IEC TR 62343-6-3:2010

IEC/TR 62343-6-3 ®
Edition 1.0 2010-05
TECHNICAL
REPORT
colour
inside
Dynamic modules –
Part 6-3: Round robin measurement results for group delay ripple of tunable
dispersion compensators
IEC/TR 62343-6-3:2010(E)
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IEC/TR 62343-6-3 ®
Edition 1.0 2010-05
TECHNICAL
REPORT
colour
inside
Dynamic modules –
Part 6-3: Round robin measurement results for group delay ripple of tunable
dispersion compensators
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
U
ICS 33.180 ISBN 978-2-88910-992-0
– 2 – TR 62343-6-3 © IEC:2010(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Abbreviated terms .7
4 Types of tunable dispersion compensators (TDCs) .8
4.1 Virtual imaged phased array (VIPA).8
4.2 Fibre Bragg grating (FBG) .8
4.3 Planar lightwave circuit (PLC) .8
4.4 Etalon .9
5 Measurement methods .9
5.1 Modulation phase shift (MPS) method .9
5.2 Modulation phase shift-Mueller matrix (MPS-Mueller) method.10
5.3 Polarization phase shift (PPS) method .10
5.4 Swept wavelength interferometry (SWI) method .10
6 DUTs and test parameters.10
7 Measurement results .11
7.1 VIPA.11
7.2 FBG .14
7.3 PLC.16
7.4 Etalon .19
8 Data analysis.21
8.1 Repeatability .21
8.2 Measurement method differences.22
9 Consideration of phase ripple .24
10 Conclusion .27

Figure 1 – Structure of the VIPA .8
Figure 2 – Chirped fibre grating .8
Figure 3 – PLC (MZ interference circuit) .9
Figure 4 – Etalon (Gires-Tournois interferometer) .9
Figure 5 – GD and IL of the VIPA.12
Figure 6 – GD deviation with each measurement method of the VIPA .12
Figure 7 – GD deviation at different RBWs of the VIPA .13
Figure 8 – Summary of GDR measurement results of the VIPA .13
Figure 9 – Summary of GDR repeatability of the VIPA .14
Figure 10 – GD and IL of FBG1.14
Figure 11 – GD deviation with each measurement method of FBG1 .15
Figure 12 – GD deviation at different RBWs of FBG1 .15
Figure 13 – Summary of GDR measurement results of the FBGs .16
Figure 14 – Summary of GDR repeatability of the FBGs.16
Figure 15 – GD and IL of the PLC .17
Figure 16 – GD deviation of the PLC with different measurement methods .17

TR 62343-6-3 © IEC:2010(E) – 3 –
Figure 17 – GD deviation of the PLC at different RBWs .18
Figure 18 – Summary of GDR measurement results of the PLC .18
Figure 19 – Summary of GDR repeatability of the PLC.19
Figure 20 – GD and IL of the etalon .19
Figure 21 – GD deviation of the etalon with different measurement methods.20
Figure 22 – GD deviation of the etalon at different RBWs .20
Figure 23 – Summary of GDR measurement results of the etalon .21
Figure 24 – Summary of GDR repeatability of the etalon.21
Figure 25 – RBW, measurement methods and GDR repeatability.22
Figure 26 – Differences in GDR measurement results between measurement methods.23
Figure 27 – GDR differences produced when measuring a TDC with GDR of less than
6 ps at RBW of 8 pm.23
Figure 28 – Typical measurement result of GDR .24
Figure 29 – Phase ripple calculated from GDR.25
Figure 30 – Amplitude, period, and EOP of GDR.25
Figure 31 – Phase ripple of the VIPA and FBGs.26
Figure 32 – Phase ripple repeatability of the VIPA and FBGs.26
Figure 33 – Differences in phase ripple between measurement methods .27

Table 1 – DUTs and measurement methods used in round robin testing .10
Table 2 – RBW and modulation frequency .11

– 4 – TR 62343-6-3 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DYNAMIC MODULES –
Part 6-3: Round robin measurement results
for group delay ripple of tunable dispersion compensators

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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The main task of IEC technical committees is to prepare International Standards. However, a
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data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 62343-6-3, which is a technical report, has been prepared by subcommittee 86C: Fibre
optic systems and active devices, of IEC technical committee 86: Fibre optics.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86C/917/DTR 86C/952/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.

