SIST EN 61746:2005

SLOVENSKI SIST EN 61746:2005

STANDARD
november 2005
Kalibriranje optične časovne domene reflektometrov (OTDR) (IEC 61746:2005)
Calibration of optical time-domain reflectometers (OTDR) (IEC 61746:2005)
ICS 17.180.30; 33.180.99 Referenčna številka
SIST EN 61746:2005(en)
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

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EUROPEAN STANDARD EN 61746
NORME EUROPÉENNE
EUROPÄISCHE NORM March 2005

ICS 33.180.01 Supersedes EN 61746:2001


English version


Calibration of optical time-domain reflectometers (OTDR)
(IEC 61746:2004)


Etalonnage des réflectomètres optiques Kalibirerung optischer
dans le domaine de temps (OTDR) Rückstreumessgeräte (OTDR)
(CEI 61746:2004) (IEC 61746:2004)






This European Standard was approved by CENELEC on 2005-02-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61746:2005 E

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EN 61746:2005 - 2 -
Foreword
The text of document 86/230/FDIS, future edition 2 of IEC 61746, prepared by IEC TC 86, Fibre
optics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61746 on 2005-02-01.
This European Standard supersedes EN 61746:2001.
Specific changes to EN 61746:2001 include the development of Clause 9, “Reflectance calibration”,
and the introduction of Annexes E, F and G.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2005-11-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2008-02-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61746:2005 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60825-1 NOTE Harmonized as EN 60825-1:1994 (not modified).
IEC 60825-2 NOTE Harmonized as EN 60825-2:2004 (not modified).
IEC 61300-3-6 NOTE Harmonized as EN 61300-3-6:2003 (not modified).
__________

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- 3 - EN 61746:2005
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 60793-1 Series Optical fibres EN 60793-1 Series
Part 1: Measurement methods and test
procedures

1) 2)
IEC 60793-1-40 - Optical fibres EN 60793-1-40 2003
(mod) Part 1-40: Measurement methods and
test procedures – Attenuation

1) 2)
IEC 60794-1-2 - Optical fibre cables EN 60794-1-2 2003
Part 1-2: Generic specification - Basic
optical cable test procedures

1) 2)
IEC 61300-3-2 - Fibre optic interconnecting devices and EN 61300-3-2 1999
passive components - Basic tests and
measurement procedures
Part 3-2: Examinations and
measurements - Polarization dependence
of attenuation in a single-mode fibre optic
device

ITU-T 2004 Definitions and test methods for linear, - -
Recommendation deterministic attributes of single-mode
G.650.1 fibre and cable

ITU-T 2002 Definitions and test methods for statistical - -
Recommendation and non-linear attributes of single-mode
G.650.2 fibre and cable




1)
Undated reference.
2)
Valid edition at date of issue.

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NORME CEI
INTERNATIONALE IEC
61746
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2005-01
Etalonnage des réflectomètres optiques
dans le domaine de temps (OTDR)
Calibration of optical time-domain
reflectometers (OTDR)
© IEC 2005 Droits de reproduction réservés ⎯ Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any
utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including
électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
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Pour prix, voir catalogue en vigueur
For price, see current catalogue

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61746¤ IEC:2005 – 3 –
CONTENTS
FOREWORD . 9
1 Scope .13
2 Normative references .13
3 Terms, definitions and symbols.15
4 Calibration test requirements .27
4.1 Preparation .27
4.2 Test conditions .27
4.3 Traceability .29
5 Distance calibration – General .29
5.1 Location error model.29
5.2 Using the calibration results.33
5.3 Measuring fibre length .33
6 Distance calibration methods .35
6.1 External source method .35
6.2 Concatenated fibre method.45
6.3 Recirculating delay line method .53
7 Loss calibration – General .63
7.1 Determination of the displayed power level F .63
7.2 Selection of an appropriate reference loss A .65
ref
7.3 Development of a test plan .65
7.4 Polarization dependence .69
7.5 Calculation of the calibration results .71
7.6 Using the calibration results.73
8 Loss calibration methods .73
8.1 Loss calibration with fibre standard.73
8.2 External source method (see Figure 16).81
8.3 Splice simulator method .89
8.4 Power reduction method .97
9 Reflectance calibration .105
9.1 Reflectance measurements (see Figure 23) .105
9.2 Use of the backscatter parameter, K .107
9.3 Range of reflectance measurement.109
9.4 Development of a test plan .111
9.5 Equipment .113
9.6 Measurement procedure .115
10 Documentation .117
10.1 Measurement data and uncertainties .117
10.2 Test conditions .119
Annex A (normative) Recirculating delay line for distance calibration.121
Annex B (normative) Optical fibre standard for loss calibration .129
Annex C (normative) Standard splice simulator for loss calibration .137
Annex D (informative) Mathematical basis.147

