IEC 61300-3-4:2023

IEC 61300-3-4 ®
Edition 4.0 2023-05
REDLINE VERSION
INTERNATIONAL
STANDARD
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Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures –
Part 3-4: Examinations and measurements – Attenuation

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IEC 61300-3-4 ®
Edition 4.0 2023-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures –
Part 3-4: Examinations and measurements – Attenuation
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.20 ISBN 978-2-8322-7021-9

– 2 – IEC 61300-3-4:2023 RLV © IEC 2023
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 7
4 General description . 7
4.1 General . 7
4.2 Precautions . 8
5 Apparatus . 8
5.1 Launch conditions and light source (SLS) . 8
5.2 Optical power meter (DPM) . 9
5.3 Temporary joint (TJ) . 10
5.4 Fibre . 10
5.5 Reference plug (RP) . 10
5.6 Reference adaptor (RA) . 10
5.7 Termination . 10
6 Procedure . 11
6.1 Preconditioning . 11
6.2 Visual inspection . 11
6.3 DUT configuration types and test methods . 11
6.4 Attenuation measurements with a power meter LSPM . 13
6.4.1 General . 13
6.4.2 Cutback method . 13
6.4.3 Substitution method . 13
6.4.4 Insertion method (A) . 14
6.4.5 Insertion method (B) with direct coupling to power meter . 15
6.4.6 Insertion method (C) with additional test patchcord . 15
6.4.7 Insertion method (D) with additional test patchcord . 16
6.5 Attenuation measurements with an OTDR . 17
6.5.1 Measurement description . 17
6.5.2 Bidirectional measurement . 18
6.5.3 Measurement method . 19
6.5.4 Evaluation procedure . 19
7 Details to be specified and reported. 20
Annex A (informative)  Consideration of multicore fibre . 21
A.1 General . 21
A.2 Additional apparatus . 21
A.2.1 Optical switch (OSW) . 21
A.2.2 Fan-in/fan-out device (FIFO) . 21
A.3 Test setup and procedure – LSPM . 21
A.4 Test setup and procedure – OTDR . 22
Bibliography . 23

Figure 1 – Cutback method – Type 1, type 2 and type 3 DUT . 13
Figure 2 – Substitution method – Type 4, type 7, and type 8 DUT . 14

Figure 3 – Insertion method (C1A) – Type 2 DUT . 15
Figure 4 – Insertion method (C2B) – Type 5 and type 6 DUT . 15
Figure 5 – Insertion method (C3C) – Type 4, type 5, type 7 and type 8 DUT . 16
Figure 6 – Insertion method (D) – Type 4, type 5, type 7 and type 8 DUT . 16
Figure 7 – Method 1 – One launch section . 17
Figure 8 – Method 2 – Two launch sections . 18
Figure 9 – Non-reflective event evaluation . 19
Figure 10 – Reflective event evaluation . 20
Figure A.1 – FIFO device example . 21
Figure A.2 – Insertion method B – Type 5 MCF DUT . 22
Figure A.3 – Method 1 – One launch section MCF DUT . 22

Table 1 – Preferred source conditions . 9
Table 2 – Preferred power meter parameters . 10
Table 3 – DUT configuration types . 12

– 4 – IEC 61300-3-4:2023 RLV © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC INTERCONNECTING
DEVICES AND PASSIVE COMPONENTS –
BASIC TEST AND MEASUREMENT PROCEDURES –

Part 3-4: Examinations and measurements – Attenuation

FOREWORD
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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 61300-3-4:2012. 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 61300-3-4 has been prepared by subcommittee 86B: Fibre optic interconnecting devices
and passive components, of IEC technical committee 86: Fibre optics. It is an International
Standard.
This fourth edition cancels and replaces the third edition published in 2012. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of Clause 3 containing terms, definitions and abbreviated terms;
b) addition of a new LSPM measurement method, insertion method (D);
c) addition of Annex A describing attenuation measurement of multicore fibre;
d) changed reference test method to insertion C and alternative test method to substitution or
insertion D for power meter and type 4 DUT.
The text of this International Standard is based on the following documents:
Draft Report on voting
86B/4656/FDIS 86B/4675/RVD
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 International Standard 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 the parts in IEC 61300 series, published under the general title, Fibre optic
interconnecting devices and passive components – Basic test and measurement procedures,
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.

