PhRC NEWSLETTER PHOTONICS'La - Nanyang Technological ...

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PhRC NEWSLETTER PHOTONICS'La - Nanyang Technological ...

hotonics'a

A Publication of the Photonics Research Centre, Nanyang Technological University

Issue 1

September 2003

Research

Activities

in Photonics

Research

Centre

A special inaugural issue

to commemorate the launch of

the Photonics Research Centre

Biophotonics

Fibre and Laser

Optics

Photonic Materials

and Devices

Features

Optics in

Healthcare

Optical Tweezers


Research Map

Students

Activities

ISSUE 1—SEPTEMBER 2003

Contents 2

Forewords 2

About the Photonics Research Centre 4

Some Statistics 4

Biophotonics Research 7

Fibre and Laser Optics Research 8

Femtosecond soliton fibre lasers 10

Electrically tunable dispersion compensator

using fibre Bragg grating 11

MEMS Technology and Devices 12

Thermal characterization of GaAsN epilayer

on GaAs 13

Photonic Materials & Devices Research 14

Photonic Integrated Circuits Research 15

Quantum Well Intermixing 16

Development of High Power Laser Diode

Arrays 17

Lasing Characteristics of Nano-Rods 18

Sol-Gel Materials & Applications 18

Organic Light Emitting Diodes (OLED) 20

Liquid Crystal Devices 21

Thermal Imaging 22

Optical Tweezers 25

News Brief 28

Features hotonics'a

National Lecture Competition 2003 29

Photonics Gathering 2003 30

Announcements 33

Photonics’La is published by the Photonics Research Centre, School of

Electrical and Electronic Engineering, Nanyang Technological University.

Block S1, Nanyang Avenue, Singapore 639798. Opinions expressed herein

do not necessarily reflect the views of the University.

Copyright c○ 2003 Photonics Research Centre

All rights reserved. Material in this publication may not be reproduced

without written permission. MITA (P) No. 148/09/2003

2 hotonics'a

Forewords

My congratulations to all the students and

staff of the Photonics Research Centre for

the launch of their newsletters—hotonics'a —in

commemoration of the official inauguration of the

Centre.

Photonics research in the School of EEE began back

in 1992, when a few academic staff members started

by setting up experiment stations in makeshift space

in the School. In 1994, a designated laboratory was

finally allotted for the first-ever Photonics Research

Laboratory in Singapore, thus laying the groundwork

for the Photonics Research Centre almost 10 years

later.

Today the Centre boasts 23 academic staff, 25research

staff and about 48 research students. Over the

years, 16 Ph.Ds and 48 M.Eng and M.Sc have been

produced in this research area, and well over 200 students

have graduated from NTU with a concentration

in Photonics, and are working in the industry, contributing

to the economy of Singapore.

Photonics is identified by the Singapore Economic

Development Board as a strategic industry and a critical

technology. The School will continue to support

efforts in this area and strive towards making the Centre

a niche of excellence in the Asia-Pacific region.

I encourage readers of this newsletter to browse

carefully the pages of this issue to find avenues for

research collaboration and other meaningful interactions.

Godspeed!

Prof.ErMengHwa

Dean,

School of Electrical and Electronic Engineering

emher@ntu.edu.sg


My warmest greetings to all the students and

staff of the Photonics Research Centre for initiating

an innovative Newsletter cum e-magazine —

hotonics'a in conjunction with the establishment

of this new Photonics Research Centre that is

a spin-off from the Photonics Research Group within

the Microelectronics Centre.

The aim of this newsletter to reach out beyond

NTU, especially to the industries and touch base with

the Junior College and Polytechnic students is commendable.

Photonics is still a young and emerging

technology and will continue to appeal to the young

and brightest talents. It is gratifying to note that for

this year, out of the 10 first batch A*STAR Graduate

Scholarships awarded to the NTU graduates, 3 are

joining the Photonics Research Centre.

Today the Centre is poised to grow further, expanding

in cutting-edge areas such as biophotonics,

while strengthening the more traditional areas in optical

communications and photonic materials and devices.

Research in all these areas will bring benefits to

the economy in time to come.

In this inaugural issue of Photonics’La, some of the

current research projects conducted in the Photonics

Research Centre are showcased. I hope you will find

the information useful, and I further encourage you

to follow up with the Centre should you be interested

to find out more.

Cheers!

Assoc. Prof. Tan Ooi Kiang

Head of Division

Division of Microelectronics

eoktan@ntu.edu.sg

This inaugural issue of hotonics'a marks

a major milestone for the Photonics Research

Centre. I take this opportunity to express my sincere

thanks to both staff and students who have put in so

much effort to make this a success.

Photonics, the technology of generating and harnessing

light, is a fast expanding field. While the 20th

Century was known as the Microelectronics Era, the

21st Century is touted to be the Photonics era. The

Microelectronics Era has brought great advances on

all fronts from Science and Engineering to Entertainment

and Communications. A century ago, it took

days or even months for news to propagate from one

end of the world to the other. Today, we can obtain

instant update on all sorts of news at the tap of a button.

It seems true that there is no end to technology

development except for the limitation of our imagination.

Technology that is not available today can be

made available tomorrow if we, in the scientific community,

pull our resources together to make it happen

and this is what Research and Development is all

about. It is with this goal in mind that the Photonics

Research Centre was established.

As a Research Centre, we must aim to harness every

talent within the Centre to make significant contributions

to the scientific community through patents

and the dissemination of our research results through

scientific publications. At the same time, both students

and researchers should work together to maximize

the mileage that can be achieved from the limited

resources that we have. Finally, in this knowledgeintensive

society, we must train our students to think

outside the box and make things that are undoable today,

doable tomorrow even if it means just sowing the

seed.

This newsletter reflects the creativity and potential

of the Photonics Research Centre. I hope the readers

will find the information useful.

Assoc. Prof. Tjin Swee Chuan

Director

Photonics Research Centre

esctjin@ntu.edu.sg

FOREWORDS September 2003 3


About the Photonics

Research Centre

The 21st Century is often called the Information

Age. The backbone for a digital information-rich

society is a pervasive fibre-optic network that

carries information in the form of optical pulses transmitted

by semiconductor lasers and received by photodetectors.

Today’s quality of life is directly linked to lasers

and the harnessing of light, which is the basis of Photonics

technology. An enabling technology that underlies

many strategic industries, its importance is universally

recognized, and it is identified by EDB as a critical technology

for Singapore.

The Photonics Research Centre (PhRC) in the Nanyang

Technological University (NTU) is dedicated to research

and teaching in the fast-paced field of Photonics science

and technology. The culture of openness, and the broad

range of expertise and equipment in the Centre provide

a stimulating and dynamic environment for researchers

and students from many countries worldwide.

The Centre was founded in 1994 as a photonics research

laboratory, the first of its kind in Singapore. Today

it encompasses 23 academic staff, 26 research staff, and

37 research students, conducting research in three laboratories

in many cutting-edge areas of Photonics. The

research area may be broadly classified in three groups:

Biophotonics

• Fluorescent Lifetime studies

• Fluorescent Imaging

• Optical Tweezers

• Bioassay Devices

• Bio-sensors

Fibre and Laser Optics

• Fibre optic and wireless communication

• Fibre Optic Sensors

• Diffractive Optics

4 hotonics'a

• Optical MEMS

• Laser Engineering (Laser Systems)

• Optical Engineering (Discrete Optics Systems)

Photonics Materials and

Devices

• Compound semiconductor photonics

• Sol-Gel photonics

• Polymer photonics

• Display devices (OLED, TFEL, LCD)

• Advanced materials and device integration

Our mission is to spearhead research in these strategic

areas, and to facilitate the training of professional manpower

and the transfer of technology to industry.

Some Statistics

Research

The PhRC family:

• 23 Academic Staff (including 3 from School of Materials

Engineering and 1 from School of Mechanical

& Production Engineering)

• 26 Research Staff

• 34 full-time Research Students and 3 part-time

• 10 Technicians

• Two research laboratories

• One teaching laboratory

• One joint laboratory with the Network Technology

Research Center.


Research Funding:

Total cumulative research funding = S$20,948,154

(63 projects; average funding/project = S$332,510)

Total current research funding S$11,025,006

(18 projects; average funding/project = S$612,500)

Publications:

Journals Conferences

2002 43 45

2003 (todate) 56 26

Patents:

12 patents awarded.

Spin-off companies:

2 (one existing)

International collaborations:

The Centre has signed MOUs with international collaborators,

including the TNO Institute of Applied Physics

in Delft, Ècole Nationale Supèrieure, Hong Kong University

of Science and Technology, and Monash University.

Two major MOUs, under final stage of preparation, will

be signed in the near future. The first is to develop a joint

Photonics Laboratory facility with Institut d’Optique,

France and Thales Training Centre, Singapore. The second

is to spearhead joint research activities in Photonics

with Imperial College, U.K.

Education and Training

The Centre has produced 15 PhD’s and 48 MEng and

MSc.

The undergraduate Photonics Final Year Option was

launched in July 2000 with an initial batch of 23 students.

The cohort increased to 51 students in 2001, and 157 students

in 2002. The core subjects for this option are:

• Semiconductor Optoelectronics

• Optical Engineering

• Laser Engineering

• Fibre Optic Communications

• Optical Design

• Photonic System Design

In the Postgraduate level, with the support of the

Economic Development Board of Singapore, an

MSc(Photonics) program will be launched in July 2003.

16 full-time and 12 part-time students have been offered

admission, out of a total of 195 applicants. The Centre is

also looking for possible collaboration in this MSc Programme

with Imperial College (U.K.) leading to a joint

degree in Photonics.

The curriculum for the MSc program is as follows:

Core Subjects

• Modern Optics

• Laser Technology and Applications

• Opto-Electronic Devices

• Optical Fibre

Optional Subjects (Students choose any 4)

• Microoptics and Optical MEMS

• Biophotonics

• Compound Semiconductor Epitaxial Growth

Technology

• Display Technologies

• Optical Data Storage

• Optical Fibre Communications

• Quality and Reliability Engineering

• Advanced Semiconductor Physics

The Centre staff is active in promoting the teaching of

photonics in secondary as well as tertiary institutions.

TheCentrestaff has provided leadership role in organizing

international conferences and local chapters of

professional societies, including SPIE and IEEE LEOS.

*LATEST

Three out of 10 A*STAR postgraduate scholarships

awarded to NTU in 2003 chose Photonics as their research

field.

For enquiries about the Centre please contact

A/P Tjin Swee Chuan at ESCTJIN@ntu.edu.sg. For

enquiries about the MSc Course please contact A/P

Yuan Xiaocong at EXCYUAN@ntu.edu.sg.

