EN 61300-3-38:2012

SLOVENSKI STANDARD
01-oktober-2012
2SWLþQLVSRMQLHOHPHQWLLQSDVLYQHNRPSRQHQWH2VQRYQLSUHVNXVQLLQPHULOQL
SRVWRSNLGHO3UHLVNDYHLQPHULWYH6NXSLQVND]DNDVQLWHYEDUYQD
UD]SUãHQRVWLQID]QDYDORYLWRVW,(&
Fibre optic interconnecting devices and passive components - Basic test and
measurement procedures - Part 3-38:Examinations and measurements - Group delay,
chromatic dispersion and phase ripple (IEC 61300-3-38:2012)
Lichtwellenleiter - Verbindungselemente und passive Bauteile - Grundlegende Prüf- und
Messverfahren -- Teil 3-38: Untersuchungen und Messungen - Gruppenlaufzeit,
chromatische Dispersion und Phasenwelligkeit (IEC 61300-3-38:2012)
Dispositifs d’interconnexion et composants passifs à fibres optiques - Procédures
fondamentales d'essais et de mesures - Partie 3-38: Examens et mesures - Retard de
groupe, dispersion chromatique et fluctuation de phase (CEI 61300-3-38:2012)
Ta slovenski standard je istoveten z: EN 61300-3-38:2012
ICS:
33.180.20 3RYH]RYDOQHQDSUDYH]D Fibre optic interconnecting
RSWLþQDYODNQD devices
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61300-3-38
NORME EUROPÉENNE
August 2012
EUROPÄISCHE NORM
ICS 33.180.10
English version
Fibre optic interconnecting devices and passive components -
Basic test and measurement procedures -
Part 3-38:Examinations and measurements -
Group delay, chromatic dispersion and phase ripple
(IEC 61300-3-38:2012)
Dispositifs d’interconnexion et Lichtwellenleiter -
composants passifs à fibres optiques - Verbindungselemente und passive
Procédures fondamentales d'essais Bauteile -
et de mesures - Grundlegende Prüf- und Messverfahren -
Partie 3-38: Examens et mesures - Teil 3-38: Untersuchungen und
Retard de groupe, dispersion chromatique Messungen -
et fluctuation de phase Gruppenlaufzeitverzögerung,
(CEI 61300-3-38:2012) chromatische Dispersion und
Phasenwelligkeit
(IEC 61300-3-38:2012)
This European Standard was approved by CENELEC on 2012-07-03. 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 CEN-CENELEC Management Centre 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 CEN-CENELEC Management Centre has the same status as the official versions.

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

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

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2012 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61300-3-38:2012 E
Foreword
The text of document 86B/3394/FDIS, future edition 1 of IEC 61300-3-38, prepared by SC 86B "Fibre
optic interconnecting devices and passive components" of IEC TC 86 "Fibre optics" was submitted to
the IEC-CENELEC parallel vote and approved by CENELEC as EN 61300-3-38:2012.
The following dates are fixed:
(dop) 2013-04-03
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2015-07-03
• latest date by which the national
standards conflicting with the
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 61300-3-38:2012 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 60793-1-42 NOTE Harmonised as EN 60793-1-42.
IEC 61300-1 NOTE Harmonised as EN 61300-1.
IEC 61300-3-1 NOTE Harmonised as EN 61300-3-1.
IEC 61300-3-32 NOTE Harmonised as EN 61300-3-32.

- 3 - EN 61300-3-38:2012
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60050-731 - International Electrotechnical Vocabulary - -
(IEV) -
Chapter 731: Optical fibre communication

IEC 61300-3-29 - Fibre optic interconnecting devices and EN 61300-3-29 -
passive components - Basic test and
measurement procedures -
Part 3-29: Examinations and measurements
- Measurement techniques for characterising
the amplitude of the spectral transfer
function of DWDM components
IEC 61300-3-38 ®
Edition 1.0 2012-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic interconnecting devices and passive components – Basic test and

measurement procedures –
Part 3-38: Examinations and measurements – Group delay, chromatic dispersion

and phase ripple
Dispositifs d’interconnexion et composants passifs à fibres optiques –

Procédures fondamentales d'essais et de mesures –

Partie 3-38: Examens et mesures – Retard de groupe, dispersion chromatique et

fluctuation de phase
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 33.180.10 ISBN 978-2-83220-115-2