The contents of the corrigendum 1 (2023-06) have been included in this copy.

– 6 – IEC 61300-3-4:2023 RLV © IEC 2023
FIBRE OPTIC INTERCONNECTING
DEVICES AND PASSIVE COMPONENTS –
BASIC TEST AND MEASUREMENT PROCEDURES –

Part 3-4: Examinations and measurements – Attenuation

1 Scope
This part of IEC 61300 describes the various methods available to measure the attenuation of
optical components. It is not, however, applicable to dense wavelength division multiplexing
(DWDM) components, for which IEC 61300-3-29 should be used. It is not, however, applicable
to random mate attenuation measurements as described in IEC 61300-3-34 and IEC 61300-3-
45 nor for attenuation measurements of dense wavelength division multiplexing (DWDM)
devices as described in IEC 61300-3-29.
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 60793-2, Optical fibres – Part 2: Product specifications – General
IEC 60793-2-10, Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for
class B single-mode fibres
IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 61300-1:2011, Fibre optic interconnecting devices and passive components – Basic test
and measurement procedures – Part 1: General and guidance
IEC 61300-3-1, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-1: Examinations and measurements – Visual examination
IEC 61300-3-2, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-2: Examinations and measurements – Polarization
dependent loss in a single-mode Fibre optic device
IEC 61300-3-35, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-35: Examinations and measurements – Visual inspection of
fibre optic connectors and fibre-stub transceivers
IEC 61755 (all parts), Fibre optic interconnecting devices and passive components – Connector
optical interfaces for single-mode fibres
IEC/TR 62316, Guidance for the interpretation of OTDR backscattering traces

IEC 63267 (all parts), Fibre optic interconnecting devices and passive components – Connector
optical interfaces for enhanced macro bend loss multimode fibres
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61300-1 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
ATM alternative test method
C passive optical component
CWDM coarse wavelength division multiplexing
D optical detector
DUT device under test
FIFO fan-in/fan-out device
LED light emitting diode
LS optical light source
LSPM optical light source and power meter
MCF multicore fibre
OSW optical switch
OTDR optical time domain reflectometer
PDL polarization dependent loss
PM optical power meter
RA reference adaptor
RP reference plug
RTM reference test method
SCF single core fibre
TJ temporary joint
4 General description
4.1 General
Attenuation is intended to give a value for the decrease of useful optical power, expressed in
decibels, resulting from the insertion of a DUT, within a length of optical fibre cable an optical
link. The term "insertion loss" is sometimes used in place of "attenuation".
The DUT may have more than two optical ports. However, since an attenuation measurement
is made across only two ports, the DUT in this document shall be described as having two ports.
Eight different DUT configurations are described. The differences between these configurations
are primarily in the terminations of the optical ports. Terminations may consist of bare fibre, a
connector plug, or a receptacle.

