SPP waveguide sensors

SPP waveguide sensors

1. Optical sensor - Properties

- Surface plasmon resonance sensor

- Long-range surface plasmon-polariton sensor

- SPP properties in a waveguide

- Asymmetric double-electrode waveguides

- Basic ADW sensor structure with -fluidic channel 2. LR-SPP waveguide

- Influence of temperature fluctuation

- LR-SPP waveguide index sensor

- LR-SPP waveguide bio sensor

3. Proposed waveguide sensors

Contents

Optical sensors

1. properties

2. Surface plasmon resonance sensor

3. Long-range surface plasmon-polariton sensor

Source

Measurement

Detector Properties

1. Immune to electromagnetic interference 2. Capable of performing remote sensing

3. Provide multiplexed detection within a single device

1. properties

1. properties

Label-free detection Fluorescence-based detection

2. Surface plasmon resonance sensor

-Properties

1. Label free sensor (Real-time detection)

2. High sensitivity (Large filed enhancement at the interface between dielectric and metal)

Reference : Biosensors and Bioelectronics 23 (2007) 151-160

Prism is too bulky !!!!

Difficult to integrate

First SPR bio-sensing was demonstrated by Liedberg (1983) Commercial SPR sensor : 1 ×10^-6RIU (Biacore^TM)

2. Surface plasmon resonance sensor

Other SPR sensor approaches (various SPP excitation method)

1. Only penetrates into the surrounding medium for about 100 nm.

2. How can sensitivity be increased ?

3. Transmit both light signal and electrical signal ? Metallic waveguide with

Long-range surface plasmon mode

Ref. : Biosensors and Bioelectronics 23 (2007) 151-160

Contents

LR-SPP ^waveguide

1. SPP properties in a metallic waveguide 2. Asymmetric double-electrode waveguides

3. Basic ADW sensor structure with -fluidic channel

1. SPP properties in a metallic waveguides

Long-range surface plasmon mode Short-range surface plasmon mode

1. Highly enhanced electromagnetic field 2. High propagation loss.

1. Longer penetration depth into dielectric material 2. Low propagation loss.

Therefore, LRSPP produce a narrower SPR features.

Higher sensitivity!!

2. LRSPP waveguide sensors

Breakthrough : To excite a LRSPP mode, symmetry requirement is needed !!

Metal

Dielectric Dielectric

The refractive index difference between two embedding materials

should be lower than ~ 10

. To use LRSPP mode and high Integration for a device.

Solution :

LRSPP metallic waveguide sensor !!

To overcome the symmetry requirement

3. asymmetric double-electrode waveguides

Substrate Substrate Metal (Au)

-fluidic channle Metal (Au)

Substrate

3. asymmetric double-electrode waveguides

1. High degree of freedom of structure. (easy to apply to various applications) 2. Adjusting of core thickness, the symmetry requirement can overcome.

3. LRSPP mode is confined around the core layer.

4. Double metal layers for detecting bio-molecules.

5. Easily tuning the core dielectric layer by sending a current or voltage to double-electrodes







D w

core

cladding



X-axis

Y-axis

D

SPP mode metal strip

metal slab

Substrate

3. asymmetric double-electrode waveguides

1.0 1.1 1.2 1.3 1.4 1.5

10 100 1000 10000

Cutoff Thickness "D c"(nm)

Core reflactive index ( )

1.45 895 nm

(a)

ε

CoreCore

1.0 1.1 1.2 1.3 1.4 1.5

10 100 1000 10000

Cutoff Thickness "D c"(nm)

Core reflactive index ( )

1.45 895 nm

(a)

ε

CoreCore

0 200 400 600 800 1000

1.470 1.471 1.472 1.473 1.474 1.475

_r 

k

 r 

k

Core Thickness "D" (nm) (b)

0 200 400 600 800 1000

1.470 1.471 1.472 1.473 1.474 1.475

_r 

k

 r 

k

Core Thickness "D" (nm) (b)

