DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER

Author’s full name : Siti Fatimah Az Zahra binti Yusoff

Date of Birth : 21-03-1992

Title : Fiber Tip Temperature Sensor Based On Michelson Interferometry

Academic Session : 2014/2015

I declare that this thesis is classified as:

CONFIDENTIAL (Contains confidential information under the Official

Secret Act 1972)*

RESTRICTED (Contains restricted information as specified by the

organization where research was done)*

OPEN ACCESS I agree that my thesis to be published as online

open access (full text)

I acknowledged that Universiti Teknologi Malaysia reserves the right as follows:

1. The thesis is the property of Universiti Teknologi Malaysia

2. The Library of Universiti Teknologi Malaysia has the right to make copies for the

purpose of research only.

Certified by:

SIGNATURE SIGNATURE OF SUPERVISOR

920321-03-5012

Dr. Asrul Izam bin Azmi

(NEW IC NO/PASSPORT) NAME OF SUPERVISOR

Date: 24 June 2015

Date: 24 June 2015

UNIVERSITI TEKNOLOGI MALAYSIA

PSZ 19:16 (Pind. 1/13)

NOTES: * If the thesis is CONFIDENTAL or RESTRICTED, please attach the letter from the

organization concerned stating the reason/s and duration for the

confidentiality or restriction.

ii

“I hereby declare that I have read this work and in my opinion this work is adequate

in terms of scope and quality for the purpose of awarding a degree of

Bachelor of Engineering (Electrical-Telecommunication)”.

Signature

Name of Supervisor

Date

:......................................................

: DR. ASRUL IZAM BIN AZMI

: 24 JUNE 2015

iii

FIBER TIP TEMPERATURE SENSOR BASED ON MICHELSON

INTERFEROMETRY

SITI FATIMAH AZ ZAHRA BINTI YUSOFF

Submitted to the Faculty of Electrical Engineering

in partial fulfillment of the requirements for the degree of

Bachelor of Engineering (Electrical- Telecommunication)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JUNE 2015

iv

“I hereby declare that this undergraduate project paper entitled “Fiber Tip Temperature

Sensor based on Michelson Interferometry” is the result of my own research except as

cited in the references. The undergraduate project paper has not been accepted for any

degree and is not concurrently submitted in candidature of any other degree.”

Signature : ……………………………………………………..

Name : SITI FATIMAH AZ ZAHRA BINTI YUSOFF

Date : 24 JUNE 2015

v

Specially dedicated to

To my beloved Umi and Abah, thank you for all of the support and encouragement that

you have given me. It is more than everything and I know if I write down millions or

many more thank you, it will never enough. But thank you Umi, thank you Abah.

To my beloved younger sisters and brother, thank you for giving me the endless support

whenever I need you guys.

vi

ACKNOWLEDGEMENT

First of all, I would like to take this opportunity to record my great and genuine

appreciation to my supervisor, Dr. Asrul Izam bin Azmi, who has supported me

throughout my final year project with his patience, time and knowledge. Without his

encouragement and effort, this thesis would not have been completed or written. I think I

could not wish for a better or friendlier supervisor.

I also want to thank my fellow lab mates Siti Nur Izzati and Sarina for their

kindness in helping me during my critical time. Also, thank you to my close friends in

university, especially my best friends and my cheerful classmates, 4SKET for their

support, for the sleepless nights we were working together before deadlines, and for all

memories we had in the last four years.

Lastly, I give my special thanks to my lovely family for their endless support and

encouragement. Thank you my beautiful parent, Umi and Abah for all the things that

you have given to me. I know of no other way for me to honor both of you except

through this thesis.

vii

ABSTRACT

In recent years, fiber tip sensors have been extensively used in many fields,

especially in the biomedical field. This type of sensor is usually used as temperature

sensors because it possess the key aspects including small in size, robustness in harsh

environment and high sensitivity to temperature. Thus, a fiber tip temperature sensor

based on Michelson interferometer using single mode-multimode-single mode (SMF-

MMF-SMF) structure is proposed. Fusion splicing technique is used to construct the

proposed sensor. Experimental work is done to characterize the temperature sensitivity

using the Labview program that is connected to an optical spectrum analyzer (OSA). A

linear wavelength shift is observed as the temperature goes up and down between 30°C

and 180°C. The proposed scheme attains a wavelength shift at the rate of 0.0631 nm per

1°C. Thus, the proposed fiber tip temperature sensor is suitable to be used in high

temperature applications because of its high dynamic range and also have good linearity

and stability.

viii

ABSTRAK

Sejak kebelakangan ini, sensor hujung gentian telah digunakan secara

meluas dalam pelbagai bidang, terutama dalam bidang bio-perubatan. Sensor jenis

ini biasanya digunakan sebagai sensor suhu kerana ia mencapai ciri-ciri yang

dikehendaki iaitu bersaiz kecil, tahan lasak dalam persekitaran yang ekstrem dan

sensitivity yang tinggi kepada suhu. Oleh itu, sensor suhu hujung gentian

berdasarkan interferometri Michelson menggunakan struktur mod tunggal-mod

berbilang-mod tunggal (SMF-MMF-SMF) telah dicadangkan. Teknik gabungan

digunakan untuk mereka cipta sensor. Kerja uji kaji dilakukan untuk mencirikan

sensitiviti suhu menggunakan program Labview yang disambung dengan

penganalisis spektrum optik (OSA). Anjakan panjang gelombang yang linear telah

diperhatikan dengan kenaikan dan penurunan suhu dengan banjaran 30 ° C hingga

180 ° C. Keputusan analisis menunjukkan perubahan panjang gelombang adalah

pada purata 0.0631 nm setiap 1 ° C. Oleh itu, sensor suhu hujung gentian yang

dicadangkan sesuai digunakan dalam aplikasi suhu tinggi kerana julat dinamik

yang tinggi dan juga mempunyai kelinearan dan kestabilan yang baik.

