Nano-Photonic Circuits for Optical Communication

This Ph.D. project falls within the framework of nanophotonic circuits for optical communication, emphasizing single-photon sources (SPSs). The overall thesis deals with aspects of theory, numerical analysis, and design related to these sources. Additionally, nanophotonic waveguides supported with cavity structures are investigated, too.

These designed devices have been fabricated and measured in collaboration with the Technical University of Berlin, Institute of Solid State Physics. The thesis is divided into two main parts. The first part is devoted to the development and implementation of an efficient, rigorous full-vectorial modal method (MM) that allows simulating SPSs in order to calculate key performance parameters of SPSs such as spontaneous emission rates, modal reflection coefficients, and spontaneous emission beta factor.

The proposed MM is based on the expansion of the electromagnetic field on transverse electric and transverse magnetic modes, which significantly simplifies the computation with respect to the modal method implementations encountered in the literature. The method incorporates true open boundary conditions without the need for artificial absorbing boundary conditions or matched layers.

The method is generalized to orthogonal curvilinear coordinates with specific examples given for the rotationally symmetric and elliptical geometries. The second part of the thesis presents some SPS designs. The presented designs have been synthesized with the MM solver developed in part 1 and commercial finite element method solvers.

With the MM, SPSs with vertical emission are analyzed. Various quantum-dot nanowires and multilayer structures, including micropillars, are examined. Specifically, elliptical cross-section micropillar SPSs are investigated. An optimum elliptical micropillar SPS is designed, leading to a very high polarized spontaneous emission beta factor together with a very high collection efficiency to a Gaussian fiber mode in the far zone.

Finally, SPSs with in-plane emission are studied. Specifically, a broadband high-efficiency ridge waveguide-based nanobeam cavity for low-index-contrast materials is designed for on-chip quantum information processing applications. The designed device has been fabricated and measured at the facilities of the Technical University of Berlin, Institute of Solid State Physics.

Measurements and simulations show a very good agreement, fully validating the design.