0 200 400 600 800 1000

0.0 2.5 5.0 7.5

Propagation Loss(dB/mm)

Core Thickness "D" (nm) (1)

(2) (3)

(c)

0 200 400 600 800 1000

0.0 2.5 5.0 7.5

Propagation Loss(dB/mm)

Core Thickness "D" (nm) (1)

(2) (3)

(c)

- Fabrication process

3. asymmetric double-electrode waveguides

Si



a.polymer _) 코팅

Si



b. u coating

Si





d. PR patterning

Si





e. u coating

Si





c.polymer _) 코팅

Si





f. PR lift-off

Si







g.polymer _) 코팅







D w

core

cladding



X-axis

Y-axis

D

SPP mode metal strip

metal slab

3. asymmetric double-electrode waveguides

Y-branch S-band

metal strip metal slab

20㎛ 20㎛

<S-band> <Y-branch>

: 6.67



1.5mm 1.65mm 1mm

:1.91



2mm 3mm 0.5mm

Metal (Au)

width :5 ㎛, Thickness:20nm Core thickness :680nm

3. asymmetric double-electrode waveguides

3. asymmetric double-electrode waveguides

4. Basic ADW sensor structure with -fluidic channel

Sensing Material

Detection process ( protein )

Cladding Cladding

Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y

Substrate

Y Y Y Y

< Basic LR-SPP sensor structure >

Metal (Au) Substrate

-fluidic channle Dielectric

material

Bio-molecule

1. Reduced the size of the sensor structure comparing to the Kretschmann-reather configuration which use a prism.

2. Double LR-SPP structure can detect low index materials. ex) water, air, etc.

4. Double detecting metal layers. ( 1.5 times higher sensitivitythen single metallic waveguide biosensor ) 3. Easily excited the LR-SPP using end-fire coupling method with single mode fiber.

-Advantages of double LR-SPP bio-sensor structure

5. Compensate the temperature fluctuation (self referencing) .

- Fabrication process

4. Basic LRSPP sensor structure with -fluidic channel

Core layer coating

y z x

y z

silicon wafer cladding

cladding

core fluidic channel

gold slab y

z

cladding (b)

cladding cladding

cladding

4. Basic LRSPP sensor structure with -fluidic channel

Si



Si



Observing the LRSPP mode image

1. Inserting 1.45 index matching oil in the channel.

2. After 10 min inserting the matching oil, inserting an acetone ( n : 1.36 ) in the channel.

3. The LRSPP mode is gradually disappears.

10 m

Substrate

Index matching oil

n = 1.45

acetone

n = 1.36 1.47

1.47 1.45

4. Basic LRSPP sensor structure with -fluidic channel

1.0 1.1 1.2 1.3 1.4 1.5

10 100 1000 10000

Cutoff Thickness "D c"(nm)

Core reflactive index ( ) 1.45 895 nm

(a)

ε1

Core Core

1.0 1.1 1.2 1.3 1.4 1.5

10 100 1000 10000

Cutoff Thickness "D c"(nm)

Core reflactive index ( ) 1.45 895 nm

(a)

ε1

Core Core

1

1.36 130 nm

895 nm

Contents

Proposed waveguide ^sensors

1. Influence of temperature fluctuation

2. LR-SPP waveguide index sensor

3. LR-SPP waveguide bio sensor

1. Influence of temperature fluctuation

- To increase measurement accuracy

Temperature fluctuations should be reduced !!

ex ) Thermal optic coefficient of aqueous solution for the solvent of the bio-molecules : - 1×10

RIU/°C ~ 10

~ 10

RIU (Sensitivity of SPR sensors)

- Using reference channel for compensating temperature changes

Ref : Proc. Of SPIE Vol. 5728.

Ref : Applied Optics, Vol. 41, No. 29, PP. 6211 (2002)

Ref : IEEE Photonics Tech., Vol. 19, No. 24, 2007.

