Title Page
Abstract
Contents
Chapter 1. Introduction 16
1.1. Introduction to optical metasurfaces 16
1.2. Motivation of this dissertation 18
1.3. Scope and organization 21
Chapter 2. Independent multichannel wavefront modulation for angle multiplexed metasurface holograms 23
2.1. Introduction to metasurface hologram 24
2.2. Design principles 26
2.2.1. Design of angle-multiplexed holograms 26
2.2.2. The detour phase 28
2.2.3. Design of anisotropic meta-atom 30
2.2.4. Numerical demonstrations 32
2.3. Experimental demonstration 37
2.3.1. Fabrication process and measurements 37
2.3.2. Angle-multiplexed hologram with two channels 39
2.3.3. Angle-multiplexed hologram with four channels 42
2.4. Conclusion 46
Chapter 3. Broadband achromatic metasurface doublet for wide-angle imaging in the visible range 48
3.1. Introduction to metasurface lens 49
3.2. Design of dispersion-engineered metasurface doublet 51
3.2.1. Forward model of metasurface doublet 52
3.2.2. Design of each metasurface layer 55
3.2.4. Optimization of metasurface doublet 62
3.3. Simulation results 65
3.3.1. Focusing characteristics of metasurface doublet 65
3.3.2. Imaging performances of metasurface doublet 69
3.3.3. Bandwidth limit of metasurface doublet 72
3.4. Conclusion 74
Chapter 4. Radiation reshaping metasurfaces on III-nitride light emitter 75
4.1. Introduction 75
4.2. Design and analytic model 78
4.2.1. Design of metasurface-integrated light emitter 78
4.2.2. Analytic model for metasurface-integrated light emitter 80
4.3. Experimental demonstrations 83
4.3.1. Fabrication process and measurement setup 83
4.3.2. Radiation patterns of metasurface-integrated emitters 85
4.3.3. Improvement in PL intensity and extraction efficiency 91
4.4. conclusion 96
Chapter 5. Conclusion 97
Bibliography 99
Appendix 106
초록 107
Table 3.1. Optimized coefficients of the metasurface doublet 66
Table 3.2. Quantitative comparison of image quality between metasurface lens design methods. 71
Figure 2.1. Schematic illustration of the detour phase holograms. (a) Functionality of the detour phase holograms using apertures. Two phase profiles for different images... 26
Figure 2.2. (left) Top-view of a composite composed of meta-atom 1 and meta-atom 2. (right) Diffraction characteristics of the composite, depending on the incident angels. 27
Figure 2.3. Schematic illustrations of the detour phase. The phase difference between two adjacent waves is proportional to the displacement △x (△y) of the meta-atoms... 28
Figure 2.4. (a) Schematic illustration of a single amorphous silicon (a-Si) pillar with square cross section, thickness 350 nm and side length s in a unit cell of period (P=... 30
Figure 2.5. Theoretical and simulated results for engineering scattering characteristics using multiple a-Si pillars. (a) A schematic illustration of two a-Si... 31
Figure 2.6. Design configuration of the constructed quadrumers. (a) A top-view schematic of the formulated quadrumer with a period (P) of 700 nm. The a-Si pillars,... 33
Figure 2.7. (a,b) Simulated diffraction efficiencies directed vertically for angles (a) θ₀=sin⁻¹(λ/P) and (b) -θ₀ across the wavelength range of 400 nm to 700 nm. (c)... 34
Figure 2.8. Measured refractive index and extinction coefficient of amorphous silicon by spectroscopic ellipsometer from 200 nm to 800 nm. 37
Figure 2.9. Fabrication process for metasurface holograms using the electron beam lithography. 38
Figure 2.10. Optical measurement setup for capturing the reconstructed images. 39
Figure 2.11. (a) Schematic representation of the proposed meta-atom from a top view, showing the displacement (dₓ and dy) in both the x- and y-axes for modulating the...[이미지참조] 40
Figure 2.12. Experimental results for the metasurface hologram made up of identical quadrumers. (a, b) The computed (left) and measured (right) far-field intensity... 42