– 8 – IEC 61300-3-4:2023 RLV © IEC 2023
The reference method for measuring attenuation is with an optical power meter. Optical time
domain reflectometry (OTDR) measurements are presented as an alternative method. Three
variations in the measurement of attenuation with a power meter are presented. The reference
and alternative methods to be used for each DUT configuration are defined in Table 3. Different
test configurations and methods will result in different accuracies of the attenuation being
measured. In cases of dispute, the reference test method should be used.
The reference method for measuring attenuation is with an LSPM. OTDR measurements are
presented as an alternative method. Three variations in the measurement of attenuation with a
LSPM are presented.
4.2 Precautions
The power in the fibre and DUT shall not be at a level high enough to generate non-linear
scattering or DUT overloading effects.
The position of the fibres in the test should be fixed between the measurement without the DUT,
P , and with the DUT inserted, P , to avoid changes in attenuation due to bending loss.
0 1
In multimode measurements, a change in modal distribution in the measurement system due to
fibre disturbance, will can affect the attenuation measurement.
Components with PDL will show different attenuation depending on the input state of
polarization from the source. If the component PDL can exceed the acceptable uncertainty in
the attenuation measurement, then either an unpolarized or polarization scrambled source can
should be used to measure the polarization averaged attenuation, or the methods of IEC 61300-
3-2 should be used to measure PDL and attenuation together.
The laser safety recommendations in IEC 60825-1, Safety of laser products, should shall be
followed.
5 Apparatus
5.1 Launch conditions and light source (SLS)
The launch condition for LSPM and OTDR shall be specified in accordance with IEC 61300-
1:2011 and shall be measured at the output of the launch reference connector.
The source unit consists of an optical emitter, the associated drive electronics and fibre pigtail
(if any). Preferred source conditions are given in Table 1. The stability of the single-mode fibre
source at 23 °C shall be ±0,01 dB from the initial value over the duration of the measurement.
The stability of the multimode fibre source at 23 °C shall be ±0,05 dB from the initial value over
the duration of the measurement. The source output power shall be greater than or equal to
20 dB above the minimum measurable power level.

Table 1 – Preferred source conditions
No. Type Central wavelength Spectral width Source type
RMS
nm nm
S1 Multimode 660 ± 30 Monochromator or LED
≥30 ≥ 10
S2 Multimode 780 ± 30 ≥30 ≥ 10 Monochromator or LED
S3 Multimode 850 ± 30 Monochromator or LED
≥30 ≥ 10
S4 Multimode 1 300 ± 30 Monochromator or LED
≥30 ≥ 10
S5 Single-mode 1 310 ± 30 To be reported Laser diode monochromator or LED
S6 Single-mode 1 550 ± 30 To be reported Laser diode monochromator or LED
S7 Single-mode 1 625 ± 30 To be reported Laser diode monochromator or LED
NOTE 1 It is recognized that some components, for example for CWDM, may can require the use of other source
types such as tunable lasers. It is therefore recommended, in these cases, that the preferred source characteristics
are specified on the basis of the component to be measured.
NOTE 2 Central wavelength (centroidal wavelength) and spectral width are defined in IEC 61280-1-3.

5.2 Optical power meter (DPM)
The power meter unit consists of an optical detector (D), the mechanism for connecting to it
and associated detection electronics. The connection to the detector will should either be with
an adaptor that accepts a bare fibre, or a connector plug of the appropriate design.
The measurement system shall be stable within specified limits over the period of time required
to measure P and P . For measurements where the connection to the detector must shall be
0 1
broken disconnected between the measurement of P and P , the measurement repeatability
0 1
shall be within less than or equal to 0,02 dB. A detector with a large sensitive area may should
be used to achieve this.
The precise characteristics of the detector shall be compatible with the measurement
requirements. The dynamic range of the power meter shall be capable of measuring the power
level exiting from the DUT at the wavelength being measured.
The preferred power meter parameters are given below in Table 2. The power meter shall
should be calibrated for the operational wavelength range and power level to be measured. The
power meter stability should be less than or equal to 0,01 dB over the measurement time and
operational temperature range. The stability and validity of dark current corrections from zeroing
calibration can influence this.

