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Refraction and Optical Fibres
Dr Murray ThompsonUniversity Senior [email protected]
Prof Tanya MonroCentre of Expertise in [email protected]
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“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
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•When light travels from one medium to another it changes speed.
•It also changes direction.
Refraction and Optical Fibres
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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
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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
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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
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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
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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.”
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• 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
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Total Internal Reflection• Beyond the critical angle, no refraction
is possible and the light is said to ‘totally internally reflect.’
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Total Internal Reflection
• No refraction is possible beyond the critical angle.
Slow mediumeg glass
Fast medium eg air
normal
Angle ofIncidence iGreater than ic
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Below the critical angle
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At the critical angle
Note the reflected ray
Note the refracted ray at grazing angle – colour dispersion
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Beyond the critical angle
Total internal reflection.
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Total Internal Reflection
Snell’s law:
2
1
1
2
sin
sin
n
nqc
Water (n=1.3)
Air (n=1.0)
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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
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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.
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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…
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Microstructured Optical Fibres
fibres with micron-scale transverse features
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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
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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
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Extrusion
Stainless steel
die
OD=29mmh=34mm
glass billet
Structured glass preform
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Extrusion – Preform Variety
• Structured preforms in one step
• Flexible geometry
• Geometric reproducibility
• Successfully applied to: lead silicates, tellurites, chalcogenides, bismuthates, lead germanates
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Careers in Photonics
Centre of Expertise in PhotonicsSchool of Chemistry & PhysicsUniversity of Adelaide
Professor Tanya MonroDirector
www.chemphys.adelaide.edu.au/physics/research/photonics
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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
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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:
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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
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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
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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)