biomimetics : compound eyes

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Understanding of light sensing organs in biology creates opportunities for the development of novel optic systems that cannot be available with existing technologies. The insect's eyes, i.e., compound eyes, are particularly notable for their exceptional interesting optical characteristics, such as wide fields of view and infinite depth-of-field. While the construction of man-made imaging systems with these characteristics is of interest due to potential for applications in micro air vehicles (MVAs) and clinical endoscopes, currently available devices offer only limited capabilities due to their use of compound lens systems in planar geometries. In this presentation, I discuss a complete set of materials, design layouts and integration schemes for digital cameras that mimic fully hemispherical compound eyes. Certain of the concepts extend recent advances in ‘stretchable electronics’ that provide previously unavailable options in design. I also discuss another interesting hierarchical micro- and nanostructures that can be found in eyes of night-active insects such as moth and mosquito. I present research trends on fabrication methods, optical characteristics, and various applications for artificial micro-/nanostructures that resemble ‘moth eye’ structure.

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Page 1: Biomimetics : Compound eyes

Biomimetics : Compound eyes

Young Min SongAssistant Professor

Department of Electronic EngineeringPusan National University

http://sites.google.com/site/youngminsong811

Page 2: Biomimetics : Compound eyes

A Future for Electronics: Stretchy, Curvy, Bio-Integrated

Bio-Integr. / Bio-Insp.Industrial Personal

Past Current Future

PNAS 106, 10875 (2009). Science 327, 1603 (2010).

Page 3: Biomimetics : Compound eyes

Flexible/Stretchable Electronics

3

LG

NokiaSamsung

Sony

MarketCurved/Flexible

ResearchFlexible/Stretchable

UIUC

UCLA

UIUC

Univ. Tokyo

Page 4: Biomimetics : Compound eyes

Bio-integration: examples

4

Optogenetics

Science 340, 211 (2013)

Page 5: Biomimetics : Compound eyes

Bio-integration: examples

5

Transient Electronics

Science 337, 1640 (2012)

Page 6: Biomimetics : Compound eyes

Eyes in animal kingdom

Fly Ant Shrimp

Compound eye (Arthropods eye) : 80% of animal species

Human Bird Fish

Camera-type eye, single lens system

Page 7: Biomimetics : Compound eyes

Anatomy of Eyes

Compound Eye(apposition type)

Camera-type Eye(single lens system)

LensRetina

Optic Nerve Optic Nerve

Microlens

Screening pigment

Rhabdom

Ommatidium

7

Page 8: Biomimetics : Compound eyes

Artificial (camera) vs. biological (human eye) imaging

• High field of view, high resolution imaging

• Simple lens system

• Curved (hemispherical) detectors (retina)

CCD detectorDouble Gauss focusing lens

• Small field of view, high resolution imaging

• Complex multi-component lens systems to achieve focal imaging plane with small aberrations

• Planar CCD detectors

lens

Light receptors(hemispherical)

Page 9: Biomimetics : Compound eyes

Imaging With a Single Lens

Planar CameraRay Tracing

Distance (mm)-60 -40 -20 0 20 40

-40

-20

0

20

40

lens

- Planar (commecial camera)- Hemispherical (human eye)- Parabola (ideal)

Page 10: Biomimetics : Compound eyes

10

Mimicking the human eye

cure adhesive; flop over substrate

hemispherical focal plane array

integrate optics &interconnect to control electronics to complete the device

compressedinterconnect

~1 cm

adhesive

cure adhesive; flop over substrate

hemispherical focal plane array

integrate optics &interconnect to control electronics to complete the device

compressedinterconnect

~1 cm

adhesive

form hemispherical PDMS transfer element

radially stretch PDMS

transfer focal plane array onto PDMS

form Si focal plane arrayand release from underlyingwafer substrate

compressibleinterconnect

Si device island(photodetector& pn diode)

~1 cm

Nature 454, 748 (2008)

Page 11: Biomimetics : Compound eyes

11

Mimicking the human eye

5 mm

With single lens Image

1012

50 5 5

05

(axis scale: mm)

Hemispherical detector

1 cm1 cm

Eyeball camera mounted on PCB

Nature 454, 748 (2008)

Others: Hawk eye, zooming, etc.

Page 12: Biomimetics : Compound eyes

Anatomy of Eyes

Compound Eye(apposition type)

Camera-type Eye(single lens system)

LensRetina

Optic Nerve Optic Nerve

Microlens

Screening pigment

Rhabdom

Ommatidium

12

Page 13: Biomimetics : Compound eyes

Research Trends

13

Europe – CURVACE (Curved Artificial Compound Eyes): 2009-2013, Collaborative project (EPFL, ISF Fraunhofer, etc. )

the Future and Emerging Technologies (FET) programme within the Seventh Framework Programme for Research of the European Commission, under FETOpen grant number: 237940

Japan – TOMBO (thin observation modules by bound optics): 2000-present, Osaka Univ., etc.

