Nanophotonic structures, which offer a sub-wavelength control over light and nearby emitters, promise to advance, for example, our ability to harvest light, process information and detect (bio-) chemical compounds. In general, the optical field distributions near nanophotonic structures are much more complex than those in the far field. That is, nanophotonic structures achieve much of their unique functionalities because both the electromagnetic fields and the emission modification of nearby emitters spatially vary on the nanoscale with respect to their orientation, amplitude and phase. Furthermore, unlike for conventional microscopic structures, the interaction between the optical magnetic fields and nanophotonics structures frequently plays an important role. Hence, an understanding of light-matter interactions at the nanoscale requires a method to spatially map nanoscale electric and magnetic optical vector fields and the emission modification of electric and magnetic dipole emitters. This thesis demonstrates that an aperture type near-field microscope can be used to achieve such a mapping. Firstly, we use the microscope to map the electric and magnetic optical fields of the photonic mode in a benchmark structure, a photonic crystal waveguide. Then, in both the electric and magnetic optical fields we identify points where a property of the field is undefined; optical singularities. For example, we identify polarization singularities, where the light is circularly polarized and the local orientation of the local polarization ellipse is undefined. We measure the local helicity of the circularly polarized light and we trace the position of the singularities in three-dimensional space. Finally, we use the near-field microscope to mimic the emission modification of dipolar emitters and circularly polarized dipoles in particular. We show that the handedness of electric and magnetic circular dipoles, in combination with the local helicity of the photonic mode, can determine the direction of the light emitted into the waveguide. Additionally, we demonstrate that the optical wavelength can be used to tune the positions of efficient helicity-to-path coupling.
|Award date||30 Jan 2015|
|Place of Publication||Enschede|
|Publication status||Published - 30 Jan 2015|