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.@en

In the past decade, lithium niobate (LiNbO₃ or LN) photonics, thanks to its heat-free and fast electro-optical modulation, second-order non-linearities, and low-loss, has been extensively investigated. Despite numerous demonstrations of high-performance LN photonics, processing lithium niobate remains challenging and suffers from incompatibilities with standard complementary metal-oxide-semiconductor (CMOS) fabrication lines, limiting its scalability. Silicon carbide (SiC) is an emerging material platform with a high refractive index, a large non-linear Kerr coefficient, and a promising candidate for heterogeneous integration with LN photonics. Current approaches of SiC/LN integration require transfer-bonding techniques, which are time-consuming, expensive, and lack precision in layer thickness. Here, we show that amorphous silicon carbide (a-SiC), deposited using inductively coupled plasma enhanced chemical vapor deposition at low temperatures (<165 °C), can be conveniently integrated with LiNbO₃ and processed to form high-performance photonics. Most importantly, the fabrication only involves a standard, silicon-compatible, reactive ion etching step and leaves the LiNbO₃ intact, hence its compatibility with standard foundry processes. As a proof-of-principle, we fabricated waveguides and ring resonators on the developed a-SiC/LN platform and achieved intrinsic quality factors higher than 1.06 × 10⁵ and a resonance electro-optic tunability of 3.4 pm/V with a 3 mm tuning length. We showcase the possibility of dense integration by fabricating and testing ring resonators with a 40 μm radius without a noticeable loss penalty. Our platform offers a CMOS-compatible and scalable approach for the implementation of future fast electro-optic modulators and reconfigurable photonic circuits, as well as nonlinear processes that can benefit from involving both second- and third-order nonlinearities.

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