Refraction and Optical Fibres

Dr Murray ThompsonUniversity Senior CollegeMurray.thompson@adelaide.edu.au

Prof Tanya MonroCentre of Expertise in Photonicstanya.monro@adelaide.edu.au

“This material has been developed as a part of the Australian School Innovation in Science, Technology and Mathematics Project funded by the Australian Government Department of Education, Science and Training as a part of the Boosting Innovation in Science, Technology and Mathematics Teaching (BISTMT) Programme.”

Refraction and Optical Fibres

•When light travels from one medium to another it changes speed.

•It also changes direction.

Refraction and Optical Fibres

Refraction• From a fast medium to a slow

medium, the light bends towards the normal.

Slow mediumeg glass

Fast medium eg air

normal

Angle ofIncidence i

Angle ofRefraction R

Partially reflected beam

Refraction• From a slow medium to a fast medium, the

light bends away from the normal.

Slow mediumeg glass

Fast medium eg air

normal

Angle ofIncidence i

Angle of Refraction R

Partially reflected beam

Snell’s Law of Refraction

which is the refractive index from medium 1 to medium 2.

1 21 2

2 1

sin

sin

v nin

R v n

Normal

Angle of incidence i

Angle of refraction R

Refraction towards the normal

Normal

Angle of incidence i

Angle of refraction R

Refraction away fromnormal

Refraction away from normal

Total Internal Reflection

• When the light goes from slow to fast, as the angle of incidence is increased, the angle of refraction increases as well, until it reaches 90.

• The angle of incidence when this happens is called the “critical angle.”

• Fast medium eg air

Slow mediumeg glass

Fast medium eg air

normal

Angle of refraction = 90º

Critical angle ic

Refracted beam

Partially reflected beam

Total Internal Reflection – Critical Angle

Total Internal Reflection• Beyond the critical angle, no refraction

is possible and the light is said to ‘totally internally reflect.’

Total Internal Reflection

• No refraction is possible beyond the critical angle.

Slow mediumeg glass

Fast medium eg air

normal

Angle ofIncidence iGreater than ic

Below the critical angle

At the critical angle

Note the reflected ray

Note the refracted ray at grazing angle – colour dispersion

Beyond the critical angle

Total internal reflection.

Total Internal Reflection

Snell’s law:

2

1

1

2

sin

sin

n

nqc

Water (n=1.3)

Air (n=1.0)

Guiding Light

• Need to guide light to communicate optically between points

• First observation of light guiding made by John Tyndall

• Based on total internal reflection

Optical fibres for structural strain

sensing

Compact tunable lasers for optical

telecommunications

Sea mice use photonic crystal effects to warn

off predators

Photonics is EverywherePhotonics is the science of the photon, the fundamental

particle of light.

Optical Fibres Beyond Telecommunications

• Optical fibres can also have applications in:– Medicine– Biological and genetics research– Defence– Industrial materials processing– Chemical and pollution sensing– Next generation lasers– Optical data processing– Transmitting light beyond the near-IR

• And so new types of optical fibres are needed…

Microstructured Optical Fibres

fibres with micron-scale transverse features

Why Microstructure?• Engineering materials on the scale of the

wavelength of light can lead to materials with new optical properties

• Using air as the cladding of an optical fibre means that fibres can be made from a single material

• Light can be used to probe the properties of materials located within the air holes

• Here at Adelaide University, we are setting up facilities to develop a whole new class of optical fibres – soft glass microstructured optical fibres

Materials Development

Basic glass

melting facilities

Advanced glass development &

processing

Overview of Fibre Activities at Adelaide University

Preform Manufacture

Extrusion

ORCasting

Make preform with mm-scale structure

Fibre DesignSoftware

Device ConceptDevelopmentCapabilities

Fibre Test &CharacterisationEquipment

Draw TowerPreform Fibre

Extrusion

Stainless steel

die

OD=29mmh=34mm

glass billet

Structured glass preform

Extrusion – Preform Variety

• Structured preforms in one step

• Flexible geometry

• Geometric reproducibility

• Successfully applied to: lead silicates, tellurites, chalcogenides, bismuthates, lead germanates

Careers in Photonics

Centre of Expertise in PhotonicsSchool of Chemistry & PhysicsUniversity of Adelaide

Professor Tanya MonroDirector

www.chemphys.adelaide.edu.au/physics/research/photonics

Science Degrees at Adelaide University

• Bachelor of Science (BSc)- Biomedical sciences- Biophysics- Chemistry- Environmental biology and Ecology- Geosciences (Geology and Geophysics)- Molecular biology and Biotechnology- Physics- Psychology and Behavioural Sciences

A Science Degree Provides…

• Scientific knowledge• Technical skills• Problem solving skills• Analytical skills• Critical thinking• Communication skills

• Government• Health• Education• Private industry

• Initiative• Teamwork• Time management• Responsibility• Confidence

• Consultants• Research laboratories• Own business

And Leads to a Career in:

Pre-requisitesBSc

Two science subjects, one chosen from Chemistry, Maths Studies, Specialist Maths, Physics

& one from Biology, Chemistry, Geology, Physics

Specialist Programs with Physics• Physics,• Maths Studies and • Specialist Maths

BSc (Optics and Photonics)

• Optics and Photonics is a steadily growing sector in industry

• Australian tertiary institutions are not producing enough trained people

– (even allowing for the “bust” in the boom/bust cycle ! )

• Physics graduates are readily employable in this industry– Named degree makes qualification more recognisable

• Adelaide is rapidly developing strength in defence photonics (potential employers include: DSTO, Tenix, BAE systems

• Wide range of other opportunities including in medicine (eg ophthalmology), communications, etc

• Attractive career opportunities with scope for creativity and practical relevance

Job opportunities in photonics

• There are opportunities for people with photonics training in Academia, Industry, Defence

• Requires study of physics and mathematics• Bachelor of Science (Optics and Photonics)