burn/melt induced by tight fibre bending . 13
4.6 Summary of the fibre damage . 14
5 Maximum transmissible optical power to keep eyes and skin safe . 15
5.1 Maximum transmissible exposure (MPE) on the surface of eye and skin . 15
5.2 Maximum permissible optical power in the fibre for the safety of eye and skin. 15
5.2.1 General . 15
5.2.2 Need for APR . 17
5.2.3 Wavelengths . 17
5.2.4 Locations . 17
5.2.5 Nominal ocular hazard distance (NOHD). 17
5.2.6 Power reduction times . 17
5.2.7 Medical aspects of the safety of eyes and skin in existing standards . 18
6 Maximum optical power permissible for optical amplifiers from the viewpoint of
fibre damage as well as eye and skin safety . 19
7 Conclusion . 19
Annex A (informative) General information for optical fibre fuse . 20
A.1 Introduction . 20
A.2 Generating mechanism . 20
A.3 Figure A.3 – Calculated fibre fuse propagation behaviour simulated with the
SiO absorption modelVoid formation mechanism . 23
A.4 Propagation characteristic of a fibre fuse . 24
A.5 Prevention and termination . 26
A.5.1 General . 26
A.5.2 Prevention methods . 26
A.5.3 Termination methods . 26
A.6 Conclusion . 29
Bibliography . 30

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

Figure 7 – Thermo-viewer image of tightly-bent SMF with optical power of 3 W at
1 480 nm . 14
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 . 18
Figure A.1 – Front part of the fibre fuse damage generated in the optical fibre . 20
Figure A.2 – SiO absorption model . 22
Figure A.3 – Calculated fibre fuse propagation behaviour simulated with the SiO
absorption modelVoid formation mechanism . 23
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 . 24
Figure A.5 – Images of fibre fuse ignition taken with an ultra-high speed camera and
an optical micrograph of the damaged fibre. 25
Figure A.6 – Power density dependence of the fibre-fuse propagation velocity . 25
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) . 26
Figure A.8 – Principle of the optical fibre fuse passive termination method and
photograph of the fibre fuse terminator which adopted TEC structure . 27
Figure A.9 – Photograph of hole-assistant fibre and fibre fuse termination using a hole-
assistant fibre . 28
Figure A.10 – Example of fibre fuse active termination scheme . 29
Figure A.11 – Transformation of electric signal by optical fibre fuse . 29

Table 1 – Threshold power of fibre fuse propagation for various fibres . 9
Table 2 – Measurement conditions. 10
Table 3 – Examples of power limits for optical fibre communication systems having
automatic power reduction to reduce emissions to a lower hazard level . 16
Table 4 – Location types within an optical fibre communication system and their
typical installations . 17

– 4 – IEC TR 61292-4:2014 © IEC 2014

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
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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.
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 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 third edition cancels and replaces the second edition, published in 2010, and constitutes
a technical revision with updates reflecting new research in the subject area.

The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86C/1158/DTR 86C/1200/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 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 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.
– 6 – IEC TR 61292-4:2014 © IEC 2014

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 report can be
expected.
Many new types of optical amplifiers are entering the marketplace and research is also
stimulating many new types of fibre and non-fibre based optical amplifier research. With the
introduction of such technologies as long-haul, over 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. 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.
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.
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 provides a simple informative guideline on the maximum optical power
permissible for optical amplifiers for optical amplifier users and manufacturers.

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:
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
consequential 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 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.
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 documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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
– 8 – IEC TR 61292-4:2014 © IEC 2014

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
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 their 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 that a higher power might be allowed under
different conditions.
4.2 Fibre fuse and its propagation
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 clause
experimentally analyses the fibre fuse and its propagation caused by high optical power and
discusses the threshold power of fibre fuse propagation [1] . It is defined that the fibre fuse is
the phenomenon in which an intense blue-white flash occurred and ran 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 the threshold power of fibre fuse
propagation. The fibre fuse is initiated by heating the optical fibre from outside of the fibre by
using an independent heat source, while a high optical power is continuously launched into
the fibre. Once the fibre fuse began propagating, the optical source power is continuously
reduced until the fuse propagation stopped for measuring the threshold power. Table 1 shows
the threshold powers which were measured at various wavelengths of the high-power optical
source 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.
Sample 10 m - 20 m
SMF SMF
High power
Optical power
optical source
meter
SMF/DSF
Splicing
Heating
(Initiation for fibre fuse)
IEC
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
W
µm
Standard single mode fibre 1,064 1 [2]
1,467 1,4 [2]
1,48
∼1,2 [3]
1,55 1,39 [4]
Dispersion shifted fibre 1,064 1,2 [2]
1,467 0,65 [2]
1,55 ~1,1 [5]
Dispersion compensation fibre 1,55 ~0,7 [5]

The difference in the fibre mode-field diameter has been the major reason for the difference in
the threshold powers because the fibre fuse depends on the power density [1].
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
___________
Figures in square brackets refer to the Bibliography.