ix

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION i

DEDICATION v

ACKNOWLEDGEMENTS vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS ix

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xv

LIST OF SYMBOLS xvi

1 INTRODUCTION 1

1.1 INTRODUCTION 1

1.2 PROBLEM STATEMENT 4

1.3 RESEARCH OBJECTIVE 5

1.4 SCOPE OF PROJECT 5

1.5 MARKET SURVEY 6

1.6 PROJECT MANAGEMENT 7

1.6.1 Gantt Chart 7

1.6.2 Cost Estimation 9

1.7 FLOWCHART OF THE PROJECT 9

x

1.8 NEED, APPROACH, BENEFITS AND

COMPETITION (NABC) 11

1.9 THESIS OUTLINE 12

2 LITERATURE REVIEW 13

2.1 INTRODUCTION 13

2.2 BASICS OF OPTICAL FIBER 14

2.2.1 Single Mode Fiber (SMF) 15

2.2.2 Multimode Fiber (MMF) 16

2.3 FIBER OPTIC SENSOR 17

2.3.1 Types of fiber optic sensor 19

2.3.1.1 Intensity-modulated FOS 19

2.3.1.2 Wavelength-modulated FOS 20

2.3.1.3 Phase-modulated FOS 20

2.3.1.4 Polarization-modulated FOS 20

2.4 TYPES OF INTERFEROMETER 21

2.4.1 Fabry-Perot interferometer 21

2.4.2 Mach-Zender interferometer 22

2.4.3 Michelson interferometer 23

2.5 PRINCIPLE OF MICHELSON

INTERFEROMETER 24

2.6 COMPARISON OF THE PREVIOUS WORKS

ON FIBER BASED TEMPERATURE SENSORS 25

2.7 APPLICATIONS OF FIBER OPTIC

TEMPERATURE SENSOR 28

3 METHODOLOGY 29

3.1 INTRODUCTION 29

3.2 SENSOR FABRICATION PROCESS 30

3.3 STRUCTURE DESIGN AND

CONFIGURATION 34

3.4 EXPERIMENTAL SETUP 36

3.4.1 Broadband Optical Source 38

xi

3.4.2 Optical Spectrum Analyzer (OSA) 39

3.4.3 3-Port Optical Circulator C-Band 40

3.4.4 National Instruments GPIB-USB

(NI GPIB-USB) Cable 41

3.4.5 Labview Program 42

4 RESULT AND DISCUSSION 44

4.1 INTRODUCTION 44

4.2 ANALYSIS ON TEMPERATURE

SENSITIVITY OF SENSOR 45

5 CONCLUSION AND RECOMMENDATION 48

5.1 CONCLUSION 48

5.2 RECOMMENDATION 49

REFERENCES 50

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 Gantt chart for semester 1 7

1.2 Gantt chart for semester 2 8

2.1 Comparison between fibers based temperature sensors 26

2.2 Applications of fiber optic temperature sensor 28

3.1 Description of scanning parameters for the Labview program 42

xiii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Flowchart of the project 10

2.1 Schematic diagram of optical fiber 14

2.2 Construction and light ray travels in a single mode fiber

(SMF) 16

2.3 (a) Step-index MMF 16

2.3 (b) Graded-index MMF 16

2.4 Extrinsic sensor 18

2.5 Intrinsic sensor 18

2.6 Schematic diagram of Mach-Zender interferometer 22

2.7 Schematic diagram of the Michelson interferometer 23

3.1 Fiber splicing process 30

3.2 Fiber jacket stripper 30

3.3 Alcohol and delicate task wipers 31

3.4 Fiber cleaver 32

3.5 Fujikura fiber fusion splicer 33

3.6 Condition of SMF and MMF before and after

splicing process 33

3.7 The microscopic image of the condition of

SMF and MMF after splicing process 34

xiv

3.8 Structural design of the fiber tip temperature sensor

based on Michelson interferometry 35

3.9 (a) Schematic diagram of experimental setup 37

3.9 (b) Actual experimental setup 37

3.10 Broadband optical source 38

3.11 Optical spectrum analyzer (OSA) 39

3.12 3-port optical circulation C-Band 40

3.13 NI GPIB-USB cable 41

3.14 Graphical user interface of the Labview data

acquisition program 42

4.1 Transmission spectra of the fiber tip temperature sensor

based on a Michelson interferometer with different

temperature 46

4.2 (a) Graph of dip wavelength shifted with temperature rise 47

4.2 (b) Graph of dip wavelength shifted with temperature drop 47

xv

LIST OF ABBREVIATIONS

FOS - Fiber Optic Sensor

MI - Michelson Interferometer

SMF - Single Mode Fiber

MMF - Multimode Fiber

OSA - Optical Spectrum Analyzer

FPI - Fabry-Perot Interferometer

FBG - Fiber Bragg Grating

MZI - Mach-Zender Interferometer

FTMI - Fiber-Taper Michelson Interferometer

PCF - Photonic Cyrstal Fiber

PM-PCF - Polarization Maintaining Photonic Crystal Fiber

NI GPIB-USB - National Instrument GPIB-USB

xvi

LIST OF SYMBOLS

nm - nanometer

- interference intensity

- phase delay condition

- coupling loss

- input beam waist

- output beam waist

- effective refractive index

L - length of Multimode fiber

- wavelength of free space

°C - degree Celcius

CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

Fiber optic has been used as light wave guiding media during its early

development and has been undergoing tremendous growth since then. With the advance

technologies nowadays, fiber optic has been widely used in many fields and the

advancement of fiber optic is due to the advantages of optical transmission compared to

electrical transmission [1]. Development of fiber optic technology has been increased,

especially in telecommunication engineering field. Its capability in carrying large bits of

data at the speed of light makes the research potential in fiber optic to be increased [2].

