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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.

Published in: Technology

Biomimetics : Compound eyes

  1. 1. Biomimetics : Compound eyes Young Min Song Assistant Professor Department of Electronic Engineering Pusan National University http://sites.google.com/site/youngminsong81 1
  2. 2. A Future for Electronics: Stretchy, Curvy, Bio-Integrated Past Current Future Industrial Personal Bio-Integr. / Bio-Insp. PNAS 106, 10875 (2009). Science 327, 1603 (2010).
  3. 3. Flexible/Stretchable Electronics Samsung Nokia Research Flexible/Stretchable UIUC Sony UCLA LG Market Curved/Flexible Univ. Tokyo UIUC 3
  4. 4. Bio-integration: examples Optogenetics Science 340, 211 (2013) 4
  5. 5. Bio-integration: examples Transient Electronics Science 337, 1640 (2012) 5
  6. 6. Eyes in animal kingdom Camera-type eye, single lens system Human Fly Bird Ant Fish Shrimp Compound eye (Arthropods eye) : 80% of animal species
  7. 7. Anatomy of Eyes Camera-type Eye (single lens system) Compound Eye (apposition type) Microlens Lens Retina Optic Nerve Rhabdom Screening Optic Nerve pigment Ommatidium 7
  8. 8. Artificial (camera) vs. biological (human eye) imaging • Small field of view, high resolution imaging • Complex multi-component lens systems to achieve focal imaging plane with small aberrations • Planar CCD detectors Double Gauss focusing lens CCD detector Light receptors (hemispherical) • High field of view, high resolution imaging lens • Simple lens system • Curved (hemispherical) detectors (retina)
  9. 9. Imaging With a Single Lens Planar Camera Ray Tracing 40 20 lens 0 -20 -40 - Planar (commecial camera) - Hemispherical (human eye) - Parabola (ideal) -60 -40 -20 0 Distance (mm) 20 40
  10. 10. Mimicking the human eye form hemispherical PDMS transfer element compressed interconnect ~1 cm ~1 cm radially stretch PDMS form Si focal plane array and release from underlying wafer substrate adhesive cure adhesive; flop over substrate compressible interconnect integrate optics & interconnect to control electronics to complete the device transfer focal plane array onto PDMS Si device island (photodetector & pn diode) hemispherical focal plane array Nature 454, 748 (2008) 10
  11. 11. Mimicking the human eye Eyeball camera mounted on PCB Hemispherical detector 1 cm 1 cm With single lens Image 5 5 mm 10 12 0 5 5 0 5 Nature 454, 748 (2008) (axis scale: mm) Others: Hawk eye, zooming, etc. 11
  12. 12. Anatomy of Eyes Camera-type Eye (single lens system) Compound Eye (apposition type) Microlens Lens Retina Optic Nerve Rhabdom Screening Optic Nerve pigment Ommatidium 12
  13. 13. Research Trends 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) 13
  14. 14. Compound Eye Camera Compound Eye Challenge Microlens Rhabdom Ommatidium Optic Nerve Screening pigment Requirement – Full set of microlens/photoreceptor units with hemispherical geometry 14
  15. 15. Approach – Stretchable Optical/Electrical Subsystem Optical subsystem Elastomeric microlens array Combine, stretch Electrical subsystem Stretchable photodiode array Hemispherical Compound eye camera Y. M. Song et al., Nature 497, 95 (2013) 15
  16. 16. Optical Design Flat ∆φ ∆φ ∆Φ n0 L0 f r Deformed L H rs R n d β Inter-ommatidial angle (∆Φ) ρL0 2Rβ ∆Φ = ,ρ= R 2rs ∆φ0 n0 = 1.0 (air) n = 1.43 (PDMS) > Acceptance angle (∆φ) ∆φ = d rn , f= f n-1 16
  17. 17. Polymeric Microlens Arrays Mechanical modeling PDMS membrane FEM Strain (%) 50 25 0 Optical design Aluminum mold Target FOV ~160°  ∆Φ = 11°, ∆φ = 9.7° L0 r = 0.4 mm, dpost = 0.8 mm, L0 = 0.92 mm r f dpost d Mechanical design h t f = 1.35 mm, h = 0.4 mm, t = 0.55 mm d = 0.16 mm
  18. 18. Electrical Subsystem (Photodiode/Blocking Diode) 2nd 1st Encapsulation metal layer 2nd PI layer metal layer 1st PI layer N+ doped Imaging pixel P+ doped N+ doped Blocking diode Photodiode 200 μm
  19. 19. Integration of Optical/Electrical Subsystem Microlens array Integrated form of lens/pixel arrays (flat state) Photodetector array 5 mm 19
  20. 20. Hemispherical Deformation Fluidic chamber PD/BD array Compound eye camera PDMS Inlet Outlet Flat Deformed 2 mm Y. M. Song et al., Nature 497, 95 (2013) 20
  21. 21. Compound Eye Cameras Natural Artificial Black matrix Microlens array PD/BD array 2 cm Compound eye cameras mounted on PCB Thin film contact pads Black support Integrated form 21
  22. 22. Operating principle Image from scanning 10 x 10 scanning Image from activated PDs ‘+’ image at each microlens Central portion of a camera (8x8 array) 22
  23. 23. Measurement setup - 10 x 10 scanning for high resolution imaging 23