1. Influence of temperature fluctuation

- Other method to reduce temperature effects

1. Influence of temperature fluctuation

Ref : Sens. And Act. B., Vol. 134, pp. 854, 2008.

Ref : Measurement science and tech., Vol. 12, 2001.

2. LR-SPP waveguide index sensor

L

region : Detecting temperature changes

L

region : Detecting refractive index changes of the bulk solutions.

Claddings : n=1.47, thickness=15 m Bragg gratings : n=1.6, thickness=120 nm Core : n=1.46, thickness=700 nm period=528.8 nm

Buffer layers : 300 nm wavelength : 1550 nm

Au coating ( 20nm ) Bragg grating

(150nm /525.8nm) Buffer layer coating (250nm ) 1.47 polymer

(15m)

Removing the PR core layer

- Fabrication process

Core and Channel layer ( 500nm )

Buffer layer coating (250nm )

Au metal stripe

(20nm , 5m) 1.47 polymer (15m)

2. LR-SPP waveguide index sensor

Tunable LD

broad sourceASE ^Polarizer

0

OSA

0

LRSPP sensor

2. LR-SPP waveguide index sensor

Measurement various bulk index solutions in the same sample.

To detect other refractive index of the bulk solution,

the inserted bulk solution was removed by methanol.

Measurement order : 1.47 1.474 1.48 1.484

( 130 nm/RIU ≈ ~10

RIU with 1 pm OSA resolution)

1554 1556 1558 1560 1562

-60 -50 -40 -30

Wavelength (nm)

Transmittance (dB)

1.470 1.474 1.480 1.484

1554 1556 1558 1560 1562

-60 -50 -40 -30

Transmittance (dB)

Wavelength (nm)





experimentTMM

2. LR-SPP waveguide index sensor

1.470 1.475 1.480 1.485 -2

-1 0 1 2 3 4

Sample index





(nm)

TMM

experiment 0.3 0.6 0.9 1.2 1.5

FWH M ( n m )

1551 1554 1557 1560



(n m)

-20 -10 0 10 20

0.9 1.2 1.5 1.8 2.1 2.4

Temperature variation (  K )





(nm)

(c) (d)

2. LR-SPP waveguide index sensor

1554 1556 1558 1560 1562

-60 -50 -40 -30

Wavelength (nm)

Transmittance (dB )

1.470 1.474 1.480 1.484

- 130 nm/RIU ≈ ~10^-6RIU

- _D– _R = ± 540 pm ≈ ± 27 pm/K - _R = ± 4.12 nm

(with 1 pm OSA resolution and ± 20 K variation) - Thermal optic coefficient

Polymer : -1.7×10^-4 RIU/K Sample oil : -1.0× 10^-5 RIU/K

3. LR-SPP waveguide bio sensor

a. Before inserting bio-material with solution

x

z y

Substrate z

y Cladding

Bragg grating unit cell

L_w L_g L_w

D_c: core thickness ( 500 nm ) D_g: grating depth

t : bio-molecule thickness L_g: grating length

D_c D_g

L_g

Cladding

Substrate

Solution Bio-molecule

1 2

( )

bragg

n

n

   

D_g area D_c area 575 nm

b. After inserting bio-material with solution

Substrate z

y Cladding

Cladding

D_c D_g

L_g

- Two important properties of a bio-sensor

Sensitivity, S

, t : bio-molcule layer thickness



t



 



3. LR-SPP waveguide bio sensor

1. Sensitivity : The ratio of the change in sensor output to the change in the measurand.

2. Resolution : The smallest change in measurand which produces a detectable change in the sensor output.

Sensitivity, FWHM

D_g

min

10% 10%

Resolution , ( )

B

FWHM FWHM

t nm t

S



 

    



