Investigation Of Super-resolution Imaging Functional Devices By Geometric Phase Metasurfaces

Higher resolution is the target of optical imaging and lithography system.But the resolution is limited by the diffraction effect of optical system.Scientists developed various of different methods to achieve super-resolution imaging and got many significant results.However,these systems are usual complex and hard for integrated design.For example,it is necessary to modulate two beams with different wavelengths for the stimulated emission depletion(STED)fluorescence microscopy.Metasurface consisted of sub-wavelength structures is a kind of two dimensional optical element which can achieve light intensity,phase and polarization modulation,which could open a door for the optical engineering at the subwavelength scale.Thus metasurface can be used to design fancy and integrated optical systems which are difficult to be realized in traditional ways(such as fancy phase distribution).Therefore we can design functional elements by metasurfaces to overcome these difficulties in super-resolution imaging system.Geometric phase metasurfaces have advantages of simple design,large tolerance,easy for fabrication and wide range among several different types of metasurfaces.Focusing on the key problems of super-resolution imaging system,we studied functional metasurfaces based on geometric phase:1.We proposed a design method for multi-spectral achromatic metasurfaces based on holography principle and designed a triple wavelengths achromatic focusing lens which demonstrated the method.Based on that,a metasurface STED element iwas designed to achieve double wavelength modulations with single piece of device.We got focused hollow spot and solid spot at same detection plane and same position.The element realized the designed function.2.We proposed a new type of self imaging effect(named as “quasi-Talbot effect” in this thesis)of orbit angular momentum(OAM)beams and studied the mathematic model and physical properties.We found that there was extremely considerable multiplexing factor by quasi-Talbot effect which can be used to generate OAM beam arrays.We designed metasurface OAM arrays generator by this method and validated the design by simulation and experiment.On this foundation,we designed metasurface element with two regions which were responding to different wavelengths and generated hollow spots arrays and solid spots arrays,separately.We validated our design by simulation and experiment.3.We proposed the principle of planar Bessel lens which consisted of the phase maps of focal lens and axicon.The fancy phase distribution of planar optical device was achieved by metasurface.We tested the device in optical imaging system and realized super-resolution imaging with 0.7 times of diffraction limitation.