Figure 2.13. (a) A top view schematic illustration of a composite pixel consisting of a-Si quadrumers (referred to as meta-atom 1) and the rotated quadrumers (referred... 43
Figure 2.14. Experimental results of angle-multiplexed metasurface holograms utilizing a composite arrangement of quadrumers. (a-d) Simulated (left side) and... 44
Figure 2.15. Experimental results of spatially multiplexed holograms. Targeted images are generated on right side of the zeroth order and conversely undesired... 45
Figure 3.1. Schematic illustration of metasurface lenses: (a) Single-layered, achromatic metasurface lens and (b) corresponding normalized intensity... 51
Figure 3.2. Schematic illustration of forward model for calculating an intensity profile at focal plane. 53
Figure 3.3. Flowchart for modelling dispersive phase profiles which are supposed to be continuous and differentiable. Based on the simulation results, phase delays of... 54
Figure 3.4. Modelling meta-atoms on the frontside: (a) A schematic of the frontside metasurface composed of isotropic meta-atoms with square cross-sections, a period... 56
Figure 3.5. Angle-dependent optical response of meta-atom: (a,b) Magnetic field intensity |H| distributions in xz-plane for incident angles of (a) 0° and (b) 25°. (c)... 59
Figure 3.6. Angle-dependency on wavefront modulation: (a) Simulated far-field intensities of a supercell structure composed of 10 varying isotropic nano-pillars.... 60
Figure 3.7. Modelling of meta-atoms on the backside: (a) Schematic of the metasurface on the backside composed of anisotropic meta-atoms with rectangular... 61
Figure 3.8. Optimization flowchart: Each calculation from optimization coefficients to the objective function is differentiable function. Using the gradients of the... 64
Figure 3.9. Optimization results of the metasurface doublet: Optimized phase profiles at different wavelengths on (a) the frontside and (b) the backside. 65
Figure 3.10. Simulation results for the focal spots and modulation transfer functions (MTF) of the designed lens: (a) Normalized intensity distributions at the focal spot... 67
Figure 3.11. Focusing performance indicators of the designed metasurface doublet: (a) Strehl ratios (SRs) as a function of incident angle for different wavelengths of... 69
Figure 3.12. Image formation of metasurface lenses: (a) A binary image of the checker pattern and (b) a captured image of the color checkerboard numerically... 71
Figure 3.13. Comparison of the bandwidth for the designed doublet and the singlet. 73
Figure 4.1. Design of the proposed device. (a) A schematic illustration of the metasurface on III-nitride LED. The LED epitaxy with a peak wavelength of 460 nm... 79
Figure 4.2. Fabrication of metasurfaces. (a) Flowchart of fabrication process for metasurface-integrated light emitter. (b) Top-view image and (c) tilted view image... 83
Figure 4.3. Optical measurement setup for obtaining (a) emission spectrum and (b) back focal plane image. 84
Figure 4.4. Measured back focal plane images of PL emission. (a) A planar III-nitride epitaxy. (b,c) A uniform array of nano-pillars on III-nitride light emitters with... 87
Figure 4.5. Measured back focal plane images of PL emission of metasurfaces on III-nitride light emitter. Metasurfaces are designed to redirect the light along x-axis with... 88
Figure 4.6. Comparison of wavelength-resolved PL back focal plane images of metasurface-integrated light emitters according to imparted momenta. 90
Figure 4.7. Measured back focal plane images of PL emission of beam splitting metasurface-integrated light emitters. Metasurfaces are designed to split the light... 91
Figure 4.8. Comparison of measured PL intensity spectra for planar epitaxy and metasurface-integrated light emitters. Blue area indicates the estimated bounds for... 92
Figure 4.9. Comparison of absorption and Purcell factor between planar epitaxy and metasurface-integrated light emitters. (a,b) Simulated distributions of (a) electric... 94