Electromagnetic Wavefront Manipulation with Metasurfaces

Conventional optical devices such as lenses with aberration correction, quarter-wave plate made of birefringent and chiral materials, spatial light modulators, and spiral phase-plates may meet the performance demand in both bandwidth and efficiency, but they are usually bulky, and difficult to integrate in nanophotonic systems. Nevertheless, the market constantly demands cheaper and thinner devices with better performance. In the last few years with the availability of nanoscale fabrication tools, plasmonic metasurfaces with subwavelength unit cells have attracted increasing attention in optics and photonics due to their capability to manipulate beams’ wavefront over a subwavelength distance. Metasurfaces can introduce vast flexibility in the design of optical devices by tailoring the polarization state and wavefront of the beams. The manipulation of the light beams can be realized with resonant elements, which provide phase change discontinuities as the light travels across the metasurface (i.e., structured surface). The possibility of creating abrupt phase changes at optical/infrared frequencies can eliminate the need for propagation path compensation in lensing, or reduce the physical dimensions required for a quarter-wave plate or a phase-plate, because the tailoring of the beam is achieved by resonant printed elements on a metasurface with an extremely subwavelength thickness. Probably even more importantly such abrupt phase changes recently enabled the generation of complex optical beams with orbital angular momentum a reality. Such beam characteristics are desired in many applications such as free space communications, remote sensing, multi-mode communication systems and secure communications. This dissertation focuses on flat thin metasurfaces for wavefront engineering. We demonstrate the exotic capability of the metasurface in local phase, amplitude and polarization control of the electromagnetic waves along the surface populated with resonant antennas. A new class of flat, compact, multifunctional components, so-called polarizing lens, is introduced in an attempt to merge two important optical components, a circular polarizer and a lens, into a thin plasmonic metasurface. The concept of polarizing lens is then further extended to the investigation and development of multi-focus lenses and lenses with extended depth of focus. Another exotic application of metasurfaces is transforming incident beams into complex beams such as vector beams with non-uniform local polarization distributions. In particular, we focus on realizing azimuthally polarized beams which contain a magnetic dominant region within which longitudinal magnetic field is strong and electric field is ideally null. Such beams are promising for studying weak magnetic transitions in optical frequency range. Lastly, the exotic properties of the orbital angular momentum carrying beams, such as annular-shaped intensity profile and helical wavefront, motivated us to generate such beams in radio frequencies. We demonstrate that reflectarrays are an efficient vehicle to generate such beams and show their potential novel applications in wireless communication systems