Abstract
This thesis deals with the fundamental concepts of SOI (Silicon-on insulator) slot waveguides using Ultra-Silicon rich Nitride (USRN) platform, which includes theory, fabrication, and applications of a typical slot waveguide. First, we have discussed the science behind working of slot waveguides and modal field equation of fundamental modes derived from Maxwell’s equations. Slot waveguide structures are simulated using FDTD to get the electric field data which is plotted to get the field profile of modes and shown to be matching with the theoretically derived modal field equation. We have also simulated slot waveguides for characteristic values like effective refractive index. Mode confinement factor for slot waveguides is defined and determined using simulated field data. Structural parameters of slot waveguides are optimized in order to get maximum field confinement for its enhanced application. Then, general applications of slot waveguides are discussed. We have also shown that slot waveguides show large birefringence as compared to normal ridge waveguide which can be exploited for various optical phenomenon. We have optimized all the geometrical parameters of slot waveguides to get maximum birefringence and shown that one can get group index birefringence value greater than one i.e. (????? > 1) for a particular range of values of height and width of slot waveguides. Then, we have discussed about difficulties faced to couple light into slot waveguides due to mode mismatch between modes of slot waveguides and the fiber mode. Various techniques to overcome fiber-chip coupling loss are discussed and the one which we have chosen is elaborated. Then, step by step fabrication 5 processes are described to fabricate slot waveguides on chip using ultra-silicon rich nitride. The fabricated devices are experimentally characterized for different applications. Firstly, we characterized slot waveguides of different lengths for loss analysis and used linear-fit plot to determine the transmission loss and total insertion loss to check the efficacy of tapers to couple light from fibre to device. We showed that insertion loss is minimized significantly by incorporating the given tapers. Next, we tested our slot waveguide device for high- speed data transmission and shown that the fabricated device can handle 30Gb/s NRZ and 56Gb/s PAM4 data. Finally, to test the presence of a particular mode and to find its respective group index, we had included Fabry-Perot cavity in the device to deduce group index from the FSR (free spectral range) of the generated Fabry-Perot oscillations in transmission spectrum. It is shown that experimentally deduced group index closely matched with the simulated value. We had also introduced the ring resonator with our slot waveguides device, which again can give the value of group index of the mode transmitting in device