2

Besides, the fiber optic technologies are also being developed as sensing

elements, known as a fiber optic sensor (FOS). Usually, fiber optic is mainly used as a

sensor that has its own functions which is transmitting signals from light rays and

converts it into electronic signals. The fiber optic sensor can be used in many physical

quantities and measurements such as temperature, pressure, liquid level, radiation,

humidity and also pH values and transforms it into a readable form in instrument [3].

The fiber optic sensor is an excellent device as they offer many advantages over

a conventional electronic sensor in many extreme fields making it to have a very high

demand in industrial applications. There are some examples of the advantages of optical

sensors is robustness in extreme conditions [4] such as in explosive environments, the

fiber optic sensor is completely passive and in microwave environment, it is

unsusceptible to the interference of electromagnetic. Besides, the main reasons fiber

optic sensor were being chosen are because of their good stability, response and high

dynamic range. Because of the growing interest of fiber optic sensor technologies and

also its excellent performance, the fiber optic sensor has been commercialized

tremendously as it meets the needs of nowadays evolving technology.

Typical fiber optic sensors usually use the principle of the interferometer as this

type of sensors offers high sensitivity due to small propagation loss in fiber and also

interferometric detection [1]. If the sensor produced interference between two light

waves, the sensor is referred as interferometer sensor [6]. Michelson interferometer (MI)

is an optical configuration that has been commonly used for interferometry [1]. In

Michelson interferometer, the basic principle that has been used is reflection modes as

the interference happens between the optical signals is in two arms, but one of the beams

is reflected at the end of each arm [6].

3

Nowadays, fiber tip temperature sensor has a very high demand because it has

many advantages which are simple, compact in size and more stable. Moreover, this

type of sensor usually used in high temperature applications such as oil and gas

explorations, nuclear reactors and also high temperature furnaces because it can measure

at temperature up to melting point of silica as fiber optic is made from silica. Because of

the dominant features and exceptional benefit, the needed of fiber tip temperature sensor

based on Michelson interferometer is widely available.

Because of the complicated fabrication techniques in previous configurations, a

new approached of fiber tip sensor based on MI is designed using simple fabrication

technique and also suitable to be used in high temperature applications.

4

1.2 PROBLEM STATEMENT

There are various types of fiber in-line MI configurations have been

demonstrated using different fabrication techniques such as femtosecond laser

micromachining and also thin-film coating [6], coupling between liquid-core mode and

defect mode [7], and also superconducting nanowire single-photon detectors and single-

photon counting techniques [8]. However, all of these approaches encounter difficulties

as they used limited source of optical fiber that made the fabrication process becomes

more complicated and costly.

The disadvantages can be overcomed by designing fiber tip temperature sensor

that uses simple configuration and fabricated using simple technique such as fusion

splicing. It is widely used in extreme fields such as high temperature applications. This

is it fulfills the main requirements needed, such as having compact size, have excellent

stability and response and also have high dynamic range.

5

1.3 RESEARCH OBJECTIVE

Based on the problem statement, the research objectives for this project are given as

follows;

I. To design and construct a simple fiber tip temperature sensor based on single

mode fiber-Multimode fiber-single mode fiber (SMF-MMF-SMF) configuration

II. To establish the sensitivity of temperature response of the sensor through an

experimental work.

1.4 SCOPE OF PROJECT

The scope of this project will include four stages which are; the stage of literature

review, the stage of sensor fabrication, the stage of experiment, and also the stage of

data analysis. The details of this project scope are outline as follows;

I. Review on fiber optic temperature sensor based on an interference technique by

referring to the collections of journals

II. Fabrication of sensor using simple fusion splicing technique

III. Experimental work to establish the temperature sensitivity of the sensor

a. Labview based real-time data acquisition program connected to an optical

spectrum analyzer (OSA)

6

IV. Data analysis

a. Spectra smoothing and dip detection using the Matlab program

b. A graph of wavelength shift versus temperature using Microsoft Office

Excel

1.5 MARKET SURVEY

The market survey was done in order to see the feasibility of fiber optic sensor in the

market. Based on the survey, the temperature sensor has been used in many fields;

a. The fiber optic temperature sensor has high demand in the biomedical field for

cell manipulation and blood perfusion measurement

b. In oil and gas exploration, fiber optic temperature sensor is used in the

hydrophone sensor system

c. In communication system, fiber optic sensor is commonly used in military and

commercial aircraft.

7

1.6 PROJECT MANAGEMENT

1.6.1 Gantt chart

The time management of this project in semester 1 and semester 2 is shown in

the Gantt chart shown in Table 1.1 and Table 1.2 respectively;

Table1.1: Gantt chart for semester 1

Week

Activities 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Brief idea

Literature and

theoretical study

Design and

fabrication of

hardware

Collect and

analyze data

Presentation slide

and report

preparation

Presentation

Report

submission

8

Table1.2: Gantt chart for semester 2

Week

Activities 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Brief idea

Literature and

theoretical study

Design and

fabrication of

hardware

Collect and

analyze data

Poster and journal

preparation

Presentation

(EESS 2015)

Report and thesis

submission

9

1.6.2 Cost Estimation

Table 3.3 shows the total cost to cultivate the fiber tip temperature sensor. In

addition, the material that has been used to implement this sensor described in this table.