– 2 – 61300-3-38 © IEC:2012
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and abbreviations . 7
4 General description . 8
5 Apparatus . 9
5.1 Modulation phase shift method . 9
5.1.1 General . 9
5.1.2 Variable wavelength source VWS . 9
5.1.3 Tracking filter (optional) . 9
5.1.4 Reference branching device RBD1, RBD2 . 10
5.1.5 Wavelength monitor (optional) . 10
5.1.6 Device under test DUT . 10
5.1.7 Detectors D1, D2 . 10
5.1.8 RF generator . 11
5.1.9 Amplitude modulator . 11
5.1.10 Phase comparator . 11
5.1.11 Temporary joints TJ1, TJ2 . 11
5.1.12 Polarization controller (optional) . 11
5.1.13 Reference jumper . 12
5.2 Swept wavelength interferometry method . 12
5.2.1 General . 12
5.2.2 Tunable laser source TLS . 12
5.2.3 Wavelength monitor . 13
5.2.4 Reference branching devices RBD1, RBD2, RBD3 . 13
5.2.5 Detectors D1, D2 . 13
5.2.6 Polarization controller . 13
5.2.7 Polarization analyzer . 13
5.3 Polarization phase shift method . 13
5.3.1 General . 13
5.3.2 Tunable laser source TLS . 14
5.3.3 RF generator . 14
5.3.4 Amplitude modulator . 15
5.3.5 Polarization controller . 15
5.3.6 Polarization splitter . 15
5.3.7 Detectors D1, D2 . 15
5.3.8 Amplitude and phase comparator . 16
6 Measurement procedure . 16
6.1 Modulation phase shift method . 16
6.1.1 Measurement principle . 16
6.1.2 RF modulation frequency . 16
6.1.3 Test sequence . 18
6.1.4 Special notice for measurement of GDR . 19
6.1.5 Calculation of relative group delay . 19
6.2 Swept wavelength interferometry method . 19
6.2.1 Measurement principle . 19

61300-3-38 © IEC:2012 – 3 –
6.2.2 Test sequence . 20
6.2.3 Special notice for measurement of GDR . 20
6.2.4 Calculation of group delay . 20
6.3 Polarization phase shift method . 21
6.3.1 Modulation frequency . 21
6.3.2 Wavelength increment . 22
6.3.3 Scanning wavelength and measuring CD . 22
6.3.4 Calibration . 22
6.3.5 Calculation of relative group delay and CD . 23
6.4 Measurement window (common for all test methods) . 23
7 Analysis . 25
7.1 Noise reduction of group delay measurement . 25
7.1.1 Averaging . 25
7.1.2 Spectral filtering . 25
7.2 Linear phase variation . 25
7.3 Chromatic dispersion . 25
7.3.1 General . 25
7.3.2 Finite difference calculation . 26
7.3.3 Curve fit . 26
7.4 Phase ripple . 27
7.4.1 General . 27
7.4.2 Slope fitting . 27
7.4.3 GDR estimation . 27
7.4.4 Phase ripple calculation . 28
8 Examples of measurement . 28
8.1 50GHz band-pass thin-film filter . 28
8.2 Planar waveguide filter component . 29
8.3 Tunable dispersion compensator (fiber bragg grating) . 30
8.4 Random polarization mode coupling device . 30
9 Details to be specified . 31
Annex A (informative) Calculation of differential group delay . 32
Bibliography . 40

Figure 1 – MPS measurement method apparatus . 9
Figure 2 – SWI measurement method apparatus . 12
Figure 3 – PPS measurement method apparatus . 14
Figure 4 – Sampling at the modulation frequency . 18
Figure 5 – Measurement window centred on an ITU wavelength with a defined width . 24
Figure 6 – Measurement window determined by the insertion loss curve at 3dB . 24
Figure 7 – Calculated CD from fitted GD over a 25 GHz optical BW centred on the ITU
frequency . 26
Figure 8 – A 6th order polynomial curve is fitted to relative GD data over a 25 GHz
optical BW centred on the ITU frequency . 27
Figure 9 – Estimation of the amplitude of the GD ripple and the period . 28
Figure 10 – GD and loss spectra for a 50 GHz-channel-spacing DWDM filter . 28
Figure 11 – Measured GD and loss spectra for planar waveguide filter . 29
Figure 12 – Measured CD and loss spectra for planar waveguide filter . 29

