Integrated visible-light liquid-crystal devices

Abstract

Integrated photonics systems at visible wavelengths have many wide-reaching potential applications, including image-projection systems, underwater optical communications, and optogenetics. Generally, visible-light integrated systems are based on silicon-nitride waveguides since silicon nitride has a low absorption coefficient within the visible spectrum and is CMOS compatible. However, silicon nitride has a low thermo-optic coefficient and does not exhibit significant electro-optic properties, which makes integrated phase and amplitude tuning at visible wavelengths a challenge. Current silicon-nitride phase and amplitude modulators, based on conventional heaters, are on the order of several millimeters long and require high power consumption, which places unreasonable constraints for many systems and applications. As such, compact and low-power integrated silicon-nitride phase and amplitude modulators are essential advancements for the field. In this thesis, integrated liquid-crystal devices are introduced as a solution to compact integrated visible-light modulation. Foremost, integrated liquid-crystal visible-light phase and amplitude modulators are proposed, designed, and experimentally demonstrated. Both devices leverage the birefringence of liquid crystal to manipulate the mode in a silicon-nitride waveguide to induce either a tunable phase shift or variable power coupling between two waveguides. Furthermore, these liquid-crystal phase and amplitude modulators are implemented in both a cascaded phased-array architecture and a system of phased-array pixels to experimentally demonstrate dynamic visible-light manipulation and beam steering. These liquid-crystal devices and phased-array systems enable compact and low-power visible-light manipulation for the next generation of integrated visible-light systems.