Magic silicon dioxide for widely tunable integrated photonics

Abstract: Integrated photonic circuits have transformed data communication, biosensing, and light detection and ranging, and hold wide-ranging potential for optical computing, optical imaging and signal processing. These applications often require tunable and reconfigurable photonic components, most commonly accomplished through the thermo-optic effect. However, the resulting tuning window is limited for standard optical materials such as silicon dioxide and silicon nitride. Most importantly, bidirectional thermal tuning on a single platform has not been realized. For the first time, we show that by tuning and optimizing the deposition conditions in inductively-coupled plasma chemical vapor deposition (ICPCVD) of silicon dioxide, this material can be used to deterministically tune the thermo-optic properties of optical devices without introducing significant losses. We demonstrate that we can deterministically integrate positive and negative wavelength shifts on a single chip, validated on amorphous silicon carbide (a-SiC), silicon nitride (SiN) and silicon-on-insulator (SOI) platforms. We observe up to a 10-fold improvement of the thermo-optic tunability and, in addition, demonstrate athermal ring resonators with shifts as low as 1.5 pm/{\deg}C. This enables the fabrication of a novel tunable coupled ring optical waveguide (CROW) requiring only a single heater. In addition, the low-temperature deposition of our silicon dioxide cladding can be combined with lift-off to isolate the optical devices resulting in a decrease in thermal crosstalk by at least two orders of magnitude. Our method paves the way for novel photonic architectures incorporating bidirectional thermo-optic tunability.