US – UCB, UIUC, Harvard Univ., Ohio Univ., etc.: 2000~present, Optic components/systems Science (2006)

Page 14: Biomimetics : Compound eyes

Compound Eye Camera

ChallengeCompound Eye

Optic Nerve

Microlens

Screening pigment

Rhabdom

Ommatidium

Requirement – Full set of microlens/photoreceptor units with hemispherical geometry

14

Page 15: Biomimetics : Compound eyes

Approach – Stretchable Optical/Electrical Subsystem

Stretchablephotodiode array

Combine, stretch

Elastomericmicrolens array

Hemispherical Compound eye camera

Y. M. Song et al., Nature 497, 95 (2013)

Optical subsystem

Electrical subsystem

15

Page 16: Biomimetics : Compound eyes

∆Φ ∆φ

L

R

Hrs

β

r

Optical Design

f

d

n0

n

n0 = 1.0 (air)n = 1.43 (PDMS)

∆φ

∆φ0

L0

Flat

Deformed

Inter-ommatidial angle (∆Φ)

∆Φ = RρL0 , ρ = 2rs

2RβAcceptance angle (∆φ)

∆φ = fd

, f = n-1rn

>

16

Page 17: Biomimetics : Compound eyes

Polymeric Microlens Arrays

Aluminum mold

PDMS membrane

r = 0.4 mm, dpost = 0.8 mm, L0 = 0.92 mm

f = 1.35 mm, h = 0.4 mm, t = 0.55 mm

d = 0.16 mm

L0

ht

d

r

dpostf

Target FOV ~160° ∆Φ = 11°, ∆φ = 9.7°

FEM

Strain (%)

2550

0

Optical design Mechanical design

Mechanical modeling

Page 18: Biomimetics : Compound eyes

1st metal layer

2nd metal layer

P+ dopedN+ doped

Encapsulation

2nd PI layer

1st PI layer

N+ dopedImaging pixel

Electrical Subsystem (Photodiode/Blocking Diode)

Blocking diode

Photodiode

200 μm

Page 19: Biomimetics : Compound eyes

Integration of Optical/Electrical Subsystem

5 mm

Integrated form of lens/pixel arrays(flat state)

Microlens array

Photodetector array

19

Page 20: Biomimetics : Compound eyes

Hemispherical Deformation

2 mm

PD/BD array

PDMS

Inlet Outlet

Fluidic chamber

Flat

Deformed

Compound eye camera

Y. M. Song et al., Nature 497, 95 (2013) 20

Page 21: Biomimetics : Compound eyes

Compound Eye Cameras

Natural Black matrix

Black support

Thin film contact pads

Microlens array

PD/BD array

2 cm

Compound eye

cameras mounted on PCB

Artificial

Integrated form

21

Page 22: Biomimetics : Compound eyes

Operating principle

‘+’ image at each microlens

Image fromscanning

Image from activated PDs

(8x8 array)

Central portion of a camera

10 x 10scanning

22

Page 23: Biomimetics : Compound eyes

Measurement setup

- 10 x 10 scanning for high resolution imaging

23

Page 24: Biomimetics : Compound eyes

Representative output images

- 10 x 10 scanning for high resolution imaging

90°60°30°

xy

z xy

z

90°60°30°

90°60°30°

xy

z xy

z

90°60°30°

Mea

sure

men

tM

odel

ing

Y. M. Song et al., Nature 497, 95 (2013) 24

Page 25: Biomimetics : Compound eyes

Imaging with Wide Field of View

Object movement

Center (0°) Right (50°)Left (- 50°)

Laser spot illumination

y

x z

20°40°60°80°

0° 20° 40° 60° 80°

Y. M. Song et al., Nature 497, 95 (2013) 25

Page 26: Biomimetics : Compound eyes

Depth of field experiment

DA = 12 mmDB = 12 mm

DA = 12 mmDB = 22 mm

DA = 12 mmDB = 32 mm

40°

- 40°

Camera

Y. M. Song et al., Nature 497, 95 (2013) 26

Page 27: Biomimetics : Compound eyes

Applications and future works

Novel imaging systems- Apposition type- Superposition type (refractive, reflective, neural)- Polarization, color, etc.

27

http://paulmader.blogspot.com/

Surveillance, Military, etc.

Page 28: Biomimetics : Compound eyes

Night-active insects – Moth, Mosquito, etc.

