Abstract
Optical devices are important for ever increasing bandwidth requirements for modern communication and sensing systems. The emergence of phase modulated (PM) photonic links utilizing optical phase locked loops (OPLL) is allowing for higher gain and bandwidth modulation techniques to further increase data transfer rates and allow for data offloading in communications systems. Being an object of recent research, in order to enhance linear operation and achieve higher bandwidth of current PM links, thin film lithium niobate (TFLN) modulators and high-speed semiconductor photodetectors are desired. This thesis works to provide a more detailed model via simulations to predict the feasibility of utilizing a III-V semiconductor modified uni-traveling carrier (MUTC) photodetector integrated directly onto a TFLN modulator/waveguide for use in a coherent optical PM link. The first part of this thesis’ work deals with investigating, modeling, and simulating Silicon Dioxide (SiO2), Silicon Nitride (SiN), and Aluminum Oxide (Al2O3) as buffer layer materials between the base of the photodetector and the TFLN waveguide to determine their effects on transmission and beam shape of the optical signal. Continuing from that work the resulting beam shape is imported into a model of the photodetector to simulate the coupling and power absorption. Lastly, important characteristics such as bandwidth, phase group delay, and responsivity of the photodetector design are simulated and used to replace the previous equation-based model in the PM link to determine the open loop gain, bandwidth, and stability limitations of the PM link.