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

IEC/TR 61292-4:2014(E) 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. 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. 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. Keywords: guideline on the threshold of high optical power, maximum permissible optical power, optical amplifiers, Raman amplifiers, semiconductor optical amplifiers (SOAs)

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Status
Published
Publication Date
28-Oct-2014
Current Stage
PPUB - Publication issued
Start Date
29-Oct-2014
Completion Date
29-Oct-2014
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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
61292-4
IEC TR 61292-4:2014-10(en)
---------------------- Page: 1 ----------------------
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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
ICS 33.160.10 33.180.30 ISBN 978-2-8322-1907-2

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 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

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IEC TR 61292-4:2014 © IEC 2014 – 3 –
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

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– 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

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

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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

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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

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.
---------------------- Page: 6 ----------------------
IEC TR 61292-4:2014 © IEC 2014 – 5 –
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.
---------------------- Page: 7 ----------------------
– 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.

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IEC TR 61292-4:2014 © IEC 2014 – 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:

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
---------------------- Page: 9 ----------------------
– 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.
---------------------- Page: 10 ----------------------
IEC TR 61292-4:2014 © IEC 2014 – 9 –
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
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.
---------------------- Page: 11 ----------------------
– 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 i

...

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