Magic Silicon Dioxide for Widely Tunable Photonic Integrated Circuits.

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. This enables the fabrication of a novel tunable coupled ring optical waveguide (CROW) requiring only a single heater. In addition, we observe up to a 10-fold improvement of the thermo-optic tunability and demonstrate athermal ring resonators with shifts as low as 1.5 pm/°C. 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 2 orders of magnitude. Our method paves the way for novel photonic architectures incorporating bidirectional thermo-optic tunability.