– 10 – IEC 61300-3-4:2023 RLV © IEC 2023
Table 2 – Preferred power meter parameters
Number Type Maximum nonlinearity Relative uncertainty
dB dB
D1 Multimode ±0,05
≤ 0,05
(–60 dBm < input power < –5 dBm)
D2 Single-mode ±0,01
(attenuation < 10 dB)
≤ 0,02
±0,05
(10 dB < attenuation < 60 dB)
NOTE 1 In order to ensure that all light exiting the fibre is detected by the power meter, the sensitive area of the
detector and the relative position between it and the fibre should be compatible with the numerical aperture of the
fibre.
NOTE 2 Common sources of relative uncertainty are polarization dependence and interference with reflections
from the power meter and fibre connector surfaces. The sensitivity of the power meter to such reflections can be
characterized by the parameter spectra ripple, determined as the periodic change in responsivity vs. the wavelength
of a coherent light source.
5.3 Temporary joint (TJ)
A temporary joint is a method, device or mechanical fixture for temporarily aligning two fibre
ends into a stable, reproducible, low-loss joint. It is used when direct connection of the DUT to
the measurement system is not achievable by a standard connector. It may, for example, be a
precision V-groove, vacuum chuck, a micromanipulator or a fusion or mechanical splice. The
temporary joint shall be stable to within ±10 % of the required measurement accuracy
uncertainty in dB over the time taken to measure P and P . A suitable refractive index matching
0 1
material may be used to improve the stability of the TJ.
5.4 Fibre
The fibre in the lead from the source to the TJ, in the test patchcord, and in the substitute
patchcord, shall belong to the same category as that used in the DUT.
Fibres should shall be in accordance with IEC 60793-2-10 or IEC 60793-2-50.
5.5 Reference plug (RP)
Where a RP is required to form complete connector assemblies in any of the test methods, the
RP becomes, in effect, a part of the DUT during the measurement of attenuation. The RP shall
be specified in meet the requirements of the relevant specification optical interface standard
found in the IEC 61755 series or IEC 63267 series.
5.6 Reference adaptor (RA)
Where a RA is required to form complete connector assemblies in any of the test methods, the
RA becomes, in effect, a part of the DUT during the measurement of attenuation. The RA shall
be specified in meet the requirements of the relevant specification optical interface standard
found in the IEC 61755 series or IEC 63267 series.
5.7 Termination
A termination may consist of a bare fibre, a connector plug, or a receptacle. When a bare fibre
is used as a termination, a TJ or bare fibre adaptor is used depending on the configuration of
the test and the location of the bare fibre end. When a DUT has multiple connector plugs or
receptacles, they can consist of the same or different types. If the DUT has different connector
plugs or receptacles on either end of the DUT, the ATM may be necessary.

6 Procedure
6.1 Preconditioning
The optical interfaces of the DUT shall be clean and free from any debris likely to affect the
performance of the test and any resultant measurements. The manufacturer’s cleaning
procedure shall be followed.
The DUT shall be allowed to stabilize at room temperature standard atmospheric conditions
according to IEC 61300-1 for at least 1 h prior to testing.
Care should be exercised throughout the test to ensure that mating surfaces are not
contaminated with oil or grease. It is recognized that bare fingers can deposit a film of grease.
6.2 Visual inspection
The optical interfaces shall be free from defects or damage which may affect the performance
of the test and any resultant measurements. It is recommended that a visual inspection of the
optical interfaces of the DUT is made in accordance with IEC 61300-3-1 prior to the start of the
test.
All connector end faces shall be inspected for cleanliness according to IEC 61300-3-35 and
cleaned as needed. Recommended cleaning methods for connector end faces are described in
IEC TR 62627-01.
6.3 DUT configuration types and test methods
Eight different DUT configuration types are described in Table 3. The differences between these
configuration types are primarily in the terminations of the optical ports. Terminations may
consist of bare fibre, a connector plug, or a receptacle.
The RTM and ATM to be used for each DUT configuration type are defined in Table 3. Different
test configurations and methods can result in different uncertainties of the attenuation being
measured. In cases of dispute, the RTM should be used.
Consideration for devices with multicore fibre can be found in Annex A.