– 10 – IEC TR 61292-4:2014 © IEC 2014

1,4 W and 1,2 W for standard single mode fibre (SMF) and dispersion shifted fibre (DSF)
respectively.
Further information such as the generating mechanism, the characteristics of fibre fuse and
the prevention and the termination for the fibre fuse is 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. This subclause
provides experimental data and considerations for the information of the thermal effects
induced by connector and splice losses in high-power amplifiers [6].
Figure 2 shows temperature increase versus connection loss, which are measured by the
conditions that shown in Table 2. MU type optical connectors 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 [7].
Larger increase in temperature is observed in DSF 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 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, and accordingly the danger of fibre fuse, for non-zero dispersion
shifted single-mode optical fibre (NZ-DSF) connectors will be worse than SMF connectors but
better than DSF connectors; the effective areas are SMF>NZDSF>DSF. Further quantitative
studies are needed. Other types of physical contact (PC) connectors such as SC connectors
will show similar temperature responses because only their ferrule radii differ.
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 to eliminate dust and contamination from the
connector end faces and splice points that could locally induce high-temperature increases
according to the power density absorbed.
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

S M F
D S F
0 0,2 0,4 0,6 0,8 1,0 1,2
Connection loss  (dB)
IEC
Figure 2 – Connection loss versus temperature increase
4.4 Connector end-face damage induced by dust/contamination
The purpose of this clause is to show the increase in attenuation of the connector under test
when the light power into the fibre is extremely high [8].
Figure 3 shows the scheme of the measurement set-up used in the test. The laser pump of a
Raman amplifier is used with a maximum nominal power of 2 W, at a wavelength of 1 455 nm.
PC for acquisition
and data analysis
Climatic chamber
Branching Branching
device device
Variable power
laser source
Connector
1 1
under test
Power Power
meter 2 meter 1
IEC
Figure 3 – Test set-up
The optical connectors used is SC-PC type with a perfectly clean surface, with skin grease
(from operators), with dust (from the floor of the lab) and with metal filings (from a metallic
sleeve).
a) Test result on clean connectors
Two plugs without defects on the polished fibre surface are used. The laser power is
increased in steps to 1,2 W after a thorough cleaning. The test was conducted at ambient
Temperature increase (degr.)
– 12 – IEC TR 61292-4:2014 © IEC 2014

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
polishing 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 polishing surface of the plugs.
After the initial increase of the attenuation from zero (= normalized value) 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, we put down on the plug surfaces metal dust obtained by filing a metallic
sleeve of an adapter. This condition simulates the presence of metallic particles produced
by the friction of the ferule during the insertion into a metallic sleeve.
The first test was performed by heavily contaminating the surfaces, as Figure 4 shows.
This is clear from the initial attenuation value that was 3 dB to 4 dB higher than the ones
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 was evident with attenuation increased to 1,1 dB (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 on the fibre cores. These clots are not
removable by cleaning the surfaces.

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

Connection of two plugs contaminated with metal filing
1,6 1,6
1,4 1,4
1,2 1,2
1 1
0,8 0,8
0,6 0,6
0,4 0,4
0,2 0,2
0 0
0 50 100 150 200 250 300
Time  (min)
IEC
Figure 5 – Variation of the power attenuation during the test at several
power input values for plugs contaminated with metal filings
Plug 1 Plug 2
IEC
Figure 6 – Polishing surface condition contaminated with metal filing, after the test
In conclusion, it is confirmed that there is no risk of damage on 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 to 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
This subclause provides some examples of the fibre coat burn/melt induced by tight fibre
bending where the fibre coatings used were
a) UV curable resin: white, blue, green and uncoloured, and
b) nylon white [2].
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
Variation of attenuation  (dB)
Launched power  (W)
– 14 – IEC TR 61292-4:2014 © IEC 2014

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 >20 mm and
>30 mm for the 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.
IEC
Figure 7 – Thermo-viewer image of tightly bent SMF with optical power
of 3 W at 1 480 nm
200 °C
150 °C
100 °C
50 °C Nylon (white)
UV (transparent)
0 °C
Ø 20 Ø 15 Ø 10 Ø 5
Diameter of the loop  (mm)
IEC
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 not to momentarily push the fibre across a
sharp edge that may 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 by 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 end faces.
In addition, IEC TR 62627-01 has been published in order to prevent damage to the connector
and IEC 62547 in order 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
Definition 3.59 of IEC 60825-1:2014 defines MPE as follows:
" level of laser radiation to which, under normal circumstances, persons may be exposed
without suffering adverse effects"