– 4 – 61300-3-38 © IEC:2012
Figure 13 – Measured GD deviation of a fibre Bragg grating . 30
Figure 14 – Measured phase ripple of a fibre Bragg grating . 30
Figure 15 – Measured GD for a device with random polarization mode coupling . 31
Figure 16 – Measured CD for a device with random polarization mode coupling . 31
Figure A.1 – Mueller states on Poincaré sphere . 32
Figure A.2 – DGD spectrum for a 50 GHz bandpass filter, measured with 30 pm
resolution BW . 35
Figure A.3 – DGD versus wavelength for a random polarization mode coupling device
(example) . 37
Figure A.4 – DGD versus wavelength for a fibre Bragg grating filter (example) . 37

Table 1 – Modulation frequency versus wavelength resolution for C-band . 17
Table A.1 – Example of Mueller set . 33

61300-3-38 © IEC:2012 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC INTERCONNECTING DEVICES
AND PASSIVE COMPONENTS –
BASIC TEST AND MEASUREMENT PROCEDURES –

Part 3-38: Examinations and measurements –
Group delay, chromatic dispersion and phase ripple

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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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 61300-3-38 has been prepared by subcommittee 86B: Fibre optic
interconnecting devices and passive components, of IEC technical committee 86: Fibre optics.
This first edition cancels and replaces the IEC/PAS 61300-3-38 published in 2007. This edition
constitutes a technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
86B/3394/FDIS 86B/3438/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.

– 6 – 61300-3-38 © IEC:2012
The list of all parts of 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 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.
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.
61300-3-38 © IEC:2012 – 7 –
FIBRE OPTIC INTERCONNECTING DEVICES
AND PASSIVE COMPONENTS –
BASIC TEST AND MEASUREMENT PROCEDURES –

Part 3-38: Examinations and measurements –
Group delay, chromatic dispersion and phase ripple

1 Scope
This part of IEC 61300 describes the measurement methods necessary to characterise the
group delay properties of passive devices and dynamic modules. From these measurements
further parameters like group delay ripple, linear phase deviation, chromatic dispersion,
dispersion slope, and phase ripple can be derived. In addition, when these measurements are
made with resolved polarization, the differential group delay can also be determined as an
alternative to separate measurement with the dedicated methods of IEC 61300-3-32.
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 60050-731, International Electrotechnical Vocabulary – Chapter 731: Optical fibre
communication
IEC 61300-3-29, Fibre optic interconnecting devices and passive components – Basic test
and measurement procedures – Part 3-29: Examinations and measurements – Measurement
techniques for characterizing the amplitude of the spectral transfer function of DWDM
components
3 Terms and abbreviations
For the purposes of this document, the terms and definitions given in IEC 60050-731 and
IEC 61300-3-29 apply, together with the following.
BW Bandwidth: the spectral width of a signal or filter.
CD Chromatic dispersion (in ps/nm): change of group delay over wavelength:
CD=d(GD)/dλ
D Detector
DGD Differential group delay (in ps): difference in propagation time between two
orthogonal polarization modes
DUT Device under test
DWDM Dense wavelength division multiplexing
δ Step size of the VWS during a wavelength swept measurement
f Modulation frequency
RF
GD Group delay (in ps): time required for a signal to propagate through a device
GDR Group delay ripple (in ps): the amplitude of ripple of GD
LN LiNbO
– 8 – 61300-3-38 © IEC:2012
LPV Linear phase variation (in deg)
λ Centre channel or nominal operating wavelength for a component
c
MPS Modulation phase shift
PBS Polarising beam splitter
PMD Polarization mode dispersion (in ps): average value of DGD over wavelength
PPS Polarization phase shift
PSP Principle state of polarization
Φ Phase delay
RBD Reference branching device
SOP State of polarization
SSE Source spontaneous emission
SWI Swept wavelength interferometry
∆θ Phase ripple
TDC Tunable dispersion compensator
TJ Temporary joint
TLS Tunable laser source
VWS Variable wavelength source
4 General description
This document covers transmission measurements of the group delay properties of passive
devices and dynamic modules. In order to interpret the group delay properties, it is essential
to also have the amplitude spectral measurement available. For this reason, loss
measurements are also covered to the extent that they are required to make proper
dispersion measurements.
The methods described in this procedure are intended to be applicable in any wavelength
band (C, L, O, etc.) although examples may be shown only in the C band for illustrative
purposes.
This document is separated into two sections, one concentrating on measurement methods,
and one concentrating on analysis of the measurement data. The measurement methods
covered in this document are the modulation phase shift method, the swept-wavelength
interferometry method and the polarization phase shift method. The modulation phase shift
method is considered the reference method. The methods are selected particularly because of
their ability to provide spectrally resolved results, which are often necessary for passive
components and especially for wavelength-selective devices.
The appropriate measurement parameter to evaluate the group delay ripple, and the method
of estimating the phase ripple from the measurement result of GDR are shown in 7.4. The
phase ripple is important as a measure of the influence that GD of an optical device has on
the transmission quality since many tunable dispersion compensators use the interference
effect where ripple is a significant effect.

