Tunable Edge-enhanced Images Based On Computing Metasurfaces

Image processing and edge detection are at the core of many emerging technologies,such as augmented reality,autonomous driving,and more generally face recognition,and so on.Nowadays,image processing usually uses integrated electronic circuits and algorithms for digital processing,which means that its image processing speed is not fast enough and its power consumption is large.In recent years,optical analog computing has attracted extensive attention because of its ultrafast computing speed,low power consumption and parallel computing capability.Optical analog computing shows unique advantages in all-optical imaging processing.In this thesis,a scheme that can realize tunable edge imaging and rapidly switches between bright-field imaging and edge-enhanced imaging has been proposed.The scheme combines the Pancharatnam-Berry phase computing metasurface and the electrically tunable liquid-crystal phase plate.When a beam of linear polarized light propagates through this computing metasurface,the handedness of the left-handed and right-handed circular polarization components of the linearly polarized light reverses,and at the same time,the two components aquires an additional positive or negative Pancharatnam-Berry phase,respectively.This phase gradient causes a small shift of the beam in the momentum space.As the beam propagates forward in momentum space,the shift in momentum space can eventually lead to a small shift of the beam in real space.Notably,the left-handed and right-handed circular polarization components are not completely separated,their superposition area still appears as linear polarization.If a polarizer is employed behind the metasurface,one can realize the edge detection of the object.The scheme introduces different phase retardances on these two components by regulating the external voltages applied on the liquid-crystal phase plate.This allows the output light field to be a linear combination of the input field and the differentiation of the input field,and by adjusting the phase retardances of the liquid-crystal phase plate one can change the coefficients of the two fields,thus enabling fast switching between bright-field imaging and edge-enhanced imaging.This thesis demonstrates the feasibility of the scheme in theoretical,software simulation and experimental,respectively,and finally uses the software to simulate the output images of the scheme in different bands and expand the one-dimension edge imaging to two-dimension edge imaging.