ABOUT THE PHOTONICS RESEARCH CENTRE September 2003 5


Fibre and Laser

Optics

Program Director:

Dr Tang Dingyuan

Members

A/P Tang Dingyuan

A/P Tjin Swee Chuan

A/P Liu Ai Qun

A/P Yuan Xiaocong

A/P M. K. Rao

Ast/P John Ngo Quoc Nam

Ast/P George Chen Kit Chung

Ast/P Julian Chan Chi Chiu

Ast/P Murukeshan (MPE)

Organization Chart of PhRC

Photonics Research Centre

Centre Director: Dr Tjin Swee Chuan

Biophotonics

Program Director:

Dr Tjin Swee Chuan

Members

A/P Tjin Swee Chuan

A/P Yuan Xiaocong

A/P Lim Tuan Kay

Ast/P Ng Beng Koon

Photonic Materials

and Devices

Program Director:

Dr Chin Mee Koy

Members

A/P Chin Mee Koy

Prof. Kam Chan Hin

A/P Terence Wong Kin Shun

A/P Au Yeung Tin Cheung

A/P Yuan Shu (SME)

Ast/P Mei Ting

Ast/P Tang Xiaohong

Ast/P Yu Siu Fung

Ast/P Pita Kantisara

Ast/P Sun Xiaowei

Ast/P Ricky Ang Lay Kee

Ast/P Ng Beng Koon

Ast/P Rajesh Menon

Ast/P John Ngo Quoc Nam

External Seminars and Workshops given by Photonics Research Centre Staff

Date Speaker Workshop Topic

14 March A/P Chin Mee Koy 1st Workshop on Microphotonics,

A*Star/IME, Singapore

24 July Ast/P Pita Kantisara and A/P Photonics Workshop,

Yuan Xiaocong

A*star/SIMTech, Singapore.

24 July A/P Terence Wong Kin Shun Photonics Workshop,

A*star/SIMTech, Singapore

6 hotonics'a

A Roadmap for III-V Photonics

Sol-Gel Photonics

Phosphorescent and low-k materials

for organic LED


Biophotonics Research

Ast/P Ng Beng Koon and A/P Tjin Swee Chuan

Biophotonics, at the crossroads between biosciences

and photonics, is an emerging field with

great potential and a fertile ground for research.

It is the science of generating and harnessing light to

image, detect and manipulate biological matters. It is

multidisciplinary in nature and incorporates many scientific

disciplines including physics, chemistry, mathematics,

biology, and engineering.

There are currently 4 academic staff in this group

working on optical bioimaging, fibre-optic sensors for

pressure and flow measurements in biological system,

and advanced optical tweezers for the micromanipulation

of biological specimens. The group is engaged in a collaborative

alliance with the University of Washington, Seattle

(US).

In the area of optical bioimaging, we are interested in

the application of lasers for the diagnosis of diseased tissues.

In particular, fluorescence spectroscopy has been

used to study diseased tissues, such as plaque in the arteries

of the human body. There is also an ongoing research

programme to develop a handheld optical bioassay

system for monitoring biochemicals in biological fluids.

Such a device will allow healthcare to be decentralised to

the various point-of-care environments, thereby improving

the quality of medical care and resulting in cost savings

through early diagnosis of medical conditions.

Research in fibre-optic biosensors is being pursued to

develop sensors for applications in medical diagnosis and

health monitoring. Some examples are fibre-optic pressure

sensors for orthopaedic applications and total knee

joint replacement surgery, and continuous cardiac output

sensors for the in-vivo monitoring of blood flow.

Advanced optical tweezers that will enable the transfer

of optical gradient force, spin angular momentum,

and orbital angular momentum is currently being investigated

using a double hologram interferometer. This new

optical tool allows dual rotation within the laser beam

and is much more compact than setups employing conventional

techniques. Potential applications include the

simultaneous angular deformation of cell structures and

force measurements [please refer to the feature article on

Optical Tweezers].

Figure 1: Fibre Bragg grating embedded into a patella button to

perform pressure mapping during total knee joint replacement

surgery (courtesy of Ms Lipi Mohanty, PhD student)

Figure 2: Manipulating yeast cell with optical tweezer (courtesy

of Mr Lee Woei Ming, PhD student)

BIOPHOTONICS RESEARCH September 2003 7


Fibre and Laser Optics

Research

A/P Tang Dingyuan

The fibre and laser optics (FLO) research

group involves 7 academic staff and 5 research

fellows. Research activity of the group spans a

wider range of topics within the areas of fibre optics and

optic communications, laser physics and engineering, as

well as modern optics such as diffractive optics and nonlinear

optics.

Fibre optics and optic communications

During the past decade there has been a tremendous

growth in fibre-optic communication to accommodate

the ever-increasing demand on the capacity

of the global communication systems. Two approaches

are being pursued to increase the capacity of fibre communication

systems: (i) Wavelength division multiplexing

(WDM) technology, where multiple lower bit-rate

communication channels are simultaneously transmitted

in a single optical fibre, and (ii) Soliton communication,

which makes use of the properties of optical solitons to

achieve ultrahigh bit-rate transmissions. Both technologies

require various fibre-based optical devices and components

with special functionality. Our research in this

area has focused on grating-based devices and soliton

lasers.

In the first area, two fibre Bragg grating fabrication

systems have been built, one based on a pulsed excimer

laser and the other on a CW frequency-doubled argonion

laser. Both systems produce high quality fibre Bragg

gratings (FBG). We are now in the position of design-

8 hotonics'a

ing FBGs of arbitrary transmission. Using these FBGs

we have demonstrated tunable dispersion compensators

with fixed center wavelengths [see article by Prof. John

Ngo].

In the area of soliton fibre laser, our research has attracted

world-wide attention. For the first time we have

experimentally obtained a new type of double-pulse soliton

in passively mode-locked fibre lasers and theoretically

confirmed the existence of this type of optical solitons.

Other related activities in the area include free-space

optic communication and optical MEMS. In the former

area, Prof. George Chen’s group is working on diffuse

holograms for infra-red (IR) wireless communication

and angle diversity photoreceivers. IR has advantage over

Bluetooth for ultra-short reach inter-device communication

because IR radiation offers a virtually unlimited

and unregulated bandwidth. In addition, since IR doesn’t

penetrate through walls, the wavelengths can be reused

and this is particularly suited for office application. In the

MEMS area, the optical MEMS group, under Prof. Liu Ai

Qun, is working on MEMS switches and attenuators, and

discrete-wavelength tunable MEM lasers for optical communications

applications [please see article by Prof. Liu].

Diode-pumped solid-state (DPSS) lasers

Compact, all-solid-state pulsed lasers with large

single pulse energy and variable repetition rate have

wide applications, e.g. in the range finder and laser radar

systems. Such a laser system can be developed based on


the laser active Q-switching technique combined with the

high power diode quasi-cw pumping technology. In a

previous project, in collaboration with Charted Electro-

Optics, Singapore, we have developed a high power 50W

CW diode-pumped solid-state (DPSS) laser. Through

this project we have gained tremendous experience in developing

high power DPSS lasers.

In the development of new types of DPSS lasers, we

have collaborated with scientists in Japan and Russia to

develop the first diode pumped Yb-ions doped ceramic

laser in the world. Pumped with 12.8 W of 940 nm

light we have achieved 0.78 W cw laser emission at the

1.078 µm. By putting a saturable absorber in the laser

cavity, we have also achieved passive Q-switching of the

ceramic laser. The advantages of ceramic lasers are that

large pieces of ceramic are easily available, very high doping

concentrations can be obtained, and the low cost.

Another on-going research project is the investigation

of the diode pumped Nd:GdVO4 lasers. Nd:GdVOV4

is a new laser crystal with high thermal conductivity and

optical efficiency. We have achieved a Q-switched laser

with stable high power, and large single-pulse energy, and

are working toward a high-power mode-locked laser in

collaboration with Shandong University, China.

Apart from the continuous improvement of the conventional

laser Q-switching and mode-locking techniques,

we are also working on other novel techniques to

manipulate the operation of lasers, such as the control of

the emission and the intensity pattern of a laser beam.

It is expected that by using specially designed diffractive

optical element inside the laser cavity, and through manipulating

the laser gain and cavity dispersion laser emission

with novel beam shape and pulse profile could be

obtained.

Lasers are intrinsically a nonlinear dynamical system.

Our study of the nonlinear dynamics in lasers, which

are well described by the laser equations, have included

the laser chaotic dynamics and its control, laser chaos

synchronization, the temporal and spatial solitons, laser

cavity soliton interactions, etc. For the first time we

have both experimentally and numerically proven that

the Q-switched pulse intensity fluctuation of passively Qswitched

DPSS lasers are in fact a deterministic chaos

phenomenon. This discovery has not only provided a

deep understanding on the phenomenon itself, but also

suggested a completely new technical approach in controlling

or eliminating the fluctuations. Our research on

temporal soliton and its dynamics in a passively modelocked

fibre laser has revealed a new type of twin-pulse

form of solitons. Potentially this new type of solitons

could be used to combat polarization mode dispersion in

high-bit rate optical communication systems.

Modern optics

Our research in the area comprises the diffractive

optics and nonlinear optics research activities.

Nonlinear optics is one of the wonderful areas of modern

optics. It is a direct consequence of the interaction

of high-power, high-brightness coherent laser beams with

materials, resulting in a nonlinear response of the material

property to the light radiance. Using these nonlinear

interactions, one can convert light from one wavelength

to another, and also control light by light to realise lightcontrolled

self-switching photonic devices. Our research

activities in nonlinear optics currently are mainly focused

on optical wavelength conversion, such as laser intracavity

frequency doubling, and parametric optical oscillators.

The past decade has witnessed new developments in

micro-optics based on new materials. In particular,

sol-gel glass, as a low-cost material with good, tunable

optical properties, has been extensively used in the fabrication

of planar waveguides, computer generated holograms,

and micro-optics (especially microlens arrays). In

our research, we have used a hybrid sol-gel technology to

develop the following micro-optical elements:

• A microlens array used as a coupler between a

waveguide array and a fibre array

• A microlens array used as a Shack-Hartmann wavefront

sensor

• Micro-optics for extra-cavity and intra-cavity

beam shaping

• Computer generated holograms (CGHs)

• Micro-optics for laser beam addition

Sol-gel Microlens array using an HEBS grey scale mask.

FIBRE AND LASER OPTICS RESEARCH September 2003 9


Femtosecond soliton fibre lasers

A/P Tang Dingyuan

Fiber lasers are a new type of laser system made of

special optical fibre. They have the characteristics of

compact size, ultra stable operation and low cost. Various

modes of operation can be achieved in the lasers: they can

emit either high power continuous light beams, or singlefrequency

ultra-stable optical waves, or ultra stable, ultrashort

optical pulse trains.

A femtosecond soliton fibre laser generates high quality

special optical pulses with pulse duration of merely hundreds

of femtosecond. Unlike conventional optical pulses,

these special pulses, known as solitons, maintain their

pulse shape and width without any distortion in propagating

through long lengths of optical fibre, a property

that is very useful for fibre-optic communication.

If the soliton laser is further operated in combination

with chirp pulse amplification and nonlinear wavelength

conversion techniques, ultra-high peak power, frequencytunable

optical pulses can be generated. This kind of

optical pulses have wide-ranging applications in scientific

research as well as military devices and medical surgery.

Researchers in my group have conducted intensive theoretical

and experimental research on passively modelocked

soliton fibre lasers. They have developed compact,

ultra-stable femtosecond soliton fibre lasers of various

configurations and achieved transform-limited soliton

pulses of duration as short as 250 fs, and high-energy

femtosecond optical pulses of single pulse energy as large

as several tens of nJ. These lasers can be used in a number

of applications, e.g. the injection seeding, two-photon

microscopy and laser radar systems.