The materials that had been chosen were based on the price and quality that benefits to

the device.

Table 3: Cost estimation for the development of fiber tip temperature sensor

No. Material Quantity Price per meter Subtotal

1 Single mode fiber (SMF) 1 m RM 4.00 RM 4.00

2 Multimode fiber (MMF) 1 m RM 6.00 RM 6.00

Total RM 10.00

1.7 FLOWCHART OF THE PROJECT

The flowchart shown in Figure 1.1 summarizes all of the steps needed in order to

complete the project. First, a survey of the sensing scheme of the fiber tip temperature

sensor by referring to the collections of journals was carried out. After the survey was

done and the type of interferometer that will be used was decided, the design

configuration (SMF-MMF-SMF) was proposed and the fiber tip sensor was fabricated

using simple fusion techniques. Next step, the response of the sensor was tested and

output data were analyzed by using Labview and Matlab software. After the

performance of the sensor was convincing, the outcome of this project was presented

and demonstrated on the Electrical Engineering Student Showcase (EESS) 2015.

10

Figure 1.1: Flowchart of the project

11

1.8 NEED, APPROACH, BENEFITS AND COMPETITION (NABC)

The customer needs a temperature sensor that acquires better design and also can

help to accomplish some problems that is related to temperature measurements.

Nowadays, a compact size of the sensor becomes a demand from customers as it can be

used in many small devices. Also, the sensor must fulfill all the requirements which are

safe to use, have good stability and response.

Meanwhile, the approach that can be done in order to satisfy the customer’s need

is to design a fiber tip temperature sensor based on Michelson interferometry. This

sensor has been constructed because it has many advantages which are compact size,

have good stability and response and also a high dynamic range.

The benefit per cost is the main criteria that should consider when designing the

fiber tip temperature sensor. Because of the great advantages shown by such sensors,

they have become unique when comparing with the conventional sense and this makes

them the ideal solution for many applications especially for high temperature

applications. Moreover, this sensor was fabricated using simple fabrication technique

which is fusion splicing technique. The sensor also was less costly since it uses only two

typical types of fiber optic that are easily found in the markets. In addition, the sensing

part of this sensor is only a few mm in length, making it to be low cost.

Since this sensor has many advantages which are small size, low cost, has good

stability and response and also high dynamic range, this sensor could provide better

performance for many applications, especially for high temperature application such as

oil and gas exploration, high temperature furnaces, and nuclear reactor.

12

1.9 THESIS OUTLINE

This is divided into a total of five chapters. Chapter 1 discusses about the

understanding of this study toward optical fiber sensors and fiber tip temperature sensor,

with the research objectives, problem statements, scope of projects, and also planning

management of this study. Chapter 2 is discusses about the literature review and details

on the optical fiber sensor and types of interferometer used. Meanwhile, Chapter 3

explains about the methodology that was used when conducting this project. This

chapter describes more on the description of the sensor design and parameters used for

optical properties. Chapter 4 focuses on the outcome and results coming from this study,

also an analysis of the results being discussed in this chapter. Lastly, Chapter 5 gives a

conclusion of the project thesis and some recommendation which can be used for future

enhancement of this study.

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

This chapter presents the background study and theory that is related to optical

fiber, fiber optic sensor, types of interferometers and also interference intensity.

14

2.2 BASICS OF OPTICAL FIBER

A basic optical fiber consists of three parts which are the core, cladding and the

coating. The core of the fiber is customarily made of silica or glass and has a value of

refractive index n1. The core will act as a path as light propagates mainly along its [9].

Meanwhile, the cladding of the fiber is made of a dielectric material that has value of

refractive index, n2. Also, the refractive index of the cladding is less than the refractive

index of the core. The glass fiber is covered by outer coating or buffer as this coating

will give extra protection to the fiber from physical damage as optical fiber is very

fragile. The schematic diagram of optical fiber is shown in Figure 2.1.

Figure 2.1: Schematic diagram of optical fiber

There are two types of optical fibers commonly available in the markets, namely

single mode fiber (SMF) and Multimode fiber (MMF).

15

2.2.1 Single Mode Fiber (SMF)

Single mode fiber has a smaller core with typical values of only about 9 µm,

causing the light to travel in a single ray (mode). Meanwhile, the diameter of cladding

for single mode fiber is 125 µm. Figure 2.2 shows the construction of single mode fiber.

The SMF is typically used to transmit data for long distance because the data able to

travel at faster speeds. In addition, low propagation loss of SMF gives big advantage for

communication purpose.

Figure 2.2: Construction and light ray travels in a single mode fiber (SMF)

16

2.2.2 Multimode Fiber (MMF)

When comparing with single mode fiber (SMF), Multimode fibers have a larger

diameter size of the core and the diameter size of cladding is the same as SMF which is

125 microns. Moreover, because of the different diameter size of core, the Multimode

fiber is divided into two types which are Step-index Multimode fiber and Graded-index

Multimode fiber. The standard diameter size of core for Step-index MMF is 62.5

microns and for Graded-index MMF, the diameter size of the core is 50 microns. The

difference between these two Multimode fibers is the propagation of light rays that

travels inside the fibers. The construction and propagations of light ray are shown in

Figure 3 (a) and 3(b).

