Evanescent Spectroscopy

Evanescent Spectroscopy - Theory andExperiment

Alina Karabchevsky

Optoelectronics Research CentreUniversity of Southampton, UK

7th July 2014, 53/4025Planar meeting

Talk

1 / 18

Evanescent Spectroscopy

Outline

1 Introduction

2 Literature Overview

3 Photonic-Plasmonic WaveguideStructureModellingTheory

4 ResultsOptical TransmittanceLoss of Fundamental Mode in a Gold RegionOptical Surface Intensity

5 NIR Spectrosocpy - Experiment

6 Conclusions

7 Acknowledgements

2 / 18

Evanescent Spectroscopy

Introduction

Surface Enhanced Spectroscopy

M My• B By•M

MyB

MyL

MyE

MyN

My•

MyV

MyO

Myw

My9

B

kx©k

p

ω©ω

p

Dispertion7relation7of7photon7in7vacuum

Dispertion7relation7of7photon7hitting7SFBBprism7

ωp©LB©L

Dispertion7relation7of7surface7plasmon7in77air

dkx

at7•MM

Surface Enhanced Spectroscopy on Waveguides

ByNOB7RIU

Ambient

ByNOw7RIU

Gold

N7um

L7um

L

VEE7nm

First Step

of disontinuity

Second Step

of disontinuity

MB

L

Transmittance

γ=i, j

,m

i

i

Surface7Intensity

BNVM BNwM B•MM B•LM B•NM B•VM B•wM BVMM

wavelength7nm

ayuy

NH overtone

N-Methylaniline spectroscopy on waveguide

NH

©7LMBL7Materials7Research7SocietyOLw MRS7BULLETIN• VOLUME7EO • AUGUST7LMBL • wwwymrsyorg©bulletin

3 / 18

Evanescent Spectroscopy

Literature Overview

Coupling over Discontinuities inPhotonic-Plasmonic Waveguide

Theoretical study of planar waveguides with plasmonicOverlayer [1].

Coupling of hybrid real field distributions over adiscontinuity in a waveguide horns [2].

[1] J. Ctyroky...J. S. Wilkinson et al, “Theory and modelling ofoptical waveguide sensors utilising surface plasmon resonance,”SAB 54(10), 66–73 (1999).

[2] A. Milton and W. K. Burns, “Mode coupling in opticalwaveguide horns,” IEEE J. Quantum Electron. 13(10), 828–835(1977).

4 / 18

Evanescent Spectroscopy

Photonic-Plasmonic Waveguide

Structure

Structure

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Figure 1: Schematic of a two dimensional waveguide structure withgold overlayer for excitation of surface plasmons. Calculateddistribution of surface intensity |Ey(x, y = 50 nm, 0 < z < L)|2 issuperimposed on the gold surface.

5 / 18

Evanescent Spectroscopy

Photonic-Plasmonic Waveguide

Modelling

Numerical Approach

Supercomputer Iridis4

FEM, COMSOL 4.3b

with MATLAB

6 / 18

,2 ,1 µ 1 2 3 4µ

5E7

1E8

1z5E8

2E8

2z5E8

|Ey.

x=µ=

y=z=

µ||

µm

Guiding1Layer

Gold1Overlayer1

AnalyteSubstrate

Depth

Fundamental1guided1mode1of

input1waveguideFundamental1guided1mode1within1gold1

overlayer

Symmetric1guided1mode1

within1gold1overlayer

Asymmetric1guidedmode1within1gold

overlayer

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

Photonic-Plasmonic Waveguide

Theory

Orthogonality of Complex Modes

∀i 6= j Ii,j = 0

Ii,j =

∫ ∞−∞

∫ ∞−∞

(Ei×Hj)zdxdy (1)

Exi0 =∑

γ=i,j,m

Exγ1. (2)

Eyi0 =∑

γ=i,j,m

Eyγ1. (3)

Hxi0 =∑

γ=i,j,m

Hxγ1. (4)

Hyi0 =∑

γ=i,j,m

Hyγ1. (5)

7 / 18

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

Photonic-Plasmonic Waveguide

Theory

Normalization

Power 1W

Pi,i = 1/2<(a2i Ii,i)

While:a = Enan (6)

a = Hnan (7)

FinallyEi0n[2/<(Ii0,i0)]

1/2 exp(−ıαi0)(Ii0,j1 + Ij1,i0) =Ej1n[2/<(Ij1,j1)]

1/2 exp(−ıαj1)2Ij1,j1AndHi0n[2/<(Ii0,i0)]

1/2 exp(−ıαi0)(Ii0,j1 + Ij1,i0) =Hj1n[2/<(Ij1,j1)]

1/2 exp(−ıαj1)2Ij1,j18 / 18

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

Photonic-Plasmonic Waveguide

Theory

Coupled Mode Equations

Aγ1∑γ=i,j,mAγ1 =

∑γ=i,j,m ciγAi0

Ai2

Ai2 =∑

γ=i,j,m cγiAγ1

ciγIi0,γ1+Iγ1,i0

2Iγ1,γ1[<(Iγ1,γ1)<(Ii0,i0)