Here, the MPE values IEC uses have been specified in ANSI-Z136 [10] based on animal
experiments. Clause 4 of IEC TR 60825-14:2004 gives more details of MPE.
Subclause 4.8.2 of IEC 60825-2:2004 includes the following normative text in which it is
requested that optical fibre communication systems be designed not to exceed the maximum
permissible exposure (MPE), including the time period before an automatic power reduction
(APR) system completes its function:
“Where the OFCS uses an automatic power reduction feature to meet the limits of a hazard
level that is lower than that which would have to be assigned if no automatic power reduction
feature would be present, the irradiance or radiation exposure during the maximum time to
reach the lower hazard level shall not exceed the irradiance or radiant exposure limits (MPE).
For controlled locations the measurement distance is 250 mm for this subclause only”.
Here, the hazard levels of the laser products including OAs are determined based on the
classification rule of IEC 60825-1. In the existing standards, automatic laser shutdown (ALS)
could have the same meaning as automatic power reduction (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 
 
(1)
 λNOHD 
 
 
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;
– 16 – IEC TR 61292-4:2014 © IEC 2014

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).
Table 3 – Examples of power limits for optical fibre communication systems
having automatic power reduction to reduce emissions to a lower hazard level
Wavelength Fibre mode Maximum Maximum Maximum Shutdown Measurement
field power output power output power output times distance
diameter unrestricted restricted controlled
nm µm mW mW mW s m
980 7 9,4 9,4 – 1 0,1
980 7 N/A 7,2 – 3 0,1
980 7 N/A – 39 3 0,25
1 310 11 78 78 – 1 0,1
1 310 11 N/A 59 – 3 0,1
1 310 11 N/A – 314 3 0,25
1 400 . 1 500 11 1 598 1 598 – 0,3 0,1
1 400 . 1 500 11 650 650 – 1 0,1
1 400 . 1 500 11 N/A 389 – 2 0,1
1 400 . 1 500 11 N/A 288 – 3 0,1
1 400 . 1 500 11 N/A – 2 403 2 0,25
1 400 . 1 500 11 N/A – 1 774 3 0,25
1 550 11 2 539 2 539 – 0,5 0,1
1 550 11 1 273 1 273 – 1 0,1
1 550 11 N/A 639 – 2 0,1
1 550 11 N/A 428 – 3 0,1
1 550 11 N/A – 2 640 3 0,25
NOTE 1 The fibre parameters used are the most conservative case. Listed figures for λ = 1 310 nm . 1 550 nm
are calculated for a fibre of 11 microns mode field diameter (MFD) and those for λ = 980 nm are for 7 microns
MFD.
Many systems operating at 1 550 nm with the use of erbium doped fibre amplifiers (EDFAs) pumped by 1 480 nm
or 980 nm lasers use transmission fibres with smaller MFDs. For example, 1 550 nm dispersion shifted fibre
cables have upper limit values of MFD of 9,1 microns. In this case, the maximum power outputs for unrestricted
and restricted areas at 1 480 nm and 1 550 nm are 1,44 times the values in Table D.14, and those for controlled
areas at 1 480 nm and 1 550 nm are 1,46 times the values in same table.
NOTE 2 Times given in the table are examples; shutdown at any shorter time than the maximum is permissible,
and may permit the use of higher powers (the maximum times are 1 s for unrestricted locations and 3 s for
restricted and controlled locations, respectively).

Here, it is assumed that the user does not employ any optical instrument or viewing optics
within the beam. When optical instruments or viewing optics are not used, devices classified
as 1M are considered safe under the conditions indicated in Clause 8 of IEC 60825-1:2007.
However, they may be hazardous if the user employs optical instruments or viewing optics
within the beam.
5.2.2 Need for APR
Appendix II of ITU-T Recommendation G.664:2012 states the following, suggesting that the
APR is needed not only on the main optical signal sources but also on all pump-lasers
employed:
“In particular Distributed Raman amplification systems will need specific care to ensure
optically safe working conditions, because high pump powers (power levels above + 30 dBm
are not uncommon) may be injected in optical fibre cables.
“Therefore APR procedures are required in order to avoid hazards from laser radiation to
human eye or skin and potential additional hazards such as temperature increase (or even fire)
caused by local increased absorption due to connector pollution/damages or very tight fibre
bends.
“In order to ensure that the power levels emitting from broken or open fibres connections are
at safe levels, it is necessary to reduce the power not only on the main optical signal sources
but also on all pump-las
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