Arc-induced long-period fibre gratings fabrication and their applications in optical communications

250 Pages·2006·9.04 MB·English

Gaspar Mendes do Rego

Arc-Induced Long-Period Fibre Gratings. Fabrication and
Their Applications in Optical Communications and Sensing

Thesis presented to the University of Porto for the degree of Ph.D. in Engineering Sciences

Department of Electrical and Computer Engineering
Faculty of Engineering, University of Porto
July 2006
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Projecto co-financiado pelo fundo Social Europeu no âmbito do concurso Público
2/5.3/PRODEP/2001, pedido de financiamento nº 1012.007, da medida 5/acção 5.3 –
Formação Avançada de Docentes do Ensino Superior submetido pela Escola Superior de
Tecnologia e Gestão do Instituto Politécnico de Viana do Castelo.
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Arc-Induced Long-Period Fibre Gratings
Fabrication and Their Applications in Optical Communications and Sensing

Thesis approved by

José Alfredo Ribeiro da Silva Matos, Chair
Full Professor of the Department of Electrical and Computer Engineering
Faculty of Engineering, University of Porto
Oleg G. Okhotnikov, External examiner
Head of Ultrafast and Intense Optics Group
Tampere University of Technology
Paulo Miguel Nepomuceno Pereira Monteiro, External examiner
Associate Professor of the University of Aveiro
Henrique Manuel de Castro Faria Salgado, Supervisor
Associate Professor of the Department of Electrical and Computer Engineering
Faculty of Engineering, University of Porto
José Luís Campos de Oliveira Santos, Co-Supervisor
Associate Professor of the Department of Physics
Faculty of Sciences, University of Porto
Armindo Luís Vilar Soares Lage
Assistant Professor of the Department of Electrical and Computer Engineering
Faculty of Engineering, University of Porto

Date approved: July 17, 2006
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It is not because things are difficult that we do
not dare; it is because we do not dare that they
are difficult.

Não é porque as coisas nos parecem
inacessíveis que não ousamos; é porque não
ousamos que elas nos parecem inacessíveis.

Lucius Annaeus Seneca
Roman Philosopher (4 BC-AD 65)

To my wife, Elda and to my sons, Rodrigo and Pedro

To my mother, Isilda and to the memory of my father, Joaquim
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Acknowledgements

To my supervisors, José Luís Santos and Henrique Salgado, for their dedication,
encouraging and on time help. I also would like to thank José Luís Santos for giving me the
opportunity to develop this research in the Unity of Optoelectronics and Electronics Systems
of INESC-Porto.
To Paulo Marques for his permanent dedication through out this project.
To Manuel Carlos Torres for his friendship, for his company during the three years that
we spent commuting between Barroselas and Porto and also for his technical support. Indeed,
without his interest and commitment this work would be much poorer. Therefore, thank you,
thank you very much for all.
To Oleg Okhotnikov who gave the first step towards the fabrication of arc-induced
gratings and to Vladimir Sulimov for his knowledge and dedication allowing me to start this
project on the right foot!
To Florian Durr for his friendship and hard work regarding stress measurements. To
Hans Limberger for his interest, helpful discussions and in particular, for allowing me to work
at EPFL-Lausanne.
To Alberto Fernandez Fernandez and Andrei Gusarov for a fruitful collaboration
regarding the study on the effect of gamma radiation on long-period fibre gratings.
To Evgeny Dianov, Sergei Semjonov, Sergei Vasiliev and Konstantini Golant for
supplying most of the fibres used in this work and also for helpful discussions.
To Walter Margulis for supplying the silica capillaries used in the estimation of the
fibre temperature.
To Bernd Shröder and Luís Belchior for their collaboration, interest and dedication
regarding the measurement of the fibre temperature with the thermocouples.
To Filipe Pinto and Alberto Maia for their dedication concerning the development of
the power supply.
To Oleg Ivanov for his help regarding the theory and simulations of long-period fibre
gratings.
To Paulo Caldas for his excellent work whilst replacing me at Escola Superior de
Tecnologia e Gestão de Viana do Castelo.
To José Manuel Baptista for his friendship, genuine interest, support and fruitful
collaborations.
To João Ferreira for his help regarding the elaboration of the Labview programs.
To Francisco Araújo for his interest and helpful discussions. In particular, I would like
to congratulate him for his interesting idea regarding the fusion between fishing and Optics!
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To Modesto Morais for his friendship, interest and dedication regarding the
measurement of geometrical parameters of the fibres and also on the measurement of the
polarisation dependent loss of long-period gratings.
To João Chamma for his dedication regarding gratings simulations and to Rosane Falate
for her collaboration in performing experimental work.
To Orlando Frazão e Rosa Romero for their collaboration concerning the applications of
the electric arc technique, namely, apodisation of fibre Bragg gratings and the fabrication of
sampled fibre Bragg gratings.
To Albano Costa, Ernesto Pinheiro and Joaquim Cardoso for their technical support in
an initial part of this project. A special thanks to Francisco Carpinteiro for his help regarding
electrode’s polishing and mechanical gratings.
To João Abrantes and Vítor Leal for their interest and helpful discussions regarding the
measurement of the fibre temperature.
To José Luís Costa and Luís Miguel Bernardo for their collaboration regarding the
measurement of the fibre temperature based on the blackbody radiation.
To Lourenço Castro, from Cabelte S.A., for allowing using their facilities and to Nuno
Pontes and Alexandre Rodrigues for measuring the refractive index profiles of the fibres.
To Ireneu Dias for his interest and help on the thermocouple’s patent submission.
To my colleagues and friends from UOSE, Miguel Melo, Rui Morais, Daniel
Alexandre, Joel Carvalho, Paulo Moreira, Pedro Jorge, Jaime Viegas, Susana Silva, Carla
Rosa, Nuno Pinto and Dionísio Pereira for their interest, support and mainly for being so
comprehensive! A special thanks to Luísa Mendonça for being so kind and professional.
To my colleagues and friends of ESTG, in particular, Joana Santos, Paulo Costa,
Preciosa Pires and Paulo Fernandes. I also would like to thank Lígia Martins as far as the
Prodep funding is concerned.
To my family, for their support and understanding along this project.
Finally, to the European Community through the program PRODEP III - Medida 5 -
Acção 5.3. - Formação Avançada de Docentes do Ensino Superior, integrada no Eixo 3, for
the grant conceded allowing me fulltime dedication to research.
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Summary of the thesis

