Simulating Surface Plasmons at Metal Surfaces and its … · 2017. 10. 16. · • Prism coupling...

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Simulating Surface Plasmons at Metal Surfaces and its Application in Optoelectronic Devices with COMSOL Multiphysics

Leiming Wang, Senior Researcher

Konica Minolta Laboratory USA

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Outline

Introduction

• Surface plasmon polaritons (SPP)

Simulation of SPP using COMSOL Wave Optics

• Prism coupling

• Scattering configuration (grating coupling)

• Explore SPP properties via scattering simulation

Application examples

• Plasmon energy loss in OLED

• Surface plasmon-enhanced fluorescence spectroscopy (SPFS)

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Plasmonics: merging electronics and photonics at the nanoscale

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Surface plasmon polaritons – a guided surface wave

Transverse magnetic (TM, or p-polarized) mode – Hz, Ex, Ey

“Phase-matching” (ΔK) condition for SPP excitation

K0sin(ө) Kspp

ΔK

Ag

475nm

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SPP excitation – prism coupling

“Phase-matching” condition:

өn1

n0

Ɛm

өn1n0

Ɛm

sppkkn )sin(01

Kretschmann-Raether Otto

Yushanov, et al, COMSOL Conference 2012

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SPP excitation – scattering

Symmetry breaking by discontinuity/defect provides a

broad spectrum of spatial frequency, allowing the phase

matching (Δk) to be attained for SPP excitation.

ө

(1) Full-field simulation w/o the slit to generate incident field for step 2 (ө = 30o).

(2) Scattered-field simulation with the output from step 1 as the incident field.

Scattering configuration enables the local excitation of SPP and opens the way for further study on its

wave properties such as attenuation, interference, focusing, etc.

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SPP excitation – grating coupling

Finite grating is a special case of scattering configuration,

with resonance:

ө

p

sppkpmk )2()sin(0

Ө = 0o

Ө = 16.5o (resonance)

Ө = 30o

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Coupled SPPs at thin metal film

SPPs at the two interfaces of thin metal film interact to form

two coupled SPP modes:• Anti-symmetric bound mode (ab): strong confinement, strong damping (short range SPP).

• Symmetric bound mode (sb): weak confinement, small damping (long range SPP).

ө+ - + -+ - + -

+ + + +- - - -

ab sb

|Ey|

|Ey|

ab

sb

Ө = 0o

Ө = 65o

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Adiabatic focusing of SPP by thin wedge

The dispersion with respect to film thickness

leads to adiabatic focusing of the thin film

coupled SPP in a wedge structure.

ө

Wang, et al, PHYSICAL REVIEW B 86, 165408 (2012)

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SPP focusing lens

Engineering the wave front of SPP by 2D

arrangement of local coupling structures.

k0

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Konica Minolta OLED lighting

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Plasmon energy loss in OLED

Typical power distribution spectrum of an

OLED viewed in the k-space*

*Reineke et al., Rev. Mod. Phys. 85, 1245–1293 (2013)

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Reducing plasmon loss in OLED by nanostructured cathode

|E

z|

Pz @ 535 nm

“Let there be light: a brighter future for OLED”,

IEEE Spectrum, September 2016

Wang, et al, COMSOL Conference 2015

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Surface plasmon-enhanced bio-sensing

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Trade-off btw SP-enhanced excitation and –quenched emission in SPFS

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 20 40 60 80 100 120 140 160 180 200

SP

(%)

d (nm)

12

10

8

6

4

2

0

I/I 0

10008006004002000

y (nm)

FEM simulation exponential fitting

water

prism

50nm Au

Excitation field enhancement SP quenching of fluorescence emission

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Leiming.wang@hl.konicaminolta.us