Enhanced Negative Thermo-Optic Coefficient in Sputtered Versus Sol-Gel TiO 2 Waveguides

Titanium dioxide (TiO2) has garnered significant attention in integrated photonics due to its unique negative thermo-optic coefficient (TOC), a property essential for developing athermal devices and efficient thermo-optic switches on flexible platforms. In this paper, we compare sol-gel and magnetron-sputtered TiO2waveguides, highlighting the dependence of their propagation loss and TOC on the deposition method. Sol-gel amorphous TiO2waveguides exhibit propagation loss of 4.64 dB/cm at 1296.42 nm and TOC of − 2.58 × 10-5K-1, while sputtered amorphous TiO2waveguides show similar propagation loss (4.32 dB/cm at 1304.20 nm) but a three times larger TOC (−7.98×10-5K-1), which is attributed to their higher density and lower porosity. These results provide new insights for the development of waveguide-integrated high-performance thermo-optic devices and are expected to accelerate the advancement of next-generation photonic integrated circuits.