28

Apposition(daylight)

Superposition(night active)

Imaging type

Moth eye

500 nm

Hierarchical micro/nano structure

Additional nanostructures

Page 29: Biomimetics : Compound eyes

Subwavelength Structures (SWSs)

im nn

nm sinsin

2

1

2

0 m

Λ

h

W

neff

n2

n1,eff

n2

n4,eff

Effective medium theory

Zeroth order grating (ZOG)

Λ0 1 2-1-2

λ

Λ0 1-1

λ

Λ0

λ

0 1 2-1-2

0 11

0

Grating Equation

2

2 1

2 1

n nRn n

Reflectance @ normal incidence

Antireflective subwavelength structures29

Page 30: Biomimetics : Compound eyes

Previous works / Challenges

From nature

500 nm

Moth eye

Opt. Lett. 26, 1642 (2001)Nano Lett. 9, 279 (2009)

To optical materials

Ideal geometry (period, height, shape, packing density)

Optical device applications (PVs, LEDs, etc.)

Key Challenges

30

Page 31: Biomimetics : Compound eyes

Ideal geometry of SWSs

(3) Shape

0 100 200 300 400

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Ref

ract

ive

inde

x

Height (nm)

Flat surface SWS (parabola) SWS (cone)

GaA

s su

bstra

te

nGaAs = 3.7nair = 1.0

Air

(4) Packing density

0 100 200 300 400

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Ref

ract

ive

inde

x

Height (nm)

100 % 95 % 90 % 85 % 80 %

GaA

s su

bstra

te

Air

Index discontinuity

500 nm

Cone Parabola Moth eyeBroadband AR:(1) Shorter period(2) Taller height

- Difficult to integration

31

Page 32: Biomimetics : Compound eyes

Ideal geometry of SWSs

2.0%

10%

500 1000 1500 2000 2500 3000100

200

300

400

500

600

700

800

Wavelength (nm)

Hei

ght (

nm)

10%

2.0%

2.0%

10%

500 1000 1500 2000 2500 3000

Wavelength (nm)

0%

4.0%

8.0%

12%

16%

20%

Reflectance

>

Y. M. Song et al., Small 6, 984 (2010)

Optical modeling:Rigorous Coupled-Wave Analysis(RCWA) Method

Parabola shapeCone shape

32

Page 33: Biomimetics : Compound eyes

Parabola shape SWSs

Parabola-shaped SWS

PR patterns Reflowed PR patterns

SubstratePhotoresist

Interference lithography

Period : 300nm

Approach – Lens-like shape transfer

Y. M. Song et al., Small 6, 984 (2010)33

Page 34: Biomimetics : Compound eyes

Reflectance characteristics of SWS

Bulk GaAs SWS GaAs

GaAs substrate with and without SWS

Reflectance measurement results

500 1000 1500 2000

10

20

30

40

50

Bulk GaAs

R

efle

ctan

ce (%

)

Wavelength (nm)

Normal incidence

500 1000 1500 2000

2

4

6

8

10

12

Ref

lect

ance

(%)

Wavelength (nm)

Cone Parabola

34

Page 35: Biomimetics : Compound eyes

Optical device applications

Photovoltaic devicesLight emitting

diodes/materials Transparent

glasses/materials

Back reflector

Absorbing materials

,sin sinr m i

m

n

Grating equation (reflection) θr,m : m-th order reflected diffraction angleθi : incidence anglem : diffraction orderλ : incident wavelengthΛ : grating periodn : refractive index of incident medium

n ~ 3.5

n = 1.0Λ ≈ λ

n ~ 3.5

n = 1.0

m = +1-1 0

Λ ≈ λ

Active medium n ~ 1.5

- Higher order diffraction- Total internal reflection Multiple internal reflection

m = +1-1

- Higher order diffraction- Reflection minima

35

Page 36: Biomimetics : Compound eyes

Optical device applications

100 200 300 400 500 600 700 800100

200

300

400

500

600

700

800

Period (nm)

Hei

ght (

nm)

11.50%

12.10%

12.71%

13.31%

13.92%

14.52%

Cell efficiency

Hei

ght

PeriodC

ell e

ff.

Y. M. Song et al., Opt. Lett. 35, 276 (2010)Y. M. Song et al., Sol. Mat. 101, 73 (2012)

-0.5 0.0 0.5-2

-1

0

1

2i = 20o

X (um)

Z (u

m)

-0.5 0.0 0.5

i = 0o

Y. M. Song et al., Appl. Phys. Lett. 97, 093110 (2010)Y. M. Song et al., Opt. Express 19, A157(2011)

300 400 500 600 700 80090919293949596979899

100

Tran

smitt

ance

(%)

Wavelength (nm)

100 nm, 200 nm 300 nm, 400 nm 500 nm, flat surface

Wavelength

Bare glass

One-side SWS

Both-side SWS

Y. M. Song et al., Opt. Express 18, 13063 (2010)K. Choi et al., Adv. Mater. (2010)

Photovoltaic devices Light emitting diodes/materials

Tran

smitt

ance

Transparent glasses/materials

Y. M. Song et al., ‘Antireflective nanostructures for optical device applications’36

Page 37: Biomimetics : Compound eyes

Nature Bio-inspiration ‘Beyond biology’

37

Contact InformationYoung Min [email protected], 010-2992-8182http://sites.google.com/site/youngminsong81

Thank you!