]1/2

cγiIγ1,i2+Ii2,γ1

2Ii2,i2[<Ii2,i2<Iγ1,γ1 ]1/2

Note: Ii2,i2 = Ii0,i09 / 18

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

Results

Optical Transmittance

Prediction of Transmittance

Sensing: Refractometers and Spectrometers

Transmittance dB

|∑

γ=i,j,m[Ii0,γ1+Iγ1,i0]

2

4Ii0,i0Iγ1,γ1exp(−ıαγ1L)|2

Reproduced Figure 5c from [1]overlapped with calculatedtransmitted power based on our model.

10 / 181.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

Results

Loss of Fundamental Mode in a Gold Region

Loss of Fundamental Mode in a Gold Region

Sensing: Refractometers and Spectrometers

Loss dB

20 log10 exp 2π=Neffλ

Reproduced Figure 5c from [1]overlapped with calculatedtransmitted power based on our model.

11 / 18

Loss of Ai1

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

Results

Optical Surface Intensity

Prediction of Surface Intensity

Spectroscopy: SERS, SEIRA

Surface Intensity V2/m2

|∑

γ=i,j,mEγ1|2 = |Ei0|2|∑

γ=i,j,m cij |2

Cross sections of calculated surface intensityat w = 0 um on top of gold and alonga gold overlayer interaction lengthas a function of optical propertiesof an analyte.

12 / 18

0

1E14

2E14

3E14

4E14

5E14

Inte

nsity

V2 /m

2

Gold length mm0.10 0.2 0.3 0.4 0.5

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

NIR Spectrosocpy - Experiment

Conventional Spectroscopy

1460 1480 1500 1520 1540 1560 1580 1600

Spectrophotometer

Tra

nsm

ittan

ce a

.u.

NH overtone

Wavelength nm

N

H

13 / 18

N-Methylaniline

Evanescent Spectroscopy

NIR Spectrosocpy - Experiment

Tapered Fiber Spectroscopy

1460 1480 1500 1520 1540 1560 1580 1600

Spectrophotometer

Tra

nsm

ittan

ce a

.u.

Tapered Fiber

NH overtone

Wavelength nm

N

H

14 / 18

N-Methylaniline

Evanescent Spectroscopy

NIR Spectrosocpy - Experiment

Waveguide Spectroscopy

1460 1480 1500 1520 1540 1560 1580 1600

Spectrophotometer

Tra

nsm

ittan

ce a

.u.

Tapared Fiber

Waveguide

NH overtone

Wavelength nm

N

H

15 / 18

N-Methylaniline

Evanescent Spectroscopy

Conclusions

Coupling over Discontinuities inPhotonic-Plasmonic Waveguide

Numerical study of photonic waveguide with plasmonicoverlayer.

General expression of coupling coefficient.

Expression of guided complex field amplitudes.

Prediction of optical transmittance.

Optical transmittance of photonic waveguides withplasmonic overlayer is defined primarily by the losses of thecomplex fundamental mode excited in a gold region.

Prediction of surface intensity

16 / 18

1.471,RIU

Analyt

e

1.478,RIU

Gold

4,um

2,um

L

633,nm

First step

of disontinuity

Second step

of disontinuity

01

2

Transmittance

γ=i, j

,m

i

i

Surface,Intensity

Evanescent Spectroscopy

Conclusions

NIR spectrosocpy on Waveguideand Tapered Fiber

Identification of N-Methylaniline overtone by conventionalspectroscopy

Donor-Acceptor study of N-Methylaniline

Tapering SiO2 fiber and fabricaiton of waveguide

Measured NIR spectrum of N-Methylaniline on oxygentreated waveguide

Measured NIR spectrum of N-Methylaniline onpolyethylene glycol ligands (PEG) passivated colloidalAuNP on tapered fiber

17 / 18

1460 1480 1500 1520 1540 1560 1580 1600

wavelength nm

a.u.

NH overtone

NH

Evanescent Spectroscopy

Acknowledgements

Acknowledgements

Coupling over Discontinuities inPhotonic-Plasmonic WaveguideMN Zervas and JS Wilkinson

yellow!5

NIR Spectroscopy on Tapered FiberG Buscemi, Abdul Khudus MIM, P Lagoudakis, MN

Zervas and JS Wilkinson

Special Thanks to IPD group members:GS Murugan, P Hua, MN Mohd Nazir, A Aghajani, DJ Rowe, JButement, Z Wang, V Mittal, E Tull

18 / 18

A.Karabchevsky@soton.ac.ukhttp://wipfab.southampton.ac.uk

(FP7/2007 -2013) ERCgrant agreement no. 291216

Outstanding Womanin Science Awardworth 45k$