Design of Erbium-Doped Tellurium Oxide Optical Amplifiers on a Low-Loss Silicon Nitride Waveguide Platform

Abstract

Research interest in optical amplifiers has remained intensive over the years due to their widespread application in high-speed telecommunication systems. The requirement for amplification arises from the need to strengthen weakened signals as they propagate through optical fibers or through waveguides on chips and in order to meet strict system power budgets. Erbium-doped fiber amplifiers offer high, broadband and low-noise gain for wavelength-division multiplexed systems. Nevertheless, fiber amplifiers are bulky and many applications, including the development of compact transceiver modules for the data center, require an integrated on-chip solution. Erbium-doped waveguide amplifiers (EDWAs), which are integrated onto silicon chips, could potentially replace EDFAs in many instances. Of prospective materials for EDWAs, erbium-doped tellurium dioxide has a range of advantages including its high refractive index for compact waveguides and bends, large erbium light emission bandwidth, high Er3+ ion solubility and high gain. However, fabrication of erbium-doped tellurium oxide waveguides has proved challenging, and methods developed to date are not compatible with standard silicon-based photonic integration platforms. Meanwhile, silicon nitride is a standard high-quality light guiding platform due to its fairly high refractive index, high transmission throughout the visible and infrared spectrum and the compatibility of silicon nitride fabrication process with standard CMOS fabrication lines. The combination of erbium-doped tellurium oxide with silicon nitride technology could lead to compact and high performance optical amplifiers that are scalable and compatible with existing photonic integration platforms. This thesis describes research on different designs of erbium-doped tellurium oxide optical amplifiers integrated on a low-loss silicon nitride waveguide platform. Both theoretical and experimental work is described in the context of improving the amplitude, capacity and stability of erbium-doped tellurium oxide optical amplifiers for communications. Specifically, Chapter 2 studies the theory and background of optical waveguides and rare earth dopants and their transitions. Chapter 3 presents the finite element method waveguide mode solver, tellurium oxide-coated silicon nitride waveguide design and amplifier model. In Chapter 4, simulation results on the optimization of the tellurium dioxide-coated silicon nitride waveguides are presented. Modelling and comparisons between Er-doped Al2O3 and TeO2 waveguides are also described using a MATLAB code that provides predictive results for both of their performance. Fabrication and initial measurements results are generally shown in this chapter as well.