Beside the conventional soliton pulse laser our group is

also the first to discover a novel twin-pulse soliton emission

in the lasers. This observation not only confirms

experimentally the existence of the multi-hump temporal

optical solitons, but also makes available for the first

time a unique novel laser system that generates closely

paired optical pulses. A laser beam with such a property

may have a number of special applications, e.g. in

triggered ultrafast photography, laser spectroscopy, and

time-division multiplexing optical communication systems.

In addition, our group has also studied other features

of the soliton fibre lasers, such as the noise-like pulse

10 hotonics'a

emission in which the emitted pulses have very large energy

and ultra-broad optical spectrum. Lasers of such

property are an ideal high power broadband light source,

which may be used for testing fibre optic communication

systems and for optical metrology.

Theoretically, we have developed a model that can accurately

reproduce all features of the lasers observed experimentally.

With this model we can not only understand

the physical mechanism of a specific experimental

effect observed, but also predict and design new features

of the laser and other ultrashort pulse laser systems.

Figure 1: Femtosecond soliton fibre laser developed in NTU.

Figure 2: Optical spectrum of a double-pulse soliton laser

emission.

Figure 3: Double-pulse soliton emission of the lasers numerically

simulated.


Electrically tunable dispersion compensator using fibre

Bragg grating

Ast/P John Ngo Quoc Nam, Li Songyang, Zheng Ruitao, A/P Tjin Swee Chuan, A/P Shum Ping

One of the most critical challenges in nextgeneration

high-speed long-haul optical transmission

systems is to overcome the fibre’s chromatic dispersion.

The tunable dispersion compensator (TDC) can

be used to optimise network performance. We have proposed

and developed a novel TDC that can electrically

adjust the chirp of the FBG while maintaining a fixed

centre wavelength. This new method can minimise signal

distortion and crosstalk in a WDM system.

This electrically tunable TDC consists of a uniform

FBG in a fibre that is etched to a prescribed diameter profile,

an on-fibre thin-film heater whose local resistance

varies with position in a prescribed manner along the

grating length, and a negative thermal expansion coefficient

(NTEC) ceramic in which the FBG is mounted [see

Figure 1]. Electrical current flowing through the thin film

will generate a temperature gradient because of the pre-

+

λB1

Fiber with FBG in the center Copper thin-film coating

Conductive paint layer

DC

λB0 λB2

Epoxy

Negative thermal-expansion coefficient (NTEC) material

Figure 1: Schematic diagram of the proposed tunable dispersion compensating

FBG with fixed central wavelength. When current flows through the thin-film

coating and the conductive paint layer, the bandwidth and chirp of the FBG can

be tuned while the center wavelength is kept fixed.

_

scribed thickness profile of the metal film. Shrinkage of

the NTEC ceramic imposes a strain gradient on the FBG

because of the prescribed diameter profile of the fibre

with FBG. Both the temperature gradient and the strain

gradient affect the chirp and hence dispersion of the FBG.

At the same time, the center wavelength is kept fixed because

the effects of temperature rise and of compression

of the FBG are such that they offset each other.

To our knowledge, this is the first proposal to combine

the temperature gradient and the strain gradient as a dispersion

tuning technique. As an example to demonstrate

the effectiveness of the proposed method, we have developed

a TDC of 25 mm length, which has a dispersion tuning

range of −178 ps/nm to −302 ps/nm with a central

wavelength shift of as small as 0.17 nm and an applied

electrical power smaller than 0.68 W.

Fiber

1cm

Epoxy

Electrodes

Conductive paint layer

on surface of NTEC

ceramic

Epoxy

NTEC ceramic

with FBG inside

Figure 2: Photograph of a packaged tunable

FBG dispersion compensator.

Group Delay (ps)

250

200

150

100

50

0

B: Volt=0.4 V; Dispersion= -190 ps/nm

-50

1549.0 1549.2 1549.4 1549.6 1549.8 1550.0 1550.2 1550.4 1550.6

Wavelength (nm)

Figure 3: Measured group delay characteristics

of the tunable dispersion compensator.

FIBRE AND LASER OPTICS RESEARCH September 2003 11


MEMS Technology and Devices

A/P Liu Ai Qun

Microelectromechanical systems (MEMS) has

become a key optical technology for making optical

networking components and devices for dense wavelength

division multiplexing (DWDM) systems. Examples

include optical switches, optical crossconnects

(OXCs), reconfigurable optical add/drop multiplexers

(OADMs) and tunable lasers.

A variable optical attenuator (VOA) with a footprint

of 1 × 0.6 mm has been developed using MEMS technology

in the MEMS research group [see Fig. 1]. Exploiting

the surface micromachining technology, the whole device

has achieved a response time of 37 ms, an attenuation dynamic

range of 45 dB, an insertion loss of 1.5 dB, and

a driving voltage of 3.5 − 8 V (better than conventional

VOA systems). The wavelength dependent loss over the

C-band (1528 nm - 1561 nm) is less than 0.9 dB. This

achievement was reported in the magazine Fibre Systems

Europe in 2002.

Figure 1: A scanning electron micrograph of the MEMS VOA

The first achievement of the research team was a

MEMS tunable laser in 2001, which was highlighted in

the U.S. magazine WDM Solutions. In 2003, an “Optical

MEMS Integrated System” was successfully demonstrated

[Fig. 2] and was awarded a Gold Prize at the College of

Engineering (CoE) Technology Exhibition. The contributions

of the MEMS group have generated positive publicity

for NTU as well as the Photonics Research Centre.

References

[1] A. Q. Liu, X.M. Zhang, and V.M. Murukeshan, “A novel

device level micromachined tunable laser using polysilicon

3D mirror,” IEEE Photonics Technology Letters, vol.

13, no. 5, pp. 427-429, May 2001.

12 hotonics'a

[2] “Fully Integrated Micromachine Laser is Tunable”, WDM

Solutions, pp. 10, July 2001.

[3] A. Q. Liu, X. M. Zhang, V. M. Murukeshan, C. Lu and

T. H. Cheng, “Micromachined wavelength tunable laser

with an extended feedback model”, IEEE Journal of Selected

Topics on Quantum Electronics, vol. 8, no. 1, pp.

73-79, January/February 2002.

[4] X. M. Zhang, A. Q. Liu, C. Lu and D. Y. Tang, “MEMS

variable optical attenuator using low driving voltage for

DWDM systems”, IEE Electronics Letters, vol. 38, no. 8,

pp. 382-383, April 2002.

[5] “Low-driving-voltage VOAs Exploit MEMS”, Fibreystems

Europe, pp. 11, June 2002.

[6] A. Q. Liu, X. M. Zhang, C. Lu, F. Wang, C. Lu and Z. S.

Liu, “Optical and mechanical models for a variable optical

attenuator using a micromirror drawbridge”, Journal

Micromechanics and Microengineering, vol. 13, pp. 400-

411, 2003.

Figure 2: A micrograph of a MEMS tunable integrated system

Figure 3: Assoc. Prof. Liu’s team won a gold prize at the CoE

Technology 2003.


Thermal characterization of GaAsN epilayer on GaAs

Zhao Yimin and Ast/P George Chen Chung Kit

Photothermal technique has gained popularity

because of its non-contact nature. We use pulsed

photothermal reflectance technique to characterise thermal

properties of thin films. As shown in Figure 1, this

technique basically consists of a pump laser and a probe

laser. The pump source is a Nd:YAG laser with a pulse

width of 8 ns. The probe laser is a continuous wave He-

Ne 1-mW laser. To enhance the heat absorption, a metal

layer, preferably gold, is deposited on top of the sample.

The measurement begins with the Nd:YAG laser pulse

incident on the sample surface. The sample surface temperature

rises sharply, and then relaxes with time. This

gives rise to a temperature excursion profile that depends

on the thermal properties of the underlying films and the

thermal resistance between the layers. The heating up of

the sample induces a change in the refractive index on

the surface and hence a change in the reflectance of the

probe beam. Since the temperature and the reflectivity of

gold are inversely related, the temperature profile can be

obtained by capturing the changes in the reflected probe

beam. The thermal properties of the film to be measured

can be obtained by fitting the measured data with

analytical expression for heat conduction.

HeNe

Laser

Nd:YAG Laser

Detector

Au Film

GaAsN

Substrate

Figure 1: Experimental geometry of pulsed photothermal

reflectance measurement

We have applied this method to measure the thermal

properties of Gallium Arsenic Nitride (GaAsN), which is

a relatively novel material for optoelectronic devices. The

advantage of this material is that it can be grown on a

GaAs substrate. The addition of nitrogen (N) into GaAs

decreases the material bandgap, making it suitable for the

fabrication of laser diodes operating at wavelengths of

1.3 µm and 1.55 µm. As high power laser diodes may

be fabricated in GaAsN, characterization of the material

thermal conductivity becomes important, as the material

must be able to dissipate the large amount of heat generated

in the laser diode emitters in order to maintain good

performance and reliability.

To extract the thermal conductivity (KGaAsN) and diffusivity

(αGaAsN = KGaAsN/ρc, whereρ and c are density

and specific heat, respectively) of the GaAsN thin

film from the obtained thermal profiles, we used a threelayer

heat conduction model, which incorporates thermal

resistance (R1, R2) of the two interfaces, based on a

transmission-line theory. Simulated annealing, a global

optimization method, is applied to obtain the optimal fit

to the experimental data. The fitted result is shown in

Table 1. To our knowledge, this is the first time the thermal

conductivity of GaAsN is being reported. No significant

thickness dependence was found within our samples’

thickness range. The average thermal conductivity

is about 27 W/mK and the average thermal diffusivity is

about 0.4 × 10 −6 m 2 s −1 . As expected, the thermal resistance

(R2) of the epitaxial interface between GaAsN and

GaAs is much less than the thermal boundary resistance

between Au and GaAsN (R1).

Figure 2: Surface temperature excursion profile of sample with

thickness of 80 nm

Table 1: Thermal property versus thickness of GaAsN epilayers

on GaAs substrate

Thickness (nm) 20 40 50 80

KAU (W/mK ) 250 235 212 241

KGaAsN (W/mK ) 27 25 28 29

αGaAsN (×10 −6 m 2 s −1 ) 0.9 0.4 0.3 0.4

R1 (×10 −8 m 2 K/W ) 5.8 9.2 6.7 7.1

R2 (×10 −8 m 2 K/W ) 9.4 7.4 5.9 7.4

FIBRE AND LASER OPTICS RESEARCH September 2003 13


Photonic Materials and

Devices Research

A/P Chin Mee Koy

The photonic materials and devices (PM&D)

is a broad and diverse program involving about

12 academic staff and 16 research fellows. The

material-based research can be classified in three broad

categories: (i) compound semiconductors, (ii) glass, solgel

and other oxides, and (iii) Polymers and liquid crystals.

As usual, no single material is perfect. The best scenario

may be to combine the advantages of each material

to form hybrid integrated modules and systems, where

different materials perform useful functions for which

they are eminently suited. The ability to achieve this

hinges on the availability of a wide array of materials with

novel properties. Materials research provides the foundation

for technology development that will lead to important

applications.

III-V Semiconductor Photonics

The largest material-based group is in the compound

semiconductors area, especially the III-V

group, which has about 7 academic staff and 8 research

fellows. Besides a slew of equipment for processing, the

group also operates a Metal-Organic Chemical Vapor Deposition

(MOCVD) system for the epitaxy of both GaAs

and InP-based materials.