TR 62343-6-3 © IEC:2010(E) – 5 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of IEC 62343 series, published under the general title Dynamic modules, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – TR 62343-6-3 © IEC:2010(E)
INTRODUCTION
The most important means of enhancing the technology for communication systems are
networking, faster speed, and longer distance. In long-distance, high-speed communication
systems operating at 40 Gbps or more, dispersion is known to limit transmission distance.
Various tunable dispersion compensators (TDCs) have been commercialized in order to
minimize the degradation of signals caused by chromatic dispersion. However, the group
delay (GD) in TDCs is known to have ripples dependent on the principles of TDC operation,
and such GD affects signal degradation.
IEC TC86 (Fibre optics) describes several methods of measuring chromatic dispersion (CD).
One example is IEC 61300-3-38, but it does not specify a measurement method for group
delay ripple (GDR). The representative passive component for compensating for chromatic
dispersion is dispersion compensation fibre (DCF), but given its principles, the GD has no
ripples. Conversely, many TDCs use the interference effect, which explains why there are
ripples.
Under these circumstances, round robin testing has been conducted by using various TDCs
and diverse GD measurement methods. This technical report, based on the findings from
round robin testing, examines the direction of standardization for GDR measurement methods.
This technical report is based on and translated from OITDA document- TP06/SP DM-2008
(Group Delay Ripple Measurement Method for Tunable Dispersion Compensators－Technical
Paper).
TR 62343-6-3 © IEC:2010(E) – 7 –
DYNAMIC MODULES –
Part 6-3: Round robin measurement results
for group delay ripple of tunable dispersion compensators

1 Scope
This technical report describes the round robin measurement results for the group delay ripple
(GDR) of tunable dispersion compensators (TDCs). It briefly explains the four typical TDCs
measured and four typical methods of measuring group delay (GD), as well as the GDR round
robin measurement results of TDCs, and an analysis of repeatability and differences among
these measurement methods. This technical report also proposes suitable measurement
parameters and a new parameter of phase ripple instead of GDR.
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/PAS 61300-3-38, Fibre optic interconnecting devices and passive components – Basic
test and measurement procedures – Part 3-38: Group delay and chromatic dispersion
IEC 62343-1-2, Dynamic modules – Part 1-2: Performance standards – Dynamic chromatic
dispersion compensator with pigtails for use in controlled environments (Category C)
3 Abbreviated terms
For the purposes of this document, the abbreviated terms apply.
CD chromatic dispersion
DGD differential group delay
DUT device under test
EOP eye opening penalty
FBG fibre Bragg grating
FSR free spectral range
GD group delay
GDR group delay ripple
MPS modulation phase shift
MZ Mach-Zender
PLC planar lightwave circuit
PPS polarization phase shift
RBW resolution bandwidth
SWI swept wavelength interferometry
TDC tunable dispersion compensator
VIPA virtually imaged phased array

– 8 – TR 62343-6-3 © IEC:2010(E)
4 Types of tunable dispersion compensators (TDCs)
Various TDCs have been announced and commercialized in the market. The following briefly
describes typical TDCs.
4.1 Virtual imaged phased array (VIPA)
Figure 1 shows the structure of a virtually imaged phased array (VIPA). The input light from a
single-mode fibre is line-focused onto a glass plate. The glass plate is coated on both sides
and collimated light is emitted from the reverse side of the glass after multiple reflections on
the glass plate. The light from the glass plate is focused onto a curved mirror. The reflected
light travels back to the glass plate and is finally coupled to the fibre. The 3-dimensional
mirror is moved to vary the optical distance for each wavelength, thereby changing the CD.

