High efficient optical spot size converter (SSC) is one of the most important building blocks for dense optical interconnection network and high-speed optical fiber communications due to efficient optical power transfer between different optical modules. Using tapered optical direction coupler (TODC) as SSC can reduce the dimension with high efficiency because of resonant condition and tapered structure. However, the strong dependence of operation on wavelength leads to narrow band operation, reducing the usage of wavelength division multiplexer (WDM) technique for upgrading optical data capacity through optical spectrum. In this work, based on multi- resonant points of TODC, a broadband SSC integrated with optical electroabsorption modulator (EAM) is proposed, designed, and fabricated. By tapering quantum well of the top active waveguide (AW), the integration with bottom passive waveguide (PW) can form a TODC. With the tapered structure, the gradually varied effective index forms a resonant point along wave propagation, inducing strong coupling, collecting optical power after resonant point, and thus leading to high efficient coupling. With multi-section of resonant conditions and also tapered structure, broadband operation can be realized. Through 3 section of tapered AW of TODC, the calculated coupling efficiency from bottom PW with larger than 70% is found for the regime of 1530nm~1550nm wavelength. The EAM-integrated SSC is also fabricated. With counter direction of optical coupling, the measured photocurrent in EAM shows a broadband of flap coupling from 1570nm~1585nm is observed, suggesting the multi-section TODC can bring out broadband operation.

This research revolves around the concept design and theoretical validation of a new type of wave energy converter (WEC), comprising a pitching floater integrated with a resonant U-tank (RUT) and a Wells turbine as power take-off (PTO). Theoretical formulation of a fully coupled multi-body dynamic system, incorporating the thermodynamic processes of the RUT air chamber, its interaction with the PTO dynamics and their coupling with the floater is presented. Inaccuracies of the dynamic modeling of RUT based on Lloyd's low order model, which assumes constant hydrodynamic parameters irrespective of the frequency, are demonstrated by a series of high fidelity CFD simulations. These simulations are a systematic series of fully viscous turbulent simulations, using unsteady RANSE solvers, of the water sloshing at different frequencies of oscillation. Calibration of Lloyd’s model with CFD results evidenced that the RUT hydrodynamic parameters are not invariant to frequency. A numerical model was developed based on Simulink WEC-Sim libraries to solve the non-linear thermo-hydrodynamic equations of the device in time domain. For power assessment, parametric investigations are conducted by varying the main dimensions of the RUT and power RAOs were computed for each iteration. Performance in irregular sea state are assessed using a statistical approach with the assumption of linear wave theory. By superimposing spectrum energy density from two resource sites with RAO, mean annual energy production (MEAP) are computed. The predicted MEAP favorably compares with other existing devices, confirming the superior efficiency of the new proposed device over a larger range of incident wave frequency. / M.S. / This study present results of an investigation into a new type of wave energy converter which can be deployed in ocean and by its pitch response motion, it can harvest wave energy and convert it to electrical energy. This device consist of a floater, a U-tank (resonant U-tank) with sloshing water free to oscillate in response to the floater motion and a pneumatic turbine which produces power as air is forced to travel across it. The pneumatic turbine is used as the power take-off (PTO) device. A medium fidelity approach was taken to carry out this study by applying Lloyd’s model which describes the motion of the sloshing water in a resonant U-tank. Computational fluid dynamics (CFD) studies were carried out to calibrate the hydrodynamic parameters of the resonant U-tank as described by Lloyd and it was discovered that these parameters are frequency dependent, therefore Lloyd’s model was modelled to be frequency dependent. The mathematical formulation coupling the thermodynamic evolution of air in the resonant U-tank chamber, modified Lloyd’s sloshing water equation, floater dynamics and PTO were presented for the integrated system. These set of thermo-hydrodynamic equations were solved with a numerical model developed using MATLAB/Simulink WEC-Sim Libraries in time domain in other to capture the non-linearity arising from the coupled dynamics. To assess the annual energy productivity of the device, wave statistical data from two resource sites, Western Hawaii and Eel River were selected and used to carrying out computations on different iterations of the device by varying the tank’s main dimensions. This results were promising with the most performing device iteration yielding mean annual energy production of 579 MWh for Western Hawaii.