– 12 – IEC 61300-3-4:2023 RLV © IEC 2023
Table 3 – DUT configuration types
Test methods
Reference test Alternati
Type Description DUT
method ve test
RTM method
ATM
1 Fibre to fibre Power meter OTDR
(component) (cutback)
2 Fibre to fibre Power meter Power
(splice or field-mountable (insertion A) meter
connector set) (cutback)
Or OTDR
3 Fibre to plug Power meter OTDR
(cutback)
4 Plug to plug Power meter Power
(component) (insertion BC) meter
(substitut
ion or
insertion
CD)
or OTDR
5 Plug to plug Power meter Power
(patchcord) (insertion B) meter
(insertion
C or
insertion
D)
or OTDR
6 Single plug Power meter OTDR
(pigtail) (insertion B)
7 Receptacle to receptacle Power meter Power
(component) (insertion C) meter
(substitut
ion or
insertion
D)
or OTDR
Receptacle to plug Power meter Power
(component) (insertion C) meter
(substitut
ion or
insertion
D)
or OTDR
An OTDR can be used on components with more than two ports, but in this case the reflected power from the ports
not being measured should be suppressed in the attenuation zone.
NOTE 1 C is a passive optical component which may can have more than the two ports indicated.
NOTE 2 Insertion measurements and cutback measurements may can be expected to give equivalent
measurements for type 2 DUTs.
NOTE 3 Due to measurement considerations, the OTDR method may be less accurate can have more
uncertainty than other measurement methods but may can be the only test applicable.

6.4 Attenuation measurements with a power meter LSPM
6.4.1 General
The measurement of attenuation using cutback, substitution or insertion is based on the use of
an optical power meter a PM, as described in 5.2.
Two measurements of power are required for each measurement of attenuation, A, with a power
meter:
P
A = −10log dB
(1)
P
where
P is the measurement of power with the DUT in the path;
P is the measurement of power without the DUT in the path.
Suitable connections shall be provided between the fibre and the detector. Connections may
be with either an adaptor to connect a bare fibre or with a connector adaptor for the appropriate
connector plug.
6.4.2 Cutback method
For a type 1 and type 2 DUT, one lead of the DUT is connected to the source with a TJ. The
other lead is connected to the detector, and P is measured (see Figure 1). The fibre is cut at
CP, and P is measured.
Figure 1 – Cutback method – Type 1, type 2 and type 3 DUT
For a type 3, fibre-to-plug DUT, a RA and a RP with a pigtail are added to the DUT to form a
complete connector assembly. Attenuation of a type 3 DUT is the attenuation of the complete
connector assembly (plug-adaptor-plug) with pigtail leads and is measured as a type 1 DUT.
6.4.3 Substitution method
In the substitution method, P is measured with the DUT in the circuit measurement set-up, and
P is measured with a substitute patchcord in place of the DUT (see Figure 2).
– 14 – IEC 61300-3-4:2023 RLV © IEC 2023
For a type 4 DUT, a RA is added to the RP on both the source lead and the test patchcord (see
Figure 2).
Figure 2 – Substitution method – Type 4, type 7, and type 8 DUT
For a type 7 DUT, the measurement is made in the same way as a plug-to-plug DUT, except
that reference adaptors are not required for the measurement of P (see Figure 2).
For a type 8 DUT, the measurement is made in the same way as for a plug-to-plug DUT, except
that only one reference adaptor is required for the measurement of P (see Figure 2). In this
case, the reference adaptor shall be the one nearest the source.
Substitution measurements may can be expected to give somewhat lower results of attenuation
than insertion measurements for types 4, 5, 6, and 7, and 8 DUTs. This is due to the fact that
in the substitution method the reference power, P , includes the attenuation of the "substitute
patchcord" with its connections to the measurement system. Therefore, the value of P in the
substitution method is lower than in the insertion method.
6.4.4 Insertion method (A)
For a type 2 fibre-to-fibre DUT (splice- or field-mountable connector set), P is measured with
a length of fibre between the temporary joint and the detector, the fibre is cut, the splice- or
is measured (see Figure 3). The fibres can
field-mountable connector set is installed, and P
be similar fibres or dissimilar fibres as long as they are compatible with each other. If dissimilar
fibres are used, care should be taken to ensure the effects of dissimilar fibres are considered
in the measurement results (see IEC TR 62000 for guidance on single-mode fibres).

