Measurement method of a half-wavelength voltage for Mach-Zehnder optical modulator in wireless communication and broadcasting systems

IEC 62801:2020 specifies a measurement method of half-wavelength voltage applicable to Mach-Zehnder optical modulators in wireless communication and broadcasting systems. In addition, this method is also effective for the estimation of the intermodulation distortion of Mach-Zehnder optical modulators. The method applies for the following:
– frequency range: 10 MHz to 30 GHz;
– wavelength band: 0,8 µm to 2,0 µm;
– electro-optic material based Mach-Zehnder optical modulators and their modules.

Méthode de mesure de la tension à une demi-longueur d'onde relative aux modulateurs optiques Mach-Zehnder dans les systèmes de communication et transmission radiofréquence

IEC 62801:2020 spécifie une méthode de mesure de la tension d’une demi-longueur d’onde applicable aux modulateurs optiques de Mach-Zehnder dans les systèmes de communication et de transmission radiofréquence. De plus, cette méthode est également efficace pour estimer la distorsion d’intermodulation des modulateurs optiques de Mach-Zehnder. La méthode s'applique à ce qui suit:
– plage de fréquences: 10 MHz à 30 GHz;
– bande de longueur d’onde: 0,8 µm à 2,0 µm;
– modulateurs optiques de Mach-Zehnder fondés sur matériau électro-optique et leurs modules associés.

General Information

Status
Published
Publication Date
23-Sep-2020
Current Stage
PPUB - Publication issued
Completion Date
24-Sep-2020
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IEC 62801
Edition 1.0 2020-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Measurement method of half-wavelength voltage for Mach-Zehnder optical
modulator in wireless communication and broadcasting systems
Méthode de mesure de la tension à une demi-longueur d’onde relative aux
modulateurs optiques Mach-Zehnder dans les systèmes de communication
et transmission radiofréquence
IEC 62801:2020-09(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 62801
Edition 1.0 2020-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Measurement method of half-wavelength voltage for Mach-Zehnder optical
modulator in wireless communication and broadcasting systems
Méthode de mesure de la tension à une demi-longueur d’onde relative aux
modulateurs optiques Mach-Zehnder dans les systèmes de communication
et transmission radiofréquence
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.060.20; 33.180.99 ISBN 978-2-8322-8761-3

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

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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 62801:2020 © IEC 2020
CONTENTS

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

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

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

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

3 Terms, definitions, symbols and abbreviated terms .......................................................... 7

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

3.2 Symbols and abbreviated terms .............................................................................. 8

4 Electro-optic material based Mach-Zehnder optical modulator ......................................... 9

4.1 Mach-Zehnder optical modulator ............................................................................. 9

4.1.1 Component parts ............................................................................................. 9

4.1.2 Structure ......................................................................................................... 9

4.2 Requirements for Mach-Zehnder optical modulator ............................................... 10

4.2.1 General ......................................................................................................... 10

4.2.2 Substrate material ......................................................................................... 10

4.2.3 Optical waveguide design .............................................................................. 10

5 Sampling for quality control ........................................................................................... 10

5.1 Sampling............................................................................................................... 10

5.2 Sampling frequency .............................................................................................. 10

6 Measurement method of half wavelength voltage ........................................................... 10

6.1 Circuit diagram ..................................................................................................... 10

6.2 Measurement conditions ....................................................................................... 11

6.2.1 Temperature and environment ....................................................................... 11

6.2.2 Warming up of measurement equipment ........................................................ 11

6.3 Principle of measurement method ......................................................................... 12

6.3.1 General ......................................................................................................... 12

6.3.2 Measurement principle................................................................................... 12

6.4 Measurement procedure ....................................................................................... 14

6.4.1 General ......................................................................................................... 14

6.4.2 Circuit diagram (Type A) ................................................................................ 15

6.4.3 Circuit diagram (Type B) ................................................................................ 16

Annex A (normative) Conventional measurement method of optical modulation index ......... 18

A.1 Overview............................................................................................................... 18

A.2 Circuit diagram ..................................................................................................... 18

A.3 Measurement procedure ....................................................................................... 19

A.3.1 Spectrum analyser method ............................................................................ 19

A.3.2 Oscilloscope method ..................................................................................... 19

Annex B (informative) Calculation method of intermodulation distortions using driving

voltage and half-wavelength voltage of Mach-Zehnder optical modulator .............................. 20

B.1 Overview............................................................................................................... 20

B.2 Explanation of calculation method ......................................................................... 20

B.3 Conventional measurement methods of intermodulation distortion ........................ 26

B.3.1 General ......................................................................................................... 26

B.3.2 Circuit diagram .............................................................................................. 26

B.3.3 Precautions to be observed ........................................................................... 27

B.3.4 Measurement procedures .............................................................................. 27

Annex C (informative) Characteristics of Mach-Zehnder optical modulator .......................... 29

---------------------- Page: 4 ----------------------
IEC 62801:2020 © IEC 2020 – 3 –

C.1 Electrical and optical characteristics of Mach-Zehnder optical modulator .............. 29

C.2 Mechanical and environmental characteristics ...................................................... 29