61300-3-38 © IEC:2012 – 9 –
5 Apparatus
5.1 Modulation phase shift method
5.1.1 General
The measurement set-up for the characterisation of the group delay (GD) properties of optical
components is shown in Figure 1. A detailed explanation of the various components of this
system and their functions is contained in 5.1.2 to 5.1.13.
RF
Detector
generator
(D1)
DUT
Phase
TJ1 TJ2 comparator
Detector
Tracking RBD1
Amplitude Polarization
(D2)
filter
VWS controller
modulator
Phase
(optional) (optional)
comparator
RBD2
(optional)
Data collection,
Wavelength
computation and
monitor
instrumentation
control
Electrical control and data interface
Temporary reference optical connection
Optical connection
Electrical RF connection
IEC  986/12
Figure 1 – MPS measurement method apparatus
5.1.2 Variable wavelength source VWS
The variable wavelength source (VWS) is a polarized light source that can select a specific
output wavelength and can be tuned across a specified wavelength range. The power stability
at any of the operating wavelengths shall be sufficient so as not to cause significant errors in
the phase comparators. The relative accuracy and repeatability of wavelength, as determined
by the VWS and wavelength monitor together, shall be accurate to 3 pm for each point in the
measuring range and the absolute wavelength accuracy should satisfy the wavelength
specifications of the device under test. The linewidth of the source shall be less than 100 MHz.
The tuning range of the VWS shall cover the entire spectral region of the device and the
source shall also be free of mode hopping over the tuning range. The output power of the
VWS shall be sufficient to provide enough signal to ensure good comparison of the phase.
The minimum increment of the wavelength of the VWS should be adjusted to one tenth of
expected GDR period of the DUT.
5.1.3 Tracking filter (optional)
The tracking filter may be used for any DUT measurements if the dynamic range of the VWS
and the detector does not allow for measuring dynamic range of at least 40 dB due to the

– 10 – 61300-3-38 © IEC:2012
shape of the DUT and the broadband source spontaneous emission (SSE) of the VWS. The
filter shall track the VWS so as to provide the maximum SSE suppression and the maximum
transmitted power as the VWS is scanned across the measurement region. The spectral
shape of the filter shall provide enough out of band attenuation to allow for 40 to 50 dB
dynamic range at the transmission detector.
5.1.4 Reference branching device RBD1, RBD2
The configuration of the RBD is 1 × 2 or 2 × 2. If its configuration is 2 × 2, one port of the RBD
shall be terminated to have a return loss better than 50 dB. The splitting ratio of the RBD shall
be stable with wavelength. It shall also be insensitive to polarization. The polarization
sensitivity of transmission attenuation shall be less than one tenth of the device wavelength
dependency of attenuation or less than 0,1 dB. The directivity shall be at least 10 dB higher
than the maximum return loss. The split ratio shall be sufficient to provide the dynamic range
for the measurement of the transfer function and the power necessary for the wavelength
monitor to operate correctly.
5.1.5 Wavelength monitor (optional)
In this test procedure, the wavelength accuracy of the source needs to be closely monitored.
If the tuning accuracy of the VWS is not sufficient for the measurement, a wavelength monitor
is required. For this measurement method, it is necessary to measure the spectral peak of any
input signal within the device BW to an accuracy of 3 pm. Acceptable wavelength monitors
include an optical wavelength monitor or a gas absorption cell (such as an acetylene cell). If a
gas absorption cell is used, the wavelength accuracy of the VWS must be sufficient to resolve
the absorption lines. The VWS must be sufficiently linear between the absorption lines.
Included under this specification, is the wavelength repeatability of the VWS + monitor. It
should be understood by the operator that if the test apparatus has 0,1 ps of ripple with a
30 pm period, then a random 3 pm wavelength variation from reference scan to device scan
can result in as much as 0,03 ps of GD noise.
5.1.6 Device under test DUT
For the purposes of this document, the test ports shall be a single “input-output” path. The
method described can be extrapolated to obtain a single measurement system capable of
handling an m x n device. The device shall be terminated on either pigtails or with connectors.
Because this measurement set up is very sensitive to reflections, and is useful for detecting
reflections in the DUT it is important that reflections are not introduced by the measurement
system.
In many cases, the characteristics of DWDM components are temperature dependent. This
measurement procedure assumes that any such device is held at a constant temperature
throughout the procedure. The absolute accuracy of the measurement may be limited by the
accuracy of any heating or cooling device used to maintain a constant temperature. For
example, if a device is known to have a temperature dependence of 0,01 nm / C, and the
temperature during the procedure is held to a set temperature ± 1 °C; then any spectral
results obtained are known to have an total uncertainty of 0,02 nm due to temperature.
5.1.7 Detectors D1, D2
The detectors consist of an optical detector, the associated electronics, and a means of
connecting to an optical fibre. The use of a detector (D2) is considered optional, but provides
correction for any instability in the GD of the instrument setup between the modulator and the
DUT between Step 3 and Step 4 of 6.1.3. The optical connection may be a receptacle for an
optical connector, a fibre pigtail, or a bare fibre adapter. The back-reflection from detectors
D1 and D2 shall be minimised. The preferred option would be to use an APC connector. It
should be noted that the use of an APC connector would contribute approximately 0,03 dB of
PDL to the measurement if terminated in air.