This thesis is dedicated to the fabrication, through electric arc discharges, of long-period fibre
gratings and to their applications in optical communications and sensing fields.
The main theoretical aspects of long-period gratings are presented. The several
mechanisms proposed in the literature for the formation of arc-induced gratings are discussed.
In particular, the effect of stress relaxation is investigated for the first time through the
measurement of the tomographic stress profiles of these gratings.
The temperature is a key parameter for the understanding of the formation mechanisms
and, therefore, two methods to estimate the temperature reached by the fibre whilst being
submitted to electric arc discharges are presented. One method is based on the blackbody
radiation and the other on electrically insulated thermocouples assembled in situ. The latter
technique was submitted to the Portuguese Patent Institute.
The fabrication of long-period gratings using the electric arc technique is described in
detail. The several setups that were implemented during this work in order to improve the
fabrication method are also presented.
The influence of the fabrication parameters on the characteristics and properties of arc-
induced gratings is discussed. It was found that by changing the fabrication conditions it is
possible to modify the sensitivity of the gratings to physical parameters, such as, temperature
and strain. This important property of the electric arc technique has not been demonstrated, so
far, by any other technique.
The thermal behaviour of the produced gratings was also investigated and it was
demonstrated that the ones induced in Ge-free fibres, in particular, in Er/Al co-doped fibres
show a linear behaviour on temperature up to 700 ºC. Arc-induced gratings were also shown
to exhibit very high temperature stability. These are important properties for development of
high temperature sensors.
The effect of gamma radiation on the properties of gratings arc-induced in pure-silica-
core fibres was also studied for the first time, and the results obtained enable one to conclude
that those gratings are very promising to perform sensing in radiation environments.
A new technique to mechanically induce long-period fibre gratings is presented. A fully
characterisation of the produced gratings is given. Two straightforward applications of
mechanical gratings are also demonstrated.
Other devices fabricated with the electric arc technique, such as, phase-shifted short and
long-period gratings are briefly discussed. Special attention is given to the apodisation of
fibre Bragg gratings and to the fabrication of sampled fibre Bragg gratings. The fabrication of
core mode blockers to implement bandpass filters is also presented.
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Finally, several applications of arc-induced gratings in optical communications and
sensing are given, being of particular importance the sensor head developed for the
simultaneous measurement of temperature and strain based on a single long-period grating
having two sections fabricated with different parameters.