Annex D (informative) Notes on measurement .................................................................... 31

D.1 Factors of measurement uncertainty ..................................................................... 31

D.1.1 Measurement equipment ............................................................................... 31

D.1.2 Measurement range ....................................................................................... 32

D.2 RF power source ................................................................................................... 33

D.2.1 Limitation from resolution of applied RF power .............................................. 33

D.2.2 Limitation from the resolution of oscilloscope screen ..................................... 34

D.3 Examples of measurement results ........................................................................ 34

Bibliography .......................................................................................................................... 37

Figure 1 – Transfer curve of a Mach-Zehnder optical modulator .............................................. 8

Figure 2 – Structure of Mach-Zehnder interferometer type optical modulator ........................... 9

Figure 3 – Schematic block diagram of the measurement setup ............................................ 11

Figure 4 – Zero-order Bessel function ................................................................................... 13

Figure 5 – Waveform change on the oscilloscope screen ...................................................... 13

Figure 6 – Driving voltage measurement setup ..................................................................... 15

Figure 7 – Driving voltage measurement setup using a power divider ................................... 16

Figure 8 – Waveforms on the oscilloscope ............................................................................ 17

Figure A.1 – Measurement setup referred in IEC 62007-2 ..................................................... 18

Figure A.2 – Time variation of photo current ......................................................................... 19

Figure B.1 – Mach-Zehnder interferometer type optical modulator ........................................ 20

Figure B.2 – Quadrature points of a transfer curve for a Mach-Zehnder optical modulator ..... 25

Figure B.3 – Dependency of IM2 on NOMI and bias voltage of a Mach-Zehnder optical

modulator ............................................................................................................................. 25

Figure B.4 – Relation between IM3 and OMI of a Mach-Zehnder optical modulator ............... 26

Figure B.5 – Conventional intermodulation method ............................................................... 27

Figure B.6 – IMD2 and IMD3 ................................................................................................. 28

Figure D.1 – Errors of half-wavelength voltage measurements caused by limitations from

the resolution of RF power .................................................................................................... 33

Figure D.2 – Relative errors of half-wavelength voltage measurement caused by

limitations from the resolution of RF power ........................................................................... 34

Figure D.3 – Relation between NOMI and IM3 for the Mach-Zehnder modulator

(sample #1) .......................................................................................................................... 35

Figure D.4 – Relation between NOMI and IM3 for the Mach-Zehnder modulator

(sample #2) .......................................................................................................................... 36

Figure D.5 – Relation between NOMI and IM2 for the Mach-Zehnder modulator

(sample #1) .......................................................................................................................... 36

Table 1 – Symbols and abbreviated terms .............................................................................. 9

Table C.1 – Characteristics of optical modulator ................................................................... 29

Table C.2 – Mechanical and environmental characteristics ................................................... 30

Table D.1 – Spectrum analyser uncertainty ........................................................................... 31

Table D.2 – Uncertainty budget of power meter at only 2 GHz .............................................. 32

Table D.3 – Measurement results of half-wave voltages for Mach-Zehnder modulators ......... 35

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– 4 – IEC 62801:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT METHOD OF HALF-WAVELENGTH VOLTAGE
FOR MACH-ZEHNDER OPTICAL MODULATOR IN WIRELESS
COMMUNICATION AND BROADCASTING SYSTEMS
FOREWORD

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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 62801 has been prepared by IEC technical committee 103:

Transmitting equipment for radiocommunication.
The text of this International Standard is based on the following documents:
CDV Report on voting
103/120/CDV 103/133/RVC

Full information on the voting for the approval of this International Standard can be found in the

report on voting indicated in the above table.

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

---------------------- Page: 6 ----------------------
IEC 62801:2020 © IEC 2020 – 5 –

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---------------------- Page: 7 ----------------------
– 6 – IEC 62801:2020 © IEC 2020
INTRODUCTION

A variety of microwave-photonic devices may be used in wireless communication and

broadcasting systems. An optical modulator is an interface which converts an electronic signal

to an optical signal. In the field of optical fibre communication systems, the first editions of the

IEC 62007 series "Semiconductor optoelectronic devices for fibre optic system applications"

were published in 1997. In the field of wireless systems, specifications of intermodulation and

composite distortion of modulators have been the important issue and have been typically

negotiated between users and suppliers. During the International Meeting on Microwave

Photonics, a proposal was announced to address standardizations for key devices for

radio-over-fibre (RoF) systems.

An RoF system is comprised mainly of two parts; one is the RF to photonic converter (E/O), and

the other is the photonic to RF converter (O/E). Radio waves are converted into an optical signal

at E/O, and the signal is transferred through the optical fibre, and then the radio waves are

regenerated at O/E. The nonlinear distortion characteristics of both E/O and O/E are important

for the performance of the system. Semiconductor photodiodes are commonly used for O/E.

Several types of optical modulator are used for E/O, such as Mach-Zehnder modulators (MZM),

electro-absorption modulators and directly modulated laser diodes (LDs).

