Fabrication And Performance Of Optical Metalenses

With the development of nanofabrication technology,metasurfaces composed of subwavelength unit cells achieved a new breakthrough in optical design principles and provided a new means of manipulating light.Metalens has ultrathin and ultralight structural feature as one of the typical applications.High performance metalenses are expected to be put into practical application and production to improve the existing optical systems.Focusing on the fabrication and performance of metalenses,this thesis proposes the development and optimization of the nanofabrication process according to the performance improvement and application requirements of metalenses in different material systems.The new design of a bilayer metallic metalens and the filter-integrated dielectric achromatic metalens are proposed,respectively.The particular contents are as follows:1.The nanofabrication technology of metasurfaces was introduced systematically.The principle and critical parameters of the two processes including electron beam lithography and inductively coupled plasma etching were discussed in detail.To meet the requirements of high aspect ratio structure of metalens,we optimized the process parameters.After completing the fabrication of the metalens in different material systems,we investigated their morphological characteristics and measured their optical properties in the experiment.2.Based on the conventional metallic metalens,a cavity enhanced bilayer metalens composed of aluminum nanobars and its complementary structures was demonstrated.By introducing a layer of resist and a metal film on top of the resist,a bilayer nanostructure unit which is similar to an optical resonator cavity was demonstrated to enhance the interaction between the light and structures.We proved that the diffraction efficiency and the total efficiency of the bilayer metalens are greatly improved,including the focusing and imaging performance compared with the conventional metallic metalens in both simulation and experiment.The physical mechanisms involved in the performance enhancement of the new designed metalens were calculated and discussed.3.High-quality achromatic microscopic imaging under white light illumination was realized using the bandpass filter-integrated achromatic metalens.Based on a kind of searching optimization algorithm,we first designed a high efficiency achromatic metalens working at red,green and blue wavelengths and then demonstrated the corresponding multi-layer bandpass filter using optimized parameters.We proved that the designed metalens has good achromatic property and high focusing efficiency in simulation and experiment.Finally,the complete device of the filter-integrated achromatic metalens was measured and compared with the achromatic metalens without the bandpass filter which proves the necessity of the filter in the white light imaging system.Our method provides a new way to control the phase and spectral response of metasurfaces simultaneously.