Composite metasurfaces for functional optical elements

It is known that the amplitude, polarization and behavior of the light can be controlled through wavefront manipulation. Currently, there are optical elements that can achieve such a manipulation. These optical elements are conventional optical components such as lenses, mirrors and optical filters. Due to their bulky and uneven structures, they manipulate light with their surface forms. This manipulation is accomplished by shaping the surface forms of the optical materials, changing their thickness or opening slits on their surfaces. However, in general, the length of the path the light travels in the structure is considerably larger than the operating wavelength of the system. This severely limits the range of materials that can be employed and also complicates the fabrication processes, which include cutting, grinding and polishing. In addition, conventional optical elements need to be aligned and retained with tight tolerances. Together with this, wearable, portable, mobile electronic and medical devices have rapidly increased demand for low-cost, high-performance optical systems that are compact in size. The need for high-performance optical systems and such production, volume and material problems in traditional optics has recently triggered the acceleration of research in this area and the development of metasurfaces. The metasurfaces are flat optic surfaces that can control the phase of the light by their nano-pillar array with a certain array of patterns. In this thesis, different design approaches of metasurface are explained and various metasurface design topologies are compared. With this comparison, the most efficient topology has been identified. In addition, various application designs are proposed by using metasurfaces. One of these is a three-focus optical system. With this optical system operating at a wavelength of 600nm, the distances between the metalenses are changed to achieve three different focal lengths. Finally, a focal plane array operating in the mid-infrared spectrum is implemented using metasurfaces. This paper presents a polarization independent focal plane array operating in wideband spectrum with superior optical crosstalk. The efficiency of this focal plane array was obtained above 0.85. In this design, focusing efficiency is above 85% while optical crosstalk is below 2.8%. This study has shown that meta-lens array has great potential to increase the sensitivity and the signal-to-noise ratio. Keywords: Metasurfaces, Metalenses, Focal plane arrays