This document has been prepared to provide industry standard measurement methods for

evaluating electro-optic material based Mach-Zehnder optical modulators, to be used in wireless

communication and broadcasting systems. The nonlinear distortion characteristics are also

important for the performance of the systems. The intermodulation distortion of the MZM is

calculated from the driving voltage and the half-wavelength voltage. The details of calculations

of the second-order intermodulation distortion (IM2) and the third-order intermodulation

distortion (IM3) are described in Annex B. General characteristics of Mach-Zehnder optical

modulators in wireless communication and broadcasting systems are described in Annex C.

Notes on measurement of the half-wavelength voltage are described in Annex D.

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subject of patent rights other than those in the patent database. IEC shall not be held

responsible for identifying any or all such patent rights.
---------------------- Page: 8 ----------------------
IEC 62801:2020 © IEC 2020 – 7 –
MEASUREMENT METHOD OF HALF-WAVELENGTH VOLTAGE
FOR MACH-ZEHNDER OPTICAL MODULATOR IN WIRELESS
COMMUNICATION AND BROADCASTING SYSTEMS
1 Scope

This document specifies a measurement method of half-wavelength voltage applicable to

Mach-Zehnder optical modulators in wireless communication and broadcasting systems. In

addition, this method is also effective for the estimation of the intermodulation distortion of

Mach-Zehnder optical modulators. The method applies for the following:
– frequency range: 10 MHz to 30 GHz;
– wavelength band: 0,8 µm to 2,0 µm;

– electro-optic material based Mach-Zehnder optical modulators and their modules.

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 62007-1, Semiconductor optoelectronic devices for fibre optic system applications – Part 1:

Essential ratings and characteristics

IEC 62007-2, Semiconductor optoelectronic devices for fibre optic system applications – Part 2:

Measurement methods
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 62007-1 and

IEC 62007-2 and the following 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
3.1.1
half-wavelength voltage

voltage required for a Pockels effect material based Mach-Zehnder optical modulator to induce

a phase shift of one-half a wavelength between the lightwaves of two arms of the Mach-Zehnder

interferometer

Note 1 to entry: It corresponds to an ON/OFF voltage of the Mach-Zehnder optical modulator as shown in Figure 1

---------------------- Page: 9 ----------------------
– 8 – IEC 62801:2020 © IEC 2020
Figure 1 – Transfer curve of a Mach-Zehnder optical modulator
3.1.2
normalized optical modulation index
NOMI

for the Mach-Zehnder optical modulator, ratio of driving voltage and half-wavelength voltage of

the modulator, defined as
NOMI = (V / V ) × 100 [%] (1)
pp π
where
V is the driving voltage (peak to peak voltage);
V is the half-wavelength voltage

Note 1 to entry: NOMI does not denote actual optical modulation index (OMI), defined as the ratio of the optical

modulated signal power and the average optical power. Detailed explanations of OMI including measurement methods

are described in Annex A.
Note 2 to entry: This note applies to the French language only.
3.1.3
extinction ratio
ext

ratio of two optical power levels of the optical signal generated by the optical modulator, defined

R = 10log(P /P ) (2)
ext 1 2
where
P is the optical power level generated when the output power is "on";
P is the power level generated when the output power is "off"
3.2 Symbols and abbreviated terms
The symbols and abbreviated terms used in this document are shown in Table 1.
---------------------- Page: 10 ----------------------
IEC 62801:2020 © IEC 2020 – 9 –
Table 1 – Symbols and abbreviated terms
R extinction ratio
ext
V half-wavelength voltage
CSO composite second-order distortion
CTB composite triple-beats distortion
DUT device under test
ESA electrical spectrum analyser
IMD intermodulation distortion
IM2 second-order intermodulation distortion
IM3 third-order intermodulation distortion
LD laser diode
MZM Mach-Zehnder modulator
NOMI normalized OMI
OMI optical modulation index
PD photodiode
RoF radio-over-fibre
4 Electro-optic material based Mach-Zehnder optical modulator
4.1 Mach-Zehnder optical modulator
4.1.1 Component parts
The optical modulators and their modules consist of basic parts as follows:
– Mach-Zehnder interferometer type optical modulator;
– input and output fibre pigtails (where appropriate);
– bias control port (where appropriate);
– photodiode for bias monitoring (where appropriate);
– laser diode for light source (where appropriate);
– thermal sensor (where appropriate);
– Peltier element (where appropriate).
4.1.2 Structure

A basic structure of the Mach-Zehnder interferometer type optical modulators is shown in

Figure 2. The modulators are grouped by electrode types and options.
– Electrode: lumped type, traveling-wave type, etc.
– Options: optical isolator, photodiode, half-mirror, laser diode, etc.
Figure 2 – Structure of Mach-Zehnder interferometer type optical modulator
---------------------- Page: 11 ----------------------
– 10 – IEC 62801:2020 © IEC 2020
4.2 Requirements for Mach-Zehnder optical modulator
4.2.1 General

This method is based on the theoretical transfer curve of the electro-optic material based

Mach-Zehnder interferometer, where the phase shift of traveling light on each arm of the

interferometer should be proportional to the applied voltage, a
...

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