The benefits and threats of “nano” in polymer photonics · Nano-features in polymer photonics...
Transcript of The benefits and threats of “nano” in polymer photonics · Nano-features in polymer photonics...
The benefits and threats of “nano” in
polymer photonics
Arjen Boersma
Photonics Event, Veldhoven, 24/25 April 2013
Introduction
This presentation will give an overview of the influence of nano-sized
features in polymer photonics
Polymers are a very interesting alternative for semiconductor components
in e.g.
– Optical interconnects
– Chemical Sensors
Large area manufacturing
Low cost
Suitable for flexible substrates
Versatile chemistry, which enable integration of functionalities
Large feature sizes
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Polymer versus silicon photonics
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Polymer Silicon
Refractive index 1.5 3.4
Waveguide size 4-10 µm (fiber matched) 0.5 µm
Bend radius 5 mm 250 µm
Features size PhC 500-1000 nm 100-400 nm
Optical loss @ 800 nm 0.01 dB/cm 15 dB/cm
Optical loss @ 1300 nm 0.2 dB/cm 3 dB/cm
Optical loss @ 1500 nm 0.5 dB/cm 1 dB/cm
Process Litho/NIL – large area CMOS – small area
Tolerances 100 nm 10 nm
Thermo-optic coeff. -2.10-4 /K +2.10-4/K
Nano-features in polymer photonics
Although tolerances in polymer photonics are larger, the presence of
nano-sized features (10-100 nm) can still have significant influence:
Waveguides
– Contaminations, additives
– Surface roughness
– Residual layers resulting form the manufacturing process
– Dimensions, such as bend radius and cross section
Photonic Crystals
– Feature sizes: nanoparticles, nanoholes
– Tolerances of array
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Contaminations in waveguides - molecules
Contaminations in optical polymers may cause too much loss
Cleaning of polymer is essential
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Optical polymer by Momentive
Contamination in waveguides - nanoparticles
Refractive index of polymers can be tuned by adding high refractive index
nanoparticles
However, too large particles
increase optical loss
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50 µm polymer composite coating with RI=1.75
Loss of polymer composite versus particle size
Surface roughness of waveguides
Surface roughness depends on:
– Manufacturing process
• Optical lithography
• Nano imprint lithography
• Laser Direct imaging
• Etching
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Process Surface roughness,
RMS (nm)
Laser Direct Imaging 200
Laser ablation 100
Reactive Ion Etching 50
UV lithography 20
Nano Imprint
Lithography
10
– Polymer characteristics
• Chemistry
• Physical parameters
LDI waveguide by IBM
NIL waveguide by VTT
Residual layer during Nano Imprint Lithography
In the case of Nano Imprinted waveguides, the residual layer results in
higher losses
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Photonic Crystals - Concept
Photonic crystals reflect specific wavelengths depending on periodicity
and refractive index contrast
Feature size ranges between 100 and 1000 nm
Application in:
– Bends and components for tele/data communication
– Chemical sensing
Can be made by:
– Stacking of nanoparticles
– Etching in thin slabs
– Imprinting in polymer
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Photonic Crystals (particles) – Reflection at 1550 nm
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� Fcc stacking of core-shell particles
� Reflection of 80 % can be obtained
Sam
e re
sult
as w
ithou
t sh
ell
Photonic Crystals (particles) – Manufacturing
Random particle stacking leads to poor reflection of light
Long range order required for optimized reflection
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SEM picture of particles deposited without template
Photonic Crystals (particles) – Manufacturing
The use of a template for stacking introduces better control of array
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SEM picture of particles deposited with template
Cubic template forces particles (1 µm) into fcc crystal
Photonic Crystals for chemical sensing
Feature size in optical sensors has significant influence on performance
Feature size in sensor element correlates with sensitivity
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Photonic crystal – Imprinted in polymers
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Imprint mould and polymer replicas
Sinusoidal Photonic Crystal
Circular hole Photonic Crystal
Imprinted structure reflects
specific spectrum that will
be used for read-out
Photonic Crystals - Results
Chemical sensitivity is achieved by functionalisation of nanostructured surfaces
with responsive layers
Nanostructured receptor layer in Photonic Crystal holes also improves sensitivity
Immobilisation on nanoparticles enhances the response of a formaldehyde receptor
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Thin film Immobilised on TiO2 nanoparticles
Photonic Crystals – Results
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Change in absorption corresponds
to change in refractive index
Extrapolation to ∆n = 10-5
leads to values of 10-100 ppb
Combining nanostructured Photonic Crystals and nanoparticle
immobilized receptors lead to new sensing opportunities
Change in refractive index of TiO2-receptor layerwhen exposed to formaldehyde
Benefits and threats of “nano” in polymer photonics
Benefits:
– Controlling light at nano/micro scale
– Increase sensitivity in sensors
Threats:
– Nano-sized irregularities may lead to enhanced optical loss
• Nanoparticles
• Molecules
• Roughness
Good control of feature sizes and morphology is required
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Acknowledgement
These results have been obtained with sponsoring of TNO and the European
FP7 program:
TNO – Enabling Technology Program
FIREFLY – www. fp7-firefly.eu
PHOTOSENS – www.photosens.eu
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Thank you for your attention
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For more information please contact:
Dr. Arjen BoersmaTNO
De Rondom 1PO Box 62355600 HE EindhovenThe Netherlands
E-mail: [email protected]: +31 (0)88 866 57 13General: +31 (0)6 533 843 20www.tno.nl