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61746¤ IEC:2005 – 5 –
Annex E (normative) Reflectance standard.155
Annex F (normative)  Simple version of reflectance standard.169
Annex G (informative)  OTDR basis: Backscatter theory – Reflectance measurements
using an OTDR – Determination of fibre backscatter parameter.177
Bibliography .189
Figure 1 – Definition of attenuation dead zone .15
Figure 2 – Representation of the location error ∆L(L) .31
Figure 3 – Equipment for calibration of the distance scale – External source method .37
Figure 4 – Set-up for calibrating the system insertion delay .39
Figure 5 – Concatenated fibres used for calibration of the distance scale .47
Figure 6 – Distance calibration with a recirculating delay line .55
Figure 7 – OTDR trace produced by recirculating delay line .57
Figure 8 – Determining the reference level and the displayed power level.63
Figure 9 – Measurement of the OTDR loss samples .65
Figure 10 – Region A, the recommended region for loss measurement samples .67
Figure 11 – Possible placement of sample points within region A .69
Figure 12 – External source method for testing the polarization dependence of the OTDR .69
Figure 13 – Reflection method for testing the polarization dependence of the OTDR.71
Figure 14 – Loss calibration with a fibre standard.75
Figure 15 – Placing the beginning of section D outside the attenuation dead zone .77
1
Figure 16 – Loss calibration with the external source method .83
Figure 17 – Location and measurements for external source method .87
Figure 18 – Set-up for loss calibration with splice simulator.91
Figure 19 – OTDR display with splice simulator.91
Figure 20 – Measurement of the splice loss .93
Figure 21 – Loss calibration with "fibre-end" variant of the power reduction method.101
Figure 22 – Loss calibration with "long-fibre" variant of the power reduction method .101
Figure 23 – Parameters involved in reflectance measurements.107
Figure 24 – The same reflectance at the end of three fibres with different values of
the backscatter parameter shows different pulse amplitudes .109
Figure 25 – Maximum and minimum values for the pulse amplitude, ∆F .111
Figure 26 – Range of reflectance measurement .111
Figure 27 – Determining the default displayed power level and the default location.113
Figure 28 – Set-up for reflectance calibration .115

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61746¤ IEC:2005 – 7 –
Figure A.1 – Recirculating delay line .121
Figure A.2 – Measurement set-up for loop transit time T .123
b
Figure A.3 – Calibration set-up for lead-in transit time T .125
a
Figure B.1 – Determination of a highly linear power range .131
Figure B.2 – Testing the longitudinal backscatter uniformity of the fibre standard.133
Figure C.1 – Splice simulator and idealized OTDR signature .137
Figure C.2 – Determination of the reference loss A .141
ref
Figure D.1 – Deviation and uncertainty type B, and how to replace both by an
appropriately larger uncertainty.149
Figure E.1 – Reflectance standard description and trace .155
Figure E.2 – Calibration set up and reference points for calibration .163
Figure F.1 – Reflectance standard description and trace .169
Figure F.2 – Calibration set up and reference points for calibration.175
Figure G.1 – OTDR signals used for determining reflectance.181
Figure G.2 – Set-up for measurement of the backscatter coefficient .185
Table 1 – Attenuation coefficients defining region A .67

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61746¤ IEC:2005 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CALIBRATION OF OPTICAL TIME-DOMAIN
REFLECTOMETERS (OTDR)
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61746 has been prepared by IEC technical committee 86: Fibre
optics.
This second edition cancels and replaces the first edition published in 2001. It constitutes a
technical revision. Specific technical changes include the development of Clause 9,
“Reflectance calibration,” and the introduction of Annexes E, F and G.
The text of this standard is based on the following documents:
FDIS Report on voting
86/230/FDIS 86/232/RVD
Full information on the voting for the approval of this standard 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.

