Fibre optic communication system design guides - Part 9: Guidance on polarization mode dispersion measurements and theory

IEC TR 61282-9:2016(E) which is a Technical Report, describes effects and theory of polarization mode dispersion (PMD) and provides guidance on PMD measurements. This second edition cancels and replaces the first edition published in 2006. This second edition includes the following significant technical changes with respect to the previous edition:
- much of the theory has been condensed - focusing only on content that is needed to explain the test method;
- symbols have been removed, but abbreviations are retained;
- the material in the Clause 5 has been significantly reduced in an effort to avoid repeating what is already in the actual International Standards. Instead, the focus is on explaining the International Standards;
- measurement methods that are not found in International Standards have been removed;
- there are significant corrections to the modulation phase shift method, particularly in regard to the Mueller set technique;
- there are significant corrections to the polarization phase shift method;
- the proof of the GINTY interferometric method is presented. This proof also extends to the Fixed Analyser Cosine transfer technique;
- another Fixed Analyser method is suggested. This is based on the proof of the GINTY method and is called "spectral differentiation method";
- Clause 6 has been renamed "Limitations" and refocused on the limitations of the test methods. This Technical Report is not intended to be an engineering manual;
- the annexes have been removed;
- the bibliography has been much reduced in size;
- the introduction has been expanded to include some information on system impairments. Keywords: polarization mode dispersion (PMD)

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Status
Published
Publication Date
23-Mar-2016
Current Stage
PPUB - Publication issued
Start Date
24-Mar-2016
Completion Date
24-Mar-2016
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IEC TR 61282-9
Edition 2.0 2016-03
TECHNICAL
REPORT
colour
inside
Fibre optic communication system design guides –
Part 9: Guidance on polarization mode dispersion measurements and theory
IEC TR 61282-9:2016-03(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 61282-9
Edition 2.0 2016-03
TECHNICAL
REPORT
colour
inside
Fibre optic communication system design guides –
Part 9: Guidance on polarization mode dispersion measurements and theory
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.01 ISBN 978-2-8322-3236-1

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 61282-9:2016 © IEC 2016
CONTENTS

FOREWORD ......................................................................................................................... 4

INTRODUCTION ................................................................................................................... 6

1 Scope ............................................................................................................................ 7

2 Normative references..................................................................................................... 7

3 Terms, definitions, and abbreviations ............................................................................. 7

3.1 Terms and definitions ............................................................................................ 7

3.2 Abbreviations ........................................................................................................ 8

4 Theoretical framework ................................................................................................... 8

4.1 Limitations and outline .......................................................................................... 8

4.2 Optical field and state of polarization ..................................................................... 8

4.3 SOP measurements, Stokes vectors, and Poincaré sphere rotations .................... 11

4.4 First order polarization mode dispersion .............................................................. 14

4.5 Birefringence vector, concatenations, and mode coupling ..................................... 16

4.6 The statistics of PMD and second order PMD ...................................................... 17

4.7 Managing time .................................................................................................... 20

5 Measurement methods ................................................................................................. 20

5.1 General ............................................................................................................... 20

5.2 Stokes parameter evaluation ............................................................................... 22

5.2.1 Equipment setup and procedure ................................................................... 22

5.2.2 Jones matrix eigenanalysis .......................................................................... 23

5.2.3 Poincaré sphere analysis ............................................................................. 24

5.2.4 One ended measurements based on SPE [3] ................................................ 26

5.3 Phase shift based measurement methods ............................................................ 27

5.3.1 General ....................................................................................................... 27

5.3.2 Modulation phase shift – Full search ............................................................. 28

5.3.3 Modulation phase shift method – Mueller set analysis [4] .............................. 29

5.3.4 Polarization phase shift measurement method[5] .......................................... 31

5.4 Interferometric measurement methods ................................................................. 33

5.4.1 General ....................................................................................................... 33

5.4.2 Generalized interferometric method [6] ......................................................... 35

5.4.3 Traditional interferometric measurement method ........................................... 40

5.5 Fixed analyser .................................................................................................... 41

5.5.1 General ....................................................................................................... 41

5.5.2 Extrema counting ......................................................................................... 42

5.5.3 Fourier transform ......................................................................................... 43

5.5.4 Cosine Fourier transform .............................................................................. 44

5.5.5 Spectral differentiation ................................................................................. 45

5.6 Wavelength scanning OTDR and SOP analysis (WSOSA) method [7] ................... 46

5.6.1 General ....................................................................................................... 46

5.6.2 Continuous model ........................................................................................ 48

5.6.3 Large difference model ................................................................................. 49

5.6.4 Scrambling factor derivation ......................................................................... 50

6 Limitations ................................................................................................................... 53

