Investigation On Metasurface-Based Multi-Channel Image Display Device

Metasurface,a subwavelength periodic planar structure with unprecedented capabilities of precisely manipulating the phase,amplitude,polarization,and frequency of light,can be utilized to design optical devices with high resolution,high fidelity,ultra-compactness,and high integration,such as metalenses,holograms,nanoprints,vortex beam generators,and beam splitters,etc.In recent years,due to the extensive and intuitive applications,metasurface-based image display has gradually become a research hotspot.At the beginning,the study of the metasurface-based image display mainly focused on the substitution of the traditional display technologies,which aimed to improve the image quality and make the device lightweight.The employment of multiplexing enabled metasurface with simultaneously controlling multiple optical properties,and granted metasurface-based image display higher information density,better display quality,wider display range,and more display approaches.However,commonly used multiplexing technologies suffer from complex design,sophisticate optical path,and low safety,which hinders the applications on a large scale.Based on the above background,this thesis aims at the field of image display and proposes a multi-channel polychromatic image display technology by combing orientation degeneracy and supercell design.In addition,an image encryption technology is also presented with the help of VC algorithm.The main content of the thesis is given below:1.The interaction between light and matter is introduced and analyzed,the principles of phase and intensity modulated by metasurface unit cell are derived,and the impact of Mie resonance on reflectivity is simulated.By analyzing the transmissivities,reflectivities,and phase modulation along the long and short axes of the nanobrick,the anisotropic nanobrick can be designed as various kinds of wave plate and polarizer.When the nanobrick is optimized as half-wave-plate,the cross-polarization conversion efficiency reaches its maximum.Meanwhile,the phase modulation efficiency comes up to be highest,and the intensity modulation range also becomes widest.Mie resonance theory is introduced,along with the demonstration of the high reflectivity when the magnetic/electric resonance occurs inside the nanobrick under incidence at resonance wavelength by employing electromagnetic simulation software,CST Studio Suite.2.The nanobrick with specific spectrum response is simulated,optimized,and analyzed.According to the primary colors used in additive color mixing,electromagnetic simulation software is applied to model the unit cell based on Al₂O₃substrate and Si nanobrick.The length and width of the nanobrick are set as parameters to be swept,and the reflected cross-polarization（cro-pol）conversion efficiencies from simulated results are carefully selected for an optimal solution with high cro-pol efficiency and low crosstalk.At the same time,the electromagnetic field distributions,dimension error,and coupling effect of the finally picked structures are analyzed.3.The orientation degeneracy of the Malus law is introduced and theoretically analyzed,and the supercell distribution is designed.Proceeding from the Malus law,incident light with different linearly polarization directions can generate the identical output intensity,which indicates that the modulation of the nanobrick has multiple design degrees of freedom,and the metasurface can manipulate the phase and intensity simultaneously.The supercell for balancing the red and green light energy is designed,so that the red and green light have more even energy distribution and higher efficiencies.4.The tri-channel polychromatic image display device and image encryption device are designed and experimentally demonstrated.The distortion correction and energy compensation are conducted on the holographic image.Then,the orientation angle distribution of the nanobrick array is calculated on the basis of intensity modulation function and Simulated Annealing algorithm.The tri-channel polychromatic image display device is manufactured,and the image display ability is tested by subtly set up the optical path.The image encryption device is fabricated with the help of VC algorithm,and the same optical path is applied to test the image encryption capability.In conclusion,this thesis introduces the phase and intensity modulation principle of the metasurface,and the tri-channel polychromatic image display device and image encryption device are designed and fabricated by employing orientation degeneracy,supercell design,and VC algorithm.The desired image display and encryption functionalities of the devices are demonstrated and proven to be extraordinary.