3. LR-SPP waveguide bio sensor

0 20 40 60 80 100

0.0515 0.0520 0.0525 0.0530

Grating depth, Dg (nm) Se ns itiv ity , S

Substrate z

y Cladding

Cladding

450 nm D_g

L_g

0 2 4 6 8 10

0.0 0.4 0.8 1.2 1.6

Grating length, Lg (mm) Resolution,  t

(nm)

20nm 40nm 60nm 80nm

1 nm

Over 2 mmgrating length (L_g), possible to detect under 1 nmthickness variation of bio-molecule layer (t)

n_cladding : 1.35, n_core: 1.33

Bio-molecule : n_protein (1.5), n_solution: 1.33

3. LR-SPP waveguide bio sensor

< Experiment scheme of LR-SPP waveguide bio-sensor>

L_w L_g L_w

Substrate

L_g

L_w L_w

Circulator

Outputsignal

Input signal

2 2 2

loss max

Total Loss, T (dB) = 10 log(    



 

R )

Propagation loss path length

( )

out in 10

where

Propagation efficiency, η = P /P = 10

10 log (Pout in/P ) Propagation loss (dB/mm) =

Path length (mm)





Coupling efficiency ( _c)

Propagation efficiency ( _w)

Propagation efficiency ( _g)

Coupling efficiency ( _c) : 80 %( Overlap integral method ) Propagation efficiency ( _w) : 42 %( at 450 nm core thickness

with 1mm length ) Maximum reflection ( R_max)

3. LR-SPP waveguide bio sensor

Substrate z

y Cladding

Cladding

450 nm D_g

L_g

0 2 4 6 8 10

0.0 0.2 0.4 0.6 0.8 1.0

Maximum reflection, R max

Grating length, Lg (mm)

0 2 4 6 8 10

0.0 0.1 0.2 0.3 0.4 0.5



Grating length, Lg (mm)

20 nm 40 nm 60 nm 80 nm

2 2 2

loss max

Total Loss, T (dB) = 10 log(    



 

R )

constant

3. LR-SPP waveguide bio sensor

0 2 4 6 8 10

15 20 25 30 35 40 45 50

Grating length, Lg (mm) Total Loss "T

" (dB)

20nm 40nm 60nm 80nm

Detectable limit line

- Possible detecting grating length (L

) is under 5.5 mm.

- 1 nm thickness variation of the bio-molecule layer can be detected over 2 mm grating length (L_g).

- Calculated minimum thickness variation of the bio-molecule layer is 0.36 nmat 40 nm grating depth..

0 2 4 6 8 10

0.0 0.4 0.8 1.2 1.6

Resolution,  t

(n m)

Grating length, Lg (mm)

20nm 40nm 60nm 80nm

1 nm

Detectable range

grating length, L

(mm)

The sensitivity increases as increasing the Bragg grating length or thickness ( ~ 10^-6 RIU )

Bragg grating

-fluidic channel

gold strip x

y z

Cladding index : 1.35 Core index : 1.33

Grating period : 528 nm Wavelength : 1550 nm

3. LR-SPP waveguide bio sensor

2 3 4 5 6 7

0 1 2

3 20 nm

40 nm 60 nm 80 nm

Index resolution( x10 RIU)

Substrate z

y Cladding

Cladding

450 nm D_g

L_g

Sample index : 1.325 ~ 1.340

3. LR-SPP waveguide bio sensor

6. Conclusion

• Proposing a novel model of LRSPP sensor on asymmetric double metallic structure.

- Easy to excite the LRSPP mode using end-fire coupling method.

- Still having the advantages of double metallic waveguide.

- Easy to control the sensor properties adjusting the core thickness or grating depth.

- Compensating temperature fluctuation (self-referencing) due to thermal-optic polymers.

- ~ 10^-6RIU (sensitivity), ± 27 pm/K (temperature inaccuracy)

• Possible to detect the under 1 nm thickness variation of a target bio-molecule layer.

- Possible Bragg grating length under 30dB: 2 mm ~ 5.5 mm - Maximum detectable resolution is 0.36 nm