(a)

(b)

Figure 2.3: (a) Step-index MMF, (b) Graded-index MMF

17

The large diameter size of the core allows multiple light rays propagate at the

same time and this shows that the ability of this fiber to transmit high bits of data in

communication fields. Unfortunately, because of the large diameter size of the core,

there will be a higher propagation loss being produced when the data were transmitted

causing this type of fiber to be used in short distance.

2.3 FIBER OPTIC SENSOR

Fiber optic had been discovered to be used as sensing elements and being

patented in the mid 1960s [10]. The ability in carry high bit of data at the speed of light,

causing the optical fibers potentially available in the market. As the research on fiber

optic getting increased, the revolution of it also grows from sending data in

telecommunication fields to sense changes in phase, intensity and wavelength in sensing

the environment, known as fiber optic sensing [2]. The fiber optic sensor (FOS) has

many advantages which makes them to have a very high demand in many fields.

Moreover, many researchers tend to extend their researches on FOS deeply as they want

to create better invention of the FOS [11].

A FOS is a component that can be categorized into three elements which are the

location of sensing, the operating principle and also the application [2]. There are two

types of sensing location which is extrinsic and intrinsic sensing. In the intrinsic optical

sensor, the fiber optic itself acts as a sensing element which modulates the light signal

[12]. Meanwhile, in extrinsic optical sensor, the fiber optic acts as information carriers

that transfer light signal in or out of the sensors [13]. Figure 2.3 and 2.4 show the two

types of sensor which are extrinsic and intrinsic sensor.

18

Figure 2.4: Extrinsic sensor

Figure 2.5: Intrinsic sensor

19

2.3.1 Types of fiber optic sensor

There are four main types of fiber optic sensors which are [2];

I. Intensity-modulated FOS

II. Wavelength-modulated FOS

III. Phase-modulated FOS

IV. Polarization- modulated FOS

2.3.1.1 Intensity-modulated FOS

In an intensity-modulated sensor principle, the changes in light intensity are the

physical measurement that can be predicted [13]. The intensity-modulated fiber optic

sensor needs a large quantity of light and usually used Multimode fiber with large core

diameter [2]. The advantage of this type of sensor is that the implementation is simple

and low cost since no advanced components are needed [13]. Contrastingly, the

sensitivity and also the accuracy of the light measurements are limited unless another

system is added to the sensor [2].

20

2.3.1.2 Wavelength-modulated FOS

Distinguished from intensity-modulated FOS; the wavelength-modulated FOS

principle is depending on the difference of wavelength of light transmitted [2]. The

examples of wavelength-modulated FOS that commonly used in many fields are

blackbody sensor, Bragg grating (FBGs) sensor and also fluorescent sensor.

2.3.1.3 Phase-modulated FOS

This type of sensor used laser as a light source which will be injected into single

mode fiber [12]. The change in the phase of light produced by comparing the phase of

the light signal with the reference light is called an interferometry [2]. This kind of

sensor is accurate, but highly cost since it is using laser and other advance components

[13].

2.3.1.4 Polarization-modulated FOS

For this type of sensor, the principle used is different in polarization state of light

fields which are linear, elliptical and circular [14]. Linear polarization state principle

says that the electric field is not moving and remains in the same line. Contrastingly, for

elliptical polarization state, the electric field is moving during propagation of light is

happening.

21

2.4 TYPES OF INTERFEROMETER

The principle of the interferometer is based on phase-modulation fiber optic sensor

which is about the changing in phase difference [14]. They are using an interference of

two light waves which have propagated through different paths of similar or different

fibers. There are several types of interferometer that are being used in fiber optic sensor

including [15];

I. Fabry-Perot

II. Mach-Zender

III. Michelson

2.4.1 Fabry-Perot interferometer

The principle of Fabry-Perot interferometer (FPI) is using multiple-beam

interference of transmitted and reflected light [16]. The types of fabrication that

commonly used for Fabry-Perot interferometer sensor are air glass reflectors, fiber

Bragg grating (FBGs) and also semi-reflective splices [17]. Usually, Fabry-Perot

interferometric sensor is divided into two categories which are; extrinsic FPI sensor and

intrinsic FPI sensor. The extrinsic FPI sensor uses reflection light coming from the

outside cavity of the fiber [5]. The advantage of extrinsic FPI sensor is that they can

utilize more, reflecting mirror and also finesse interference signal [5]. Meanwhile, in an

intrinsic FPI sensor, the reflected mirrors are built inside the fiber itself and light signal

will not propagate outside the fiber [18].

22

2.4.2 Mach-Zehnder interferometer

This type of sensor uses two-fiber arms which are reference and sensing arm [5].

Figure 2.6 shows the Mach-Zehnder interferometer (MZI) schematic diagram. Two

couplers are being used for this design. The transmitting light will be divided by Coupler

1 into two parts, and will propagate in two different paths and then will recombine back

by Coupler 2 [19].

Figure 2.6: Schematic diagram of Mach-Zender interferometer [5]

23

2.4.3 Michelson interferometer

The principle of the Michelson interferometer (MI) is similar as a MZI principle,

except that it acts like a half of MZI or folded MZI [2]. The advantage of MI over MZI

is that their phase is more sensitive as the light waves travel twice the sensing length of

fiber optic [2]. MI uses reflection modes and based on interference of two different

signals on the same wavelength, but using a different path length [20].

Figure 2.7 shows the schematic diagram of a MI. As shown below, transmitted light

is divided into two different paths by the coupler and reflected back after reached Mirror

1 and 2 respectively [1]. Then, the reflected light will combine together by the coupler

before entering the receiver.