The MOCVD

system (courtesy of

Dr Tang Xiaohong)

The primary advantage of III-V semiconductors is that

they can be used to make active optical devices such as

laser diodes with the right wavelengths for optical communication

applications. Members of the group are pur-

14 hotonics'a

suing high-power lasers, tunable lasers, modulators, and

photodetectors. In fact, so many devices can be made

from the same material that monolithic integration of all

the devices on the same substrate is in principle achievable.

Multi-wavelength laser arrays, for example, has been

achieved by using a technique called quantum-well intermixing

(QWI). Our next goal is to develop photonic integrated

circuits (PIC) that combine a broad range of active

devices with passive devices in the same chip.

Sol-Gel and Silica Photonics

Sol-gel is a colloidal suspension of gelled silica

particles. It can be chemically purified and consolidated

at high temperatures into high purity silica. The

silica can then be modified with a variety of dopants to

produce new glass properties unattainable by conventional

means. One such novel derivative is the photosensitive

hybrid sol-gel glass, which has excellent optical

properties and usually involves a single-step low temperature

fabrication process. This material has provided

a low-cost way to fabricate diffractive optical elements,

such as microlens arrays that may be used to facilitate

coupling between a waveguide array and a fibre array.

We have worked on both passive and active optical

waveguide devices over a number of years. Silica based

materials have been fabricated by the sol-gel technique.

This technique enables various oxide dopants such as

GeO2, TiO2, B2O3, Al2O3, etc. to be easily incorporated

into the SiO2 host to obtain the desired optical properties

of the materials (e.g. refractive index). Recently, the SiO2-

GeO2 system has been developed for various waveguide

based devices. The refractive index can be tailored easily

by varying the GeO2 dopant concentration. Low optical

absorption has been achieved and the technique to obtain

highly photosensitive films has also been developed.

High refractive index change upon UV exposure has been

obtained.


Polymer Photonics

Polymeric materials are broad and specific properties

can be engineered for specific applications, including

a wide bandwidth of transparency, high electrooptic

(EO) coefficients, or high thermo-optic (TO) coefficients,

making them suitable for very fast (picosecond)

switches as well as low-power, millisecond switches and

variable attenuators. Polymeric passive and active devices

can be easily integrated on any surface of interest, and

passive waveguides can be fabricated easily and at low cost

with excellent control of refractive index and geometry.

This makes polymer-based channel waveguides ideal for

board-level chip-to-chip optical interconnects, and as interlayer

dielectrics and protective overcoats.

Research on polymer and polymer photonics has been

Photonic Integrated Circuits Research

A/P Chin Mee Koy

Integrated optics, or photonic integrated circuits

(PIC), began in Bell Labs over 40 years ago, but has

only entered the industry lexicon in the last 10 years. This

is because of its emerging importance as the surest way to

reduce components cost, which forms a major portion

of systems cost. Integration reduces the number of parts

and hence the level of packaging and assembly required.

It also results in parts with smaller footprints that save

valuable space in central offices. Integrated components

tend to be more reliable and power efficient and hence cut

down operating cost. Because of these advantages, photonic

integration is considered a key to opening the floodgate

of low-cost optical subsystems that will make longterm

sustainable investment in optical networks possible.

Just as microelectronic integration has brought about the

relentless reduction in the price of IC’s, photonic integration,

likewise, can be expected to bring about similar

benefits, and ultimately give the whole industry a path to

long-term growth.

The future networks are also migrating toward alloptical

in order to eliminate the optical-electronic-optical

(O-E-O) bottleneck. Based on this evolution, the next

technology requirements are expected to be dominated

by optical switching and routing functionality, with subsystems

such as optical cross-connects (OXCs) and optical

add/drop multiplexers (OADMs) as the lynchpin

products. Many competing switching technologies are

being developed, such as micro-electromechanical systems

(MEMS), arrayed-waveguide gratings (AWG), liq-

carried out jointly in the School of Materials Engineering

and the School of Electrical and Electronic Engineering

for a number of years. A niche area is highlighted below.

Conjugated polymers are organic macromolecules with

alternating single and double bonds along the molecular

chains. The overlap of the pz orbitals gives rise to two

molecular orbitals (HOMO, LUMO) that resemble the

conduction and valence bands in semiconductors. So just

like semiconductor materials, they can conduct electricity

and in some cases, emit or absorb light. This makes

them an interesting (and indeed fascinating) class of electronic

materials to study. Conjugated polymers are strong

candidates for flat panel displays. We have demonstrated

organic LEDs (OLED) using both conjugated polymers

and molecular complexes.

uid crystals, fibre-based Mach-Zehnder, thin-films, and

fibre Bragg gratings. However, all of these switches tend

to be bulky and space-hungry and require complicated

assembly and fibre management. Next-generation product

development will need to drive down both cost and

space. These requirements provide the motif for integration

and favors technologies that are amenable to highdensity

integration.

Microphotonic integration is more challenging, and

hence much less mature, than microelectronic integration.

Partly this is due to the large diversity of photonic

devices that need to be integrated. Unlike transistors

which form the bedrock building block for all of electronics,

no photonic equivalent of transistors exists.

Figure 1: A popular commercial laser-modulator product is an

assembly of 10 or more components aligned in free space with

tedious precision. 70% or more of the cost goes into assembly and

packaging. Most of this cost could be eliminated if the laser and

modulator were integrated in a single chip.

Given the strategic significance of photonic integration,

we have formed a PIC research group to spearhead

research in this area. This will be the first such research

PHOTONIC MATERIALS & DEVICES RESEARCH September 2003 15


group in Singapore. Our goal is to develop an integration

platform - a systematic methodology for integrating

as many different devices as possible on the same chip in

a scalable, robust, and low-cost manner. “Scalable” here

means that the complexity of the process does not increase

exponentially with the number of devices; “robust

and low-cost” means that the end products will be much

more manufacturable and low-cost than current technology

can achieve. This technology, therefore, has a good

potential for commercialization.

Active Passive

Figure 2: A prototypical photonic integrated circuit consists of

active and passive device building blocks coupled via some

passive transition block (brown). The PIC is coupled to the

outside world via some coupling modules (green blocks) designed

to improve coupling efficiency with optical fibre (red). Many

PIC’s can be formed this way with a consistent architecture. Such

an integration platform is modular and hierarchical.

Quantum Well Intermixing

Ast/P Mei Ting

By integrating several discrete devices on the same

chip, Photonic Integrated Circuits (PIC) can directly

provide functional modules for optical communication

systems, thus giving more freedom and benefit to the system

designers.

Such foreseen evolution has to face many challenges,

foremost among which is the different bandgap energy

requirements for different types of devices. For example,

transparent waveguides need a material with wider

bandgap than that for the laser devices.

Quantum well intermixing (QWI) is an enabling technology

that performs the task of tuning the local bandgap

energy on an epi-wafer after the growth of the epilayers.

Compared to multiple regrowths or selective-area

growths, QWI is a relatively simple technique, involving

only a single-step growth, but capable of generating

multiple devices with different bandgaps in a single postgrowth

process.

16 hotonics'a

The PIC research group is led by Dr Chin Mee Koy,

and consists of Dr Tang Xiaohong, Dr Mei Ting, Dr Yu

Siu Fung, Dr Ng Beng Koon, all of the School of EEE, and

Dr Shu Yuan from the School of Materials Engineering

(SME). The group intends to form collaborations with local

research institutes and industry as well as universities

abroad.

Figure 3: Examples of compact building blocks: (a) multimode

interferometer and (b) micro-resonator optical filter.

For more information please send inquiries to

emkchin@ntu.edu.sg or Tel: 6790-4011.

Did You Know? The definitions of time and length rely on photonics.

The unit of time (second) is based on atomic clocks, which use lasers

to probe the structure of caesium atoms. Length is determined by the

speed of light (c), and the metre is defined as how far a light beam

travels in 1/c seconds.

Ar plasma exposure

SiO2 mask

MQW laser structure

Annealing step

Waveguide Laser

(Intermixed)

(Unintermixed)

Butt joint with perfect allignment

(a)


(b)

Figure 1: (a) the selective area ICP-QWI process; and (b) SEM

photograph of the extended-cavity laser. [1]

Prof. Mei Ting’s group in PhRC has pioneered the

research of plasma-based QWI technology and has

obtained several promising preliminary results. Using

Inductively Coupled Plasma (ICP) enhanced QWI,

we have demonstrated large bandgap energy blueshifts

(> 100 nm), selective area bandgap tuning and integration

of laser and low-loss waveguide (with losses less than

12.9 dBcm −1 ). Further study in ICP-QWI will be carried

out as part of the larger program to develop PIC.

Reference

[1] H.S. Djie, et al, “Photonic Integration using Inductively

Coupled Argon Plasma enhanced Quantum Well Intermixing”,

Electron. Lett., vol. 38, no. 25, pp. 1672-1673,

2002.

Development of High Power Laser Diode Arrays

Ast/P Tang Xiaohong

High power laser diode arrays are of great interest

because of their compact size and the numerous

applications in diode-pumped solid-state lasers,

Erbium-doped fibre amplifiers, space communication,

smart welding of metals and plastics, thermal printing

and medical treatment, etc.

In PhRC, laser diode bar arrays with optical powers in

excess of 20 watts in continuous-wave (CW) operation,

and a high slope efficiency of 1.1 W/A, have been developed.

The threshold current is about 6 A for a 19-emitter

array, and the threshold current density per device is as

low as Jth = 200 A/cm2 .

Fabrication of high power laser diode arrays involves

device design, material growth, post-growth processing,

device packaging and characterization. The materials

were grown with our own Metal-Organic Chemical

Vapour Deposition (MOCVD) system. The keys to

the success of this project are good material quality and

good packaging for thermal management, and most of all

the dedication of the research team consisting of Dr Bo

Baoxue, Dr Huang Gensheng, Dr Zhang Baolin, and

Dr Zhang Yuanchang.

Did You Know? One of the most powerful ultraviolet laser in the

world, (the 60-terawatt omega, at the Laboratory for Laser Energetics

at the University of Rochester, New York) is used to test fusion experiments.

In less than a billionth of a second, the laser sends the temperature

in a tiny pellet from just a few degrees above absolute zero

to nearly 30 million degrees Celsius—twice as hot as the core of the

sun. For this brief period of time the laser power is about 100 times the

peak power of the entire U.S. power grid.

(a)

(b)

Figure 1: (a) Laser bars in perspective (b) Laser bar under test on

a copper heatsink.

PHOTONIC MATERIALS & DEVICES RESEARCH September 2003 17


Lasing Characteristics of Nano-Rods

Ast/P Yu Siu Fung

Zinc oxide nano-rods attract special interest

for high efficiency short-wavelength optoelectronic

nanodevices, due to their large excitonic binding energy

of 60 meV and high mechanical and thermal stabilities.

Many zinc oxide nano-rods at a time can be grown vertically

on a sapphire substrate, as seen in Figure 1. The diameters

of the rods range between 60 to 90 nm and their

lengths between 1 to 2 µm. The zinc oxide nano-rods can

be fabricated by MOCVD on sapphire substrates. Our research

interest is on the investigation of the lasing mechanism

inside the nano-rod cavities, and the possibility of

using zinc oxide nano-rods for the future development of

ultraviolet optoelectronics.

