Control of light coherence, polarization, and propagation using nanostructures

The field of nanophotonics has evolved rapidly in the past few decades due to significant advancements in the technologies of numerical computation and nanofabrication. It has become possible to design and fabricate optical materials with designed structural units that are smaller than the wavelength of light. This has opened new avenues for control of light-matter interactions and led to a variety of new applications, including optical materials with unprecedented properties and miniaturized optical devices using nanostructured building blocks. The work presented in this thesis extends these advancements further by developing new calculation methods and introducing new optical micro- and nanostructures for free-space and on-chip optics. The thesis contains a description of novel optical components that control the polarization of light by using nanostructured materials. One of the components is a subwavelength-thick wave retarder that operates in the transmission mode and has low losses and a large bandwidth. Also, several designs for ultrathin tunable partial polarizers are presented. By using these devices, the degree of polarization of an initially unpolarized light can be tuned by changing the angle of incidence. The designed polarization-sensitive components are based on highly anisotropic metal-dielectric nanostructures, which enable the devices to have subwave length thickness.The thesis also introduces a semianalytical model for calculation of the near-field spatial coherence properties of optical sources. Spatial coherence plays an important role in optical science and technology. However, a proper model for calculating the transverse coherence length of light in the near-field zone of a nanostructured optical source had not been proposed. The model presented in the thesis uses optical reciprocity and a plane-wave decomposition of the source radiation to enable fast and reliable calculation of the degree of spatial coherence. It also helps one to design nanostructured optical sources with desired coherence properties. Furthermore, the thesis investigates on-chip optical waveguides as an essential component of the future integrated photonic devices. The overall miniaturization of photonic integrated circuits is limited by the crosstalk between neighboring optical components, especially between waveguides.In the thesis, the use of higher-order modes is proposed to significantly reduce and in some cases completely eliminate the crosstalk between silicon waveguides positioned at extremely short distances from each other. This improves considerably the achievable integration density of optical waveguides on a photonic chip. The calculation methods and designs described in the thesis contribute to the development of next-generation optical devices and can find applications in novel optical displays, imaging systems, equipment for optical ranging and detection, and systems used in optical communication.The accelerating technological progress in this direction underlines the importance of current and future research work on fundamental and applied aspects of nanoscale light-matter interaction