Figure 2.7: Schematic diagram of the Michelson interferometer [5]

24

2.5 PRINCIPLE OF MICHELSON INTERFEROMETER

The main principle of the Michelson interferometer that is used to design the sensor is

discussed. When two optical waves at the same wavelength but travel at different path

are combined, the detected interference intensity of the combined waves at photodetector

is given by [21];

(1)

where is a phase delay conditions, I1 and I2 are the intensity of interferences of core

and cladding modes. The formula of intensity of interferences, I1 and I2 [22] are;

(2)

(3)

where α is the coupling loss of the two fibers and R1 and R2 are the Fresnel reflection

coefficient and can be calculated using formula;

(4)

For the value of α, it can be calculated using input and output of Gaussian beam waist

[22];

25

(5)

Meanwhile, the formula of phase delay, [22] is;

(6)

where is the effective refractive index of fundamental mode, L is the length of the

Multimode fiber (MMF) and is the wavelength of free-space.

2.6 COMPARISON OF THE PREVIOUS WORKS ON FIBER BASED

TEMPERATURE SENSORS

Table 2.1 shows the comparison between some of the fiber based temperature

sensors that had been proposed. The comparison was done based on the complexity of

fabrication techniques, the size of the sensor, the types of fiber optics that was being

used to design the sensor and the performance of the sensor in terms of temperature

range and also sensitivity.

26

Table 2.1: Comparison between fibers based temperature sensors

Temperature

sensors Configuration Performance

Drawback/

advantage

High-temperature

sensor based on an

abrupt-taper

Michelson

interferometer in

single-mode fiber

[23]

An abrupt fiber-

taper Michelson

interferometer

(FTMI) in SMF

Temperature

range:

(500- 800) °C

Sensitivity:

0.1186 nm/ °C

Advantages:

Good sensitivity

Drawback:

Complex

fabrication

technique

(Fabricated by a

fiber-taper machine

and electric-arc

discharge)

High temperature

sensor based on

SMS structure with

large core all solid

bandgap fiber as

MMF [24]

SMF-MMF-SMF-

SMF-MMF-SMF

Temperature

range:

(20-950) °C

Sensitivity:

0.035 nm/ °C

Advantages: High

temperature range

Drawback:

Complex splicing

technique and large

in size

In-fiber quasi-MI

with a core-

cladding-mode fiber

end-face mirror [20]

SMF-MMF-SMF

(End-face

terminated by the

thick silver film)

Temperature

range:

(25-115) °C

Sensitivity:

0.061 nm/ °C

Advantages:

Good sensitivity

Drawback:

Complex splicing

technique and low

temperature range

27

Temperature

sensors Configuration Performance

Drawback/

advantage

All-fiber Mach

Zehnder

interferometers for

sensing applications

[25]

SMF-MMF-TF-SMF

Temperature

range:

(20- 80) °C

Sensitivity:

0.0667 nm/ °C

Advantages:

Good sensitivity

Drawback:

Low temperature

range and large in

size

Temperature Sensor

by using selectively

filled Photonic

Crystal Fiber (PCF)

Sagnac

interferometer [26]

A selectively filled

polarization-

maintaining photonic

crystal fiber (PM-

PCF)

Temperature

range:

(25- 45) °C

Sensitivity:

2.58 nm/ °C

Advantages:

Good sensitivity

Drawback:

Low temperature

range and complex

fabrication

technique

(fabricated by

blocking the small

holes, immersing

the sensor in the

water and splicing

with the 3-dB

coupler)

High-temperature

sensor using a

Fabry-Perot

interferometer based

on solid-core

photonic crystal

fiber [27]

SMF-(PM-PCF)

Temperature

range:

(33- 600) °C

Sensitivity:

0.0138 nm/ °C

Advantages: High

temperature range

Drawback:

Limited source of

PM-PCF in market

28

2.7 APPLICATIONS OF FIBER OPTIC TEMPERATURE SENSOR

Nowadays, optical fiber based sensor have been broadly used for real-time

temperature monitoring [3]. Table 2.2 shows some of the applications that has been

demonstrated by fiber optic temperature sensor.

Table 2.2: Applications of fiber optic temperature sensor

Fields Application

Biomedical [28] Thermal distribution mapping in cancer

phototherapy, magnetic-resonance imaging and

cardiac-output monitoring

Oil and gas exploration[29] Reservoir temperature monitoring

Civil engineering[30] Temperature monitoring of concrete in massive

structures

Power transformer[31] Power transformer hot spot temperature

measurement

Dam monitoring[32] Temperature distribution of an old earth dam

during thawing

CHAPTER 3

METHODOLOGY

3.1 INTRODUCTION

This chapter discusses about the process and procedures involved during the

completion of this project, which includes materials processing and equipment

operation. In addition, details on Labview data acquisition coding for real time

monitoring also discussed in this chapter.

30

3.2 SENSOR FABRICATION PROCESS

In this project, a fiber tip temperature sensor based on Michelson interferometry

is proposed and designed. The structure can be simply constructed using direct fusion

splicing techniques in order to fuse or attached the single mode and multimode fiber

together.

Figure 3.1: Fiber splicing process

Figure 3.1 shows the process of fiber splicing. At first, the fiber optic is stripped

in order to remove the entire protective jacket from the end of the fiber. The protective

coating of SMF and MMF are stripped out by using stripper as shown in Figure 3.2. This

process has to be done carefully in order to prevent any breakage of fiber due to its

brittleness.

Stripping Cleaning Cleaving Splicing

31

Figure 3.2: Fiber jacket stripper

After the stripping process is done, the next step is to clean the stripped fiber.

