Efficient Light Coupling Techniques for Integrated Photonics

Given the fact that efficient and compact light emitters on a silicon (Si) platform yet do not exist, in most cases, light is still coupled to photonic chips from an external source (i.e. off-chip lasers) through single mode optical fibers (SMF). In this thesis, my investigations are focused on the problem of efficient light coupling to nano-photonic devices of different types. I propose and demonstrate a few compact on-chip solutions to efficiently couple light to specific modes of conventional photonic devices. The size mismatch between an optical fiber mode and the on-chip nano-photonic/plasmonic mode of a photonic circuitry is the major contributing factor to an inefficient fiber-to-chip coupling. Additionally, due to the inherent birefringence of the on-chip waveguides (i.e. silicon-on-insulator waveguides) the coupling efficiencies are also polarization dependent. In this thesis, I propose and demonstrate a compact bilayer inverse taper edge-coupler with enhanced fiber-to-chip coupling efficiencies for both TE and TM polarizations of commercial Si photonic circuitry. The current commercial practice of CMOS-photonics integration is limited to separate fabrication of the respective devices and connecting them by chip-to-chip interconnect systems. In this thesis, I propose and demonstrate a broadside beam routing mechanism in the telecom wavelength using a high index dielectric (i.e. Si) micro-prism structure. I extended the design to an elastic PDMS (Polydimethylsiloxane) platform to achieve beam scanning capability in both telecom and visible wavelength ranges diversifying its applications. I have further extended my work to the field of plasmonics and have designed a compact and highly efficient surface plasmon polariton (SPP) mode excitation scheme at the telecom wavelength regime using a gable shaped Si-tip with an optimized geometry. Fabrication of the Si-tip is compatible with standard Si processes. I have demonstrated the effectivity of the proposed scheme via a proof-of-principal experiment showing the high efficiency excitation of the SPP mode at an Au/SiO2 interface. Furthermore, I present a detailed design of an SPP excitation device capable of efficiently exciting an SPP mode at an Au/air interface, facilitating an easy access to the excited SPP mode from the outside environment, making it more suitable for plasmonic sensing applications.Ph.D