biomimetics : compound eyes
DESCRIPTION
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.TRANSCRIPT
Biomimetics : Compound eyes
Young Min SongAssistant Professor
Department of Electronic EngineeringPusan National University
http://sites.google.com/site/youngminsong811
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).
Flexible/Stretchable Electronics
3
LG
NokiaSamsung
Sony
MarketCurved/Flexible
ResearchFlexible/Stretchable
UIUC
UCLA
UIUC
Univ. Tokyo
Bio-integration: examples
4
Optogenetics
Science 340, 211 (2013)
Bio-integration: examples
5
Transient Electronics
Science 337, 1640 (2012)
Eyes in animal kingdom
Fly Ant Shrimp
Compound eye (Arthropods eye) : 80% of animal species
Human Bird Fish
Camera-type eye, single lens system
Anatomy of Eyes
Compound Eye(apposition type)
Camera-type Eye(single lens system)
LensRetina
Optic Nerve Optic Nerve
Microlens
Screening pigment
Rhabdom
Ommatidium
7
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)
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)
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)
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.
Anatomy of Eyes
Compound Eye(apposition type)
Camera-type Eye(single lens system)
LensRetina
Optic Nerve Optic Nerve
Microlens
Screening pigment
Rhabdom
Ommatidium
12
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)
Compound Eye Camera
ChallengeCompound Eye
Optic Nerve
Microlens
Screening pigment
Rhabdom
Ommatidium
Requirement – Full set of microlens/photoreceptor units with hemispherical geometry
14
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
∆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
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
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
Integration of Optical/Electrical Subsystem
5 mm
Integrated form of lens/pixel arrays(flat state)
Microlens array
Photodetector array
19
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
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
Operating principle
‘+’ image at each microlens
Image fromscanning
Image from activated PDs
(8x8 array)
Central portion of a camera
10 x 10scanning
22
Measurement setup
- 10 x 10 scanning for high resolution imaging
23
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
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
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
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.
Night-active insects – Moth, Mosquito, etc.
28
Apposition(daylight)
Superposition(night active)
Imaging type
Moth eye
500 nm
Hierarchical micro/nano structure
Additional nanostructures
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
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
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
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
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
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
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
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
Nature Bio-inspiration ‘Beyond biology’
37
Contact InformationYoung Min [email protected], 010-2992-8182http://sites.google.com/site/youngminsong81
Thank you!