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61746¤ IEC:2005 – 11 –
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.

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61746¤ IEC:2005 – 13 –
CALIBRATION OF OPTICAL TIME-DOMAIN
REFLECTOMETERS (OTDR)
1 Scope
This International Standard provides procedures for calibrating single-mode optical time
domain reflectometers (OTDR). It only covers OTDR measurement errors and uncertainties.
This standard does not cover correction of the OTDR response.
In order for an OTDR to qualify as a candidate for complete calibration using this standard, it
must be equipped with the following minimum feature set:
a) a programmable index of refraction, or equivalent parameter;
b) the ability to present a display of a trace representation, with a logarithmic power scale
and a linear distance scale;
c) two markers/cursors, which display the loss and distance between any two points on a
trace display;
d) the ability to measure absolute distance (location) from the OTDR's zero-distance reference;
e) the ability to measure the displayed power level relative to a reference level (for example,
the clipping level).
f) the ability to evaluate the reflectance of a reflective event.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60793-1 (all parts), Optical fibres – Part 1: Measurement methods and test procedures
IEC 60793-1-40, Optical fibres – Part 1-40: Measurement methods and test procedures –
Attenuation
IEC 60794-1-2, Optical fibre cables – Part 1-2: Generic specification – Basic optical cable
test procedures
IEC 61300-3-2, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-2: Examinations and measurements – Polarization
dependence of attenuation in a single-mode fibre optic device
ITU-T Recommendation G.650.1:2004, Definitions and test methods for linear, deterministic
attributes of single-mode fibre and cable
ITU-T Recommendation G.650.2:2002, Definitions and test methods for statistical and non-
linear attributes of single-mode fibre and cable

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61746¤ IEC:2005 – 15 –
3 Terms, definitions and symbols
For the purposes of this document, the following definitions apply.
NOTE For more precise definitions, the references to IEC 60050-731 should be consulted.
3.1
attenuation
A
loss
optical power decrease in decibels (dB)
NOTE If P (watts) is the power entering one end of a segment of fibre and P (watts) is the power leaving the
in out
other end, then the attenuation of the segment is
§ ·
P
in
¨ ¸
A = 10log dB (1)
10
¨ ¸
P
© out¹
[IEV 731-01-48, modified]
3.2
attenuation coefficient
α
attenuation of a fibre per unit length
[IEV 731-03-42, modified]
3.3
attenuation dead zone
for a reflective or attenuating event, the region after the event where the displayed trace
deviates from the undisturbed backscatter trace by more than a given vertical distance ∆F
NOTE The attenuation dead zone will depend on the following event parameters: reflectance, loss, displayed
power level and location. It may also depend on any fibre optic component in front of the event.
Initial dead zone
∆F
Attenuation
dead zone
Location  km
IEC  1627/04
Figure 1 – Definition of attenuation dead zone
Displayed power F  dB

