Study On Nonreciprocal Optical Waveguides

In this dissertation, several fundamental problems of concern in nonreciprocal optic waveguides have been studied. The rapid development of integrated Optics is proceeding towards the goal of realizing system on chip (SOC), raising a higher standard of small, system-integrated, smart and specialized (4S standards) to all integrated devices. As a crucial role in integrated photonic circuit, nonreciprocal devices also need to develop towards the4S standard. The most common nonreciprocal devices include optic isolator and circulator. The isolator can protect the laser source from reflecting light while the circulator can circulate the optic signals among its ports, enabling the separation of transmission and reflection signals. Traditional isolators and circulators are still too large to be integrated, becoming big obstacles for realizaing SOC. Recently, novel nonreciprocal devices based on different principles have been greatly developed during these years, moving towards the4S standards.Starting from the principle of reciprocity of magnetic-electrics, this dissertation extensively studies the material properties of nonreciprocal device, the light propagation properties, numerical simulation approaches, device design methods and fabrication techniques. The details are presented as follows:1. Starting from the Lorentz reciprocal law (LRL) deducted from Maxwell’s equations, three basic approaches to break LRL and realize nonreciprocity are concluded. Then the analysis of magneto-optic (MO) material is presented, with properties of the major MO material clarified.2. After understanding the physical principles, we need to build mathematic models in order to better solve the design problems. Since the major optic simulation tools are for reciprocal materials, we need to develop specific simulators for nonreicprocal materials. First the effective index method is presented, then beam propagation (BPM), finite-difference-time-difference (FDTD) and transfer matrix method (TMM) combined with MO properties are developed. Several devices including Mach-zehnder interfereror (MZI), Multimode interfereror (MMI) and periodic devices are simulated. Simulation provides good prediction for the device design.3. The two profiles for MO devices design are analyzed, with the principle of nonreciprocal phase shift (NPS) clarified and general solution for NPS enhancement proposed. On this basis, a series of devices were designed including MMI isolator, ring isolator and circulator, photonic crystal waveguide MZI isolator as well as a proposal for zero-leakage optic combiner. Several experiments were carried out to realize the nonreciprocal devices including MO material sputtering, MO fiber and silicon waveguide and MO material bonding.This research work covers the basic physical principles, material properties, numerical simulation approaches, device design and fabrication techniques of nonreciprocal devices, providing the analysis to several fundamental problems. This dissertation is intended to provide a guidance and reference to the following research of nonreciprocal guided-wave optics.