6.1 General ............................................................................................................... 53

6.2 Amplified spontaneous emission and degree of polarization ................................. 53

6.3 Polarization dependent loss (or gain) ................................................................... 53

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IEC TR 61282-9:2016 © IEC 2016 – 3 –

6.4 Coherence effects and multiple path interference ................................................. 54

6.5 Test lead fibres ................................................................................................... 54

6.6 Aerial cables testing ............................................................................................ 55

Bibliography ....................................................................................................................... 56

Figure 1 – Two electric field vector polarizations of the HE mode in a SMF ....................... 10

Figure 2 – A rotation on the Poincaré sphere ....................................................................... 13

Figure 3 – Strong mode coupling – Frequency evolution of the SOP .................................... 16

Figure 4 – Random DGD variation vs. wavelength ............................................................... 18

Figure 5 – Histogram of DGD values from Figure 4 .............................................................. 18

Figure 6 – SPE equipment diagram ..................................................................................... 22

Figure 7 – Relationship of orthogonal output SOPs to the PDV ............................................ 24

Figure 8 – Stokes vector rotation with frequency change ...................................................... 25

Figure 9 – Setup for modulation phase shift ......................................................................... 27

Figure 10 – Setup for polarization phase shift ...................................................................... 28

Figure 11 – Output SOP relation to the PSP ........................................................................ 30

Figure 12 – Interferometric measurement setup ................................................................... 33

Figure 13 – Interferogram relationships ............................................................................... 35

Figure 14 – Mean square envelopes .................................................................................... 38

Figure 15 – Fixed analyser setup ........................................................................................ 41

Figure 16 – Fixed analyser ratio .......................................................................................... 42

Figure 17 – Power spectrum ............................................................................................... 44

Figure 18 – Fourier transform .............................................................................................. 44

Figure 19 – WSOSA setup .................................................................................................. 46

Figure 20 – Frequency grid ................................................................................................. 47

Table 1 – Map of test methods and International Standards ................................................. 22

Table 2 – Mueller SOPs ...................................................................................................... 29

---------------------- Page: 5 ----------------------
– 4 – IEC TR 61282-9:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC COMMUNICATION SYSTEM DESIGN GUIDES –
Part 9: Guidance on polarization mode dispersion
measurements and theory
FOREWORD

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The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a technical report when it has collected

data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC TR 61282-9, which is a Technical Report, has been prepared by subcommittee 86C: Fibre

optic systems and active devices, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2006.

This second edition includes the following significant technical changes with respect to the

previous edition:

a) much of the theory has been condensed – focusing only on content that is needed to

explain the test method;
b) symbols have been removed, but abbreviations are retained;
---------------------- Page: 6 ----------------------
IEC TR 61282-9:2016 © IEC 2016 – 5 –

c) the material in the Clause 5 has been significantly reduced in an effort to avoid repeating

what is already in the actual International Standards. Instead, the focus is on explaining

the International Standards;

d) measurement methods that are not found in International Standards have been removed;

e) there are significant corrections to the modulation phase shift method, particularly in

regard to the Mueller set technique;
f) there are significant corrections to the polarization phase shift method;

g) the proof of the GINTY interferometric method is presented. This proof also extends to the

Fixed Analyser Cosine transfer technique;

h) another Fixed Analyser method is suggested. This is based on the proof of the GINTY

method and is called "spectral differentiation method";

i) Clause 6 has been renamed "Limitations" and refocused on the limitations of the test

methods. This Technical Report is not intended to be an engineering manual;
j) the annexes have been removed;
k) the bibliography has been much reduced in size;

l) the introduction has been expanded to include some information on system impairments.

The text of this Technical Report is based on the following documents:
Enquiry draft Report on voting
86C/1342/DTR 86C/1366/RVC

Full information on the voting for the approval of this Technical Report can be found in the

report on voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 61282 series, published under the general title Fibre optic

communication system design guides, 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 website under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
---------------------- Page: 7 ----------------------
– 6 – IEC TR 61282-9:2016 © IEC 2016
INTRODUCTION

This Technical Report is complementary to the International Standards describing PMD

procedures (IEC 60793-1-48, IEC 61280-4-4, IEC 61290-11-1, IEC 61290-11-2 and

IEC 61300-3-32) and other design guides on PMD (IEC 61282-3 and IEC 61292-5), as well as

ITU-T Recommendation G.650.2.

