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

Photonics Event, 24/25 April 2013 10

� Fcc stacking of core-shell particles

� Reflection of 80 % can be obtained

Sam

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as w

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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: arjen.boersma@tno.nlOffice: +31 (0)88 866 57 13General: +31 (0)6 533 843 20www.tno.nl