61300-3-38 © IEC:2012 – 11 –
The dynamic range and sensitivity of the detectors shall be sufficient for the required
measurement range, given the power level provided by the modulated source. The linearity of
the detectors shall be sufficient to provide accurate representation of the modulated signal.
The detector shall transfer the optical modulation phase to the RF output phase with good
stability and little dependence on the optical signal level.
Where during the sequence of measurements a detector shall be disconnected and
reconnected the coupling efficiency for the two measurements shall be maintained to at least
the accuracy of the mated connector.
5.1.8 RF generator
The RF Generator delivers an electrical signal that is used for driving the intensity modulator.
In addition, the signal is delivered to the phase comparator in detectors D1 and D2 as a
reference signal. The RF Generator produces a waveform with a single dominant Fourier
component, for example, a sinusoidal wave modulation. Typically, a sinusoidal signal with a
frequency in the range of 100 MHz up to 3 GHz is used. The RF generator shall have
sufficient frequency accuracy and stability for the required measurement accuracy,
considering that the frequency provides the time base for the GD measurement.
5.1.9 Amplitude modulator
The amplitude modulator uses the modulated signal from the RF generator to induce the
equivalent amplitude modulation on a continuous wave optical signal. The modulator converts
the modulated signal from the RF generator to a modulated optical signal. The modulator
shall have sufficient linearity to produce a good sinusoidal modulation. The modulation
amplitude should be matched to the dynamic range of the detector system.
5.1.10 Phase comparator
The phase comparator is built into the detectors D1 and D2, which compare the phase of the
modulated optical signal and the RF reference signal. Typically, a network analyser, or lock-in
amplifier is used as a phase comparator. A method known as phase sensitive detection is
used to single out the component of the signal at a specific reference frequency and phase.
Noise signals at frequencies other than the reference frequency are rejected and do not affect
the phase measurement. The RF signal level shall not affect the phase measurement.
5.1.11 Temporary joints TJ1, TJ2
Temporary joints are specified to connect the test input signal to the device under test to the
device output to the transmission detector (D1).
Examples of temporary joints are typically connectors or splices. However other methods
such as vacuum chucks, or micromanipulators may be applied. Due to the high sensitivity to
back reflections, it is necessary to ensure that all of these joints have back-reflection <-50 dB.
5.1.12 Polarization controller (optional)
The modulated laser signal is optionally sent to a polarization controller, wherein the
polarization can be adjusted to the 4-Mueller-states located on the surface of the Poincaré
sphere, three of them on the equator of the Poincaré sphere and separated by 90 degree
consisting of the 0º, 45º and 90º linear polarization states, and the fourth state on the pole of
the Poincaré sphere for circular polarization. If the DUT exhibits polarization mode dispersion,
averaging results from orthogonal polarization states allows the GD average over all input
polarization states to be determined. From a set of GD measurements at all the 4-Mueller-
states, the differential group delay (DGD) can be calculated. The polarization controller shall
be able to provide satisfactory polarization stability over the wavelength range of the
measurement.
– 12 – 61300-3-38 © IEC:2012
5.1.13 Reference jumper
The reference jumper is a single-mode fibre. The optical connection may be an optical
connector, a fibre pigtail, or a bare fibre. The reference jumper must have the same optical
connection as the DUT.
5.2 Swept wavelength interferometry method
5.2.1 General
The measurement set-up for this method is shown in Figure 2. A detailed explanation of the
various components of this system and their functions is contained in 5.2.2 to 5.2.7. The
setup shown illustrates a transmission measurement of a DUT with two optical ports.
The measurement of GD is usually of interest to determine its dependence on wavelength and