Sol-Gel Materials and Their Applications

Ast/P Pita Kantisara

A sol

is a fluid colloidal suspension of solid particles

in a liquid phase where particles are sufficiently

small to remain suspended by Brownian motion, and a

gel is a solid consisting of at least two phases where three

dimensional inter-connected network solid phase entraps

and immobilizes a liquid phase [1]. Sol-gel process is

a process to produce bulk or thin film oxide materials

through the sol-gel chemistry, which involves two reactions

namely: hydrolysis and condensation reactions. The

commonly used precursors are metal alkoxides. Metal salt

solutions and other solutions containing metal complexes

can also be used as precursors. In the hydrolysis reaction,

the alkoxide materials are hydrolyzed by water to form

reactive monomers. The reactive monomers continue to

grow, through series of hydrolysis and condensation reactions,

to form three-dimensional inter-connected network

throughout the sol, which can then subsequently be

made into metal oxides gel. Various solid structures can

be obtained by applying different heat treatment. The

main advantage of the sol-gel process is the ability to

synthesis stoichiometric multi-component oxide materials

with various structures, which are very difficult or almost

impossible to achieve using other techniques. This

enables us to obtain materials with great variety of desired

properties (e.g. photosensitive, luminescent, specific op-

18 hotonics'a

Figure 1: A scanning electron micrograph shows zinc oxide

nanorods grown on a sapphire substrate. Individual nanorods,

when properly detached, can be made to lase when pumped with

355 nm light.

tical constant etc.) for various applications, especially in

photonics. The sol-gel process is also inexpensive compared

to other techniques.

In PhRC, we have used the sol-gel process to synthesize

photonic materials for waveguide based devices, low

k materials, micro-lenses and phosphor thin films.

Waveguide Devices

In our laboratory, we have worked on the sol-gel technique

for both passive and active optical waveguide devices

for a number of years. Recently, we have been developing

the SiO2-GeO2 system for waveguide based devices

such as AWG and other devices based on the materials

photosensitivity. The deposition parameters to obtain

high quality films for photonic devices have been developed

and optimized [2-4]. The refractive index can

be tailored easily by varying the GeO2 dopant concentration.

The technique to obtain photosensitive materials

has also been developed. We have obtained high refractive

index change ∆n, of about 0.01, after UV treatment.

The change in ∆n can be tailored by varying the UV treatment.

Project team: K. Pita, Ngo Quac Nam John, C H Kam,

S C Tjin, Zhang Qinyuan, Charles Ho Kin Fai, Rajni


Low k material

Porous dielectric materials are now finding applications

in high speed IC interconnects and solid state lasers.

Pores are necessary to reduce the material density and

hence the dielectric constant. In addition, pores can act

as nanometer sized receptacles for the embedding of optically

active particles. The technique we have used for

synthesis is a multi-step sol-gel process whereby two precursors

instead of one are used. One of the precursors

crosslink to form a basically linear network while the

other with a different molecular structure forms a highly

branched network. This overcomes the shrinkage problem

that commonly plagues sol-gel films. The reason is

that the precursor forming the highly branched structure

acts as a cushion and provides greater structural integrity

to the film against surface tension forces. By this approach,

a dielectric constant ∼2.5 has been obtained in

silica. This compares well with 3.9 for bulk silica.

Project Team: A/P Terence Wong.

Micro-lenses

(please refer to Modern Optics under Fibre and Laser Optics

Group)

Phosphor thin films

Various phosphor thin films have been developed for

display and lighting applications. Red, green and blue

phosphor thin films have been developed based on the

Zn2SiO4 and Y2SiO5 host materials doped with various

dopants such as Mn, Eu, Ce and Tb [5-9]. The solgel

technique has been employed to obtain stoichiometric

multi-component oxide thin films. Efficient emission

from the phosphor thin films has been obtained. Fig. 1

below shows the green emission of Mn doped Zn2SiO4

thin films for various Mn concentration under UV excitation.

Currently, Y2O3 host materials with various

dopants and co-dopants is being developed to further increase

the emission efficiency.

Project team: K. Pita, CHKam,ChongMunKit.

References

[1] C. J. Brinker, G. W. Scherer, “Sol-gel chemistry of sol-gel

processing”, Boston: Academic Press, 1990

[2] Charles K. F. Ho, Dexter C. L. Gwee, Rajni, K. Pita, Q.

N. Ngo, C. H. Kam, “Planar optical waveguides fabricated

by sol-gel derived inorganic silicate glass”, Proceedings of

11th European Conference on Integrated Optics: Prague-

Czech Republic, 1, 2-5 Apr (2003) 305-308

[3] Charles K. F. Ho, Dexter C. L. Gwee, Rajni, K. Pita, Q.

N. Ngo, C. H. Kam, “Fabrication and characterization of

optical waveguide material by the inorganic sol-gel process”,

Proceedings of Conference on the Optical Internet

& Australian Conference on Optical Fibre Technology:

Melbourne-Australia, 13–16 July (2003).

[4] Charles K. F. Ho, K. Pita, Q. N. Ngo, Q. Y. Zhang, C. H.

Kam, “Low optical absorption and high refractive index

GeO2:SiO2 films for waveguide devices by the sol-gel process”,

submitted to Journal of Non-crystalline Solids.

[5] R. Selomulya, S. Ski, K. Pita, C. H. Kam, Q. Y. Zhang and S.

Buddhudu, “Luminescence Properties of Zn2SiO4:Mn +2

Thin Films by a Sol-Gel Process”, Materials Science and

Engineering B100 (2003), 136–141

[6] Q. Y. Zhang, K. Pita and C. H. Kam, “Sol-Gel derived zinc

silicate phosphor films for full-color display applications”,

Journal of Physics and Chemistry of Solids 64 (2003), 333–

338

[7] Q. Y. Zhang, K. Pita, S. Buddhudu and C. H. Kam, “Luminescent

properties of rare-earth ion doped yttrium silicate

thin film phosphors for a full-colour display”, J. Phys. D:

Appl. Phys. 35 (2002), 3085–3090

[8] Q. Y. Zhang, K. Pita, W. Ye and W. X. Que, “Influence

of annealing atmosphere and temperature on photoluminescence

of Tb 3+ or Eu 3+ -activated zinc silicate thin film

phosphors via sol-gel method”, Chemical Physics Letters

351 (2002), 163–170

[9] Q. Y. Zhang, K. Pita, W. Ye, W. X. Que and C. H. Kam,

“Effects of composition and structure on spectral properties

of Eu 3+ -doped yttrium silicate transparent nanocrystalline

films by metallorganic decomposition method”,

Chemical Physics Letters 356 (2002), 161–167

Figure 1: Display of bright green

emission from a Zn2SiO4:Mn2

+ single layer film on SiO2/Si

wafer under a 10 watt UV source

in ambient light

PHOTONIC MATERIALS & DEVICES RESEARCH September 2003 19


Organic Light Emitting Diodes (OLED)

A/P Terence Wong Kin Shun

Organic light emitting devices are like the conventional

inorganic LEDs except that the active

layer are made from molecular thin films composed

mainly of carbon and hydrogen. This emerging optoelectronics

technology began in 1987 with the first small

molecule OLED developed at Eastman Kodak and received

a further boost with the observation of electroluminescence

in thin film conjugated polymers at Cambridge

University.

The most promising area of application for organic

electroluminescent materials is in information displays,

especially large area emissive displays and displays on

curved or flexible surfaces, which have been gaining in

importance in recent years as a result of the growth

of portable wireless devices. OLED provides a viable

medium for a sheet of light on a nonplanar substrate,

something that inorganic LED cannot achieve.

All OLEDs are based on a capacitor type structure

(fig.1). The active organic layers are sandwiched between

two electrodes one of which is transparent. Before a bias

is applied, there are no carriers within the organic layer.

The carriers must be injected from the electrodes. Within

the organic layer, the carriers-electrons and holes - meet

and form entities called excitons. When these excitons

decay, a photon is emitted.

Organic layer

ITO

glass

(anode)

Cathode

Figure 1: Schematic diagram of an OLED

Research on OLEDs at the PhRC began in 1995. The

initial effort has focused on the synthesis of molecular

complexes and conjugated polymers and the study of

their optical properties. The conjugated polymer studied

was the homopolymer polythiophene and its alkylsubstituted

derivatives. The structural, thermal and thermomechanical

properties of these polymers were studied.

20 hotonics'a

In addition, the direct patterning of the polymer films by

an ultraviolet laser was demonstrated. Discrete OLED devices

were fabricated in-house using these materials (see

Figure 2).

Figure 2: Discrete OLED with patterned emission area. Emission

color is yellow

We have worked on improving the efficiency of the devices

by incorporating charge transport layers. We have

studied the use of a mixed organic/inorganic solvent to

electropolymerize polybithiophene at low voltage, and of

an electrochemically deposited polybithiophene layer to

enhance the performance of an OLED. Chemical synthesis

of rare earth metal chelate complexes and oligomers

emitting in the blue and violet part of the spectrum, and

synthesis of conjugated polymer blends and copolymers

are other ongoing works. At present, we are collaborating

with industry to build better devices and the end goal is a

multicolor panel with possibly an active matrix driver.

N

N

N

N

DMDPQPY

N

N

N

N N N N

BMBPYEB

N N N

N

DMBPYBPY

( )

n

N

( )

n

N N

(

(

N

N N

Figure 3: Examples of conjugated oligomers synthesised

)

n

PPy

PBPy

PPyV

) PBPy

n

Did You Know? In 1964, William Bennett invented the argon-ion

laser at Yale University. In 2000 his failing eyesight was corrected with

retinal surgery using an argon-ion laser.


Liquid Crystal Devices

Ast/P Sun Xiaowei

With the recent advances in matrix liquid crystal

displays (LCD) in monitor and television (TV)

applications, most of the technical issues including poor

viewing angle and color definition have been addressed to

an acceptable level. However, the response time of LCDs

using nematic liquid crystal (tens of millisecond) is still

not sufficiently fast for video displays. Blurred edge in

moving images impede its acceptance in the television

market. We shall show here a fast response LCD with

three-electrode driving [1].

Liquid crystal (LC) has the largest birefringence

known. It can be used to fabricate various kinds of optical

devices apart from display devices. For example, it has

been used to fabricate spatial phase modulator (SLM),

optical communication devices, adaptive optical devices

and so on. In the second part, we shall show a LC spiral

phase plate that can be used to generate doughnut beam

of any charge number [2].

Fast-response hybrid-aligned nematic LC

A new, three-electrode, hybrid-aligned nematic (HAN)

liquid crystal (LC) device for fast response applications

has been developed. The three-electrode configuration

generates electric field horizontally and vertically which

alternately turn the LC cell on and off. The fast response

is realised with both the turn-on and turn-off processes

driven by an electric field. The transmission and response

time of such a LC device as a function of the rubbing angle

were studied. A total response time (rise time plus

fall time) of less than 2 ms (more than ten-time improvement

over traditional twisted nematic LC) was obtained

for a non-optimised HAN LC cell with a cell gap (i.e., separation

between the glass plates sandwiching the LC) of

6 µm. Such a device is promising for video and other applications

where fast response is required.

