Developing photonic components for nulling applications

Nulling is a promising parallel pathway to coronagraphy for starlight suppression. Photonic integrated circuits (PICs) provide an avenue to efficiently realizing nulling by allowing critical components, such as splitters, phase and amplitude modulators, and beam combiners to be integrated onto a single, miniaturized platform. Further, PICs can be actively controlled by applying currents to traces printed on the top surface of a PIC instigating thermal changes, and/or piezo's which actively tune/modulate the light. In this study we explore the design, simulation, and laboratory characterization of test components developed on a silica-on-silicon platform for nulling applications. Silica-on-silicon waveguides were chosen to offer low coupling losses to standard single mode fibers, low propagation losses and low polarization dependence. Devices that we explore include splitters, Mach-Zehnder Interferometers for amplitude modulation, thermo-optic phase shifters, tri-couplers for nulling and waveguide crossings. We show the laboratory performance of these devices around the astronomical H-band with specific focus on the chromatic performance. By understanding the limitations of these components we aim to design deep and achromatic nulling PIC architectures in future.