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61746¤ IEC:2005 – 17 –
3.4
backscatter parameter
K
at a given point along the fibre, the backscattered propagating power per unit incident energy
NOTE 1 K is given by the following formula:
ν
−1
K = Sα  s (2)
s
2
where
1
−
α  is the scattering coefficient, e.g.; in m
s
S  is the backscatter capture fraction. It depends on other standard fibre parameters such as the mode field
diameter in single mode fibre;
ν  is the group velocity, in metres per second;
   = c / N where c is the speed of the light in vacuum, N the group index of the fibre.
NOTE 2 See also Annex G.
3.5
backscatter coefficient
C
for a given pulse, the ratio of backscattered power at the input side of the fibre to the pulse
input power
NOTE 1 It represents the backscatter parameter for a given pulse width. The backscatter coefficient is defined
from the backscatter parameter using the following formula:
C()∆T = K∆T (3)
where ∆T is the pulse width, e.g. in seconds.
Usually the backscatter coefficient is expressed in dB for a given pulse width, ∆T.
C ()∆T = 10log (K∆T) (4)
dB 10
NOTE 2 The pulse width, ∆T in the previous formula is used to normalise C()∆T . Usual values for ∆T are
1 ns and 1 µs. See also Annex G.
3.6
calibration
set of operations which establish, under specified conditions, the relationship between the
values indicated by the measuring instrument and the corresponding known values of that
quantity
NOTE See ISO Guide International vocabulary of basic and general terms in metrology.
3.7
centre wavelength
λ
centre
power-weighted mean wavelength of a light source in vacuum, in nanometres (nm)
NOTE For a continuous spectrum, the centre wavelength is defined as:
1
λ = p(λ)λdλ (5)
centre
³
P
total
For a spectrum consisting in discrete lines, the centre wavelength is defined as:
PȜ
¦ i i
i
λ = (6)
centre
P
i
¦
i

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61746¤ IEC:2005 – 19 –
where
p(λ) is the spectral power density of the source, for example in W/nm;
th
λ is the i discrete wavelength;
i
P is the power at λ , for example in watts;
i i
P = Σ P is the total power, for example in watts.
total i
The above integrals and summations extend over the entire spectrum of the light source.
3.8
confidence level
estimated probability that the true value of a measured quantity lies within a given expanded
uncertainty
NOTE In this standard, the confidence level is standardized to 95 %. See "expanded uncertainty" for further
clarification.
3.9
distance
spacing (actual or simulated) between two features in a fibre, for example in metres
3.10
distance sampling error
maximum distance error attributable to the distance between successive sample points,
specified in metres
NOTE The distance sampling error is repetitive in nature; therefore, one way of quantifying this error is by its
amplitude.
3.11
distance scale deviation
∆S
L
average error of the distance scale, that is difference between the average displayed
distance < D > and the correspondent reference distance D divided by the reference
otdr ref
distance, for example in m/m
NOTE 1 ∆S is given by the following formula:
L
< D >− D < D >
otdr ref otdr
∆S = = − 1 (7)
L
D D
ref ref
where < D > is the displayed distance between two features on a fibre (actual or simulated) averaged over at
otdr
least one sample spacing
NOTE 2 It is assumed that a relatively long distance, for example 2 000 m, is used in this formula.
3.12
distance scale factor
S
L
average displayed distance divided by the correspondent reference distance
NOTE 1 S is given by the following formula:
L
< D >
otdr
S = (8)
L
D
ref
where < D > is the displayed distance between two features on a fibre (actual or simulated) averaged over at
otdr
least one sample spacing
NOTE 2 It is assumed that relatively long distances are used in this formula.
3.13
distance scale uncertainty
σ
∆SL
uncertainty of the distance scale deviation, for example in m/m

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61746¤ IEC:2005 – 21 –
NOTE 1 σ is given by the following formula:
∆SL
§ · § ·
< D > < D >
otdr otdr
¨ ¸ ¨ ¸
σ = σ −1 = σ (9)
∆SL ¨ ¸ ¨ ¸
D D
© ref ¹ © ref ¹
NOTE 2 It is assumed that the distance is relatively long, because short distances may lead to larger
uncertainties.
NOTE 3 In the above formula, σ() is understood as the standard uncertainty of ().
3.14
dynamic range (one-way)
amount of fibre attenuation that causes the backscatter signal to equal the noise level
NOTE It can be represented by the difference between the extrapolated point of the backscattered trace (taken at
the intercept with the power axis) and the noise level expressed in decibels, using a standard category B fibre (see
IEC 60793-1)
3.15
expanded uncertainty
range of uncertainties within which the true value of the measured quantity lies, at the given
confidence level
NOTE 1 For further information, see Annex D and the ISO Guide for the expr
...