Shaping Nanowire Tapers… With A CO 2 Laser Powered Micro-Furnace By David Kedziora Supervisors:...
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Transcript of Shaping Nanowire Tapers… With A CO 2 Laser Powered Micro-Furnace By David Kedziora Supervisors:...
![Page 1: Shaping Nanowire Tapers… With A CO 2 Laser Powered Micro-Furnace By David Kedziora Supervisors: Eric Magi, Ben Eggleton.](https://reader035.fdocuments.in/reader035/viewer/2022062516/56649d7f5503460f94a62bed/html5/thumbnails/1.jpg)
Shaping Nanowire Tapers… With A CO2 Laser Powered
Micro-Furnace
By David Kedziora
Supervisors: Eric Magi, Ben Eggleton
![Page 2: Shaping Nanowire Tapers… With A CO 2 Laser Powered Micro-Furnace By David Kedziora Supervisors: Eric Magi, Ben Eggleton.](https://reader035.fdocuments.in/reader035/viewer/2022062516/56649d7f5503460f94a62bed/html5/thumbnails/2.jpg)
The Project
Aim:
•To test a CO2 Laser Powered Micro-Furnace in tapering fibres.
Method:
•Stretching heated fibres so that they thin down.
•Pass light in, detect light out, work out optical loss.
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Definitions
• Fibre Optic Cable: “Flexible, optically transparent wire through which light can be transmitted by total internal reflection.”
•Taper: “A section of optical fibre that has a continuously changing outer dimension along its length.”
•Taper’s waist included!
Centre for Photonics and Photonic Materials, University of Bath 2007
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Nanowires!
• Nanowire: Optical fibre with diameter on the micron or, ideally, submicron scale.
Why do we care?
• Nanowires transmit some of the light energy OUTSIDE cladding!
• This is called ‘Evanescent Field’.
• Other fibres and crystals can interact with this field.
Examples of uses:
•Photonics circuitry
•Photonic sensing
Grillet, CUDOS 2006
Centre for Photonics and Photonic Materials, University of Bath 2007
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Outline
• Tapering: The Basic Concept
• Brushing With Fire
• The Limitations…
• The CO2 Laser Powered Furnace
• Tapering: In Action
• Results And Conclusion
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Tapering: The Basic Concept
• Heat a section of the fibre.
• Stretch the fibre.
• Conservation of mass implies increase in length is matched with decrease in diameter.
• Variable elongation velocity determines taper shape.
• Theory states taper adiabaticity (gradual decrease) required for low optical loss.
Birks and Li, Journal Of Lightwave Technology, 1992
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Brushing With Fire
• Standard tapering procedure: flame brushing method.
• Flame sweeps over a section (heated to >1600 degrees C).
• Two clamps stretch fibre.
• Note: It works. Dimensions can be reduced by up to 100 times.
Centre for Photonics and Photonic Materials, University of Bath 2007
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The Limitations
Problem 1: Increasing Viscous Forces
• Problem encapsulated by Reynolds Number theory.
• Fibre diameter decreases, friction of fibre increases.
• The expelled gas literally pushes fibre out of flame.
• Not optimal due to irregularities in taper shape.
Problem 2: Contaminants
• OH- ions are a by-product of flame process.
• The ions are absorbed into fibre over time.
• Contamination results in optical loss.
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CO2 Laser Powered Furnace (1)
• Solution: CO2 Laser
• Beam of EM-radiation in infrared.
• Operates at 10.6 micrometer wavelength.
• Why CO2 Laser?
• No chemical by-products (contaminants).
• The Silica fibres are opaque to infrared. Therefore absorption.
• Highest-power continuous wave gas lasers currently available.
• Can have as large as 20% efficiency. (This is among the best.)
• Gives system greatest flexibility with heat-zone temperature.
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CO2 Laser Powered Furnace (2)
• Problem: Laser by itself won’t do.
• Criticism of Local Heating:(Energy Loss)/(Energy Input) = e-α(Diameter)
• Solution: Sapphire Furnace
•Consists of two Sapphire Tubes heated by laser.
•Allows radiative heating, which leads to more absorption.
•Also aids in disrupting friction-inducing air convection currents.
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Tapering: In Action
•Clamp fibre down to two stages.
•Turn on laser.
•Stages move left and right allowing heating section to sweep over fibre.
•Over time, elongates fibre.
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Results (1)
0.3 dB loss = 6.7% loss
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Results (2)
125 Microns 24.8 Microns
Before Tapering After Tapering
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Results (3)
Profile Of Outer Diameter
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Conclusion
• There is a lot left we can do with the system.
• Have additional degree of freedom: laser.
• Potential applications of local heating…
• Example: Fibre bending.
• Ultimately though… success! The system works!
• Will lead to higher yield for CUDOS.
• Smaller nanowires with higher performance.