  24. 24. Measurement Representative output images z y 30° 60° 90° z x y 30° 60° 90° x y 30° 60° 90° z Modeling z x x y 30° 60° 90° - 10 x 10 scanning for high resolution imaging Y. M. Song et al., Nature 497, 95 (2013) 24
  25. 25. Imaging with Wide Field of View Object movement Left (- 50°) Center (0°) Right (50°) Laser spot illumination 0° 20° 40° 60° 80° 20° 40° 60° 80° x z y Y. M. Song et al., Nature 497, 95 (2013) 25
  26. 26. Depth of field experiment Camera 40° - 40° DA = 12 mm DB = 12 mm DA = 12 mm DB = 22 mm DA = 12 mm DB = 32 mm Y. M. Song et al., Nature 497, 95 (2013) 26
  27. 27. Applications and future works Surveillance, Military, etc. http://paulmader.blogspot.com/ Novel imaging systems - Apposition type - Superposition type (refractive, reflective, neural) - Polarization, color, etc. 27
  28. 28. Night-active insects – Moth, Mosquito, etc. Imaging type Apposition (daylight) Additional nanostructures Moth eye Superposition (night active) 500 nm Hierarchical micro/nano structure 28
  29. 29. Subwavelength Structures (SWSs) Grating sin   m  n1 sin  m i n2 n2 Equation -2 -1 0 λ 1 Effective medium theory W 2 h Λ neff Λ -2 -1 1 0 1 0 n2 2 1 n1,eff λ … n4,eff Λ -1 0 0 λ Λ 0 n2 1 Zeroth order grating (ZOG)     m  0 Reflectance @ normal incidence  n2  n1  R   n2  n1  2  Antireflective subwavelength structures 29
  30. 30. Previous works / Challenges From nature To optical materials Moth eye 500 nm Opt. Lett. 26, 1642 (2001) Nano Lett. 9, 279 (2009) Key Challenges  Ideal geometry (period, height, shape, packing density)  Optical device applications (PVs, LEDs, etc.) 30
  31. 31. Ideal geometry of SWSs Cone Broadband AR: (1) Shorter period (2) Taller height Parabola Moth eye 500 nm - Difficult to integration (3) Shape (4) Packing density Index discontinuity 4.0 4.0 Flat surface SWS (parabola) SWS (cone) nGaAs = 3.7 2.5 2.0 Air 1.5 3.0 100 % 95 % 90 % 85 % 80 % GaAs substrate 2.0 nair = 1.0 Refractive index 2.5 3.5 Air 3.0 GaAs substrate Refractive index 3.5 1.5 1.0 1.0 0 100 200 Height (nm) 300 400 0 100 200 300 400 Height (nm) 31
  32. 32. Ideal geometry of SWSs Cone shape Parabola shape 800 Reflectance Height (nm) 700 0% 600 4.0% 500 8.0% 2.0% 400 12% 2.0% 16% 10% 300 2.0% 200 > 20% 10% 10% 100 500 1000 1500 2000 2500 3000 500 Wavelength (nm) 1000 1500 2000 2500 3000 Wavelength (nm) Optical modeling: Rigorous Coupled-Wave Analysis(RCWA) Method Y. M. Song et al., Small 6, 984 (2010) 32
  33. 33. Parabola shape SWSs Approach – Lens-like shape transfer Interference lithography PR patterns Reflowed PR patterns Parabola-shaped SWS Photoresist Substrate Y. M. Song et al., Small 6, 984 (2010) Period : 300nm 33
  34. 34. Reflectance characteristics of SWS Reflectance measurement results Reflectance (%) 50 Normal incidence 40 Bulk GaAs GaAs substrate with and without SWS 30 20 10 500 1000 1500 2000 Wavelength (nm) Reflectance (%) 12 Cone Parabola 10 8 Bulk GaAs SWS GaAs 6 4 2 500 1000 1500 Wavelength (nm) 2000 34
  35. 35. Optical device applications Grating equation (reflection) sin  r , m  m n  sin  i Photovoltaic devices n = 1.0 Λ≈ λ -1 Absorbing materials m = +1 n ~ 3.5 Back reflector - Higher order diffraction - Reflection minima θr,m : m-th order reflected diffraction angle θi : incidence angle m : diffraction order λ : incident wavelength Λ : grating period n : refractive index of incident medium Light emitting diodes/materials Transparent glasses/materials n = 1.0 Λ≈ λ -1 m = +1 0 Active medium n ~ 1.5 n ~ 3.5 - Higher order diffraction - Total internal reflection Multiple internal reflection 35
  36. 36. Optical device applications Transparent glasses/materials Light emitting diodes/materials Photovoltaic devices 800 2 Height o 12.71% 400 13.31% 13.92% 300 1 0 -1 14.52% 200 100 nm, 300 nm, 500 nm, 99 12.10% 500 Z (um) Height (nm) i = 20 o Transmittance (%) Cell eff. 11.50% 600 100 i = 0 Cell efficiency Transmittance 700 98 200 nm 400 nm flat surface 97 96 95 94 93 92 91 100 100 200 300 400 500 600 700 800 Period Period (nm) -2 -0.5 0.0 0.5 -0.5 0.0 0.5 90 300 400 X (um) Y. M. Song et al., Appl. Phys. Lett. 97, 093110 (2010) Y. M. Song et al., Opt. Express 19, A157(2011) 600 700 Wavelength Bare glass Y. M. Song et al., Opt. Lett. 35, 276 (2010) Y. M. Song et al., Sol. Mat. 101, 73 (2012) 500 800 Wavelength (nm) Oneside SWS Bothside SWS Y. M. Song et al., Opt. Express 18, 13063 (2010) K. Choi et al., Adv. Mater. (2010) Y. M. Song et al., ‘Antireflective nanostructures for optical device applications’ 36
  37. 37. Thank you! Nature  Bio-inspiration  ‘Beyond biology’ Contact Information Young Min Song ysong@pusan.ac.kr 051-510-3120, 010-2992-8182 http://sites.google.com/site/youngminsong81 37

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