The system power penalty associated with PMD varies depending on transmission format and

bit rate. It also varies with optical frequency and state of polarization (SOP) of the light

source. At the output of a link, the signal can shift from a maximum delay to a minimum delay

as a result of using different SOPs at the source. The difference in these delays is called the

differential group delay (DGD), which is associated with two extremes of input SOP. At these

extremes, a signal in the form of a single pulse appears shifted up or down by half the DGD,

about a midpoint, at the output. At intermediate SOPs, the single pulse appears as a weighted

total of two pulses at the output, one shifted up by half the DGD and one shifted down by half

the DGD. This weighted total of two shifted pulses is what causes signal distortion.

The system power penalty is partly defined in terms of a maximum allowed bit error rate and a

minimum received power. In the absence of distortion, there is a minimum received power

that will produce the maximum allowed bit error rate. In the presence of distortion, the

received power should be increased to produce the maximum bit error rate. The magnitude of

the required increase of received power is the power penalty of the distortion.
The term PMD is used to describe two distinctly different ideas.

One idea is associated with the signal distortion induced by transmission media for which the

output SOP varies with optical frequency. This is the fundamental source of signal distortion.

The other idea is that of a number (value) associated with the measurement of a single-mode

fibre transmission link or element of that link. There are several measurement methods with

different strengths and capabilities. They are all based on quantifying the magnitude of

possible variation in output SOP with optical frequency. The objective of this Technical Report

is to explain the commonality of the different methods.

The DGD at the source’s optical frequency is what controls the maximum penalty across all

possible SOPs. However, in most links, the DGD varies randomly across optical frequency

and time. The PMD value associated with measurements, and which is specified, is a

statistical metric that describes the DGD distribution. There are two main metrics, linear

average and root-mean square (RMS), that exist in the literature and in the measurement

methods. For most situations, one metric can be calculated from the other using a conversion

formula. The reason for the dual metrics is an accident of history. If history could be

corrected, the RMS definition would be the most suitable.

For the non-return to zero transmission format, DGD equal to 0,3 of the bit period yields

approximately 1 dB maximum penalty. Because DGD varies randomly, a rule of thumb

emerged in the system standardization groups: keep PMD less than 0,1 of the bit period for

less than 1 dB penalty. This assumes that DGD larger than three times the PMD, and that the

source output SOP produces the worst case distortion, is not very likely. For 10 Gbit/s non-

return to zero, this rule yields a design rule: keep the link PMD less than 10 ps.

ITU-T G.sup.39 [1] has more information on the relationship of PMD and system penalties.

___________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 8 ----------------------
IEC TR 61282-9:2016 © IEC 2016 – 7 –
FIBRE OPTIC COMMUNICATION SYSTEM DESIGN GUIDES –
Part 9: Guidance on polarization mode dispersion
measurements and theory
1 Scope

This part of IEC 61282, which is a Technical Report, describes effects and theory of

polarization mode dispersion (PMD) and provides guidance on PMD measurements.
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 60793-1-48, Optical fibres – Part 1-48: Measurement methods and test procedures –

Polarization mode dispersion

IEC 61280-4-4, Fibre optic communication subsystem test procedures – Part 4-4: Cable

plants and links – Polarization mode dispersion measurement for installed links

IEC 61290-11-1, Optical amplifier – Test methods – Part 11-1: Polarization mode dispersion

parameter – Jones matrix eigenanalysis (JME)

IEC 61290-11-2, Optical amplifier – Test methods – Part 11-1: Polarization mode dispersion

parameter – Poincaré sphere analysis method

IEC 61300-3-32, Fibre optic interconnecting devices and passive components – Basic tests

and measurement procedures – Part 3-32: Examinations and measurements – Polarization

mode dispersion measurement for passive optical components
3 Terms, definitions, and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
PMD phenomenon
polarization mode dispersion phenomenon

signal of fibre-optic transmission signal induced by variation in the signal output state of

polarization with optical frequency
Note 1 to entry: PMD can limit the bit rate-length product of digital systems.
3.1.2
PMD value
polarization mode dispersion value

magnitude of polarization mode dispersion phenomenon associated with a single-mode fibre,

optical component and sub-system, or installed link
---------------------- Page: 9 ----------------------
– 8 – IEC TR 61282-9:2016 © IEC 2016

Note 1 to entry: The polarization mode dispersion value is usually expressed in ps.