C

B

A

Figure 1: The alignment of the LC in the x − z plane and y − z

plane

C

B

A

Respons time (ms)

8

6

4

2

0

T_on+T_off

T_off

T_on

0 10 20 30 40

0.2

50

Rubbing Angle (Degree)

Figure 2: The response time, normalised transmittance as a

function of the rubbing angle

Liquid crystal spiral phase plates

1.0

0.8

0.6

0.4

Normalized Transmittance

Doughnut beam, a Laguerre-Gaussian (LG) beam, has

been found to contain orbital angular momentum

(OAM), which can be applied in guiding cooled atom,

optical transformation, frequency shifting and study of

optical vortices. To fully explore the potential of LC, LC

spiral phase plates with cell gaps of 7 µm, 20 µm and

30 µm have been fabricated and used to generate doughnut

beams. By stacking these liquid crystal spiral phase

plates, doughnut beams with any charge number (i.e., the

number of 2π phase change across the beam) can be obtained.

High efficiency and flexibility are the advantages

of generating doughnut beams by stacking liquid crystal

spiral phase plates [2].

For more information please refer to:

[1] C.Y. Xiang, J.X. Guo, X.W. Sun, X.J. Yin and G.J.

Qi, “A Fast Response, Three-Electrode Liquid Crystal

Device”, Jpn. J. Appl. Phys. 42, L763 -L765 (2003).

[2] Q. Wang, X.W. Sun and P. Shum, “Generating

doughnut beam with any charge number by liquid

crystal spiral phase plates”, Appl. Opt. (accepted).

article continued on page 27. . .

PHOTONIC MATERIALS & DEVICES RESEARCH September 2003 21


FEATURE

ARTICLE

Thermal Imaging

Fu Chit Yaw, Eddie Tan Khay Ming, Yang Kwang Wei

During the SARS epidemic, thermal imaging camera has become almost a household name. Just how does it work and how reliable is

it? The authors explain, and provide some suggestions for improvement.

Thermal infrared (IR) imaging is commonly used for

night vision. During the recent SARS epidemic, thermal

imaging cameras were used for fast and non-contact measurement

of a person’s temperature to determining if the

person has a fever [1]. In many medical cases, temperature

rise or abnormal distribution of temperature may

appear as one of the first symptoms. Therefore, thermal

imaging is also a useful complementary clinical tool to aid

in the diagnosis of other medical condition, most notably

breast cancer (see Ref. 2 for more details).

Let’s first explore how thermal imaging works [3]:

Figure 1: Image courtesy of Infrared, Inc.

1. The focused light is scanned by a phased array of

infrared-detector elements. The detector elements

create a very detailed temperature pattern called a

thermograph. It only takes about one-thirtieth of

a second for the detector array to obtain the temperature

information to make the thermograph.

This information is obtained from several thousand

points in the field of view of the detector array.

22 hotonics'a

2. The thermograph created by the detector elements

is translated into electric impulses.

3. The impulses are sent to a signal-processing unit,

a circuit board with a dedicated chip that translates

the information from the elements into data for the

display.

4. The signal-processing unit sends the information

to the display, where it appears as various colors depending

on the intensity of the infrared emission.

The combination of all the impulses from all of the

elements creates the image.

A thermograph of a human face, taken by one of the authors

(Joel Yang) is shown in Fig. 2 [4].

Figure 2: A thermograph of a human face take by a commercial

IR camera [courtesy Photonitech Pte Ltd., Singapore]


Now let’s take a look at the physics behind thermal

imaging.

Infrared Radiation

According to the Planck’s Law (as shown in Fig. 3), the

radiation of an object is determined by the object temperature.

A room-temperature object radiates at the peak

in the wavelength range of 7–14 microns, which is called

long-wave infrared (lwir) waveband. For high temperature

(∼ several hundred ◦ C ) object, the radiation peak

not only rises but also shifts to shorter wavelength, e.g.

the mid-wave infrared (mwir) waveband 3–5 microns).

The Stefan-Boltzmann Law relates the total radiant intensity

I (over the whole frequency range) of a blackbody

with temperature T by I = σT 4 ,whereσ is the Stefan-

Boltzamann constant (5.67 × 10 −8 Wm −2 K −4 ). Therefore,

in principle, the temperature of an object can be determined

from the radiation emitted by the object integrated

over all wavelengths. However, the Planck’s Law

describes the radiation from an ideal object with unity

coefficient of emissivity, the so-called blackbody. Real objects,

however, will emit less radiation as the emissivity

is less than unity. For example, the emissivity of human

body is commonly accepted as 0.95. One can determine

the nominal temperature from the measured radiation by

assuming the real body as a blackbody, but the emissivity

has to be known in order to determine the actual temperature.

Power Exitance [W/(cm 2 ·s·µm)]

0.1

0.08

0.06

0.04

0.02

600 K

500 K

400 K

300 K

0 5 10 15 20

Wavelength (µm)

Figure 3: Planck’s blackbody radiation law

Bolometer—the sensor of the thermal

imager [5]

There are two fundamental types of infrared detectors -

thermal detectors and photon detectors. In photon de-

tectors, photo-carriers are generated by absorbing the infrared

photons and the electric signal is proportional to

the number of the received photons. These detectors may

operate in photoconductive, photovoltaic, or photoelectromagnetic

modes. Because the infrared photon energy

(∼ 0.1 eV) is very small, narrow bandgap materials, such

as InSb, PbSnTe and HgCdTe, or multiple quantum wells

have to be used for infrared detection. In order to suppress

the current leakage due to thermionic emission, the

detectors have to work inside a cryogenic cooling system

which is bulky, costly and cumbersome to use.

In thermal detectors, the infrared radiation interacts

with the lattice of material and changes the material

temperature, which is subsequently converted to a measurable

electrical quantity. The electric signal is proportional

to the radiation power. Typical thermal detectors

are thermistors, thermocouples, and pyroelectric/ferroelectric

detectors. The thermal imagers in the

market today use the resistive microbolometer, where a

membrane, thermally isolated from the substrate, is used

to obtain a high temperature rise in response to the incoming

radiation, and an embedded temperature sensitive

resistor subsequently transfer the temperature deviation

into electric signal. A material with large temperature

coefficient of resistivity (tcr) is used to enhance the

sensitivity of the bolometer.

The most promising benefit of thermal detectors is

their ability to operate near room temperature (or an uncooled

environment), where only a temperature stabilizer

(i.e. thermo-electric cooler, tec) is needed rather

than the more complicated cryogenic cooling system,

thus lowering costs and increasing reliability. A commercial

imager uses an array of microbolometers, called Uncooled

Imaging Array, and a Germanium lens to focus the

IR radiation from the target object onto the sensors.

How accurate can an IR detector

measure body temperature?

This question has been raised in response to the rather

controversial claims made by some companies about the

accuracy of the imagers they are marketing. We asked our

expert, Prof Mei Ting, a member of PhRC, who has this

to say:

In thermal imaging cameras, the object temperature is

not measured directly, but indirectly through the IR radiation

incident on the detector in the imager. This received

radiation is determined not only by the object temperature,

but also by several other factors.

THERMAL IMAGING September 2003 23


The surface emissivity of the object being imaged is

the biggest unknown affecting infrared thermal measurements.

At present there is no model to describe the precise

relation between the skin temperature and the body

temperature. The practical way of correction is just to

setanoffset, say 0.5 ◦ C. Further work has to be done

to explore this issue for the thermal camera in SARS application.

The emissivity should be determined for each

specific measurement situation.

Other factors that can introduce uncertainties are ambient

temperature, atmospheric transmittances, path radiance,

as well as the intrinsic non-linearities of the

instrument’s electronics. Remote infrared calibration

sources placed in the detection plane can help to suppress

the uncertainty from environment.

Typical radiometric system has a radiometric accuracy

of 2%, which corresponds to a temperature accuracy

±2 ◦ C for a detection range of −20 ∼ 500 ◦ C. Since human

skin temperature varies in a small range, narrowing

down the detection range (i.e. 0 ∼ 40 ◦ C) greatly reduces

the instrument errors. Now, many infrared cameras manufacturers

are able to achieve ±0.2 ◦ Cwithadetection

rangeof0− 40 ◦ C with the above improvements.

References

[1] R.James Seffrein, “Thermal Imaging for Detecting

Potential SARS Infection”.

Photonics Research Centre Seminars in 2003

Date Speaker Topic

[2] Maxtech International Inc., http://www.maxtechintl.com/infrar.htm

[3] http://www.howstuffworks.com/nightvision.htm

[4] Joel Yang from Network Research Centre (NTRC) is

currently working on a project in collaboration with

Photonitech Pte Ltd., Singapore.

[5] A. Rogashki, “Infrared Photon Detectors”, Bellingham,

Washington: SPIE Optical Engineering Press,

c1995.

[6] P. W. Kruse, “Principles of Uncooled Infrared Focal

Plane Arrays” in Semiconductors and Semimetals, vol.

47: Uncooled Infrared Imaging Arrays and Systems

ed by P.W. Kruse and D.D. Skatrud, pp. 17–42, San

Diego: Academic Press, c1997.

[7] John Wallace and Kathy Kincade, “Infrared

cameras find hot spots in nuclear

reactor”, Laser Focus World, July 2003.

(http://lfw.pennnet.com/Articles/Article_Display.cfm?

Section=ARTCL&ARTICLE_ID=182133&VERSION

_NUM=1)

24 January A/P Chin Mee Koy Photonic Integrated Circuits

7March Ast/P Yu Siu Fung Modeling of Optoelectronics Devices - Past, Present and Future

24 March Prof. Paul French

Imperial College, U.K.

Time-resolved Fluorescence Microscopy

24 March Prof. Kenny Weir

Imperial College, U.K.

Fibre Optic Sensors

4April Ast/P Ricky Ang Lay Kee Intense Beam Interaction with Surrounding Structures

25 April Ast/P John Ngo Quoc Nam Electrically tunable dispersion compensator with fixed center

wavelength using fiber Bragg grating

5 June Ast/P Pita Kantisara Electrochromic Materials and Devices

13 August Dr. Chye Yew Hee

Ferromagnetic/Semiconductor Hybrid Structures for Spin Ma-

IMRE, Singapore

nipulation

18 August Dr. Zhu Furong

Low temperature transparent conducting oxide for flexible or-

IMRE, Singapore

ganic light emitting devices

20 August Ast/P Rajesh Menon Zone-Plate-Array Lithography (ZPAL):A novel approach to maskless

nanolithography

8SeptemberDr Han Mingyong

IMRE, Singapore

TBD

24 hotonics'a


FEATURE

ARTICLE

Optical Tweezers

Lee Woei Ming, Zhang Dianwen, Tao Shaohua and Yuan Xiaocong

In nature, light from the Sun provides plants with the

means of making food, and hence energy that sustains

the cycle of life on Earth. In science, light from

laser beams is providing biologists with a new means of

studying the intricate details and functions within single

living cells. It has become a tool to discover life itself.

Laser beams used to trap and manipulate microscopic

particles are called optical tweezers. The first optical

tweezer was demonstrated by Dr Arthur Ashkin [1] and

co-workers in the 1980s at Bell Labs. They demonstrated

that light can move matter because photons carry linear

momentum (a photon of wavelength λ has a momentum

p = hc/λ, where h is the Planck’s constant, and c

is the speed of light). In their experiment, a highly focused

Gaussian beam was used to create an optical gradient

force on a particle with a higher refractive index

than the surrounding medium. As light refracts when it

passes through the micro-objects, the refraction of light

will cause a change in the photon linear momentum, and

due to the conservation of momentum, a force will result

which acts on the particle in the opposite direction. This

force is directed towards the area of the highest intensity;

hence the particle is trapped in the center of the beam.

