Biomimetics : Compound eyes

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.

1. Biomimetics: Compound eyes
Young Min Song
Assistant Professor
Department of Electronic Engineering
Pusan National University
http://sites.google.com/site/youngminsong81
1

2. A Future for Electronics: Stretchy, Curvy, Bio-Integrated
Bio-Integr. / Bio-Insp.
Industrial
Personal
Past
Current
Future
PNAS106, 10875 (2009). Science327, 1603 (2010).

3. Flexible/Stretchable Electronics
3
LG
Nokia
Samsung
Sony
Market
Curved/Flexible
Research Flexible/Stretchable
UIUC
UCLA
UIUC
Univ. Tokyo

4. Bio-integration: examples
4
Optogenetics
Science 340, 211 (2013)

5. Bio-integration: examples
5
Transient Electronics
Science 337, 1640 (2012)

6. Eyes in animal kingdom
FlyAntShrimp
Compound eye (Arthropods eye) : 80% of animal species
Human Bird
Fish
Camera-type eye, single lens system

7. Anatomy of Eyes
Compound Eye
(apposition type)
Camera-type Eye
(single lens system)
Lens
Retina
Optic
Nerve
Optic Nerve
Microlens
Screening
pigment
Rhabdom
Ommatidium
7

8. Artificial (camera) vs. biological (human eye) imaging
•High field of view, high resolution imaging
•Simple lens system
•Curved (hemispherical)detectors (retina)
CCD detector
Double Gauss focusing lens
•Small field of view, high resolution imaging
•Complex multi-component lens systems to achieve
focal imaging plane with small aberrations
•PlanarCCD detectors
lens
Light receptors
(hemispherical)

9. Imaging With a Single Lens
Planar Camera
Ray Tracing
Distance (mm)
-60-40-20 02040
-40
-20
0
20
40
lens
- Planar (commecial camera)
- Hemispherical (human eye)
- Parabola (ideal)

10. 10
Mimicking the human eye
cure adhesive; flop over substrate
hemispherical focal plane array
integrate optics &
interconnect to control
electronics to complete
the device
compressed
interconnect
~1 cm
adhesive
cure adhesive; flop over substrate
hemispherical focal plane array
integrate optics &
interconnect to control
electronics to complete
the device
compressed
interconnect
~1 cm
adhesive
form hemispherical PDMS transfer element radially stretch PDMS
transfer focal plane array onto PDMS
form Si focal plane array
and release from underlying
wafer substrate
compressible interconnect
Si device island (photodetector
& pn diode)
~1 cm
Nature454, 748 (2008)

11. 11
Mimicking the human eye
5 mm
With single lens
Image
10 12
5
0
5
5
0
5
(axis scale: mm)
Hemispherical detector
1 cm
1 cm
Eyeball camera mounted on PCB
Nature454, 748 (2008)
Others: Hawk eye, zooming, etc.

12. Anatomy of Eyes
Compound Eye
(apposition type)
Camera-type Eye
(single lens system)
Lens
Retina
Optic
Nerve
Optic Nerve
Microlens
Screening
pigment
Rhabdom
Ommatidium
12

13. 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)

14. Compound Eye Camera
Challenge
Compound Eye
Optic Nerve
Microlens
Screening
pigment
Rhabdom
Ommatidium
Requirement –Full set of microlens/photoreceptor units
with hemispherical geometry
14

15. Approach –Stretchable Optical/Electrical Subsystem
Stretchable
photodiode array
Combine,
stretch
Elastomeric
microlens array
Hemispherical Compound
eye camera
Y. M. Song et al., Nature 497, 95 (2013)
Optical subsystem
Electrical subsystem
15

16. ∆Φ
∆φ
L
R
H
r
s
β
r
Optical Design
f
d
n
0
n
n
0
= 1.0 (air)
n= 1.43 (PDMS)
∆φ
∆φ 0
L
0
Flat
Deformed
Inter-ommatidial angle (∆Φ)
∆Φ=
R
ρL
0
,ρ=
2r
s
2Rβ
Acceptance angle (∆φ)
∆φ=
f
d
,f =
n-1
rn
>
16

17. Polymeric Microlens Arrays
Aluminum mold
PDMS
membrane
r= 0.4 mm, d
post
= 0.8 mm, L
0
= 0.92 mm
f = 1.35mm, h= 0.4 mm,t = 0.55 mm
d= 0.16 mm
L
0
h
t
dr
d
post
f
Target FOV ~160°∆Φ= 11
°
, ∆φ= 9.7
°
FEM
Strain (%)
25
50
0
Optical design Mechanical design
Mechanical modeling

18. 1
st
metal layer
2
nd
metal layer
P+ doped N+ doped
Encapsulation
2
nd
PI layer
1
st
PI layer
N+ doped
Imaging pixel
Electrical Subsystem (Photodiode/Blocking Diode)
Blocking diode
Photodiode
200 μm

