Research On Large Field Of View Broadband Super-resolution Imaging Method By Manipulating Super-oscillatory Field

As an inherent property of light wave,diffraction causes the existence of resolution limit for optical imaging systems,which cannot meet the increasing demand for high-resolution imaging.Breaking the diffraction limit and realizing super-resolution imaging enable people to understand the world more clearly,contribute to the progress of science and technology,and gradually become one of the key topics of current scientific research.Current super-resolution imaging methods are mainly suitable for microscopic imaging system.Near-field super-resolution imaging methods,such as scanning near-field optical microscopy and super-lens,can achieve nano-resolution sub-diffraction imaging by detecting and collecting high-frequency evanescent wave components bound to the surface of object,but these methods require complex and precise near-field operation.Stimulated emission depletion microscope,photoactivated localization microscopy and stochastic optical reconstruction microscope have achieved far-field super-resolution imaging based on the stimulated emission characteristics of fluorescent molecules,and have been widely applied in super-resolution microscopic imaging systems.However,these methods need pre-dying and labeling for samples and complicated image reconstruction algorithm,which may influence the performance of the target sample.In recent years,as one kind of far-field super-resolution imaging method,optical super-oscillatory imaging can construct the desired super-oscillatory field by fine interference and generate high-frequency sub-diffraction information containing object details in the local area of far-field.In this way,real-time noninvasive super-resolution imaging can be realized without posterior processing.Compared with other super-resolution imaging methods,the optical super-oscillatory imaging method is simple to implement and is expected to be widely used in imaging systems such as microscopy and telescope.However,there are still some complicated problems,such as harmful sidelobes around the mainlobe,limited working bandwidth and field of view.In order to solve these problems,we have carried out the research on large field of view broadband super-resolution imaging method by manipulating super-oscillatory field.The content of the thesis includes:(1)The construction of super-oscillatory light field is divided into two parts to realize fine interference and focusing respectively,and an achromatic super-resolution imaging system working in the whole visible waveband is designed and built.The sub-wavelength structures with different rotation directions based on geometric phase principle are used to realize dispersionless phase modulation of different wavelengths.Combined with traditional achromatic lens,the broadband dispersionless super-oscillatory light field is constructed,which solves the problems of material dispersion and axial chromatic aberration in the traditional phase modulation method based on diffractive optical elements.In the experiment,broadband super-resolution imaging of the extended target was verified in the visible spectrum from 400 nm to 700 nm,and the resolution of up to 0.625 times diffraction limit was obtained.(2)A super-oscillatory scanning imaging method is proposed.A pinhole diaphragm with a certain size is placed on the primary image plane of the imaging system to limit the imaging area,and the super-resolution image of the corresponding area is extracted and stitched together to form the super-resolution image of the object.Compared with traditional super-oscillatory imaging,it effectively avoids the influence of high-intensity sidelobes outside the field of view of the super-oscillatory focal spot.In addition,the influence of pinholes with different sizes on the subsequent light field of the system is simulated by scalar angular spectrum diffraction method,and it is found that the existence of the pinhole diaphragm will cause the light field distribution of the exit pupil plane to deviate from the ideal plane wave.Specifically,there is slight phase change,while the amplitude has an oscillatory profile,and the smaller the pinhole is,the more obvious the amplitude oscillates.It is proved that the pinhole diaphragm will affect the sub-diffraction performance,leading to the widening of the main lobe of the super-oscillatory focal spot and the rising of the sidelobes within the local field of view,which have been demonstrated in the experiments.At last,the design requirement of the super-oscillatory device for super-oscillatory scanning imaging mode(NA=0.009)is obtained.The local field of view of the super-oscillatory spot should not be less than the diameter of the pinhole and the semi-diameter of the pinhole should be larger than5.4 times of the diffraction-limit.(3)To solve the problem of limited field of view in super-oscillatory lenses,a design method working for large field of view is proposed.Based on the particle swarm optimization algorithm,a super-oscillatory phase optimization method that can be used in optical imaging system with a large numerical aperture is developed.Benefiting from traditional wide-angle optical imaging systems,a double-layer metasurface doublet based on the geometric phase principle is designed,which can substantially correct off-axis aberrations.High-aspect-ratio titanium dioxide nanopillars with different rotation directions are used to achieve the desired geometric phase modulations with high efficiency to construct the required super-oscillatory light field.The simulation results verify the sub-diffraction focusing performance of up to 0.65 times diffraction limit within the field of view of 50°.Additionally,the focusing efficiencies for different field of views are nearly the same.(4)The optical super-resolution imaging method based on super-oscillatory phenomenon is applied to the field of apodization imaging,and a design method for broadband achromatic super-oscillatory apodization filter is proposed.Through the fine modulation for light of different frequency components,the sidelobe intensity within the local field of view of the sub-diffraction focal spot is considerably suppressed with resolution of diffraction limit or even sub-diffraction.Compared to phase apodization filters,the systematic working efficiency increases by 2 and the bandwidth is improved from 10 nm to 300 nm.Compared to Gaussian apodization filters,the imaging contrast increase by 3.In the simulation,the apodization imaging with a relative intensity of 10^-5 in the designate field of view was demonstrated.The experiment verified the good performance of the super-oscillatory apodization filter on the compression of sidelobes within the local field of view of the focal spot in the visible waveband ranging from400 nm to 700 nm.