Figure 3 – Insertion method (C1A) – Type 2 DUT
6.4.5 Insertion method (B) with direct coupling to power meter
For a type 5 and type 6 DUT, P is measured with the detector connected to a RP on the fibre
from the TJ. An RA and the DUT are added, and P is measured (see Figure 4).
Figure 4 – Insertion method (C2B) – Type 5 and type 6 DUT
This measurement includes only the connector plug on the source end of the DUT in the
measurement. To measure both ends of the DUT, the measurement shall be repeated with the
patchcord reversed.
For a type 6 DUT, the measurement requires an adaptor for a bare fibre at the detector.
6.4.6 Insertion method (C) with additional test patchcord
For a type 4 plug-to-plug (component) DUT or a type 5 plug-to-plug (patchcord) DUT, P is
measured with the test patchcord connected between the detector and the lead from the TJ.
The DUT and another RA are added to measure P (see Figure 5). In the case where the DUT
has two different connector plugs, it may be useful to consider using the insertion method (D).

– 16 – IEC 61300-3-4:2023 RLV © IEC 2023

Figure 5 – Insertion method (C3C) – Type 4, type 5, type 7 and type 8 DUT
For a type 7 receptacle-to-receptacle DUT, an RA is not required for the measurement of P .
For a type 8 receptacle-to-plug DUT, only one RA is required for the measurement of P .
6.4.7 Insertion method (D) with additional test patchcord
For a type 4 plug-to-plug (component) DUT or a type 5 plug-to-plug (patchcord) DUT, P is
measured with the detector connected to a RP on the fibre from the TJ. The DUT, test patchcord,
and RA are added to measure P (see Figure 6). This insertion method is especially useful
when the DUT has two different conntector plug types.

Figure 6 – Insertion method (D) – Type 4, type 5, type 7 and type 8 DUT
For a type 7 receptacle-to-receptacle DUT, an RA is not required for the measurement of P .
For a type 8 receptacle-to-plug DUT, only one RA is required for the measurement of P .
6.5 Attenuation measurements with an OTDR
6.5.1 Measurement description
An OTDR measures the level of radiation scattered back by the optical line and collected by the
receiver of the instrument. Using an OTDR, it is possible to measure and to evaluate both point
events due, for example, to passive components such as splices, connectors, attenuators, etc.
or losses due to the attenuation of fibre sections terminated by passive components.
There are two principal measurement methods used methods of OTDR measurement depending
on the DUT configuration type (see Table 3):
• method 1 – one launch section (see Figure 7) is applicable to DUT types 1, 2, 3;
• method 2 – two launch sections (see Figure 8) are applicable to DUT types 4, 5, 6, 7, 8.

b
a
LS1
OTDR DUT
L L
1 X
IEC  2186/12
Key
a, b reflective events
L fibre launch section optical length
L DUT section optical length
X
Figure 7 – Method 1 – One launch section