19. Integration of Optical/Electrical Subsystem
5 mm
Integrated form of lens/pixel arrays
(flat state)
Microlens array
Photodetector array
19

20. 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

21. 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

22. Operating principle
‘+’ image at each
microlens
Image from
scanning
Image from
activated PDs
(8x8 array)
Central portion of
a camera
10 x 10
scanning
22

23. Measurement setup
- 10 x 10 scanning for high resolution imaging
23

24. Representative output images
- 10 x 10 scanning for high resolution imaging
90°
60°
30°
x
y
z
x
y
z
90°
60°
30°
90°
60°
30°
x
y
z
x
y
z
90°
60°
30°
Measurement Modeling
Y. M. Song et al., Nature 497, 95 (2013)
24

25. 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

26. Depth of field experiment
D
A
= 12 mm
D
B
= 12 mm
D
A
= 12 mm
D
B
= 22 mm
D
A
= 12 mm
D
B
= 32 mm
40°
-40°
Camera
Y. M. Song et al., Nature 497, 95 (2013)
26

27. 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.

28. Night-active insects –Moth, Mosquito, etc.
28
Apposition
(daylight)
Superposition
(night active)
Imaging type
Moth eye
500 nm
Hierarchical
micro/nano structure
Additional nanostructures

29. Subwavelength Structures (SWSs)
i m
n
n
n
m



sin sin
2
1
2



0



m

Λ
h
W
n
eff
n
2
n
1,eff
n
2
n
4,eff
…
Effective medium theory
Zeroth order
grating (ZOG)
Λ
012 -1 -2
λ
Λ
01 -1
λ
Λ
0
λ
012 -1 -2 01 1
0
Grating
Equation
2
21
21
nn
R
nn




Reflectance @
normal incidence
Antireflective
subwavelength structures
29

30. 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

31. 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


Refractive index
Height (nm)
Flat surface SWS (parabola) SWS (cone)
GaAs substrate
n
GaAs
= 3.7
n
air
= 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


Refractive index
Height (nm)
100 % 95 % 90 % 85 % 80 %
GaAs substrate
Air
Index discontinuity
500 nm
ConeParabolaMoth eye
Broadband AR:
(1) Shorter period
(2) Taller height
- Difficult to integration
31

32. Ideal geometry of SWSs
2.0%
10%
500 1000 1500 2000 2500 3000
100
200
300
400
500
600
700
800
Wavelength (nm)
Height (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 shape Cone shape
32

33. Parabola shape SWSs
Parabola-shaped
SWS
PR patterns
Reflowed PR
patterns
Substrate
Photoresist
Interference
lithography
Period : 300nm
Approach –Lens-like shape transfer Y. M. Song et al., Small 6, 984 (2010)
33

34. Reflectance characteristics of SWS
Bulk GaAsSWS GaAsGaAs substrate with and
without SWS
Reflectance measurement results
500 1000 1500 2000
10
20
30
40
50
Bulk GaAs


Reflectance (%)
Wavelen
g
th
(
nm
)
Normal incidence
500 1000 1500 2000
2
4
6
8
10
12


Reflectance (%)
Wavelen
g
th
(
nm
)
Cone Parabola
34

35. Optical device applications
Photovoltaic devices
Light emitting
diodes/materials
Transparent
glasses/materials
Back reflector
Absorbing
materials
,
sin sin
rm i
m
n





Grating equation (reflection)
θ
r,m
: m-th order reflected diffraction angle
θ
i
: incidence angle
m : diffraction order
λ: incident wavelength
Λ : grating period
n : refractive index of incident medium
n ~ 3.5
n = 1.0
Λ
≈
λ
n ~ 3.5
n = 1.0
m = +1
-10
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

36. Optical device applications
100 200 300 400 500 600 700 800
100
200
300
400
500
600
700
800
Period (nm)
Height (nm)
11.50%
12.10%
12.71%
13.31%
13.92%
14.52%
Cell efficiency
Height
Period
Cell eff.
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
2

i = 20
o
X (um)
Z (um)
-0.5 0.0 0.5

i = 0
o

Y. M. Song et al., Appl. Phys.
Lett. 97, 093110 (2010)
Y. M. Song et al., Opt.
Express 19, A157(2011)
300 400 500 600 700 800
90
91
92
93
94
95
96
97
98
99
100


Transmittance (%)
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
TransmittanceTransparent
glasses/materials
Y. M. Song et al., ‘Antireflective nanostr uctures for optical device applications’
36

37. Nature Bio-inspiration ‘Beyond biology’
37
Contact Information
Young Min Song
[email protected]
051-510-3120, 010-2992-8182 http://sites.google.com/site/youngminsong81
Thank you!