3.2 Abbreviations
CFT cosine Fourier transform
DGD differential group delay
DOP degree of polarization
EC extrema counting
FA fixed analyser
FT Fourier transform
GINTY general interferometric method
JME Jones matrix eigenanalysis
MPS modulation phase shift
OTDR optical time domain reflectometer
PDL polarization dependent loss
PDV polarization dispersion vector
PMD polarization mode dispersion
PPS polarization phase shift
PSA Poincaré sphere analysis
PSP principal state of polarization
SMF single-mode fibre
SOP state of polarization
SPE Stokes parameter evaluation
TINTY traditional interferometric method
WSOSA wavelength scanning OTDR and SOP analysis method
4 Theoretical framework
4.1 Limitations and outline

The theory presented in Clause 4 does not include the effects of polarization dependent loss

or gain, or nonlinear effects. See 6.3 for information on polarization dependent loss.

The outline for Clause 4 is
• optical field and state of polarization;
• measurement of SOP, Stokes vector, and rotation;
• first order polarization mode dispersion;
• birefringence vector, concatenations, and mode coupling;
• the statistics of PMD and second order PMD.
4.2 Optical field and state of polarization

This subclause is intended to show the linkage between the propagation of an optical field in

a single-mode fibre (SMF) and the transmission signal state of polarization (SOP). This

information is fundamental to the PMD phenomena because variation in output SOP with

optical frequency is the distortion inducing mechanism.

The solution of the wave equation has degenerated eigenvalues. This means that even the

fundamental solution is degenerated. A SMF supports a pair of polarization modes for a

monochromatic light source. In particular, the lowest order mode, namely the fundamental

---------------------- Page: 10 ----------------------
IEC TR 61282-9:2016 © IEC 2016 – 9 –

mode HE (LP ) can be defined to have its transverse electric field predominately along the

11 01

x-direction; the orthogonal polarization is an independent mode, as shown in Figure 1.

In a lossless SMF, the electric field vector of a monochromatic electromagnetic wave

propagating along the z-direction can be described by a linear superposition of these two

modes in the x-y transverse plane as shown in Equation (1) and in Figure 1.
{ ( )}
E = [ j exp(iβ z)]+ [j exp β z ] exp(− iϖt)
x x y y
= [j exp(− ∆βz / 2) + j exp(i∆βz / 2)]exp[− i(ϖt − βz)]
x y
(1)
where

j and j are complex coefficients describing the amplitude and phase of the x/y initial

x y
SOPs;
E (x,y) and

E (x,y) are the spatial variation (in the x-y transverse plane) of the E vector of the

PM along the x/y-direction (see Figure 1);

β and β are the propagation constants (also called effective index or wavenumber)

x y
of the PM along the x/y-directions with the index of refraction n /n . Using
x y
i = x or y, β = k⋅n . The index of refraction has a dependence on frequency
i i
ϖ, frequency ν, or wavelength λ;
∆β is the difference of β and β ;
x y
is the average of βx and βy;
k is the propagation constant with the wavelength λ in vacuum
(= 2πν/c = 2π λ = ω c);
/ /
ν is the frequency in s or Hz;
ϖ is the angular frequency in rad s (the bar indicates absolute frequency
rather than deviation from some particular value);
c is the speed of light in vacuum (299792458 m/s);
∆’ is the birefringence coefficient (s/m), = ∆n/c
z is the distance (m) in the DUT along the optical axis (axis of propagation);
z = L at the output of the DUT with length L.
---------------------- Page: 11 ----------------------
– 10 – IEC TR 61282-9:2016 © IEC 2016
Axis of propagation, z
Fibre
core
E (x,y);β
x x
E (x,y);β
y y
Axis of
polarization, x
Axis of polarization, y
Cladding
IEC
Figure 1 – Two electric field vector polarizations of the HE mode in a SMF

The complex pair, [j exp(− i∆βz / 2), j exp(i∆βz / 2)], describes the SOP defined in the x-y plane

x y

of the wave propagating along the z-direction. This pair can be considered as a vector, and is

often called a Jones vector.

In the case where the transmission media is an ideal SMF with perfect circular symmetry,

β = β ,
y x
• the two polarization modes are degenerate (when two solutions have the same
eigenvalue, they are said to be degenerate);

• any wave with a defined input SOP will propagate unchanged along the z-direction

throughout the output of the SMF.

However, in a practical SMF, the circular symmetry is broken by imperfections produced by

the fabrication process, cabling, field installation/use or the installation environment:

• β ≠ β , implying a phase difference, an index-of-refraction difference ∆n, and a phase-

y x
velocity difference between the
...

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