polarization. However, the GD of optical fibre and other components of optical fibre networks
is also sensitively dependent on outside parameters such as temperature, pressure,
mechanical stress, and noise. Therefore a setup for measuring GD should provide for stability
against fibre movement and external changes during the measurement. Since the SWI
method relies on tracing the optical phase, which is very sensitive to GD and GD changes in a
fibre, such provision is particularly important for this method.
Detector
DUT
(D1)
TJ1 TJ2 Data
RBD1 computation,
Polarization Detector
TLS collection and
controller (D2)
instrumentation
RBD2 RBD3
control
PBS
Wavelength
monitor
Electrical control and data interface
Temporary reference optical connection
Optical connection
IEC  987/12
Figure 2 – SWI measurement method apparatus
5.2.2 Tunable laser source TLS
The SWI method uses coherent interference, so a tunable laser source is necessary to
provide the variable wavelength signal. The TLS must be tunable across the required
wavelength range. Considering typical coherence and wavelength resolution requirements,
the line-width shall be less than 1 MHz. A typical device length of about 10m, including patch
cords, will give an interferogram period of about 20 MHz. Accurate characterization of this
requires a substantially smaller resolution. Typically closely spaced measurements are
required (depending on the length and GD range of the DUT as discussed in 6.2.1), so it is
highly recommended to perform the measurements during continuous wavelength scanning by
the source. Therefore the setup shall provide specified control and monitoring of the
wavelength while sweeping.
61300-3-38 © IEC:2012 – 13 –
5.2.3 Wavelength monitor
If the TLS does not itself provide adequate wavelength accuracy, this shall be achieved with
the wavelength monitor. The monitor improves absolute wavelength accuracy and relative
wavelength accuracy for each measurement point during the wavelength scan.
5.2.4 Reference branching devices RBD1, RBD2, RBD3
The branching devices, RBD2 and RBD3, are used to establish the interferometer by splitting
the optical path so that part of the light passes through the DUT and the other part passes
along a reference path. The light from the two paths is then recombined so that it interferes at
the detectors. These couplers will typically have a 50:50 coupling ratio. Further branching
devices may be used to tap light for monitoring, as for the wavelength monitor. These should
be selected to provide adequate signal for the monitoring function. The branching devices
have 1 × 2 or 2 × 2 configuration. Unused ports of the RBD shall be terminated to give less
than -50 dB back-reflection.
5.2.5 Detectors D1, D2
The detectors are used to trace the optical power with respect to wavelength. As described
below, the recommended configuration produces two such traces for light at two orthogonal
polarization states. The traces will generally yield oscillations in power with very short
wavelength period as explained in 5.2.1, so that a high density of measurements vs.
wavelength will be required. Therefore a high-speed data acquisition detection system is
recommended. The discussion below assumes that the output signal corresponds to optical
power. Since relative changes in power will be evaluated, the detectors should have good
linearity, and care should be taken to avoid approaching saturation.
5.2.6 Polarization controller
To obtain sufficient interference signal from the interferometer, it must be assured that light
from the two paths combines with the same polarization, since signals with orthogonal
polarization will not produce interference. Since in general the polarization state of the light at
the DUT output will be unknown, some control of the polarization is required. The polarization
controller and polarization analyzer of 5.2.6 combine to satisfy this function, as described in
Clause 5. Generally the polarization controller is used to establish the polarization at the DUT
input and to “balance” the power at the two detectors from the reference path of the
interferometer. The polarization controller shall be able to provide satisfactory polarization
stability over the wavelength range of the measurement, for example by using zero-ord
...