– 18 – IEC 61300-3-4:2023 RLV © IEC 2023

a
b
LS2
LS1
OTDR DUT
L L L
X
1 2
IEC  2187/12
Key
a, b reflective events
L fibre launch section optical length
L fibre launch section optical length
DUT section optical length
L
x
Figure 8 – Method 2 – Two launch sections
Fibre launch sections LS1L and LS2L provide separation between the OTDR equipment and
1 2
the events to be measured and ensure stable measurement conditions. Their minimum optical
length is determined by the ability of the OTDR to resolve the measurement of attenuation and
is commonly referred to as the attenuation dead zone (DZatt). The maximum optical length of
the launch section is limited by requirement to minimize the OTDR distance resolution and to
minimize optical losses of measured route.
If the DUT section length, L , is greater than the OTDR resolution (L > DZ attenuation dead
att
X X
zone), then the attenuation for each event, a and b, will be displayed separately. Where L <
X
DZ attenuation dead zone, the OTDR will be unable to distinguish between events a and b
att
and the DUT will be shown as one attenuation event.
Where the DUT is terminated with either a connector plug or a receptacle, an RP and RA are
added, as necessary, to form complete connector assemblies. These connector assemblies are
considered part of the DUT.
Where the component has pigtails, connector points are required. The pigtail lengths shall be
greater than the OTDR resolution for each event to be displayed separately.
6.5.2 Bidirectional measurement
The value of attenuation is determined from the intensity difference of back-scattering before
and after the DUT, so the launch section LS2L is needed if the DUT does not itself have
sufficiently long pigtails, compared to the attenuation dead zone. Since the backscattering
coefficient of the fibre before and after the DUT can differ, the OTDR measurement shall be
made from both ends of the assembly of DUT and launch sections, without changing the
ordering of this assembly. The attenuation result is the average of the apparent attenuation
from the two OTDR measurements.
Differences in the backscatter coefficient of the fibre on either side of the DUT will result in an
error in a one-way OTDR measurement. The error in a measurement made in one direction will
be positive and the error in the other direction will be negative. The use of an average of

readings taken in opposite directions cancels the error due to differences in the backscatter
coefficient of the two fibres.
Referring to the two measured attenuation values, illustrated in 6.5.4, as A and A , the average
1 2
attenuation is calculated as:
AA+
A = (dB). (2)
See IEC TR 62316 for further details.
6.5.3 Measurement method
Configure the apparatus as shown in Figure 7 or Figure 8 with the OTDR equipment connected
to side a.
– Set the OTDR measurement characteristics.
– Take an attenuation measurement in direction a-b and save the resulting OTDR data for
evaluation.
Configure the apparatus as shown in Figure 7 or Figure 8 with the OTDR equipment connected
to side b.
– Set the same OTDR measurement characteristics as for the side a.
– Take an attenuation measurement in direction b-a and save the resulting OTDR data for
evaluation.
6.5.4 Evaluation procedure
6.5.4.1 General
A typical OTDR display of the backscatter signal from a DUT with a non-reflective event is
illustrated in Figure 9 a) and Figure 9 b).

a) Five-point evaluation b) Four-point evaluation

Figure 9 – Non-reflective event evaluation
A typical OTDR display of the backscatter signal from a DUT with a reflective event is illustrated
in Figure 10 a) and Figure 10 b). To avoid the reflection peak affecting the attenuation
measurement, the distance between the reference markers and the peak should be suitably
long. Alternatively, a suitable filter, specified in the relevant specification, should be used to
mask the reflection.
– 20 – IEC 61300-3-4:2023 RLV © IEC 2023

a) Five-point evaluation b) Four-point evaluation

Figure 10 – Reflective event evaluation
6.5.4.2 Five-point evaluation
Set evaluation points (1) and (2) on the fibre section in front of the DUT and (3) and (4) on the
fibre section behind the DUT. Set the position of decision point (5). Attenuation, A, shall be
calculated as the power level difference at point (5) between the least squares approximation
curve of the fibre section in front of the DUT and the least squares approximation curve of the
fibre behind the DUT.
6.5.4.3 Four-point evaluation
Set evaluation points (1) and (2) on the fibre section in front of the DUT and (3) and (4) on the
fibre section behind the DUT. Attenuation, A, shall be calculated as the power-level difference
between point (2a) of the least squares approximation curve of the fibre section in front of the
DUT and point (3a) of least squares approximation curve of the fibre behind the DUT.
7 Details to be specified and reported
The following details, as applicable, shall be specified in the relevant specification and shall be
reported in the test report:
• test method;
• source characteristics;
• performance requirements (allowable attenuation);
• power meter characteristics;
• relevant fibre parameters;
• OTDR characteristics:
– wavelength;
• refractive index value used,
– range;
– pulse width;
–
...