Shaping Classical and Quantum Light with Gap-Surface Plasmonic Metasurfaces

The miniaturization of optical components is fueling advances in many fields like communication technology, display technologies for AR/VR and many more. Metasurfaces have emerged as quasi planar flat optics, that enable the manipulation of light on the nanoscale. This unprecedented step of miniaturization has led to a big step in the design and experimental demonstration of quasi 2D optical components. Gap-surface plasmonic metasurfaces have enabled specifically high control over amplitude, phase and polarization of the reflected light. These structures consist of periodically arranged metallic nanostructures, called metaatoms, that are separated from a metal mirror by a thin dielectric layer.

This PhD thesis presents investigations into the versatility of gap-surface plasmonic waveplates to create multi-functional metasurfaces. In a first step, different approaches to combine or interleave two metasurfaces are compared. The two metasurface create holograms through the encoded phase distribution. Since the phase distributions for the holograms are distinct, four different approaches to combine them in a single metasurface, using only half-wave plate metaatoms, were compared experimentally. Secondly, the findings were used to create a single metasurface, that generates a full polarization set consisting of four linear and two circular polarizations, which are pairwise orthogonal to each other, from a single incident beam. Additionally, the six outgoing beams are spatially separated by introducing different phase gradients for each sub metasurface. This approach is facilitated by a combination of half-wave plate and quarter-wave plate metaatoms. The last step included in this thesis, is to extend the manipulation of light using gap-surface plasmonic waveplates to the quantum light regime. To do this, a quantum emitter was placed on a dielectric thin film, separating it from a metallic mirror. After excitation of the quantum emitter, it decays to a large extent into outgoing surface waves, called surface plasmon polaritons. From the polarization of this surface plasmon polaritons and the accumulated propagation phase, an approach was developed to couple them out out into propagating free space light waves. For this the phase between the surface plasmon polariton and the outcoupled light needs to be matched at every point surrounding the quantum emitter. Several cases for differently polarized single and multiple outcoupled beams are demonstrated experimentally.

The thesis project ultimately investigated approaches and design methodology to manipulate classical and quantum light with gap-surface plasmonic metasurfaces. In this work it was demonstrated how the functionality of such structures can lead to more versatility.