Compensation of refractive dispersion of materials with metasurfaces

Abstract

Metasurfaces are a class of two dimensional nano-engineered materials capable of controlling light-matter interaction at interfaces. These materials which are composed of subwavelength phase-shifters can tailor properties of light at will. Today, efforts are taken to improve functionality and minimize the size and weight of optical devices. Metasurfaces being planar, light weight and providing light control are good candidates in revolutionizing a new class of flat optics. This thesis addresses the problem of chromatic aberration in conventional optical components which when ruled out can enhance visible light optical imaging.

Conventional diffractive planar components like flat lenses, diffraction gratings are very much wavelength specific. Such optical components exhibit dispersion phenomenon as the refractive index of the material changes with wavelength. A change in the wavelength then causes focussing problems and chromatic aberrations giving poor image quality. In this thesis, we study the method of compensating for the dispersion of materials by coupling light at the interface of material with metasurfaces.

The study takes into account the dispersive phase compensation approach to achieve achromatic response in optical components. We theoretically show that dispersion of material can be compensated with dispersion of metasurfaces. We experimentally show a single prism turning achromatic, that is, light refracting independent of wavelength because of the modified optical response occurring due to metasurfaces at interface. This achromatic response is achieved for 300 nm visible range bandwidth from 500 to 800 nm. Dispersion of material is measured using Fourier plane imaging microscopy.

The compensation of dispersion being observed in a simple optical component as that of a prism provides motivation for designing achromatic metalenses in the visible range. Since this work addresses the fundamental problem in imaging which is affected by dispersive aberrations, it immediately finds applications in designing broadband visible range achromatic metalenses for imaging systems. These interesting applications towards achieving super-resolved diffraction limited focusing are the major goals regarding the future of this work.