Figure 1: 1st type of optical tweezers

Another type of optical tweezer is based on the orbital

angular momentum property of a Laguerre-Gaussian

(LG) beam, TEM∗ 0l , also known as an optical vortex [2].

In this case, the particles are trapped in the region of zero

intensity at the center of the LG beam [see Fig. 2]. The

optical traps created by the helical LG beams of light (due

to a phase singularity) can also exert optical torques on

the trapped objects. The special intensity profiles of these

beams are created by engineering the phase of the laser

beam’s wavefront.

Figure 2: 2nd type of optical tweezers

Figure 3: Irregular shaped optical tweezers

In NTU, we have begun a research project on optical

tweezers only in the past year. Our initial focus is to build

a strong foundation for the fundamental understanding

of optical tweezers. At the moment, we are able to generate

irregular shaped beams to be used as a new form

OPTICAL TWEEZERS September 2003 25


of optical tweezer [4] [see Fig.3]. These irregular shaped

beams have patterns of dark zones in their cross sections

due to an asymmetric spiral phase. It is possible to generate

tight optical trapping by matching the intensity distribution

with the objects to be trapped.

In addition, we have also created a new version of optical

tweezers with multiple optical forces [5]. The basic

theory behind the multiple-force optical tweezers is

that when two LG beams with opposite and unequal order

of helicity interfere, the resulting beam will appear in

the form of bright invariant spots arranged in a circular

manner. This resulting beam may allow effective stacking

of micro-particles and the creation of 3-dimensional

structures at each of the bright spots (as demonstrated

by Dhlokia [6]), while still being able to transfer orbital

angular momentum, something which was not possible

before.

The multiple force optical tweezers will be a new optical

tool used for the simultaneous angular deformation

of cell structures. Furthermore, by being able to create

3-dimensional objects, it may be used to create photonic

crystals as well. The novel double hologram set-up

[see Fig. 4] that is used to generate the multiple optical

tweezers can be easily transformed into an attachable

laser module system. This will be much more feasible

than using an expensive SLM or a conventional interferometer.

Such a system is being built in our laboratory [see

Fig.5].

Figure 4: The double hologram set-up.

26 hotonics'a

Figure 5: Optical trapping experiment

Potential Applications of Optical

Tweezers

Optical tweezers clearly have many applications in life

and medical sciences. A 1994 study by the U.S. National

Academy of Sciences placed high priority on research into

highly promising new technologies for the control and

manipulation of atoms, molecules, charged particles and

light. The report also predicted that the “optical tweezers

are likely to be invaluable in the Human Genome Project”.

Recently in March’02, Optics Report identified three

additional industries that laser tweezers will have impact

on. These include the $3 billion fertility market, the 100

million electrophoresis (molecular separation) market,

and the micro-machine market expected to reach $100

billion in the next decade.

In in-vitro fertilization, optical tweezers can be used

to assist sperms in swimming towards the eggs, instead

of being surgically inserted which may cause damage to

both sperm and egg. In the study of how viral DNA infects

cells of other organisms, researchers were able to use

optical tweezers to study how the viral DNA infects a living

cell. Better design of drugs to interfere with the viral

DNA packing and new gene therapies may be made possible

by transporting new genetic materials into the cells

using optical tweezers.


References

[1] Ashkin, A., Dziedzic, J. M., Bjorkholm, J. E. and Chu,

S.,“Observation of a single-beam gradient force optical

trap for dielectric particles”, Opt. Lett. 11, 288-

290 (1986).

[2] He, H., Friese, M. E. J., Heckenberg, N. R.

and Rubinsztein-Dunlop, H. “Direct observation of

transfer of angular momentum to absorptive particles

from a laser beam with a phase singularity,”, Phys.

Rev. Lett. 75, 826-829 (1995).

[3] V. Garcés-Chávez, D. McGloin, H. Melville, W. Sibbett

and K. Dholakia, “Simultaneous micromanipu-

continued from page 21. . .

lation in multiple planes using a self-reconstructing

light beam”, Nature 419, 145 (2002).

[4] D. W. Zhang and X.-C. Yuan, “Novel optical doughnut

for optical tweezers”, Optics Letters (USA), Vol.

28, p. 740-742, (2003).

[5] W. M. Lee, X.-C. Yuan and D. Y. Tang, “Optical

tweezers with multiple optical forces using double

hologram interference”, Optics Express (USA), Vol.

11, p. 199-207, (2003).

[6] M.P Macdonald, L Paterson, K Volksepulveda, J.Arlt,

W. Sibbett, K Dohlakia, “Creation and Manipulation

of three dimensional optically trapped structure”,

Science 296, 1101 (2002).

(b)

(a)

Figure 6: (a) Photograph of the LC spiral phase plate and (b) The doughnut beams with charges 1, 2 and 3 generated

(top) and the corresponding simulated doughnut beams (bottom)

Figure 7: Demonstration of a rotating fan-like interference pattern (vortex) generated by the inference of a doughnut

beam with charge 3 and a Gaussian beam.

OPTICAL TWEEZERS September 2003 27


NEWS

BRIEF

Physicists Produce Photons Ideal for

Quantum Networking

Compiled by Zhao JingHua

Advances in Photonics Around the World

Physicists at the Max Planck

Institute for Quantum Optics

in Garching, Germany,

have used a rubidium atom

that was strongly coupled

to a high-finesse optical

cavity (above) to produce,

on demand, a sequence of

single photons with welldefined

and identical properties.

The photons are created

by an adiabatically driven stimulated Raman transition

between two atomic ground states. This process is performed

in a unitary way and is therefore reversible, which

the researchers say makes it ideal for sending and receiving

single photon states within a quantum-computing network.

The group described the process in the Aug. 5 issue

of Physical Review Letters.

Electrical pulses break light speed

Pulses that travel faster than light have been sent over a significant

distance for the first time. Alain Hache and Louis

Poirier of the University of Moncton in Canada transmitted

the pulses through a 120-metre cable made from a coaxial

“photonic crystal”. To create their cable, the Canadian

researchers joined together five-metre sections of coaxial

cable with alternating electrical impedance. They sent

electromagnetic pulses with frequencies between 5 and

15 MHz through the cable, and found that the group velocity

reached 3 times the speed of light for frequencies

in the absorption band. This was remarkable in comparison

with many existing information systems that are based

on coaxial cables with data speed of just two-thirds the

speed of light. The achievement that utilized the backreflection

caused by impedance mismatch raise hopes that

data could travel through electronic communications systems

at almost the speed of light.

A Hache and L Poirier 2002 Appl. Phys. Lett. 80 518

A breakthrough in teleportation

When physicists teleported photons for the first time in

1997, they had to destroy the photons to be sure that the

teleportation had been successful. Now a team at the University

of Vienna has managed to teleport photons without

destroying them. Jian-Wei Pan and colleagues believe

that their method could be the next step towards longdistance

quantum communication. In a standard telepor-

28 hotonics'a

tation experiment, a laser is directed at a crystal with nonlinear

optical properties. Occasionally the photon will

be “down-converted” into two lower energy photons, and

sometimes these photons will have their polarizations entangled

wherein one of them is vertically and the other

horizontally polarised. By using a filter to reduce the intensity

of the photons that are going to be teleported, the

researchers were able to significantly reduce the number

of spurious detection events. The Vienna team could be

97% certain that the state had been teleported to a photon

without actually having to detect it. Such a high accuracy

means that the teleported photons could be used

in “quantum repeaters” for long distance communication.

The team now hopes to combine these results with a technique

known as entanglement purification to further develop

quantum communication over long distances. (J -.W

Pan et. al. ,Nature, 421 721, 2003).

Laser takes up gene therapy

Scientists in Germany have used a Ti:sapphire laser to

transfer DNA into a cell. Femtosecond lasers improve the

transfer of DNA into cells and could advance the fields

of gene therapy and DNA vaccination, according to Uday

Tirlapur and Karsten König of Friedrich Schiller University

in Jena.

U. Tirlapur and K. König, Nature, 418 290

See-Through Thin-Film Transistor

Unveiled

Transparent electronics may

seem the stuff of science

fiction, but engineers from

Oregon State University and

Hewlett-Packard Co. in

Corvallis, Ore., have developed

zinc-oxide-based thinfilm

transistors that they hope

will find applications in liquid

crystal displays and elsewhere.

They reported the devices,

which display optical

transmission in the visible portion of the electromagnetic

spectrum of approximately 75 percent, in the Feb. 3 issue

of Applied Physics Letters.

The team fabricates the N-type semiconductor devices

by depositing a layer of indium tin oxide and aluminium

titanium oxide on a glass substrate. The zinc-oxide channel

and indium-tin-oxide source and drain electrodes are

subsequently added to the stack by ion-beam sputtering.


S tudent

ACTIVITIES

Making presentations work:

National Lecture Competition

Charles K. F. Ho

3rd price overall: Development of optical materials

by the sol-gel process

Competition Organizers: Institute of Minerals, Metals

and Materials, UK and Institute of Materials, East

Asia, Singapore

Flashback: March 2003 – South-east Asia Regional

Competition in NTU, Singapore.

Now the Finals, London, UK

Taking the london tube to the venue on the East

End, I really felt that I could not have been more

prepared (with all the first year presentation trials,

onfig progress report and the regional qualifier presentation).

Upon arrival, I found myself submerged in a

crowd of academic and industry representatives from the

world of material science. Like everyone else, I was overwhelmed

by the unique ambience and the interior decoration

of the building (see photos). It was full of medieval

armour suits, which gave me shivers down my spine. Just

can’t help the thought that these suits might be haunted

by their owners. Furthermore, the Master of the Worshipful

Company of Armourers and Brasiers (the main corporate

sponsor and they make armours!), indicated that this

very same building dates back all the way to the 1600s. It

survived the ‘Great London Fire’ in 1666 and ‘The Blitz’

during wwii. This just helped to feed my imagination

about these armours jumping down from the wall!

With all the opening addresses, the finals officially

kicked off with the first contestant taking the stage.

Scrolling down the program, I found that I was the only

oversea representative. So it was me versus the entire

United Kingdom! WOW, it could be rough. Then I

thought to myself with some pride...it did somewhat

made sense for me to represent the overseas region as I

was born in Hong Kong, studied in UK, moved to Canada

and now studying in a Singapore University. These countries

represent a good portion of the commonwealth!

The presentations of the other finalists from different

regions of the UK covered a broad spectrum of applications:

biomaterials, instrumentation, composite materials,

materials simulation, making of bells, etc. They were

all entertaining and informative in their own way. Soon,

it was my turn to educate the audience about materials in

photonics. Taking a deep breath, I cracked a joke with the

crowd, and I was 15 mins away from the hope that all my

extravagant expenditure in London could be covered by

the prize money. I started my timer...The presentation

was so well rehearsed that I was actually finished with one

minute to go! It took me about 10 seconds to bring myself

to believe my stopwatch and another 10 to figure out

what to say to make the most out of the remaining 40 s.

And then I said my grace and took my next breath!

After a delicious buffet dinner, the long awaited moment

arrived. VIPs assembled on the stage. The announcement

came with me taking the third place overall.