3-dimensional mirror
Optical circulator
IEC  1248/10
Figure 1 – Structure of the VIPA
4.2 Fibre Bragg grating (FBG)
An FBG periodically changes the refraction index of the optical fibre core, thereby forming a
grating to generate Bragg diffraction, which functions as a reflection filter. Gradually changing
the pitch of Bragg diffraction varies the reflection return time according to wavelength, thereby
generating CD. The temperature of the fibre formed in the FBG can be varied or given tension
to change the FBG pitch. This principle is used to change the CD.
IN
Chirped FBG
λ λ
2 1
OUT
IEC  1249/10
Figure 2 – Chirped fibre grating
4.3 Planar lightwave circuit (PLC)
A ring resonator can be formed on a quartz lightwave circuit. The resulting interference effect
can then be used to produce periodic loss and GD characteristics over the wavelength.
Moreover, the ring resonator can be replaced with MZ interference circuits in multiple stages
to produce similar effects. The temperatures of some of these interference circuits can be
varied to change the CD.
TR 62343-6-3 © IEC:2010(E) – 9 –

Thermo-optic Tunable 3 dB
phase shifter coupler coupler
θ1 θ3 θ5 θ7
Output
ΔL ΔL ΔL ΔL
φ0 φ1 φ2 φ3 φ4 φ5 φ6 φ7 φ8
Input
ΔL ΔL ΔL
ΔL
Silica
θ2 θ4 θ6 θ8
waveguide Delay arm
IEC  1250/10
Figure 3 – PLC (MZ interference circuit)
4.4 Etalon
Etalon is an optical cavity housing a pair of parallel reflective mirrors. Multiple reflection
interference between two filters yields a cyclic spectrum and dispersion characteristics. The
period of the cyclic spectrum is called free spectral range (FSR). The operating wavelength
and FSR can be adjusted by changing the optical distance between both mirrors. A Gires-
Tournois interferometer (shown in Figure 4 below) is suitable for dispersion compensation.
High reflection
Low reflection
mirror
mirror
IN
OUT
Optical cavity
IEC  1251/10
Figure 4 – Etalon (Gires-Tournois interferometer)
5 Measurement methods
The following describes the representative methods of measuring GD. Refer to IEC/PAS
61300-3-38 for details.
5.1 Modulation phase shift (MPS) method
The MPS method is used to calculate GD and CD by adding amplitude modulation to output
light from a wavelength-variable light source, receiving it with a receiver through a device
under test (DUT), and then analyzing the wavelength dependence of the phase of the
demodulated signal received. The wavelength resolution depends on the signal’s modulation
frequency. Because there is a trade-off between wavelength resolution and measurement
accuracy, modulation frequency is an important measurement parameter.

– 10 – TR 62343-6-3 © IEC:2010(E)
5.2 Modulation phase shift-Mueller matrix (MPS-Mueller) method
The MPS-Mueller method combines the MPS method with a process to produce four
polarization states of modulated light entering the DUT, and then solving the Mueller matrix
for each phase calculated, thereby calculating GD and CD in an average polarization state.
Similarly to the MPS method, modulation frequency becomes an important measurement
parameter.
5.3 Polarization phase shift (PPS) method
The PPS method expands on the MPS method by adding hardware to divide the light beam
transmitted through the DUT into two orthogonal polarized beams. The two polarization states
are analyzed and GD and CD are calculated for an average polarization state. Similar to the
MPS method, modulation frequency becomes an important measurement parameter.
5.4 Swept wavelength interferometry (SWI) method
Unlike the method above, the SWI method does not modulate the light beams measured. The
wavelength of the wavelength-varied light source is swept before entering the receiver via the
Mach-Zehnder (MZ) interferometer. With two paths through the MZ interferometer, one as the
reference path and one through the interfered signal into the receiver are analyzed to
determine the phase of light. The resultant findings are then used to calculate GD and CD.
That is how this method works. Since the setting of wavelength resolution and measurement
accuracy can be changed to oppose each other, wavelength resolution becomes an important
measurement parameter.
6 DUTs and test parameters
Table 1 lists the DUTs measured and the measurement methods used. For the MPS and SWI
methods, products from two different manufacturers identified as (A) and (B), respectively,
were used depending on the test date. The PPS and MPS (A) methods used the same
measuring equipment, with only the measurement method being switched over. The same is
true of the MPS-Mueller and MPS (B) methods. Moreover, the SWI (A) method is based on a
homodyne-type interferometer, while the SWI (B) method is based on a heterodyne-based
interferometer.
Table 1 – DUTs and measurement methods u
...