The Research On Super-resolution Achromatic Metalens

Super-resolution microscopic imaging system is essential for life science research because it can observe subcellular structure.However,the reported super-resolution microscopy techniques either require the use of probes,or rely on fluorescent labeling or post-processing techniques.In this context,the development of far-field unlabeled optical super-resolution microscopy has become an urgent need.The key to develop the microscope system is the lens,which has the problems of diffraction limit and chromatic aberration.Optical superoscillation provides an effective way for lens to break through the diffraction limit.However,the super-oscillation lens is designed only for single wavelength or multiple discrete wavelengths.At present,there is no report on broadband achromatic super-oscillation lens.On the other hand,the metasurface has become an effective carrier of broadband achromatic lens own to its excellent regulation ability in optical field.However,most of the achromatic metalens are diffraction limited with small numerical aperture.The reported super-resolution achromatic metalens utilise amplitude control,so it is difficult to improve the focusing efficiency.Based on the above problems,it has scientific significance and application prospect to carry out the research on the super-resolution achromatic metalens(SAML).The main work of this thesis is as follows:(1)In order to solve the problem that the existing achromatic lens is difficult to realize super-resolution and achromatic focusing simultaneously,a design method of SAML based on phase shaping and dispersion engineering is proposed here.The method integrates the phase shaping with superoscillation and the dispersion engineering in metasurface.Based on this method,a THz SAML with numerical aperture 0.4,diameter 12.48 mm,focal length 14.4mm and working wavelength 105 μm-135 μm is designed.The optical simulation results of SAML designed show that it can achieve super-resolution achromatic focusing in the designed band.(2)To solve the problem that the numerical aperture of SAML reported is hard to be improved due to the limitation of meta-atoms’ group delay,Optimization for large group delay dispersive meta-atoms is carried out in this thesis.The meta-atoms using double-stripes structure with high refractive index have period of 60 μm(0.5 λ)and depth of 65.7 μm.The maximum relative group delay is 2154.76 fs.Based on the meta-atoms,Here we have designed a lens with larger numerical aperture(NA = 0.4)than the existing SAML,which is more suitable for the application of high resolution broadband microimaging.(3)The designed lens is processed and tested.Under the broadband illumination under the wavelength of 114.5μm-120μm,the lens achieves super-resolution focusing in the depth of focus.The theoretical focal length is within the depth of focus,the focal spot size of the focal plane is smaller than the diffraction limit calculated by the minimum wavelength,and the sidelobe ratio is less than 40%;Under the illumination wavelength of 119.0μm,118.1μm,117.2μm,116.3μm and 115.4μm,the focal spot size(FWHM)is between 1.02-1.24λ,which is less than the diffraction limit of 1.25λ.At the same time,the theoretical focal length is within the depth of focus,within which the lens achieves super-resolution focusing.