Well, I really didn’t mind to hear my name a few

more minutes later (when they announced the 2nd and

NATIONAL LECTURE COMPETITION 2003 September 2003 29


1st place). Anyway, I realized soon after that the most precious

gift from the competition was not the prize money,

but the recognition. VIPs and other attendees then came

to extend their congratulations. For those who could appreciate

my work, they even offered me employment and

collaboration in the future. This, I think, is pretty priceless.

On the whole, I feel that I had put on an impressive

performance and established a respectable image for ntu

and Singapore. Mission Accomplished!

Publishing our work in renowned journals or magazines

is of course the big thing in research. However, I

would like to encourage my colleagues to be aware of all

the opportunities around you. You maybe able to submit

Benjamin Tay Chia Meng

The very first social gathering under the aegis of Photonics

Research Center (PhRC) was held earlier this year at

Yunnan Corner, NTU. 80% of the lecturers, staff, technicians

and postgraduate students attended this momentous

event which was packed with games, prizes, food

and loads of fun. Everyone got to mix over drinks

and games, a pleasant respite from laboratories and lecture

classes...The Guest of Honour was our Head of the

Microelectronics Division, A/Prof Tan Ooi Kiang, and

30 hotonics'a

your work to competitions, awards and scholarships held

by institutes and professional societies. With a little luck,

youmaybeabletogoalongway.

At last, I would like to give credits to my two supervisors

(Asst. Prof. Ngo Quoc Nam and Asst. Prof. Kantisara

Pita) for their generous and effective guidance. And I

must complement the Admin team in the School of eee,

on the First Year Evaluation process for research students.

It has ultimately contributed to the success of my showing

at this competition.

For details on this competition, please see the following

link: http://www.iom3.org/students/competitions.htm

the Chairman of the event was the Director of PhRC,

A/Prof Tjin Swee Chuan. They kicked off the event by

revealing some of the hard work behind the scene that

paved the road to the establishment of the PhRC. Dr Tjin

reported the future plans for the Centre, including research

collaborations with Imperial College (U.K.) and

Thales Training Centre (Singapore). The logo for the

Centre, selected from a pool of entries, was then unveiled

for the first time.


Congratulations to Hery Djie who designed the winning

logo!

After a refreshing international lunch buffet, the guests

were treated to an audio-visual delight presented by the

Photonics Production team. The video drama covered

the different facets and faces of our Labs with a bit of sitcom

to spice things up. The film is a tribute to all the

members of the Centre and a reminder that as a team,

nothing is impossible. Then we ‘excited’ our guests into

motion through a series of games like “Lossy Waveguides”

in which contestants had to finish a drink using

straws with holes in them. A difficult task, indeed, be-

sides the mess. Other games include “Who wants to be

a MUUUMMMMIE” in which the contestants raced to

wrap a MUMMY in toilet paper, and also “Optical Message

Transmission”, where members of a group try their

hands at charades.

The climax of the event was marked by the exotic Indian

dance performed by members of the Centre drawn

from various nationalities, who gave their best to show

the audience the nifty footwork and choreography that

made up traditional Indian dances. The event closed with

prize presentation to the winners of the games and lucky

draws. A fruit cake topped with Snow White and the

Seven Dwarfs figurines and a single candle was cut to celebrate

of the fresh start of Photonics Research Group as

a research Centre. At the end of the day, everyone took

something home, some good laughs, a full stomach, some

prizes and best of all good times with friends, colleagues

and professors.

Thanks to all the volunteers who had contributed their

time and effort in planning the event and making it come

true. It would not be as successful were it not for the enthusiasm

and creativity of the organizers. You know who

you are!

PHOTONICS GATHERING 2003 September 2003 31


Some pictures from the gathering

32 hotonics'a

The Event Organizing Team.

In case you haven’t notice,

we are getting bigger!

Enjoying the buffet lunch.

The game is about to begin!

P

h

otonics

G

2

0

0

3

a

t

h

e

r

i

n

g

Everybody is having a good time.

Prof. Tjin and his rendition

of the Hare & Turtle race.

Indian food, anyone?

“Dandiya”, or dance with sticks,

performed by a group of PhD students.


Announcements

New Faces

The Centre welcomes the following staff and students

whojoinedusrecently.

• Staffs

– Asst/P Julian Chan Chi Chiu

– Asst/P Rajesh Menon

– Dr Tamil Selvan, January 2003

– Dr Wu Jiu Hui, February 2003

– Dr Rudi Irawan, March 2003

– Muhammad Fueyz Karim, March 2003

– Dr Li He Ping, April 2003

– Chen Qing, June 2003

– Moh Ken-Jin, June 2003

• PhD students

– Zhao JingHua, January 2003

– Fu Chit Yaw, February 2003

– Balpreet Singh Ahluwalia, March 2003

• MEng students

MOU

– Yu Jia, January 2003

A Memorandum of Understanding (MOU) has been

signed between NTU (School of EEE), Institut d’Optique

(France) and Thales Research and Technology (France).

The purpose of the MOU is to promote closer relations

and exchanges in the fields of signal and image processing,

optics, telecommunications, microelectronics and

nanophotonics.

Professor André Ducasse, Director Général from Institut

d’Optique, Mr Dominique Vernay, Thales Technical

Director, Mr Patrick Plante, Director of Thales Singapore

and Professor Er Meng Hwa, Dean of School of EEE,

NTU, signed the MOU on July 2003, bringing into existence

a collaboration between the institutions which will

bring research to new heights.

Events which are covered in the MOU includes:

• The exchange of teaching and research staff between

the parties

• The exchange of information on academic and research

programmes available in each institution

• The formation research teams on subjects of common

interest

• To welcome undergraduates, Posgraduate students

and Post doctoral fellows in appropriate programs,

both current and future

• To encourage mutual participation in conferences,

seminars and courses organized by each institution

Good News

Lipi Mohanty has given birth to a baby girl on 17th July.

She is healthy and weight in at 3.7kg! Best wishes from all

of us.

Upcoming Photonic Conferences

IOOC 2003 14th International Conference on Integrated

Optics and Optical Fibre Communication.

September 21–25, 2003. Rimini, Italy

http://www.ecoc.it/

LEOS 2003 16th Annual Meeting of the IEEE

Lasers & Electro-Optics Society. October

26–30, 2003. Tucson, Arizona

http://www.ieee.org/organizations/society/leos/

LEOSCONF/LEOS2003/LEOS03.htm

ICMAT 2003 International Conference on Materials

for Advanced Technologies. December 7–12, 2003.

Singapore http://www.mrs.org.sg/icmat2003/

CLEO/Pacific Rim 2003 The 5th Pacific Rim

Conference on Lasers and Electro-Optics.

December 15-19, 2003. Taipei, Taiwan

http://cc.ee.ntu.edu.tw/˜cpr2003/

Did You Know? The vibrant colours on many butterflies are not due to

pigments (i.e. biochemistry) but optical diffraction (photonics) caused

by the physical structure of the wing surface. An aquatic creature

called a sea mouse produces iridescent colours using hairs with arrays

of microscopic holes, creating what is known as a photonic band gap.

Natural structures such as these are being studied for their application

to photonic devices.

PHOTONICS GATHERING 2003 September 2003 33


A message from the Editor

It is definitely an exciting time for us at the PhRC in Singapore.

As a PhD student myself, it is most certainly a

benefit for us to have the Centre gaining more exposure.

And this was the vision that Lee Woei Ming saw early on

this year: an e-magazine to promote our work in photonics

both at home in Singapore and abroad. True to

our passion, we swiftly put together an editorial team and

made this publication a reality in a short time span of a

few months. As much as this issue of Photonics ’La marks

the first year of the PhRC, it is the first time for many of

the student editors participating in an editorial team of a

scientific literature. I would like to take this opportunity

to acknowledge all my colleagues who shared the same

vision as Steve and sacrificed their own time to help kick

start this inaugural issue. In particular, our layout/design

guru, Chrisada, has become the backbone of our production

team in this special issue. He had contributed im-

Advisor’s Memo

hotonics'a —what a feisty name! It is a name that

conjures up many images—for me, the vigour of Latin

dances and romance on a Caribbean beach. . .

What is Photonics? Simply put, it is the knowledge that

revolves around the Photon, the particle of Light, just as

Electronics is the knowledge around the Electron, the unit

of electric charge.

If this seems abstract, think of the first moment in your

life, when you opened your eyes for the first time, and

were greeted with dazzling brightness and images...Such

were the first gifts of Light! Without light from the sun,

Life as we know it would be impossible.

The study of light and its interaction with matter led

to a special form of light not found in nature, the Laser,

which in turn led to a myriad form of applications. Advances

in the technology for harnessing the power of

light continue unabated. Discoveries are constantly being

made in the laboratories worldwide.

Some of these discoveries are being made here in

NTU’s Photonics Research Centre, as you will find out

in these pages.

In Biophotonics, optical tweezers for manipulating

DNA, and femtosecond optical pulses for taking snapshots

of the molecules, are exciting examples of how light

may be used to understand life itself.

In this information age, light is the superhighway in

which information flows without friction. New fibre-

34 hotonics'a

mensely to the uniqueness of our publication with his

personal touches from the front to the back cover. And

most of all, we salute our faculty advisors Assoc. Profs.

Chin Mee Koy and Tjin Swee Chuan for their tremendous

effort in enlightening us with their invaluable suggestions

and editorial assistance.

In the future, we hope to involve a bigger team of students

and staff alike to put together an even bigger feast of

good articles, both technically and visually. If you would

like to experience the thrill of editing future issues of

hotonics'a , or to contribute in any other way, please

feel free to email us at phrc@ntu.edu.sg.

Let’s enjoy Photonics’La!

Charles K.F. Ho

Editor-in-chief

optic components and high-speed optical devices are

constantly being invented to push the limits of optical

communication.

Started 10 years ago, the Photonics Laboratory has matured

into a research center with some renown and a

wide range of activities, attracting some of the best students

from the region and producing graduates who have

helped to build a nascent photonics industry in Singapore.

This inaugural issue of Photonics’La is an appropriate

and timely vehicle to mark the 10th year milestone, and

to commemorate the inauguration of the research group

asaCentre.

In addition, the special collectible edition provides useful

information on the research and teaching activities

within the Centre for our sponsors, collaborators, supporters,

and the public at large.

The idea for the newsletter and its name was conceived

by a group of enthusiastic students. As their faculty advisor,

I applaud the zest and creativity with which they have

brought to the editorial process. I also wish to acknowledge

my colleagues for contributing the many research articles

for this special issue. Thanks!

Vive Le Photonics!

A/P Chin Mee Koy

Faculty Advisor


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Editorial Team

Contact us at phrc@ntu.edu.sg

Editor-in-chief Charles K. F. Ho

Technical advisors

Assoc. Prof. Chin Mee Koy

Assoc. Prof. Tjin Swee Chuan

Editor Benjamin Tay

Writers/Reporters Fu Chit Yaw,

Zhao Jing Hua, Chong Mun Kit

Eddie Tan Khay Ming

Layout/Design Chrisada Sookdhis

Graphics Designer Steve Lee Woei Ming

Photographer Eddie Tan Khay Ming

Public Relations Joanne Huang

Supporting staff Hery Djie,

Jesudoss Arokiaraj, Zhang Xu Ming

Treasurer Yong Kim Lam

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