The cleaning process need to be done in order to remove foreign particles that will lead

to high splicing loss. The typical cleaning agents used are alcohol and delicate task

wipers which are shown in Figure 3.3.

Figure 3.3: Alcohol and delicate task wipers

32

The third step is the cleaving process. Figure 3.4 shows the fiber cleaver tool that

was used in this process. This process is important in order to make sure the end face of

the fiber was perfectly flat and perpendicular to the axis. In addition, this process is

crucially important as it will determine the quality of splicing process. The value of

splicing loss depends on the cleave angle of the end face fiber. If the cleave angle is

closer to 90°, the value of splicing loss is lower.

Figure 3.4: Fiber cleaver

Lastly, the MMF section is spliced with both SMFs using fiber fusion splicer as

shown in Figure 3.5. The fiber is placed in the guides of the splicer and the end face of it

need to be tested in order to ensure the fiber is located correctly before it is aligned into

a position. The splicer will then show the estimated value of splicing loss based on the

digital image shown in the splicer. The conditions of SMFs and MMF before and after

splicing process are shown in Figure 3.6. In addition, the microscopic image of the

condition of SMF and MMF after splicing process are shown in Figure 3.7.

33

Figure 3.5: Fujikura fiber fusion splicer

Figure 3.6: Condition of SMF and MMF before and after splicing process

34

Figure 3.7: The microscopic image of the condition of SMF and MMF after splicing

process

3.3 STRUCTURE DESIGN AND CONFIGURATION

Firstly, the design of the fiber tip temperature sensor based on Michelson

interferometer was carried out. The structural design of the sensor is shown in Figure

3.8. Basically, the fiber tip temperature sensor based on SMF-MMF-SMF configuration

was fabricated by splicing the two ends of MMF with two SMFs. The lengths of MMF

and SMF2 used are 0.5 mm and 1.2 mm respectively. While the core diameters of SMF

and MMF fiber used are 9 µm and 105 µm respectively.

MMF SMF

Splicing point

35

Figure 3.8: Structural design of the fiber tip temperature sensor based on Michelson

interferometry

Based on Figure 3.8, light will enter SMF1 towards MMF as usual. But, the light

will then travel in two different paths as it enters SMF2 (n1 and n2). When the light

reflected back after reach the end of SMF2 due to Fresnel reflection and travels toward

MMF. The refractive indices of the core and cladding will vary differently if the

surrounding temperature is changed due to the small difference of thermo-optic

coefficient of the core and cladding. Hence, the light propagated in these two paths also

will experience different phase change. Then, interference occurred at the SMF2 and

MMF interface as the reflected light from different paths recombined together.

Interference is made possible due to the overlapped of MMF core with SMF core and

cladding. The reflected light is travelling back to SMF1 and will enter the optical

spectrum analyzer (OSA). Due to the phase change difference, the interference spectrum

detected at OSA also will change accordingly.

Although there were losses exist at the SMF2- air and SMF2- MMF interfaces,

the losses are irrelevant as long as the power can be detected at optical spectrum

analyzer (OSA) because sensing principle is based on wavelength change.

36

3.4 EXPERIMENTAL SETUP

Figure 3.9 shows the experimental setup of the fiber tip temperature sensor based

on Michelson interferometry. The broadband source is connected to the circulator in port

1, meanwhile, the optical spectrum analyzer (OSA) is connected to port 3 and the fiber

tip sensor is connected to port 2. The fiber tip sensor is placed inside an oven so that it

can measure different temperature. The initial temperature of the oven is kept stabilized

for a few minutes to ensure a well-distributed temperature inside the oven. The OSA is

then connected to the computer by NI GPIB-USB cable in order to analyze the output

spectrum in LabView program. The range of temperature was gradually increased from

30 °C up to 180 °C.

37

(a)

(b)

Figure 3.9: (a) Schematic diagram of experimental setup (b) actual experimental setup

38

3.4.1 Broadband Optical Source

Figure 3.10 shows the broadband optical source that has been used in this

project. The type of broadband source used was C-Band, which has wavelengths in the

range of 1530 mm until 1565 nm. The light from the broadband source is launched

through the SMF1 to the MMF. The light transmitted will then go through SMF2 and will

be reflected back at air interface. The light will be received by an optical spectrum

analyzer (OSA), which is shown in Figure 3.11. The output spectrum is then recorded

manually by user using the Labview program.

Figure 3.10: Broadband optical source

39

3.4.2 Optical Spectrum Analyzer (OSA)

The function of the optical spectrum analyzer (OSA) shown in Figure 3.11 is to

measure the output spectrum of the sensor.

Figure 3.11: Optical spectrum analyzer (OSA)

40

3.4.3 3-Port Optical Circulator C-Band

Figure 3.12 shows the 3 port optical circulator C-band. The function of circulator

in the experimental setup (shown in Figure 3.9) is to reroute reflected light from the

sensor to OSA.

Figure 3.12: 3 port optical circulators C-Band

41

3.4.4 National Instruments GPIB-USB (NI GPIB-USB) Cable

Figure 3.13 shows the National Instruments GPIB-USB (NI GPIB-USB) cable

that connects the optical spectrum analyzer (OSA) with the computer. This cable helps

to remodel a device that has a USB cable into a functional IEEE-488.2 Controller. In

addition, it is beneficial for a device that was built-in with no internal I/O channels.

