| Computer-generated holography(CGH)is regarded as a promising display technology due to its powerful light field reconstruction ability.CGH provides a proven solution for naked-eye 3-dimensional display,augmented reality,and virtual reality.Meanwhile,CGH based on metasurface has extra significant advantages in viewing angle,integration,and efficiency compared to other hardware.However,the existing research on metasurfaces-based CGH still has major defects in holographic image quality,information density,and application scenarios,which cannot meet the development needs of the practical applications.To promote the development and application of metasurfaces-based CGH,the following research contents are carried out in this thesis:All-dielectric metasurfaces-based CGH has been suffering from the lowquality reconstructed images.Firstly,the coherence artifacts in metasurfaces-based CGH were suppressed using the degenerate cavity laser(DCL),which can finely turn the spatial coherence of the output light.Three origins of the coherence artifacts were clearly shown in the thesis: local optical vortices,the coupling effect of the neighboring antennas,and the random scattering by the nanoparticle.The thesis proved that the coherence artifacts from all the origins and all kinds of metasurfaces could be suppressed by lowering the spatial coherence of DCL.The theoretical holography projecting model was established to predict the key parameters(image uniformity,sharpness,and contrast-to-noise ratio)for hologram images versus spatial coherence.with different spatial frequencies.The method of adjusting spatial coherence to suppress artifacts is universal and economical.Compared with the traditional method of adjusting temporal coherence,it shows unique advantages in avoiding dispersion in the CGH.This work is of great significance for realizing metasurfaces-based CGH with uniform intensity and sharp edges.Besides the low image quality,all-dielectric metasurfaces-based CGH has also been suffering from the statistic limit.Then the reconfigurable metasurfaces-based CGH with bigger information density and more multiplexing channels was demonstrated by modulating the incident light field.Dual-functional switching CGH was realized by modulating the amplitude profile of the incident light.Arbitrary metasurfaces-based CGH was further realized by modulating the phase profile.Based on reconfigurable metasurfaces-based CGH,the thesis demonstrated its application in optical encryption.By considering the incident light field as the ciphertext and the metasurface as the secret key,optical encryption with high degree of encryption was realized.The thesis increases the information density of metasurfaces-based CGH and provides a possible solution for real-time applications such as holographic video encrypted transmission.Based on the previous results of reconfigurable metasurfaces-based CGH,the thesis further studied its application on optical computing,riching the application scenario of all-dielectric metasurfaces-based CGH.By carefully designing the response of metasurfaces to light sources with different patterns,the recognition of handwritten digits was demonstrated.A hybrid optical-electronic neural network(OENN)was proposed by combining a single-layer metasurface with a fullyconnected layer.The OENN achieved a blind test accuracy of 98.65% and 98.05%in simulation and experiment on the MNIST handwritten digit dataset.Compared with the previous optical computing work,the framework of this paper showed high experimental robustness,and thus achieved the highest experimental blind test accuracy on the MNIST dataset.The unique mechanism of the diffraction processes and recording processes of computational holography to enhance the optical computing capacity was theoretically discussed in detail.The OENN is of great significance for expanding the application scenarios of CGH and realizing optical neural networks with high robustness,strong computing ability,and easy deployment. |
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