Figure 3.13: NI GPIB-USB cable

42

3.4.5 Labview Program

Labview program was used to record the interference intensity wavelength shift

from an OSA. Figure 3.14 shows the wavelength spectrum displayed on the screen of

the program. Scanning process was done automatically, and data saving only performed

when user click on the save button on the program. All the scanning parameters are set

by the user. The values of scanning parameters used in the experiment are shown in

Table 3.1;

Table 3.1: Description of scanning parameters for the Labview program

SCANNING PARAMETERS VALUES

Center wavelength 1545 nm

Span 80

Resolution 0.2

Reference level -55 dBm

Log scale 5.0 dB/D

Sensitivity Mild

Sampling auto On

Sampling point 100.1

Average times 1

43

Figure 3.14: Graphical user interface of the Labview data acquisition program

CHAPTER 4

RESULT AND DISCUSSION

4.1 INTRODUCTION

This chapter presents findings and analysis obtained from the experiment

conducted on the proposed sensor. Analysis of output spectrum, response and sensitivity

of the sensor to temperature are discussed.

45

4.2 ANALYSIS ON TEMPERATURE SENSITIVITY OF SENSOR

The proposed sensor is sensitive to ambient temperature because of the different

thermo-optic dependences of the fiber core and cladding. The mode group which

consists of core mode and cladding mode changes differently with temperature variation.

This leads to the difference phase shift of the interference fringe which contributes to

wavelength shift. In other words, if the temperature changed, the refractive index of

SMF and MMF will change, causing the wavelength of interference intensity to change.

Several measurements have been carried out to verify the temperature response

of the sensor correspond to the actual temperature. The reference measurement of

temperature was obtained from a calibrated digital thermometer. The initial dip

wavelength of 1540.2 nm was used as an indicator for temperature change. Figure 4.1

shows the wavelength of the dip shift toward longer wavelength as the temperature

increased. The wavelength shift was resulting from the higher thermo-optic coefficient

inside the core compared to cladding.

When the temperature was increased from 30 °C to 180 °C, the center

wavelength of the dip was changed from 1540.2 nm to 1549.4 nm, corresponds to the

value of total wavelength shift of 9.2 nm. In addition, the first peak wavelength was

unchanged because the response was differing compared to the dip wavelength. Besides,

the wavelength shift pattern only has two peaks because it is depended on the length of

multimode fiber (MMF).

46

Figure 4.1: Transmission spectra of the fiber tip temperature sensor based on a

Michelson interferometer with different temperature

Meanwhile, the shifted of the wavelength of the dip for increased and decreased

temperature are plotted in Figure 4.2(a) and Figure 4.2(b), respectively. From the graph,

result shows that the relationship between the sensor and the temperature is linear, with a

moderate temperature sensitivity of 0.0631 nm/ °C. This moderate sensitivity was

considered as typical sensitivity because of another type of fiber based temperature

sensor also produced sensitivity, which is almost the same as the proposed temperature

sensor.

From the analysis, when the temperature started to drop, the dip wavelength

seems to follow another path of shifting, probably because of the residual stress that has

been released inside the fiber. There are small irregularities exists to the measured dip

wavelength as the temperature changed. One of the reasons for this problem is that the

low scanning speeds of the OSA. Furthermore, another reason is that the temperature of

the oven was changing drastically and difficult to be controlled. To minimize this

foregoing problem, the scanning rate of the OSA needs to be enhanced by having a high

speed OSA with high resolution.

47

(a)

(b)

Figure 4.2: (a) Graph of dip wavelength shifted with temperature rise (b) Graph of dip

wavelength shifted with temperature drop

CHAPTER 5

CONCLUSION AND RECOMMENDATIONS

5.1 CONCLUSION

In this project, a compact fiber tip temperature sensor based on Michelson

Interferometry was enabled for high temperature applications using SMF-MMF-SMF

configuration. This sensor was fabricated using a simple fusion splicing technique by

splicing short length of MMF in between SMF1 and SMF2. In addition, this fiber tip

temperature sensor system was considered excellent as it is able to respond well with the

temperature measurements. Its response to temperature is investigated experimentally

from room temperature, which is 30 °C up to 180 °C. A sensitivity of 0.0631 nm/ °C

was obtained after analysis was done using LabView and Matlab program. Furthermore,

in terms of stability, this sensor has a good stability as the spectrum of wavelength shift

has a fixed pattern and unchanged. Moreover, the proposed fiber tip temperature sensor

has the advantages which are compact size, have good stability, response and high

dynamic range. Therefore, the performance of this sensor possesses a great potential in

many fields, especially in high temperature sensing applications.

49

5.2 RECOMMENDATION

Future works would be crucially important in order to improve the project. The

high sensitivity of the sensor can be realized using several techniques. First, by having

better splicing technique with correct length of Multimode (MMF) and SMF2 can help to

reduce loss inside the fibers. Besides, to improve the sensitivity of the sensor, SMF2 can

be replaced with a polymer cladded fiber. As polymer materials are known to have high

thermo-optic coefficient, the phase difference between core and cladding will be more

drastic. This will enhance temperature sensitivity as more wavelength shift of the

interference spectrum will be observed.

Furthermore, the reflectivity of the light ray that comes through the fiber optic

can be improved by adding reflected materials such as silver thick film or mirror at the

end face of the fiber tip temperature sensor. This will help to enhanced the value of

power (dB) produced from the reflections. This is because, if there is no reflected

materials exist, the power produced is low as high losses will occur because of the weak

reflection at the SMF2- air interface.

The improvement of the temperature measurement during experimental work can

also be accomplished by improving the resolution and scanning rate of the optical

spectrum analyzer (OSA). Furthermore, the temperature control of the oven also needs

to be handled so that the results produced during experimental work are accurate.

50

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